Characterization of N Dynamics and Soil Microbial Communities As a Result of Biological Nitrification Inhibition By Brachiaria Grasses from Bovine Urine Patches.

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.