| Straw application could bring both economic and environmental benefits from improving the physical properties and fertility of soil so that to promote microbial growth; Bentonite could improve structure and moisture retention of soil, increase soil fertility, adjust soil pH, thereby increase crop yield; Polyacrylamide(PAM) could change soil structure to increase moisture, nutrient retention and the adsorption and desorption of the fertilizer. It could also produce positive effect on yield. Straw, bentonite and PAM were made into straw amelioration materials by different ratio. We proceeded field experiments for investigating how different ratio of straw-bentonite-PAM in straw amelioration materials impact on soil pH, soil nutrient supply, crop yields, nutrient absorption and utilization of rape. The main conclusions are listed as follow.(1) The pH values of different soil all became weak acid after application of straw amelioration materials. The pH of Typic Udi-Alluvic Primosols were changed from 4.9 to 5.4-6.5, the pH of Typic Purpli-Udic Cambosols were changed from 6.3 to 6.5-6.9, and that of Calcaric Purpli-Udic Cambosols was from 8.3 to 8.1-7.6. The bentonite had a significant effect on soil pH.(2) Application of straw amelioration materials had a significant effect on content of total Nitrogen, Phosphorus and Potassium. Such effect was better and better over time, and it varied from different soil. The data of June showed that:after amelioration, the total Nitrogen were increased by 19.15%～22.25%, total Phosphorus were increased by 14.09%-17.87%, total Potassium were increased by 19.09%～22.90% in Typic Udi-Alluvic Primosols; The total Nitrogen, total Phosphorus and total Potassium were increased by 22.38%～24.43%,27.32%～31.15%,29.79%～38.57% in Typic Purpli-Udic Cambosols; And they were increased by 16.66%～18.83%,16.70%～19.62%,16.34%～20.91% respectively in Calcaric Purpli-Udic Cambosols. Such effects of straw amelioration were related to original content of total Nitrogen, Phosphorus and Potassium in soil. The lower content, more obvious the effects. There were significant difference between CK and all treatments (p< 0.01). However, no significant difference was observed among different treatments (p> 0.05). The main factor which influenced total Nitrogen, Phosphorus and Potassium in soil was the dosage of straw.(3) The available Nitrogen, Phosphorus and Potassium in soil were affected by straw amelioration materials. There were significant difference between all treatments and CK (p< 0.01). The sequence of increasing available Nitrogen, Phosphorus and Potassium was:straw+bentonite+PAM> straw+bentonite> straw. The effect varied from different soil. The available Nitrogen and Phosphorus content were increased mostly in Calcaric Purpli-Udic Cambosols, while available Potassium were increased mostly in Typic Udi-Alluvic Primosols. For available Nitrogen, the optimum dosages of bentonite were 825 kg/hm2. When the dosage of PAM was more than 166.65 kg/hm2, it did not affect available Nitrogen significantly. The content of available Phosphorus were increased significantly if the dosage of bentonite lower than 825 kg/hm2; The available Phosphorus content were increased with the dosage of PAM, and they were significantly correlated in Typic Udi-Alluvic Primosols. For available Potassium, the optimum dosages of bentonite and PAM were 825 kg/hm2 and 166.65 kg/hm2.(4) The yield of rapeseed and rape straw were increased significantly after application of straw amelioration materials. The production of rapeseed increased with the amount of bentonite and PAM, The production of rapeseed were increased significantly if the dosage of bentonite lower than 825 kg/hm2. The amount of PAM produced affect production of rapeseed significantly when the amount was 83.25kg/hm2, and no significant effect was observed when PAM was more than 166.65kg/hm2. The production of rape straw varied slightly from different soil, the overall sequence was:straw+bentonite+PAM> straw+bentonite> straw.(5) Application of straw amelioration materials affect total N, total P, and total K in rapeseed and rape plant significantly. But total N, total P, and total K were not affected significantly by straw only, they were increased significantly by bentonite and PAM with straw. The optimum dosages of bentonite and PAM for total N, total P, and total K in rapeseed and rape plant were1650kg/hm2 and 166.65 kg/hm2.(6) The accumulation of N, P and K in rapeseed and rape were improved significantly by straw amelioration materials, and the tendency of such accumulation was increased with the dosage of PAM and bentonite. The accumulation was increased significantly reached maximum when dosage of PAM was 83.25 kg/hm2, and no significant difference was observed when PAM was more than 166.65kg/hm2. There were significant difference among the accumulation of N, P and K when the bentonite was 825 kg/hm2.
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