Study On Precipitation Potential Productivity Of Afforestation By Water Harvesting In Semiarid Region On Loess Plateaus

Based on the theory of soil-plant-atmosphere continuum, the observation of waterdistribution, movement and consumption in water harvesting afforestation system of semiaridregion on Loess plateaus was carried out. With analyse of relation between wood productionwith water consumption, the question as follows was discussed.●Relation between precipitation resource in semiarid region with protection forest construction.●Technology of afforestation by water harvesting with soil moisture condition.●The soil moisture circumstance in different wood density with forest physiological active.●In order soil moisture condition with wood water requirement and consumptive use.●Water Use Efficient and water Potential Productivity of Afforestation by water harvestingThe measurement was conducted in May of 1998 and terminated in October of 1999. Main experiment was established in the station of 'Runoff Forestry'of BFU. The testing material are as follows:●Black Locust (Robinia pseudoacacia L.) of 13-14 years old with different density.●Black Locust at the age of 6-7 by different water harvesting treatment.●Apple (Malus pumila) of 8-9 years old by system water harvesting. The main apparatuses used in study include as follows.●SJ1 Siphon recording pluviometer and standard udometer, evaporating dish of Φ20cm, ГГИ-500 soil evaporator.●LNW-50A Neutron soil-moisture system, DIK-3130 tensimeter and KADEC-U2 recording edaphicl-thermometer.●LI-3000A leaf area meter, Li-1600 portable steady porometer and LI-6200 portablephotosynthesis system.. Main research results ●In research region, the precipitation distribution of each season is fasten on midsummer, is lacking in spring and early summer. This is key obstacle for spring afforestaton. The rate of annual precipitation change, 28% is main reason of insecure stand structure. Precipitation resource and annual precipitation change are key factor influenced wood growth all the same. In the case of canopy wood, each water harvesting treatment can not do very well as them do for small intensity rain in early time of afforestation. At spring ,water harvesting is low. Runoff on each hillslope are 50% to 70% of total form July to August. The effect of each water harvesting treatment are mostly relied on intensity rain process of rain season. ●Although same as normal year, precipitation of 1998 in growth season be, the mean soil moisture in Ripe Locust forest was drop down 3% to 4% at large, especially in spring, comparing with it to be in early time of afforestation. But the trouble of edaphic arid trend was slow down in forest site with water nutrient area of 10m2 more. Using waterabsorbent, bestrow and water harvesting with 3m×3m area and more, the soil moisture in site was good enough. In one year, the soil water expense in spring season was supplied with water accumulated in last year. The only convenient path forward buffer of water supply with wood water use, is extending the water nutrient area and changing density of wood, however. ●High efficiency technique for controlling soil evaporation is an important method for improving soil capacity of keeping moisture. At the same time, abundant catchment area is key one for maintaining normal evaporation rate of forest. In 1998 and 1999, total evapotranspiration in all plots kept in a same level. It amounts to 350~370mm in 1998, 350~370mm in 1999, possessing 10~30mm and 20~40mm of water deficiency. Respectively, reduction in soil evaporation in planting stripes meanly amounts to 20% by grass covering and 16% by using waterabsorbent, 33% by using two method together. When the cathment slope was sprayed YJG#1 after pressing treatment, soil evaporation on slope can be decreased 8~20% in spring, 14~33% in Summer and Autumn, and 20% during the whole growth season. Dealt of spraying lichen coat can effectively relax the negative influence of bald soil. This treatment can reduce 2.7~4.0℃on top soil temperature, 11~25% of soil thermal flux and 11%~18% of soil evaporation. The bigger catchment area be, the more water harvesting quantity and the bigger the ratio between evaporation and evapotranspiration. The ratio between evaporation and.vi.evapotranspiration kept in 0.52 to~0.6 on experiment plots with the area of 8m2.●According to the relation between photosynthesis rate, carboxylation rate, water useefficiency with soil moisture, research was done as follows:In semiarid zone of Loess Plateau, the suitable soil moisture range for Locust and Applegrowth be, respectively 11%-14% and 10%-15%. Optimum soil moisture and compen-sation point of soil moisture, 13.2% with 4.55% for former and 12.4% with 4.49% forother one. 11~13% is minimum soil moisture which fits for Locust wood normal growth,11~12% is for Apple.Potential evapotranspiration during growth season in experimental area is 560~570mm.Mean plant coefficient is 0.66~1.06 for 2~13 years olds Locust, 0.5 for 4 years olds appletree and 0.84 for 8 years Apple.In the year of 80% rainfall assurance degree: Single Tree Consumptive Use amounts to57.5% of minimum wood water requirement In 13 years old Locust mature forest with thedensity of 833 stock/hm2, and 70.8% in 7 years old Locust immature forest with the densityof 1000 stock/hm2 under the lichen coat. Wood Water Requirement would be 1280, 1540,3250 and 4520kg/a, respectively for 3 , 5, 7 and 13years old Locust forest.In Apple's case, STCU of 8 years old one under pressing dealt amounts to 60%~95% ofminimum WWR. Single tree water requirement is 1070kg/a for 4 years old one and2755kg/a in age of 8.●In some extent, the growth amount of single Locust standing woody biomass increaseswith the increases of catchment area.Under present economic and technical level, the biggest productivity be displayed in themature Locust of 833 stock/hm2 with 58.8~64.1kg/stock of biomass, 5.6~6.4kg/stock ofyearly biomass increment and 56.3%~65.7% of Wood Water Use Efficiency. In catchmenttesting plots, the biggest productivity of immature wood was showed in plot of 833stock/hm2 density with biomass of 26.2~31.6t/hm2 and in lichen coat plots of 1000stock/hm2 with 25.4~32.4t/hm2. Stock increment of biomass amounted to 5.1~7.1kg,standing increment of biomass 5.1~5.9t/hm2, standing WUE with 56.1%~62.5%. Apple plotwith YJG treatment in density of 833 stock/hm2 achieved the biggest economic productivityof 16.4kg/stock and 13.7t/hm2. The bigger the distance of stock and row be, the higher theWUE.In local region, the climatic potential productivity is 6146.7kg/hm2 and the economicclimatic potential productivity of Apple is 19208.44 kg/mm.hm2.a. In 1998 and 1999, thetheoretical potential productivity by precipitation in Locust standing was 15.91 and 15.78...