August 19, 2009 | General

Science Vs. Action

BioCycle August 2009, Vol. 50, No. 8, p. 44
Climate Change Connections
Sally Brown

SO what does a 100 percent increase in total soil water at 1 bar of pressure mean to the plant and the regulator? In my last column I talked about climate change and water shortages. I talked about how compost can increase both the rate at which water infiltrates into soil (for clay soils) and the ability of the soil to hold water (sandy soils). I talked about data we’ve collected that says compost can do wonders for both.
So, all of you people that work for State Department of Ecology or Environment, all of you that work regulating solid waste, this is your call to compost! This is a reason to provide farmers with financial incentives to start using compost! This is a great thing, a wonderful tool that helps the soils helps sustainability – what more can you ask?
Well it turns out that people from these agencies have other questions to ask. Very reasonable questions, I might add. Like how much water you save per ton of compost. And they are not at all happy if I just say “it depends.” The topic of this month’s column is that phrase I keep trying not to say while maintaining some level of scientific integrity: It depends.
I was excited to learn about science after four years of liberal arts in college. Science was going to teach me solid, irrefutable answers to so many questions. Science was also going to train me so that I could do research and find my own irrefutable answers. And that is what soil science does train you to do.
What my soil science education also taught me was to watch my step. Write down how you do things in great detail so anyone else could do the same thing. When doing a study make sure you have enough replication. Include controls to make sure that what you are seeing is the result of what you have or have not done to the soils.
Essential tools of the trade, statistics and probability, teach you how to design your experiment and how to look at your data so that you can say whether or not anything happened. You also learn that just because something happened in your study, it doesn’t mean that the same thing would happen for all plants or all soils.
So when you do your study and see that compost increased lettuce yield by 50 percent compared to the control, and 20 percent compared to synthetic fertilizer, you are not allowed to say, “This stuff is amazing! It will make your plants grow like gangbusters. Everybody you NEED some of this stuff.”
I admit that is what I’d like to say. Instead what I am supposed to say is, “Results indicate that for the Paris Island Cos cultivar with plants grown on a Christiana fine sandy loam soil, addition of compost produced from MSW increased plant yield by 50 percent in comparison to the control treatment and 20 percent… This increase was statistically significant at p>0.05.” You can see why I like saying the first version of the results much more. But those results might be different on a different soil with a different plant, and as a scientist you don’t want to put your foot in your mouth.
The problem is, these years of training not to put our feet in our mouths have left many of us scientists either incapable of or unwilling to say things in a way that regulators who need this information can understand. The regulators then continue making decisions not based in science. Meanwhile, scientists stand in the middle of the forest and wonder how we’ve missed seeing it through all of the trees. Or we say things with so many qualifications that our clear black and white results start looking grayer and grayer and duller and duller.


So how do you manage to communicate your results to others while maintaining your scientific integrity, without sounding like one of those commericals where the qualifiers at the end are longer than the ad, and get people to realize that you have something really important to tell them?
The IPCC (Intergovernmental Panel on Climate Change) does this pretty well in many cases. After each statement you will find parenthesis that categorizes how strong the argument for the statement is. High agreement, moderate agreement and so on. This gives you a sense of how good the case for some of the stuff that they are saying is, and where more information is needed.
The question is how good of a job am I doing on this? Last month I wrote about how compost can help soil use water more efficiently. I said it in black and white last month but tried to sneak in some qualifiers to better explain the situation without having you readers really notice what I was doing. You see, soil water is a big confusing issue. Texture is generally the main determining factor of how well water infiltrates into soil and how much of it stays there. And texture is something that you really can’t change on any scale greater than a portion of a backyard. Organic matter is the thing that you can change. And while organic matter won’t turn sand into clay it will help to even out the playing field.
I showed the amazing results last time from the one farm that we sampled extensively in California. There were other farms where compost didn’t change the water holding capacity at all. We’ve seen the same thing in Washington. It seems pretty much related to soil texture but it could also be related to how much compost was used and over how long a time period. We’re still working on analyzing that data.
It is true that for all of the soils the compost reduced bulk density, and we seem to have gotten pretty consistent results on improvements in infiltration rates, except for that very sandy soil. So, what I can say and still consider myself a scientist is that high rates of compost addition will improve water retention in sandy soils and will increase water infiltration rates in high clay soils. These are both very good things.
But I get in trouble when the regulator asks me just how good those things are, e.g., to provide a gallon of water saved per ton of compost used. A really good scientist would say that it is difficult to estimate and would take a pass. It is a soil and compost specific question, but it will also vary by plant species. It is also not clear whether it is important to use gravimetric or volumetric measures of water, and what moisture tension comparisons are most important for these parameters.
I may say stuff like that to my scientific colleagues, but I want to save the world more than I want to be a great scientist. So I compromise. I look at previous literature, make sure to express the fact that this answer will vary by site-specific factors, and say “0.125 percent increase in water use efficiency per dry metric ton of compost used.” Compost and other organics may not be the perfect answer, but in my mind it is one of the best ones we’ve got. And I have to do my part to communicate that.

Sally Brown – Research Associate Professor at the University of Washington in Seattle – is a member of BioCycle’s Editorial Board, and authors this regular column on the connections of composting, organics recycling and renewable energy to climate change. Email Dr. Brown at

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