Soil nutrient contents and stoichiometry as affected by land-use in an agro-pastoral region of northwest China

Stoichiometry is an important indicator of the elemental balance in ecological interaction and process. However, the effect of land-use on stoichiometry of soil nutrient along soil profile remains uncertain. In this study, soil samples (0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm and 80–100 cm) were collected from six different land-uses including maize field (MZ), wheat field (WT), paddy field (PD), apple orchard (OC), grassland (GL) and wetland (WL) in a traditional agro-pastoral region of the Ili River Valley, northwest China, to evaluate the influences of land-use on contents and stoichiometry of soil carbon (C), nitrogen (N), phosphorus (P) and potassium (K) along a 100 cm soil profile. The results showed that natural land (GL and WL) had significantly higher soil organic C (SOC), soil total nitrogen (STN) and soil available N (SAN) contents than those of croplands (MZ, WT, PD and OC) in all soil layers. However, differences in soil P and K contents between the two land-uses were not significant in most soil layers. Such characteristics of soil nutrient contents led to significant differences in soil C: P (RCP), C: K (RCK), N: P (RNP) and N: K (RNK), while no significant differences in soil C: N (RCN) and P: K (RPK) between cropland and natural land, indicating that nutrient stoichiometry of deep soils can be also affected by land-use. In the 0–20 cm soil layer, soil RCN of different land-uses, as well as their average in our study were similar to those on Chinese and global scales. However, since our study area has relatively lower SOC and STN contents while higher STP contents than the global averages, the average soil RCP, RNP and C: N: P (RCNP) of our study were lower than the those on the global scale. Therefore, we suggest that more nutrient inputs, such as manure and crop residues should be applied to the croplands of the Ili River Valley to improve the levels of soil C and N.