## AMMONIUM ION ADSORPTION OF SOME PADDY SOILS

**C.F.CHEN AND P.S.CHIANG(Institute of Soil Science,Academia Sinica)**

Present investigation involves the rate of adsorption of ammonium by some paddysoils in solutions of 0.5,0.2,0.1,0.05,0.025 and 0.01N NH_4Cl with a soil-solution ratioat 1:5.Samples used consist of seven soils collected from Southern Kiangsu with predominant clay minurals of 2:1 types and two from Kiangsi with 1:1 types.Results ob-tained are according to the Langmuir's and Ereundlich's adsorption equations and the correlation coefficients are given.In the Langmuir's equation the r_∞ and Sm are usually considered as representativesof the exchange capacity of soils.However,these figures,both r_∞ and Sm,obtainedfrom calculation and experiment differ from the value of exchange capacity.The application of the Langmuir's equation to soil exchange cation seems to be not feasible forNH_4Cl solutions of above mentioned concentration.A better correlation will be obtained,if the concentration of equilibrium solution(C)in the Freundlich's equation is expressed in term of milliequivalent per 100 grams soilinstad of grams equivalent per litre as used in the original device.In this case,thecalculated value of K is more close to the value of measurement.The constant K in the Freundlich's equation,as a measurement of the intensity ofadsorption of soils,is a maximum value of ions adsorbed by soils from the equilibriumsolution at a low salt concentration(2 m.e.per litre).The relations of K value to thecontent of organic matter and base exchange capacity can be explained by the followingequations with corresponding correlation coefficients.K=0.42+0.45 M(r=0.877,n=9)K=0.03+0.095 S(r=0.945,n=10)K=3.20-0.27 R(r=-0.606,n=11)K=4.85-15.6 E(r=0.835,n=7)where,M denotes the content of organic matter of soils,S is the exchange capacity ofsoils,R is the ratio of organo-mineral complexes of soils(G_0+G_1/G_2),and E is theratio of the “easily releasable ammonium” to total amounts of adsorbed ammonium.Removal of soil organic matter by H_2O_2 decreases the K-value of soils from theoriginal figures about 48—67%.Maintaining the soil u terlogged condition for25 days,the K-value is decreased about 26—56% as compared with the air dried soilsamples.

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