Soil health benefits of compost persist two decades after single application to winter wheat

The effectiveness of frequent compost application in improving soil health is well-documented. Less is known on the long-term effects of infrequent compost application to semiarid soils. Compost made of dairy manure and straw bedding was applied once in a dryland organic hard red winter wheat (Triticum aestivum L. emend. Thell.)–fallow system at 50 Mg ha⁻¹ dry wt. in 1994 in a randomized complete block design with three replicates. Twenty-eight years later, yields in composted plots (1.4 Mg ha⁻¹) remained higher (p < 0.1) than in control plots (0.79 Mg ha⁻¹). Plant-available P, acid phosphatase activity (ACP), and total N were higher in composted plots by 143%, 37%, and 29%. Soil organic carbon (SOC) and dehydrogenase enzyme activity were greater by 25% and 20% with compost compared to the control, as were aggregate stability determined using SLAKES method, autoclave-extractable protein, and CO₂-96 h by 143%, 22%, and 16%. Soil extractable K and Zn also increased with compost application. The interaction of ACP and estimated evapotranspiration (ET) emerged as a pivotal factor in explaining the variation in yield. These findings suggest that growers may see some yield improvements from periodic compost applications to dryland organic winter wheat–fallow systems. This strategy could help rebuild SOC and partially counter the challenges of low and variable precipitation.