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Tillage and residue management effects on soil carbon and nitrogen under irrigated continuous corn

Schmer, M. R, Jin, V. L., Wienhold, B. J., Varvel, G. E., Follett, R. F.
Soil Science Society of America journal 2014 no.6 v.78 pp. 1987-1996
Zea mays, biofuels, biomass production, carbon, carbon cycle, continuous cropping, conventional tillage, corn, corn stover, discing, forage, grain yield, irrigation, isotopes, nitrogen, no-tillage, nutrient content, soil amendments, soil nutrients, soil organic carbon, soil profiles
Demand for corn (Zea mays L.) stover as forage or as a cellulosic biofuel has increased the importance of determining the effects of stover removal on biomass production and the soil resource. Our objectives were to evaluate grain yield, soil organic C (SOC), and total soil N (0 to 150 cm) in a 10-year, irrigated, continuous corn study under conventional disk tillage (CT) and no-till (NT) with variable corn stover removal rates (none, medium, high). Natural abundance C isotope compositions were used to determine C additions by corn (C4-C) to the soil profile and to evaluate the retention of residual C3-C. After ten years of management treatments, mean grain yields were 7.5% to 8.6% higher for NT when residue was removed compared with no stover removal, while grain yields were similar for CT in all stover removal treatments. Turnover of SOC occurred as C3-C stocks were replaced by C4-C in the 0- to 120-cm soil profile. Total SOC and N stocks changed mainly in surface soils (0 to 30 cm), with no detectable cumulative changes at 0 to 150 cm. Specifically, SOC declined after 10 yr under CT at 0 to 15 cm and was affected by residue management at 15 to 30 cm. Total soil N was greater when no stover was removed (P = 0.0073) at 0 to 15 cm and from residue management at 15 to 30 cm. Total soil N was greatest when no residue was removed (P=0.0073) compared to high stover removal at 0 to 15 cm. Long-term NT ameliorated medium stover removal effects by maintaining near-surface SOC levels. Results support the need to evaluate SOC cycling processes below near-surface soil layers.