The Study On The Control Of Cadmium Enrichment In Rice By Different Foliar Iron Fertilizers

As one of the main foods of human beings,the annual areas for rice cultivation in China are more than 30 million hectare and produces 210 million tons of rice which accounts for18%of global sown areas and 28%of global total yields.It thus is capable of providing more than 65%of Chinese population with staple food.However,the corresponding heavy metal pollution has become common,especially the heavy metal pollution in rice because of the rapid development of the economy.According to the Ministry of Environmental Protection and the Ministry of Land and Resources jointly issued the"National Soil Pollution Status Survey Bulletin",the rate of farmland pointed with cadmium?Cd?pollution exceeded 7.0%in terms of the standard,ranking the first among eight types of inorganic pollutants.Cd affected the ecosystem structure and function of the soil,reduces soil fertility.On the one hand,it was absorbed by rice,affected the composition of mitochondria and chloroplasts in this crop,inhibited the growth of mesophyll cells and the synthesis of chlorophyll,resulted in the decline of leaf photosynthesis rate,and reduced the efficiency of rice nutrient absorption,ultimately led to a reduction in rice yield.The serious pollution even can directly cause the death of rice plants.Cd in rice grains will enter into the human body through food chain and cause irreversible damage to the lungs,bones,kidneys,liver,reproduction and immune system of the human bodies.Therefore,studying the Cd heavy metal pollution and control in rice can fulfil extremely important theoretical significance and practical value.To effectively control the absorption of Cd in rice,the common ways to remove Cd included physical,chemical and biological techniques so far.Foliar fertilizer technology is one of them.Based on Cd pollution in farmland,this study aims to spray foliar iron fertilizer to control Cd accumulation in rice.It mainly carried out a field experiment at a moderately contaminated area in Zhuzhou County and a soil polling experiment in a slightly contaminated land in Changsha County to explore the effects of applying different types of foliar Fe fertilizer so that Scientific basis and technical support to heavy metal pollution and food safety in farmland can be offered.The main results were as following:?1?Random sampling of rice samples in the wild showed that there was a significant positive correlation between Cd content in rice leaves and Cd content in rice husks and brown rice.the correlation between Cd content in the first leaves and Cd content in brown rice was the most significant?R²=0.8578?so that the result can provide the use of foliar fertilizer with a theoretical basis to control rice enrichment of Cd.According to this finding,there were four types of foliar fertilizers?Ca fertilizer,Si fertilizer,N fertilizer,Fe fertilizer?purchased in the market which can effectively promote rice yield and reduce the content of Cd in rice.The best yield increase of foliar Fe fertilizer purchased on the market can increase the yield by 27.27%and can reduce the Cd content in brown rice by 32.66%,but there was an increase in Cd concentration as the concentration of spraying fertilizer gets increasing in rice.the Cd concentration of rice did not reach the national food hygiene standards as well.Therefore,it was suggested the use of foliar fertilizer to control the enrichment of Cd in brown rice,and combine with other control measures such as water management and soil pH to ensure the safe production of rice.?2?the polling experiment of spraying four-type Fe fertilizers(Fe²⁺,Fe³⁺,Fe?II?,Fe?III?)was useful.Compared with CK under slight Cd polluting conditions can increase the yield of rice by 2.45%?13.14%,and fulfill the best effectiveness under medium concentration Fe?II?.Spraying proper concentrations of Fe?II?and Fe?III?can increase the chlorophyll content and net photosynthesis rate in rice leaves,and reduce the concentration of intercellular carbon dioxide in leaves.Meanwhile,the content of POD,SOD and CAT enzymes in rice leaves can be increased,and the increasing results were better than Fe²⁺and Fe³⁺,but excessive spraying may lead to an increase in MDA content.In mild Cd contaminated areas,spraying four types of foliar Fe fertilizer can significantly increase the content of Fe in leaves,husks and brown rice,but the effect of lifting in stems and roots was not obvious.Spraying four kinds of foliar Fe fertilizer can effectively reduce the content of Cd in the leaves,but only in the middle and high concentration spray can effectively reduce the content of Cd in brown rice and husks and can reduce maximally the content of 29.03%in brown rice.This study provided evidences to the promotion of field trials.?3?Under moderately contaminated field conditions,spraying four different types of foliar Fe fertilizer can increase the yield of rice from 0.99%to 9.68%.Spraying proper concentration of Fe?II?and Fe?III?could increase the chlorophyll contents,net photosynthesis rate and decrease the intercellular carbon dioxide concentration in rice in the field.The spraying of Fe fertilizer on the field had few impact on stomatal conductance and transpiration rate.Spraying high concentrations of Fe?II?and Fe?III?can significantly increase the content of POD and CAT enzymes and reduce the content of MDA in rice leaves.Spraying foliar Fe fertilizer in the field hardly influenced SOD activity in rice leaves.Spraying high concentration of Fe?II?and high concentration of Fe?III?can significantly increase the content of Fe in brown rice,husks,leaves and stems,but the effect of improving Fe in roots is not remarkable.Spraying high concentrations of Fe²⁺,Fe?III?and medium concentration Fe?II?can significantly reduce the content of Cd in husks,leaves and stems.Meanwhile the application of four types of foliar Fe fertilizers had a tendency to decrease the content of Cd in rice but no significant influence.The largest Cd contents was decreased by12.90%in brown rice.It was suggested to combine with other measures to control the absorption of Cd in rice.