Changes in soil carbon, nitrogen, and phosphorus contents, storages, and stoichiometry during land degradation in jasmine croplands in subtropical China

Soil degradation is characterized by loss of soil organic matter, decline in fertility, imbalance in elemental content, deterioration of soil structure, and overall a deterioration of soil environment. According to the classification method of Pieri et al. (1992), the soil is classified into different degradation classes by calculating the soil structural stability index (St) of each sample point. We aimed to investigate changes in the contents, storages and stoichiometry of soil carbon (C), nitrogen (N), and phosphorus (P) together with changes in soil physical traits along a soil degradation gradient in jasmine croplands in Fuzhou area (China). The content and storage of soil C and N decreased with increasing intensity of land degradation. Soil organic C content was 15.4%, 32.3%, and 38.8% lower, respectively, in the low, medium, and high degree of degradation soils, than in the nondegraded soils. The soil C:N ratio was 18.5% higher in soils in the middle degree of degradation than in the nondegraded soils. Compared with nondegraded soils, the bulk density of the degraded soils increased and water content decreased. The decrease of soil pH coupled with salinity (conductivity) and the loss of aggregate stability are the main traits that distinguish degraded from nondegraded soils. We also detected a general N and P deficiency that is aggravated by the degradation process. Unreasonable management easily leads to degradation associated with a loss of organic C and total soil nutrients, thus impairing even more a general N and P deficiency in this area. Therefore, higher inputs of organic fertilizer should be added to alleviate the lack of organic matter, and appropriate burial should be conducted to reduce nutrient loss. Moreover, a rise of N and P fertilizer application is also advisable.