Saving Water in the Capay Valley

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One of the things we’ve been committed to experimenting with in the past few years is reducing tillage on our farm—in other words, fewer tractor passes through our fields and less turnover of the soil. We normally use tractors to cull weeds, turn under our cover crops, and make beds ready for planting after we have disked a field. We’re trying to reduce the use of tractors and soil turnover in two ways. The first is by using black poly mulch on our beds, and the second is by using our cover crops as mulch. The former has proven itself to have been an interim success, while the latter is our ultimate hope and long-term strategy.

Plastic Fantastic
The use of poly mulch on the surface of our beds started about three or four years ago, despite our immense dislike of plastic. We trialed it in our early tomato plantings, and what we quickly realized was that the plastic cover significantly reduced our energy and water use. Petroleum comes in many different forms—plastic is one, diesel fuel is another. After using the plastic only one time, it was clear to us that we were seeing several big benefits with regard to energy, water, and soil/plant health.

First, when the beds are covered with plastic, the weed pressure is next to nothing, and we might end up doing one very light tractor cultivation on the sides of the beds in the furrows, rather than having to do multiple cultivations across the fields. This significantly reduces not only tractor traffic, but also the hand labor we might otherwise need for weeding and hoeing. In the past, we needed to do a lot of hand weeding in the early tomatoes. We’d cover the early plants to protect them from frost. When the beds are covered, it creates a great environment for the plants, but also for the weeds, and when we uncovered the beds, there was always a bit of a jungle to deal with. Now that we’re using black plastic mulch in the early tomatoes, we have the tomato plants growing through a hole in the plastic, and there’s very little weed pressure. The savings in labor is tremendous.

There’s a second reason that we’ve tempered our dislike of black plastic: we’re seeing a reduction in water use of 25 to 30 percent. The mulch covers the bed and helps the soil to retain moisture much longer—it’s not being lost to evaporation. Because of the drought conditions, we’ve been looking at ways to increase our already fairly proactive water efficiency practices, and we are really impressed by the water conservation from the plastic mulch. We used it not only on summer crops last year, but also on some fall crops that were planted in late summer. The water conservation and the success of those crops was remarkable. They may have been some of the most productive and best crops we’ve ever grown.

The third (and in many respects the most important) reason we came around was that we’ve found that the ground is incredibly friable under the black plastic. Without mulch, the biology dives deeper and all the critters and microorganisms remain deeper in the soil, out of the heat and dry zone. With the plastic mulch, moisture is retained in the bed all the way to the surface, so we see roots and biological activity all the way to the surface as well. The effective biologically active rooting zone has increased, which means direct plant benefit from this soil improvement.

Other Options
But plastic is still plastic, no matter what you call it. Unfortunately, the plastic is used for only one year, after which we pick it up out of the field and send it to be recycled. We understand that there is a downside to using it, but we see it as a stepping stone to a more regenerative, cover crop–based mulching system.

Our long-term experimental approach, an alternative to the plastic mulch, is to figure out how to use cover crops to mulch our beds and reduce or even eliminate our tillage. There are a couple of ways we’ve been experimenting with this. In one system, we chop the cover crops in place with a tractor implement that chops and drops the biomass, creating a coarse mulch. After the chopped-up cover crop dies, it creates a dry mulch in place that we leave on the bed to smother out weeds. We then plant our crop through the mulch using a coulter disk that slices open enough of the soil to sow seed or transplant small plants.

The other thing we’ve tried is to roll the cover crop down with a chevron-shaped crimper. This tool was developed by the Rodale Institute in Pennsylvania and has been on loan to us from UC Davis. This tool rolls down the full-standing, waist-high cover crop right in place and crimps the stems every six to eight inches. This kills the cover crop, leaving it lying on the ground as a heavy mulch. Again, we plant through the mulch and hope that weeds will be smothered by the cover crop on top of the soil.

There are some big practical hurdles around weed and moisture management in the systems we’re experimenting with. Whenever we irrigate, some of the cover crop may regrow. If the mulch is not totally effective, some weed seeds will germinate. And this year, because the beds are all so dry since there’s been no spring rain, we aren’t sure how to get the optimal moisture window for planting.

We’re making this up as we go along. It’s a grand experiment. We have a compass bearing, but don’t know exactly how to get where we’re going. But we’re interested because, as farmers, our primary focus is on soil health. In that pursuit, we spend a lot of effort to build soil structure. Soil health is the net result of biologically dynamic, nutrient-rich, intrinsically populated conditions. When we turn the soil over using tractors and tillage implements we are disturbing it, if not destroying the physical structure that has formed. We recognize that we have crucial biology in the soil, and we’re realizing that tillage is counterproductive to establishing and maintaining underground habitat for the diverse community of microbes, fungi, arthropods, and earthworms. In the final analysis, it’s the health of that community that ultimately defines the health of our soil.

Andrew Brait and Judith Redmond are part of Full Belly Farm’s ownership team. This story first appeared in the Full Belly Farm newsletter.


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