Abstract
Micrometeorological variables of tabasco pepper cultivated under greenhouse and drip irrigated conditions have not been presented to date in literature, especially the water consumption of these plants, in terms of crop evapotranspiration (ETc) and crop coefficient (Kc). The determination of these variables is extremely important for the application of the correct amount of water to irrigated crops in these environments because PM FAO (56) standard methodology was idealized for outdoor environments. The objective of this work was to develop models of estimation of micrometeorological variables in greenhouse conditions and to determine the water demand, in terms of evapotranspiration (ET) and Kc, of the pepper (Capsicum frutescens L.), cv. Tabasco McIlhenny, drip irrigated using drainage lysimeters. The research was carried out in an experimental area located at the University of Sao Paulo (USP) in Piracicaba, SP, Brazil. The following micrometeorological variables were monitored: air temperature, air relative humidity (digital thermohygrometer) and evaporation (mini-pan) (EMT). Drainage lysimeters were used to obtain the ETc and the reference evapotranspiration (ETo) was estimated outside the greenhouse by the Penman Monteith (EToPM), Hargreaves and Samani (EToHS) methods and the class “A” pan method (ECA). It was concluded that the total value of mini-pan evaporation (EMT) inside the greenhouse was practically equal to EToPM, 5% lower than EToHS and 31% higher than ECA in the outdoor environment. ET values ranged from 0.28 to 2.42 mm day-1 and total crop ET was 446.43 mm. The Kc values for the first pepper production cycle were: 0.17 in the initial phase, 0.76 in the flowering and fruiting phase and 0.39 in the harvest phase, for the second production cycle, the value of Kc was 0.50 at the harvest phase.
Highlights
Changes in micrometeorological variables as air temperature, relative humidity, radiation and evapotranspiration for crops under plastic-covered environments have been studied in several locations in Brazil (Andrade Júnior et al, 2011; Costa et al, 2015; Chavaria et al, 2009) and the world (Kittas and Bartzanas, 2007; Meiri et al, 2011; AbdelGhany and Helal, 2011; Giménez et al, 2013; Qiu et al, 2015), either for research as well as commercial purposes, where the methodology FAO (56) EToPM standard that is recommended for outdoor use requires some adaptations to be used under greenhouse conditions
Allen et al (1998) suggested that for the reference evapotranspiration calculation (ETo) under greenhouse conditions, the wind speed at two meters height should be set at 0.5 m s-1, because according to the same authors, this improves the accuracy of estimates in very low wind speed conditions, do not present any experiments that support this practical suggestion
Studies show that the ratio between crop evapotranspiration (ETc) in greenhouse and ETo in outdoor environment can cause a variation in the estimate of crop coefficient (Kc)
Summary
Studies show that the ratio between crop evapotranspiration (ETc) in greenhouse and ETo in outdoor environment can cause a variation in the estimate of crop coefficient (Kc). In the specific case of Capsicum species, which have a growing cycle of 120 to 150 days and consume between 600 and 1250 mm of water, depending on climatic conditions and the variety planted, the average Kc is 0.40 immediately after transplantation, 0.95 to 1.10 during the period of full coverage and, for green peppers, 0.80 to 0.90 at harvest (Doorenbos and Kassam, 2000). Chaves et al (2005) and Miranda et al (2006) studied the water demand of the tabasco pepper (Capsicum frutescens L.) under field conditions in the semi-arid climate region (Northeast Brazil) and observed a total evapotranspiration of 1083 mm of water for one cycle of 135 days, based on sprinkler irrigation and using three drainage lysimeters to determine water consumption. The average water consumption during crop cycle was 7.4 mm day-1
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