Irrigação com efluentes da piscicultura no cultivo da goiabeira em ambiente de semiárido

Abstract

The integration of agriculture-aquaculture production is considered as a sustainable alternative for regions that suffer from water resources shortage and a way to rationalize the water use even in regions without problems of water security. However, in order to ensure the optimization of this integrated system some variables and processes need to be studied and well known such as the amount of effluent to be applied to crops, the real contribution of aquaculture effluent on the supply of nutrients and the possibility of restrictive use of raw effluent. The objective of this study was to evaluate the effect of irrigation with effluent from the cultivation of tilapia in guava plantation in an experiment installed on the Pilot Project for Irrigated Fruit Crop Production of Santa Rosa do Piauí, in Piauí state, Brazil, which is administered by Codevasf. The experimental design used was the randomized blocks design with six treatments and four replications, based on irrigation levels, which accounted for 25 %, 50 %, 75 %, 100 %, 125 % and 150 % of ETo estimated by Penman-Monteith/FAO method. During two years several different variables were monitored such as the soil water status; growth and production of guava; distribution of root system; development of the crop canopy; coefficient of reduction of evapotranspiration (Kr); tilapia cultivation; aquaculture effluent; and soil fertility. The data of the evaluated variables were subjected to analysis of variance by F test. When significant effect was observed, the Tukey test was used to compare those variables with qualitative nature and regression analysis was used for those variables with quantitative nature. The growth, production and physical quality of fruits of guava crop tend to increase linearly with the increment of water depth with effluent from fish farms. The total yield of guava increases linearly with the increase of irrigation depth with aquaculture effluent up to the productivity of 6,537 kg ha-1 for 1,059 mm of irrigation per year. The distribution of the root system was influenced by the irrigation with effluent from aquaculture applied. The water deficit caused by the application of smaller irrigation depths induces the elevation of guava root growth, both horizontally and vertically. The addition of nutrients to the soil through application of fish farming wastewater tends to reduce application of nutrients (N and P2O5) necessary for the development and production of guava crop. Multiple use of water as a result of integration aquaculture-agriculture foment the development of the guava plants, optimizes water use, and reduces production costs of the integrated system.