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Use of On-farm Cover-crops for Fertility in Organic Fruit Production - A Three Year Study


Project Leader: Steve Ela, Colorado Organic Crop Management Association, Hotchkiss, CO

Technical Advisors:

  • Ron Godin, CSU Rogers Mesa Research Center
  • Rick Zimmerman, CSU Rogers Mesa Research Center
  • Curt Rom, University of Arkansas

Project Years: 2002, 2003, 2004


Click here for:

2002 Annual Report (Word Document)



Project Summary 2002

Organic fruit producers on the Western Slope of Colorado face significant challenges in fertility management; soils are shallow and typically very low in organic matter, poorly structured, and have high pHs and carbonate levels.

Crop rotations and plowing-in manures are not practical options for perennial production systems.

This project has initiated studies to manipulate cover crops to enhance soil fertility in perennial cropping systems. The treatments are as follows:

  1. Alfalfa/grass mix planted in alleyways was cut with a sicklebar and residue left in place
  2. As above but residue was chopped finely and left in place
  3. Alfalfa green-chop from neighboring field was side dressed in the tree row in addition to chopping of alleyway alfalfa/grass cover crop
  4. Berseem clover was planted and treated as in 1.
  5. Yellow sweet clover was planted and treated as in 1.
  6. Nature Safe Organic fertilizer ( 12-2-0 ) applied at 100 lb./ac in early May
  7. Nature Safe Organic fertilizer ( 12-2-0 ) applied at 100 lb./ac in early May, in addition to practice 1.

Leaf and soil analysis, tree trunk growth, fruit production, soil moisture and weed pressure were measured.

Due to a freeze during bloom in 2002, there was no harvestable fruit, so fruit numbers were not much different between treatments. In 2003, the average fruit number per tree ranged from 7.3 for the chopped alfalfa/grass treatment, to 11.0 for the imported alfalfa treatment. In 2004, the average fruit number increased dramatically and ranged from 50.3 per tree for the chopped alfalfa/grass treatment to 57.7 fruit per tree for the imported alfalfa treatment. The increase in size is probably due to the maturity of the trees and their increased size between 2003 and 2004. Fruit yield was significantly different between treatments in 2003, but not in 2004. In 2003, the imported alfalfa treatment yielded significantly higher, 2.8 tons per acre, than the cut alfalfa and grass, chopped alfalfa and grass, Berseem, and Yellowsweet treatments. The two Nature Safe fertilizer treatments were not significantly lower than the imported alfalfa treatment. In 2004, there were no significant differences in fruit yield that ranged from 8.8 tons per acre, produced with the chopped alfalfa and grass treatment and 10.1 tons per acre, produced by the imported alfalfa treatment.

The soil nutrients were also studied in this project. Despite the fact that Nitrogen was being added to the soil, Nitrogen consistently went down from 2002 to 2004. This is probably due to the growth of the tree and the increased uptake of nutrients. Soil organic matter also decreased over the seasons. In the spring 2002, the organic mass was 3.7% and in the fall of 2004, the organic mass was 3.2%. This is also attributed to the tree growth. Soil phosphorus, however, went up from 43 parts per million in 2002 to 48 parts per million in 2004. At the end of the three years, potassium went down in all treatments but the imported alfalfa and the Nature Safe treatments. Soil pH went up from 7.25 in 2002 to 7.7 in 2004.

The conclusion that can be reached in this study is not that one treatment is necessarily better at producing larger yields than any other treatment, but that better attention needs to be paid to soil nutrient status as trees begin their large growth spurts in their sixth or seventh year.

If You Would Like a Copy of The Full Text of This Report, Please Click Here to Contact the Specialty Crops Program.


Colorado State University College of Agricultural Sciences Department of Horticulture and Landscape Architecture