Evaluating Cover Crops for Soil Conservation and Food Security in High Tunnel Sweet Potato Production

Evaluating Cover Crops for Soil Conservation and Food Security in High Tunnel Sweet Potato Production | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Evaluating Cover Crops for Soil Conservation and Food Security in High Tunnel Sweet Potato Production Wilberforce Twinamatsiko, Kigambo Monica This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6135967/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Cover cropping has been demonstrated as a viable solution to mitigate soil challenges and improve subsequent crop yield, particularly in open-field conditions. However, their impact in high tunnels remains relatively unknown. This study assessed the short-term effect of single and mixed species of cover crops on selected soil properties, nutrient concentration and yield of sweet potatoes in high tunnels at the University of Arkansas at Pine Bluff research farm. using a randomized complete block design and two over crops; Crimson clover ( Trifolium incarnatum ), winter barley ( Hordeum vulgare) , and no-cover crop (control). The results indicated that single and mixed cover crops had no significant (P ˃ 0.05) effect on macronutrients and yield of sweet potatoes. However, soil microbial activity and micronutrient concentration in sweet potato leaves were significantly increased by use of winter barley. The combination of species of winter barley and crimson clover showed the highest microbial biomass (56.01 nmoles/g) compared to other study treatments despite the effects not being statistically significant. Therefore, the decision to incorporate cover crops in high tunnel cultivation should be decided judiciously. A long-term study is needed to draw more conclusive findings. Agronomy Food Science & Technology Cover crops Microbial activity Soil Conservation Environmental sustainability Food security Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Globally, soil-based crop production in ventilated and insulated structures, known as high tunnels or hoop houses, is gaining popularity. In the United States of America (USA), using high tunnels has improved tremendously with over 12,000 high tunnels constructed countrywide between 2010 and 2014 (NRCS, 2024). The gain in traction of the high tunnels is mostly linked to benefits such as early and extended seasonal production of crops, protection of high-value food crops against harsh climatic conditions, pests, and diseases. Consequently, resulting in crops with outstanding yields and quality as well as increased marketability and improved farmers’ incomes (Blomgren et al ., 2007, Reeve and Drost, 2012 ; Foust-Meyer and O’Rourke, 2014). Additionally, the current cost-sharing initiative in the US for establishing and managing high tunnels has attracted investors, leading to their increased adoption (Blomgren & Frisch, 2007 ). Despite their great prominence, crop productivity has been reported to gradually decrease in the high tunnels over the years (Warren et al., 2015 ). This decline in crop productivity is mainly attributed to soil health deterioration (Rudisill et al., 2015 ). Since high tunnels provide off-season growing possibilities and for farmers to maximize production of high-value food crops, cultivation is mostly intensive. This increased agricultural intensity allows for reduced intervals between successive crops, necessitates frequent tillage, requires additional irrigation and fertilizer usage which altogether deteriorates soil structure, reduces organic matter, and nutrient availability and diminishes microbial biomass (Pikul et al., 2006 ; Larsen et al ., 2014). Notably, the high temperature variations in the high tunnels especially during winter causes rapid soil moisture loss consequently harming soil health (Knewtson et al., 2010 ; Foust-Meyer and O'Rourke, 2015). Cover crops have been reliably used and reported by researchers as a viable solution to mitigate soil challenges. The cover crops improve soil structure and water infiltration; increase soil biological activity, organic matter and nutrient availability; reduce nutrient loss as well as conserve soil moisture and suppress weeds thereby increasing the yield of the next crop (Demir et al., 2019 ; Badon et al., 2021 ; Fengxia et al ., 2022; Van Eerd et al., 2023 ). Legumes and cereals are the two main groups of cover crops and are grown either as monocultures or mixtures with the latter providing significant effects (Dabney et al., 2001 ; O'Connell et al ., 2012; Demir et al., 2019 ; Tubana et al., 2020 ). Despite the enormous benefits cover crops offer, most research in the focuses on their incorporation in open field settings while their impact in high tunnels have received very little attention. There is also meager information on the effect of using single and mixed cover crops on soil properties in high tunnels with soil sampling time put into consideration. Additionally, there is inadequate knowledge on the effect of the previous cover crops on the nutrient concentration and subsequent yield of the next crop. This study therefore assessed the effect of single and mixed cover crops on soil properties of high tunnels across three soil sampling times as well as investigated the influence of cover cropping on nutrient concentration and subsequent yields of sweet potatoes ( Ipomoea batatas ) in the high tunnels. Materials and Methods Study area The study was conducted in a high tunnel at the Pine Bluff research farm station found at the University of Arkansas (36°04 ¹ 07"N, 94°10 ¹ 34"W), south-eastern USA. The high tunnel was covered with a single polyethylene sheet stretched over metal frames, extending midway down the length of the sidewalls. The width sidewalls were left uncovered to permit adequate ventilation. The soil type at the study site is Calloway silt loam with 0 to 2% slope, pH of 5.4 and 1.15% organic matter content. Experimental design and field management The experiment was organized into two sequential phases. In the first phase, we planted and terminated cover crop between November 2019 and April 2020. In the second phase we planted cash crop between May and September 2020 while collecting soil samples at intervals during both phases. This experiment, conducted from October 2019 to April 2020, evaluated the effects of single and mixed cover crop species on soil properties. The study treatments included single and mixed species. The mixed-species treatment consisted of crimson clover ( Trifolium incarnatum ), a widely used legume cover crop known for its high nitrogen contribution, and winter barley ( Hordeum vulgare ), a winter-hardy cereal cover crop effective in weed suppression (Smith et al., 2016 ). A no-cover crop treatment was included to serve as control. The four treatments which included: