How do methane rates vary with soil moisture and compaction, N compound and rate, and dung addition in a tropical...

Soil moisture and compaction, and source of N and bovine urine can reduce methane (CH₄) rates from agricultural soils. However, the magnitude of the effect is unknown in tropical soil under different conditions, as well as the potential of different urine-N concentration, volume, and sources of N in such an effect. This study aimed to investigate the effects of different soil conditions (moist, dry, compacted, moist-dung, moist-dung-compacted), N concentration in urine (2.5, 5.0, 10.0, and 15.0 g N L^-1), volume of urine (25, 50, 100, and 200 ml kg^-1 dry soil), and source of N (ammonium, nitrate, and urea) on CH₄ emissions. A tropical Ferralsol soil from marandu-grass pasture was incubated during 106 days and the CH₄ concentration determined by gas chromatography. The CH₄ rates varied significantly according to the soil conditions when manipulated the urine-N (p < 0.01) and averaged 0.75, - 0.50, 1.14, 6.23, and 8.17 μg C-CH₄ m^-2 h^-1for the moist, dry, compacted, moist-dung, and moist-dung-compacted soil, respectively, and, not responded to the level of N (p = 0.73) averaging 2.57 μg C-CH₄ m^-2 h^-1. When evaluated, the volumes of urine cumulative CH₄ averages were - 0.52, - 1.24, - 0.88, 14.48, and 18.56 μg C-CH₄ m^-2 h^-1 for the moist, dry, compacted, moist-dung, and moist-dung-compacted, respectively. Soils were affected by soil treatments (p < 0.001) but not by urine volumes (p = 0.30). The source of N did not influence the CH₄ rates (p = 0.1) averaging 0.88, - 1.26, and - 1.19 μg C-CH₄ m^-2 h^-1 respectively, for urea, nitrate, and ammonium. The CH₄ fluxes in tropical Ferralsols are controlled by the soil characteristics and dung addition.