Effects of deposited bovine urine, nitrogen fertilizers and nitrification inhibitors on nitrate leaching in a grazed pasture system of humid tropics.

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Universidad EARTH

Nitrate leaching from excessive use of nitrogen-based fertilizers and dispersed livestock excretes in livestock production contributes to widespread eutrophication posing danger to aquatic life and health risk to humans. A study was done at Livestock Farm and Soil Science Laboratory at EARTH University to assess the role of bovine urine, plant root architecture and dimethylpyrazole phosphate (DMPP) nitrification inhibitor, on nitrate leaching in pastures. The project was executed in three phases; (i) spatial distribution of urine patches through visual identification and use of Global Positioning System (GPS), (ii) examination of the root architecture of pastures and their capacity to curb nitrate leaching and (iii) a lysimeter study to evaluate the effect of DMPP on nitrate leaching and biomass production. Three treatments were established: (i) control (ii) conventional N-P-K fertilizer (12-12-17) and (iii) conventional N-P-K fertilizer (12-12-17) with (DMPP) nitrification inhibitor. Treatments were applied at different rates of 50 kg N/ha and 100 kg N/ha. Leachates were collected every seven days after fertilizer applications for 28 days for two grazing periods: pH, electrical conductivity and nitrate content were measured. Results showed an uneven distribution of bovine urine influenced by temporal factors and presence of physical features of the paddock. Mombasa grass showed a desired root architecture system with potential to reduce nitrate leaching. DMPP application showed no effect on biomass production. However, greater reduction of nitrate content in leachates of the NPK +DMPP treatment at 100kg N/ha was noted. The results show that NPK +DMPP at 50 kg N/ha and 100 kg N/ha presented 84 % and 44 % nutrient recovery efficiency, respectively. It was determined that bovine urine and N fertilizer create nitrate leaching hotspots. The use of DMPP nitrification inhibitor reduces nitrate leaching into deeper soil and improves nutrient uptake by grasses in a grazed pasture system of humid tropics.

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