Cecilia M. Tojo Soler

Determining FAO-56 crop coefficients for peanut under different water stress levels

Accurate estimates of peanut (Arachis hypogaea L.) water requirements are needed for water conservation. The objective of this study was to evaluate the FAO-56 crop coefficients for peanut grown under various levels of water stress in a humid climate. Two experiments were conducted in three automated rainout shelters located at the University of Georgia Griffin Campus in Griffin, Georgia, USA in 2006 and 2007. Irrigation was applied when the modeled soil water content in the effective root zone dropped below a specific threshold of the available water content (AWC). The irrigation treatments corresponded to irrigation thresholds (IT) of 40, 60 and 90% of AWC. The soil water balance was used to compute observed evapotranspiration (ETcm) from measured soil water content at six different soil depths. The length of the four developmental stages was different than the values listed in FAO-56. The 2-year average absolute relative error of Kcini was 8, 19 and 6% for 40, 60 and 90% IT, respectively. For the 90% IT, the FAO-56 Kcmid and Kcend were almost identical to the 2-year averages of the observed Kcmid and Kcend, respectively. The findings of this study confirmed that the FAO-56 procedure was reasonably accurate for estimating peanut ET under water stress in a humid climate.

Determination of the FAO-56 Crop Coefficients for Peanut under Deficit Irrigation in a Humid Climate

There is a lack of information about crop coefficients to be used with the FAO-56 reference evapotranspiration (ETo) approach for peanut grown in humid climates in general and under deficit irrigation in particular. The objective of this study was to determine the crop coefficients for peanut under different deficit drip irrigation treatments for a humid climate. Peanut was grown in 2006 in three automated rainout shelters located at the University of Georgia Campus in Griffin, Georgia, USA. The irrigation treatments were 40%, 60% and 90% irrigation thresholds (IT). The least irrigated treatment corresponded to the 40% IT and the most irrigated was the 90% IT. When the modeled soil water content in the effective root zone dropped below a specific threshold of the available water content (AWC), irrigation was applied until the soil water reached 100% of AWC. The length of the initial stage was similar for the different treatments, while 40% IT had longer development and mid-season stages and shorter late stage than the other two treatments. The length of the development, mid-season, and late stages were close for the 60 and 90% IT. Deficit irrigation had a pronounced impact on the crop coefficient values, especially for the mid-season stage. The crop coefficient values for the 90% IT may be used in humid climates to calculate the peanut water requirements under full irrigation. The use of the appropriate crop coefficient values along with the appropriate length of the development stages will result in more efficient irrigation scheduling and water use planning in humid climates.

Determining Irrigation Scheduling for Cotton and Peanut using Cropping System Models

Irrigation scheduling is an important management practice for farmers who grow irrigated crops. Effective irrigation is possible by regular monitoring of soil water and crop development conditions in the field. However, this methodology requires frequent field visits and, consequently, it is time consuming. Computer simulation models can be an important aid for irrigation scheduling, as they integrate the soil-plant-atmosphere complex. The main objectives of this study were to determine the impact of different irrigation scheduling regimes on cotton and peanut growth and development and to evaluate the application of a crop simulation model as a tool for irrigation scheduling. Two experiments were conducted in four rainout shelters, located at the Griffin Campus of The University of Georgia, during 2005 and 2006. Cotton was grown in 2005 and peanut was grown in 2006. The CSM-CROPGRO-Cotton and CSM-CROPGRO-Peanut models were used to define the irrigation treatments by estimating the timing of irrigation and the amount of water to apply. The irrigation event was triggered when the actual soil water content in the effective root zone dropped below a specific threshold of the available water content (AWC) and then irrigation was applied until the soil water reached 100% of AWC. The irrigation treatments corresponded to 30%, 40%, 60% and 90% of the irrigation threshold (IT). The models require daily weather data, including maximum and minimum temperature, solar radiation and precipitation as input. Actual