Contents and depth distribution of nitrogen fractions in Kandic Paleustalf soil following long-term cropping with fertilizer and farmyard manure applications

Abstract

Under finger millet - maize - fodder cowpea system, the influence of 13-year long-term cropping with different fertilizer and farmyard manure (FYM) inputs on the contents and depth distribution of organic C, total N (Ni), soil mineralizable N, and organic and inorganic N fractions was investigated in a Kandic Paleustalf. Continuous application of 100% NPK( + S), 150% NPK( + S) and 100% NPK( + S) + FYM led to a marked increase in organic C, total N, hydrolyzable N (viz., amino acid N, hydrolyzable NH(4)-N, hexose amine N and unidentified hydrolyzable N) and nonhydrolyzable N as compared to an adjacent fallow. The contents of various organic N fractions were largest in surface soil and thereafter decreased with the depth. However, at 3045 cm depth the content of organic C was not affected by different treatments except 100% NPK ( + S) + FYM and 150% NPK( + S). On other hand, continuous cropping without fertilization resulted in a depletion of total hydrolyzable N in control over fallow by 16% (0-15cm, 15-30cm) and 13% (30-45cm). The incorporation of FYM with 100% NPK ( + S) resulted in greater contents of soil mineralization N as compared to 100% NPK ( + S) (0-15cm, 15-30cm). The portion of hydrolysable N (56-74%) of N decreased and that of non hydrolysable N (23-42%N) increased with the depth. The portion of amino acid N (19-26%N) hexose amine N (2.5-4% of N) and unidentified hydrolyzable N (13-25% of N) decreased with the depth, whereas that of hydrolyzable NH4-N (18-22% of N) had shown no definite trend. All organic soil N fractions including even nonhydrolyzable N in both surface and subsurface soils were highly significantly correlated with soil mineralyzable N derived from incubations under water logged and aerobic conditions. The best correlation to mineralizable N was found for amino acid N