Atmospheric dryness impacts on crop yields are buffered in soils with higher available water capacity

Abstract

Atmospheric dryness has been recognized as a dominant driver for agroecosystem functioning due to its limiting controls on stomatal behavior, even under sufficient soil moisture. Due to its relative importance in influencing carbon and water fluxes, atmospheric dryness has emerged as an important element of global change, jeopardizing food security and agricultural profitability via negative impacts on crop yields. Although negative impacts of atmospheric dryness are well recognized at various scales, it is unknown how heterogeneity in soils’ ability to retain water for plant uptake affects crop yields’ response to increasing atmospheric dryness. To address this, we analyzed how soil available water capacity (AWC) affects the response of crop yields to space and time variation in summer (June-July-August) vapor pressure deficit (VPDJJA) across the conterminous U.S. (CONUS) during 1980–2020 using 77,701 and 51,190 county-year records for maize and soybean, respectively. A distinct co-distribution of VPDJJA and AWC regimes is experienced by maize and soybean acreage and is subject to significant yield variation. Accounting for entire AWC heterogeneity in CONUS, both crops showed a positive yield response to increasing VPDJJA until 0.8 kPa, thereafter showing a gradually increasing negative response to VPDJJA increase. Upon soil-specific investigation of yield response to VPD, the yield sensitivity parameter to VPDJJA became less negative as soil AWC increased, implying buffering of dryness impacts on yields as the ability of soils to retain water increased. For VPDJJA increase between 1.0 kPa and 1.4 kPa, mean VPDJJA impacts on maize yields in soils with 10 %<AWC < 12.5 % were buffered by one-half (50.6 %) as compared with 7.5 %<AWC < 10 % soils. Increasing AWC from 10 to 12.5 % class to 12.5–15 % class further buffered VPDJJA impacts on maize yields by 26.2 %. VPDJJA impacts on soybean yields in soils with 15 %<AWC < 17.5 % were buffered by 40 % as compared with 12.5 %<AWC < 15 % soils. Further increase in AWC (17.5–20 %) resulted in additional 15.5 % buffering of VPDJJA impacts on soybean as compared to impacts recorded for 15 %<AWC < 17.5 % soils. The greatest buffering of negative impacts from VPDJJA were found when AWC is>10 % and 15 % for maize and soybean, respectively. Possible physical mechanisms responsible for this buffering are improved plant physiological function and fulfilment of evaporative demand due to additional soil water resulting from higher AWC, given sufficient water supply. This empirical large-scale evidence of mediating role of AWC for crop yield impacts from a dryer atmosphere underscores the critical nature of soils to support climate-smart agricultural practices via building soil organic matter as well as providing co-benefits for improved crop performance to meet current and future population’s food and fiber needs.