Field trials were conducted with a tomato-cucumber (double crop)-sweet corn-tomato rotation in Florence, SC (coastal plain) and Chattahoochee Hills, GA (piedmont) to determine whether diversified organic inputs and conservation tillage can build organic matter and fertility in the region’s challenging Ultisol soils. Factorial treatments included cover crops (rye, vetch, rye + vetch, or none), reduced vs full tillage, and with vs without composted poultry manure (3-4-3) at 2.4 Mg/ha-yr. Data were collected on soil organic carbon (SOC) and nitrogen (N), microbial C, N, and P cycling, soil physical properties, and crop nutrient use efficiency, yield, and quality.

Rye, vetch, and manure compost had qualitatively different and potentially complementary impacts on soil microbial communities and nutrient cycling functions. Vetch and manure increased plant-available N but not SOC and reduced microbial diversity. Cover crops sustained microbial activity, stimulated nutrient mineralization, mitigated impacts of full tillage on SOC, reduced nitrous oxide (N2O) emissions, and sometimes boosted vegetable yields. Timely planting, sufficient duration, and adequate soil fertility enhanced cover crop biomass and associated benefits. However, none of the organic input combinations yielded a net increase in active or total SOC over the three-year period.

Yield responses to treatments varied among crops. Tomato yields did not respond to cover crops or manure and decreased in reduced tillage because of subsurface hardpan. Reduced tillage improved cucumber yield while rye cover crop reduced yield. Sweet corn yield was unaffected by tillage, higher with manure compost, and lower after rye.