Johanie Rivera Zayas, Crops and Agroenviromental Sciences, Kansas State University, Manhattan, KS and Charles W. Rice, 2701 Throckmorton Hall, Kansas State University, Manhattan, KS
In grazed pastures the use of Brachiaria cultivars offer a chance for sustainable grazing system by using this plant genetic material with the appropriate agricultural practices in a suitable environment. Some Brachiaria cultivars have been highly studied for its capacity to exudate a biological nitrification inhibitor (BNI) which can increase nitrogen (N) use efficiency in the soil and mitigate N losses in grazed pastures. To better understand the direct effect of BNI in pastures we studied the soil N dynamics and microbial communities in high N hotspots created by urine patches. The trial, still in process, took place in a 10 year-old trial at the International Center of Tropical Agriculture (CIAT) located in Cali, Colombia. This 56-day in situ incubation tested two Brachiaria cultivars B. humidicola 16888, B. mulato hybrid 1, and a bare soil as a control. During the incubation greenhouse gas emissions for CO2, N2O and CH4 were measured. Plant N uptake was analyzed by cutting the grass every15 days to simulate grazing by cattle. Soil samples to a depth of 5 cm will be analyzed for nitrification capacity, pH, ammonia oxidizing bacteria, ammonia oxidizing archaea and microbial composition by phospholipids fatty acid analysis. Soil inorganic N will be measured in the surface 30 cm to assess inorganic N leaching. Preliminary results showed N2O suppression by Brachiaria cultivars. Final results are expected to show higher soil microbial diversity, an efficient soil N dynamics and a decrease in GHG and soil inorganic N leaching from the Brachiaria treatments.