Daytime, Temporal, and Seasonal Variations of N2O Emissions in an Upland Cropping System of the Humid Tropics

Abstract

Nitrous oxide (N2O) contributes to global climate change, and its emission from soil–crop systems depend on soil, environmental, and anthropogenic factors. Thus, we evaluated the variability of N2O emissions measured by microchambers (cross section: 184 cm2) from a groundnut–fallow–maize–fallow cropping system of the humid tropics. The crops received inorganic nitrogen (N) plus crop residues (NC), inorganic N alone as ammonium sulfate (RN), and half of the inorganic N along with crop residues and chicken manure (N1/2CM), amounting for the crop rotation to 322, 180, and 400 kg N ha−1 yr−1, respectively. The N2O fluxes during the groundnut–maize crop rotation were log‐normally distributed, and the frequency distributions were positively skewed. Daytime changes in N2O fluxes were inconsistent, and the 50% of total N2O emission during the 12 h measurement periods was attained earlier under maize (∼11∶00 h) than groundnut covers (∼13∶00 h). Spatial variability in each treatment with eight gas chambers was large but smaller during the cropping periods than the fallow, indicating masking efficiency of crop covers for the soil heterogeneity that was accelerated presumably by antecedent climatic variables. The temporal variability of N2O emissions was also large (coefficients of variation, CV, ranged from 60 to 81%), involving both input differences between treatments and measurement periods. As such, the relative deviation from the annual mean of total N2O emission was high during the period after a large N application with a maximum of +480%, due to addition of chicken manure. The seasonal contribution of summer and monsoon to N2O emissions was insignificant. However, intensive rainfall negatively (−0.65**) and the amount of added N from either source positively (0.83***) correlated with the integrated N2O emissions, and those were exponential. Results suggest that around noon (12∶00 h) gas collection could represent well the daily N2O fluxes, increasing the number or size of the gas chambers could minimize the large variability, and mainly the rainfall and N inputs regulated its emissions in the humid tropics of Malaysia.