Factors affecting soil quality changes in the North China Plain: A case study of Quzhou County

At the end of the 1970s there were 3,300,000 ha of salt-affected land in the North China Plain. After the successful removal of the salt in the 1980s, the land has gradually been used for increasing intensive forms of agriculture. The Household Responsibility System (HRS) was adopted in Chinese rural areas at the time of the economic reform of the early 1980s. Farm households became the basic decision-making units that could directly control soil quality. This paper describes the change in soil fertility after 20 years of intensive agriculture and the driving factors of soil fertility change. Quzhou County was selected as it is representative for the North China Plain. The soil fertility status and nutrient flows of the salt-affected land for 1980–1981 and 1999 in Quzhou County were evaluated. Over 20 years, the total nitrogen (N), the extractable phosphorus (P) and the soil organic matter (SOM) in salt-affected land increased by 127%, 601% and 51% respectively; but exchangeable potassium decreased by 31%. The N, P, K and SOM balance in 1980–1981 was −15, −2, −29 and −24 kg ha⁻¹ y⁻¹, but in 1999 the N and P balance had changed to 24 kg ha⁻¹ y⁻¹ and 25 kg ha⁻¹ y⁻¹ as a result of the widespread use of N and P fertilizer. With the rapid increase in crop production and the sparse use of K fertilizer, the K balance continues to be negative. Straw production increased along with crop yields and there was a development of stock breeding. Together with better straw restitution practices, the SOM balance increased to a positive 613 kg ha⁻¹ y⁻¹. The analysis of farm household land-use and inputs indicated that there were significant differences in behaviour between almost totally off-farm households and other household types. These differences were in the choice of land-use type, the use of fertilizers and crop residue management. However, there was no significant relationship between socio-economic factors and fertilizer inputs. Current nutrient management is not optimal. Therefore, it is important to establish a better system for bottom-up knowledge collection and transfer of scientific information to farmers.