Associations Between Soil Physical Properties And Soil Fertilities, And The Response To Afforestation Practices In The Typical Reclamation Area Of NE China

Long-term unreasonable development have caused soil fertility decline in northeast China, with serious soil physical property deterioration, but few studies focus on the importance of soil physical properties and the possibility of afforestation recovery here. Therefore, we collected the soil samples of northeast China as research materials, and measured soil physical parameters (soil porosity, specific gravity, bulk density, specific surface area, water content, the biggest hygroscopic water) and other parameters (pH, electrical conductivity (EC), soil organic carbon (SOC), total and alkali-hydrolyzable N (TN, AN), total and available K and P (TK, AK, TP, AP), easily extracted glomalin-related soil protein (EEG) and total extracted glomalin-related soil protein (TG)). We not only studied the correlations between soil physical properties and fertility parameters, but the influence of afforestation (farmland and poplar plantation) and tree species (coniferous and broad-leaved forest) on the correlations. This study reached the following results:(1) Aspect of the correlations between soil physical properties and fertility parameters: Number of significant correlation and R2 of various correlations between 3 physical properties (soil specific surface area, bulk density, porosity) and other soil parameters showed that soil bulk density had the most significant correlation with variable soil fertility, soil physic-chemical parameters. Different physical parameters differed in their predicating ability of variable aspect of soil fertility:Soil specific surface area is capable of predicting soil water owing to the fact of strongest positive correlation between this parameters and soil water content (R2=0.24, slope=0.085); Soil bulk density was strongest correlated with SOC (R2=0.21, slope=-24.92), while soil porosity was strongest correlated with TN (R2=0.08, slope=0.02). The correlation analysis between 3 soil physical parameters and different forms of nutrients showed that soil physical parameters were generally highly correlated with total nutrients (TN, TK, TP)(R2=0.058), but had relatively weak relations with their available forms (AN, AK, AP)(R2=0.026).(2) Aspect of the influence of afforestation:Over 30-yr poplar afforestation significantly improved soil porosity (1.89%), and reduced soil bulk density (60 mg/cm3) and soil water content (0.93%) in the upper 1 m, tended to increase soil K, and decrease P, but no evident changes in soil N, TG, EEG and SOC. The soil porosity-related improvements was associated with the increases of glomalin and SOC regulating efficiency in soil physical structure, and the linear slopes, R2 values in poplar plantations was respectively 1.2-2.8 fold and 1.6-2.4 fold higher than those in farmlands. Nutrient alternations were markedly interacted with sites and soil depths. More water consumption was observed in poplar shelterbelt compared with farmlands across sites, and soil specific surface area was closely associated with soil water content. Our findings support the evaluation and management of agroforestry practices from the view of soil improvements.(3) Aspect of the influence of tree species:Compared with coniferous forest, broad-leaved forest significantly improved soil water content (21.4%), porosity (9.5%), SOC (2.2 g/kg), AN (9.5 mg/kg), TN (0.1 g/kg), AP (1.4 mg/kg), TP (0.05 g/kg), and significantly reduced soil bulk density (2.7%) in the whole soil layer of 0-60cm. In addition, the analysis of relations between soil physicochemical and fertility related indicators between coniferous and broad-leaved forest showed, the difference of blade type could significantly affect the relationships between soil water content and SOC, soil pH and soil P (TP, AP). And the change of soil water content influenced SOC in coniferous forest greater than broad-leaved, while the change of soil pH influenced soil phosphorus in broad-leaved forest greater than coniferous. And the change of soil physicochemical indicators influenced soil TN more significantly, especially the change of soil bulk density (R2=0.68). Our study will provide support for the evaluation of degradation and guidance for soil rehabilitation in northeastern China.