Long-Term Fertilization Effect on Fertility of Salt-Affected Soils

The long-term effects of annual fertilizer applications on the fertility of salt-affected soils under the rotation system ofwheat (Triticum aestivum L.) and maize (Zea mays L.) are not well documented. In 1984, research plots were establishedto test the effects of annual applications of different rates of nitrogen (N) and phosphorus (P) fertilizers on the fertilityof a salt-affected soil (Typic Ustochrept) at the Quzhou Experimental Station, Quzhou County, Hebei Province, China.In October 2001, composite soil samples (0-20 and 20-40 cm) were collected from each plot and analyzed for soil fertilityindices. Seventeen years of N and P fertilizer applications increased the soil organic matter (SOM) in the surface layer.With combined N, 270 (N1) and 540 (N2) kg N ha-1 year-1, and P, 67.5 (P1) and 135 (P2) kg P2O5 ha-1 year-1,fertilizer applications, total soil N mostly significantly decreased (P < 0.05). Soil total P in the 0-20 cm layer of theP2 treatment significantly (P < 0.05) increased as compared to those of the other treatments. Rapidly available P (RP)in the 0-20 cm layer of the N1P2 treatment was significantly higher than those in the other treatments except the P2treatment; and RP in the 0-20 cm layer of the P2 treatment significantly increased as compared to those of the othertreatments except the P1 and N1P2 treatments. RP in the subsurface soil layer (20-40 cm) of the P2 treatment (4.2 mg Pkg-1) was significantly (P < 0.05) higher than those in the other treatments. Nevertheless, long-term N fertilization didnot significantly increase the alkali-hydrolyzable N in the soil. However, in the salt-affected surface soils the applicationof combined N and P fertilizers over 17 years significantly (P < 0.05) decreased rapidly available potassium (K). Theresults suggested that while under long-term fertilizer applications some soil fertility parameters could be maintained orenhanced, careful monitoring of soil fertility was necessary as other nutrients such as K could become depleted.