Chemical stabilization of soil organic nitrogen by phenolic lignin residues in anaerobic agroecosystems

Abstract

This review summarizes independent reports of yield decreases in several agricultural systems that are associated with repeated cropping under wet or submerged soil conditions. Crop and soil data from most of these agroecosystems have led researchers to attribute yield decreases to a reduction in crop uptake of N mineralized from soil organic matter (SOM). These trends are most evident in several long-term field experiments on continuous lowland rice systems in the Philippines, but similar trends are evident in a continuous rice rotation in Arkansas, USA and with no-till cropping systems in North American regions with cool, wet climatic conditions in Spring. Soil analyses from some of these systems have found an accumulation of phenolic lignin compounds in SOM. Phenolic compounds covalently bind nitrogenous compounds into recalcitrant forms in laboratory conditions and occurrence of this chemical immobilization under field conditions would be consistent with field observations of reduced soil N supply. However, technological shortcomings have precluded its demonstration for naturally formed SOM. Through recent advances in nuclear magnetic resonance spectroscopy, agronomically significant quantities of lignin-bound N were found in a triple-cropped rice soil in the Philippines. A major research challenge is to demonstrate in the anaerobic agroecosystems that these lignin residues bind sufficient quantities of soil N to cause the observed yield decreases. A key objective will be to elucidate the cycling dynamics of lignin-bound N relative to the seasonal pattern of crop N demand. Anaerobic decomposition of crop residues may be the key feature of anaerobic cropping systems that promotes the accumulation of phenolic lignin residues and hence the covalent binding of soil N. Potential mitigation options include improved timing of applied N fertilizer, which has already been shown to reverse yield decreases in tropical rice, and aerobic decomposition of crop residues, which can be accomplished through field drainage or timing of tillage operations. Future research will evaluate whether aerobic decomposition promotes the formation of phenol-depleted SOM and greater in-season N mineralization, even when the soil is otherwise maintained under flooded conditions during the growing season. r

Spatial variability and classification of soils on a Legon hill catena in the Accra Plains, Ghana

“…The relatively higher amounts of organic C content in the surface horizon of Alajo series might be due to slower rate of mineralization as a result the hypoxic and anaerobic conditions prevailing in this soil (Olk et al, 2006). The dark colour of Alajo series could however not be attributable to the level of organic C but rather to the parent material (Acquaye and Oteng, 1972 ) in Alajo series indicates that it probably contained 2:1 clay minerals.…”

Electrospray and photoionization mass spectrometry for the characterization of organic matter in natural waters: a qualitative assessment

“…They are classified as lignins for the purpose of comparison to the 13 C NMR mixing model, but perhaps they are more likely to be aromatic amines such as alkaloids or the products of polyphenol-peptide binding reactions that are known to occur in the tannin-rich acidic conditions that exist in Lake Drummond. Polyphenol-peptide reaction products have been documented in soils and sediments (Hsu and Hatcher 2005;Olk et al 2006;Mutabaruka et al 2007).…”

Evaluation of structural chemistry and isotopic signatures of refractory soil organic carbon fraction isolated by wet oxidation methods

“…These N compounds could be directly bonded to aromatic rings in lignin residues. Although aromatic binding of N has been demonstrated under laboratory conditions, the field detection attempts using NMR techniques were unsuccessful until when Schmidt-Rohr et al (2004) developed saturation-pulse-induced dipolar exchange with recoupling (SPIDER), an NMR technique involving MAS for selective detection of C that are bonded to N. With this advanced technique, significant amounts of N-bonded aromatic C around 134 ppm (N-C arom ) and N-bonded aliphatic C (N-CH) around 56 ppm were detected (Schmidt-Rohr et al 2004;Olk et al 2006). From the observed signal removal at 56 ppm and signal intensity reduction at 110-160 ppm upon NaOCl oxidation (Figs.…”