Biological N fixation (BNF) alone in soybean [Glycine max (L.) Merrill] crops is efficient as a N source to the soybean crop at yield levels up to 3,800 kg ha–1. However, for yields above 4,000 kg ha–1, the N cannot be sufficient to fill the last seed, considering that the activity of the radicular system and the nodules acting in BNF decrease exponentially towards the end of the development cycle when the pods are formed.
In an article recently published in Agronomy Journal, researchers reported that BNF was not sufficient to meet the requirements of a soybean crop with high yield under no-till (NT) system and that foliar N fertilizer application at the R3 (beginning of pod) to R4 (full pod) growth stage may be needed to fill the last seed of the upper third of the plant.
The researchers found that foliar N fertilizer was efficient at improving the yield but may not be sufficient to offset additional fertilizer cost, even though the additional cost of applying 5 to 10 kg N ha–1 is minimal. These results demonstrated that N foliar applications increase the yield of soybean under certain tropical and subtropical environmental conditions.
Adapted from Moreira, A., L.A.C. Moraes, G. Schroth, F.J. Becker, and J.M.G. Mandarino. 2017. Soybean yield and nutritional status response to nitrogen source and rate of foliar fertilization. Agron. J. 109. View the full article online at http://dx.doi.org/doi:10.2134/agronj2016.04.0199