Changes of soil carbon and nitrogen in Shouguang intensive vegetable production fields and their impacts on soil properties

Soil quality deterioration in Shouguang vegetable fields has become more serious, which directly affects the sustainable development of vegetable production. Variations of soil carbon and nitrogen will influence soil physical, chemical and biological processes, and the objective of this research is to have a better understanding of these influences. The results of this research indicated that C/N ratio, organic matter and total nitrogen in Shouguang vegetable fields were 2.4 unit lower, 4.1 g/kg and 0.61 g/kg higher than that in the grain fields, respectively. The increased amount of soil total nitrogen was two times higher than that of organic matter. Dramatic increase in NO3--N content in protective fields was not the critical reason for the decrease in C/N ratio in vegetable fields. Carbon input in vegetable fields was 1.9 times higher than that in grain crop fields, and nitrogen input in protective fields was 9.9 and 8.5 times higher than that in wheat and grain crop fields, respectively. The ratio of input carbon and nitrogen was 4.2:1 in protective fields and 9.9:1 in grain fields, respectively. The lower ratio of carbon and nitrogen input in vegetable fields may be the important reason for the decrease in C/N ratio in those soils. The increase in soil carbon and nitrogen contents and the decrease in C/N ratio obviously induced soil acidification, stalinization and accumulation of soil nitrogen, phosphorus and potassium in vegetable fields.