COMPARISON OF FALL AND SPRING APPLICATION OF NITROGEN FERTILIZERS IN NORTHERN AND CENTRAL ALBERTA

Abstract

Fall and spring applications of N fertilizers (56 kg N ha−1) were compared for yield, and for N uptake, of spring-sown barley in 41 experiments in central and northern Alberta and three in north-central Saskatchewan. In addition, loss of fertilizer N from fall to spring was measured by determining mineral N in the soil samples taken before seeding. The N fertilizers were incorporated into the soil, to a depth of 10–12 cm for 42 experiments and to a depth of 4–5 cm for two experiments. The mineral N contents of soils, sampled in May to 60- or 90-cm depths in 22 experiments, indicated an average of 41% of the fall-applied urea N disappeared from the mineral N pool. The losses tended to be greater with fall-applied calcium nitrate than with fall-applied urea. The average increase in yield of barley grain was only 55% as great from fall application compared with spring application. The effect was slightly greater for N uptake in grain. Of the 44 experiments, the lower yield increase, and the lower N uptake from fall application was significant in 40 and 41 cases, respectively. The N uptake by grain tended to be less with calcium nitrate than with urea when the fertilizers were fall-applied. In multiple regression analyses, the ratios of fall:spring for yield increase from urea and for the recovery of urea N in grain were regressed upon date of fall application, soil drainage, fall soil moisture content, soil texture, and soil organic matter content. Of the independent variables, only date of fall application was statistically significant, with more effectiveness of the urea with later date of application. Key words: Fall application of N, mineral N losses, N fertilizers, N uptake, spring application of N, urea fertilizer