crimson clover, winter barley, crimson clover and winter barley mixture and no-cover crop were deployed in a randomized complete block design with four replications. Using a broadcasting method, seeds of the cover crops were planted in plots measuring 15 ft. x 6 ft using a seeding rate of 20 kg/ha of crimson clover, 100 kg/ha of winter barley and half the rates of each cover crop to form the mixture. A 1-ft spacing was maintained between plots and replications. The experiment was irrigated until full growth. During the first two months of growth, the cover crops were irrigated twice daily (morning and evening) and once every three days subsequently. At physiological maturity, the cover crops were terminated using the herbicide round up (glyphosate) based on the manufacturer’s recommended rate of 190ml per 2.5 gallons. In May 2020, a month after termination and drying up, they were tilled back into the soil. Soil samples were collected by zone soil sampling method where we collected one soil sample from each treatment plot in all the four replicates. Soil samples were obtained from a depth of 20cm using an auger in three phases: before planting cover crops; two months after planting the cover crops and three weeks after the cover crops were tilled back into the soil. However, soil samples for assessment of microbial biomass were collected once after tilling back the cover crops. At each sampling phase, soil samples of similar treatments were mixed to form a composite while eliminating foreign materials like roots, stones and pebbles. Laboratory samples were obtained by quartering the composites to obtain an average composition and sent to the University of Arkansas laboratory extension for analysis. One month after the cover crops were tilled back into the soil, slips of Beauregard, the most common sweet potato variety in the US were planted within the previous experimental plots to assess the effect of previous cover crops on nutrient concentration and subsequent tuber yield of the sweet potatoes. Sweet potatoes were chosen as the test crop because they are one of the crops that yield exceptionally during the warm season (Brandenberger et al., 2022 ), the time when the study was conducted. Sweet potato slips were planted 1ft apart on raised beds which were made by digging rows in each treatment plot using a tractor and thereafter leveled on the sides using hand hoes. Irrigation was done when needed throughout the growing period. To suppress emerging weeds, hand weeding and a mixture of two herbicides were used. The herbicide mixture of select (clethodim 26.4% and others 73.6%) at a rate of 1 pint per acre and Poast (sethoxydim 18% and others 82.0%) at rate of 0.5 pint per acre mixed with water was used to kill most of the weeds with exception of the pig weed. Hand weeding by pulling out the pig weed was done twice during the growing season. In September 2020, when the sweet potatoes were at physiological maturity, they were harvested by first pulling off the vines using a garden fork and thereafter the tubers were removed manually from the rows using hand shovels and garden forks. In all the replications, soil-free sweet potato tubers of similar treatments were combined in labelled crates and taken to storage rooms for subsequent assessments. Data collection Microbial activity Microbial activity was determined using the Solvita soil carbon dioxide burst method. In this method, 4g of air dried and sieved soil using a 2mm sieve was put into a plastic beaker where 9ml of water was added. The plastic beaker with the soil was transferred into the Solvita jar where a gel-embedded carbon dioxide sensing probe was inserted and sealed. After 24hours, the probe was inserted in a Digital Color Reader (DCR) to determine the amount of carbon dioxide that was released (mg/kg). The color probe was also matched with the Solvita color chart to determine the color code for each sample. The level of color change was consequently related to the amount of carbon dioxide released which was also related to the amount of microbial activity in the soil. Microbial biomass Total microbial biomass was determined by analyzing the total phospholipid fatty acids (PLFA) extracted from the soil samples. Collected soil samples were immediately inserted into zip-lock bags and placed in coolers with ice cubes prior to being stored overnight in a refrigerator at a temperature of 4°C. Following overnight cold storage, 5g of soil was lyophilized by a modified Bligh-Dyer extraction using 19ml of the extractant fluid. The lipids were then evaporated under a stream of nitrogen and separated on a solid-phase extraction column while the phospholipids were eluted with 5ml of methanol. The phospholipids were trans esterified to fatty acid methyl esters, extracted into 4ml of hexane, evaporated, and analyzed by gas chromatography. Nutrient concentration and yields of sweet potatoes Nutrient concentration in the sweet potato plants was determined three months after planting the crop using leaf samples. A sweet potato vine was randomly selected from each treatment plot where the sixth leaf from the apex was selected. Leaf samples were transferred to the high tunnel, air dried for two weeks, ground with a Wiley mill, sieved using a 1 mm sieve and then analyzed for different macro-nutrients (Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg) and Sulphur (S)) and micro-nutrients (Sodium (Na), Iron (Fe). Manganese (Mn), Zinc (Zn), Copper (Cu) and Boron (B)) For the yield parameters, the harvested sweet potato tubers were graded per treatment according to size (diameter) as: Jumbos (1¾ to 3¼ inches), U.S. No. 1 (1¾ to 3½ inches), canners (1½ to 2¼ inches) and culls (1½ inches) (Brandenberger et al., 2022 ). The weight of the different tuber grades (kg) per treatment were obtained and later aggregated to obtain the total tuber weight (kg) per treatment Statistical analysis The effect of cover crop treatments on microbial activity for the three sampling times was analyzed using analysis of variance (two-way ANOVA) using R-software version 3.5.3. Same software was used to conduct a one-way ANOVA to analyze data for soil microbial biomass and sweet potato yield. When significant differences were found, the Tukey test was used to separate the means (P < 0.05). Results Effect of cover crop treatments on microbial activity for the three sampling times Microbial activity varied significantly (P 0.05) effect on microbial activity (Table 1 ). Soil samples tested from winter barley plots produced the highest amount of carbon dioxide (4.31 mg/kg) thus the highest microbial activity although it was statistically like plots with the mixture of crimson clover and winter barley cover crops. The no-cover crop (control) plots exhibited the lowest microbial activity, releasing 3.81 mg/kg of carbon