Effect of organic manures on soil organic matter quality in groundnut growing soils

Abstract

A study on changes in organic matter quality as influenced by continuous application of organic manures was carried out during Kharif, 2016 in an ongoing long-term (9-years old) experiment at RARS, Tirupati. It is essential to know about the organic manure quality and transformation of soil OM which inturn influenced by the humic fraction. The continuous application of organic manures significantly increased humic acid fraction and oxygen containing functional groups of humic acid but decreased optical density (E4/E6 ratio) over control and RDF (Recommended dose of fertilizer i.e.20:40:50 N, P2O5, K2O kg ha-1 for groundnut crop in kharif season). This indicated more aromatic character of humic acid. Different treatments recorded the following ranges of humic acid content from 0.23 to 1.26 g kg1,total acidity (3.4 to 10.1 me g-1), carboxyl groups (1.8 to 3.7 me g-1), phenolic-OH groups (1.6 to 6.5 me g-1) and E4/E6 ratio with narrow range (3.45 to 5.63) at harvest of crop. Potentiometric titrations curves of humic acid obtained from different organic manure treatments were sigmoid in nature, indicating their weak acidic nature. The conductometric titration curves showed slow conductance and the UV spectra were feature less i.e. similar in nature inspite of differences in composition and showed decreased optical density with increased wavelength.