Good stuff happens from adding compost to the soil or mulching it under the drip line, says Glenn McGourty, University of California Cooperative Extension. Growers can make their own, especially if they have easy access to fruit packing or processing wastes or grape pomace from wineries.
As wine grape advisor for Mendocino and Lake counties, California’s hotbed for organic wine grapes, McGourty has much experience working with organic fertilizers and soil amendments. Many of the growers he works with use green waste from landfills and manure to make their own.
“It’s not hard to make compost,” he said in a telephone interview with the Good Fruit Grower. “You need a front-end loader and preferably a location in the south 40 where neighbors are not nearby. And it’s good to locate your compost pile near a water source because you’ll want to add moisture when you’re turning it.”
In his experience, compost piles are turned four to six times. Aeration and moisture are important because the microbes need oxygen and water; aerobic composting reduces phytotoxins. The rate of decomposition depends on ambient temperature, temperatures generated by the compost, moisture content of the compost, particle size, and physical size and shape of the system. California laws require that the ground of the composting area first be compacted to prevent leaching into groundwater. Black, plastic tarp is sometimes used to keep the rain off the compost piles, but it could also be used to keep the moisture in and heat things up. The composting process can take about a year.
A general composting recipe he recommends uses an equal part of green wastes (grape pomace, fruit wastes, vineyard or orchard prunings) and manure. In some areas, municipal landfills are mandated to recycle or reduce the amount of green waste sent to the landfill, and may be a good source for growers, he said.
McGourty acknowledged that getting the compost to go to work in high desert soils and dry climates like eastern Washington is more challenging than northern California, which receives around 30 inches of rainfall annually. However, he said that Northwest growers would be amazed at the improvement in water infiltration from adding soil organic matter, such as compost.
Previous research in wine grape vineyards by Washington State University showed that compost at rates of two tons per acre protected soil from erosion and reduced soil moisture loss.
He prefers compost to raw manure, because manure is likely to contain weed seeds and have high salt levels, and raw manure has a harvest interval.
He encourages growers to test their own or purchased compost so they know what they’re putting on. Samples are relatively inexpensive and cost around $35 each. Mature compost can contain from 20 to 60 pounds of total nitrogen per ton, 10 to 20 pounds of phosphorus, 10 to 60 pounds of potassium, and many micronutrients.
“The problem with the organic form of nitrogen is that it’s not water soluble like synthetic fertilizers,” he said. “Nutrients are tied up in the organic form, and they want to leach easily. It’s not predictable when the nutrients are available, which is why farmers moved away from the old way of fertilizing with compost and manures and went to synthetics.”
He recommends that growers apply compost to the berm, incorporating it into the soil if possible. Tillage equipment is available for such a task.
There is also value in putting material under the drip line, especially compost that is coarse in texture, he noted. “It lets the water in, helps conserve soil moisture, and keeps the soil surface from sealing.” For example, tree and vine prunings can be run through a chipper, allowed to rest for a year, and then shoveled under drip emitters, targeting areas where vines or trees are stressed.
Getting it right
Using organic fertilizer is challenging and involves things like nutrient ratios and knowing when nitrogen is available, said Dan Nickolaus of Vigneron Management LLC, Grandview, Washington. “It takes a lot of time and energy to get it right,” he said during a composting panel at the annual meeting of the Washington Association of Wine Grape Growers.
Vigneron Management, the managing arm of Wallula Vineyards and Wallula Gap Biodynamics Vineyard, and the den Hoed family vineyards, makes its own compost and uses it in preplant and established vineyards. For preplant, they use five to seven tons per acre, applying, incorporating, and watering only the rows where vines will be planted. In established vineyards, three to five tons per acre are spread over both sides of the berm. A Pellenc Sunflower flail-type implement is used to lightly incorporate the compost into the soil, disturbing only the top two to three inches.
Moisture is important when using compost, Nickolaus said, adding that if the compost dries out before application, it becomes inactive. They always water the vines after the compost has been applied to ensure there is good soil moisture.
The rate of nitrogen release from compost is highly variable and depends on the moisture of the material, temperature, and soil moisture. Knowing when nitrogen and other nutrients from compost are available to the plant is always a question, he said. Nickolaus bases his fertility management strategy on the following: he plans that of the total available nitrogen, 40 percent will be released in the first year, 40 percent released in the second, and 20 percent in the third.
This means that if one ton of compost contained 15 pounds of total nitrogen, the plant would have available 6 pounds in the first year, 6 pounds in the second, and 3 pounds in the third, he explained. “For nitrogen, you’ve got to put on a lot of compost to get the full source of nitrogen in your soil.”