长期水耕植稻对水稻土耕层质地的影响

Effect of Long-term Rice Plantation on Texture of Tillage Layer in Paddy Soils

为了解长期水耕植稻对南方地区水田表土层颗粒组成的影响,以浙江省为研究区,采用历史资料分析、典型样区调查及定点观察相结合的方法,研究水稻土耕作层(包括犁底层)与心土层间黏粒含量的差异,分析植稻时间对水稻土不同土层颗粒组成的影响,比较植稻期间稻田排水中泥砂物质的颗粒组成与对应土壤间的差异,探讨了长期植稻对水稻土剖面质地分异的影响。对浙江省456个代表性剖面统计,与水稻土心土层比较,耕作层和犁底层黏粒含量平均下降了14%和10%。对植稻不同时间的浅海沉积物(从10～20年至>80年)、第四纪红土(从5～20年至>70年)和玄武岩风化物(从5～20年至35～70年)发育的水稻土比较发现,随植稻时间的增加,耕作层和犁底层土壤砂粒含量呈现增加趋势,黏粒含量明显下降,耕作层、犁底层与心土层黏粒含量的比值逐渐下降。农田排水中泥砂物质的黏粒和粉砂含量高于对应农田土壤,而砂粒含量则低于相应的土壤。分析认为,长期水耕植稻可导致耕作层土壤砂化(即砂粒含量增加,黏粒含量下降),其原因除与水耕过程中黏粒淋淀外,排水中黏粒和粉砂细颗粒的选择性流失对耕作层砂化也有较大的贡献。

To understand the effect of long-term rice cultivation on the particle composition of surface soil layer in paddy field of the southern China,the difference in clay content between tillage layer(including plow layer)and subsurface of paddy soils was studied using historical data,the influence of rice cultivation time on the particle composition of different soil layers in the paddy soils was investigated in three typical areas,the difference in particle composition between field drainage sediments and corresponding paddy soils was compared in21fixed-point observation fields.The effect of long-term rice plantation on the texture differentiation of the paddy soil profiles was discussed.All investigations were carried out in Zhejiang province.Statistical results of456representative paddy soil profiles in Zhejiang province showed that,the clay content in plough and plow layers decreased by14%and10%,respectively,as compared with their subsurface soils.Comparison investigation from three types of paddy soils developed from coastal sediment(from10~20years to>80years),quaternary red clay(from5~20years to>70years),and basalt(from5~20years to35~70years),respectively,showed that contents of sand in the plough and plow layers in the soils increased with increasing rice plantation time,while that of clay decreased with increasing rice plantation time.The ratio of the clay content of the plough and plow layers to their subsurface decreased gradually with the increase of the rice plantation time.The contents of clay and silt in the sediments from farmland drainage were higher than those in the corresponding farmland soils,while the sand content was lower than that in the corresponding soils.It was considered that long-term rice cultivation could result in soil sanding with increase of sand and decrease of clay.That was due to both the selective loss of clay and silt particles in the drainage and mechanical eluviations of clay particles during anthropogenic tillage.