dioxide, though the difference from the crimson clover treatment was minimal (Fig. 2 ). Effect of cover crop treatments on microbial biomass Significant (P < 0.01) differences in microbial biomass were observed among cover crop treatments (Table 1 ). Microbial biomass was significantly different among treatment plots of winter barley and crimson clover mixture; winter barley; crimson clover and no-cover crops with means at 56.01, 54.24, 50.60 and 49.14 nmoles/g respectively (Fig. 3 ). Gram negative bacteria, gram positive bacteria, actinomycetes and fungi in that order were the abundant soil microorganisms regardless of the cover crop treatment (Fig. 4 ). Effect of previous cover crop treatments on the nutrient concentration, and total yield of sweet potatoes In respect of micronutrients concentration (Na, Fe, Mn, Zn, Cu and B), leaf samples obtained from plots that previously had single species of cover crops generally performed exceptionally with the highest concentration of micronutrients accruing from the winter barley treatment plots. Leaf samples from the winter barley and crimson clover mixture plots resulted in the lowest micronutrient concentration although they were significantly similar with the no-cover crop (control) treatment plots. Manganese (Mn) was the dominant micronutrient found in the leaf samples across all the treatment plots (Fig. 5). For the macronutrients (N, P, K, Ca, Mg and S), they did not significantly differ for all the leaf samples obtained from the different treatment plots and were generally low except for nitrogen (N) and potassium (K) (Fig. 6). Table 1 Effect of previous cover crop treatments on graded and total tuber yield of sweet potatoes evaluated in the high tunnel Treatments Average yield (kg) Jumbos U.S. No. 1 Canners Culls Total Winter barley 2.02 7.07 3.09 0.27 12.45 Crimson clover 0.78 6.82 5.56 0.30 13.46 Winter barley + crimson clover 0.47 5.84 3.75 0.35 10.41 Control 3.33 8.10 3.45 0.33 15.21 Previous cover crop treatments had no significant (P > 0.05) effect on graded and total tuber yield of sweet potatoes (Table 1 ). However, there was a general trend towards lower graded and total tuber yield after use of cover crops compared to the control. Discussion With respect to microbial biomass and microbial activity, generally plots with cover crop treatments displayed superior performance compared to the no-cover crop (control) treatment. The increase in microbial biomass and microbial activity under cover cropping has been reported before by numerous researchers (Jones and Lennon, 2010 ; Schipanski et al., 2014 ; Venter et al., 2016 ; Daryanto et al., 2018 ; Nakian et al ., 2019), though these studies were not in high tunnels. This can be attributed to the increase in above and below ground plant biomass and root exudates provided by the cover crops which stimulate microbial growth and activity (Chavarría et al., 2016 , Schmidt et al., 2019 ; Vukicevich et al., 2016 ). Moreover, Acosta-Martinez et al . (2011) indicated that there is a significant positive correlation between microbial biomass and activity therefore the increase in microbial activity could be attributed to an overall increase in microbial biomass. Additionally, in this study, the mixture of winter barley and crimson clover outperformed other study treatments in terms of microbial biomass probably due to the complementary effect of the cereal-legume mixture on plant biomass, nitrogen and water availability which altogether might have influenced this positive outcome (Krstic et al ., 2018). Moreover, the more microbial activity noted in winter barley plots may probably be due to the well-developed cereal root system with lateral roots and root hairs which provides exudates to various microbiota in the different parts of the rhizosphere consequently boosting microbial activity (Krstic et al ., 2018; Pascale et al., 2020 ). Gram-positive bacteria were the most dominant microbiota across all treatments mainly because of its leading importance in plant debris degradation (Hashemi et al ., 2013; Wendling et al ., 2015). This study found that single-species winter barley plots resulted in the highest micronutrient concentration in sweet potato leaves, outperforming the mixed cover crop treatment. This finding is in accordance with that of Krstic et al . (2018) although contradicts with the outcomes of Tubana et al. ( 2020 ) who indicated that cover crop mixes of hairy vetch, crimson clover and tillage radish substantially recovered the highest amount of nutrients than the single species and no-cover crop plots. As earlier mentioned, this could be attributed to the well-developed winter barley root system which has an increased ability to forage for micronutrient (Krstic et al ., 2018) and thus when it was terminated, the decaying biomass released many micronutrients to the sweet potato plant in usable form. Indeed, the high microbial activity noted in the winter barley plots in this study possibly contributed to the hastened release of the micronutrients consequently making them readily available for uptake by the sweet potato plants. However, the difference in root morphology, development and rooting depth exhibited by the mixture of winter barley and crimson clover (Tubana et al., 2020 ) probably had a negative antagonistic effect on the micronutrient absorption and thus the least micronutrients were stored and made available to the sweet potato plants. Regarding macronutrients, the general trend of most of the macronutrients being low in sweet potato leaf samples across all treatment plots could be explained hypothetically by the initial low concentrations of these nutrients in the soil (data not taken) which could not be replenished within a short period of cover crop establishment to make them present for the sweet potato plant. Alternatively, this result was probably due to the delayed release of the stored macronutrients from the cover crop biomass since most of macronutrients are organically bound in amino acids, proteins and nucleic acid thus requiring extended processes for their release (Tubana et al., 2020 ). Depending on the climatic conditions, soil characteristics, cover crop type, duration of cover cropping, production practices and the main crop, some studies report positive effects (Blanco-canqui et al., 2015 ; Chu et al., 2017 ; Marcillo and Miguez, 2017 ; Sanderson et al., 2018 ), negative effects (Nielsen et al., 2016 ; Cupina et al., 2017 ; Handlirova et al ., 2017; Reddy, 2017 ) while others reported little or no effect (Acuna and Vilamil, 2014; Smith et al., 2014 ; Hunter et al., 2019 ; Florence and Mcguire, 2020 ; Rodriguez et al., 2021 ). In the present research, cover crops had no significant effect on both graded and total tuber yield of sweet potatoes. This could mainly be due to the short-lived period of eight months