Study On Soil Moisture Ecology Of Compound Patterns Of Eucaiyptus Grandis+herbages At Its Initial Stage

Soil moisture, one of the most active and influential factors in forest ecosystem, isnecessary and important for the growth of trees and for the soil development. Transfer ofsoil moisture is not negligible to maintain the environment and agroforestry production.Soil moisture is an important and restrictive factor for the vegetation distribution at theecosystem level and limits the plant photosynthesis efficiency and absorption of soilnutrition at the species level, affecting the biomass of ecosystem. Therefore, the study ofsoil moisture plays an important role in vegetation restoration. Three patterns, E.grandis+Hemarthria compressa (shortening patternⅠ), E.grandis+Dactylis glomerata (patternⅡ),E.grandis+Trifolium repens (patternⅢ), five stand densities,2 222 trunk·hm^-2 (1.5m×3.0m),1667 trunk·hm^-2 (1.5m×4.0m),1333 trunk·hm^-2(1.5m×5.0m),1111trunk·hm^-2(1.5m×6.0m),833 trunk·hm^-2(1.5m×8.0m),shortening row 3m/4m/5m/6m/8m respectively, were set.Characters of soil moisture distribution and influencingfactors were studied at the initial stage of different stand densities of E. grandis +grasscompound patterns. The main results are as follows:1) At the same period, soil moisture content among three patterns existed difference.The soil moisture content of patternⅢwas lower than the other two patterns from Marchto May, then the order of soil moisture was chaotic in June, and the order presentedpatternⅠ＞patternⅢ＞patternⅡin July. There was more obvious differentiation amongfive densities in August.The order presented patternⅢ＞patternⅡ＞patternⅠunder highand medium densities (row 3m/4m/5m) and presented patternⅠ＞patternⅢ＞patternⅡunder the low density (row 6m/8m). Overall, soil moisture content and rainfallpresented consistent, and the average minimum soil moisture content was in May and thehighest soil moisture content was in July. During the drought season, soil moisture of the upper content existed obvious variation one day, with a significant declining trend frommorning to afternoon.2) The soil moisture content was affected by vegetation and character of ecosystem,showing evident canopy effect. The content under canopy was lower than that outsidecanopy of the same density of the three patterns from March to May. The canopy effectwas not evident from June to August, and the content was affected by rainfall more.3) PatternⅠ, soil moisture effects was not only on the soil surface(0-15cm) but also onthe underlayer(15-30cm).The so-called "dry soil layer" phenomenon were found.Differences between the upper and underlayer of the soil moisture content were relatedwith the distance from the trunk, which under canopy were greater than that outsidecanopy. PatternⅡ, soil moisture content of underlayer was higher than the upper lay. Thedifference of soil moisture content between the upper and underlayer outside canopywere more obvious than that surrounding tree trunks.4) Rainfall was redistributed through forest+grass system. The interception was relatedto state of vegetation and rainfall characteristics. E.grandis performanced a majorposition of the rainfall interception, and interception of grass lay was almost negligible.5) Soil bulk density of upper layof three patterns were lower than that of underlayer,the one of under canopy lower than that outside. The lowest soil bulk density were inAugust.The difference between the upper lay and underlayer were significant (P＜0.05).Difference among the three patterns was significant in May(P＜0.05) and there were nosignificant difference during other phases. Difference among five stand densities of thesame pattern was not significant. The total soil porosity of patternⅠwas the lowest andthe capillary pore of patternⅢwas the best, and the non-capillary pore of patternⅡwasbetter than the other two patterns in November.The soil organic matter and hydrolablenitrogen, available P, K of three patterns the upper soil was higher than that of underlayer.Throughout a season, the content of soil organic matter increased in different degree,while the three available nutrients showed decline. 6) Significant difference of herbages biomass among three patterns were existed(P＜0.05). Herbage biomass as follows: patternⅠ＞patternⅢ＞patternⅡ. The herbagebiomass was contacted with the forest density in patternⅠand patternⅢ, showingbiomass increase with densities reducing. While the highest herbage biomass of patternⅡwas row 5 m. The order of diameter growth of E. grandis was from May to August, fromMarch to May and from August to November. The best growth of height was from Mayto August. Aboveall, patternⅠwas regarded as the most suitable for the area and row 5m(1.5m×5.0m) was the most suitable density.7) There were significant difference between E. grandis forest land and other lands inreducing runoff and soil erosion, preventing soil nutrient loss. Based on the observationon runoff plots, the properties of runoff and sediment and nutrient loss on the differentplots(bare land, farmland, wide grassland, E.grandis forestlandⅠ(with disturbs) and E.grandis forestlandⅡ(without disturbs) were observed from June to November in2006.(1) The runoff depth and sediment yield had remarkable difference among thepatterns (P＜0.05).The order of runoff depth and sediment yield loss were bare land(250.9mm)＞farmland(232.9 mm)＞wide grassland(175.4 mm)＞E.grandisforesttandⅠ(170.5 mm)＞E.grandis forestlandⅡ(141.3 mm) and farmland(313.63kg·km^-2)＞bare land(176.80 kg·km^-2)＞wide grassland(94.45 kg·km^-2)＞forestlandⅠ(90.58 kg·km^-2)＞E. grandis forestlandⅡ(36.37 kg·km^-2) respectively. (2)The nutrientloss yields had remarkable difference among the patterns(P＜0.05). The order of nutrienttoss was K＞P＞N. 96.16% of total phosphorus (P) and 69.45% total Nitrogen (N) weredissolved in runoff, while 74.93% Potassium (K) was transported as particulate form byrunoff. (3) Different slops were affected by every factor in different degree. Bare landand farmland were affected more by rainfall, while wide grassland and E. grandisforestland were affected more by human activities.(4) It was significant to soil and waterconservation of slope land through adjusting farming and improving management andreducing disturbs of human.