High Yielding Cotton Produced without Excessive Nitrous Oxide Emissions

Excessive N fertilizer use leads to enhanced nitrous oxide (N2O) emissions from cotton (Gossypium hirsutum L.) production systems. The objective of the study was to quantify nitrous oxide emissions from the ridges within a furrow-irrigated field during the growth of a cotton crop that had been fertilized with urea at 0, 120, 200, or 320 kg N ha(-1). No measurements were taken from the furrows; we assumed similar N2O emissions from the furrows in this system. The N2O emissions increased exponentially with N fertilizer rate. Over the cotton-growing season, N2O emissions totalled 0.51, 0.95, 0.78, and 10.62 kg N2O-N ha(-1), for the four respective N fertilizer rates. The cotton phase of the cotton-faba bean (Vicia faba L.)-fallow rotation was the main contributor to the total N2O emission. Over this 2-yr rotation, emissions totalled 1.23, 1.65, 1.44, and 11.48 kg N2O-N ha(-1). However, <0.35% of the N fertilizer applied was emitted as N2O for the complete rotation where the economic optimal N fertilizer rate for the cotton crop was not exceeded. More than 3.5% of the N fertilizer was emitted as N2O where 320 kg N ha(-1) was applied, which was estimated to represent about 11 kg N ha(-1). These data indicate that supra-optimal N fertilizer applications increase the net emissions of N2O from the ridges in high-yielding furrow-irrigated cropping systems. The N2O emissions could be decreased further by reducing or eliminating the time in fallow.