GRAIN-YIELD AND WATER-CONSUMPTION OF ETHEPHON-TREATED CORN UNDER DIFFERENT IRRIGATION REGIMES

Ethephon (2-chloroethyl phosphonic acid) has been widely studied under field conditions as a growth regulator to enhance yield in corn (Zea mays L.) by controlling lodging. However, few studies have examined th e interaction between ethephon and soil water availability on grain yi eld and growth patterns of corn. The objective of this research was to study the effects of ethephon rates and timing of applications in com bination with different irrigation levels on water use, yield and its attributes, total dry matter accumulation, LAI, and plant height. The 2-yr study (1993-1994) was carried out at the CNR Irrigation Institute experimental farm in southern Italy (14 degrees 50' E, 40 degrees 07' N; sandy-clay soil) using corn (cv. Aida, FAO class 500). Treatments consisted of four irrigation regimes and four and six ethephon treatme nts for 1993 and 1994, respectively, in a randomized complete block de sign with three replicates. Irrigation regimes were a rainfed control (T-0) and three treatments replenishing the soil water profile to fiel d capacity to a depth of 0.7 m at different frequencies: T-w, weekly i rrigation; T-2, irrigation at two growth stages (VT and R1); and T-4, irrigation at four stages (V7, VT, R1, and R4). Ethephon was applied b oth years at the V5 stage at rates of 280, 560, and 840 g a.i. ha(-1). In 1994, two additional treatments were included by applying, at the V9 stage, an additional 280 g ha(-1) of ethephon to treatments that ha d previously received 280 or 560 g a.i. ha(-1). Increasing ethephon ra tes caused a significant reduction in LAI, plant height, and dry matte r accumulation, resulting in a reduction in water consumption. In the rainfed control, increasing the ethephon rate resulted in a linear inc rease in yield, with maximum increase of about 200% (1.6 t ha(-1)) and 75% (1.7 t ha(-1)) in 1993 and 1994, respectively. By contrast, treat ments irrigated four times showed a linear decrease of about 13% in bo th years. Ethephon treatment had no effect on grain yield in the T-w, and T-2 treatments. Kernel number was the yield component with the gre atest influence on grain production. Our results suggest that ethephon may increase grain yield when natural or artificial water supply is a limiting factor.