Cover crops have been proposed as a tool for adapting cropping systems to drought stress caused by climate change. However, little research has directly evaluated whether cover crops reduce drought stress in the following cash crop. We grew maize in both ambient and imposed drought conditions following four functionally diverse cover crops and a fallow control in a two-site-year study. We looked for evidence that cover crops reduced drought stress by improving cash crop water access or nitrogen (N) status. The study was embedded in an organic cropping systems trial in Pennsylvania, USA. Cover crops and manure fertilizer were incorporated with full inversion tillage.

Overall, cover crops neither ameliorated nor exacerbated drought stress in the following maize crop. There was no interaction between cover crop and moisture treatment in a mixed model ANOVA predicting maize kernel yield in either year. Drought reduced yield by 33 % in 2014 and 17 % in 2015. Cereal rye (Secale cereale L. cv. Aroostook) reduced yield relative to cover crop treatments that contained legumes by up to 43 %. There were no other yield differences among cover crop treatments, including the fallow control. Our results are likely influenced by the short legacy of cover cropping (only one or two preceding cover crops) and the use of full inversion tillage. Cover crops may have greater potential to reduce maize drought stress after long-term use, in systems with less soil disturbance, and when residues are retained on the soil surface. Further research is needed to assess the potential for cover crops and other soil-building practices to reduce drought stress by increasing infiltration rates, improving soil water-holding capacity, enhancing cash crop root exploration, and reducing evaporation from the soil surface.

Multiple lines of evidence in this study lead to a new hypothesis: cropping systems that rely on cover crops and other organic amendments for N supply may be at risk for N limitation under drought. First, drought reduced mineralization of N from cover crop residues, especially cereal rye. Second, drought reduced maize N status when topsoil drying was more severe. Since cover crop residues and manure were concentrated in the plow layer (top 20 cm) and maize roots extended into the subsoil, topsoil drying may have reduced N mineralization more than crop water uptake. Further research is needed to determine whether and under what circumstances the hypothesized effect meaningfully reduces crop yield.

有人建议将覆盖作物作为使作物系统适应气候变化引起的干旱胁迫的工具。但是，很少有研究直接评估覆盖作物是否能减轻随后的经济作物的干旱压力。在一项为期两年的研究中，在四种功能多样的覆盖作物和休耕控制之后，我们在环境干旱和强旱条件下都种植了玉米。我们寻找的证据表明，有盖作物通过改善经济作物的水供应或氮（N）状况而减轻了干旱压力。该研究被嵌入美国宾夕法尼亚州的有机种植系统试验中。覆盖作物和肥料施以充分的反向耕作。

总体而言，在随后的玉米作物中，覆盖作物既没有改善也没有加剧干旱胁迫。在混合模型ANOVA中，在任何一年中预测玉米籽粒产量的覆盖作物和水分处理之间都没有相互作用。干旱导致2014年减产33％，2015年使减产17％。谷物黑麦（Secale谷物L.简历 相对于包含豆类作物的覆盖作物处理，Aroostook）的产量降低了43％。包括休耕控制在内的覆盖作物处理之间没有其他产量差异。我们的结果可能会受到覆盖作物耕作的短暂遗留（仅一种或两种先前的覆盖作物）和完全倒置耕作的使用的影响。在长期使用之后，在土壤干扰较小的系统中以及当残留物保留在土壤表面时，覆盖作物可能具有更大的潜力来减轻玉米的干旱胁迫。需要进行进一步的研究，以评估通过增加渗透率，提高土壤持水能力，加强经济作物根系探索和减少土壤表层蒸发来减少农作物和其他土壤建设措施以减轻干旱压力的潜力。

这项研究中的多条证据导致了一个新的假设：依靠覆盖作物和其他有机改良物供应氮素的种植系统可能会在干旱下面临限制氮素的风险。首先，干旱减少了农作物残留物特别是谷类黑麦中氮的矿化。第二，当表土干燥更加严重时，干旱降低了玉米的氮素状态。由于覆盖的农作物残余物和肥料集中在耕作层（最高20厘米）中，而玉米根部延伸到土壤中，因此表土干燥比作物吸收水分更能减少氮矿化。需要进行进一步的研究以确定假设的效果是否以及在什么情况下有意义地降低了农作物的产量。