| Assodiate prof. Yang Jianhong Assodiate prof. Qu MingRocks (or parent materials) are considered as the framework or basic materials building soils. Soils are formed from rocks (parent materials), along with the substances and energy exchange between rocks (parent materials) and animals, plants and atmospheric factors (sunlight, heat, water and air). Therefore, many properties of soil tend to be qualified by the rocks (parent materials). The mineral constituent of the parent materials correlates closely to the quality of the soil. It is also the original source of plant mineral nutrition (nitrogen is an exception). However, the weathering of rocks is a long-term course, which is generally takes nearly 120 to 3000 years to change to soils. Therefore, it is difficult to investigate the substance exchange between rocks and soils to understand the process of soil formation from rocks. Whereas, the purple rocks are quite different. They are exposed to the air can be weathered simultaneously to soil in about 10 years. This brings us about the feasibility of this research.Three typical purple rock types in Three-Gorge Reservoir Area (TGRA) were taken as subjects in this research: J2s and J3s which formed in Jurassic period and T2b which formed in Triassic Period. The study focuses on following aspects: (i) weathering characteristics and its influence factors of these three kinds of rocks; (ii) release laws of seven nutrient elements (K. Ca.. Mg.. Fe. Mm Cu and Zn) from the fragments of the first two kinds of rocks extracted by four types of low organic acids; and (iii) measures to improve the fertility and productivity of new weathered soil inTGRA.Results of the study were indicated as follows:1.Weathering of the purple rockThe result of pot weathering experiment showed that 18.4% of purple rock developed to small particles (diameter < 5mm) and 5.1% to soil (diameter < 2mm) after one year weathering; disturbances, such as frequent moving and overturning, contributes to the weathering rate and disturbances made the rocks weathering 32% quicker than that which non-disturbances. Field weathering experiment result showed that 3 7.6% of the purple rock was weathered to be small particles and 15.4% that tosoil in one yeaL The speed of weathering is highcr in the field than in the pot, duringto more exposition to the sunlight and rainfall. The rate of weathering of purple rockis also influenced by the character of its parent rock. The rate of weathering sequenceis mudstone > sandsIone according to their quality and is JP > J2s >T2b according totheir geologic Period. The weathering rate of J3s pmplish mud shOne, which isquickest in the three pmple rocks, is 26.4% to be soil in field experiment in one yearNutrient release of pmple rock is in the same step with weathering. RaPid release ofnurients frOm weathering of pmple rock is of paramount to nutrient replenishments ofpurplish soil and it also provides the essence of fertility to purple soil.2. Extraction with low wcight oraanic acid8(1 ) The results indicated that low weight organic acids can accelerate obviouslyre1ease of the 7 nutrient elements (K. Ca. Mg. Fe. Mn. Cu and Zn) from the soilsand pmple rocks, and the release rate is far qulcker than that trbed by pure waterunder the same condihon, the former is as l~275 times as that of the latteL Thesequences of caPability of fOur kinds of orgboc acids to extract the same nutrientelements frOm different soils (or rocks) are comparable. As a whole, the order ofrelease ~ity of seven llndientS is most when taking 0.05moUL citric acid tO extract,then is 0.05moUL tartaric acid and 0.05moUL oxalic acid, 0.05mol/L malic asid is theleast among the four organic acids.(2) The results showed that the same nutrient release order in the same soil orpurple rock is different in taking differ organic acids to extract. Take the potassiumrelease quantity in J2s purplish mudstone as example, the 0.05moUL oxalic acid is themost, but the 0.05moim tartaric a... |
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