A fundamental shift has taken place in agricultural research and world food production. In the past, the principal driving force was to increase the yield potential of food crops and to maximize productivity. Today, the drive for productivity is increasingly combined with a desire for sustainability. For farming systems to remain productive, and to be sustainable in the long-term, it will be necessary to replenish the reserves of nutrients which are removed or lost from the soil. In the case of nitrogen (N), inputs into agricultural systems may be in the form of N-fertilizer, or be derived from atmospheric N2 via biological N2 fixation (BNF).

Biological nitrogen fixation: An efficient source of nitrogen for sustainable agricultural production?

http://directory.umm.ac.id/Data%20Elmu/jurnal/A/Agriculture,%20Ecosystems%20and%20Environment/Vol83.Issue1-2.Jan2001/1692.pdf

Organic inputs for soil fertility management in tropical agroecosystems: Application of an organic resource database

Dissolved and water-extractable organic matter in soils: a review on the influence of land use and management practices

Tannins make up a significant portion of forest carbon pools and foliage and bark may contain up to 40% tannin. Like many other plant secondary compounds, tannins were believed to function primarily as herbivore deterrents. However, recent evidence casts doubts on their universal effectiveness against herbivory. Alternatively, tannins may play an important role in plant–plant and plant–litter–soil interactions. The convergent evolution of tannin-rich plant communities on highly acidic and infertile soils throughout the world, and the intraspecific variation in tannin concentrations along edaphic gradients suggests that tannins can affect nutrient cycles. This paper reviews nutrient dynamics in forest ecosystems in relation to tannins. Tannins comprise a complex class of organic compounds whose concentration and chemistry differ greatly both among and within plant species. Because the function and reactivity of tannins are strongly controlled by their chemical structure, the effects of tannins on forest ecosystem processes are expected to vary widely. Tannins can affect nutrient cycling by hindering decomposition rates, complexing proteins, inducing toxicity to microbial populations and inhibiting enzyme activities. As a result, tannins may reduce nutrient losses in infertile ecosystems and may alter N cycling to enhance the level of organic versus mineral N forms. The ecological consequences of elevated tannin levels may include allelopathic responses, changes in soil quality and reduced ecosystem productivity. These effects may alter or control successional pathways. While a great deal of research has addressed tannins and their role in nutrient dynamics, there are many facets of tannin biogeochemistry that are not known. This lack of information hinders a complete synthesis of tannin effects on forest ecosystem processes and nutrient cycling. Areas of study that would help clarify the role of tannins in forest ecosystems include improved characterization and quantification techniques, enhanced understanding of structure-activity relationships, investigation of the fate of tannins in soil, further determination of the influence of environmental factors on plant tannin production and decomposition, and additional information on the effects of tannins on soil organisms.

Tannins in nutrient dynamics of forest ecosystems- a review

The ecological activities of plant phenolics are diverse and highly variable. Although some variation is attributable to differences in concentration, structure, and evolutionary history of association with target organisms, much of it is unexplained, making it difficult to predict when and where phenolics will be active. I suggest that our understanding is limited by a failure to appreciate the importance of oxidative activation and the conditions that influence it. I summarize examples of oxidative activation of phenolics in ecological interactions, and argue that physicochemical conditions of the environment that control phenolic oxidation generate variation in ecological activity. Finally, I suggest that measurements of oxidative conditions can improve our predictions of phenolic activity and that experiments must be designed with conditions appropriate to the biochemical mode of phenolic action.

Phenolics in ecological interactions: The importance of oxidation.

A 12-week greenhouse experiment was conducted to determine the effect of the polyphenol, lignin and N contents of six legumes on their N mineralization rate in soil and to compare estimates of legume-N release by the difference and 15N-recovery methods Mature tops of alfalfa (Medicago sativa L), round leaf cassia (Cassia rotundifolia Pers, var Wynn), leucaena (Leucaena leucocephala Lam, deWit), Fitzroy stylo (Stylosanthes scabra Vog, var Fitzroy), snail medic (Medicago scutellata L), and vigna (Vigna trilobata L, var verde) were incorporated in soil at the rate of 100 mg legume N kg-1 soil The medic and vigna were labeled with 15N Sorghum-sudan hybrid (Sorghum bicolor, L Moench) was used as the test crop A non-amended treatment was used as a control Net N mineralization after 12 weeks ranged from 11% of added N with cassia to 47% of added N for alfalfa With the two legumes that contained less than 20 g kg-1 of N, stylo and cassia, there was net N immobilization for the first 6 weeks of the experiment The legume (lignin + polyphenol):N ratio was significantly correlated with N mineralization at all sampling dates at the 005 level and at the 001 level at 6 weeks (r2=0866) Legume N, lignin, or polyphenol concentrations or the lignin:N ratio were not significantly correlated with N mineralization at any time The polyphenol:N ratio was only significantly correlated with N mineralization after 9 weeks (r2=0692) The (lignin + polyphenol):N ratio appears to be a good predictor of N mineralization rates of incorporated legumes, but the method for analyzing plant polyphenol needs to be standardized Estimates of legume-N mineralization by the difference and 15N recovery methods were significantly different at all sampling dates for both 15N-labeled legumes After 12 weeks, estimates of legume-N mineralization averaged 20% more with the difference method than with the 15N recovery method This finding suggests that estimates of legume N available to subsequent crops should not be based solely on results from 15N recovery experiments

The nitrogen mineralization rate of legume residues in soil as influenced by their polyphenol, lignin, and nitrogen contents

The recovery of fertiliser N by sugarcane crops is low in comparison with most other field crops. Application of urea in subsurface bands instead of by broadcasting can greatly reduce loss of fertiliser N due to ammonia volatilisation, but the fertiliser N is still susceptible to loss from leaching or denitrification, which could be affected by soil internal drainage, trash management, or tillage practice. The recovery of fertiliser N in crops and soil from 15N-labelled urea applied as subsurface bands was measured in ratoon crops in southern Queensland and northern New South Wales. Two soil types, with contrasting internal drainage, were used in each region. In Queensland, the cultural practice was either trash burnt with inter-row cultivation or trash retained on the surface ('trash blanket') with no cultivation. In northern New South Wales, where the trash was burnt prior to harvest, the practice was either inter-row cultivation or zero tillage. Crop recovery of fertiliser N was nearly always in the range 20-40% of the amount applied. Residual fertiliser N in the soil at crop maturity ranged from 13 to 42% (average 26%). Total recovery of fertiliser N in the soil-plant system ranged from 35 to 76% (average 52%) at 6 months after application, and from 35 to 96% (average 56%) at crop maturity. Urea fertiliser supplied only 20-40% of the crop N uptake in a given season. Neither crop recovery nor loss of fertiliser N from the soil-plant system were related to the soil type or cultural practice used, indicating that compensatory effects occurred.

I Vallis

Papers

The nitrogen mineralization rate of legume residues in soil as influenced by their polyphenol, lignin, and nitrogen contents

Recovery in plants and soils of 15N applied as subsurface bands of urea to sugarcane

Recovery in plants and soils of