Grazing and cover crop effects on soil health during transition to organic production

The authors studied the efficacy of six objective-based, reduced tillage cover cropping systems with or without livestock grazing to induce changes in soil condition and soil health on a fine sandy loam during the organic transition phase in the northern Great Plains. A randomized complete block design with a split-plot arrangement and four replicates was used in an experiment conducted at the USDA-ARS Northern Great Plains Research Laboratory, Mandan, ND. Main-plot factors were grazing versus no grazing, while six cover crop mixtures (soil building cover crop mix, pollinator cover crop mix, weed suppression cover crop mix, multipurpose cover crop mix, annual crop rotation, or perennial forage biculture) were the split-plot factors. Soil parameters were analyzed at the beginning and end of the 3-year organic transition period from 0- to 10-cm and 10- to 30-cm depth samples. No cover crop mixtures or grazing effect was observed on wet aggregate stability. However, wet aggregate stability decreased in all treatments after 3 years of organic transition. In general, soil pH decreased with the transition to organic systems. Soil organic C increased in both the grazed and ungrazed perennial forage biculture treatments and the ungrazed soil building, annual crop rotation, and multipurpose cover crop mixes. Soil total N increased under the grazed annual crop rotation. Aggregated soil quality index values did not vary between cover cropping systems after organic transition. Outcomes from this study provided useful insight into perennial and cover crop effects on key chemical and physical properties of soil known to influence crop productivity in semi-arid regions.