| The zinc and chromium were applied in the test soil in accordance with the characteristics of the heavy metal pollution (zinc and chromium pollution) of rice areas in the Chengdu Plain and also five modifiers were added in the test soil at the high application level (straw, rape straw and rabbit manure:10g/kg, lime: 1g/kg, superphosphate:8g/kg, respectively) and low application level (straw, rape straw and rabbit manure:5g/kg, lime:0.5g/kg, superphosphate:4g/kg, respectively). Pot experiment was carried out to study the changes of soil pH, available zinc, chromium and nutrient (alkaline hydrolyze N, available phosphorus and potassium) when the soil was treated by the modifiers before planting; and to study the effects on the zinc and chromium accumulation as well as the nutrient absorption of rice (Sichuan Aromatic Rice 5) at different growth stages. Base on above, we selected out the optimal modifiers which could both reduce the zinc and chromium accumulation in the plants and improve the absorption of the nutrient by the plants to provide a reference to the safety and stable rice production for the zinc and chromium contaminated soil in Chengdu plain. The results were as follows:1. Before planting, five modifiers changed the soil pH. Superphosphate, straw and rape straw decreased the soil pH, otherwise, lime and rabbit manure increased the soil pH. Five modifiers decreased the contents of available zinc and chromium in the soil, which could be helpful for reducing the uptake of soil zinc and chromium by the rice roots. The order of the decrease of the available zinc contents by different modifiers was as follows: straw>rape straw＞superphosphate>lime>rabbit manure, and the available zinc content was the lowest in the soil treated with straw (high application level treatment,20.00mg/kg of available zinc), which was reduced by 53.25% compared to the CK; the order of the decrease of the available chromium contents was as follows: lime>straw>rape straw> superphosphate>rabbit manure, and the available chromium content was the lowest in the soil treated with lime (high application level treatment,3.18mg/kg of available chromium), which was reduced by 60.15% compared to the CK.2. Before planting, five modifiers significantly increased soil alkaline hydrolyze N and available phosphorus contents; the maximum of alkaline hydrolyze N (124.56mg/kg, increased by 41.51% compared to the CK) appeared in the high application level treatment of rabbit manure and that of the soil available phosphorus (42mg/kg, increased by 133.33% compared with the CK) appeared in high application level treatment of superphosphate. Five modifiers had different impacts on the soil available potassium. The inorganic modifiers (superphosphate and lime) decreased soil available potassium content, while the organic modifiers (straw, rabbit manure and rape straw) increased soil potassium content, and the largest increasing range was in the high application level of straw, increased by 136.88% compared to the CK.3. At the different rice growth stages, except the lime, other modifiers significantly decreased the zinc content in the roots and shoots. The order of the decrease of the zinc content by the five modifiers in the roots and shoots was as follows:straw>rape straw> superphosphate>rabbit manure>lime. The zinc content of the high application level treatment of straw in the roots at rice tillering, booting and filling stages was:108.74, 77.77 and 82.88 mg/kg, respectively, which decreased by 40.40%,34.79%,48.54% compared to the CK, respectively. And that in the shoots was:32.66mg/kg,26.10mg/kg and 34.50mg/kg, respectively, which decreased by 52.09%,52.22% and 34.11%, respectively, compared to the CK. This indicated that the straw treatment was the most suitable for the decrease of the zinc accumulation in the zinc and chromium contaminated area among the five modifiers.4. At the different rice growth stages, the five modifiers significantly decreased the chromium content in the roots and shoots. The order of the decrease of the chromium content by the five modifiers in the roots was as follows:lime>straw>rape straw> superphosphate>rabbit manure. The chromium content of the high application level treatment of lime in the roots was increased most significantly:64.37,74.04 and 47.88 mg/kg, respectively, which decreased by 65.18%,54.44% and 65.88% compared to the CK, respectively. And the order of the decrease of the chromium content by the five modifiers in the shoots at the tillering stage was:lime>straw>rape straw> superphosphate>rabbit manure, and that at the heading and filling stages of rice was: straw>rape straw>lime>superphosphate>rabbit manure. This illustrated that the straw and lime treatments were the most suitable for the decrease of the chromium accumulation in the zinc and chromium contaminated area among the five modifiers.5. At the different rice growth stages, the five modifiers significantly reduced the nitrogen content in the roots, while increased it in the shoots. The results indicated the modifiers could adjust the balance of the nitrogen metabolism between different organs of rice and promote the rice growth. Meanwhile, the five modifiers significantly decreased phosphorus content and increased potassium content in roots and shoots.6. The five modifiers significantly reduced the zinc and chromium content of grains, so that the zinc accumulation of grains met the limits of national food security (Zn≤50mg/kg), the order of the reduction of the zinc accumulation was:straw> rape straw> superphosphate>lime>rabbit manure. The chromium accumulation of grain treated by the modifiers could meet the limits of national food security (Cr≤1.0mg/kg) except the high and low application levels of the rabbit manure, the order of the reduction of the chromium accumulation was:lime>straw>rape straw>superphosphate>rabbit manure. This showed that the straw was the most suitable for the reduction of the zinc of grains among the five modifiers, the lime was the most suitable for the reduction of the chromium in the heavy metal contaminated district among the five modifiers.7. The five modifiers significantly increased the content of the nitrogen, potassium and phosphorus of grains with the best effects by the straw. The results showed that the modifiers improved the rice to absorb soil nutrients, reduced the accumulation of the zinc and chromium in the rice plants to improved growth condition of the rice plant, which would help to lay a good foundation for improving rice quality and promoting safety production of rice.8. According to the experimental data, the five modifiers significantly increased the dry weight in the roots and shoots, reduced the ratio of the root to the shoot at the different rice growth stages and increased the yield of the single plant. This showed the modifiers could decrease the zinc and chromium accumulation of the rice, and play an active role in the production of rice in the zinc and chromium contaminated district. |
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