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 in 21 fixed-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 of 456 representative paddy soil profiles in Zhejiang province showed that

the clay content in plough and plow layers decreased by 14% and 10%

respectively

as compared with their subsurface soils. Comparison investigation from three types of paddy soils developed from coastal sediment (from 10~20 years to>80 years)

quaternary red clay (from 5~20 years to >70 years)

and basalt (from 5~20 years to 35~70 years)

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.