EFFECTS OF AMENDMENTS AND IRRIGATION WATER COMPOSITION ON SALT LEACHING FROM DIFFERENT TEXTURED SOILS AND AMELIORATION OF SALINE- SODIC SOILS FOR CROP PRODUCTION

Abstract

Soil degradation caused by salinization and/or sodification is of great concern in modern world because it reduces potential of agricultural lands. It usually leads to deteriorate soil properties like structure, water retention, porosity, electrical conductivity, sodium adsorption ratio and soil flora and fauna. Mostly saline-sodic and/or sodic soils have poor internal drainage which otherwise is pre-requisite for their reclamation. The present studies were conducted to evaluate differential response of soil texture for leaching of salts under different treatments. Three experiments were conducted in the wire house to evaluate the leaching response of different textured (loamy sand, silty clay loam and sandy clay loam) soils. In Study1, different pore volumes of water were added to evaluate the leaching response of different textured soils. The highest amount of salts was removed from SCL soil (1943 kg ha-1) with leaching fraction (LF) 0.59 with the application of four PV water. The decreasing order of treatment effectiveness for salt removal was T3 > T2 > T4 > T1 with LF 0.69, 0.64, 0.61 and 0.60, respectively. The ECe of 0-25 cm columns (post-experiment) decreased from 8.2 to < 4 dS m-1 in LS with 2.0 PV (1.88 cm), from 33.9 to < 4 dS m-1 in SCL with 2.5 PV (2.67 cm) of applied water and SiCL with 2.5 PV (2.72 cm) of water, it decreased from 23.9 to < 4 dS m-1 only of 0- 10 cm of soil layer. Regarding SAR, 2.5 PV of applied water decreased SAR to < 13 in LS up to 0-20 cm depth, 0-10 cm soil depth of SiCL and 0-15 cm soil depth of SCL. It was found that leaching of soluble slats does occur with simple addition of water of any quality in different textured saline-sodic soils but could convert these into sodic soils if external source of Ca2+ is not added. In study 2, irrigation water of different EC : SAR ratios was used after amending different textured soils with gypsum @ 100% soil gypsum requirement (SGR), farm manure (FM) @ 10 Mg ha-1 and mulch @ 10 Mg ha-1. It was observed that amendments significantly decreased pHs, ECe and SAR of all the three soils using different EC: SAR ratio waters. With four PV of applied water, LF of 0.75, 0.77 and 0.78 was attained that removed 3008, 4965 and 5048 kg ha-1 salts in LS, SiCL and SCL soils, respectively. For the 1st, 2nd, 3rd and 4th irrigations with LF of 0.82, 0.79, 0.75 and 0.71 removed 5682, 5000, 3967 and 2941 kg ha-1 salts, respectively. For amendments, the decreasing order for salt removal was FM > G > M > C with LF= 0.85, 1 0.84, 0.71 and 0.68. The use of amendments in all the three soils decreased the pHs, ECe and SAR of soils that depended upon with different EC to SAR ratio of irrigation waters. Overall, decreasing order of effectiveness of amendments for soil amelioration was FM > G > M > C. In Study 3, pot experiment was conducted following sorghum-oat and rice-wheat crop rotations with same amendments as for Study 2. Three different waters (EC 0.6 + SAR 6, EC 1.0 + SAR 12 and EC 2.0 + SAR 18) were used for irrigation. The results showed that as the brackishness of water increases more salts leached. Water of different EC : SAR ratios (EC 0.6 + SAR 6, EC 1.0 + SAR12 and EC 2.0 + SAR 18) were applied. From results, it may be inferred that 1 PV of brackish water with higher EC: SAR (EC 2 and SAR 18) ratio could be used beneficially, if proper amendments are selected. For rice crop, the order of effective amendments was in the decreasing order of G > FM > M > C. With sorghum, the order was FM > G > M > C. For wheat, the order was FM > G > M > C, and for oat it was G > FM > M > C. Leaching effectiveness decreased with increasing irrigation water salinity without accumulation of salts in soils. It depicts that for initial reclamation of salt-affected soils, low quality irrigation waters could be useful and sometimes even better with amendments than canal water alone owing to favorable effect of electrolytes in former water on soil infiltration and hydraulic conductance. In the present studies, salt removal from soils was the lowest when LF was 0.20 and was the highest when LF was 0.32, i.e. direct positive relationship. The Study 4 was conducted under field conditions following rice-wheat crop rotation using saline-sodic water (SSW), canal water (CW) and their combination. The amendments applied in sub-plots were control, gypsum at 100% SGR, FM at10 t ha-1 and mulch at10 t ha-1. The soil reclamation with respect to pHs, ECe and SAR remained considerably better with the application of gypsum and FM. Overall, the results indicate that amendments like gypsum, FM and mulching could favor the desodication of saline- sodic soils. The soil reclamation with respect to pHs, ECe and SAR remained considerably better with the application of gypsum and FM with all the irrigation waters. It is concluded that cyclic use of SSW and CW could be better for initial reclamation of SiCL soil by following rice-wheat crop rotation. The salt leaching efficiency decreased over time, being highest after rice crop that decreased with time. Gypsum and FM 2 application significantly increased crop yields even with SSW irrigation. Net benefit from rice-wheat rotation was the highest with FM receiving SSW−CW followed by gypsum. Hence gypsum and FM amendments are essential for growing crops during soil reclamation, even if poor quality water is used for irrigation. Since salinity/sodicity has to persist in irrigated agriculture, under arid land conditions, a strong follow up program in such mega development projects must be ensured to harvest maximum and sustainable benefits from such activity.