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Journal of Letters

Publication Date

2022-12-28

Abstract

This research evaluates the adequacy of rainfall and irrigation for economic crop cultivation in Rayong province, Thailand, in 2013, 2016, 2018 and 2020. The methodology starts with an estimation of the water demand of 23 crop types at each growth stage, based on the FAO Penman-Monteith equation for crop evapotranspiration. Next, soil water balance was calculated on a monthly basis, given components of rainfall, soil water from the previous month, percolation from the plant root zone, and crop water uptake. Calculations were made in a grid of 40 x 40 metre using the Geographic Information System. Adequacy of rainfall supply was assessed as the amount of water surplus and deficit from soil water at the threshold of plant water stress for the various crops. Results show that rainfall is sufficient for crop cultivation for 3-4 months per year on average, starting from June to October. Soil water deficit occurs for the entire dry season as well as in the lower rainfall period of the rainy season in August. The water deficit is largest for oil palm plantations and rice paddies, as these need a lot of water, and on sandy clay loam soil due to its relatively low water-holding capacity. Water deficit in the east of Rayong is lower than other parts of the province due to a relatively large amount of yearly rainfall. The crop water stress period lasts about 5-7 months in the east, while it can extend to 8.5-11 months in the west and centre, even with the same crop types. Irrigation demand is highest in April and May (7.0-33.6% of reservoir storage) as a result of the increased water demand at the start of the growing period and during fruit harvest season. This period poses the highest risk of water inadequacy, particularly if the reservoirs do not hold sufficient water from the previous year.

First Page

21

Last Page

50

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