Effect of split application of fertilizer nitrogen on N₂O emissions from potatoes

The timing of fertilizer nitrogen (N) application influences the availability of NO 3 − as a substrate for denitrification. This study examined the effect of split application of fertilizer N on N 2 O emissions and denitrification rate in potato (Solanum tuberosumL.) production over 2 yr. Three treatments were used: 0 or 200 kg N ha -1 at planting, and 120 kg N ha -1 at planting plus 80 kg N ha -1 at final hilling. Fertilizer N application increased cumulative N 2 O emissions. Split fertilizer N application decreased cumulative N 2 O emissions in 2003, but not in 2002, compared with all fertilizer N applied at planting. A greater proportion of N 2 O emissions occurred between planting and hilling in 2003 (67%) compared with 2002 (17%). In 2003, the higher emissions during this period resulted from the coincidence of high soil NO 3 − availability and increased rainfall resulting in reduced aeration. Split N application was effective in reducing N 2 O emissions by minimizing the supply of NO 3 − when demand for terminal electron acceptors was high. N 2 O emissions were higher in the potato hill relative to the furrow; however, denitrification rate was higher in the furrow. Nitrate intensity (NI) expresses the exposure of the soil microbial population to NO 3 − and was calculated as the summation of daily soil nitrate concentration over the monitoring period. Cumulative N 2 O emissions were positively related to NI across year, N fertility treatment and row location. Denitrification was not related to NI, reflecting the primary role of NO 3 − in influencing the N 2 O:N 2 ratio of denitrification rather than the magnitude of the overall process. Split N application was an effective strategy for reducing N 2 O emissions in years where there was significant rainfall during the period between planting and hilling.