Effect of cyclic use and blending of alkali and good quality waters on soil properties,yield and quality of potato,sunflower and Sesbania

Degradation of soils through the use of alkali waters constitutes a major threat to irrigated agriculture especially for the cultivation of sodicity sensitive crops. The response of potato (Solanum tuberosum), sunflower (Helianthus annus) and Sesbania (Sesbania sesban) green manure to the combined use of a good quality canal water (CW, ECcw 1.1 dS/m, RSC nil, SAR 1.8) and an alkali water (AW, ECaw 3.6 dS/m, RSC 15.8 me/L, SAR 12.4) was evaluated for 5 years (1998–2003) on a well drained sandy loam soil (ECe 2.5 dS/m, pH 7.9, exchangeable sodium percentage, ESP 5.3). Increase in soil pH (8.9–9.1), salinity (4.7–5.1 dS/m) and sodicity (ESP 25–41) as a consequence of irrigation with alkali water affected the growth and yields of all the crops. The sustainability yield index (SYI) when irrigated with AW was 0.063 and 0.133 for potato and sunflower, respectively, indicating that these crops should not be irrigated with such high alkalinity waters. Cyclic use treatments included alternating irrigations with CW and AW, with CW to start with (1CW:1AW), alternating two irrigations each with CW and AW and applying CW to start with (2CW:2AW), alternating two irrigations each with CW and AW and applying AW to start with (2AW:2CW), four irrigations with AW to start with and followed by two with CW (4AW:2CW) and crop-wise alternations of CW and AW, with application of CW to potato and AW to sunflower (CWp:AWs). The SYI of potato improved to 0.703, 0.642, 0.442 and 0.579, respectively with the cyclic 1CW:1AW, 2CW:2AW, 2AW:2CW and CWp:AWs treatments. The values of SYI were 0.633 and 0.415 for potato when irrigated with blends of CW and AW in the ratio 2:1(2CW:1AW) and 1:2 (1CW:2AW), respectively. Similarly, the SYI for sunflower ranged between 0.481–0.736 and 0.512–0.592 for cyclic use and blending but was reduced to 0.394 with 4AW:2CW in cyclic use mode. When averaged for 5 years, the relative yields (compared to CW) ranged between 65–85 and 61–94% for cyclic use in potato and sunflower, respectively. However, the values ranged between 66–83 and 71–81% for blended waters. Considerable deterioration in produce quality was observed in terms of potato grade and weight loss on storage as well as the smaller seeds along and lower oil content in the case of sunflower. The overall deterioration in soil properties under different modes was related to the proportions of AW applied. Computations further indicated that with a similar proportion of CW and AW, cyclic application CW during the initial stages would minimise the adverse effects of alkali water.