of cover crop incorporation in this study which was not sufficient for realization of benefits of cover crops on sweet potato yields. Many authors have concluded that significant increases in main crop yields occur after the long-term use of cover crops in crop rotations (Justes et al., 2009 ; Doltra and Olesen, 2013 ; Blanco-Canqui et al., 2015 ). Further long-term studies are required to determine whether significant benefits of cover cropping emerge over time. Boselli et al. ( 2020 ) and Basche et al. ( 2016 ) reported no significant effect on crop yields after six and seven years respectively of cover cropping in open field trials. This therefore poses a major challenge in increasing adoption of cover crops by growers thus highlighting copious need for research to enhance understanding especially in high tunnels. Conclusion The single species of winter barley increased microbial activity and micronutrient concentration in sweet potato plants compared to other study treatments. The mixture of winter barley and crimson clover manifested outstanding microbial biomass compared to other study treatments. Based on these findings, the incorporation of cover crops in high tunnel cultivation should be carefully evaluated, particularly regarding their long-term benefits. However, a longer study period may be needed to make coherent conclusions. References Cupina B, Vujic´ S, Krstic´ DJ, Radanovic´ Z, ˇCabilovski R, Manojlovic´ M, Latkovic´ D (2017) Winter cover crops as green manure in a temperate region: The effect on nitrogen budget and yield of silage maize. Crop Pasture Sci 68:1060–1069 Acosta-Martínez V, Dowd SE, Bell CW, Lascano R, Booker JD, Zobeck TM, Upchurch DR (2010) Microbial community composition as affected by dryland cropping systems and tillage in a semiarid sandy soil. 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Sci Total Environ 858:159990 Venter ZS, Jacobs K&, Hawkins HJ (2016) The impact of crop rotation on soil microbial diversity: a meta-analysis. Pedobiologia 59:215–223. https://doi.org/10.1016/j.pedobi.2016.04.001 Vukicevich E, Lowery T, Bowen P, Urbez-Torres JR, Hart M (2016) Cover crops to increase soil microbial diversity and mitigate decline in perennial agriculture. A review. Agron Sustain Dev 36:48. https://doi.org/10.1007/s13593-016-0385-7 Warren ND, Sideman RG, Smith RG (2015) Performance of high tunnel tomato cultivars in northern New England. Hort Technol 25(1):139–146 Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6135967","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":422734405,"identity":"3eedc8ae-fba2-487e-a16e-bb9dbf249fc5","order_by":0,"name":"Wilberforce Twinamatsiko","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIiWNgGAWjYDACZuY2MM3GwMD4AEjz8BHWwgjSYgDSwmwA0sJG2BqoFpBFElDr8AOD44xtDz7u+ZPYJ938rPJrjp0MGwPzw0c38Gk5zNhuOOOZQWKbzDGz27LbkoEOYzM2zsGjxewwY5s0zwGD3DaJBLPbktuYgVp42KQJavkD1pL+rVhyWz2RWhjAWnLMGD9uO0xYiz3ILz0HjOuBWoqlGbcd52FjJuAXyf7Dxx78OCBnLD8jfePHn9uq7fnZmx8+xqcFBTDzgElilYMA4w9SVI+CUTAKRsGIAQC/BEQgabBBlAAAAABJRU5ErkJggg==","orcid":"","institution":"University of Arkansas at Pine Bluff","correspondingAuthor":true,"prefix":"","firstName":"Wilberforce","middleName":"","lastName":"Twinamatsiko","suffix":""},{"id":422734451,"identity":"8f3bcaf7-675c-4147-814c-d5cd5e070adb","order_by":1,"name":"Kigambo Monica","email":"","orcid":"","institution":"Makerere University","correspondingAuthor":false,"prefix":"","firstName":"Kigambo","middleName":"","lastName":"Monica","suffix":""}],"badges":[],"createdAt":"2025-03-01 17:35:38","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-6135967/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6135967/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":77660427,"identity":"f6ac28b0-8ec4-41b8-8873-741b2c923952","added_by":"auto","created_at":"2025-03-04 04:35:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":15165,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of previous cover crop treatments on the soil microorganisms’ concentration. (NN-control; WB-Winter barley; CC-Crimson clover; WB+CC-Winter barley+ Crimson clover)\u003c/p\u003e","description":"","filename":"image.png","url":"https://assets-eu.researchsquare.com/files/rs-6135967/v1/6ad2d052412e9e2ede0dc036.png"},{"id":77660359,"identity":"45f22b7a-f7e2-4e31-b329-57893b928d12","added_by":"auto","created_at":"2025-03-04 04:27:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":26032,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of cover crop treatments on the soil microbial biomass (nmoles/g). Error bars represent standard deviation. Bars with the same letters are not significantly different\u003c/p\u003e","description":"","filename":"image.png","url":"https://assets-eu.researchsquare.com/files/rs-6135967/v1/24a304b9ca09108002bc300a.png"},{"id":77660372,"identity":"0217fe1b-9dab-459d-84ad-5ae24aadb67f","added_by":"auto","created_at":"2025-03-04 04:27:03","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":67833,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of previous cover crop treatments on the micronutrient concentration (mg/kg) in sweet potato leaf samples.\u003c/p\u003e","description":"","filename":"image.png","url":"https://assets-eu.researchsquare.com/files/rs-6135967/v1/17bd8125ad304ad72cd7bf52.png"},{"id":77660361,"identity":"0c201ed5-13cc-4491-8051-f6643ff8c72a","added_by":"auto","created_at":"2025-03-04 04:27:02","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":45269,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of previous cover crop treatments on the macronutrient concentration (%) in sweet potato leaf samples.\u003c/p\u003e","description":"","filename":"image.png","url":"https://assets-eu.researchsquare.com/files/rs-6135967/v1/0d55af5f8a138f5f553a87b9.png"},{"id":77660955,"identity":"4e9b1917-5fb8-4a3b-b9ff-66340a5786d0","added_by":"auto","created_at":"2025-03-04 04:43:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":710272,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6135967/v1/4adeade1-afc4-4020-b40c-02b217fed66e.