Study On Soil Ecological Characteristics Of Shelter Forest In Silting Coastal Area

At present the mankind is facing the conflicts between of environment protection and economic development. Resource shortage crisis becomes worse and worse. So it is very important to speed up ocean resource exploitation and to develop ocean economy all over the world. The silting coastal area of China is extensive and plain, which needs to be developed and utilized imperatively. However,there are a lot of soil problems to be solved systematically and deeply.The experimental plots were located in Dongtai sea-wall ,Dongtai forest farm and Sheyang forest farm. Besides there were some other temporal experimental plots in sandy coastal plain area of Jiangsu province. The author systematically investigated and studied the depth of ground water, salt contnet, physical and chemical property, biological activity and erodibility of soil etc. According to the results, some representive physical and chemical soil factors were selected to build up predictive equation of soil loss in the coastal plain area of northern Jiangsu province.The depth of ground water was greatly influenced by topography, precipitation and forest type. The nearer the distance from river and ditch was, the deeper the ground water was. There existed close relationship between ground water depth and precipitation (the correlation coefficient 0. 9036). The ground water depth in forest land was deeper than that outside,because of loose soil and canopy trans- evaporation, especially in growing season.With drainage and biological improvement, the salt content in top soil of shelter-forest land in the silt coast area decreased, and the composition of dissoluble ions was also changed. The contents of Na⁺ and Cl^- reduced,but those of Ca²⁺ and Mg²⁺ increased. It meant that the soil had no characteristics of typical salt one. There was close relationship between soil salinity (g/ kg) and mineralization degree of ground water (g/L) (r = 0. 9940). The regression equation could be described as: y= - 0. 2868 + 0. 2985x. The older stand had lower soil salinity. The seasonal variation of soil salinity in forest was as follow: From top to bottom of soil profile, soil salinity increased gradually. In spring the soil surface had no phenomenon of salt-return. In summer the salinity of the top soil was slightly higher, and it was lower in the 10⁸0cm depth. But it increased abruptly below 80cm. In autumn soil salinity tended to decrease. The salt content in the soil of 0⁶0cm depth was much lower than that below 60cm.In spring soil water content was high. It was higher in forest than that in farmland. The older the stand age was,the higher the soil water content was. In June the water content in the soil decreased to the minimum due to intensive trans-evaporation. After that time soil water contnet increased gradually with increasing precipitation. In September, it reached the maximum. In autumn it reduced with the abrupt decrease of precipitation. The water contentof the top soiKO—10cm) in forest land was usually higher than that in the farmland. But it was lower within root distribution layer. Furthermore,the depth became larger with forest age increasing. The progressive regression equation of soil water content was: y = 48- 6709 + 0. 2061x4-t-0.1786x9 —0. 4451xl0(y—soil water content(%),x4—content of water-stable soil aggregate (%) ,x9,x]0 —precipitation (mm) and evaporation (mm) within 15 days before the measurement of soil water content).Forests can obviously improve soil property. With forest age increasing, soil bulk density reduced but porosity increased. There was more non-capillary porosity in forest land than that in beach land,especially in the top level of soil. Soil capillary porosity was slightly higher in forest land than that in coastal saline meadow soil. Soil texture was even in experimental area. The content of silt particles (0. 05⁰. 001mm) was 72.1%⁷4-1% ,and sandy particles (> 0. 05mm) only 9. 2%¹0. 5%. The content of clay particles (< 0. 001mm) increased from top to bottom of soil profile. Although the coastal soil was even, there was still some variance in different plots and levels. The shelter-forest can promote formation of soil aggregate. With forest growth,the quantity of small water-stable soil aggregate reduced,but large aggregate increased. The correlation coefficient between water-stable soil aggregate and texture and organic matter in the first level of soil(0—20cm) was higher than that in the second level. From the second level to the bottom, the correlation coefficient was becoming higher, which indicated that soil aggregate formation was mainly influenced by soil parent material because of less root in the deep soil.Except for K.the nutrient content in the top soil was highest. From top to bottom.it decreased gradually. The older stand had more intensive soil improvement capacity and higher soil nutrients. The content of available K in the top soil was much higher than that in the second layer. From the second layer to the bottom,the content gradually restored to the original value. Besides,pH value gradually reduced with salt loss. Among the physical and chemical soil properties, soil structure, non-capillary porosity, salinity, organic matter and pH value played an important roles.The activity of alkaline phosphatase in the soil was highest among the three kinds of phos-phatase. The average value was 0. 607 phenol mg/g, which took 62. 6% of total phosphatase. The correlation coefficient between alkaline phosphatase x (phenol mg/g) and total phosphatase y (phenol mg/g) was 0. 9731. The regression equation was:y= —0. 0476 + 1. 6743x. So alkaline phosphatase activity could be used to represent the total phosphatase.Enzyme activity of forest soil was higher than that of beach land. From top to bottom a-long soil profile,the activity of all kinds of enzymes reduced. Compared with farmland,the enzyme activity of forest top soil was higher,but other layers were higher or lower. In shelter-forest of silt coast,if the sampling depth of profile was 60cm, there needed at least three profiles for testing in order to meet the precision a = 0. 05. If the depth was 40cm,four profilesshould be sampled.There existed close relationship between soil enzyme activity and physical, chemical properties. The correlation coefficient of the first pair canonical variates was 0. 9443,which reached the level of great significance. In this paper the progressive regression equations of the four soil enzyme activity were also studied. There was close relationship between soil enzyme activity and micro-organism. Their correlation coefficient of the first pair canonical variates was as high as 1. 0000. Because soil enzyme activity had a close relationship with micro-organism and reflected biological activity,it could be used as the indicator to evaluate site productivity.Soil erodibility includs anti-scourability and anti-erodibility. Soil anti-erodibility of forest land was high. Mostly the soil water-stability index at the depth of 0⁵cm and 5 20cm was about 1. 00. From the third layer to the bottom,the index reduced to some extent. The anti-scourability of soil surface in most forest lands was the highest, which was very important to prevent soil erosion. Whereas the anti-scourability of deep soil was less. Soil erodibility was obviously influenced by root system. The fine roots had greater influence. There was close relationship between erodibility and root with diameter of less than 1mm. Besides,soil anti-scourability had a closer relationship with root than erodibility. Artificial disturbance had a great influence on erodibility. Cultivation can improve soil erodibility. But mechanical silt-elimination had an adverse effect.Physical and chemical soil properties had great effects on erodibility. There was significant correlation between soil texture,structure,bulk density .organic matter etc. and erodibility. Physicial and chemical soil property had a close relationship with anti-erodibility than with anti-scourability.Generally, soil permeability rate changed very much even in the same stand and in different plots. The primary permeability rate of forest land was very high,which can absorb a lot of precipitation. Whereas the stable permeability rate might be less than that of bare land.Soil permeability process of forest land followed logarithm curve. The correlation coefficient reached significant level. But the permeability rate of both bare land and mechanical silt-eliminating land was not similar. Soil permeability rate was determined by content of organic matter and non-capillary porosity in the soil. Besides it was also affected by erodibility.According to the analysis on physical and chemical soil property,erodibility and permeability, eight factors related to soil loss were selected as explanatory variates,and soil erosion modulus as response variate. The equation was established as follows;y= 7758. 00—1986. O6x2 — 60. 51x7(y — soil erosion modulus (t/km2 * a),x2 —soil scourability (cm"*),x7 — content of physical clay particles (<0. 01mm)(%)).