Compost Input Effect on Dryland Wheat and Forage Yields and Soil Quality

Organic agricultural systems rely on organic amendments to achieve crop fertility requirements, and weed control must be achieved without synthetic herbicides. Our objective was to determine the crop yield and soil quality as affected by a transition from grass to dryland organic agriculture in the Central Great Plains of North America. This study evaluated three beef feedlot compost (BFC) treatments in 2010-2015 following biennial application rates: 0 (control), 22.9, and 108.7 t ha−1 on two dryland organic cropping systems: a wheat (Triticum aestivum)-fallow (WF) rotation harvested for grain and a triticale (Triticosecale)/pea (Pisum sativum)-fallow (T/P-F) rotation harvested for forage. The triticale + pea biomass responded positively to the 108.7-t ha−1 BFC treatment, but not the 22.9-t ha−1 BFC treatment. The wheat biomass was not affected by BFC addition, but biomass N content increased. Beef feedlot compost input did not increase wheat grain yields, but had a positive effect on wheat grain Zn content. Soil total C and N contents increased with the rate of 108.7 t ha−1 BFC after three applications, but not with 22.9 t ha−1 BFC. Soil enzyme activities associated with N and C cycling responded positively to the 108.7-t ha−1 BFC treatment. Saturated salts were high in the soil receiving 108.7 t ha−1 of BFC, but did not affect crop yields. These results showed that BFC was effective in enhancing forage yields, wheat grain quality, and soil C and N, as well as specific microbial enzymes important for nutrient cycling. However, the large rates of BFC necessary to elicit these positive responses did not increase grain yields, and resulted in an excessive buildup of soil P.