通讯机构：
[Ouyang, NX ; Wei, X ; Ouyang, NX] H;Hunan Univ Finance & Econ, Changsha 410205, Peoples R China.;Hunan Econ Geog Technol Dev Co Ltd, Changsha 410205, Peoples R China.;Hunan Agr Univ, Coll Resources & Environm, Changsha 410128, Peoples R China.
关键词：
Available silicon;Parent material;Machine learning;Plough layer;Subsurface layer
摘要：
Silicon can promote rice growth and reduce the toxicity of heavy metals in rice. However, controlling factors for the vertical distribution of silicon in typical paddy soils in mid-subtropical regions of China remain largely unexplored. Here, we aimed to analyze the silicon content in plough and subsurface layers derived from six parent materials in Hunan Province (southern China) based on 62 soil profile samples. Multiple stepwise regression, random forest, and gradient boosting machine learning models were used and compared to predict soil available silicon content and quantify the contribution of different variables on silicon variation. We found that plough layers in the eastern (85% of points) and western (78% of points) Hunan Province were deficient (< 100 mg kg(-1)) in available silicon content. Total silicon content in paddy soil derived from slate (623 & PLUSMN; 100 g kg(-1)) and limestone (606 & PLUSMN; 74 g kg(-1)) was higher than in other soils. The available silicon content was the lowest in granite (51 & PLUSMN; 15 mg kg(-1)). It was closely correlated with available cadmium while being mainly influenced by soil pH, organic carbon, and bulk density. The prediction model of available Si established using a random forest had the highest accuracy (R-2 = 0.74). Widespread deficiency in available silicon content in plough layers of paddy soil in mid-subtropical China highlights the importance and value of higher silicon fertilizer input in soils.
通讯机构：
[Yangzhu Zhang] C;College of Resources and Environment, Furong District, Hunan Agricultural University, Changsha, People’s Republic of China
关键词：
Paddy soil;Rice;Si plus Ca application;Cadmium;Alleviation
摘要：
Cadmium (Cd) contamination threatens the safety of rice and seriously endangers human health. In plot and field experiments, the effect of combined silicon (Si) and calcium (Ca) application on Cd toxicity and accumulation by rice was investigated in low and moderately Cd-contaminated paddy soils. Two types of Si fertilizers, limestone, and novel composite soil amendment (Si + Ca) were soil-applied before rice planting. The Si + Ca treatment increased rice yield by 1.0 to 6.0% in pot test and by 0.9 to 16.6% in field test and reduced the bioavailable soil Cd by 13.5 to 38.7%. The bioconcentration factor (BCF) of Cd depended on the level of soil contamination, being higher under slight contamination. As a result, the Cd concentration in the control rice exceeded the 0.22 mg kg(-1) standard even in low polluted paddy soil. The Si + Ca composite provided the reductions in the grain Cd by 42 to 75%, demonstrating better efficiency than Si or Ca alone. The Si and Ca mostly restrained the Cd root-to-stem transport. Comparative analysis of BCF, translocation factor, and grain Cd under different treatments evidences the synergetic reducing effect of Si + Ca on Cd uptake and accumulation by rice. To alleviate Cd contamination in the paddy soil-rice system, Si + Ca combined application could be effective and worth to be recommended.
通讯机构：
Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, National Engineering Laboratory for Improving Quality of Arable Land, Beijing, China
关键词：
Cadmium;Cd fractions;Consecutive liming;Paddy field
摘要：
Liming has been widely used to remediate Cd-contaminated acidic soils, but the effects of consecutive liming are still unclear. Four-year liming experiments were conducted to assess the remediation of Cd-contaminated acidic paddy fields in a double rice cropping system. With four-year consecutive liming (quicklime, 2.25tha(-1) per season), the soil pH was increased by an average of 0.57 units (0.10-1.16 units), while the soil DTPA-Cd and available Fe and Mn were reduced by 9%, 19% and 31% (p<0.05), respectively. The exchangeable plus water-soluble Cd fraction in soil was reduced by 17%, while the soil carbonate-, Fe/Mn oxide- and organic-bound Cd fractions were increased by 23%, 41% and 10% (p<0.05), respectively. The Cd in rice grain was reduced by 55% for early rice and 63% for late rice (p<0.05) and in some cases was reduced to below the Chinese allowable limit (0.2mgkg(-1)). High annual fluctuations in rice grain Cd could be caused by variations in the field water regime and in rainfall. With consecutive liming, the soil pH, DTPA-Cd and rice grain Cd varied greatly in the first three seasons and then remained relatively less variable. Meanwhile, soil available nutrients (N, P and K) and rice grain yield were little affected by liming. Soil DTPA-Cd linearly decreased with increasing soil pH, while the reduction of Cd in rice grain logarithmically decreased with increasing soil pH and the reduction in soil DTPA-Cd in the heading stage, indicating potential implications for forecasting rice grain Cd content. Therefore, consecutive liming with quicklime can be recommended for the remediation of Cd-contaminated acidic paddy fields, though supplementary measures are still necessary.
摘要：
Excess cadmium (Cd) in agricultural soils can be taken up by rice plants and concentrated in the grain, presenting a human health risk. In this study, we field tested the effects of three foliar treatments (zinc (Zn) alone, or combined with manganese (ZnMn) or phosphorus (ZnP)) on the Cd concentration and grain yield of six rice cultivars (C Liangyou 7, Fengyuanyou 272, Xiangwanxian 12, Tianyouhuazhan, Xiangwanxian 13, and Jinyou 284) at the grain filling stage. Our results showed that rice yield and Cd, Zn, Mn, P, and K concentrations were significantly different among the cultivars (p < 0.05); for example, Jinyou 284 recorded lower Cd levels than any other cultivar. Application of Zn, ZnMn, and ZnP had no significant effect on rice yield and Mn, P, and K concentrations for all cultivars. Compared with the control, Cd concentrations after treatment with Zn, ZnMn, and ZnP decreased by 19.03-32.55%, 36.63-55.78% (p < 0.05), and 25.72-49.10%, respectively, while Zn concentrations increased by 11.02-29.38%, 10.63-32.67%, and 11.97-36.82%, respectively. There was a significant negative correlation between Cd and Zn concentrations (p < 0.01). All three treatments increased Zn and reduced Cd concentration in rice grains, though ZnMn was most effective. Therefore, cultivar selection and Zn fertilizer application are effective strategies to minimize Cd concentration in rice grains. However, the lowest result still exceeded the Chinese Cd safety limit (0.2 mg Cd kg(-1)) by a factor of 2.6, demonstrating that additional effective measures should be simultaneously used to further reduce the accumulation of Cd in rice grains.
摘要：
The efficiency of heavy metal (HM) phytoextraction from contaminated soil directly depends on the pollutant bioavailability, which can be increased by some soil amendments. In field test, the impacts of soil-applied ethylenediaminetetraacetic acid (EDTA) and amorphous silicon dioxide (ASD) and foliar-applied monosilicic acid (MS) on cadmium (Cd) uptake by rice plants from contaminated paddy soil were investigated. Without EDTA, the solid or liquid Si materials reduced the Cd accumulation in the aboveground part of rice by 26 to 52%. If EDTA was applied, the Cd accumulation by plants was increased by 60 to 92%; however, the biomass was reduced by 16 to 35%. The combined application of Si-rich materials and EDTA provided enhanced plant tolerance to a negative influence of EDTA, while kept high Cd content in the rice stems and leaves. As a result, the Cd amounts extracted by the stems and leaves from the unit area of contaminated paddy soil were greater by 25 and 37% in comparison with those for only EDTA treatment.
