Does an increase in available nitrogen fertilization during the seed-filling period improve maximum photosynthesis and crop production in field-drought soybean?

ERGO VERÓNICA V.; SALVAGIOTTI, FERNANDO; LUNA FERNANDO; VEAS RODOLFO; CARRERA C. S.

Santa Fé

Congreso; XXXIII Reunión Argentina de Fisiología Vegetal. 2021. Santa Fé, Argentina.; 2021

Sociedad Argentina de Fisiología Vegetal

The objective of this study was to evaluate the increase in nitrogen (N) availability on maximum photosynthesis rate (Amax), total biomass (TB), and grain yield (GY), in irrigated-plots and droughtplots in soybean genotypes contrasting in grain protein (GP) concentration. We conducted field experiments testing high(42%) and low(38%) GP genotypes. Treatments included two water levels: irrigated-plots and drought-plots (with a soil water content ≤ 25% of field capacity from R5, beginning grain filling), and two N levels: unfertilized-plots and fertilized-plots (600 kg.N.ha-1 equally split at vegetative, beginning bloom, and beginning pod). The Amax was measured during the grain filling period (GF), and TB and GY at beginning of seed-filling period and full maturity, respectively. Drought-plots reduced the Amax 14%, 48%, and 41% at 6, 16, and 33 days after R5 (DAR5) compared to irrigated-plots, regardless genotype and nitrogen level. The highest Amax reduction in irrigatedplots was observed from 33 DAR5, whereas in drought-plots occurred 17 days earlier (16 DAR5) and then, GF duration was 13 days shorter than in irrigated-plots. The low GP genotype showed 15% higher Amax at 6 DAR5 than the high GP genotype, among water and N level. Independently of genotype and N treatments, drought-plots reduced 44% and 68% TB and GY, respectively, compared to irrigated-plots. In summary, an increase in N availability did not improve Amax, TB, and GY. Thus, we reject our hypothesis stating “nitrogen fertilization improves these variables under irrigation, and even more in drought in low GP genotype compared to a high GP one”.