外加氮源在Cd超标菜地上的应用效果

探讨外加氮源对Cd超标菜地不同叶菜吸收Cd及土壤Cd有效性的影响,以明确施氮对土壤Cd的影响效应,并试图对不同氮源的应用效果进行综合评价,为合理利用氮肥来降低叶菜Cd含量提供参考。在Cd含量为0.628 mg·kg?1的Cd超标菜地上,试验研究了氮用量水平为150 kg·hm?2时,4种氮肥(尿素、硝酸钙、硝酸铵、碳酸氢铵)对矮脚葵扇黑叶白菜(Brassica chinensis L.)和白梗尖叶苋菜(Amaranthus mangostanus L.)Cd含量、品质及土壤Cd有效性的效应。结果表明,田间条件下,与不施氮处理相比,4种氮肥均不同程度地增加了Cd超标菜地上2种叶菜产量,降低了其地上部和根系Cd含量。4种氮肥中,尿素对白梗尖叶苋菜的增产效果最好,增产幅度达47.5%;碳酸氢铵对葵扇黑叶白菜的增产效果最好,增幅达59.7%;硝酸钙降低2种叶菜地上部和根系Cd含量的效果均优于其他氮肥,该处理的白梗尖叶苋菜地上部和根系Cd含量分别比对照降低41.6%和24.1%,葵扇黑叶白菜降低32.2%和25.9%。4种氮源对2种叶菜地上部Cd吸收总量、NO3?-N、NO2?-N、维生素C及可溶性糖含量等的影响各异,对土壤p H和DTPA-Cd含量影响也不同。其中,硝酸铵处理的土壤p H分别比对照降低0.12和0.25个单位,而土壤DTPA-Cd含量则显著增加15.3%和14.6%;碳酸氢铵处理则呈相反变化趋势。综合评价结果显示,4种氮肥的综合加权平均值均高于对照处理,以硝酸钙相对最高,表明硝酸钙在Cd超标菜地上的综合应用效果相对最好。因此,在Cd超标土壤上,硝酸钙可作为优选氮源使用。

Effects of nitrogen addition on above-standard Cd-contaminated soils in vegetable fields

The aim of this study was to explore the effects of nitrogen application on Cd uptake by different kinds of leafy vegetables and on soil available cadmium (Cd) content in above-standard Cd-contaminated soils in vegetable fields. The study also comprehensively evaluated the effects of different nitrogen sources application with the aim of developing strategies to reduce Cd concentration in leafy vegetables by managing the application of nitrogen fertilizers. The experiment was carried out in an above-standard Cd-contaminated vegetable soil to investigate the effects of urea CO(NH2)2], calcium nitrate Ca(NO3)2], ammonium nitrate (NH4NO3) and ammonium bicarbonate (NH4HCO3) on yield, quality, Cd content, nitrogen content of two kinds of leafy vegetables — Brassica chinensis L. (BC) and Amaranthus mangostanus L. (AM). Soil DTPA-Cd content and pH as well as comprehensive effects of nitrogen addition on two vegetables were also investigated. The results showed that all nitrogen sources increased yields and decreased Cd contents in both shoot and root systems of the two leafy vegetables. Furthermore, the highest increase of BC yield (59.7%) was caused by NH4HCO3 treatment, while the largest increase of AM yield (47.5%) was caused by CO(NH2)2 treatment, respectively, compared with control. However, the lowest Cd contents in two kinds of leafy vegetables were observed under Ca(NO3)2 treatment among all nitrogen treatments. Ca(NO3)2 decreased Cd content by 41.6% and 24.2%, respectively, in AM shoot and root, by 32.2% and 25.9%, respectively, in BC shoot and root. Moreover, the total content of Cd, nitrate, nitrite, Vitamin C and soluble sugar in the shoot system of the two kinds of leafy vegetables varied with the application of different nitrogen resources. Also similar variances were noted for the changes in soil pH and DTPA-Cd content. NH4NO3 application decreased soil pH by 0.12 and 0.25 and increased soil DTPA-Cd content by 15.3% and 14.6%, respectively, in AM and BC. However, the reverse trend was noted under NH4HCO3 treatment. Comprehensive evaluation results showed that the four kinds of nitrogen resources had much higher synthetic weighted value than that of control. Among all treatments, the highest value was observed in Ca(NO3)2 treatment, which suggested that Ca(NO3)2 had the best comprehensive application effect in above-standard Cd-contaminated soils. Thus Ca(NO3)2 could be used as optimum nitrogen source in above-standard Cd-contaminated soils in vegetable fields.