Effect Of Accumulated Temperature On Accumulation Of Heavy Metals Cd In Different Rice Varieties

In order to ascertain the differences in rice Cd absorption and accumulation between different seasons,and to understand the effect of accumulated temperature on the accumulation of heavy metal Cd in different types of rice varieties,in 2019,a field experiment was carried out in stages at the Yangyang Comprehensive Teaching Experiment Base of Hunan Agricultural University.Early rice varieties(Zhongzao 39 and Xiangzaoxian32)and two indica hybrid early rice varieties(Luliangyou 996 and Zhuliangyou 819)were tested materials,and 7 sowing dates were set.The main results are as follows:The effects of the four varieties on the total growth period,yield and yield composition in different sowing periods are roughly the same.The total growth length of the four rice varieties all shows that with the delay of the sowing period,the total growth period decreases first and then rises.Among the four rice varieties,the actual yield of Zhongzao 39 was the highest in S5,which was 6140.63 kg/hm2.Xiangzaoxian 32 had the highest yield in S6,which was 4734.38 kg/hm2,and the yield of Luliangyou 996 was 2670.76 kg/hm2～6640.63.Between kg/hm2,the yield of Zhuliangyou 819 was between 4125kg/hm2～6437.50kg/hm2.The effects of different sowing dates on the dry matter accumulation of the four rice varieties in each growth period are as follows: with the delay of the sowing date,the dry matter accumulation first rises and then decreases,and the dry matter accumulation between different varieties is inconsistent.The root vigor of the four rice varieties at the full heading stage at different sowing dates showed the same trend,with S1 to S3 rising first,then decreasing,and reaching the highest value at S6.The four rice varieties had the highest chlorophyll content in the full-earning stage and the lowest maturity stage in the three key periods of tillering,full-shearing stage,and maturity stage.Under the seven sowing stages,the chlorophyll content of the full-earth stage rice was generally at S5.The highest processing.The overall performance of chlorophyll content in the mature stage is: as the sowing date is delayed,the chlorophyll content gradually decreases.At different sowing dates and different growth periods,the cadmium content of all organs as a whole is root>stem and leaf>powder>solid grain.During maturity,the Cd content in the roots,stems,leaves,and ears of the four rice varieties overall showed a trend of decreasing first and then increasing,and the overall showed a "V" shape change trend.From S1 to S7,in different growth periods,the accumulated temperature in the transplanting period-tillering period,heading period-maturity period,and the whole growth period all increased first and then decreased.The accumulated temperature change during the sowing-transplanting period is: as the sowing period is postponed,the overall trend is increasing.The accumulated temperature from the tillering period to the heading period generally showed a trend of increasing first and then decreasing.In the early stage of rice growth and development,the seedling stage-transplantation period is positively correlated with accumulated temperature.As the growth period is postponed,the correlation coefficient gradually decreases and reaches a negative value at the maturity period,such as Lu Liangyou996.The correlation coefficients between Cd content of brown rice and rice kernels and accumulated temperature during heading-maturity are-0.0078,-0.0036,-0.0021,and-0.0049,respectively,and the coefficients of determination were 0.3862,0.2733,0.48,and 0.5138,indicating that the heading-maturity The accumulated temperature in the period is negatively correlated with the Cd content of the root system,stems and leaves,brown rice,and grains during the mature period.Accumulated temperature has the greatest effect on the absorption and accumulation of heavy metals in rice,and there is no correlation between light and rainfall.Accumulated temperature is mainly negatively correlated with the cadmium content in rice plants.Therefore,it is effective to choose a suitable planting period in production and adopt suitable cultivation measures.Reduce the absorption and accumulation of heavy metals,and at the same time can effectively promote the growth and development of rice and obtain high yield.