Growth, water use and efficiency of forage cactus sorghum intercropping under different water depths/Crescimento, consumo de agua e eficiencia do consorcio palma-sorgo sob diferentes laminas de agua

The effects of the forage cactus sorghum configuration and different irrigation depths on the growth, water use and efficiency of the forage cactus production system were investigated in this study. The experiment was conducted in the municipality of Serra Talhada, Pernambuco State, Brazil, between the years 2012 and 2013. Forage cactus was distributed in randomized blocks with factorial scheme and four replicates, in split plots (5 x 2), with five irrigation depths (0, 8.75, 17.5, 26.25 and 35% of the reference evapotranspiration, [ET.sub.0]) and two cropping systems (forage cactus monocropping and forage cactus sorghum intercropping). Crop evapotranspiration was calculated through soil water balance. The ratio between crop and reference evapotranspiration, and land use and water use efficiencies, were estimated. Irrigation depths and the intercropping affected only forage cactus canopy width and cladode biomass. The ratio between crop and reference evapotranspiration increased with the increase of irrigation depths, while the highest water use efficiency based on dry matter occurred at irrigation depths higher than 1,096 mm [year.sup.-1] in the intercropping (21.8 [+ or -] 6.8 kg [ha.sup.- 1] [mm.sup.-1]). Irrigation depths did not affect land use efficiency (0.83). Water depths from 1,096 to 1,202 mm [year.sup.-1] are recommended in the forage cactus sorghum system. Key words: actual evapotranspiration drip irrigation land use semi-arid region Os efeitos da configuracao palma-sorgo e de diferentes laminas de irrigacao sobre o crescimento, consumo de agua e eficiencia do sistema de producao da palma foram investigados neste estudo. O experimento foi conduzido em Serra Talhada, PE, entre os anos de 2012 e 2013, com a palma disposta em blocos ao acaso, quatro repeticoes, em parcelas subdivididas (5 x 2) de cinco laminas (0, 8,75, 17,5, 26,25 e 35% da evapotranspiracao de referencia) e dois sistemas de cultivo (palma exclusiva e consorcio palma- sorgo). A evapotranspiracao real da cultura foi calculada por meio do balanco de agua no solo. Estimou-se a razao evapotranspiracao real e de referencia, alem das eficiencias do uso da agua e da terra. As laminas de irrigacao e a adocao do consorcio afetaram apenas a largura do dossel e a biomassa dos cladodios da palma forrageira. A razao evapotranspiracao real e de referencia aumentou com o incremento da lamina de irrigacao, enquanto as maiores eficiencias do uso da agua com base na massa seca ocorreram nas lamina