Abstract
Melon plants (Cucumis melo L.) are grown in the state of Rio Grande do Norte (RN), the largest producer of melons in Brazil, with plastic mulch and agrotextiles. Studies of crop evapotranspiration (ET) under these conditions are required to ensure adequate irrigation. This study aimed to determine the crop coefficients (Kc) of irrigated melon plants grown with mulch and agrotextiles in the region of Mossoro, RN, based on the Bowen Ratio Energy Balance (BREB) method. Two experiments were conducted at different times during the 2009/2010 season in a melon producing area (4°59'52 S, 37°23'09 W, and 54 m elevation) to define ET and Kc. Due to the plastic cover and reduced precipitation during the experiments, the Kc obtained by the BREB method was considered the basal Kc - KcbBREB. The results were compared with the Kcb from the FAO 56 Bulletin. There was close agreement between BREB and FAO ET measurements (12 % underestimation by the FAO method for the entire crop season), with sizeable differences only during the initial phenological stage. The mean KcbBREB values of the two field campaigns were 0.26, 0.96 and 0.63 for the initial, midseason and late stages, respectively. The high KcbBREB value in the initial growth phase may be related to the effect of the plastic mulch and agrotextiles on the energy balance at the surface. The relationship between KcbBREB and fc had high correlation, making possible an estimation of the melon Kcb based on the level of crop ground cover.
Highlights
The municipality of Mossoró, located in a semiarid region of northeastern Brazil, is the leading melon (Cucumis melo L.) producer in the country, with production primarily for the foreign market (IBGE, 2013)
To determine the evapotranspiration of the melon plants according to the Bowen Ratio Energy Balance (BREB) method, two experiments were conducted at different times: Experiment 1 (Exp. 1), with planting on Aug 12, 2009 and harvest on Oct 19, 2009, and Experiment 2 (Exp. 2), with planting on Nov 3, 2009 and harvest on Jan 11, 2010
We considered that the crop coefficients refer primarily to plant transpiration under the following assumptions: (i) due to the plastic bed cover and the drip irrigation systems, the soil evaporation was small, occurring only through the hole of seedling emergence, which ceased a few days after planting; (ii) most of the period of data collection occurred during the dry season, with a total rainfall of 38 mm between Aug 12, 2009 and Jan 11, 2010 of which 25 mm was recorded in Jan, when the fraction of soil covered by the crop was greater than 0.90
Summary
The municipality of Mossoró, located in a semiarid region of northeastern Brazil, is the leading melon (Cucumis melo L.) producer in the country, with production primarily for the foreign market (IBGE, 2013). Studies on the water requirements of melon produced in Mossoró are important due to the local climatic conditions and to the specific cultural practices. Polypropylene webs – agrotextiles – are installed over the plant rows to minimize insect attacks, especially by the silverleaf whitefly and the leaf miner fly. Both plastic mulch and polypropylene webs influence the microclimate near plants, including temperature, net radiation, relative humidity, wind speed and accumulated degree-days (Diaz-Perez, 2009; Gimenez et al, 2002), and this microclimate affects evapotranspiration and water use of plants (Lovelli et al, 2008, Qin et al, 2014). Melon production in Mossoró involves specific practices; local studies are important for providing information regarding the efficient use of water
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