Nitrogen Sources and Rates Affect Soybean Seed Composition in Mississippi

Gurpreet Kaur,Nacer Bellaloui,Bobby Golden,William Serson,Justin Mccoy,John Orlowski

doi:10.3390/agronomy7040077

Abstract

Soybean (Glycine max L.) seed is a major source of protein, oil, carbohydrates and other nutrients that are important for human and animal nutrition. Producers have considered applying nitrogen (N) fertilizer to soybean crop to maximize seed yield; however, its effect on seed composition is not well understood. The objective of this two-year (2015 and 2016) study was to evaluate the effects of N fertilizer sources and application rates (45, 90, 135 and 179 kg N ha−1) on soybean seed composition on two soil textures (clay and silt-loam) in Mississippi. The three fertilizer sources included in this study were urea with N-(n butyl) thiophosphoric triamide (Urea+NBPT), polymer-coated urea (PCU), and ammonium sulfate (AMS). Nitrogen application at 179 kg ha−1 on clay soil reduced seed protein by 1.05% compared to unfertilized soybeans in 2016. However, N application at 179 kg ha−1 increased oil content by 0.7% on clay soil compared to the unfertilized soybeans only in 2016. Nitrogen applications reduced stachyose content on both soil textures in 2015. The fatty acids showed variable response to N applications. Since, seed quality is not a trait from which growers receive an economic incentive, they are unlikely to adopt this practice for standard soybean production.

Highlights

Soybean fulfills its nitrogen (N) requirement mainly through symbiotic biological nitrogen fixation (BNF) or by N uptake from soil
Increase in oil concentrations due to N applications occurred on clay soil in 2016, whereas no changes occur in oil concentration in 2015
The impacts of nitrogenous fertilizer application were examined with regards to its impact on seed composition

Summary

Introduction

Soybean fulfills its nitrogen (N) requirement mainly through symbiotic biological nitrogen fixation (BNF) or by N uptake from soil. Which is enough to achieve only 80–90% of soybean yield possible with N fertilization [2,3,4]. Previous studies have reported inconsistent responses of soybean seed yield to N fertilizer applications [6,7,8,9,10,11,12,13,14,15,16,17,18]. Ray et al (2006) reported an increase in soybean seed yield by 7.7% and 15.5% for irrigated and non-irrigated environments, respectively, due to a large amount of N applications in Mississippi [17]. McCoy (2016) reported an increase in soybean seed yield of 4% and 8% on sandy/silt loam and clay soil, respectively, due to N applications in Mississippi [19]. Soybean yield response to N applications depends upon soil properties (soil temperature, pH, moisture, soil nitrate content at planting) [8,13,20], irrigation [13] and cultivars [8]

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