title: Soil carbon and nitrogen fractions and crop yields affected by residue placement and crop types.
abstract: Soil labile C and N fractions can change rapidly in response to management practices compared to non-labile fractions. High variability in soil properties in the field, however, results in nonresponse to management practices on these parameters. We evaluated the effects of residue placement (surface application [or simulated no-tillage] and incorporation into the soil [or simulated conventional tillage]) and crop types (spring wheat [Triticum aestivum L.], pea [Pisum sativum L.], and fallow) on crop yields and soil C and N fractions at the 0-20 cm depth within a crop growing season in the greenhouse and the field. Soil C and N fractions were soil organic C (SOC), total N (STN), particulate organic C and N (POC and PON), microbial biomass C and N (MBC and MBN), potential C and N mineralization (PCM and PNM), NH4-N, and NO3-N concentrations. Yields of both wheat and pea varied with residue placement in the greenhouse as well as in the field. In the greenhouse, SOC, PCM, STN, MBN, and NH4-N concentrations were greater in surface placement than incorporation of residue and greater under wheat than pea or fallow. In the field, MBN and NH4-N concentrations were greater in no-tillage than conventional tillage, but the trend reversed for NO3-N. The PNM was greater under pea or fallow than wheat in the greenhouse and the field. Average SOC, POC, MBC, PON, PNM, MBN, and NO3-N concentrations across treatments were higher, but STN, PCM and NH4-N concentrations were lower in the greenhouse than the field. The coefficient of variation for soil parameters ranged from 2.6 to 15.9% in the greenhouse and 8.0 to 36.7% in the field. Although crop yields varied, most soil C and N fractions were greater in surface placement than incorporation of residue and greater under wheat than pea or fallow in the greenhouse than the field within a crop growing season. Short-term management effect on soil C and N fractions were readily obtained with reduced variability under controlled soil and environmental conditions in the greenhouse compared to the field. Changes occurred more in soil labile than non-labile C and N fractions in the greenhouse than the field.
authors.affiliation: College of Urban and Environmental Sciences, Northwest University, Xian, Shaanxi Province, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Northern Plains Agricultural Research Laboratory, Sidney, Montana, United States of America.
authors.forename: Upendra M
authors.initials: UM
authors.lastname: Sainju
mesh_terms: D000383:Agriculture / Q000379:methods; D018533:Biomass; D002244:Carbon / Q000032:analysis*; D018556:Crops, Agricultural / Q000254:growth & development*; D009584:Nitrogen / Q000032:analysis*; D018532:Pisum sativum / Q000254:growth & development*; D012621:Seasons; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D014908:Triticum / Q000254:growth & development*
chemical_list: D012987:Soil; D002244:Carbon; D009584:Nitrogen