Atmospheric concentrations of greenhouse gasses are rising, but reducing them isn’t as simple as taking cars off the road. A significant part of the problem rests is agriculture. What is it about agriculture that is such a problem and how can we develop changes that will have the most benefit?
Agricultural Life Cycle Analysis is a useful tool in collecting information and making decisions. LCAs take every input and every output into consideration including difficult to consider ouputs like greenhouse gas emissions.
Nathan Pelletier from Dalhouse Uni in Nova Scotia presented his work on ag LCAs at Iowa State recently. He explains that actually conducting LCAs can be difficult. First, we need to define the scope of the analysis. For example, if we consider milk production, we should likely include the cow herself, food, water, and waste. We probably should include all of the inputs and outputs associated with feed production and transportation. We might include the inputs and outputs of pasteurizing and transporting the milk. Also difficult is actually quantifying all of the inputs and outputs to air, soil, and water. Finally, it is difficult to complete a meaningful impact assessment including the identification of “hotspots” or most negative impacts. Despite the difficulties, LCAs are worth the effort. Nathan reminds us that agriculture produces 1/3 of global warming emissions. The demand for food will will double by 2050, so we need to half the impact to continue a constant level of damage.
Nathan used LCAs to evaluate different cropping systems. He found that fuel and field emissions for a variety of crops was similar for organic and conventional (although he did not account for the vast variability in each category). It’s surprising that the field emissions were not different, but we have to consider that many conventional farms are no-till, instead treating for weeds with pesticides like Roundup. I imagine that the overall number of times a farmer drives over his field is similar, accounting for the similar fuel costs, even though the reasons might differ.
Even though overall farming methods don’t make that large of a difference with regard to greenhouse gasses and other negative outputs, nitrogen fertilizer source has a huge effect. Synthetic N, commonly used in conventional farming, is produced with natural gas, and CO2 is a coproduct of the process. Additionally, because of the type of N that is applied, not all of the applied N is taken up by plants, leaving the rest to evaporate as greenhouse gases or to be washed off the land into streams, rivers, and oceans.
The issue of replacing synthetic fertilizer is very complex, though, because we need to consider so many factors. For one, transporting and spreading organic N sources like manure is costly because a lot of weight is needed to provide enough N to see yield increases. Transporting and spreading all of this weight has its own greenhouse gas issues. If we use manure, the animals need food, water, and land, but some of this is offset because the animals themselves are a valuable output. Crop rotation is another option, but depending on the plants used, more land will be needed to produce the same amount of food. Nathan’s models considered out of season cover crops as non-synthetic N sources, but this method might not produce all of the N that is needed for various crop types and soil types.
It is possible that the complications of alternatives make synthetic nitrogen seem more attractive. However, a lot of these drawbacks might become non-issues when fuel costs cause synthetic N, P, and K prices to skyrocket. As you can see, deciding how to best fertilize your crops is far from easy.
One way to at least decrease the N problem is with genetic engineering. Newly developed “nitrogen use efficient” or NUE crops are able to take up more of the nitrogen that is applied, leaving less to run off. This, in combination with optomized nitrogen application techniques, could significantly decrease the amount of N needed. I asked Nathan what he thought about NUE but he said he didn’t know much about it. I hope he looks into it, because NUE crops would be useful no matter what type of fertilizer is used.
Nathan’s work with LCAs included an analysis of various types of animal agriculture, which I’ll save for another post.