{"paper_id":"39ebd70c-e8f9-4b83-a22b-d5bd80a2c9f0","body_text":"A field-based method for evaluating nitrogen delivery accuracy in flow-proportional variable-rate fertigation systems | 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 Short Report A field-based method for evaluating nitrogen delivery accuracy in flow-proportional variable-rate fertigation systems Precious N. Amori, Derek M. Heeren, Guillermo R. Balboa, Tyler Smith, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8672548/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 Purpose Flow-proportional variable-rate fertigation (VRF) systems are used to support site-specific nitrogen (N) management under center-pivot irrigation; however, field-scale evaluations of actual N delivery under spatially variable operating conditions remain limited. This research brief presents a practical, field-based method to quantify as-applied N rates for a flow-proportional VRF system integrated with variable-rate irrigation (VRI). Methods Fertilizer drawdown measurements, pivot flow-totalizer records, and irrigation prescriptions were combined with management-unit geospatial processing to quantify as-applied irrigation depths and N rates during an in-season fertigation event. System-level irrigation and fertilizer volume accounting was performed to ensure mass-balance closure. As-applied N rates were derived assuming uniform fertilizer concentration under flow-proportional injection and were compared against prescribed rates at the management-plot scale. Results Strong spatial agreement was observed between prescribed and as-applied N rates (r = 0.993). Root mean square error (RMSE) and mean absolute error (MAE) were 2.52 and 2.41 kg N ha⁻¹, respectively. A consistent positive bias was observed, attributable to irrigation hydraulic variability and small mismatches between the irrigation-flow meter displayed on the pivot control panel and the flow sensor supplying input to the fertigation controller. System-level volume closure was achieved (R ≈ 1.01), supporting the validity of the quantification approach. Conclusion Outcome-based as-applied evaluation provides a practical and reproducible means of verifying VRF performance beyond assumed prescription execution. The proposed workflow enables reliable field-scale quantification of N delivery accuracy and supports improved agronomic record keeping and performance assessment in operational VRF–VRI systems. variable-rate fertigation variable-rate irrigation center-pivot irrigation as-applied nitrogen rates site-specific nitrogen management Full Text Additional Declarations No competing interests reported. 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-8672548\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":true,\"archivedVersions\":[],\"articleType\":\"Short Report\",\"associatedPublications\":[],\"authors\":[{\"id\":582292151,\"identity\":\"f06444d5-5939-46f4-a2b5-dfc7ffc9d02d\",\"order_by\":0,\"name\":\"Precious N. Amori\",\"email\":\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+UlEQVRIiWNgGAWjYNACAxs5AwYGZiiPuYGBgY2gljRjJC2MxGhhOJy4gWgt5uynEx9XFDCnb5dIf2zwcU8dg8HtxgaGD2WHcWqx7MndbHjGgC1354wc48QZzw4zGNw52MA44xxuLQYHcrdJNhjw5G64kcN8mOfAAQaDG4kNzLxteLScfwvSIpFucCP98eE/B+ogWv7i03IDbItBgsGNBONkhgPMEC2MeLRYzni72bDBIMFww5k3xoY9Bw7zSAK1HOw5l45Tizl/7saHDX/+yxscT38s8eNAnRzfjeSDD36UWeN2GLoAD4g4gFM9Ni2jYBSMglEwCjAAAOElXCorCerXAAAAAElFTkSuQmCC\",\"orcid\":\"\",\"institution\":\"University of Nebraska–Lincoln\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"Precious\",\"middleName\":\"N.\",\"lastName\":\"Amori\",\"suffix\":\"\"},{\"id\":582292152,\"identity\":\"a33ece03-d6f6-47cd-8c71-5de9031747f6\",\"order_by\":1,\"name\":\"Derek M. 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This research brief presents a practical, field-based method to quantify as-applied N rates for a flow-proportional VRF system integrated with variable-rate irrigation (VRI).\\u003c/p\\u003e\\u003ch2\\u003eMethods\\u003c/h2\\u003e \\u003cp\\u003eFertilizer drawdown measurements, pivot flow-totalizer records, and irrigation prescriptions were combined with management-unit geospatial processing to quantify as-applied irrigation depths and N rates during an in-season fertigation event. System-level irrigation and fertilizer volume accounting was performed to ensure mass-balance closure. As-applied N rates were derived assuming uniform fertilizer concentration under flow-proportional injection and were compared against prescribed rates at the management-plot scale.\\u003c/p\\u003e\\u003ch2\\u003eResults\\u003c/h2\\u003e \\u003cp\\u003eStrong spatial agreement was observed between prescribed and as-applied N rates (r\\u0026thinsp;=\\u0026thinsp;0.993). Root mean square error (RMSE) and mean absolute error (MAE) were 2.52 and 2.41 kg N ha⁻\\u0026sup1;, respectively. A consistent positive bias was observed, attributable to irrigation hydraulic variability and small mismatches between the irrigation-flow meter displayed on the pivot control panel and the flow sensor supplying input to the fertigation controller. System-level volume closure was achieved (R\\u0026thinsp;\\u0026asymp;\\u0026thinsp;1.01), supporting the validity of the quantification approach.\\u003c/p\\u003e\\u003ch2\\u003eConclusion\\u003c/h2\\u003e \\u003cp\\u003eOutcome-based as-applied evaluation provides a practical and reproducible means of verifying VRF performance beyond assumed prescription execution. The proposed workflow enables reliable field-scale quantification of N delivery accuracy and supports improved agronomic record keeping and performance assessment in operational VRF\\u0026ndash;VRI systems.\\u003c/p\\u003e\",\"manuscriptTitle\":\"A field-based method for evaluating nitrogen delivery accuracy in flow-proportional variable-rate fertigation systems\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2026-01-30 11:30:08\",\"doi\":\"10.21203/rs.3.rs-8672548/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"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\":\"80eed8c7-d886-4a87-adfd-12717605e487\",\"owner\":[],\"postedDate\":\"January 30th, 2026\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"posted\",\"subjectAreas\":[],\"tags\":[],\"updatedAt\":\"2026-05-08T07:11:05+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2026-01-30 11:30:08\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-8672548\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-8672548\",\"identity\":\"rs-8672548\",\"version\":[\"v1\"]},\"buildId\":\"XKTyCvWXoU3ODBz1xrDgd\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}