Effect of Organic Manures on Soil Aggregate Stability and Aggregate-Associated Organic Carbon under Long-term Experiments in Subtropical India

Abstract

Inorganic fertilizers, biofertilizers and farm yard manure (FYM) application can tailor the aggregate distribution as well as aggregate associated organic carbon. We evaluated the effect of dissimilar treatments on soil aggregate stability and soil organic carbon (SOC) distribution within soil aggregates in surface (0-15 cm) and subsurface (15-30 cm) soils in a long-term fertility experiment of a rice-mustard-sesame cropping system in India. The experiment was laid out in a randomized complete block design with four treatment combinations including no NPK fertilizers or organic amendments was set as a control or T1, fertilizer nutrients (NPK) as T2, NPK with biofertilizers (Azospirillum and Phosphobacteria) as T3, and biofertilizers (Azospirillum   and Phosphobacteria) with farm yard manure (FYM) as T4. The lowest and highest aggregate stability was in the T1 and T4 in both surface and subsurface soil depths respectively. This is due to soil disturbance from prolonged history of tillage (22 years) mainly, puddling is practiced in rice cultivation. In both surface and subsurface soils, T4 had a higher proportion of water-stable macroaggregates (> 0.25 mm) than the control and the soil receiving inorganic fertilizer alone, which were rich in water-stable microaggregates (< 0.25 mm). Mean weight diameter (MWD), varied from 0.63 to 0.94 mm in 0–15 cm and from 0.66 to 1.01 mm in 15–30 cm soil layer. At 0–15 cm depth, biofertilizer and FYM raised GMD in the order T4 > T3 by 56.33% and 35.21% over control and by 38.75% and 20% over T2, respectively. Regardless of the treatments and depths studied, aggregate related organic carbon is highest in the 0.1-0.05 mm sieve size and lowest in the 5 to 2 mm sieve size. Hence it may be concluded that cultivation without organic amendments and biofertilizers results in more microaggregates (malignant to soil tilth) that could be checked by the application of organic amendments such as FYM and biofertilizers such as Azospirillum and Phosphobacteria, which increased the proportion of water-stable macro-aggregates by consolidating micro-aggregates into macroaggregates.