Cotton response to deficit irrigation during different growth stages

The objective of deficit irrigation is to increase water use efficiency by reducing of water quantity or wave off further irrigations that have not necessary. Cotton plant is sensitive to irrigation timing and quantity through different growth stages. The field trail was conducted at Hashemabad Cotton Research Station (Gorgan) to determine water consumption and cotton sensitivity to deficit irrigation at different growth stages during years 2004, 2005 and 2006. The study was carried out in a split plot design with three replications. Treatments of deficit irrigation in different growth stages were contained: deficit irrigation in flowering stage(I1), deficit irrigation in peak flowering stage(I2), deficit irrigation in boll formation stage(I3), deficit irrigation in flowering, peak flowering and boll formation stages(I4), deficit irrigation in flowering and peak flowering stages(I5), deficit irrigation in flowering and boll formation stages (I6) and deficit irrigation in peak flowering and boll formation stages (I7) as main plots and irrigation water quantities of 0% (q1), 35 % (q2), 70 % (q3) and 100% (q4) water requirement as subplots. Data from combined three years analyses showed that there were significant differences (R<0.01) among years with respect to yield, earliness percentage, boll weight and boll number per plant. Through different growth stages, deficit irrigation treatments showed significantly different yield but did not showed significantly difference earliness percentage, boll weight and boll number per plant. Irrigation treatments I7, I2, and I3 had the highest yield over 3 years. The lowest yield was found in I4 and I5. In summery, flowering and peak flowering stages can be considered the most sensitive growth stages with respect to water deficit. Irrigation water quantities were significantly different with respect to yield, earliness percentage, boll weight and boll number per plant. Treatment of 70% of water requirement(q3) had higher water use efficiency at rate of 16.7%, less water use at rate of 18.4% and 4.7% yield reduction than full irrigation (q4), so it can be applied as best treatment.