Water and nitrogen availability affects differentially senescence and seed weight in soybean genotypes with different protein concentration

ERGO VERÓNICA V.; SALVAGIOTTI, FERNANDO; NIGRO, TOMAS; ROSSIANO, LORENZO; CARRERA CONSTANZA S

Buenos Aires

Congreso; XXVIII Congreso Argentino de las Ciencia del Suelo; 2022

Asociación Argentina de la Ciencia del Suelo

In general, increases of available soil N have been linked to delay of senescence, increasing the duration of the active photosynthesis period, which in turn might result in increases of crop production. The objective of our study was to evaluate if increasing N availability during reproductive stages delays the onset of the senescence and increases the seed weight (SW) in soybean genotypes contrasting in seed protein concentration growing under contrasting water availability scenarios. We conducted two field experiments (2020-2021 and 2021-2022) testing two non-transgenic genotypes: high (HP) and low (LP) seed protein under irrigation and drought conditions (soil water content ≤ 25% of field capacity from beginning of R5), and two N levels: control-N (non-fertilized) and +N (receiving 600 kg N ha-1 as fertilizer equally split at V1, R1 and R3). The senescence was quantified as crop cycle duration (CCD) between emergence and full maturity and characterized through the SPAD dynamics (indirect indicator of leaf chlorophyll content) during the seed filling period. Under drought conditions, the CCD was reduced 12 days compared to the irrigated treatment, regardless of genotypes and N levels. The +N treatment increased 4% the SPAD value during the seed filling (around 95 days after the crop emergence, DAE) respect to non-fertilized plots, both under irrigated and drought conditions and independently of genotypes. Despite this SPAD increase, the +N treatment did not delay the onset of senescence under drought, observing a significantly decreased in SPAD value during the early seed filling (around 95 and 110 DAE) in HP genotype (5%) and mainly in LP (23%). Regardless of water and N levels, the HP genotype, exhibited greater (22%) SW than the LP, and independently of genotypes and N levels, the drought reduced 34% the SW. Highly positive and significant relationship (P