This study aimed to investigate the influence of water availability and nitrogen fertilization on plant growth, nutrient dynamics, and variables related to soybean crop yield. Trials were performed in Teresina, Piauí, Brazil, using randomized blocks in a split-split plot arrangement. The plots corresponded to water regimes (full and deficient), the split plots to N fertilization (0 and 1000 kg ha⁻¹ N-urea), and the split-split plots to harvest times of soybean plants (16, 23, 30, 37, 44, 58, 65, 79 and 86 days after emergence), with three replicates. In general, the accumulation and partitioning of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn) and boron (B) were decreased in plants subjected to water deficit and without N fertilization. Although nitrogen fertilization promoted elevated N accumulation in tissues, it did not result in any significant yield gain, and the highest seed yields were found in plants under full irrigation, regardless of N supplementation. However, deficient irrigation decreased the seed oil content of N-fertilized plants. In conclusion, N fertilization is critical for nutrient homeostasis, and water availability impairs biomass and nutrient accumulation, thereby limiting soybean yield performance.

This study aimed to evaluate the ability of vegetation indices (VIs) obtained from unmanned aerial vehicle (UAV) images to estimate soybean grain yield under soil and climate conditions in the Teresina microregion, Piaui state (PI), Brazil. Soybean cv. BRS-8980 was evaluated in stage R5 and submitted to two water regimes (WR) (100 and 50% of crop evapotranspiration - ETc) and two N levels (with and without N supplementation). A randomized block design in a split-plot scheme was used, in which the plots were the water regimes and the subplots N levels, with five replicates. Each plot contained twenty 4.5 m-long rows, spaced 0.5 m apart, with a total area of 45 and 6 m² study area for grain yield evaluations. Twenty VIs obtained from multispectral aerial images were evaluated and correlated with grain yield measurements in the field. Pearson’s correlation, linear regression, and spatial autocorrelation (Global and Local Moran’s I) were used to analyze the performance of the VIs in predicting grain yield. The R2, RMSE and nRMSE indices were used to validate the linear regression models. The prediction model based on EVI-2 exhibited high spatial randomness for all the treatments, and smaller prediction errors of 149.68 and 173.96 kg ha-1 (without and with N supplementation, respectively).

Os estresses abióticos induzem alterações de crescimento e perda de produtividade nas espécies vegetais. O presente estudo objetivou avaliar as respostas de plantas de feijão-mungo e sorgo submetidas ao estresse salino (0, 50 e 150 mM de NaCl) e por alumínio (0 e 1,0 µM de Al) de forma isolada ou em combinação com base na mensuração da taxa de crescimento absoluto, altura das plantas, massa fresca da parte aérea e das raízes e o comprimento das raízes. Observou-se que as plantas de sorgo apresentaram valores superiores de taxa de crescimento absoluto e da altura das plantas em relação ao feijão-mungo, sendo os demais parâmetros similares entre as duas culturas. A salinidade e estresse por alumínio induziram efeitos negativos quando aplicados de forma isolada ou combinada em todas as variáveis analisadas para as duas culturas testadas. A combinação de 150 mM de NaCl e 1,0 µM de Al não afetou a altura das plantas, massa fresca e comprimento das raízes de plantas de sorgo em relação ao observado nas plantas estressadas apenas com 150 mM de NaCl. O comprimento das raízes de plantas de feijão-mungo estressadas com 1,0 µM de Al foi estatisticamente similar ao observado nas plantas expostas simultaneamente a 50 mM de NaCl e 1,0 µM de Al. As plantas de sorgo apresentaram melhores respostas aos estresses salino e por alumínio em relação às plantas de feijão-mungo, possivelmente devido ao metabolismo C4 presente nestas plantas que permite maior captação de CO2 e acúmulo de biomassa.