Reconciling Opposing Soil Processes in Row-Crop Agroecosystems Via Soil Functional Zone Management.

Sustaining soil productivity in agricultural systems presents a fundamental agroecological 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). Management practices that create spatial separation between these conflicting processes may enable each to occur effectively within a single growing season, thereby supporting high crop yield while avoiding soil depletion. Soil functional zone management (SFZM), a novel strategy for annual row-crop production, may help meet this agroecological challenge by creating spatial heterogeneity in biophysical conditions between crop rows and inter-rows. We assessed the magnitude and spatial distribution of nutrient provisioning and soil building processes in SFZM and conventional tillage systems in four US states encompassing a major global agricultural production region. For soil building we measured bulk density, aggregation and organic carbon (SOC); for nutrient provisioning we measured microbial decomposition activity, nutrient mineralisation and plant-available nitrogen. After two years, SFZM increased SOC compared with conventional tillage. SFZM also enhanced nutrient provisioning processes in crop rows, increasing plant-available nitrogen in synchrony with maize peak nitrogen demand. Structural equation modelling revealed that improvement in soil building processes in SFZM enhanced nutrient provisioning processes in SOM-poor soils: increases in crop row SOC stimulated microbial decomposition activity, which was associated with increased plant-available nitrogen during the phase of maize peak nitrogen demand. The 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 increasing the range of ecosystem services provided by intensive production systems. SFZM may have particular value in regions with SOM-poor soils, which would benefit from rapid increases in surface SOC.