Effects of long-term manure application on black soil fertility and maize yield

China is rich in manure resource,and farmers are used to applying manures to cultivate the soil in history.A field experiment was established in 2003 in the black soil region of northeast China,in order to investigate the effects of manure application on maize yield and soil fertility.No fertilizer (CK),chemical fertilizer (NPK) and manure (M) were included in this experiment with four replicates and randomized block design.The manure rate of 22 500 kg·hm^-2 was applied in M treatment annually.Maize yield under CK treatment was significantly lower than NPK and M treatments during experimental years (P<0.05).Maize yield of NPK treatment was 10.7%-29.4% higher than M treatment from 2003 to 2015 (P<0.05),and was the same as M treatment after 13 experimental years.Long-term manure application has the potential in replacing chemical fertilizer for black soil fertility.Compared with initial soil,soil organic carbon (SOC),total nitrogen (TN),total phosphorus (TP),available nitrogen (AN),available phosphorus (AP) and available potassium (AK) contents were significantly increased by 48.8%-315% and 12.4%-147% under M treatment for 0-20 cm and 20-40 cm soil layers,respectively.NPK treatment significantly increased AP content.The contents of SOC,TN and AN under CK treatment were significantly decreased by 13.8%-24.0% and 17.0%-27.0% for 0-20 cm and 20-40 cm soil layers,respectively.Meanwhile,M treatment significantly decreased soil bulk density within 0-20 cm and 20-40 cm soil layers and significantly increased aeration porosity within 0-20 cm soil layer.Long-term manure application increases soil fertility and improves soil structure within 0-40 cm soil layer,which are the main reason for the enhancement and stability of crop yield by manure replacing chemical fertilizer.