Economic and risk considerations of nitrogen fertilizer use in the Brown Soil Zone
Optimum use of nitrogen fertilizer requires consideration of factors that influence plant response and those that govern the decisions of producers. The response of spring wheat to soil moisture and N fertilizer was assessed in a 9-yr zero tillage study conducted on a medium texture soil at Swift Current, Saskatchewan. These data were used to assess the economic merit and risk considerations of alternate N fertilizer management systems when combined with snow-trapping to enhance soil moisture reserves. The N fertilizer system included rates from 0 to 100 kg ha-1, spring versus fall applications and deep-banding versus surface broadcasting. The results showed that the optimum rates of fertilizer N (FN) varied directly with spring soil moisture reserves (SM) and the probability distribution for 1 May to 31 July precipitation, and inversely with soil N (SN), the ratio of FN cost to wheat price, and the level of risk aversion held by producers. The optimum FN rates were highest for spring- and fall-banding; they were 3 to 14 kg ha-1 lower for spring broadcasting and 7 to 22 kg ha-1 lower with fall broadcasting. The optimum rates increased 3.7 to 5.7 kg N ha-1 for each 10 mm increase in SM, with the higher rates associated with high SN. The FN rates declined 5 kg ha-1 for each additional year that the land was cropped continuously. For producers seeking to maximize expected profit or those with low risk aversion, the optimum FN rates were considerably higher than those recommended by the Saskatchewan Soil Testing Laboratory (SSTL) . In contrast, the FN rates for producers with high risk aversion were generally lower than those of the SSTL. The SSTL recommended rates were most appropriate for producers with medium risk aversion. The study found no single combination of timing and method of N fertilizer placement to be superior in all cases. Spring- and fall-banding provided higher net margins than broadcasting N fertilizer when SM or wheat prices were high, or if banding fertilizer can be combined with a tillage operation for weed control. The economic benefit from snow-trapping averaged $9 to $32 ha-1 depending on FN rate and wheat price; however, little benefit or a small loss was incurred in some years when infiltration of melt water was low or winter snowfall was minimal.
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