CHEMICAL STABILIZATION OF SOIL ORGANIC NITROGEN BY PHENOLIC LIGNIN RESIDUES IN ANAEROBIC AGROSYSTEMS

Authors: Olk, Daniel - Dan; CASSMAN, K - UNIV. OF NEBRASKA-LINCOLN; SCHMIDT-ROHR, K - IOWA STATE UNIVERSITY; ANDERS, M - UNIVERSITY OF ARKANSAS; MAO, J - ROCKY MOUNTAIN COLLEGE; DEENIK, J - UNIVERSITY OF HAWAII

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2005
Publication Date: 11/1/2006
Citation: Olk, D.C., Cassman, K.G., Schmidt-Rohr, K., Anders, M.M., Mao, J.D., Deenik, J.L. 2006. Chemical stabilization of soil organic nitrogen by phenolic lignin residues in anaerobic agrosystems. Soil Biology and Biochemistry. 38(11):3303-3312.

Interpretive Summary: This report summarizes independent accounts of yield losses in wet cropping systems such as rice and taro, in which soils are flooded for several months during the growing seasons. No-tillage of Midwestern crops can also lead to wet soil conditions for extended times. In our recent research and in a review of the literature, we found that yield losses reported in these cropping systems were usually associated with deficient crop uptake of soil nitrogen, an essential plant nutrient. In this report we summarized evidence that nitrogen is chemically bound by organic molecules that persist in wet soils, inhibiting its availability to the crop and that nitrogen availability may be improved by increased aeration of the soil, especially during decomposition of straw and roots from the previous crop. Identification of fundamental soil processes that cause the yield losses in these anaerobic cropping systems and the demonstration of timely soil aeration as a mitigation option would enable the development of field strategies for maintaining nitrogen availability and sustainable yields in these wet cropping systems. These results would enable farmers to obtain maximum yields while making efficient use of soil nitrogen and fertilizer nitrogen.

Technical Abstract: This review summarizes independent reports of yield decreases in agricultural systems that are associated with repeated cropping under wet or submerged soil conditions. Crop and soil data attribute the yield decreases to a reduction in crop uptake of nitrogen (N) mineralized from soil organic matter (SOM). These trends are most evident in long-term field experiments on continuous lowland rice systems in the Philippines, but similar trends are evident in a continuous rice rotation in Arkansas 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. Through recent advances in nuclear magnetic resonance spectroscopy, agronomically significant quantities of lignin-bound N were found in a triple-cropped rice soil from the long-term experiments in the Philippines. Anaerobic decomposition of crop residues appears to 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 a change in timing of tillage operations or field drainage. 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. The goal is to increase the efficiency of mineralized soil N utilization by the crop, enabling a reduction in N fertilizer rates while avoiding yield losses from N deficiency.