The Effects Of Soil Chemical Elements On Cadmium Availability And Content In Rice

Hunan is rich in mineral resources and is known as the hometown of non-ferrous metals.However,since the industrial development,the pollution of heavy metals in farmland has become more and more serious.Heavy metal cadmium not only affects the growth and development of plants,but also is difficult to be decomposed and dissipated in the biological cycle and easily enters the human body through the food chain,posing a threat to human health.In recent years,there have been a lot of research results on cadmium pollution control.However,due to the complexity of soil system,various cadmium reduction technologies have different cadmium reduction effects in different regions and different periods.It is particularly important to pay attention to and understand the current situation of cadmium pollution and soil factors in a region and adopt scientific and reasonable agronomic measures according to local conditions to reduce cadmium pollution.In this experiment,270 samples of soil from 100 mu demonstration field in Hunan province were used to measure 15 indexes such as total cadmium,available cadmium,total nitrogen and alkali-hydrolyzed nitrogen in the soil.By studying the relationship between heavy metal cadmium and soil factors,the main factors affecting cadmium accumulation in brown rice were analyzed,and the following results were obtained:(1)Soil factors could explain 92.3% of soil available cadmium,and soil available cadmium was significantly positively correlated with soil total cadmium,alkali-hydrolyzable nitrogen,available iron,available manganese,available copper,available zinc,and significantly negatively correlated with soil p H,total potassium,exchangeable calcium,exchangeable magnesium,and cation exchange capacity.There was a significant positive correlation between brown rice cadmium and soil total cadmium,available cadmium,available phosphorus,available zinc and available copper,and a significant negative correlation between brown rice cadmium and soil p H,cation exchange capacity,total potassium,exchangeable calcium and exchangeable magnesium.When p H reached 5.84,cadmium in brown rice decreased with the increase of p H value.Under the premise of satisfying the growth of rice,soil p H,alkali-hydrolyzable nitrogen,available iron,available manganese,available copper and available zinc contents could be adjusted appropriately to change the available cadmium content in paddy soil to a certain extent.(2)There was a significant positive correlation between cadmium and soil available cadmium in brown rice and soil available copper and soil available zinc,and a very significant negative correlation between its enrichment coefficient and soil available iron,exchangeable calcium and magnesium.Cadmium content in brown rice of late rice was negatively correlated with soil p H,exchangeable calcium and magnesium,and soil available cadmium content in late rice was negatively correlated with soil p H,and soil available iron,manganese,copper and zinc were positively correlated with soil available cadmium content,which could explain 90% of soil available cadmium change in late rice.(3)In the mildly polluted area,soil total cadmium,p H,organic matter,available iron,available copper,available manganese and alkali-hydrolyzable nitrogen were the main factors affecting the accumulation of cadmium in brown rice by changing the content of available cadmium in soil.Soil available Cadmium content in moderately and severely polluted areas was mainly affected by total cadmium and available zinc,and available zinc and total cadmium could explain 92.3% of the variation of soil available cadmium content in severely polluted areas.Through the above analysis,combined with the correlation analysis of cadmium enrichment coefficient of brown rice,soil available cadmium ratio of total cadmium and various soil factors,soil p H,cation exchange capacity,exchangeable calcium of total potassium and exchangeable magnesium have great influence on cadmium of brown rice.Soil p H,alkali-hydrolyzable nitrogen,available iron,available manganese,available copper and available zinc have great influence on available cadmium.For cadmium control of middle and late rice,late rice should be given priority over early rice,combined with fertilization calcium,magnesium and zinc fertilizer to prevent and control cadmium.For medium and severe polluted areas,the problem of "source control" should be discussed from the perspective of reducing soil total cadmium and available zinc.In mildly polluted areas,the "effect reduction" of soil available cadmium can be discussed by adjusting soil p H and balance of trace elements.