Impact of sand burial on maize(Zea mays L.)productivity and soil quality in Horqin sandy cropland,Inner Mongolia,China

Croplands are often suffering from sand burial in dry regions of northern China. For studying this phenomenon, we carried out a case study of field experiment including four sand burial levels, i.e. shallow （1-3 cm）, moderate （8-12 cm） and deep （15-20 cm） sand burials, and no sand burial （control, CK）, in a typical agro-pastoral transitional zone in Naiman Banner of eastern Inner Mongolia. The aim of this study was to assess the impacts of sand burial on maize （Zea rnays L.） productivity and the soil quality along a gradient of burial depths. Results showed that there was a strong negative effect of sand burial on maize productivity and soil quality, which significantly declined （P〈0.05） under moderate and deep sand burial treatments. In comparison with the CK, the maize yield and above-ground biomass reduced by 47.41% and 39.47%, respectively. The soil silt and clay, soil water, soil organic carbon and total nitrogen contents under deep sand burial decreased by 67.85%, 40.32%, 86.52% and 82.11%, respectively, while microbial biomass carbon, microbial abundance and enzyme activity decreased by 89.78%, 42.28%-79.66% and 69.51%-97.71%, respectively. There was no significant effect on crop productivity and soil quality with shallow sand burial treatment. The correlations analysis showed that there was significant positive correlations of both maize yield and above-ground biomass with soil silt and clay, soil organic carbon and total nitrogen contents, pH, electrical conductivity, soil water content, microbial abundance and biomass and all tested soil enzyme activities. Stepwise regression analysis indicated that soil water and total nitrogen contents, urease, cellobiohydrolase and peroxidase activities were key determining factors for maize productivity. This combination of factors explains reason of the decreased maize productivity with deep sand burial. We found that degradation of cropland as a result of sand burial changed soil physical-chemical properties and soil enzyme activities in the plow layer, and decreased overall maize productivity. Furthermore, decreased soil enzyme activity was a better indicator to predict sandy cropland degradation.

Effects of soil stoichiometry of the CaCO_3/available phosphorus ratio on plant density in Artemisia ordosica communities

In soil, CaCO3 can reduce the availability of phosphorus in arid and semi-arid regions, thereby influencing plant growth. However, the effects of soil stoichiometry of the CaCO3/available phosphorus ratio (CaCO3/AP ratio) on plant density are unknown. In this study, we examined 4 Artemisia ordosica communities located in arid and semi-arid regions, and performed a pot experiment with an orthogonal design to examine the relationships between the soil CaCO3/AP ratio and plant density. The results showed that the soil stoichiometry of the CaCO3/AP ratio had a greater effect on growth of A. ordosica than either CaCO3 or AP as single factor. The influence of the soil CaCO3/AP ratio on density of A. ordosica was related to the climatic zone and the types and/or amplitudes of increases in the soil CaCO3/AP ratio. When the soil CaCO3/AP ratio was within the same amplitude and was less than 2.5, the A. ordosica density increased in the semi-arid region, whereas the density decreased with increasing soil CaCO3/AP ratios in the arid region. In the semi-arid region, when the soil CaCO3/AP ratio was within the same amplitude and the increase in the soil CaCO3 content was greater than the increase in soil AP, the A. ordosica density increased with increasing soil CaCO3/AP ratios. This means that the relationship between the soil CaCO3/AP ratio and the A. ordosica density remained the same. In the arid region, an increase in the soil CaCO3/AP ratio as a result of increased soil CaCO3 content and decreased soil AP resulted in increased density of A. ordosica. Therefore, the relationship between soil CaCO3/AP ratios and density of A. ordosica was altered by these changes in soil chemistry. Thus, the soil stoichiometry of the CaCO3/AP ratio is an important factor affecting the density of A. ordosica in arid and semi-arid regions.