Fractionation of organic and inorganic nitrogen in important soil types of Kerala

Abstract

In order to study the distribution of various organic and inorganic fractions of soil nitrogen in different soil types of Kerala, 100 surface soil samples belonging to five types were selected from various places of the state. The five soil types were laterite, forest, brown hydromorphic, coastal alluvium and Kuttanad alluvium . Observations on the general characteristics of soil revealed that total nitrogen and organic carbon was highest for forest soil and was least m the case of coastal alluvium . In general all the soil types were acidic in reaction. Electrical conductivity was highest in the case of Kuttanad alluvial soil Fractionation of nitrogen showed that the most dominant fraction in the case of laterite and brown hydromorphic soils a-e AaN and that for forest, coastal alluvium and Kuttanad alluvium is NHyN. Mean total nitrogen content for laterite soils is 0.174 per cent. Of this, 27 59 percent was AaN, 20.69 per cent FAN, 16.67 per cent NHyN, 14.94 per cent HyAN, 11.67 per cent UHyN, 3.85 per cent NH4-N, 2. 64 per cent NO3-N and 1. 95 per cent HyAN. The mean value of total nitrogen content of the forest soil was 0 304 per cent. Of this 41. 45 per cent was NHyN, 1 / 86 per cent AaN, 12.24 per cent HaN, 10.63 per cent FAN, 10.36 per cent UHyN 3.36 per cent NH4-N, 2. 37 per cent HyAN and 1. 74 per cent NO3-N The mean total nitrogen content of the brown hydromorphic soil was 0 180 per cent Of this, 21.60 per cent was AaN, 21 25 per cent UHyN, 18.20 per cen4, NHyN,17.20 per cent FAN, 13.76 per cent HaN, 3.16 per cent HyAN, 3.11per cent NH4-N and 1.67 per cent NO3-N. The mean content of total nitrogen of the coastal alluvial soil was 0.161 per cent. Of this,27.65 per cent NHyN, 22.26 per cent AaN, 19.96 per cent UHyN, 12.40 per cent FAN, 6.51 per cent HaN, 6.26 per cent HyAN, 3.10 per cent NH4-N and 1.74 per cent NO3-N. The mean content of total nitrogen of the Kuttanad alluvial soil was 0.2705 per cent. Of this, 37.04 per cent was NHyN, 15 16 per cent AaN, 14.94 per cent FAN, 11.42 per cent HaN, 10.76 per cent UHyN, 3.99 per cent NO3-N, 3 70 per cent NH4-N and 2.96 per cent HyAN In all the five soil types there was significant positive correlation between cation exchange capacity and FAN On studying the relationship of various nitrogen fractions to organic carbon on the selected soil types of Kerala revealed that 75 per cent variation of organic carbon in laterite soil, 87 per cent Variation of organic carbon in forest soil and 70 per cent variation of organic carbon in brown hydromorphic soil can be explained by the nitrogen fractions of the soils The significant relationship obtained between AaN and alkaline KMnO4 -N, considers alkaline KMn04-N as a reliable method of available nitrogen estimation, in the laterite soils of Kerala. In the three soil types, viz., crown hydromorphic, coastal alluvium and Kuttanad alluvium , a significant relationship between the alkaline i KMnO4-N and nitrogen fraction could not be established. So for these types of soil, a better analytical method of available nitrogen than that of alkaline KMnO4-N has to be taken up.