Distillery effluents effect on soil organic carbon and aggregate stability of a Vertisol in India

Distillery effluent, a waste by-product of distillery industries, is usually applied to arable land near the distilleries as irrigation water or as a soil amendment. To evaluate the effect of distillery effluent, both spent wash (SW) and post-methanated effluent (PME), on soil organic carbon and aggregate stability, a field experiment on a soybean (Glysine max L.)–wheat (Triticum aestivum L.) system was conducted for five years on a Vertisol of central India. The treatments were control (no fertilizer or manure or SW or PME, T1), 100% NPK + farmyard manure (FYM) @ 4 Mg ha−1 to soybean (T2), four graded levels of SW, viz., 2.5 cm SW to soybean and none to wheat (T3), 2.5 cm SW to soybean and 1.25 cm to wheat (T4), 5 cm SW to soybean and none to wheat (T5), 5 cm SW to soybean and 2.5 cm to wheat (T6), and four graded levels of PME, viz., 2.5 cm PME to soybean and none to wheat (T7), 2.5 cm PME to soybean and 1.25 cm to wheat (T8), 5 cm PME to soybean and none to wheat (T9), 5 cm PME to soybean and 2.5 cm to wheat (T10). The organic carbon of the surface (0–15 cm) soil that received either PME or SW (treatments T3–T10), was significantly (P < 0.05) higher than in treatments T1 and T2. The mean weight diameter (MWD) of water stable aggregates in this soil layer was also significantly higher in treatments T3–T10, compared with T1 and T2. The MWD showed a positive linear relationship with the organic carbon content of the soil (R2 = 0.54**). The proportion of macro-aggregates was higher in SW treated plots than PME, no distillery effluents and NPK + FYM treatments. However, the micro-aggregates showed the reverse trend. The macro-aggregate-associated carbon was higher in SW treated plots. It was highest in T6 and lowest in T1. The plots receiving the PME and SW showed increased soil organic carbon, MWD, percentage macro- and micro-aggregate-associated carbon than T1 and T2. Application of distillery effluents increased the aggregate stability of the Vertisol through enhanced soil organic carbon as well as the aggregate-associated carbon. So application of SW or PME could be a viable option for soil aggregate stability and enhanced productivity.