Interaction effect of Irrigation regime and nitrogen fertilizer on cotton yield and quality.

Irrigation and nitrogen managements are two aspect of successful cotton production. Due to shortage of irrigation water and over application of nitrogen to ensure against yield lost, field experiment was conducted to study the effect of irrigation water and nitrogen on yield and yield components of Varamin Cotton Cultivar in Rodusht Agricultural Experiment Station in a clay loam soil. The effect of three irrigation frequencies after 90, 135 and 180 mm cumulative class A pan evaporation (I1, I2 and I3), and three level of nitrogen application rates of 120, 180 and 240 kg/ha nitrogen (N1, N2 and N3) on the cotton yield and yield components were studied for three years (1998 to 2000). The experimental design was a complete randomized block design in a split plot arrangement in four replicates. Irrigation water was in the main plot and nitrogen was in the sub-plot, respectively. In the combined analysis the effect of irrigation were highly significant (P0.01) for number main stem symbodial branch, number of bolls per plant, number of bolls per square meter, seed-cotton yield, applied water use efficiency and were significat (P0.05) for main stem diameter and wieght of boll. By increasing irrigation interval the seed-cotton yield, number of boll per plant, and number of boll per square meter were significantly decreased. In I1, I2 and I3 irrigation treatments,the applied water were 1078, 887, and 764 mmseed-cotton yield were 3278, 3378 and 2623 kg/ha, and water use efficiency were 3.01, 3.82 and 3.44 kg seed-cotton/mm applied water, respectively. The seed-cotton yield in I1 and I2 treatment were significantly different from I3 treatment. The water use efficiency in I2 and I3 were in the same group, and in I1 and I3 treatment were in the next group. The effect of nitrogen treatments and nitrogen x irrigation were not significant for any studied traits. Application of 180 kg/ha nitrogen in three split application (planting, sqaure and flowering stages) and irrigation after 135 mm cumulative class A pan evaporation is recommended due to the shortage of irrigation water. To obtain maximum applied water use efficiency allocation of 8500 to 9200 cubic meter water per ha is required.