My Interesting Experience With Biosolids

It's May 5, 2005 on a biosolids research plot somewhere between Kennewick WA and Umatilla OR . If you can use either a link to Google Maps or a Google Earth kmz file, the plots start 250' S, 150' E of the fence line and extend to 650' S, 425' E. The aerial photos Google has up as I post this were evidently taken before our field visit, probably in late winter (January?) 2005. The dark E/W swaths Google shows would be annual ryegrass (Lolium multifloruminvasive winter rye (Secale cereale) growing better than normal in areas which received aggressive application of municipal biosolids. Application was in April, 20042003.

The fellow in the distance is Tom Duebendorfer (Elmira, ID), botanist extraordinaire. Tom is carrying the quadrat to the west end of the application swath south of the one I am in. I am following about 20 minutes behind him. The wire flags (pink) are randomized sample points down the middle of the application swath. That's my soil sampler in the foreground, a Viehmeyer probe. It's a lot easier to get in than it is to get back out. The astute observers among you will have already noticed that the grass in the plot isn't looking so good: it is thick, brown and stubby whereas Tom is walking in a taller but thinner stand of green grass.

The biosolids killed the grass, but how? My thinking is that it is not a simple toxic effect. Impaired growth or necrosis would have expressed itself soon after the April 20042003 application, or prevented stand establishment at the beginning of the 2004 and 2005 season. Instead we had brief lush growth, almost like a growth hormone effect. 2,4-D works that way, but not on grasses.

My conclusion is that the effect is due to abundant nutrient availability and complex weather patterns unique to 2005. The application rate was designed to promote biomass gains. It worked, and as a result, the grass grew lush and depleted the soil moisture. With abnormally low rainfall in March, by April it had run out of moisture and had to close up shop for the year. April rains came too late for this brown grass, but helped relieve drought stress in the normal areas.

Soil nitrate levels were elevated in the brown areas but not to an alarming degree. Tom didn't see any application affect on the plant species composition, but then we have not formally analyzed the data. Composition effects are probably going to occur after 2005, beyond the scope of the study. I expect we would see an increase in annual ryegrassinvasive winter rye at the expense of other species.

Look close and you will see the ryegrass was still able to produce a fair amount of seed. L. multiflorumS. cereale is an invasive species, and was the only component in the system that really seemed to benefit from the aggressive biosolids rates to a degree that increased it's longterm competitive potential. I can think of any number of invasive species that would respond similarly.

As an aside, it is unlikely that Tom and I will be preparing a formal report based on the data. The sludge hauling client went bankrupt shortly after that May 2005 sampling. The study was a condition of satisfying a permit violation. Outside of that original context, it falls off both our urgency/importance project matrices.

Corrections: Application was in 2003, not 2004. Ryegrasss is winter rye, secale cereale, not annual ryegrass lolium multiflorum.

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