Profile Distribution Of Soil Nutrients In An Aquic Brown Soil As Affected By Land Use Change

This paper studied the storage and dynamics of soil nutrients at the Shenyang Experimental Station of Ecology, Chinese Academy of Sciences (41°31′N, 123°22′E), aimed to explore the nutrients distribution in soil profile under four land use patterns over 14 years. The four land use patterns are paddy field (PF), maize field (MF), fallow field (FF) and woodland (WL). In each profile at 0～150 cm depth, soil samples were collected from the layers 0～5, 5～10, 10～20, 20～30, 30～40, 40～60, 60～80, 80～100, 100～120, and 120～150 cm. The four test farmlands and woodland are originated from aquic brown soil. Following results were obtained. The profile distribution of SOC, total N and S were differed with different land use patterns. Soil organic C and total N contents in each soil layer were higher in WL than in FF, MF and PF. At the depth of 0～20 cm, the storage of SOC and total N were higher in WL and FF than in MF and PF, but no significant difference was found for soil total S. At the depths of 0～100 cm and 0～150 cm, The sequence of SOC, total N and S storages was WL >MF> FF > PF. Soil organic C had a significant correlation with soil total N, and the correlation was slightly closer in WL and FF than in PF and MF. The C/N ratio in the profiles of PF, MF, FF and WL decreased with soil depth, and was comparatively higher in WL and lower in PF. Soil total P contents in different soil layers were WL> FF> MF> PF. At the depth of 0～20 cm, soil total P storage had no significant difference among PF, MF, PF and WL, but at the depths of 0～100 cm and 0～150 cm, it was significantly higher in WL and FF than in MF and PF. The C/P ratio was decreased with depth in WL, PF, MF and FF, but tended to be higher in layers below 40 cm in WL and MF than in FF and PF. The storage of soil exchange base cations was tended to be higher in WL than PF, MF and FF, but the difference was not significant. Generally, soil exchangeable Ca/Mg and Ca/K ratios were in the sequence of PF>MF>FF>WL, and were significantly higher in PF and MF than in FF and WL. Under the climate conditions in South Northeast Plain of China, the effects of land use on the sorts and contents of soil exchangeable base cations in the profiles were obvious over more than a decade. DTPA-extractable soil Fe, Mn, Cu and Zn were decreased with increasing soil depth, and the differentials were obvious among WL, FF, PF and MF. The differences of DTPA-extractable soil Fe under different land uses were mainly occurred in deeper layers, while DTPA-extractable soil Mn, Cu and Zn varied significantly in most layers. The DTPA-extractable soil Fe, Mn, Cu and Zn were positively correlated with SOC, total N, alkali N and total S in WL, FF, PF and MF. Cluster analysis and principal component analysis showed that soil chemical properties could be classified into three groups, of which, SOC, total N, alkali N, NO3--N, Olsen-P, and total S were clustered in group one, NH4+-N, exchangeable Ca and the sum of exchangeable base cations were in group two, and soil pH was in group three. Of the principal components affecting the profile distributions of SOC and nutrients under different land uses, plant cycling, including the accumulation and turnover of organic matter and the uptake and transport of nutrients, was considered as the leading foctor that affecting the profile distributions of C, N, S and microelements, and leaching and anthropogenic disturbance were the secondary factors that influence the profile distributions of soil exchangeable base cations and pH. The effects of land use change on the profile distributions of SOC and nutrients were obvious. Woodland had obvious advantages in improving SOC storage and maintaining soil fertility. Compared with maize field, fallow field could significantly increase SOC content in topsoil (0～20 cm), but had no significant difference in SOC storage at the depth of 0～100 cm. The results obtained could potentially provide theoretic support for understanding the effects of land use change on soil eco-environment, nutrient use efficiency, and establishment of sustainable land use models. Moreover, it could be helpful for nutrient biogeochemical cycling.