Effects of cattle manure compost combined with chemical fertilizer on topsoil organic matter, bulk density and earthworm activity in a wheat–maize rotation system in Eastern China

Cattle manure compost (CMC) combined with chemical fertilizer (CF) was applied to a wheat–maize rotation field, in Eastern China, to assess soil physical and chemical properties, biological activity and land productivity. Indicators of organic matter, carbon storage and sequestration, bulk density, water content, total N content and earthworm population from topsoil (0–20 cm) were quantified. This consecutive study (2009–2014) was carried out on the base of the same total N, P, K application rate (375.0 kg N ha−1 yr−1, 92.4 kg P2O5 ha−1 yr−1 and 316.3 kg K2O ha−1 yr−1) in each treatment that was fertilized. Six treatments were designed as: (1) CK, without any fertilizer; (2) NPK, 100% CF; (3) NPKM1, 25% CMC combined with 75% CF; (4) NPKM2, 50% CMC combined with 50% CF; (5) NPKM3, 75% CMC combined with 25% CF; and (6) CM, 100% CMC. The results demonstrated that organic matter, water content, total N content and earthworm density from topsoil were significantly and positively (P ≤ 0.01) related to CMC input, with significantly negative correlation being observed between soil bulk density and CMC input. The average annual yield of the wheat–maize rotation system significantly increased (P ≤ 0.05) in NPK, NPKM1, NPKM2, NPKM3, and CM compared with CK, with the highest yield being obtained from NPKM1. Applying merely CF not only led to the lower SOM, water content and total N content, but also resulted in negative effects on earthworm activity, while CMC alleviated such negative effects. Our finding may help to increase food supply by improving soil conditions with organic fertilizer compost application.