Evapotranspiração e coeficiente de cultura do algodoeiro herbáceo (Gossypium hirsutum L.) cultivar BRS 187 8H na chapada do Apodi-RN.

Abstract

The experimental field campaigns were conducted in the Apodi Plateau, west of Rio Grande do Norte State, at the experimental station of EMPARN - Agricultural Research Corporation of Rio Grande do Norte, located in Apodi-RN county. The research objective was to determine the water requirements of irrigated upland cotton (Gossypium hirsutum L.), cultivar BRS 187 8H. For this purpose, two experimental field campaigns were carried out during the dry seasons of 2008 and 2009 years in which the Bowen Ratio Energy Balance method (BREB) was employed. Were obtained ETc and crop coefficient (Kc) at Apodi Plateau conditions. The ET0 was estimated by FAO-Penman-Monteith method using the meteorological data obtained from the INMET automatic station in Apodi-RN. The results showed that the accumulated ETc was 717 mm in 2008 and 751 mm in 2009, corresponding to an average of 6.5 mm day-1 in 2008 and 6.45 mm day-1 in 2009. The growth stage of highest water demand was middle stage, with 8.0 mm day-1 for in 2008 year and 7.7 mm day-1 in 2009 year and the Kc values for the 2008 year were: 0.65 in the initial stage, 1.01 in the middle stage and 0.78 in the end stage. The Kc values experimentally determined were lower than those of the FAO-56, even adjusted for local conditions. Mean differences observed in the order of 13, 18 and 10% for Kcini, kc-mid and kc-end, respectively. The use of Kc-FAO-adjusted values for estimate the cotton ETc resulted in overestimation of ETc with differences exceeding 10% compared with values obtained by BREB technique in the both observation years. It also was demonstrated that the Kc-ini was the most susceptible to irrigation applied variation, confirming what is already known from the literature. The use of Kc-Local provides a savings of pproximately 15% of water applied volume of in the both experimental campaign.