Procedures are presented for determining crop water use and crop coefficients for a row crop, using a neutron scattering probe with an efficient subsurface drip irrigation system. One procedure is called the slope-projection method, and the other is called a covariance procedure. Field tests were conducted with full-season, narrow-row cotton (Gossypium hirsutum L.) on a well-drained, sandy soil in a semiarid environment over a 5-year period. The goal was to improve automated irrigation scheduling, by relating evapotranspiration (ET) to growing degree days (GDD). The result, using a Penman-Monteith reference ET, was an average midseason crop coefficient of 1.11, with a standard error of 0.056. With class A pan evaporation as the reference ET, the average midseason crop coefficient was 0.877, with a standard error of 0.029. A fifth-order polynomial for the pan-based crop coefficient as a function of GDD was programmed into a controller and used successfully to irrigate a field automatically for one season.

cotton, equations, evapotranspiration, irrigationscheduling, irrigation systems, plant water relations, sandy soils,semiarid climate, soil types, soil water, soil water balance, subsurfaceirrigation, trickle irrigation, water use efficiency, California, USA,Gossypium, Gossypium hirsutum, Pacific States of USA, Western States ofUSA, USA, North America, America, Developed Countries, OECD Countries,Gossypium, Malvaceae, Malvales, dicotyledons, angiosperms,Spermatophyta, plants, Field Crops (FF005) (New March 2000), Plant WaterRelations (FF062), Soil Physics (JJ300), Soil Water Management(Irrigation and Drainage) (JJ800) (Revised June 2002) [formerly SoilWater Management], Mathematics and Statistics (ZZ100)

• Journal Article

• Irrigation Management
• Irrigation Systems