Main content area

Carbon and nitrogen conservation in dryland tillage and cropping systems

Schomberg, H.H., Jones, O.R.
Soil Science Society of America journal 1999 v.63 no.5 pp. 1359
Triticum aestivum, Sorghum bicolor, fallow, crop rotation, no-tillage, continuous cropping, stubble mulching, dryland farming, soil organic matter, nitrogen, carbon, soil microorganisms, biomass, biological activity in soil, biogeochemical cycles, crop residues, soil organic carbon
Soil C and N greatly influence long-term sustainability of agricultural systems. We hypothesized that cropping and tillage differentially influence dryland soil C and N characteristics in the Southern High Plains. A Pullman clay loam (fine, mixed, thermic Torrertic Paleustol) cropped to wheat (Triticum aestivum L.)-sorghum [Sorghum bicolor (L.) Moench]-fallow (WSF), continuous wheat (CW) and continuous sorghum (CS) under no-tillage (NT), and stubble mulch (SM) was sampled at three depths to determine soil C and N characteristics. For CW, CS, and WSF phases (F(WSF), S(WSF), W(WSF)), soil organic C (SOC) averaged 10.6 to 13.1 kg m(-3) and was greatest for CW. Carbon mineralization (C(MIN)) at 0 to 20 mm was 30 to 40% greater for CW and F(WSF) than for CS, S(WSF), or W(WSF). Cropping system by depth influenced soil organic N (SON) with greatest SON at 0 to 20 mm in CW (1.5 kg m(-3)). At 0 to 20 mm for SM and NT, SOC was 9.9 and 12.5 kg m(-3), soil microbial biomass C (SMBC) was 0.80 and 1.1 kg m(-3), and soil microbial biomass N (SMBN) was 0.14 and 0.11 kg m(-3). Also at 0 to 20 mm, NT had 60% greater C(MIN), 11% more SMBC as a portion SOC, and 25% more SON compared to SM. Summed for 0 to 80 mm, NT had more SOC (0.98 vs. 0.85 kg m(-2)) and SON (0.10 vs 0.9 kg m(-2)) than SM, and CW had greater or equal C and N activity as other systems. Negative correlations between yield and SOC, SMBC, C(MIN), SON, and SMBN indicate N removal in grain negatively affects active and labile C and N pools. Under dryland conditions, C and N conservation is greater with NT and with winter wheat because of less soil disturbance and shorter fallow.