Soil health explains the yield-stabilizing effects of soil organic matter under drought

Abstract

Soil organic matter (SOM) stands out as one of the foremost indicators of soil health. Soils with high SOM concentrations have been shown to be associated with high crop yield under drought conditions. However, a critical question remains unanswered: is the yield-stabilizing effect of SOM attributable to inherent soil properties, which remain unresponsive to agricultural management practices, such as soil texture and taxonomy? Or is it driven by dynamic soil properties that reflect the overall health of the soil? Following the Soil Health Assessment Protocol and Evaluation (SHAPE), we derived a soil health score (SHS; range: 0-1) from the SOM concentration by accounting for site-specific variables, including climate, texture, and soil suborder. Using county-level data of rainfed corn across the U.S. from 2000 to 2016, we found that higher SHSs were associated with higher yields. During the most severe drought events, an increase of 0.5 in SHS was associated with a 1.15 ± 0.18 Mg ha-1 increment in corn yield, suggesting that high SHS helps to stabilize yield in drought. Interestingly, smaller but statistically significant effects of SHS on yield were found during less intensive droughts. The SOM concentration was a slightly better predictor of corn yield than the SHS. We also found similar effects of SHS on yield across different soil peer groups, i.e., different textures or soil suborders, under severe drought conditions. Our results suggest that soil health was the main factor in explaining the yield benefits of SOM, while the effects of soil health were not driven by differences in soil texture or suborder. We argue that the resilience of corn yield against drought can be potentially increased by adopting agronomic practices aimed at augmenting SOM and improving overall soil health across a broad spectrum of geographical locations and site characteristics.

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