Winter, 1990 (v2n2)
	Clover Cover Shows Promise in Orchard A workshop demonstrating the conversion of grass and broadleaf weeds to clovers in a foothill orchard attracted 45 people November 11 to Penryn. The clover demonstration project in the Pilz' Hillcrest Orchards began in the spring of 1989 and is a cooperative effort between Hillcrest Orchards, UC Cooperative Extension and the California Energy Commission (CEC). The CEC provided a grant for the study in an effort to find ways to reduce dependence on fuel and synthetic fertilizers. The workshop was also co-sponsored by Placer Farm Supply. Garth Veerkamp, Placer/Nevada counties farm advisor, and grower Steve Pilz planted a cover of white Dutch-O'Connor strawberry clover mix into the ten-acre hillside citrus orchard. It is still too early to determine if the clovers will provide the entire nitrogen needs of the orchard, according to Veerkamp. He said the literature indicates an annual nitrogen fixation rate of 30-200 lbs/acre for these clovers, and Pilz predicted it may be as much as 150 lbs/acre in this orchard. Summer soil samples in fact showed a sharp increase in nitrate-nitrogen, according to Veerkamp. However, he attributed this increase to the release of nitrogen from the stubble mowed off before planting, since perennial clovers require about 18 months before fixed nitrogen will be released. Mowing time has been reduced since the cover was planted, he said. Planting Procedure Veerkamp and Pilz said the procedure they used in converting the orchard floor to perennial clovers has included both successes and setbacks. In order to increase the pH of the soil, acidified by years of commercial nitrogen fertilizers, 25 tons of beet lime were added along with 5,000 pounds of 0-20-7 fertilizer to the 10 acre site. The orchard sod was sprayed with glyphosate in early April and mowed close to the ground two weeks later, according to Veerkamp. Pilz noted that while several methods of cultivation were attempted on the steep terrain, harrowing proved to be the most effective. In early May they sowed 150 pounds of the inoculated clover seed with a "belly grinder" (hand-seeder) and later ring-rolled the soil and sprinkled it every two days until it became established. Veerkamp explained how the clovers could be planted from spring through fall with proper irrigation. The late spring planting was successful in part because the trees shaded the seedlings from heat damage, he said. He also advised using caution if seeding in the fall to allow about a month of growth, or until the clover has three true leaves, before the danger of frost. In any case, "mowing is critical before seeding in order to maximize the light received by the clover," Veerkamp noted. He said there are no selective herbicides registered for bearing citrus, so the weeds must be mowed to the height of the clover as it grows. He said most weed seeds will not germinate through a thick stand of clover. Pilz estimates they should be able to reduce orchard mowings by four per year. System Changes Pilz and Veerkamp noted that their cover crop strategy didn't solve all their problems, and they are learning that an orchard is a dynamic system. Veerkamp said that introducing this new component, clover, has resulted in several other changes in the system including an initial increase in thrips and aphids on the trees after the sod died. Pilz noted that the use of cover crops is not a new idea; their goal is to see if this older strategy will fit current needs. He said their plan is one step in reducing the use of conventional energy for food production. Index for Sustainable Agriculture Winter, 1990