| The heavy metal pollution in cultivated land in China has severe impact on the safety of crops production.Alkaline soil amendments can increase pH in soil,passivating heavy metals in suit of soil,which is commonly used to inactivate passivation of cadmium in soil.This study researched on the effects of several ways to regulate soil pH and prevent cadmium contamination in rice using alkaline soil conditioner.Pot experiments were conducted to investigate the effects of acid and alkali additions on soil pH and influence and mechanism of soil pH and water management on speciation of cadmium,soil nutrients,iron plaque of surface of rice roots and principle of accumulation and absorption of cadmium by pot experiments,providing theoretical basis and data support for using alkaline soil conditioner,cadmium pollution governance and safe production of rice in paddy fields.The main test results were as follows:(1)The effect of soil pH on cadmium forms under different water management modes(flooding,dry-wet alternating and wetting)was explored by soil incubation experiments.The results showed that three water management modes can increase the pH of acidic soil and decrease the pH of alkaline soil,and the effect on the Eh was opposite to that of the soil pH.With the increase of culture time,the pH of acidic soil increased first and then decreased.The pH of alkaline soil first decreased and then increased.The stronger the acidity and alkalinity of the initial soil,the greater the change in soil pH.And the magnitude of the soil pH change in the three water management modes was flooding mode>dry-wet alternating mode>wetting mode.The soil pH of different water management models was significantly negatively correlated with the exchangeable cadmium in the soil,and was significantly positively correlated with the reducible and residual cadmium content.While soil pH increased from 4 to 10,soil exchangeable cadmium content decreased by 0.27 mg/kg in flooding mode,and reducible and residual cadmium concentrations increased significantly by 0.14 and 0.13 mg/kg,respectively;and 0.36 mg/kg decrease,0.19 and 0.18 mg/kg increase in the wetting mode,0.32 mg/kg decrease,0.20 and 0.13 mg/kg increase in the wet-dry alternating mode,respectively.Under the same soil pH conditions,the order of the soil exchangeable cadmium content in the three water management modes was wetting mode>dry-wet alternating mode>flooding mode.The results of Two-Way ANOVA and ANCOVA showed that soil pH and water management both had significant effects on the soil exchangeable cadmium content,and there was an interaction between the two.Regardless of the effect of soil pH,the water management mode has a significant effect on soil exchangeable cadmium content.(2)The effects of different acid or alkali addition on soil pH,cadmium form of soil and cadmium uptake by rice were investigated by pot experiments with different addition amount of acid and alkali solutions.The results showed that the pH of the soil,soil cadmium fractionation and transfer coefficient and bioconcentration factor of rice of roots and stems could be affected by addition of acid and alkali.And the more addition was,the lager influence showed up.These aspects significantly changed when the concentration of acid/alkali at the concentration of 0.1 mol/L per barrel was greater than 240 mL.The regression equation was obtained based on the analysis of the amount of acid-base solution added and the soil pH during the mature period.The formula related to relationship between soil pH and the amount of acid solution added was:y=-0.001x+5.667(R~2=0.888)(0≤x≤460).The formula related to alkaline was:y=(2.767e-8)x~3-(2.269e-5)x~2+0.005x-5.655(R~2=0.882)(0≤x≤870).The more alkaline solution,the lager extent variation of soil pH,the more amount of residual and reducible cadmium speciation,the lower amount of exchangeable cadmium speciation.The behaviors was quite opposite in acid solution.(3)The effects of different soil pH on soil nutrients,soil cadmium forms,iron plaque of surface of rice roots and cadmium uptake by rice was investigated by pot experiments.The results showed that the soil pH pre-experiments and post-experiments was affected by soil buffering and flooding and other factors.The pH values of post-experiments all changed close to neutral.And the stronger the acidity and alkalinity was,the greater the change would be.Soil pH mainly affected the N,P,K and organic matter content of soil by affecting crop growth.Soil pH had a significant effect on the bioavailability of cadmium in soil,cadmium content in various parts of rice,iron content in root iron film and transport enrichment.While soil pH increased from 4 to 10,and the exchangeable cadmium contents in early rice and late rice soils decreased by 44.12%and 49.23%,respectively.The recoverable and residual cadmium contents increased by 96.81%,144.33%,142.98%,and 166.54%respectively.While soil pH increased from 4 to 9,the decline in roots,stems,leaves and brown rice in early rice and late rice was 93.93%,98.72%,95.40%,92.52%and 93.93%,98.72%,95.40%,and 99.52%respectively.The increase of iron content in the surface iron films of early rice and late rice was 96.36%and 124.39%.The decline in root-stem transport and enrichment coefficient of early rice and late rice were 79.37%,94.20%,61.54%,and82.73%,respectively.The fitting equation of soil pH and rice cadmium contamination and yield,which aimed to the guarantee of sufficient rice yield and low cadmium contamination,reached the optimum soil pH range which was for early rice was 6.49-7.34,and which for late rice was 5.17-7.68. |
