Effects of different manure application rates on soil properties, nutrient use, and crop yield during dryland maize farming

The combined application of manure and chemical fertiliser has major effects on soil physico-chemical and biological properties, and it increases crop yields. A 4-year study was conducted to study the effects of the application of high (HM 22 500 kg/ha), medium (MM 15 000 kg/ha), and low (LM 7500 kg/ha) rates of manure in combination with conventional chemical fertiliser. We evaluated the effects on soil properties, nutrient use, and crop yield in a continuous-cropping maize system. We also compared the three manure treatments with chemical fertiliser-only (CF-only) and no fertiliser (NF) treatments during 2007-2010 in semi-arid conditions. Compared with CF-only and NF, manure combined with chemical fertiliser produced a lower soil bulk density and significantly increased the >0.25-mm water-stable aggregate content, which was higher with increasing manure application rates. The duration of increased soil enzyme activity after manure application depended on the manure application rate; HM produced a significantly higher increase in soil enzyme activity than CF-only and NF during 2007-2010. Manure combined with chemical fertiliser significantly increased crop yield and nitrogen (N) content of the crop organs, showing that this treatment enhanced the use of N fertiliser. Soil properties may be conserved by the MM treatment, which improved soil properties while increasing crop yield, because there was no significant difference in the residual level of N with the MM and CF-only treatments. Therefore, the MM treatment may be an appropriate soil fertiliser treatment for dryland maize farming.