Seasonal biomass and nitrogen partitions of soybean cultivars released over 90 years

Philip Andrew Long, Purdue University

Abstract

Advancements in soybean production have occurred through plant breeding and agronomic techniques over the past century. Soybean genetics and soil fertility are foundational for high yields, but little research has documented changes in plant nutrition over this history. Our objective was to determine seasonal biomass, nitrogen (N) concentrations, and N accumulation partitioning patterns by soybean cultivars released over the last 90 years. We selected 25 cultivars from maturity group (MG) II and 26 cultivars from MG III that represented each of the past nine decades. These cultivars were grown in fertile soil of west-central Indiana in 2011 and 2012. Each MG set was arranged in a randomized complete block design replicated three times. Cultivars were sampled at V4 (four expanding trifoliolates), R2 (full bloom), R4 (full pod), R6 (full seed), and R8 (physiological maturity) and were partitioned into leaves, stems, pods, stover, and grain. Partitions were subjected to regression analysis to determine changes across release years. Biomass production increased across release years in both MGs with the first signs at R4 for MG II, which was earlier in the growing season than MG III (R6). Leaf biomass accumulation increased dramatically across release years at R6 both for MG II and MG III. Greater leaf retention likely allowed more light interception by leaves lower in the canopy (or vice versa) and thus, produced more biomass and photosynthesized longer in the modern cultivars. The increased leaf biomass during R4 and R6 across the release years translated into more grain production in MG II and MG III. The annual grain increases for MG II and the individual years of 1930, 1970, and 2010 were derived from the quadratic alone regression, which were 0.8, 17.2, and 33.6 kg ha -1, respectively. Maturity group III revealed annual grain increases of 2.5, 17.0, and 31.4 kg ha-1 for the individual release years of 1930, 1970, and 2010, respectively. Higher concentrations of N by the modern cultivars at V4 and R2 likely translated into greater photosynthesis that drove the observed biomass increases in the middle and the latter part of the season. Leaf N concentrations and accumulation in both MG II and MG III increased consistently across release years at every growth stage sampled (V4, R2, R4, and R6), which indicated a strong connection with the yield gains over the past 90 years. Nitrogen accumulation at R4 in leaves, at R6 in leaves, and at R8 in grain increased at a faster rate after 1970. The proportion of N allocated to leaves at R6 notably increased across release years in MG II from 25 to 33% (1928 to 2011) and in MG III from 21 to 32% (1923 to 2011). As a result, grain N accumulation has doubled over the past 90 years of soybean advancement. Leaf biomass, leaf N concentration, and leaf N accumulation increased across release years of soybean to prolong reproductive development, increase photosynthate production, and improve remobilization efficiency to grain.

Degree

M.S.

Advisors

Casteel, Purdue University.

Subject Area

Agronomy

COinS