Soil carbon and nitrogen dynamics as affected by inputs of dairy manure and poultry litter

Abstract

Due to increased environmental awareness and concern for cleaner drinking water, improved sustainable agricultural practices are becoming more important. Overestimating fertilizer recommendations can potentially lead to nitrate accumulation in surface and groundwater. A rapid soil test based on biological systems which are sensitive to changing soil conditions could help improve fertilizer N recommendations and prevent potential contamination from agricultural inputs. The soil microbial biomass is largely responsible for the transformation of organic matter into inorganic nutrients available for plant uptake and the microbe's pivotal role in agriculture is not completely understood. The need for a better understanding of the seasonal variation in soil microbial biomass and its effects on C and N mineralization would be valuable. The objectives of this study were to: 1) evaluate and optimize parameters for the arginine ammonification procedure to estimate soil microbial biomass C (SMBC) and N mineralization in soils receiving animal manure, 2) evaluate the one-day C02 procedure as a possible routine test for estimating N mineralization in manured soils, 3) determine soil microbial biomass C and N on a monthly basis and correlate with weather trends and animal manure inputs, 4) monitor C and N mineralization in longer term, 24-day incubations as well as initial inorganic N and soil organic carbon on a monthly basis, 5) correlate results of the above procedures with crop yield and N uptake. Arginine ammonification showed strong correlation with SMBC and N mineralization in soil receiving dairy cattle manure-amended plots on 4 of the 8 sample dates. Substrate interference from manure appeared to be a source of interference, and therefore, arginine ammonification was not recommended for estimation of SMBC or N mineralization in soils receiving animal waste. One-day C02 evolution from dairy manure- mineralization in soils receiving animal waste. One-day C02 evolution from dairy manure-amended soils correlated significantly (P<0.05) with SNMC and N mineralization in all eight sampling months. One-day C02 from samples taken prior to the growing season also correlated very strongly with forage N uptake in dairy manure-treated plots (r 2=0. 93). Nitrogen mineralization averaged 40 % from dairy manure in the field across all treatments. The C:N ratio of soil-applied manure or litter should be analyzed to better predict N mineralization potential.