Effect of superphosphate on the mobilization of nitrogen in a peat soil

Abstract

The influence of superphosphate on the mobilization of nitrogen in a fen soil from Leteensuo Experiment Station in southern Finland was studied. Samples were used from a field trial in which superphosphate had been annually applied for 35 years in amounts of 0, 100, 200, and 300 kg/ha, resp. Analyses were performed on samples of four layers: 0 to 10 cm, 10 to 20 cm, 40 to 50 cm, and 60 to 70 cm. It was found that the mineral nitrogen (NH4-N + NO3-N) content of the soil samples collected late in the autumn was in all layers highest in the plots treated with the highest amount of superphosphate. The positive effect of the treatment with 200 kg/ha of superphosphate reached down to the layer of 40 to 50 cm. In the soil treated with 100 kg/ha the mineral nitrogen content was higher than in the untreated soil only in both surface layers. In the incubation experiment of five and ten weeks the differences in the mineral nitrogen content were equalized, particularly in the samples from deeper layers. In the top layers the superiority of the heaviest treatment was maintained. The amounts of nitrogen in the hay yields harvested in the previous summer appeared, generally, to be the higher the larger the amounts of superphosphate applied. It seemed to be probable that potassium was a minimum factor in the plots of the heaviest superphosphate treatment. Comparison of the present results with data obtained from the same experiment when it had been only run for five years indicated that, in regard to the availability of nitrogen in this peat soil, the slight tendency found thirty years ago had grown to the distinct superiority of the heavy superphosphate treatment.