Nitrous oxide fluxes in soil as influenced by compaction

Abstract

Listen

Translate article

In grazed-pastures animal treading is an important cause of soil compaction. Soil compaction influences the denitrification rate as well as the amounts of nitrous oxide (N2O) and dinitrogen (N2) production in the soil mainly through its impact on soil moisture conditions and porosity. A field experiment was undertaken to determine the loss of nitrogen (N) through N2O emission from different N sources as affected by a compaction treatment. Experiment comprised of two main treatments (uncompacted and compacted) to which four N sources (cattle urine, potassium nitrate, ammonium sulphate and urea at the rate of 600kg N/ha) and a control (water only) were applied, each replicated four times. Compaction was obtained through driving close parallel tracks by the wheels of the vehicle. Var ious soil properties related to soil compaction (b ulk density, water filled pore space (WFPS), oxygen diffusion rate (ODR)) were measured. The N2O fluxes were measured for 3 months (between 10th September and 4th December, 2002) using closed chamber technique. Overall, the bulk density of compacted soil was 12.8 % higher than that of the uncompacted soil. Results suggest that maximum compaction occurred in the top 0-2 cm layer. Soil matric potential measured at the 0-5 cm soil depth suggests that uncompacted soil had lower water content, except at low matric suctions, than compacted soil. The ODR in uncompacted soil was 79.3% higher than that in the compacted soil. Compaction caused a seven fold increase in N2O emission. Nitrate source was the most effective of all the treatments in causing potential emission. Under compacted soil 9.87% of the total N applied in form of nitrate was emitted whereas under uncompacted soil this loss was only 0.54%. N2O loss was found to decrease progressively from the time of application of N treatments. Total N2O emission for the three month experimental period ranged from 2.62 to 61.74 kg N2O-N/ha for compacted soil and 1.12 to 4.37 kg N2O-N/ha for uncompacted soil. Keywords: compaction, grazed pastures, Nfertilisers, nitrous oxide emissions, urine-N