ABSTRACT Hyperspectral sensors and regression analysis have been used to analyze the most important spectral ranges for biophysical parameters of target crops, aiding in management decision-making. This study aimed to analyze the spectral response of Brachiaria brizantha cv. Marandú leaves to increasing rates of urea fertilization and predict leaf nitrogen content (LNC). Four rates of urea fertilization (0, 25, 50, and 75 kg of N ha-1) were applied. Eight leaves were collected per plot seven times at monthly intervals and subjected to hyperspectral analysis. Leaf spectral responses differed statistically within the visible region, particularly at 550 nm (green). The regression models achieved moderate to good R2 values (0.53 to 0.83) for predicting LNC and identified important wavelengths in the red edge region (715 to 720 nm). These findings demonstrate the potential of spectral analysis to detect changes and forecast leaf nitrogen content in B. brizantha cv. Marandú crops at different fertilization levels.

RESUMO Objetivando-se avaliar o efeito de diferentes lâminas de irrigação no desempenho produtivo e o fator de resposta ao rendimento da abobrinha (Cucurbita pepo L.), realizou-se um ensaio de campo na área experimental da Estação Meteorológica da Universidade Federal do Ceará, CE. O delineamento utilizado foi o de blocos ao acaso, com seis tratamentos e quatro repetições. Os tratamentos adotados foram: 30, 60, 90, 120, 150 e 180% da evapotranspiração de referência (ETo), estimada por Penman-Monteith (EToPM) e aplicadas por gotejamento. Analisou-se a: massa do fruto, número de frutos, comprimento do fruto, diâmetro do fruto, espessura da polpa, sólidos solúveis e produtividade, além da eficiência de uso da água (EUA). Para o cálculo do fator de resposta ao rendimento (Ky) utilizou-se a metodologia proposta pelo boletim 33 da FAO. A lâmina de irrigação de 567 mm equivalente a 159% da EToPM proporcionou a máxima produtividade total da cultura estimada em 24.808 kg ha-1. A EUA apresentou o maior valor de 64 kg mm-1, para a lâmina de irrigação totalizada em 186 mm (30% da ETo). Os valores de Ky indicaram que a cultura pode ser considerada pouco sensível (Ky < 1) ao déficit hídrico (50, 60, 70, 80 e 90% da lâmina ótima), com tendência a ser proporcionalmente sensível (Ky = 1) para déficits hídricos mais severos (30, 60 e 90% da EToPM).

ABSTRACT The objective of this study was to evaluate the effect of different irrigation depths on productive performance and yield response of zucchini (Cucurbita pepo L.). A field trial was carried out in the experimental area of the Meteorological Station of the Federal University of Ceará, CE, Brazil. The experimental design was randomized blocks, with six treatments and four replicates. The treatments adopted were: 30, 60, 90, 120, 150 and 180% of the reference evapotranspiration (ETo), estimated by Penman-Monteith (EToPM) and applied by drip irrigation. Fruit weight, number of fruits, fruit length, fruit diameter, pulp thickness, soluble solids and yield were analyzed, as well as water use efficiency (WUE). The methodology proposed by FAO Bulletin 33 was used to calculate the yield response factor (Ky). The 567 mm irrigation depth equivalent to 159% EToPM led to the maximum total crop yield estimated at 24,808 kg ha-1. Highest WUE (64 kg mm-1) was found for the total irrigation depth of 186 mm (30% ETo). Ky values indicated that the crop could be considered as little sensitive (Ky < 1) to water deficit (50, 60, 70, 80 and 90% of the optimal water depth), tending to be proportionally sensitive (Ky = 1) to more severe water deficits (30, 60 and 90% EToPM).