Influence of lime on the accumulation of mineral nitrogen in incubation experiments of peat soils

In the present paper the effect of lime on the mobilization of peat nitrogen was studied using incubation experiments under laboratory conditions. In the first experiment in which 13 samples of virgin peat soils were incubated for four months at 7°C, lime caused a marked nitrification of ammonium nitrogen in three samples, and a fairly low increase in the ammonium nitrogen content of five samples. The accumulation of total mineral nitrogen was benefited by lime in five samples and only in one of them could a marked increase be detected. In the second experiment the amounts of lime applied to five peat samples corresponded to 4000, 8000 or 12 000 kg/ha of CaCO3. At the end of an incubation period of four months at 9—15°C the total amounts of mineral nitrogen accumulated did not depend on the fate of liming, as did the nitrification in SCp-and BCp-samples, and also, in part, in the Sp- and CSp-samples. After the prolonged incubation up to 12 months the amount of lime applied had little or no effect upon the accumulation of nitrate-nitrogen or total mineral nitrogen except in the SCp-sample in which a positive correlation between these figures existed. Traces of nitrite-nitrogen were detected in some of the samples incubated for four months with the heaviest applications of lime. In the third experiment carried out at 7°C the treatment with lime was equal to that in the second series, but half of the pots were treated with ammonium nitrate corresponding to 100 kg/ha of nitrogen. The effect of lime on the treated samples appeared to be similar to that in the untreated one. Owing to the large variation, the fate of applied mineral nitrogen could not be distinctly detected. The loss of ammonium nitrogen through volatilization from the most heavily limed pots may be a possible explanation for the lower amounts of total mineral nitrogen in the incubated BCp-samples. Some reasons for these variable results are discussed and attention is also paid to the importance of nitrification on the nitrogen nutrition of plants