The Practice Research Of Soil Fertility Restoration And Reconstruction In Tropical Island Wasteland

Wasteland was an important reserve land resource, which had great potential for exploration, about 35 million hectares of Wasteland was suitable for farming. If making these land resource more efficiently used, it could not only expanding the amount of cultivated land, but also relieving the contradiction of cash crops and food crops. The total areal of wasteland was about 1.17 million hectares, which was important tropic soil resource in Hainan Island. According to the nature condition, it could be divided into appropriate farming, forest and grassland, costal sandy and rocky lands, which were typical wasteland in Hainan province. Because of the natural and human factors, the degradation of soil quality was the main obstacle to utilizing the land. Selecting the sandy wasteland at Shanya forest farm of Wenchang city and the rocky lands in cattle breeding factory of Haikou as research object, and the research on soil improvement by taking vegetation restoration measures and engineering measures respectively, the soil physical and chemical properties and plant growth variation characteristics were analyzed. The evaluation of soil fertility was taken under different restoration measures, and the results can provide scientific basis for reasonable exploitation of wasteland and soil improvement.1 The practice research of soil recovery:(1) The results of grey relational analysis were consistent with the soil degradation index, there were significant differences in soil quality after improvement, the highest correlation value was forest shrub mixed forest(0.7028), and the recovery effects was best, the effects of soil improvement in grassland was followed. Slop was an important factor affecting the soil nutrients in different kinds of forests. In the three kinds of forest on the same slop, the highest correlation value was the forest under the slop, the second was up down the slop, and the soil quality of forest in the middle slop was last. Therefore,vegetation restoration was an effective measure in soil improvement on costal sandy.(2) In the process of ecological restoration of degraded land in the east coast of Hainan Island, the measures of combining of forest and shrub should been taken based on natural conditions. Planting drought-tolerant plants in the early vegetation restoration period, it could be planted fast- growing trees and casuarinas when the soil quality and soil moisture was improved and matrix was stable on sand, then to achieve the optimal allocation of different vegetation types in the revegetation process. Promoting sustainable development of coastal ecosystems and changing the ecological environment of costal sand.2 Ponds sediments were used to improve soil fertility by engineering measures, to achieve resource utilization, the results showed that:(1) Because of the selective loss of soil particles in farmland, the particle fractal dimension(2.662) in sediment was slightly above the coastal farmland fractal dimension(2.591). There was a significant positive correlation between the size of the fractal dimension in sediments and its clay and silt contents,the correlation between the fractal dimension and the organic matter was significantly positive, but the correlation between the fractal dimension and the sand contents was negative. Fractal dimension could be taken as a significant index to evaluate the texture of ponds sediment.(2) Ponds sediments and soil composition in coastal farmland were very similar in size fractions, Compared with the surrounding farmland, the sediments had high fertility and the texture was loam with very fine sand and silt. The physical and chemical properties in sediments showed that the Ponds dredging sediment in the downstream can be used for soil improvement in coastal farmland.3 The results of practical research of soil improvement in wasteland showed that:(1) The contents of organic matter, total nitrogen, total potassium, and total salt content in soil were increased with the amount of sludge applied, it could improve the soil nutrients contents when sludge application was more than 10 %, and the above indicators have reached the peak when the sludge application reach 30 %. But the heavy metal contents in soil would increase when the sludge application was more than 20 %.(2) It was indicated that after the application of sludge, the heavy metal contents in Pennisetum, planted in treated soil, were decreased compared with the control. The contents of Cr, Ni, As, Cd, Pb, Hg were lower than the national feed hygiene standards(GB 13078-2001) Limits. After the sludge application, the enrichment factor of heavy metals in Pennisetum, were less than 1, and the Migration and accumulation of heavy metals was ineffective in short-term.Taking the soil quality and feeding security into consideration, the volume rate of sludge application in rocky wasteland shouldn’t more than 20 %; it not only could meet the needs of nutrients for plant growth, but also could reduce the heavy metal contents effectively. In addition, the contamination of soil and plants were reduced, and the production of Pennisetum and economic benefits could be ensured.