Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 19, 1999
Publication Date: N/A
Interpretive Summary: Use of conventional tillage in dryland cropping systems has reduced soil C which results in degradation of soil properties important for water infiltration and nutrient retention. Stubble mulch and no-till reduce the C losses because of limited soil disturbance. Increasing cropping intensity may also help conserve soil C by returning more C in the form of crop residues. The effect of tillage and cropping frequency on C and N pools was evaluated at Bushland TX. Continuous wheat consistently resulted in greater gains in soil C and N, microbial C and N, and measures of C and N activity under both tillage practices. Greater gains in these pools occurred with no-till than with stubble mulch. Differences in soil C and N pools among phases of wheat-sorghum-fallow were observed and attributed to prior differences in crop production due to climatic effects. N removal under continuous cropping resulted in a high correlation with decreasing soil N and soil C. Although N may not limit yields under dryland conditions where water is the most limiting factor, N additions are needed to maintain soil C and N pools especially in intensive cropping systems.
Technical Abstract: Biological and chemical measures were used to determine if cropping and tillage influence on soil C and N characteristics under dryland conditions in the Southern High Plains. A Pullman clay loam (fine, mixed, thermic Torrertic Paleustol) from a study comparing no-tillage (NT) and stubble mulch(SM) at Bushland, TX, using wheat (Triticum aestivum L.)-sorghum [Sorghum bicolor (L.) Moench]-fallow (WSF), continuous wheat(CW)and continuous sorghum (CS) was sampled at 3 depths. For CW, CS, and three WSF phases (FWSF, SWSF, WWSF), soil organic C (SOC)ranged from 10.6 to 13.06 kg m-3 and was greatest for CW. CW had more soil organic N (SON) (1.45 kg m-3) than other treatments (1.08 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, soil microbial biomass N (SMBN) was 0.14 and 0.11 kg m-3, mineralizable C (MC) was 60 % greater in NT, proportion of SOC as SMBC was 11% greater in NT, and SON was 25% greater in NT. When summed for the profile NT had more SOC (977 vs 848 g m-2 )and SON (98 vs 88 g m-2 ) than SM, and CW consistently had greater or equal measures of C and N activity as other cropping treatments. FWSF had more MC, MN, and SOC as SMBC than SWSF and WWSF. Negative correlations were present between yield and SOC, SMBC, MC, SON, and SMBN. A greater potential for C and N conservation exists under dryland conditions using NT with CW because of shorter fallow and reduced soil disturbance.