ABSTRACT
Irrigation provides plants with sufficient water to prevent yield-reducing stress. The frequency of irrigation and quantity of water depend on local climatic conditions, crop species, stage of plant growth and soil-plant-moisture characteristics. The need for irrigation can be determined in several ways that do not require data on rate of evapotranspiration (ET). Visual indicators such as plant color or leaf wilting and an early drop can be used [1]. However, this information appears too late to prevent reduction in crop yield or quality. Other methods of irrigation scheduling include determination of plant water stress, soil moisture status and soil water potential [2]. Methods of estimating crop water requirements using ET in combination with soil characteristics are useful in determining not only when to irrigate but also the quantity of water needed [1]. Estimates of ET have not been used in Trinidad even though necessary climatic data are available. Trinidad’s water supply is dwindling because of luxury consumption of ground water resource (e.g., sprinkler irrigation of golf courses). There is an increasing demand of ground water for domestic, municipal and industrial uses. Water quality is declining as well. Thus, water is a limiting factor in Trinidad’s goal for self-sufficiency in agriculture. Intelligent use of water will prevent sea water from entering into aquifers. Irrigation of crops in the tropics and on these soils requires appropriate working principles for the effective use of all resources peculiar to the local conditions. Adequate water supply for the entire growing season is essential for the optimum production of crops. The crop water requirements are often provided by both rainfall and irrigation. In places where sufficient rainfall is received throughout the growing period, irrigation is minimal. For good water management and irrigation planning, it is necessary to know the water consumption of crops grown in the project area. Hackbart [7] developed a computer program to estimate net irrigation requirements for various crops in which he has combined information from a modified Blaney-Criddle model [1, 4] together with the USDA-SCS Technical Release No. 21 of USDA-SCS [10]. Irrigation water requirements for vegetables and other agronomic crops have been computed by Rogers et al. [9] for Florida and by Goyal and GonzálezFuentes [3, 4] for Puerto Rico. They have estimated net irrigation requirements (NIR) with mean monthly rainfall data and with 20% rainfall probability (dry years) data. Methods presented in this chapter to estimate PET and total water consumption can be employed in other countries in the world to develop local data bases. This chapter indicates: (1) Estimation of potential evapotranspiration (PET) with Hargreaves-Samani and modified Blaney-Criddle methods; and (2) Estimation of total water consumption for agronomic crops at five locations in Trinidad in the Caribbean region.
