Core Ideas In high‐yielding conditions, biological nitrogen fixation and soil total N may not be sufficient to sustain N uptake rates during soybean seed‐filling period to meet the seed N demand required to reach the maximum attainable seed yield. Foliar N fertilization in R3 to R4 growth stages may be used to increase N supply during the final reproductive cycle of plant. The importance on nutrients application, in special N, in crop production has increased in recent years in tropical and subtropical conditions in Brazil because of intensive cultivation (soybean–wheat, soybean–corn, and soybean–cotton), use of high yielding cultivars, and increasing the cost of production. Nitrogen sources (urea, ammonium nitrate, potassium nitrate, calcium nitrate, and ammonium sulfate) and rates (0, 5, and 10 kg ha−1) have different responses and efficiency index in seed yield, when N foliar applied on soybean leaves at the R3 to R4 growth stages. The response of soybean [Glycine max (L.) Merr.] to foliar N application during pod formation has been inconsistent. The objective of this study over three growing seasons was to evaluate the effects of foliar N sources and rates of application on yield, nutritional status, and yield components of soybean. The treatments consisted of five sources [NO3NH4, CaNO3, KNO3, urea‐[CO(NH2)2], and (NH4)2SO4], two N rates (5 and 10 kg N ha−1), applied at the beginning pod growth stage, and a control (no‐N fertilization). Foliar N generally increased the seed yield, irrespective of the N source and analysis pooled over three growing seasons showed an average seed yield increase of 5.0% (211 kg ha−1) and 6.1% (259 kg ha−1) for the 5 and 10 kg N ha−1 over control, respectively. Neither N rate nor source affected seed size, protein, oil, and nutritional status of leaves or seed. Nitrogen rate affected N use efficiency, but results varied with N sources. These data suggest that foliar N application may increase yield of soybean under certain environmental conditions.

Nitrogen fertilization has a fundamental role in agricultural productivity. However, injudicious N applications to crops are common. It is important to ensure the minimum N required for satisfactory crop growth is applied but that excess amounts are avoided due to potential impacts on agroecosystem functioning. Nitrogen at 0, 60, and 150 kg ha–1 was applied as limestone ammonium nitrate to plots arranged in a randomized complete block design, on three farms to determine the impact of rate and temporal distribution of fertilizer on canola (Brassica napus L.) production in South Africa, and the effect of N fertilizer application on the composition and diversity of soil bacterial communities. The amount and distribution of N had only minor effects on canola growth (P < .05) and no effects on yield or harvest index. Splitting fertilizer into two or three applications throughout the season resulted in more mineral N available in the soil later in the season. Increasing the N rate from 60 to 150 kg ha–1 had a significant impact on bacterial community composition. The lower rate favored bacteria that are more able to break down N‐containing C sources. No effects of fertilizer amount or distribution were observed on either N fixation potential (number of nifH gene copies) or bacterial community diversity. Overall, a low rate of N fertilizer split into multiple applications is recommended for canola production, as higher rates do not increase yield and may have a detrimental impact on soil C and N cycling.