Recently in organic farming Category

There's an interesting discussion of this issue at Biology Fortified blog. The post is by my first MS student, Andy McGuire, who also has interesting things to say on a blog from Washington State University, where he works.

Andy's post was apparently inspired partly by something I wrote last year, showing my estimates of how much nitrogen flows from synthetic fertilizer to conventional corn to chicken manure to organic farms.

I don't get too excited about whether organic farmers should be allowed to use manure from conventional farms, or whether we should "blame" them for the fertilizer used to grow the corn to feed the chickens. My point was simply that this dependence limits the potential for expanding organic agriculture. (So advocates of organic farming should be showering me with money for research on nitrogen-fixing legume crops and forages -- but that's another story.)

More interesting is this open-access paper, titled "To what extent does organic farming rely
on nutrient inflows from conventional farming?
" The paper has some actual numbers on nutrient fluxes to organic farms from conventional ones in France. While my earlier diagram assumed that an organic farm relied entirely on manure whose nitrogen originally came from synthetic fertilizer, the French study estimated that only 23% of nitrogen (though 73% of phosphorus) supply to organic farms came from conventional sources. But let's look at some details.

First, there are apparently some differences from US practices:

"European regulations recommend to use organically produced animal manure but allow the use of conventionally produced manure, provided that it is not the output of 'factory farming'."

I don't think we have that restriction in the US. Second, they found that:

"More than 80% of nutrient inflows through manures (82%, 85% and 81% for N, P and K, respectively)... came from conventional farming"

So 82% of N in manure came from conventional farms, but that was only 23% of estimated total N supply. The rest (almost 60% of total N inputs) was mostly estimated to come from biological nitrogen fixation:

"N fixation was estimated using the model proposed by Høgh-Jensen et al (2004)... based on the total N amount in leguminous crop biomass, multiplied by the ratio between the amount of symbiotically fixed N and the total N amount in the crop biomass."

That seems to be about all they said about biological nitrogen fixation -- I would have liked a little more detail. They also say that unsustainable "soil nutrient mining" (failure to replace nutrients exported in crops or otherwise lost from soil) was "not considered." A simple approach to that problem would have been to estimate nitrogen and phosphorus contents of products sold off-farm, and compared that to total inputs. If inputs exceed outputs, some of the difference may end up polluting groundwater, although some may be accumulating in soil, at least for a while. If outputs exceed inputs (including biological nitrogen fixation), over the long term, they will not be able to continue farming over the long term.

My conclusion is that organic farms that rely on manure from other farms (or on manure from their own animals, which are fed grain or hay from other farms) are dependent on conventional farms and therefore not a model that can be scaled up. That doesn't mean they are not making a positive contribution, if they are using manure that would otherwise end up polluting rivers.

If we can believe the nitrogen-fixation estimates in this paper, French farms are already getting a majority of their nitrogen from symbiotic rhizobia in the root nodules of their legume crops and forages. Maybe that could be scaled up. But if 75% of their phosphorus is coming from manure from conventional farms anyway, there may be little point in trying to replace the nitrogen in that manure with biological nitrogen fixation.

Field Crops Research, a leading agricultural journal, has just published a review of Darwinian Agriculture by Jeffrey White. He suggests that there is "ample scope for debate and further research on specific propositions of Darwinian Agriculture." I agree and look forward to those debates. For example, I argued that perennial grain crops may never approach the yields of annual grains, because perenniality requires investing resources in over-wintering that could otherwise by used for grain. White agrees that this may be true in temperate climates, but maybe not in the tropics, if the "off-season" is short. He gives "perennially cropped sugarcane fields" as an example.

I agree that perennials can potentially capture a larger fraction of annual solar radiation, as I noted in the book. For example, a time-lapse movie of rice growth shows that this "annual crop" (which may be grown 2 or 3 times in a year) completely covers the ground only a small fraction of the time. Most of the time, sunlight is mainly hitting soil, evaporating water rather than powering photosynthesis. Perennials can use some of last-season's photosynthate to power rapid leaf growth, capturing a larger fraction of solar radiation sooner.

This isn't only true in the tropics. For example, the book cites a study showing that perennial Miscanthus can produce more biomass than corn. The photo below shows the Miscanthus plots Steve Hamilton showed me at Michigan State's Kellogg Biological Station, where I gave a talk earlier this month. But this Miscanthus doesn't produce any seed and I don't think sugarcane produces much.
What about perennial grasses that do produce significant amounts of grain? Sieglinde Snapp and colleagues at Kellogg Biological Station and The Land Institute have shown that perennial intermediate wheatgrass (kernza) can reduce nitrate concentrations in soil water much more than annual wheat, presumably reducing pollution of wells and rivers. But its first-year grain yield was only 112-157 kg/ha, versus 2807-3761 kg/ha for annual wheat. (Interestingly, the higher yields were with organic management.) Second year yields were 1390-1662 kg/ha for the perennial versus 4248-5017 for the annual. Unless the perennial really improves in subsequent years, the perennial would take more than three times as much land to produce the same amount of grain. I worry that the additional land will come from clearing forests or draining wetlands.

Organic vs. sustainable?

| No Comments

Do organic farming rules sometimes undermine sustainability? See this blog post by Andy McGuire, who earned an MS with me (for his research on legume cover crops) in 1996. Some of the comments are worth reading as well. The one by "RachelL" raises some of the same issues as the last chapter of my book.

Scaling up?


The online magazine Next City quotes me in an informative story about urban farming.

Dunn admits there aren't enough high-end restaurants or CSA customers willing to pay a premium for the produce generated by 10 or 20 one-acre [urban] farms, much less 10,000. He's looking for alternative buyers, such as hospitals or schools, but has yet to hit on a scalable option.

So-called "vertical farms" have additional problems, but I run into this scaling problem all the time.

When I was at UC Davis, people gushed about how much "more sustainable" a farm that grew seeds of native plants was, relative to those growing wheat, almonds, or tomatoes. Great, but that one farm pretty much saturated the market for native-plant seeds.

My brother earns a reasonable income growing wonderful vegetables and fruits organically, but that doesn't mean it would be easy to convert all our farms to organic methods. If each acre of organic farm needs manure from chickens fed corn from four acres of land fertilized with synthetic fertilizer, that seems to set an upper limit of 25% for organic farmland. Long before that, though, we might run out of customers willing to pay organic premium prices.