Economics of fertilizer-N management for zero-tillage continuous spring wheat in the Brown soil zone

Optimum use of fertilizer inputs requires consideration of factors that influence plant response and those that govern the decisions of producers. The response of spring wheat (Triticum aestivum L.) to soil water and fertilizer N (FN) was assessed in a 9-yr zero-tillage study conducted on a medium-texture, Orthic Brown Chernozem at Swift Current, Saskatchewan. These data were used to assess the economic merit and risk considerations of alternative fertilizer-N management systems when combined with snow-trapping to enhance soil-water reserves. The fertilizer-N systems included rates from 0 to 100 kg ha−1; spring versus fall applications, and deep banding versus surface broadcasting. Tall trap strips of cereal stubble (40–60 cm tall by 90–120 cm wide, spaced every 6 m and running perpendicular to prevailing winds) were used for snow trapping and compared with stubble cut at a uniform standard height of 15–20 cm. The results showed that optimum fertilizer-N rates (FN) varied directly with soil-water (SW) reserves (available water in 0–120-cm depth measured in spring) and the probability distribution for 1 May to 31 July precipitation, and inversely with soil N (SN) (NO3 N in 0–60-cm depth measured in the previous fall), ratio of fertilizer-N cost to wheat price, and the level of risk aversion held by producers. The optimum FNs were highest for spring and fall banding; they were 3–14 kg ha−1 lower for spring broadcasting and 7–22 kg ha−1 lower with fall broadcasting. The optimum rates increased 3.7–5.7 kg N ha−1 for each 10-mm increase in SW, with the higher rates associated with high SN. The FNs 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 FNs were considerably higher than those recommended by the Saskatchewan Soil Testing Laboratory (SSTL). In contrast, the FNs for producers with high risk aversion were generally lower than those of 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 fertilizer-N placement to be superior in all cases. Spring and fall banding generally provided higher net margins than broadcasting fertilizer N when SW and wheat prices were high, whereas spring broadcasting was best when SW and wheat prices were lower. The economic benefit from snow trapping averaged $9–$32 ha−1 depending on FN and wheat price; however, there was little benefit or a small loss in some years when infiltration of meltwater was low or winter snowfall was minimal.Key words: Yield, fertilizer N, soil water, optimum rates, riskiness, profit