Soil Aggregation Is Affected By Crop Phase in Organic Row Crop Rotations.

As organic growers are limited in which nutritional amendments they may apply to their fields, the health and fertility of their soil are of special concern. Soil organic carbon (SOC) is among the most important factors in soil health and structure, influencing aggregation, aggregate stability, nutrient availability, water holding capacity, and many other beneficial chemical and production properties of soils. While organic growers using practices accepted as beneficial for carbon storage and stabilization are positioned to make gains in SOC, a long-term study at the Wisconsin Integrated Cropping Systems Trial (WICST) found that SOC was being lost in every system, including organic plots in which one of these beneficial practices, cover-cropping, was well-established. These findings show that despite SOC’s importance, the plant- and microbial-mediated processes of SOC storage within soil aggregates are not well-understood.  With a sustainable intensification study at WICST, funded by the CERES Trust, we are investigating the impacts of intensified cover-cropping and reduced tillage treatments on soil aggregate carbon pools. The aim of this ongoing research is to provide information about which management practices may benefit organic growers seeking improvements in soil health and fertility. Preliminary results show proportions of various aggregate size classes (macroaggregates, microaggregates, and silt + clay) appeared to differ among crop phases within a rotation, indicating the level of SOC protection may not be static between crop phases. An implication of these results is that more frequent soil sampling is likely required to adequately characterize soil aggregation in crop rotations. Studies that sample during a single crop phase or compare entire rotations may miss nuances in soil aggregate dynamics.