The recommended method to schedule irrigation for vegetable crops is to use together (1) the crop water requirement method that takes into account plant stage of growth, (2) a measurement of soil water status and (3) guidelines for splitting irrigation.
Other irrigation uses vary according to the type of crop, system characteristics and field location. Some examples include: periodic overhead irrigation for dust control; wetting of dry row middles to settle dust and prevent sand from blowing during windy conditions; and wetting of roadways and drive aisles to provide traction of farm vehicles.
Soil water status and tension
Soil water tension represents the magnitude of the suction (negative pressure) the plant roots have to create to free soil water from the attraction of the soil, and move it into the root cells. The dryer the soil, the higher the suction needed; hence, the higher the soil water tension. Soil water tension is commonly expressed in centibars (cb) or kilopascals (kPa; 1cb = 1kPa; 7kPa = 1psi).
For most vegetable crops, soil water tension in the rooting zone should be maintained between 6 (field capacity) and 15 cb. Because of the low AWHC of Florida soils, most full-grown vegetable crops will need to be irrigated daily. During early growth, irrigation may be needed only two to three times weekly.
Crop water requirement
Crop water use is related to reference evapotranspiration (ETo) by a crop coefficient (Kc), which is the ratio of crop water use to the reference value ETo. Because different methods exist for estimating ETo, it is very important to use Kc coefficients that were derived using the same ETo estimation method as will be used to determine the crop water requirements.
E.H. Simonne is an associate professor at UF/IFAS, (352) 392-1928 ext. 208. E-mail: firstname.lastname@example.org. M.D. Dukes is an assistant professor at UF/IFAS, (352) 392-1864 ext. 107. E-mail: email@example.com. D.Z. Haman is a professor at UF/IFAS, (352) 392-1864 ext. 285. E-mail: firstname.lastname@example.org.