Cotton Irrigation Requirments

Cotton Irrigation Requirments - Irrigation Requirements of...

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Irrigation Requirements of Cotton BRAE 331 Roman Ferro March 2, 2011
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Cotton is a valuable cash crop that is grown in North America as well as all around the world. It is grown in climates that range from areas with average rainfall to desert climates. Cotton does not grow well in climates with excessive rainfall, since it is sensitive to waterlogging. The roots of the cotton plant have the ability to grow over 3 meters in length (Stewart, 2010). Cotton is commonly grown in the San Joaquin Valley and southern parts of California. Its value per acre in California is approximately $6000 (Grismer,2002). Crop Coefficients vs. a Transferable Time Scale The calculation of a crop coefficient (Kc) is a tool in which farmers use to aid in determining the necessary amount of water a field requires to be applied at irrigation. The crop coefficient is derived from the equation: ETc represents the value of the evapotranspiration of the given crop and ETo represents the evapotranspiration of a reference crop such as grass or alfalfa (Ko et al., 2009). ET rates change with change in weather conditions (Hunsaker et al.1993). The value of evapotranspiration of a reference crop is calculated with the Penmen-Moneith equation (Sentelha et al. 2009): Factors that affect the value of the reference evapotranspiration include vapor pressure, net radiation, solar heat flux, air temperature and wind speed (Sentelha et al. 2009). It is important to remember that the crop coefficient value has factors that influence it as well. The equation: demonstrates that the crop coefficient value must account for the adjustment for reduction in transpiration based on the root zone moisture available (Ks) as well as the contribution of the evaporation (Ke) when the soil surface is wet; the term Kcb refers to the basal crop coefficient, which is the crop coefficient value when the soil surface is dry and the plants experience no stress (Hunsaker et al., 2003). The value of the crop coefficient varies throughout the growing season and will alter due to the different stage at which the crop is currently in. The graph below demonstrates that the basal crop coefficient of cotton varies throughout the year.
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Figure1. Derived Kcb throughout the growing season (Hunsaker et al., 2003) It is common to separate cotton’s different crop coefficients into its different growing stages of initial, mid, and late stages. FAO lists cotton with an initial crop coefficient of 1.61 for the initial stage, 1.15-1.2 for the middle of the growing season, and .5-.7 for the end of the growing season (Suleiman et al., 2007). Critical Times for Irrigation The water demands for cotton vary throughout the season. Cotton requires smaller amounts of water during the vegetation period with an increase in demand during the reproductive stage (Vories et al.,2007). In fact, Plaut et al. (1988) claims that slight stress during the vegetative period decreases vegetative growth and increases flowering and boll formation; in turn this increases the overall yield. Seshachalam et. al (1975) claims that at days 50, 75, and 90
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Cotton Irrigation Requirments - Irrigation Requirements of...

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