Long-term effect of chemical fertilizer, straw, and manure on soil chemical and biological properties in northwest China

A field experiment was conducted to investigate the effect of long-term (30-year) fertilizer and organic manure treatments on grain yield, soil chemical properties and some microbiological properties of arable soils in Pingliang, Gansu, China. Six treatments were chosen for this work: unfertilized control (CK), nitrogen fertilizer annually (N), nitrogen and phosphorus (P) fertilizers annually (NP), straw plus N added annually and P fertilizer added every second year (NP + S), farmyard manure added annually (FYM), and farmyard manure plus N and P fertilizers added annually (NP + FYM). Mean winter wheat yields for the 20 years ranged from 1.60 Mg ha(-1) for the CK treatment to 4.62 Mg ha(-1) for the NP+FYM treatment. Maize yields for the 8 years averaged 3.40 and 7.66 Mg ha(-1) in the same treatments. The results showed that there was no interaction between farmyard manure and NP fertilizers. Compared with the CK treatment, the average soil organic carbon (SOC) and total nitrogen (TN) content were 2.0 and 3.1%, 1.9 and 13.3%, 32.7 and 24.5%, 23.0 and 19.4%, and 39.9 and 27.6% larger, respectively, for N, NP, FYM, NP + S and NP + FYM. The N only resulted in not only lowering of pH but also deficient of both P and K in the soil. Soil available K declined rapidly without straw or manure additions. The microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents increased with the application of nitrogen and phosphorus inorganic fertilizers. However, there was greater increase of these parameters when organic manure was applied along with inorganic fertilizers. Organic manure application also increased soil dehydrogenase, alkaline phosphatases, beta-glucosidasen and urease activity significantly. The results indicated that long-term additions of organic manure have the most beneficial effects on grain yield and soil quality among the investigated types of fertilization. (C) 2010 Elsevier B.V. All rights reserved.