Controlled release urea increases soybean yield without compromising symbiotic nitrogen fixation

Abstract

Summary In Brazil, high-yield soybean [Glycine Max (L). Merrill] – corn (Zea mays L.) double cropping system might be nitrogen (N)-limited and additional N fertilization can be beneficial. Early application of N in soybean reduces the symbiotic N fixation (SNF) efficiency and/or establishment. One alternative to avoid SNF impairment is to apply N between the beginning pod (R3) and seed-fill (R5) stages through the use of controlled release fertilizers. In this study, N was applied at 50 kg ha−1 as common urea (CU) or controlled release urea (CRU) with different lag periods until N release starts (30 days, 60 days, or 1:1 mix of both lag times) in a randomized complete blocks design with six treatments and four replicates under tropical and subtropical conditions. CU was applied after soybean emergence (VE) or at the beginning pod (R3), and CRU only at VE. Using urea labeled with 15N isotope, we analyzed the N source used by soybean (fertilizer, soil, or SNF) and SNF parameters. On average, CRU – 30 days, CRU – 1:1 mix (30 + 60 days) and CU applied at the R3 stage increased grain yield by 9.2% (354 kg ha−1) compared to the control. N derived from all fertilizer treatment were almost 35 kg N ha−1, a high N recovery efficiency of 68%. The SNF was not impaired by CU and CRU and accounted for 71% (220 kg N ha−1) of total N uptake. In the conditions of the experiments, fertilization of 50 kg N ha−1 as CRU was shown to be effective to supply N in late soybean demand (R3 stage), increasing yield without damaging the SNF process in high-yield environments.

Macro and Micro-Nutrient Accumulation and Partitioning in Soybean Affected by Water and Nitrogen Supply

“…In rainfed farming, sowing must be carried out at the beginning of the rainy season to ensure adequate water availability and to avoid the negative influence of water deficiency on the plants' metabolic processes. Drought is a major threat to crop production worldwide, and legumes are sensitive to drought stress by negatively affecting BNF, grain yield and protein content in seeds [17]; however, some results have shown that a rate of 50 kg N ha −1 does not impair BNF and can deliver 71% of total N uptake [18]. This is especially relevant in Brazil's agricultural frontiers, such as the specific savanna region (Cerrado) in northeastern Brazil, where there is a lack of site-specific research regarding the use of inoculants and nutrient cycling of organic matter in annual crops.…”