Study On The Characteristics Of Fine Root Distribution And Growth Of E. Grandis·herbs Compound Mode Under Different Density

Forest-grass compound model was attached more importance along with theactualization of engineering measure of converting cropland to forest. Forest-grasscompound model can effectively solve ecological benefits, economic benefits and societalbenefits. It could make the best use of the space of woodland, improve the productivity,promote growth of forest and increase farmers' economic income.At the hilly and upland farmlands areas in west Sichuan province, forest-grasscompound model is suitable for slope farmlands of converting cropland to forests. Becauseof different biological and ecological characteristic of grass, the effect of compound modelis different. According to the nature condition of an area, it is one of the key techniques tochoose reasonable kinds of grass for forest-grass compound model. The research beforeshowed that choosing appropriate grass, adopting reasonable cultivating technical,studying the nutrient regulation, and making sure of growth time limited of grass andsuitable planting density have important instructional meaning for choosing more stableand optimal forest-grass compound model. Fine root played significant role in improvingphysical and chemical property of soil. On the one hand, fine root constantly absorbednutrient and water from soil to satisfy growth of plant. On the other hand, fine rootdisplayed important effect on improving of edaphic structure, fertility and productivity bymaterial cycle and energy flow.Three models, E. grandis+Hemarthria compressa (modeⅠ), E. grandis+Dactylisglomerata (modeⅡ), E. grandis+Trifolium repens (modeⅢ) were studied at the base ofpractice teaching of Sichuan Agricultural University in Ya'an. The growth ofE. grandisplantation, yield and height of three forages, biomass of fine root in different diameter andgrass root were measured. At the same time, the Pearson correlations to planting densitieswith each growth factor were analyzed. The results indicated that:(1)In the experimental region, the growth of tree height and the ratio of height to DBHwent up with the increase of 3-year-old E. grandis. The mean DBH had negativerelationship with planting density. The stand volume growth was greatly affected byplanting density, it had a positive relationship with planting density, and the coefficientwas 0.986. High density spacing of E. grandis in early stage of plantation established integratestand. The optimum planting density orE. grandis should be controlled between 1333～1667 individual per hectare for pulp wood or pole production plantation, while 883～1111individual per hectare for cultivating timber of large or middle diameter.(2)The dynamic of average height and yield of three forages under different densitieswere different. The average height of gramineous forages went up with the decrease ofdensity, while Tr. repens declined. The dynamic yield of gramineous forages were similar,namely, it went up with the decrease of density, while Tr. repens had no obvious trendwith density. The monthly dynamic yield of three forages had each character. H.compressa and D. glomerata had three peaks, and Tr. repens had one peak.(3) The monthly changes of live and dead fine root biomass in the diameter of 0～1 mm under different densities of different modes had different trends. The live fine rootbiomass of upper layer showed double-peak trend, with peak in May and September, whilelive fine root of down layer and dead fine root in both layers showed single-peak trend,with peak in July and October respectively. The fine root biomass in the diameter of 0～1 mm in different modes increased with the decrease of planting densities. The annualaccumulation of fine root biomass in the diameter of 0～1mm under different densities ofdifferent modes showed that modeⅠ(0.1123 t·hm^-2)＞modeⅡ(0.0978 t·hm^-2)＞modeⅢ(0.0961 t·hm^-2). From the vertical distribution and monthly changes of live and dead fineroot biomass in the diameter of 1～2mm under different densities of different modes, theupper and down layer of live fine root showed single-peak trend, with peak in growingmidseason, while the annual trend of dead fine root biomass in both layers wasinconspicuous. The increase of fine root biomass in the diameter of 1～2mm in differentmodes accompanied with the decrease of planting densities. The annual accumulation offine root biomass in the diameter of 1～2mm under different densities of different modesshowed that modeⅠ(0.1274t·hm^-2)＞modeⅡ(0.1185 t·hm^-2)＞modeⅢ(0.1041 t·hm^-2).The vertical distribution of live and dead fine root and total fine root biomass in thedifferent diameter of different modes displayed a "T" distribution that was higher in theupper layer, but lower in down layer. The fine root biomass of upper layer occupied morethan 60％of total fine root biomass. The monthly changes of grass root biomass of different modes had different trends.The upper and down layer of modeⅠandⅡ, down layer of modeⅢshowed treble-peaktrend in the period of research, while the upper layer of modeⅢshowed single-peak trend.The vertical distribution of grass root biomass of different modes was upper layer＞downlayer.(4) The root biomass of forest-grass compound model increased with decrease ofdensities. The root biomass in single pasture planting mode was less than that in otherexperimental regions of compound planting mode. The total root biomass and grassbiomass of three compound planting modes increased with the decrease of plantingdensities. The Pearson correlations to planting densities with fine root and grass root wereanalyzed in different modes. The result showed that the coefficient between plantingdensities with fine root and grass root of modeⅠandⅡwere very high. Namely, plantingdensities had higher influence on the root biomass accumulation of modeⅠandⅡ.(5)Based on the comprehensive analysis the effects of the planting density on rootbiomass, grass biomass and yield of forages under 3-year-old E. grandis plantation, theoptimum planting density of Eucalyptus grandis should be controlled between 883～1111individual per hectare at initial stage. It was feasible to plant H. compressa, D. glomeraand Tr. repens under E. grandis plantation, three forages could keep certain growth all theyear. Compared to other forages, H. compressa was the optimum forage for E. grandis+grass mode. Therefore, E. grandis+H, compressa mode could be a comparatively suitablepopularization mode in the converting cropland to forest engineering at hilly region in thewest of Sichuan.