composting: Yard Wastes Boosts Crop Yield In Field Tests

Kevin P. McCarthy

Do you wish to improve soil conditions and in-crease crop yield? Try adding yard waste.

"A major problem faced by California farmers is the loss of organic matter," says Linda Cushman, an organic products specialist. Ongoing field trials are needed to measure whether or not increased organic matter levels in soil will result from applying yard materials to the land.

In San Leandro, Calif., one such field trial has been in place since 1994. Sponsored by the Davis Street Station for Material Recycling and Transfer, the trial's goal is to develop a safe, effective and sustainable ur-ban yard waste diversion program for direct agricultural land application (DALA) and on-farm composting.

The DALA trials include row crops and, to a lesser extent, orchards. Row crop experiments test: application and incorporation techniques for ef-fectiveness; cost and monitoring germination; crop growth; weed pressure; insect control; disease and crop maturity.

Under the guidance of Will Gehr-has, a soil scientist, the research uses both 40- and 80-ton per acre application rates, measuring crop yields and comparing treatments to find the most economical methods.

Orchard trials, on the other hand, test yard materials as a top mulch in young orchards. To date, these experiments have demonstrated the cost-effectiveness of using live floor trailers to unload the yard materials.

Although logistical problems have prevented gathering any additional data, a 1997 field trial is scheduled to measure soil characteristics and water infiltration rates.

Other row crop trials - including corn, canning tomatoes and lima beans - were conducted in 1995 and 1996. For example, on the Navarra farm in Tracy, Calif., the lima bean trial resulted in a crop yield increase of 5.6 percent with a net profit of $14.45 per acre in some test plots. This increase offset the extra costs for material spreading and in-row weed removal.

Davis Street also has supported on-farm composting research conducted by the University of California, which involves monitoring the composting procedures at two farming operations and two commercial composting sites. Researchers examined the ways in which different degrees of maturity are achieved in composting yard waste materials. Then, they addressed the significance of compost maturity.

"The study confirmed that you don't have to make 100 percent mature compost for all applications," says Cushman. "Top mulching and well-in-advance soil preparation doesn't require the same maturity level as specialty crops. This makes composting less time-consuming and more economical."