Sustainable Farming

The accepted agricultural wisdom is that fertilized fields in which plant residue is left in the field will actually gain soil carbon. Unfortunately, it seems the reverse is true - a study by University of Illinois scientists has shown that in their long term (1876-) test fields, soil carbon levels increased steadily till around 1965, when animal manure was used as fertilizer, and started declining after that, with the use of synthetic nitrogen fertilizers.

With decreasing soil carbon (humus), the soil structure deteriorates, as does the capacity of the soil to hold on to nitrogen. As nitrogen leaches out with water, the land needs more fertilizers to stay productive, creating a vicious cycle.

From the paper Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen: A Global Dilemma for Sustainable Cereal Production

... Overwhelmingly, the evidence is diametrically opposed to the buildup concept and instead corroborates a view elaborated long ago by White (1927) and Albrecht (1938) that fertilizer N depletessoil organic matter by promoting microbial C utilization and N mineralization. An inexorable conclusion can be drawn: The scientific basis for input-intensive cereal production is seriously flawed. The long-term consequences of continued reliance on current production practices will be a decline in soil productivity that increases the need for synthetic N fertilization, threatens food security, and exacerbates environmental degradation.

This dilemma calls for an international effort by agricultural scientists to thoroughly review, evaluate, and revise current cereal production and management systems and policies. The immediate need is to use scientific and technological advances that can increase input efficiencies. One aspect of this strategy would be to more accurately match the input of ammoniacal N to crop N requirement by accounting for site-specific variations in soil N-supplying capacity and by synchronizing application with plant N uptake. In the long term, a transition may be required toward agricultural diversification using legume-based crop rotations, which provide a valuable means to reduce the intensity of ammoniacal fertilization with the input of less reactive organic N.

Science Magazine has an excellent overview of the challenges of optimizing food production for 9 Billion people over the next 40 years:

Producing more food from the same area of land while reducing the environmental impacts requires what has been called "sustainable intensification". In exactly the same way that yields can be increased with the use of existing technologies, many options currently exist to reduce negative externalities. Net reductions in some greenhouse gas emissions can potentially be achieved by changing agronomic practices, the adoption of integrated pest management methods, the integrated management of waste in livestock production, and the use of agroforestry. However, the effects of different agronomic practices on the full range of greenhouse gases can be very complex and may depend on the temporal and spatial scale of measurement. More research is required to allow a better assessment of competing policy options. Strategies such as zero or reduced tillage (the reduction in inversion ploughing), contour farming, mulches, and cover crops improve water and soil conservation, but they may not increase stocks of soil carbon or reduce emissions of nitrous oxide. Precision agriculture refers to a series of technologies that allow the application of water, nutrients, and pesticides only to the places and at the times they are required, thereby optimizing the use of inputs. Finally, agricultural land and water bodies used for aquaculture and fisheries can be managed in ways specifically designed to reduce negative impacts on biodiversity.

This is the kind of research we need if farming is to become truly scientific:

"What is the importance of the involvement of microbes in plants? It hasn't really been examined," Bais notes. "We think that plants are doing everything on their own, but there is a whole world of microbes underground, associated with the roots of plants, that has yet to be analyzed."

Scientists have long known the symbiotic relationship between legume plants such as beans and the bacteria known as rhizobia that colonize the plants' roots and enable the plants to convert nitrogen from the air into fertilizer.

More recently, in research reported last fall, Bais and his colleagues showed that when the leaves of the small flowering plant Arabidopsis thaliana were infected by a pathogen, the plant secreted an acid to recruit beneficial bacteria in the soil (Bacillus subtilis) to come to its defense.