Long-term effects of fertilizer on soil enzymatic activity of wheat field soil in Loess Plateau, China.

The effects of long-term (29 years) fertilization on local agro-ecosystems in the Loess Plateau of northwest China, containing a single or combinations of inorganic (Nitrogen, N; Phosphate, P) and organic (Mature, M Straw, S) fertilizer, including N, NP, SNP, M, MNP, and a control. The soil enzymes, including dehydrogenase, urease, alkaline phosphatase, invertase and glomalin, were investigated in three physiological stages (Jointing, Dough, and Maturity) of wheat growth at three depths of the soil profile (0-15, 16-30, 31-45 cm). We found that the application of farmyard manure and straw produced the highest values of soil enzymatic activity, especially a balanced applied treatment of MNP. Enzymatic activity was lowest in the control. Values were generally highest at dough, followed by the jointing and maturity stages, and declined with soil profile depth. The activities of the enzymes investigated here are significantly correlated with each other and are correlated with soil nutrients, in particular with soil organic carbon. Our results suggest that a balanced application of fertilizer nutrients and organic manure (especially those containing P) has positive effects on multiple soil chemical parameters, which in turn enhances enzyme activity. We emphasize the role of organic manure in maintaining soil organic matter and promoting biological activity, as its application can result in a substantial increase in agricultural production and can be sustainable for many years.