磷、锌肥处理对降低污染稻田水稻籽粒Cd含量的影响

Effects of phosphorus and foliar zinc fertilizers on reducing grain Cd concentration of rice grown in a polluted paddy

探索农田措施控制水稻Cd吸收与籽粒积累是保障稻米食物安全的急迫需求。采用田间定位试验,研究了不同用量的钙镁磷肥及叶面喷施锌肥(ZnSO4·7H2O)等处理对污染稻田水稻籽粒Cd含量的影响。试验表明,施肥处理没有显著提高水稻产量,但籽粒Cd含量有不同程度降低。分析表明,这些处理提高了土壤的pH值,且随用量而增高,土壤中有效态Cd含量显著降低。土壤有效态Cd含量与土壤pH值存在显著负相关,推测主要是由于土壤pH升高而降低了土壤Cd活性。不过,叶面喷施ZnSO4·7H2O,并未明显提高土壤pH值,但显著降低土壤有效态Cd含量,可能是由于淹水下形成难溶性CdS而钝化了土壤Cd.因此,稻田中Cd钝化可以抑制Cd在水稻籽粒中的积累。但是,在严重污染稻田中,这些用量尚不能有效控制稻米Cd的安全。建议在严重重金属污染的土壤改种其它非Cd强积累作物。

Exploring effective countermeasures for inhibiting Cd uptake and accumulation by rice grain is urged for ensuring the food safety of rice. A field experiment was conducted to study the effects on grain Cd concentration of different dosages of calcium magnesium phosphate fertilization and foliar ZnSO4·7H2O fertilization. The results showed that most treatments had not significantly increased rice yield but decreased grain Cd concentration with varying extent. The analysis showed that soil pH was increased tender all the phosphate fertilizer treatments, in proportional to the application dosage. Accordingly, significant reduction in bioavailable Cd was observed. Statistical analysis indicated a significantly negative correlation of bioavailable Cd with soil pH. Therefore, the reduc- tion in grain Cd concentration under these phosphorus fertilization treatments was attributed to the reduced mobility of soil Cd under increased soil pH. Foliar application of ZnSO4·7H2O solution was not found to increase soil pH, but again decrease soil bioavailable Cd, which was likely to result from the formation of CdS under submerged condition. Therefore, inactivating soil Cd by the pH-increasing phosphorus fertilization and mobility reducing foliar sulphate could alleviate Cd uptake and accumulation in rice grains. However, grain Cd from this heavily polluted paddy was not reduced to meet the National food safety guideline with the studied dosages. It is suggested that alternative crops with low Cd affinity should be cultivated instead of rice for sound agro-production in polluted rice fields.