Crop evapotranspiration and crop coefficient of jatropha from first to fourth year

Abstract

Water requirements from crops in an important information to manage irrigation. Jatropha (Jatropha curcas L.) actual crop evapotranspiration (ETc) and crop coefficient (Kc) is still unknown, which is necessary to understand the plant water demand dynamic, as well as to stablish strategies to improve irrigation efficiency. The objective of this study was to determine jatropha ETc and Kc from 1 st to 4 th growing year. The experiment was performed from March 2012 to August 2015 at "Luiz de Queiroz" College of Agriculture (ESALQ)/University of São Paulo (USP), Brazil. The experiment was divided into center pivot, drip, and rainfed treatments. Two large weighing lysimeters (12 m 2 surface area) were used per treatment to perform jatropha ETc determination (one plant per lysimeter). Reference evapotranspiration (ET0) was determined by grass based Penman-Monteith method using data from a weather station located close to the experiment. Kc was determined for the irrigated treatments by the ration between ETc and ET0 (Kc=ETc/ET0). For all years analyzed, ETc values ranged from 0.7 to 8 mm d-1 for center pivot treatment, from 0.6 to 7.4 mm d-1 for drip treatment, and from 0.4 to 5.4 mm d-1 for rainfed treatment. It was observed higher values for irrigated treatments in comparison to rainfed treatment, which was explained by the higher soil water availability provided by irrigation. In the 1 st year, Kc was 0.47 for both treatments, varying from 0.4 to 0.9. In the 2 nd , 3 rd , and 4 th year, Kc ranged from 0.15 to 1.38 for center pivot treatment and from 0.15 to 1.25 for drip treatment. Kc average for 2 nd , 3 rd , and 4 th during vegetative and productive growing stages together was 0.77, 0.93, and 0.82 for center pivot treatment, respectively, and 0.69, 0.79, and 0.74 for drip treatment, respectively. The reason Kc for center pivot treatment was slightly higher than drip treatment was due the high soil moisture after irrigation event, increasing soil evaporation rates. Annual ETc and Kc fluctuation in 2 nd , 3 rd , and 4 th years was very similar, which was explained by the growing stage and the leaf area index dynamic during the year, presenting values varying from 0 to 0.5 in the 1 st year, from 0 to 1.4 in the 3 rd year, and from 0 to 2 in the 3 rd year. The comparison between Kc and leaf area index showed, for center pivot treatment, a logarithmical equation with coefficient of determination (R 2) and root mean square error (RMSE) of 0.7877 and 0.3831, respectively, and 0.8655 and 0.1419 for drip treatment, respectively. For all three years analyzed, Kc related to cumulative thermal unit showed a 3 rd degree polynomial equation for both treatments, with R 2 ranging from 0.3373 to 0.6297 in the center pivot treatment and from 0.5445 to 0.6386 in the drip treatment.

Water requirement of oil palm in two different edaphoclimatic conditions in Brazil

“…Besides, using only the crop coefficient (K c or K cb ) to manage irrigation is questionable(Cerekovic et al 2010;Majnooni- Heris et al 2012). The strong relation between K cb and LAI found in this work (R 2 =0.9856) was superior to other studies Lena (2016). determined a K c -LAI relationship for Jatropha irrigated by a center pivot (R 2 =0.79) and drip (R 2 =0.87) in the same site of our study.…”

“…In addition to the reasons presented here for divergences between the values of water use and crop coefficient reported by several authors in literature, other differences arise due to different terminologies and abbreviations along with the absence of clear information about which version of Penman equation is used to determine ET o . So, the use of crop coefficient-LAI (or crop coefficient-GC) relationships can provide additional information on the crop water consumption in a given climate (Lena, 2016 Despite of extensive existing research on the retrieval of crop coefficient-LAI relationships, we did not find any study that provides that information for oil palm. Thus, by comparing our results with those available in the literature for other crops, the K cb -LAI relationship developed herein can be useful to estimate oil palm water requirement from LAI measurements.…”