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eEvaluating Cover Crops for Soil Conservation and Food Security in High Tunnel Sweet Potato Production\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGlobally, soil-based crop production in ventilated and insulated structures, known as high tunnels or hoop houses, is gaining popularity. In the United States of America (USA), using high tunnels has improved tremendously with over 12,000 high tunnels constructed countrywide between 2010 and 2014 (NRCS, 2024). The gain in traction of the high tunnels is mostly linked to benefits such as early and extended seasonal production of crops, protection of high-value food crops against harsh climatic conditions, pests, and diseases. Consequently, resulting in crops with outstanding yields and quality as well as increased marketability and improved farmers\u0026rsquo; incomes (Blomgren \u003cem\u003eet al\u003c/em\u003e., 2007, Reeve and Drost, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Foust-Meyer and O\u0026rsquo;Rourke, 2014). Additionally, the current cost-sharing initiative in the US for establishing and managing high tunnels has attracted investors, leading to their increased adoption (Blomgren \u0026amp; Frisch, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite their great prominence, crop productivity has been reported to gradually decrease in the high tunnels over the years (Warren et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). This decline in crop productivity is mainly attributed to soil health deterioration (Rudisill et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Since high tunnels provide off-season growing possibilities and for farmers to maximize production of high-value food crops, cultivation is mostly intensive. This increased agricultural intensity allows for reduced intervals between successive crops, necessitates frequent tillage, requires additional irrigation and fertilizer usage which altogether deteriorates soil structure, reduces organic matter, and nutrient availability and diminishes microbial biomass (Pikul et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Larsen \u003cem\u003eet al\u003c/em\u003e., 2014). Notably, the high temperature variations in the high tunnels especially during winter causes rapid soil moisture loss consequently harming soil health (Knewtson et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Foust-Meyer and O'Rourke, 2015).\u003c/p\u003e \u003cp\u003eCover crops have been reliably used and reported by researchers as a viable solution to mitigate soil challenges. The cover crops improve soil structure and water infiltration; increase soil biological activity, organic matter and nutrient availability; reduce nutrient loss as well as conserve soil moisture and suppress weeds thereby increasing the yield of the next crop (Demir et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Badon et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Fengxia \u003cem\u003eet al\u003c/em\u003e., 2022; Van Eerd et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Legumes and cereals are the two main groups of cover crops and are grown either as monocultures or mixtures with the latter providing significant effects (Dabney et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; O'Connell \u003cem\u003eet al\u003c/em\u003e., 2012; Demir et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Tubana et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Despite the enormous benefits cover crops offer, most research in the focuses on their incorporation in open field settings while their impact in high tunnels have received very little attention. There is also meager information on the effect of using single and mixed cover crops on soil properties in high tunnels with soil sampling time put into consideration. Additionally, there is inadequate knowledge on the effect of the previous cover crops on the nutrient concentration and subsequent yield of the next crop. This study therefore assessed the effect of single and mixed cover crops on soil properties of high tunnels across three soil sampling times as well as investigated the influence of cover cropping on nutrient concentration and subsequent yields of sweet potatoes (\u003cem\u003eIpomoea batatas\u003c/em\u003e) in the high tunnels.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy area\u003c/h2\u003e \u003cp\u003eThe study was conducted in a high tunnel at the Pine Bluff research farm station found at the University of Arkansas (36\u0026deg;04\u003csup\u003e\u0026sup1;\u003c/sup\u003e07\"N, 94\u0026deg;10\u003csup\u003e\u0026sup1;\u003c/sup\u003e34\"W), south-eastern USA. The high tunnel was covered with a single polyethylene sheet stretched over metal frames, extending midway down the length of the sidewalls. The width sidewalls were left uncovered to permit adequate ventilation. The soil type at the study site is Calloway silt loam with 0 to 2% slope, pH of 5.4 and 1.15% organic matter content.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eExperimental design and field management\u003c/h3\u003e\n\u003cp\u003eThe experiment was organized into two sequential phases. In the first phase, we planted and terminated cover crop between November 2019 and April 2020. In the second phase we planted cash crop between May and September 2020 while collecting soil samples at intervals during both phases.\u003c/p\u003e \u003cp\u003eThis experiment, conducted from October 2019 to April 2020, evaluated the effects of single and mixed cover crop species on soil properties. The study treatments included single and mixed species. The mixed-species treatment consisted of crimson clover (\u003cem\u003eTrifolium incarnatum\u003c/em\u003e), a widely used legume cover crop known for its high nitrogen contribution, and winter barley (\u003cem\u003eHordeum vulgare\u003c/em\u003e), a winter-hardy cereal cover crop effective in weed suppression (Smith et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). A no-cover crop treatment was included to serve as control. The four treatments which included: crimson clover, winter barley, crimson clover and winter barley mixture and no-cover crop were deployed in a randomized complete block design with four replications. Using a broadcasting method, seeds of the cover crops were planted in plots measuring 15 ft. x 6 ft using a seeding rate of 20 kg/ha of crimson clover, 100 kg/ha of winter barley and half the rates of each cover crop to form the mixture. A 1-ft spacing was maintained between plots and replications.\u003c/p\u003e \u003cp\u003eThe experiment was irrigated until full growth. During the first two months of growth, the cover crops were irrigated twice daily (morning and evening) and once every three days subsequently. At physiological maturity, the cover crops were terminated using the herbicide round up (glyphosate) based on the manufacturer\u0026rsquo;s recommended rate of 190ml per 2.5 gallons. In May 2020, a month after termination and drying up, they were tilled back into the soil.\u003c/p\u003e \u003cp\u003eSoil samples were collected by zone soil sampling method where we collected one soil sample from each treatment plot in all the four replicates. Soil samples were obtained from a depth of 20cm using an auger in three phases: before planting cover crops; two months after planting the cover crops and three weeks after the cover crops were tilled back into the soil. However, soil samples for assessment of microbial biomass were collected once after tilling back the cover crops. At each sampling phase, soil samples of similar treatments were mixed to form a composite while eliminating foreign materials like roots, stones and pebbles. Laboratory samples were obtained by quartering the composites to obtain an average composition and sent to the University of Arkansas laboratory extension for analysis.