连续4a施有机肥降低紫泥田镉活性与稻米镉含量

Reduction of Soil Cadmium Activity and Rice Cadmium Content by 4-year-consecutive Application of Organic Fertilizer

商品有机肥由于可能含镉(Cd),并在施入后对水稻土中Cd的有效性具有"抑制"和"激活"的双重作用,导致施有机肥的稻米降Cd效应目前仍存在较大不确定性.通过选取湘东地区典型水稻土(紫泥田土种),连续4 a定位监测了大田施用商品有机肥对双季稻稻米的降Cd效应,探索稻米Cd含量与双季稻不同生育期土壤Cd有效性、土壤因子(pH、土壤活性有机碳组分与铁氧化物)的关系.结果表明,施有机肥降低双季稻糙米Cd含量28%~56%,且晚稻糙米Cd含量降幅(43%~56%)高于早稻糙米Cd含量的降幅(28%~45%),降幅的年际波动小.一方面,施有机肥也导致双季稻某些生育期(分蘖盛期自齐穗期)土壤有效态Cd含量平均下降6%~7%;土壤交换态Cd含量降低11%,土壤有机结合态Cd含量提高14%,直接反映土壤Cd有效性的降低.另一方面,施有机肥也稳定提升土壤pH值0.1~0.3个单位,促进土壤环境由酸性向微酸性发展,土壤活性有机碳组分(轻组有机碳、粗颗粒有机碳和细颗粒有机碳)含量大幅提升(53%、77%和107%),间接反映土壤Cd有效性的降低.本研究表明,紫泥田连续施有机肥后,土壤Cd有效性下降是双季稻米Cd含量降低的关键驱动因素.

Because commercial organic fertilizers may contain cadmium(Cd)and may cause the dual effect of"inhibition"and"activation"on Cd availability in paddy soil with organic fertilizer input,the reduction of rice Cd following organic fertilizer application is still uncertain.Herewith,typical purple mud paddy fields were selected in the eastern Hunan Province.The effect of commercial organic fertilizer input on Cd reduction of double-rice paddy ecosystem was monitored for four consecutive years.The relationships between brown rice Cd content,soil available Cd,and soil factors(pH,soil labile organic carbon fractions,and iron oxide)at different growth stages in double-rice paddy fields were investigated.Results showed that the input of organic fertilizer reduced the Cd content in brown rice by 28%-56%.Meanwhile,the decrease of Cd content in brown rice of late rice(43%-56%)was higher than that of early rice(28%-45%),and the inter-annual fluctuation of the decrease was relatively small.On the one hand,soil available Cd content decreased by 6%-7%during several growth stages of double-rice(from tillering peak stage to full heading stage)with organic fertilizer input.Additionally,the content of soil exchangeable Cd was decreased by 11%,whereas the content of organic bound Cd was increased by 14%.This directly reflects the decrease of soil Cd availability.On the other hand,the soil pH value was steadily increased by 0.1-0.3 units following organic fertilizer input,which promoted the development of soil from acidity to slight acidity.Besides,the content of soil active organic carbon(light fraction organic carbon,coarse particulate organic carbon,and fine particulate organic carbon)was increased significantly(53%,77%,and 107%,respectively).This indirectly reflects the decrease in soil Cd availability.This study implies that the decrease of soil Cd availability may be the primary driving force for the reduction of rice Cd content with consecutive organic fertilizer input in purple mud paddy fields.