Objectives Soil nutrient contents are important indices of soil fertility, it is useful to reflect change trends of soil nutrients via monitoring amounts of farmland fertilizers and soil nutrients regularly. Based on a 10-year long-term monitoring experiment of different fertilization in the gully area of the Loess Plateau, the changes of soil nutrients and crop yields were investigated and the relationships among them were analyzed.

Methods All the treatments in monitoring areas were under the field management measures. There were four treatment areas, no fertilizer (CK), chemical fertilizer (HF), combined application of chemical fertilizer and organic fertilizer (HM) and local farmland (NM). All the fertilizers were basal applied before sowing of crops. Soil samples (0-20 cm) were collected in the middle June or September, and the crops yield and the NPK contents of aboveground plants were calculated at the harvest.

Results After 10 years’ experiment, the contents of soil organic matter were decreased by 1.73 g/kg in CK, increased by 1.97 g/kg in HF, 2.20 g/kg in HM and 1.44 g/kg in NM, respectively. The soil total N contents were decreased by 0.08 g/kg in CK, and increased by 0.05-0.13 g/kg in the treatments with fertilization. The soil available N contents were increased in HF, but decreased in all the other treatments. The soil available P contents were increased obviously by 11.86 mg/kg in HM. The soil available K contents were decreased by 38 mg/kg in CK but increased significantly by 27.5 mg/kg in NM. All the fertilization treatments could increase the wheat yields significantly compared to CK, and there were no significant differences among the fertilization areas. Nutrient balance analysis showed that the combined application of chemical and organic fertilizer had N, P and K surplus, the chemical fertilizer would cause the deficiency of K, and all the nutrients would be in deficit without the fertilization.

Conclusions The precipitation, thermal condition and fertilization levels influence the wheat yield significantly. The contents of soil nutrients in the tillage layer(0-20 cm)are changed significantly after 10 years’ fertilization. The initial soil nutrient contents of CK were the highest, however, they became the lowest after 10 years, which proved the extremely importance of fertilization to keep soil fertility. The fertilization can increase the contents of soil nutrients include organic matter, total N, available P and available K, the soil available N is reduced in all the treatments except the chemical fertilization. The waste of fertilizer exists in local farmlands. It is suggested for local farmers to reduce the amount of fertilizer appropriately.