Tuesday, 11 July 2006

Slow-Release N Fertilizer to Control Soil Nitrous Oxide Losses Due to Spatial and Climatic Differences in Soil Water Content and Drainage.

Sara Merchán Paniagua, Peter P. Motavalli, Kelly A. Nelson, Stephen H. Anderson, and John E. Sadler. Univ of Missouri-Columbia, Dept of Soil, Environmental, & Atmospheric Sciences 321 Natural Resources Building, Columbia, MO 65211

Agricultural soils are a major source of nitrous oxide (N2O) which contributes to global warming and ozone depletion. The objectives of this research were to establish the relationship between soil N2O flux, temperature, soil NO3--N, and soil water content and to compare the performance and cost-effectiveness of polymer-coated urea and conventional N fertilizers in relation to soil gaseous N2O losses. A two-year field trial planted to corn was started in 2004 at the University of Missouri Ross Jones Farm in Northeast Missouri on a claypan soil. Treatments consisted of 46 m long plots with: i) no drainage or subirrigation, ii) drainage with tile drains spaced 6 m apart and no subirrigation, iii) drainage with tile drains spaced 6 m apart and subirrigation, and iv) no drainage and overhead irrigation. The plots were split into N fertilizer treatments of broadcast pre-plant-applied urea or polymer-coated urea at rates of 0, 140, and 280 kg N ha-1. For each treatment combination there were 4 replications. The results show that in the relatively high rainfall year of 2004, corn grain yield increased from an average of 878 to 1254 kg ha-1 in the polymer-coated urea-treated plots with no drainage or irrigation compared to urea. In 2005, corn grain yields were 60% higher in plots with no drainage and overhead irrigation due to the low rainfall experienced in 2005 compared to the previous year. Yields in control plots were significantly lower for both years. Soil N2O loss in both years was affected by changes in soil temperature and water content due to rainfall and the different drainage and irrigation treatments. In general, the measured soil N2O flux was highly variable, but polymer-coated urea tended to reduce N2O over the 2004 and 2005 growing seasons, especially in overhead-irrigated plots. In 2004, soil N2O efflux was significantly lower by 79% in polymer-coated urea plots with overhead irrigation compared to urea. In 2005, differences were observed among the drainage/irrigation treatments. Thus, overhead-irrigated plots released significantly more N2O than the other drainage/irrigation treatments in the control (between 74 and 82% more than the other three drainage/irrigation treatments). In the non-irrigated, non-drained plots, polymer-coated urea-treated plots had higher soil N2O flux compared to gas flux measured in plots treated with urea, but in the non-irrigated and drained plots, urea had 8% more soil N2O flux compared to the polymer-coated urea plots. Soil nitrate-N was generally higher in the urea-treated plots compared to the control and polymer-coated urea-treated plots at the beginning of the season but was lower later in the season. The results of this research suggest that polymer-coated urea may reduce soil N loss compared to conventional urea under relatively wet conditions, but additional evaluation must be conducted to determine whether this N fertilizer source is cost-effective for agronomic crops.

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