Sunday, July 26, 2009

Farm Bulletin: Worries Flow Downhill

It's more than the vagaries of the weather that grey the hairs and wrinkle the brows of farmers in Oregon. It can also be the activities, however well-intentioned, of their neighbors, as Anthony Boutard of Ayers Creek Farm elucidates in his latest essay.

It was an interesting month in the Wapato Valley. We had been pumping water from an irrigation canal for the last nine years without a hitch. Last September, a blue-green algae bloom in the canal clogged the sand media filters we use to clean the water. It was late in the season when our water needs were lower and cool weather slowed down the growth, so we cleaned things up and hoped it was a fluke of nature. The bloom had followed a brief rainy period, and we surmised that the valley's grass seed and wheat farmers, seeing record high prices, had dumped extra urea on their fields to increase the protein and seed yield and that nitrogen had washed into the canal.

In May and June of this year, the filters were back in their old form and we set aside our nagging worries about algae, having plenty else to fret about. In late June, we noticed a drop in pressure one day and checked the filters. The algae was back, and with a vengeance. The blue green algae is filamentous and has a slime coating. It completely invades the sand, forming a gritty green jello and preventing water from passing through the filter. You can slice it with a knife. At that point, it takes two hours to free up and disinfect the sand.

The filamentous growth pattern of blue-green algae.

We have developed a fine appreciation for the population dynamics of blue-green algae. At night, the populations declined, and we had about three hours of pumping time after sunrise before the population became unmanageable. Cloudy days extended the time to five or six hours. Using a venturi-type injector, we added a shot of sodium hypochlorite every 45 minutes or so to keep things flowing. It was amazing to watch the canal water color green over the course of the morning. Normally, at this time of the year, we run the low pressure drip irrigation through a series of sets that takes about 72 hours pumping time a week. Three hours for seven days doesn't get us there and some crops have suffered as a result.

Anticipating more algae blooms in the future, we have installed a chlorination system. Disinfecting water is allowed under organic certification as long as the free chlorine does not exceed the safe drinking water level of 4 parts per million. The advantage of the chlorination system is that we will be controlling human and plant pathogens as well. On the other hand, chlorine gas is pretty nasty stuff, and it adds another layer of record-keeping. That said, gas has a better safety record than the 12.5% liquid bleach we have been using and it's easier to calibrate.

Agriculture in our valley has changed over the last decade. The hayfields that greeted us when we moved here have been planted to perennial ryegrass for seed production. In the valley bottom, hundreds of acres of onions were grown. Today there are no more onion fields, and sweet corn and beets grow there instead. Prune orchards and walnut plats have been uprooted and replaced with grass seed fields. Linn County, the self-proclaimed "Grass Seed Capitol of the World," has had problems with excess use of nitrogen and phosphorous on the grass seed fields, degrading the waterways. Now the problem has landed in our lap.

Top photo from Microscopic close-up by Peter Parks.

No comments: