Genetic gain by management interactions in soybean: Nitrogen utilization
Abstract
Soybean yields in the U.S. have increased at an annual rate of 23.5 kg ha-1 since 1924 as a result of improved genetics and agronomic practices. Yield contributions to genetic gain have been well documented but yield gains from many agronomic practices has not been revealed, especially in relation to genetics. Soybean is valued for its high protein and oil grain composition and 98% of worldwide soybean production is processed and fed to livestock. Nitrogen (N) is essential to synthesis of protein, oil, and plant biomass in developing soybean plants. As production potential of newer cultivars annually increases, biological N fixation (BNF) may be a limiting factor in development of these traits. Our objectives were to supply a non-limiting supply of N to determine (1) the agronomic response and (2) the physiological mechanisms that change yield and grain quality within maturity group (MG) II and MG III cultivars released from 1923 to 2008. A research study was initiated at 4 locations in 2010 (Arlington, WI, Waseca, MN, Urbana, IL, and Lafayette, IN) and 3 locations (Arlington, WI, Urbana, IL, and Lafayette, IN) in 2011 using 59 MG II cultivars in WI and MN and 57 MG III cultivars in IL and IN. In addition to soil N, N was supplied to the cultivars from two sources: BNF vs. fertilizer N. Fertilizer N totaled 560 kg N ha-1 with half at planting and the remainder at V5. Yield, protein, oil, dry matter accumulation, and N accumulation of various plant parts were determined. Biomass accumulation increased with cultivar modernization in both MGs. Nitrogen fertilization further increased biomass production in MG III cultivars. Yield increases of MG III cultivars from N fertilization may be linked to increased N accumulation of vegetative biomass. Yield of MG II cultivars was not affected by N fertilization, but grain protein concentration increased as oil concentration decreased in MG II cultivars with N fertilization. Nitrogen fertilization increased grain N concentration of MG II cultivars; however, total N accumulation did not increase. Changes in N redistribution under increased N availability could explain grain quality increases in MG II cultivars. This suggests N supplied from the soil and BNF was insufficient to realize grain protein (MG II) and yield (MG III) potential.
Degree
M.S.
Advisors
Casteel, Purdue University.
Subject Area
Agronomy
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