石灰性物质连续培养及添加镁对土壤pH及镉有效性的影响

Effects of Consecutive Addition of Liming Materials and Magnesium on Soil pH and Available Cadmium

石灰是常用的酸性土改良剂,也是钝化土壤镉有效性和抑制植物吸收镉的有效措施之一。通过培养试验,第1年研究了3种石灰性物质[Ca(OH)_2,Mg(OH)_2和CaCO_3]不同用量对土壤pH及镉有效性的影响,第2年在评估第1年试验结果的基础上研究了连续施用不同用量Ca(OH)_2或与硫酸镁配施对土壤pH及镉有效性的影响。第1年的培养试验结果表明,3种石灰性物质对调节土壤pH的碱性强度顺序是Ca(OH)_2>Mg(OH)_2>CaCO_3。氢氧化镁对降低土壤有效Cd的效果最好,其次是石灰,石灰石粉几乎没有效果。在第2年为期60 d的淹水培养试验过程中,连续施用石灰处理的土壤pH随石灰用量的增加而增加,土壤有效Cd含量变化则呈相反趋势。从连续施用石灰对降低土壤Cd有效性的效果来看,连续施用低量石灰既经济,对土壤Cd有效性的抑制效果又较好,可以在生产中采用。在施用石灰的基础上添加硫酸镁对土壤pH和有效Cd浓度有微小降低作用。而连续施用石灰和连续施用石灰+镁处理的土壤pH变化趋势基本一致,对应的土壤有效Cd浓度变化趋势也一致。因此,石灰是提高土壤pH和降低土壤有效Cd的有效物质,以连续施用低量石灰的效果更佳,增加硫酸镁可以稍微降低土壤有效Cd的浓度,对消除Cd的毒性起到增效作用。

Lime is a commonly used conditioner for acid soil improvement and an effective immobilizer to reduce soil cadmium （Cd） availability and its uptake by crops in Cd contaminated acid soils. Incubation experiments with three liming materials [ Ca（OH） 2, Mg（OH） 2 and CaCO3 ] of different rates in year one and with continued addition of different rates of Ca（OH） 2alone or in combination with magnesium sulfate （Mg） based on the carry-on Ca（OH） 2treatments in year two were conducted to examine the treatment effects on soil pH and Cd availability. The first year results showed that the acidity neutralizing power of the three liming materials was in an order of Ca （OH） 2 〉 Mg （OF/） 2 〉 CaCO3. Mg（OH） 2 performed better than Ca （OH） 2 in reducing soil available Cd, but CaCO3 had litde effect. During the 60 d waterlogged incubation period in year two, the soil pH increased with an increase in lime rates while available soil Cd showed a reverse trend. It revealed that continued application of lower rate of lime could achieve ideal effect on soil Cd immobilization with low cost, which can be used to guide liming program in practice. Adding Mg on the carry-on lime treatments slightly reduced soil pH and available Cd content. Whether lime was consecutively added alone or in combination with Mg, the trend in soil pH and Cd availability changes resembled. It is thus substantiated that lime is an very effective material to raise soil pH and reduce Cd availability with best performance with consecutive ap-plieations of lower rates. Addition of Mg on the basis of lime could further reduce Cd availability, playing a synergistic effect on soil Cd immobilization.