\u003c/p\u003e \u003cp\u003eOne month after the cover crops were tilled back into the soil, slips of Beauregard, the most common sweet potato variety in the US were planted within the previous experimental plots to assess the effect of previous cover crops on nutrient concentration and subsequent tuber yield of the sweet potatoes. Sweet potatoes were chosen as the test crop because they are one of the crops that yield exceptionally during the warm season (Brandenberger et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), the time when the study was conducted. Sweet potato slips were planted 1ft apart on raised beds which were made by digging rows in each treatment plot using a tractor and thereafter leveled on the sides using hand hoes. Irrigation was done when needed throughout the growing period. To suppress emerging weeds, hand weeding and a mixture of two herbicides were used. The herbicide mixture of select (clethodim 26.4% and others 73.6%) at a rate of 1 pint per acre and Poast (sethoxydim 18% and others 82.0%) at rate of 0.5 pint per acre mixed with water was used to kill most of the weeds with exception of the pig weed. Hand weeding by pulling out the pig weed was done twice during the growing season. In September 2020, when the sweet potatoes were at physiological maturity, they were harvested by first pulling off the vines using a garden fork and thereafter the tubers were removed manually from the rows using hand shovels and garden forks. In all the replications, soil-free sweet potato tubers of similar treatments were combined in labelled crates and taken to storage rooms for subsequent assessments.\u003c/p\u003e\n\u003ch3\u003eData collection\u003c/h3\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eMicrobial activity\u003c/h2\u003e \u003cp\u003eMicrobial activity was determined using the Solvita soil carbon dioxide burst method. In this method, 4g of air dried and sieved soil using a 2mm sieve was put into a plastic beaker where 9ml of water was added. The plastic beaker with the soil was transferred into the Solvita jar where a gel-embedded carbon dioxide sensing probe was inserted and sealed. After 24hours, the probe was inserted in a Digital Color Reader (DCR) to determine the amount of carbon dioxide that was released (mg/kg). The color probe was also matched with the Solvita color chart to determine the color code for each sample. The level of color change was consequently related to the amount of carbon dioxide released which was also related to the amount of microbial activity in the soil.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMicrobial biomass\u003c/h3\u003e\n\u003cp\u003eTotal microbial biomass was determined by analyzing the total phospholipid fatty acids (PLFA) extracted from the soil samples. Collected soil samples were immediately inserted into zip-lock bags and placed in coolers with ice cubes prior to being stored overnight in a refrigerator at a temperature of 4\u0026deg;C. Following overnight cold storage, 5g of soil was lyophilized by a modified Bligh-Dyer extraction using 19ml of the extractant fluid. The lipids were then evaporated under a stream of nitrogen and separated on a solid-phase extraction column while the phospholipids were eluted with 5ml of methanol. The phospholipids were trans esterified to fatty acid methyl esters, extracted into 4ml of hexane, evaporated, and analyzed by gas chromatography.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eNutrient concentration and yields of sweet potatoes\u003c/h2\u003e \u003cp\u003eNutrient concentration in the sweet potato plants was determined three months after planting the crop using leaf samples. A sweet potato vine was randomly selected from each treatment plot where the sixth leaf from the apex was selected. Leaf samples were transferred to the high tunnel, air dried for two weeks, ground with a Wiley mill, sieved using a 1 mm sieve and then analyzed for different macro-nutrients (Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg) and Sulphur (S)) and micro-nutrients (Sodium (Na), Iron (Fe). Manganese (Mn), Zinc (Zn), Copper (Cu) and Boron (B))\u003c/p\u003e \u003cp\u003eFor the yield parameters, the harvested sweet potato tubers were graded per treatment according to size (diameter) as: Jumbos (1\u0026frac34; to 3\u0026frac14; inches), U.S. No. 1 (1\u0026frac34; to 3\u0026frac12; inches), canners (1\u0026frac12; to 2\u0026frac14; inches) and culls (1\u0026frac12; inches) (Brandenberger et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The weight of the different tuber grades (kg) per treatment were obtained and later aggregated to obtain the total tuber weight (kg) per treatment\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eThe effect of cover crop treatments on microbial activity for the three sampling times was analyzed using analysis of variance (two-way ANOVA) using R-software version 3.5.3. Same software was used to conduct a one-way ANOVA to analyze data for soil microbial biomass and sweet potato yield. When significant differences were found, the Tukey test was used to separate the means (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eEffect of cover crop treatments on microbial activity for the three sampling times\u003c/h2\u003e \u003cp\u003eMicrobial activity varied significantly (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) among cover crop treatments. Sampling time and the interaction between cover crop treatments and sampling time had no significant (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05) effect on microbial activity (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Soil samples tested from winter barley plots produced the highest amount of carbon dioxide (4.31 mg/kg) thus the highest microbial activity although it was statistically like plots with the mixture of crimson clover and winter barley cover crops. The no-cover crop (control) plots exhibited the lowest microbial activity, releasing 3.81 mg/kg of carbon dioxide, though the difference from the crimson clover treatment was minimal (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eEffect of cover crop treatments on microbial biomass\u003c/h2\u003e \u003cp\u003eSignificant (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01) differences in microbial biomass were observed among cover crop treatments (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Microbial biomass was significantly different among treatment plots of winter barley and crimson clover mixture; winter barley; crimson clover and no-cover crops with means at 56.01, 54.24, 