| The paper studies the root systems of the Eucalyptus and Pineapple under the model of the extra-big row's Eucalyptus-crops interplanting, also studies the the root systems of the prue Eucalyptus, discusses the root systems' distribution under the ground space and utilization to the site soil nutrient. The study has a very important practical significance in soil improvement of the Eucalyptus plantation, guiding production practice, improving fast growing performance of Eucalyptus plantation, promoting sustainable development, improving the ecological environment. At the same time, providing a theoretical basis in studying and promoting the new model of the Eucalyptus-crops interplanting in further.The main conclusions are as followed:1. Eucalyptus roots in the vertical direction are mainly distributed at 0-60cm soil layer, and there is litter root below 60cm soil layer. The trend of Eucalyptus roots is: root biomass decreased linearly with the increase of soil depth gradually. The distribution of Eucalyptus root volume in the horizontal direction concentrated in the 0-100cm soil layer, accounting for the vast majority of its total root volume. Under the model of the extra-big row's Eucalyptus-crops interplanting, the total root biomass are accounted for its 85.7% away 0-50cm from the pile and accounted for its 93.5% away 0-100cm from the pile. Under the model of pure Eucalyptus, the total root biomass are accounted for its 81.3% away 0-50cm from the pile and accounted for its 88.2% away 0-100cm from the pile. Eucalyptus roots in the horizontal direction are mainly distributed in the context of 0-100cm from the piles, especially the coarse roots which are greater than 10mm.2. The root distribution of the extra-big row's pure Eucalyptus in the North-South direction is consistent with the root distribution of pure Eucalyptus in the North-South direction, and both show that the root volume in the south direction is less than the root volume in the north direction. The fresh weight of the root volume at all levels (coarse, medium, small) between wide lines under the model of the extra-big row's Eucalyptus-crops interplanting are heavier than the fresh weight of the root volume between narrow rows, which meant that the soil nutrients of the Eucalyptus planted three years under the model of the extra-big row's Eucalyptus-crops interplanting have reached the maximum use of space and the roots have been extended to wide rows. Underground root system has played the role of edge effect, increasing the amount of Eucalyptus roots, especially fine roots, will increase the absorptive capacity of Eucalyptus roots. Available nutrient space of the site soil will be larger which helps to improve wood production and cultivate large diameter timber of eucalyptus.3. The existing biomass of the pineapple planted under the model of the extra-big row's Eucalyptus-crops interplanting was 18.860 t/hm2, among them, stem (including roots) was 6.574 t/hm2, roots (including coarse, medium, fine) for 1.355 t/hm2, litter was 0.914 t/hm2, leaves of 10.017 t/hm2. The trend of the pineapple roots, litter, stem (including roots) and leaves in bands in the intercropping is head and tail low and middle high. From beginning to end border row to the middle, the rate change of the two adjacent Pineapple's roots, dry leaves, stems (including roots) and leaves is small, and with smallest fluctuations in the middle section, and the fluctuations are quite close. Maybe due to eucalyptus planting in this study are positive east-west, China is located in the northern hemisphere, the illumination time in the north is longer than in the south. Affected by light, the time of the Eucalyptus shading in the south is slightly longer than in the north, so the fresh pineapple plant capacity in the south within the bands is smaller than the fresh pineapple plant capacity in the north, which led to pineapple roots, dry leaves, stems (including roots) and leaves are slightly lower than the north. After the harvesting of the Pineapple fruit, Pineapple's roots, dry leaves, stems (including roots) and leaves can be landfill as a green manure and cover material after crushing, total to 110.2 t/hm2, which has a very important practical significance in soil improvement in the interplanting bands, promoting the increase of the Eucalyptus roots, increasing Eucalyptus production and promoting the sustainable development of Eucalyptus. 4. The trend of the Pineapple root system in the vertical direction is:root biomass at all levels decreased linearly with the increase of soil depth gradually. The fresh weight of the Pineapple root at 0-20cm soil layer was 62.3g per plant, accounted for 91.6% of the total root biomass. The fresh weight of the Pineapple root at 20-40cm soil layer was 5.7g per plant, accounted for 8.4% of the total root biomass. The fresh weight of the Pineapple fine root at 0-20cm soil layer was 11.7g per plant, accounted for 94.4% of the total fine root biomass. The fresh weight of the Pineapple fine root at 20-30cm soil layer was 0.7g per plant, accounted for 5.6% of the total fine root biomass. There is not fine root distribution at 30-40cm soil layer. It's obvious that the soil layer at 0-20cm are the main area of the Pineapple nutrient absorption.5. Under the model of the extra-big row's Eucalyptus-crops interplanting, the root systems of the Pineapple are mainly distributed in 0-30cm surface soil, accounted for 98.1% of Pineapple root biomass, the root volume of only 1.9% below 30cm soil layer. In alternate planting band, Eucalyptus roots are distributed in soil below 30cm, without root distribution of Eucalyptus in the 0-10cm of soil. The root systems of the Eucalyptus and Pineapple under the model of the extra-big row's Eucalyptus-crops interplanting have an obvious characteristic of the hierarchical distribution, occupying different soil space which plays a positive role in hierarchical use of site soil moisture and nutrients, and promoting and improving the use of deep soil nutrients.
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