Studies On Aciduric Forages Selection And The Techniques Of Eliminating Aluminium Toxicity In Hilly Red Soils Region

The potential of developing forages is tremendous due to the high rainfall, long sunshine and high temperature in red soils hilly region. Plentiful wasteland and new developed orchard are suitable to develop forage. However, the soil is very acid in these lands, thus seriously affects forages growth. Therefore, selecting suitable aciduric forages and using suitable fertilizing and planting management measures are necessary to get better establishment and higher yield. In this study, filed experiment was set up to select aciduric forages for acid red soil, suitable soil pH range of forages growth was determined by pot experiments, the tolerant ability and mechanism of forages to aluminium toxicity were studied by a series of water culture experiments, the effects of lime and phosphorus fertilizer on forages growth were studied by pot experiments, suitable combination ratio of forage legume Lotononis bainesii and3grasses was studied in a filed experiment. Runoff plots were set up to study the effects of forage on erosion control, improving soil and ecological condition in forest plantation or orchard. The main conclusions are as follows:(1) Some of Warm season grasses such as Digit aria eriantha cv Premier Hemarthria compressa, Pennisetum purpureum, Pennisetum purpureum cv Mott, Setaria sphacelata cv Soland, and legumes such as Chamaecrista rotundifolia cv Wynn, Lotononis bainesii and Macroptilium atropurpureum cv Siratro had high acid tolerance ability. They grew well in the acid soil (pH is4.5) even no fertilizer and lime were applied. Some of cool season species such as Trifolium repens cv Haifa, Dactylis glomerata cv Porto and Lolium multiflorum cv Tetila grew poorly in the acid soil if no ferilizer and lime, however they grew well if ferilizers and lime were applied.(2) Chamaecrista rotundifolia cv Wynn was the most acid tolerant legume species which grew best in the soil with pH less than5. The suitable soil pH was5-5.5for Macroptilium atropurpureum cv Siratro and Lotononis bainesii. Trifolium repens cv Haifa was not acid tolerant which was suitable to grow in the soil with pH5.5-6.5. Digitaria eriantha cv Premier had high ability of acid tolerance and grew best in the soil with pH4.5-5. The soil pH ranges of Setaria sphacelata cv Soland, Zea Mexicana and Dactylis glomerata cv Porto were5-6,5.5-6.5and5.5-6.5, respectively.(3) The order of acid tolerant ability of8forages tested to aluminium toxicity was Chamaecrista rotundifolia cv Wynn, Digitaria eriantha cv Premier, Macroptilium atropurpureum cv Siratro, Lotononis bainesii, Setaria sphacelata cv Soland, Zea Mexicana, Dactylis glomerata cv Porto and Trifolium repens cv Haifa.(4) The effects of wiping off mucilage glue absorbed on radicle of Chamaecrista rotundifolia cv Wynn, Digitaria eriantha cv Premier and Setaria sphacelata cv Soland on radicle elongation were the highest, and the lowest for Dactylis glomerata cv Porto and Trifolium repens cv Haifa, when these forages were planted in a solution with AICl3concentration of30μmol·L-1. It shows that the radicles excreting mucilage glue is one of mechanisms of forage forbearing aluminium toxicity.(5) The roots of Chamaecrista rotundifolia cv Wynn, Setaria sphacelata cv Soland, Lotononis bainesii, Macroptilium atropurpureum cv Siratro and Zea Mexicana excreted citric acid in the solution with high concentration of Al3+. The amount of excreting citric acid was relative with the ability of forbearing aluminium toxicity of these forages. It shows that root excreting citric acid is one of reasons of forbearing aluminium toxicity of these forages.(6) Applying0.7-1.4g·kg-1lime could increase quickly the yield of Trifolium repens cv Haifa, Macroptilium atropurpureum cv Siratro, and Zea Mexicana. The yield of Trifolium repens cv Haifa increased slowly when applying2.1-2.8g·kg-1lime, however the yields of Macroptilium atropurpureum cv Siratro, and Zea Mexicana decreased, applying phosphorus could slow down the decrease trend of yield. Applying phosphorus could alleviate the damage of soil acid to forage. Applying phosphorus and0.7-1.4g·kg-1lime could increase hugely the yields of Trifolium repens cv Haifa, Macroptilium atropurpureum cv Siratro, and Zea Mexicana. The ability of Chamaecrista rotundifolia cv Wynn forbearing aluminium toxicity was very high, applying lime restrained its growth, but applying phosphorus increased its yield.(7) Lotononis bainesii could grow well when it was mixed sowing with Digitaria eriantha cv Premier or Setaria sphacelata cv Soland or Hemarthria compressa. The biomass and crude protein yields in the mixed sowing treatments were higher significantly than that in grass monoculture treatments. Mixed sowing could promote the growth of grass, sustain pasture productivity. The competitive ability of Digitaria eriantha cv Premier was the highest among3grass species. The best mixed ratio of Digitaria eriantha cv Premier and Lotononis bainesii was1:2. The competitive effect of Hemarthria compressa on growth of Lotononis bainesii was little as it has little leaf. The biomass and crude protein yield were the highest when it was mixed sowing with Lotononis bainesii as a ratio of2:1. The competitive ability of Setaria sphacelata cv Soland was middle, the best ratio sown with Lotononis bainesii was1:1(broadcast or row sowing).(8) Planting aciduric forage legume in the forest plantation or orchard could reduce soil erosion significantly, and reduce the loss of nutrients and organic matter. Soil organic matter, total N, Available N, available P and available K increased after planting forages for4years, thus improved soil fertility. Soil exchangeable Ca+and Mg2+increased and Al3+decreased, thus alleviated aluminium toxicity in the soil. Planting forages in orchard could temper the soil moisture and temperature, increase soil water content in surface soil, decrease soil temperature during hot and dry season, thus improve the ecological condition of orchard.