RESUMO
Rainfall is among the climatic factors that most affect production, as in the Brazilian Cerrado. Non-destructive and automated phenotyping methods are fast and efficient for genotype selection. The objective of this work was to evaluate, under field conditions, the morphophysiological changes, yield, and grain quality of soybean (Glycine max L. Merrill) under water stress in the Brazilian Cerrado. The plots comprised six soybean cultivars and the subplots of four water regimes, corresponding to 31, 44, 64 and 100% of crop evapotranspiration replacement. The experiments were conducted from May to September 2018 and 2019. An irrigation system with a bar of sprinklers with different flow rates was used. Gas exchange, vegetation indices (measured using a hyperspectral sensor embedded in a drone), yield and grain quality were evaluated. Water stress had different effects on gas exchange, vegetation indices, grain yield and chemical composition among the cultivars. Embrapa cultivar BRS 7280 Roundup ready (RR) and Nidera cultivar NA 5909 RG (glyphosate resistant) are yield stable and have a greater tolerance to drought. BRS 7280RR showed a higher tolerance to drought and higher water use efficiency (WUE) than all other tested cultivars. Vegetation indices, such as the NDVI (Normalized Difference Vegetation Index), correlated with the morphophysiological traits, such as plant height, were the most responsive variables to water stress. The NDVI can be used to predict soybean yield as a tool in a selection program under drought.
RESUMO
The management of nitrogen fertilization is complex due to the various transformations of the nitrogen that occur in the soil-plant-atmosphere system, reducing the efficiency of the fertilization, productivity and the profit margin of the maize production areas. This study aimed to evaluate the effect of different levels of common urea and urea treat with NBPT [N-(n-butyl) thiophosphoric triamide] on the productivity and efficiency of the nitrogen fertilization in maize, correlated with simple economic analysis. The design of the field experiment was in randomized complete blocks with six repetitions, in a 2 x 4 factorial outline, made up of by two sources of nitrogen (urea and NBPT-treated urea) and four levels of nitrogen as top dressing (60, 120, 180 and 240 kg ha-1). The sources and applied nitrogen levels influenced the productivity and the leaf and grain nitrogen contents, while the production components (size and diameter of the ear, and percentage of straw and cob) were not altered. The agronomic efficiency of the nitrogen fertilization decreased with the increase of the applied nitrogen levels. The highest gross profit margin in the maize culture is obtained with 180 kg ha-1 of nitrogen supplied in the NBPT-treated urea.
O manejo da adubação nitrogenada é complexo em razão das diversas transformações do nitrogênio que ocorrem no sistema solo-planta-atmosfera, diminuindo a eficiência da adubação, produtividade e a margem de lucro das áreas de produção de milho. Neste trabalho, objetivou-se avaliar o efeito de diferentes doses de uréia comum e com NBPT [N-(n-butyl) thiophosphoric triamide] na produtividade e eficiência da adubação nitrogenada na cultura do milho, correlacionado com análise econômica simples. O delineamento experimental foi em blocos completos casualizados com seis repetições, em esquema fatorial 2 x 4, constituídos por duas fontes de N (uréia comum e uréia tratada com NBPT) e quatro doses de nitrogênio em cobertura (60, 120, 180 e 240 kg ha-1). As fontes e doses de nitrogênio influenciaram na produtividade e nos teores de N da folha e dos grãos, enquanto que os componentes de produção (tamanho e diâmetro da espiga e porcentagem de palha e sabugo) não foram alterados. A eficiência agronômica da adubação nitrogenada diminuiu com o aumento das doses de N aplicadas em cobertura. A maior margem bruta de ganho da cultura do milho é obtida com aplicação de uréia tratada com NBPT, na dosagem de 180 kg ha-1.