50.60 and 49.14 nmoles/g respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Gram negative bacteria, gram positive bacteria, actinomycetes and fungi in that order were the abundant soil microorganisms regardless of the cover crop treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eEffect of previous cover crop treatments on the nutrient concentration, and total yield of sweet potatoes\u003c/b\u003e \u003c/p\u003e \u003cp\u003eIn respect of micronutrients concentration (Na, Fe, Mn, Zn, Cu and B), leaf samples obtained from plots that previously had single species of cover crops generally performed exceptionally with the highest concentration of micronutrients accruing from the winter barley treatment plots. Leaf samples from the winter barley and crimson clover mixture plots resulted in the lowest micronutrient concentration although they were significantly similar with the no-cover crop (control) treatment plots. Manganese (Mn) was the dominant micronutrient found in the leaf samples across all the treatment plots (Fig.\u0026nbsp;5). For the macronutrients (N, P, K, Ca, Mg and S), they did not significantly differ for all the leaf samples obtained from the different treatment plots and were generally low except for nitrogen (N) and potassium (K) (Fig.\u0026nbsp;6).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of previous cover crop treatments on graded and total tuber yield of sweet potatoes evaluated in the high tunnel\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTreatments\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eAverage yield (kg)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eJumbos\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eU.S. No. 1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCanners\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCulls\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWinter barley\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e12.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrimson clover\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e13.46\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWinter barley\u0026thinsp;+\u0026thinsp;crimson clover\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e10.41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e15.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ePrevious cover crop treatments had no significant (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05) effect on graded and total tuber yield of sweet potatoes (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). However, there was a general trend towards lower graded and total tuber yield after use of cover crops compared to the control.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eWith respect to microbial biomass and microbial activity, generally plots with cover crop treatments displayed superior performance compared to the no-cover crop (control) treatment. The increase in microbial biomass and microbial activity under cover cropping has been reported before by numerous researchers (Jones and Lennon, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Schipanski et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Venter et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Daryanto et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Nakian \u003cem\u003eet al\u003c/em\u003e., 2019), though these studies were not in high tunnels. This can be attributed to the increase in above and below ground plant biomass and root exudates provided by the cover crops which stimulate microbial growth and activity (Chavarr\u0026iacute;a et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2016\u003c/span\u003e, Schmidt et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Vukicevich et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Moreover, Acosta-Martinez \u003cem\u003eet al\u003c/em\u003e. (2011) indicated that there is a significant positive correlation between microbial biomass and activity therefore the increase in microbial activity could be attributed to an overall increase in microbial biomass. Additionally, in this study, the mixture of winter barley and crimson clover outperformed other study treatments in terms of microbial biomass probably due to the complementary effect of the cereal-legume mixture on plant biomass, nitrogen and water availability which altogether might have influenced this positive outcome (Krstic \u003cem\u003eet al\u003c/em\u003e., 2018). Moreover, the more microbial activity noted in winter barley plots may probably be due to the well-developed cereal root system with lateral roots and root hairs which provides exudates to various microbiota in the different parts of the rhizosphere consequently boosting microbial activity (Krstic \u003cem\u003eet al\u003c/em\u003e., 2018; Pascale et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Gram-positive bacteria were the most dominant microbiota across all treatments mainly because of its leading importance in plant debris degradation (Hashemi \u003cem\u003eet al\u003c/em\u003e., 2013; Wendling \u003cem\u003eet al\u003c/em\u003e., 2015).\u003c/p\u003e \u003cp\u003eThis study found that single-species winter barley plots resulted in the highest micronutrient concentration in sweet potato leaves, outperforming the mixed cover crop treatment. This finding is in accordance with that of Krstic \u003cem\u003eet al\u003c/em\u003e. (2018) although contradicts with the outcomes of Tubana et al. (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) who indicated that cover crop mixes of hairy vetch, crimson clover and tillage radish substantially recovered the highest amount of nutrients than the single species and no-cover crop plots. As earlier mentioned, this could be attributed to the well-developed winter barley root system which has an increased ability to forage for micronutrient (Krstic \u003cem\u003eet al\u003c/em\u003e., 2018) and thus when it was terminated, the decaying biomass released many micronutrients to the sweet potato plant in usable form. Indeed, the high microbial activity noted in the winter barley plots in this study possibly contributed to the hastened release of the micronutrients consequently making them readily available for uptake by the sweet potato plants. However, the difference in root morphology, development and rooting depth exhibited by the mixture of winter barley and crimson clover (Tubana et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) probably had a negative antagonistic effect on the micronutrient absorption and thus the least micronutrients were stored and made available to the sweet potato plants. Regarding macronutrients, the general trend of most of the macronutrients being low in sweet potato leaf samples across all treatment plots could be explained hypothetically by the