Irrigation depths and yield response factor in zucchini cultivation/Laminas de irrigacao e fator de resposta ao rendimento no cultivo da abobrinha

The objective of this study was to evaluate the effect of different irrigation depths on productive performance and yield response of zucchini (Cucurbitapepo L.). A field trial was carried out in the experimental area of the Meteorological Station of the Federal University of Ceara, 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.sup-1]. Highest WUE (64 kg [mm.sup.-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). Key words: Cucurbita pepo L. irrigation management reference evapotranspiration Objetivando-se avaliar o efeito de diferentes laminas de irrigacao no desempenho produtivo e o fator de resposta ao rendimento da abobrinha (Cucurbita pepo L.), realizou-se um ensaio de campo na area experimental da Estacao Meteorologica da Universidade Federal do Ceara, CE. O delineamento utilizado foi o de blocos ao acaso, com seis tratamentos e quatro repeticoes. Os tratamentos adotados foram: 30, 60, 90, 120, 150 e 180% da evapotranspiracao de referencia (ETo), estimada por Penman-Monteith (EToPM) e aplicadas por gotejamento. Analisou-se a: massa do fruto, numero de frutos, comprimento do fruto, diametro do fruto, espessura da polpa, solidos soluveis e produtividade, alem da eficiencia de uso da agua (EUA). Para o calculo do fator de resposta ao rendimento (Ky) utilizou-se a metodologia proposta pelo boletim 33 da FAO. A lamina de irrigacao de 567 mm equivalente a 159% da EToPM proporcionou a maxima produtividade total da cultura estimada em 24.808 kg [ha.sup-1]. A EUA apresentou o maior valor de 64 kg [mm.sup.-1], para a lamina de irrigacao totalizada em 186 mm (30% da ETo). Os valores de Ky indicaram que a cultura