تعيين ضريب حساسيت گندم به تنش رطوبتي در مراحل مختلف رويش در منطقه كرج

Evaluating the Wheat Response Factor to Water (Ky) in Different Growth Stages in Karaj

Water is a primary limiting factor in winter wheat production as well as yield in its most parts of Iran, with quite variable rainfall throughout the growing season and among years. With increasing demands for the limited water, improving the efficiency of irrigation is essential. One technique is to irrigate during responsive stages of crop development, but few studies have been carried out to examine this approach. This study, on a loam clay soil ( fine loamy over fragmental, mixed, thermic, shallow, Xeric Toriortent), was conducted to examine the effects of irrigation, based on stage of crop development, on winter wheat (Mahdavi cv.) yield. A completely randomized block design with four replicates was used to compare the effects in nine irrigation treatments. The treatments were: non-irrigated (Ti); through irrigation (T2); irrigated from planting date to the end of the tillering, stem elongation and flowering stages (T3) , (T4) and (T5) respectively; irrigation starting with stem elongation, booting and caryopsis development stages, respectively, up to the end of the growth period (T6), (T7) and (Tg); and finally irrigation in the booting and flowering stages (Ty). Plots were 2.5 by 4 m with 16.6 cm row spacings. Irrigation was done with the depletion of available soil water. Evapotranspiration; seasonal evapotranspiration from 24 February to harvest time (10 June); were determined according to soil water balance in root zone using TDR, total precipitation was 32.5 mm during this period. After maturity, grain yield as well as above ground dry matter were measured, with yield response factor (Ky) being calculated for each growth stage, and according to FAO paper. Irrigation at each stage significantly increased grain yield as well as above ground dry matter. Results show that, grain yield and seasonal evapotranspiration were highest, 4565.5 kg ha-land 337 mm Respectively, in T2 (complete or through irrigation), and lowest, 571.5 kg ha-l and 64 mm Respectively, in T1. Yield response factor (Ky) was 1.08 for the total growth period. Maximum Ky (1.1) was related to "vegetative growth + booting and flowering stages", with tillering stage having the minimum Ky. Results showed that tillering (Ky=0.45), stem elongation (Ky=0.56) and caryopsis development (Ky=0.48) stages were lowly sensitive to ET-deficit, while booting and flowering stages indicated the highest sensitivity.