Economic Considerations For Cover Crops
Karen Klonsky
Agricultural Economics Dept, University of California, Davis
CA 95616
Cover crops are included in cropping systems for many different reasons, including nitrogen fixation, improved soil aggregate stability and soil tilth, weed suppression, improved habitat for beneficials, reduced soil erosion and reduced nitrate leaching. All of these potential benefits will impact short run and long run farm profitability. Unfortunately, virtually all of these benefits are difficult if not impossible to measure in dollar terms. At the very least, the amount of nitrogen produced by the cover crop is not equivalent to the amount available to the crop. Further, nitrogen produced by this year's cover crop will undoubtedly have a carryover effect on subsequent crops, which is even more difficult to determine. Therefore, a single-season direct comparison of costs to application of synthetic fertilizers is not appropriate or plausible. The remainder of this discussion will focus on the annual costs of growing winter annual cover crops, with no attempt to measure benefits.
In the Sacramento Valley, winter annual cover crops are usually
planted in October to take advantage of fall rains for germination.
Some ground preparation is required before planting. Whether
or not this cost should be assigned to the cover crop or the cash
crop depends on what the typical operations would have been without
the cover crop. Most of the growth takes place in February and
March, relying on winter rains. Incorporation usually takes place
in April.
| Table 1. Sample varieties, seeding rates and costs for cover crops. | |||
| Variety | |||
| Purple vetch | |||
| 'Lana' vetch | |||
| Oats / vetch mix | |||
| Barley | |||
| Cowpeas | |||
| Phacelia | |||
| Rye | |||
| Table 2. Sample operating costs per acre to grow a cover crop. | ||
| Operation | ||
| Plant | ||
| Irrigate | ||
| Mow | ||
| Incorporate | ||
| TOTAL | ||
A number of factors will affect the cost of using a cover crop. The most obvious cost is for the seed itself. In dry years, fall irrigation may be needed for good stand establishment. This costwill vary depending on the cost of water and the type of irrigation system being used. The equipment used for thecover crop operations will vary from year to year depending on field conditions, the cover crop selected, equipment availability and crop growth. For example, when the ground is wet during incorporation a crawler may be needed which is generally more expensive than a wheel tractor. Also, cover crops with a high biomass may require two passes instead of one for incorporation, adding to costs. If you have a high moisture level in the cover crop, mowing will allow the cover to dry out before incorporation. Incorporating a very wet cover crop could delay planting and increase pest pressures. Seed may be flown on, broadcast or drilled. Broadcasting will require a second operation such as harrowing to cover the seed. Drilling (no-till or conventional) has the advantage of placing the seed at the correct depth in one operation. A stubble disc, offset disc and incorporator are among the appropriate implements for incorporation.
The total cost of each operation is the sum of the operating
costs (fuel, labor and repairs) and the ownership costs (depreciation,
interest, property taxes, insurance and housing). Therefore,
the size and type of equipment used for planting and incorporation
will also impact the overall cost of the cover crop. In general,
wider implements are less expensive to operate because they cut
down on overall field time even though repair costs and ownership
costs are higher. Ownership costs vary according to the purchase
price, age and total use of the equipment. Ownership costs are
spread out over total use for the farm. Therefore, increased
usage decreases the ownership cost per hour by spreading it out
over a number of operations and crops.
Cover Crop Research and Education Summaries