HUMUS-SOIL MINERAL INTERFACE IN ORCHARD AND FARM SOILS: NANOSCALE APPROACH
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Date
2012
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Punjab Agricultural University, Ludhiana
Abstract
Clay-Humus complexes are pivotal for understanding long-term carbon retention in
soils and founding protocols for nutrients, water and tillage management. Very little attempts
were made to decipher the complexes formed under cultivation. Therefore, the study was
undertaken for looking at bonding that different clay-minerals made with humus, imaging and
deciphering interfaces of clay–humus complexes, and their association with land-use. For this,
clays were extracted from surface soils of mango orchard (S1), guava orchard (S2) and ricewheat
cultivated field (S3) of Bahadurgarh (30°21 45 N; 76°28 03 E; 255 m) in Punjab,
India. Clays were untreated, organic matter (OM) was removed, CaCO3 was removed, and
both OM and CaCO3 were removed. They were analyzed by chemical means, by Infra-Red
Spectroscopy (IR), and by Scanning Electron Microscopy and Energy Dispersive
Spectroscopy. IR spectroscopy identified dioctahedral and trioctahedral illites, and
vermiculite, kaolinite, Al-chlorite, and montmorillonite in clays. Humic acids, amides,
quinine, ketones and polysaccharides, and fulvic acids were identified in OM. S1 had phenol,
and CH2 and CH3 groups, while S2 had aliphatic humic and fulvic acids, and aldehyde of
humic acids, and carboxyl and ketonic groups in fulvic acid, and alkenes. The ratio of
Oxydizable OC to clay-humus OC was: S1 (0.049) < S3 (0.054) < S2 (0.060). Micrographs
portrayed uniform spread, irregular spread, and scattered lump of humus on various clayminerals.
The humus from guava field had higher C content (15.60 by atom %) than humus
from mango (12.1 by atom %), and cultivated fields (9.78 by atom %). Strong bond between
clay minerals and humus deforms OH of clay minerals, and causes COO- anti-symmetric
stretching in humus. Presence of phenol compounds in humus on clay surfaces tender
resistance of these complexes to microbial degradation, and could be a crucial factor for N
management in soils.
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Keywords
Soil Science