High doses of fine biochar in sandy subsoils increase water retention, but also cause first-year yield depressions for drought-stressed barley

2025 · doi:10.1101/2025.10.09.681326
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High doses of fine biochar in sandy subsoils increase water retention but reduce first-year barley yield and nitrogen uptake due to immobilization.

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The paper investigated whether incorporating high doses of fine-grained biochar (150 or 300 Mg/ha, tested as 1%, 2%, and 4% fine biochar or 2% pellets) into coarse sandy subsoil layers could improve water retention, nutrient uptake, root development, and spring barley performance under drought conditions, using a two-year mesocosm soil-column study in 2022–2023. Ground fine biochar increased available water capacity, while intact biochar pellets showed no measurable effect; however, the first-year (2022) biochar treatments reduced plant growth and nitrogen uptake, likely due to nitrogen immobilization, and root density decreased with increasing biochar concentration in one soil type, possibly linked to higher potassium levels. In the second year (2023), after winter irrigation, yield effects shifted to neutral to positive, and phosphorus uptake remained unimproved despite wetter, P-enriched subsoils. The study’s main limitation is that it is a controlled mesocosm experiment with only two seasons, so it cannot fully characterize longer-term field-scale nutrient dynamics and application methods, which the authors call for via long-term trials. The paper does not explicitly discuss endometriosis or adenomyosis; it was included in the corpus via a keyword match in the upstream search index.

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Abstract

Context Coarse sandy subsoils often suffer from low water retention and rooting depth, limiting crop yields, especially under drought conditions. Aims To determine whether high doses of fine-grained biochar (150 or 300 Mg/ha) incorporated into sandy subsoil could improve water retention, nutrient uptake, root development and yield of spring barley under drought conditions. Methods A two-year mesocosm study (2022-2023) using soil columns containing subsoil layers of ground biochar (<80 µm, at 1%, 2% and 4%) or biochar pellets (2%) compared to unamended controls in two sandy soils. Key results Ground biochar increased available water capacity while intact pellets showed no measurable effect. First-year (2022) biochar applications negatively affected plant growth and nitrogen (N) uptake, likely due to N immobilization. Second-year (2023) results showed neutral to positive yield effects following winter irrigation. Biochar addition did not improve phosphorus uptake, despite the creation of wetter subsoils enriched with P. Root density decreased with increasing biochar concentration especially in one soil type, possibly due to increased potassium levels. Rooting depth was unaffected and greater than under field conditions. Conclusions Biochar incorporation into sandy subsoils can improve water retention, but may cause temporary N immobilization, affecting first-year crop performance. Overall benefits may emerge in subsequent growing seasons. Implications Long-term field trials are needed to assess nutrient management strategies, including additional N-application the first year. Incorporating biochar in autumn may help avoid N immobilization before spring sowing. Field-scale methods for applying fine-grained biochar to sandy subsoil must be developed. Highlights Fine-grained biochar can increase the in-situ water retention in coarse sandy subsoils In the first season (2022), biochar reduced barley growth and yield, likely due to initial soil nitrogen immobilization In the second season (2023), after intensive winter irrigation, biochar effects became neutral or positive Root density decreased with biochar use, possibly due to high potassium levels creating unfavourable subsoil conditions
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Abstract

Context Coarse sandy subsoils often suffer from low water retention and rooting depth, limiting crop yields, especially under drought conditions. Aims To determine whether high doses of fine-grained biochar (150 or 300 Mg/ha) incorporated into sandy subsoil could improve water retention, nutrient uptake, root development and yield of spring barley under drought conditions.

Methods

A two-year mesocosm study (2022-2023) using soil columns containing subsoil layers of ground biochar (<80 µm, at 1%, 2% and 4%) or biochar pellets (2%) compared to unamended controls in two sandy soils. Key results Ground biochar increased available water capacity while intact pellets showed no measurable effect. First-year (2022) biochar applications negatively affected plant growth and nitrogen (N) uptake, likely due to N immobilization. Second-year (2023) results showed neutral to positive yield effects following winter irrigation. Biochar addition did not improve phosphorus uptake, despite the creation of wetter subsoils enriched with P. Root density decreased with increasing biochar concentration especially in one soil type, possibly due to increased potassium levels. Rooting depth was unaffected and greater than under field conditions.

Conclusions

Biochar incorporation into sandy subsoils can improve water retention, but may cause temporary N immobilization, affecting first-year crop performance. Overall benefits may emerge in subsequent growing seasons. Implications Long-term field trials are needed to assess nutrient management strategies, including additional N-application the first year. Incorporating biochar in autumn may help avoid N immobilization before spring sowing. Field-scale methods for applying fine-grained biochar to sandy subsoil must be developed. Highlights Fine-grained biochar can increase the in-situ water retention in coarse sandy subsoils In the first season (2022), biochar reduced barley growth and yield, likely due to initial soil nitrogen immobilization In the second season (2023), after intensive winter irrigation, biochar effects became neutral or positive Root density decreased with biochar use, possibly due to high potassium levels creating unfavourable subsoil conditions Competing Interest Statement The authors have declared no competing interest.

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