Does Soybean Benefit from Starter Nitrogen Fertilizer in Manitoba?.

Soybean (Glycine max) acreage in Manitoba is expanding rapidly with acreage exceeding 647,497 ha in 2016 (Stat Canada, 2017). In this northern edge of soybean production environment, low soil temperatures at or after soybean planting has potential to delay emergence, biological nitrogen fixation and growth of soybean (Zhang and Smith, 1994). Small doses of N fertilizer have been suggested as a strategy to improve early soybean development, especially when initial nodulation is reduced or delayed (Mahon and Child, 1979). To evaluate effect of starter N fertilizer on soybean nodulation, growth, and seed yield, a field study was conducted in 2015 and 2016 at University of Manitoba Ian N. Morrison Research Farm, near Carman, Manitoba. Soybean seed inoculated with Brady rhizobium inoculant was planted at a target population of 444, 600 plants /ha on 38 cm row-spacing. Six N fertilizer rates (0, 17, 34, 50, 67 and 84 kg N /ha) as urea were broadcasted in a randomized complete block design with four replications. Plant roots, plant biomass, and soil samples were collected at R1 and R5.5 stages to evaluate nodulation, soybean growth, and nitrogen uptake. Application of N fertilizer did not influence soybean performance in both years. No statistical differences were observed in plant biomass, N uptake, plant height or pod height between N fertilizer treatments and the control. However, nodule number per soybean plant was significantly reduced where N fertilizer rates were applied compared to control at the R1 stage in both years. These differences in nodule number per plant due to N fertilizer application disappeared by R5.5 stage in both years except at 84 kg N /ha in 2016. At the end of the season, N fertilizer rate did not have any effect on seed yield or seed protein and oil content in both growing seasons. This study is being repeated in 2017 to validate the findings.