2.4. Sampling
At wheat maturity, three replications of total plants in a quadrate area (2.4 m × 1 m) were selected randomly for measuring wheat grain yield in each plot. When maize was harvested, three replications of 15 consecutive plants in the second row were selected randomly for estimating corn grain yield.
Soil samples were collected from surface layers (0–20 cm soil depth) of each plot on 7 October, 2014. Five random subsamples in the same plot were pooled together, placed in polyethylene bags, and transported to the laboratory immediately. In the laboratory, all visible roots, cattle manure and plant fragments were removed. The composite samples were passed through a 2-mm sieve. The sample was air-dried and ground to pass a 0.25-mm sieve for total organic carbon and total nitrogen analysis.
Earthworm population was quantified on 13 June and 9 October, 2014 with three replications being done. Earthworms were hand-sorted from three soil cubes (30 cm × 30 cm × 20 cm depth) at each plot then the density and fresh biomass of earthworms were recorded.