Urea fertigation sources affect nitrous oxide emission from a drip-fertigated cotton field in northwestern China

Abstract

Drip-fertigated systems are widely used for crop production in arid regions to improve water and nutrient use efficiency. However, the effect of fertilizer nitrogen (N) sources on nitrous oxide (N2O) emissions from such systems is not well understood. A field experiment was conducted in 2015 and 2016 on a sandy loam soil in Xinjiang, China with plastic-mulch, drip-fertigated cotton (Gossypium hirsutum L.) to determine N2O emissions from different fertilizer N sources. Treatments were established in a factorial design consisting of a 0 N control and three treatments receiving 240 kg N ha−1 as (1) polymer-coated urea (ESN), (2) urea alone, or (3) urea with both urease (NBPT) and nitrification (DCD) inhibitors. ESN was banded in the row at planting, whereas the two urea treatments were applied through banding and fertigation. In these treatments, 20% of the urea was banded in the row at planting and the remaining 80% was applied with six fertigation events over the growing season. Seasonal cumulative N2O emissions (ƩN2O) for urea alone were 330 g N ha−1 and were 27% greater than the control. Compared to urea alone, the ESN treatment increased ƩN2O by 43% due to the one-time application at planting that resulted in high soil N availability and high N2O emissions shortly after planting. Compared to urea alone, urea plus the two inhibitors decreased ƩN2O by 21%. Cotton seed yield and total N uptake was not affected by N sources, while ESN had significantly higher yield-based emission intensity compared to the other N treatments. In general, the seasonal N2O emissions and N-applied emission factors under the drip-fertigated system were lower than those reported for other agricultural systems. This was likely because of low soil moisture preventing appreciable N2O emissions. These results demonstrated that addition of urease and nitrification inhibitors could further reduce already low N2O emissions with soluble urea with drip-fertigation and under plastic mulch condition.