Tan, Ivy (Cornell University, 151 Dryden Road #228, Ithaca, NY, 14850; Phone: 607-351-3917; Email: it36@cornell.edu)

Nitrous Oxide Losses Are Increased Under No-Tillage and Early Fertilization

I.Y.S. Tan *, H.M. Van, EsJ.M. Duxbury, J.J. Melkonian, L.D. Geohring, R.R. Schindelbeck, D. Hively

Greenhouse gas emissions from nitrous oxide (N₂O) are due in part to N inputs on agricultural land that are lost through the nitrification and denitrification processes. Earlier studies have shown that late spring is a critical time period compared to other seasons, because high soil nitrate levels are susceptible to leaching and denitrification. This is especially the case with maize production when the entire seasonal fertilizer needs have been applied at planting. Quantitative information on N₂O emissions as affected by soil type and crop management practices is scarce, especially with regards to tillage and timing of N application. This study examined the effects of tillage (no-till, plow) and fertilizer timing (at planting, sidedress) on two soil types (a glacio-lacustrine Muskellunge clay loam and a Stafford loamy fine sand), each with a cropping history of orchardgrass and maize on N₂O emissions and NO₃-N leaching potential as a result of 50-mm precipitation. N₂O emissions were measured daily over a period of a week. N₂O emissions were highest on the second day after precipitation for all treatments. N₂O losses were significantly higher on the clay loam compared to the loamy sand. Early fertilization at planting under no-till on previous grass resulted in large N₂O emissions, with a cumulative N₂O loss of 4.4 kg N/ha greater than late fertilization. Similar N and tillage treatments on previous corn, however, had a relatively smaller emission, with a cumulative N₂O loss of 2.3 kg N/ha greater than late fertilization. Small N₂O emissions were observed on plots under plow-till treatments. Early fertilization under plow-till on previous grass emitted 0.96 kg N/ha greater cumulative N₂O loss than late fertilization, while early fertilization under plow-till on previous corn resulted in 0.82 kg N/ha greater cumulative N₂O loss than late fertilization. These results show that the amounts of N₂O emitted vary significantly among tillage treatments and timing of N application, and that no-till and early fertilization increase N₂O emissions. Although conservation tillage encourages sequestration of soil C, the focus on N management is equally, and perhaps more, important. A balance is needed in adopting best management practices in order to minimize total greenhouse gas impacts.