Evapotranspiração e coeficiente de cultura da palma forrageira: análise comparativa de cultivos sem e com o uso de cobertura morta

Abstract

Due to long periods of drought and the effects of climatic changes in the Brazilian semi-arid region, it is of great importance to use management that will circumvent these impacts in the rural environment. The use of plants tolerant to water deficit and the use of supplementary irrigation may be an alternative, where for good irrigation water management practice it is necessary to know the water requirement of the crop, evapotranspiration and the crop coefficient for conditions. Soil water balance is a technique that helps in the measurement of these components. Thus, the objective of this study is to quantify the evapotranspiration and the forage cactus cultivation coefficient in crops without and with the use of mulch in the semi-arid region of Pernambuco. The experiment was carried out at the Experimental Station Lauro Ramos Bezerra, belonging to the Agronomic Institute of Pernambuco - IPA, municipality of Serra Talhada-PE, from November 2014 to November 2015. The clone used was Opuntiastricta, submitted to four slides of irrigation (25, 50, 75 and 100%) based on reference evapotranspiration plus rainfed condition, and two cropping systems (without and with mulch). The experimental design was arranged in randomized blocks, in the factorial arrangement 5x2, in four replications, where the slices represented the plots, and the cropping systems, the subplots. Over time the soil moisture was monitored. The water balance method was applied in 14-day intervals, totalizing 21 periods, which was composed of evapotranspiration (ET), precipitation (P), irrigation (I), runoff (R), vertical flow of water in the soil (Q) and variation of soil water storage (Δh). The components of the water balance were integrated and compared between the treatments within each period, applying them to the tests of normality and homoscedasticity, and once significant, the analysis of variance, if necessary, the Tukey test (5%). The irrigation events added to precipitation during the 21 periods was 764.76 mm, with the months between August and November 2015 presenting the highest values of ETo (6.18 mm). There was no difference in the components of the vertical flow of water in the soil, capillary ascension and deep drainage (CA and DP, in this order) when compared to the systems of cultivation without and with mulch over the soil. When the crop evapotranspiration (ETc) was evaluated, a significant difference was observed only for periods 10, 18, 20 and 21. The ETc accumulated for both systems was -782.01 and -771.19 (SC and CC, in this order). The highest mean ETc value corresponded to periods 6 (10-Apr-2015) for the two SC and CC systems, with averages of (-5.06 and -4.75, respectively). For the crop coefficient (kc) only the periods 10,18, 20 and 21 were significant (p <0.05), the mean values of kc for the two systems were 0.57 and 0.56 (SC and CC, in this order). The use of mulching improved the conditions of forage cactus cultivation, although it did not present a difference in water consumption, providing close kc values.