Organic Soil Amendment Release Rates for Fertility in Apples

2000 Annual Report for FW00-032

Project Type: Farmer/Rancher
Funds awarded in 2000: $6,750.00
Projected End Date: 12/31/2002
Region: Western
State: Colorado
Principal Investigator:

Organic Soil Amendment Release Rates for Fertility in Apples


• Determine optimum chicken manure and compost application rates for organic and transitional apple orchards on the West Slope
• Measure the nitrogen release (timing and amount) from manure and compost applications
• Evaluate the impact of manure and compost on plant availability of other nutrients (phosphorus, potassium, calcium, magnesium, zinc, iron and boron)

This study evaluated the impact of chicken manure and compost applications to the soil of two apple orchards. The first orchard was a second-year, transitional orchard. The second orchard was certified as organic.

The chicken manure was applied at rates of 5 and 10 tons per acre, while the compost was applied at 0.5 and 1 ton per acre.

By having a general idea of release rates from these two treatments, farmers can manage their manure and compost applications at the optimum level for providing tree vigor and fruit quality. At the same time, they will be able to minimize losses from leaching and reduce negative soil effects like salt or excessive nutrient buildup.

Over two years, with annual treatment applications, soil fertility generally increased in both orchards.

In the second year (which this report covers), compost and manure applications had no effect on microbial biomass or total meters of fungus. Manure application reduced the soil’s pH and soil calcium levels, while increasing the soil salinity, organic matter levels and several nutrient levels. The levels of soil organic matter increased 2% in the two-year study when manure was applied.

Compost, on the other hand, increased soil salinity on one farm and levels of phosphorus and magnesium. Compost also did not affect the soil organic matter. So far, it appears that manure application is the best, but not in excessive quantities.

This project could potentially affect many producers using manure or compost for tree nutrition. The findings on the buildup of salt from high levels of compost or manure mean that long-term use could negatively impact the fruit production system and soil quality. Moderate use of these products may be acceptable, especially because they appear to increase organic matter and nitrogen levels. However, it is clear that they should not be the sole fertilizer source.

This study helps farmers to know whether the cost of these inputs is competitive with that from other fertilizers such as plant mulches, in-site green manures and other organic fertilizer products.

The study shows that manures can raise soil fertility levels within two years. However, it also shows that these applications may cause excess buildup of certain nutrients.

The study has raised a number of questions from growers regarding microbial action in soils, and many have encouraged further research.

Because this project is ongoing through 2001 with funding from other sources, it has yet to bring broad changes in farming practices. However, local farmers are interested in the results and will likely use the research to adjust their fertilization decisions. One farmer has already changed application rates for manures, and he is looking for alternative sources of nutrition that could complement the use of compost or manures.

The researchers recommend that farmers test their soils to determine salt loads after several years of manure or compost use, knowing that using these compounds can create soil imbalances of some nutrients like boron or phosphorus. However, they can also help amend soil deficiencies for specific nutrients such as phosphorus.

The researchers suggest securing multi-year funding to make the research more meaningful. They suggest that SARE encourage more multi-year projects, especially those involving soils or perennial cropping systems. In these systems, treatments may need to be applied for several years before differences are observed. This is because both trees and soils have extensive buffering systems, and it may take time to change the equilibriums.

New hypotheses for research include:
• The impacts of cover crops on soil fertility in tree fruit systems.
• What cover crops or plant-based inputs might increase overall soil fertility in an organic fruit system?

These findings have been presented to a range of audiences in the past year. Formal presentations were made to growers at an educational meeting held in conjunction with Colorado State University in March. Findings were also presented at the First National Organic Tree Fruit Research Symposium in Grand Junction on May 31 and June 1, 2001. Researchers and growers from the United States, New Zealand and Switzerland attended the symposium. Formal publication of these results will be pursued after more data have been collected.

This project was conceived by a group of producers. Two donated trees and land for the study and two others served as advisors and interested parties. All of these growers have been heavily involved in the research design of the project from its inception.