Different drip irrigation regimes affect cotton yield, water use efficiency and fiber quality in western Turkey

Decreasing in water availability for cotton production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant cotton varieties or water management. A field trial was conducted to observe the effects of different drip irrigation regimes on water use efficiencies (WUE) and fiber quality parameters produced from N-84 cotton variety in the Aegean region of Turkey during 2004 and 2005. Treatments were designated as full irrigation (T₁₀₀, which received 100% of the soil water depletion) and those that received 75, 50 and 25% of the amount received by treatment T₁₀₀ on the same day (treatments T₇₅; T₅₀ and T₂₅, respectively). The average seasonal water use values ranged from 265 to 753mm and the average seed cotton yield varied from 2550 to 5760kgha⁻¹. Largest average cotton yield was obtained from the full irrigation treatment (T₁₀₀). WUE ranged from 0.77kgm⁻³ in the T₁₀₀ to 0.98kgm⁻³ in the T₂₅ in 2004 growing season and ranged from 0.76kgm⁻³ in the T₁₀₀ to 0.94kgm⁻³ in the T₂₅ in 2005 growing season. The largest irrigation water use efficiency (IWUE) was observed in the T₂₅ (1.46kgm⁻³), and the smallest IWUE was in the T₁₀₀ treatment (0.81kgm⁻³) in the experimental years. A yield response factor (k y) value of 0.78 was determined based on averages of two years. Leaf area index (LAI) and dry matter yields (DM) increased with increasing water use for treatments. Fiber qualities were influenced by drip irrigation levels in both years. The results revealed that well-irrigated treatments (T₁₀₀) could be used for the semi-arid climatic conditions under no water shortage. Moreover, the results also demonstrated that irrigation of cotton with drip irrigation method at 75% level (T₇₅) had significant benefits in terms of saved irrigation water and large WUE indicating a definitive advantage of deficit irrigation under limited water supply conditions. In an economic viewpoint, 25.0% saving in irrigation water (T₇₅) resulted in 34.0% reduction in the net income. However, the net income of the T₁₀₀ treatment is found to be reasonable in areas with no water shortage.