Effects of long-term straw returning and fertilization on soil fertility and maize yield in black soil

To investigate the effect and contribution of long-term straw returning on fertility and yield, a long-term experiment (17 years)was selected as following treatments: no fertilizer(CK), chemical fertilizer alone(NPK), and chemical fertilizer plus straw(NPKS).The results showed that the soil organic matter(SOM), total nitrogen (TN), alkaline nitrogen(AN), available phosphorus(AP)and available potassium(AK) contents was significantly decreased in 0~40 cm soil layer in CK treatment compared to those in initial soil(P < 0.05).While the SOM, TN, AN, AP and AK contents in 0~20 and 20~40 cm soil layer was significantly increased by 6.6%~16.4%, 4.6%~17.3%, 8.0%~15.0% and 59.4%~61.5% in the NPKS treatment compared to those in initial soil(P < 0.05).The soil bulk density was significantly decreased by 14.8% and 4.5% in NPKS treatment in 0~20 cm and 20~40 cm soil layers, and the aeration porosity was significantly increased by 43.7% in 0~20 cm soil layer compared to that in CK treatment.The average yield of NPK and NPKS treatments were increased by 54.9% and 65.2%, respectively, compared to CK treatment.And the average yield of NPKS treatment was increased by 6.6% compared to that in NPK treatment(P < 0.05).The SOM and TN in 0~20 cm soil layer could contribute 30% for maize yield, while the AN could contribute 35.7% in 20~40 cm soil layer.Moreover, the soil bulk density and aeration porosity in 0~20 cm soil layer was the most contributor for maize yield, the soil bulk density could contribute 56.9% for maize yield in 20~40 cm soil layer.Therefore, long-term straw returning significantly increases soil fertility and improves soil bulk density and aeration porosity in the 0~40 cm soil layer, thus indirectly affecting maize yield.