Economically optimal nitrogen rate and soil nitrate after canola harvest.

Lafond, J. and Pageau, D. (2008). "Economically optimal nitrogen rate and soil nitrate after canola harvest.", Canadian Journal of Plant Science, 88(6), pp. 1035-1042. doi : 10.4141/CJPS08004

Abstract

Spring canola has high nitrogen (N) requirements to reach maximum grain yields, but excessive N applications can result in an environmental degradation. The objectives of this study were to determine the effect of N fertilization on canola grain yields, to quantify the effect of N fertilization on residual soil nitrate content and to establish relationship between residual soil nitrate and economically optimum N fertilizer application. Canola plots were established on two sites during 2 yr. The treatments were five rates of mineral nitrogen (0, 40, 80, 120 and 160 kg N ha^-1) applied before sowing. Canola grain yields significantly increased with increasing N fertilizer rates. Grain increments of 554 to 1096 kg ha^-1 were measured. The economically optimum N fertilizer application derived from regression equations was 88 kg ha^-1 except for one site where the value was 71 kg ha^-1. Residual soil nitrate content (0-40 cm) measured at harvest significantly increased with the highest N fertilizer rates. In this study, the amount of residual soil nitrate after canola harvest have been maintained at a level lower than 40 kg ha^-1 when the N fertilization was based on the economically optimum N fertilizer application. Thus, an application of N fertilizer according to canola requirements has reduced the accumulation of residual soil nitrate and reduced the risk of leaching.