initial low concentrations of these nutrients in the soil (data not taken) which could not be replenished within a short period of cover crop establishment to make them present for the sweet potato plant. Alternatively, this result was probably due to the delayed release of the stored macronutrients from the cover crop biomass since most of macronutrients are organically bound in amino acids, proteins and nucleic acid thus requiring extended processes for their release (Tubana et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDepending on the climatic conditions, soil characteristics, cover crop type, duration of cover cropping, production practices and the main crop, some studies report positive effects (Blanco-canqui et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Chu et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Marcillo and Miguez, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Sanderson et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), negative effects (Nielsen et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Cupina et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Handlirova \u003cem\u003eet al\u003c/em\u003e., 2017; Reddy, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) while others reported little or no effect (Acuna and Vilamil, 2014; Smith et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Hunter et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Florence and Mcguire, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Rodriguez et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In the present research, cover crops had no significant effect on both graded and total tuber yield of sweet potatoes. This could mainly be due to the short-lived period of eight months of cover crop incorporation in this study which was not sufficient for realization of benefits of cover crops on sweet potato yields. Many authors have concluded that significant increases in main crop yields occur after the long-term use of cover crops in crop rotations (Justes et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Doltra and Olesen, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Blanco-Canqui et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Further long-term studies are required to determine whether significant benefits of cover cropping emerge over time. Boselli et al. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and Basche et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) reported no significant effect on crop yields after six and seven years respectively of cover cropping in open field trials. This therefore poses a major challenge in increasing adoption of cover crops by growers thus highlighting copious need for research to enhance understanding especially in high tunnels.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe single species of winter barley increased microbial activity and micronutrient concentration in sweet potato plants compared to other study treatments. The mixture of winter barley and crimson clover manifested outstanding microbial biomass compared to other study treatments. Based on these findings, the incorporation of cover crops in high tunnel cultivation should be carefully evaluated, particularly regarding their long-term benefits. However, a longer study period may be needed to make coherent conclusions.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eCupina B, Vujic\u0026acute; S, Krstic\u0026acute; DJ, Radanovic\u0026acute; Z, ˇCabilovski R, Manojlovic\u0026acute; M, Latkovic\u0026acute; D (2017) Winter cover crops as green manure in a temperate region: The effect on nitrogen budget and yield of silage maize. Crop Pasture Sci 68:1060\u0026ndash;1069\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAcosta-Mart\u0026iacute;nez V, Dowd SE, Bell CW, Lascano R, Booker JD, Zobeck TM, Upchurch DR (2010) Microbial community composition as affected by dryland cropping systems and tillage in a semiarid sandy soil. Diversity 2:910\u0026ndash;931\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAcu\u0026ntilde;a JC, Villamil M (2014) Short-term effects of cover crops and compaction on soil properties and soybean production in Illinois. 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Hort Technol 25(1):139\u0026ndash;146\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"University of Arkansas at Pine Bluff","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Cover crops, Microbial activity, Soil Conservation, Environmental sustainability, Food security","lastPublishedDoi":"10.21203/rs.3.rs-6135967/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6135967/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCover cropping has been demonstrated as a viable solution to mitigate soil challenges and improve subsequent crop yield, particularly in open-field conditions. However, their impact in high tunnels remains relatively unknown. This study assessed the short-term effect of single and mixed species of cover crops on selected soil properties, nutrient concentration and yield of sweet potatoes in high tunnels at the University of Arkansas at Pine Bluff research farm. using a randomized complete block design and two over crops; Crimson clover (\u003cem\u003eTrifolium incarnatum\u003c/em\u003e), winter barley (\u003cem\u003eHordeum vulgare)\u003c/em\u003e, and no-cover crop (control). The results indicated that single and mixed cover crops had no significant (P ˃ 0.05) effect on macronutrients and yield of sweet potatoes. However, soil microbial activity and micronutrient concentration in sweet potato leaves were significantly increased by use of winter barley. The combination of species of winter barley and crimson clover showed the highest microbial biomass (56.01 nmoles/g) compared to other study treatments despite the effects not being statistically significant. Therefore, the decision to incorporate cover crops in high tunnel cultivation should be decided judiciously. A long-term study is needed to draw more conclusive findings.\u003c/p\u003e","manuscriptTitle":"Evaluating Cover Crops for Soil Conservation and Food Security in High Tunnel Sweet Potato Production","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-04 04:26:57","doi":"10.21203/rs.3.rs-6135967/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"55291fdd-98df-496d-aad9-c764aa242e63","owner":[],"postedDate":"March 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":45060300,"name":"Agronomy"},{"id":45060301,"name":"Food Science \u0026 Technology"}],"tags":[],"updatedAt":"2025-03-04T04:26:58+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-04 04:26:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6135967","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6135967","identity":"rs-6135967","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}