Response of Soil Carbon Fractions and Microbial Activities to Different Rates of Manure and Inorganic Fertilizer Applications Under Soybean Production.

Soil microbial ecology is important for soil health maintenance because of its influence on carbon and nitrogen cycling, and other soil properties. Agricultural sustainability and environmental quality are influenced directly and indirectly by the quality and quantity of soil organic carbon (SOC) contributions to soil. Soil organic matter is both synthesized and degraded by microbial enzyme activities. The balance between these two competing processes determines the rate of carbon sequestration, microbial diversity and activity; enzyme dynamics; and by extension, soil fertility and plant productivity. We therefore hypothesized that application of manure based on P and N contents can influence C and N fractions, enzymes activities and microbial communities, and hence improve soil health. Phospholipid lipid fatty acids can be used to describe viable microbial communities in terms of total biomass and community composition. The experiment had three different manure application rates: recommended manure rate based on the P concentration, recommended manure rate based on N concentration, and two times recommended N manure rate (2N). Additionally, three different commercial fertilizer application rates were used: recommended fertilizer (N-P-K) rate based on soil test recommendations, double recommended rate, and no fertilizer control. Treatments were arranged in a randomized complete block design with four replications. Soil samples were collected three times in 2015 (before planting soybean in May, one month after planting soybean, and after soybean) from 0-7.5 cm depth. Results of study indicate that 2N manure applications had higher enzyme activities and stable C during growing season in comparison to all inorganic fertilizer application rates. Inorganic fertilizer had higher urease and beta glucosidase activity before planting and after soybean. P applied plots had highest enzymes activity during growing season. These results suggest that the application of manure enhanced soil microbial properties and SOC stability.