ON THE CHARACTERICTICS AND FORMATION OF CALClFIED PADDY SOIL IN SOUTH CHINA

The calcified paddy soil induced by long time overliming is a poor agricultural soilin Southern China.Contrary to the usual soil types in this area which use to have anarrow Ca/Mg ratio in their carbonate salts,the calcified paddy soil contains mainlycalcium carbonate in its accumulated salts.The accumulation of calcium carbonate increases with the decrease of depth in soil profile.It varies from10% in surfacelayers and around 1% in deeper subsoils.A plowpan layer composed by lime concretions and pans usually presents below the surface soil.Liming is a usual practice in rice plantation in Southern China,but formation ofcalcified paddy soil confines only in soils of poor permeability with low organic mattercontent.Application of organic fertilizers and increase of green manures in rotation system seem to be effective practice for the reclamation of calcified paddy soil.The calcified paddy soil contains calcium carbonate about 33,562 to 54,451Kin/Mow to a depth of one meter.Under the present agricultal practice,an annual accumulation of 100 Kin CaCO_3/Mow will be expected,and the formation of the calcifiedpaddy soil in this area is estimated having through a period of 340—540 years.