It isn't only macroeconomics that is muddled by motivated disagreement over theory, macroecology is burdened with a closely analogous problem. Disputants don't reason from evidence to draw conclusions, they assemble evidence that supports conclusions that they favor.

Researchers have identified a link between the diversity of crops grown in farmlands and the pollution they create in lakes and rivers. . .

In areas where farming is scarce or absent, however, the authors found no perceptible change in dissolved nitrogen concentrations since the early 1900s. Broussard thinks this indicates that the impacts might be reversible if policy changes included incentives for farmers to rotate more crops, decrease their field size, increase the edges of fields and sizes of buffering zones, and incorporate more native perennial grasses into farms and in between fields.

"There has been great progress made to reduce the footprint of agriculture, but there is still room for improvement," says Broussard. "The American farmer is caught in a mode of production that has tremendous momentum and cannot be changed on the farm – it's a policy question now."

They began with the ungrounded bias that small farms and primitive agronomic systems were somehow better, and sought factoids to support the bias.

The results show that since the beginning of the last century, the average farm size in the United States has doubled and the number of farms has fallen by almost two-thirds. Broussard also says that a shift from farm animals and simple plows to the use of machines to till croplands has changed not only the culture but the environmental impact of farming.

"With the growing American farm comes the necessity to use more industrialized means of farming," says Broussard. "Our agricultural practices have always impacted water quality, but over the past century the mechanization of agriculture and the use of more potent fertilizers has caused a greater effect: the nitrogen leakage rate is higher."

Modern farms tend to produce fewer crop varieties; this lower crop biodiversity can negatively impact surrounding watersheds. According to the study, within a given area, a higher biodiversity of crops led to less dissolved nitrogen in surrounding water bodies. The explanation for this phenomenon, Broussard says, is difficult to discern.

"Diverse farms tend to have smaller fields with more edges, which can mean there's a greater buffering effect on nitrogen runoff by surrounding grasslands or woodlands," he says.

A scientist would wonder why the nitrogen leakage rate is higher, and investigate whether there are techniques to prevent that. That is the problem after all. The size of farms, their use of nutrient supplements, the mechanized means of tillage and all of the other attributes of 21st century farming rather than 19th century farming are not the problem unless you are a culture warrior abusing science to support your political preferences.

There is in fact real evidence that plant diversity makes better use of available nutrients. Any given plant doesn't use nutrients uniformly over time. The need varies with the life cycle. A diverse community of plants with different life cycles can even out nutrient use. A second factor of diversity is that different plants acquire nutrients from different soil levels. Nutrients that have leached below the root zone of one species are still available to another, deeper rooted species. The nutrients must run a gauntlet in the biotope space to escape.

Still, why do the nutrients run in the first place? Can this be stopped? The mobility of nutrients in soil is partly due to the ionic attraction or repulsion of nutrients by soil particles, and partly due to the mechanical attributes of soil - particle size and clumping. This suggests that a "smart" fertilizer could be more stable in soil.

There has been work done to solve the problem of nitrogen mobility. It is analogous to insights about human nutrition and medication and can be understood as time release formulation. Complex carbohydrates - rather than simple sugars - have benefits for human nutrition in that nutrients become available at a lower rate over a longer period. Rather than a sugar rush you get a steady burn. Medications that are encapsulated in clever ways work similarly, providing a controlled dosage for longer periods.

There are fertilizer formulations that do similar things. For example, ammonium nitrate has nitrogen in two forms - ammonium and nitrate. The nitrate is analogous to a simple sugar in that it is immediately available to plants. Ammonium is analogous to a complex carbohydrate that must be digested first. Soil bacteria do the work, for a small fee. Using ammonium nitrate is sometimes referred to as a split application, reflecting the time lag required to "digest" the ammonium portion. There's a rush from the nitrate, and then a later rush from the ammonium.

Modern and more sophisticated methods encapsulate fertilizer beads with a polymer coating that slowly dissolves. Such "medications" are comparatively expensive and are used in high value crops often grown in green houses. As the value of fertilizer rises - which seems inevitable to me - the reduced loss of fertilizer to leaching will pay for the encapsulation, and so increase the use of such formulations.

A more interesting method is to alter the ionic and mechanical properties of the soil to retain nutrients better. This is what attention to soil PH, organic matter content and tilth can achieve. A recent application of a very old method - the use of biochar - is very effective for this purpose.

Even more interesting is the doping of biochar with nutrients prior to application. The combination of its ionic character with its mechanical properties make it able to do the "time release medication" trick as well as the "complex carbohydrate" trick while improving soil characteristics. A triple benefit. See this paper which discusses one system for the production of such materials from biomass. Santa, are you listening? I want one.

As it happens my personal preference is for smaller farms and ranches producing diverse products while maintaining a landscape that includes native non-food species. I do it myself and consult with others to enable them to do so as well. Smart fertilizers will make this easier. They help both large and small operations while lowering the environmental impact of agriculture in all forms.