Replicated trials were conducted at two sites in the Palouse region and two sites in the Magic Valley region of Idaho to evaluate the efficacy of organic soil amendments and tillage on soil health. Alfalfa + orchardgrass were planted in 2021 and terminated in fall 2023 or spring 2024, followed by feed barley in 2024, and amended with compost or processed organic fertilizer. Three levels of tillage intensity were applied before alfalfa/grass planting and at termination. Treatments were compared for total soil organic carbon (TOC), microbially active (permanganate oxidizable) carbon (POxC), phosphorus (P), soluble nitrogen (N), bulk density and infiltration rate, earthworms, and crop yield. POxC, TOC, and earthworm populations increased with decreasing tillage, and the 2X compost rate enhanced TOC, available N and P, and barley yield, but had inconsistent effects on earthworms. Barley yields were highest in the high-tillage treatment.

Soil samples taken along three transects at each of 10 sites that had been under organic management for varying periods of time showed wide ranges in bulk density (0.7-1.5 g/cm3), infiltration (<1 to 600 cm/hr), SOM (1.5-10.6%), POxC (220-1,248 mg/kg), soluble N (7-139 mg/kg), available P (17-416 mg/kg), and earthworm biomass (0-200 g/m2). Soil aggregate stability, phospholipid fatty acids (PFLA, indicator of microbial biomass), POxC, and total soil N provided the most reliable indicators of soil health response to management.