Reconciling opposing soil processes in row-crop agroecosystems via soil functional zone management

Authors: WILLIAMS, ALWYN - University Of Minnesota; Davis, Adam; JILLING, ANDREA - University Of New Hampshire; GRANDY, A STUART - University Of New Hampshire; KOIDE, ROGER - Brigham Young University; SMITH, RICHARD - University Of New Hampshire; SNAPP, SIEGLINDE - Michigan State University; Spokas, Kurt; YANNARELL, ANTHONY - University Of Illinois; JORDAN, NICHOLAS - University Of Minnesota

Submitted to: Journal of Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2016
Publication Date: 1/5/2017
Citation: Williams, A., Davis, A.S., Jilling, A., Grandy, A., Koide, R.T., Smith, R.G., Snapp, S.S., Spokas, K.A., Yannarell, A.C., Jordan, N.R. 2017. Reconciling opposing soil processes in row-crop agroecosystems via soil functional zone management. Journal of Applied Ecology. 236:99-107.

Interpretive Summary: Maintaining soil fertility over the long run requires balancing practices that build soil organic matter with those that draw upon the nutrient reserves in the organic matter. Soil functional zone management (SFZM), a novel strategy for row-crop production, attempts to reconcile conflicting soil processes by placing them side by side at sub-meter spatial scales. We assessed the magnitude and spatial distribution of nutrient provisioning and soil building processes in SFZM and conventional tillage systems in four states across the US Corn Belt. For soil building we measured bulk density, aggregation and organic carbon (SOC); for nutrient provisioning we measured microbial decomposition activity, nutrient mineralization and available nitrogen. After two years, SOC increased under SFZM (0-20 cm depth) compared with conventional tillage. SFZM also enhanced soil available nitrogen within crop rows at the time of maize peak nitrogen demand. Our analyses showed that improvements in soil building processes also had a positive effect on nutrient provisioning processes. For soils with low initial levels of SOM, increases in SOC stimulated microbial decomposition activity, which was associated with increased nitrogen availability. This may particularly useful for regions with degraded soils, which would benefit from rapid increases in surface SOC. Also, by concentrating and promoting nutrient provisioning processes around crop roots during crop peak nitrogen demand, SFZM may enhance nitrogen-use efficiency and reduce current fertilizer requirements.

Technical Abstract: Sustaining soil productivity in agroecosystems presents a fundamental ecological challenge: nutrient provisioning depends upon aggregate turnover and microbial decomposition of organic matter (SOM); yet to prevent soil depletion these processes must be balanced by those that restore nutrients and SOM (soil building processes). Incorporating spatial heterogeneity at decimeter scales, i.e. across crops rows and inter-rows, may enable coexistence of these soil processes. Soil functional zone management (SFZM), a novel strategy for row-crop production, attempts to create such spatial heterogeneity, but its capacity to reconcile conflicting soil processes is unknown. We assessed the magnitude and spatial distribution of nutrient provisioning and soil building processes in SFZM and conventional tillage systems in four states across the US Corn Belt. For soil building we measured bulk density, aggregation and organic carbon (SOC); for nutrient provisioning we measured microbial decomposition activity, nutrient mineralization and available nitrogen. After two years, SOC increased under SFZM (0-20 cm depth) compared with conventional tillage. SFZM also enhanced nutrient provisioning processes in crop rows, increasing soil available nitrogen in synchrony with maize peak nitrogen demand. Structural equation modelling revealed a self-reinforcing benefit of SFZM, whereby improvements in soil building processes had a positive effect on nutrient provisioning processes. For soils with low initial levels of SOM, increases in SOC stimulated microbial decomposition activity, which was associated with increased nitrogen availability. The decimeter-scale spatial heterogeneity created by SFZM enables reconciliation of nutrient provisioning and soil building processes in row-crop agroecosystems. In doing so, SFZM promotes critical soil processes necessary for ecological intensification. This may have particular relevance for regions with degraded soils, which would benefit from rapid increases in surface SOC. Also, by concentrating and promoting nutrient provisioning processes around crop roots during crop peak nitrogen demand, SFZM may enhance nitrogen-use efficiency and reduce current fertilizer requirements.