Dairy Manure Compost Experiment


Conducted by: Natali Asplund, Brian Hrutfiord, Kirk Melhorn, Kim Prince and Alyce Werkema, Whatcom County WSU Cooperative Extension Master Gardeners

Consultation by: Joyce Jimerson, Master Composter Coordinator and Teresa Cramer, Nutrient Management Program Assistant

Dairy manure compost provided by: Smit Family Dairy

Purpose: Using scientific methods to measure benefits of composted dairy manure in vegetable gardening, to conduct an experiment in a public area to raise awareness and provide community education about benefits of using composted dairy waste.

Hypothesis: Properties of composted dairy manure are beneficial to gardening.

Part One: Selection of Specimens

In order to test benefits of compost on a variety of commonly grown vegetables, certain specimens were chosen. Each was selected with many considerations in mind (i.e. ease and speed of growth, popularity of vegetable in residential gardens within Whatcom County, natural resistance to pests and disease, and the part of the plant normally used in human consumption were major concerns). Lettuce (leaf vegetable), beets (root and leaf vegetable), and zucchini (vine or bush vegetable) met the set criteria. Seeds for lettuce and beets were taken from the same seed packet to guard against variations between packets. Lettuce seed was Ed Hume brand, Parris Island Cos variety. Beet seed was Lilly Miller brand, Early Wonder variety. Since no seed packets were available that contained enough zucchini seeds for the project, two packets of Ed Hume brand, Black Beauty Bush variety were mixed and randomly selected. In the interest of saving time while waiting for soil test results and site preparation, the zucchini and lettuce were started in a solar greenhouse, planted in cell packs in Whitney Farm Potting Soil from the same bag. The beets were direct-seeded into prepared beds at the project site.

Part Two: Site Preparation

The project site was at Hovander Park in Ferndale, directly north of the existing pumpkin patch. Since there was not enough room in the existing patch, a section of grass was tilled under. Please note that beds one through four in all plots rested within this newly tilled area and beds five through eight bordered the outskirts of the existing pumpkin patch. A soil sample was forwarded to Green Gems (P.O. Box 6007, Healdsburg, CA 95448) to be analyzed for any needed nutritional amendments.

For the lettuce and beet plots, two 10x10 areas were sectioned off, allowing for a one foot center row running east to west. Each replicate would be 2x46", for a total of eight in each plot (four with compost and four without compost). The zucchini plot was 10x20, allowing for a one foot center row and eight replicates measuring 4x46" each. Replicates for each of the three plots were assigned numbers (indicated on the maps) for record keeping purposes. Which replicates would receive compost treatments and which were controls (without compost) were randomly drawn by 2 individuals (see figures one through three).

Click here for link to plot maps

Soil in each of the replicates for each plot was worked equally. Replicates drawn to have compost added in the lettuce and beet beds received two 5 gallon bucketfuls (equal to approximately 2 inches) each to ensure exact measurement. Replicates drawn to have compost added in the zucchini beds received four 5 gallon buckets a piece. Compost was worked into the soil 4 inches deep. Control replicates were also reworked to a depth of 4 inches, however no compost was added.

Soil testing recommended that 4 1/2 pounds per 1000 square feet of ammonium sulfate (21-0-0) be applied to the area and was added to all replicates. Furthermore, soil testing concluded that the average pH of the entire site was 6.4 (see figures 4a through 4e).

Part Three: Specimen Planting and Care

The beet plot was sown at the rate of three seeds per hole, 14 holes per replicate at 6" apart (two rows of seven holes each). To ensure consistency of depth, spacing and watering, the same person did one task for all replicates within the plot (figure two represents the placement of beet bed treatments).

Lettuce starts were transplanted at the rate of six plants per replicate (see figure one). Zucchini starts were transplanted at the rate of four plants per replicate (see figure three). Each plant within each replicate for the lettuce and zucchini were assigned numbers for record keeping purposes (indicated on figures one and three as p1, p2, p3, etc...as geographically located within the plot.).




The same individual watered all replicates within a plot on a given day to ensure consistency. This was done weekly or biweekly depending on the weather conditions. Weeding was conducted weekly.




Part Four: Germination Rates for Beets

Since the beet seeds were directly sown into the prepared site, germination rates were recorded as follows:

R1 (control): 33 seedlings R5 (treated): 24 seedlings
R2 (treated): 30 seedlings R6 (treated): 32 seedlings
R3 (treated): 29 seedlings R7 (control): 26 seedlings
R4 (control): 28 seedlings R8 (control): 35 seedlings

Totals: 112 seedlings germinated within treated replicates, 115 seedlings germinated in the controlled (untreated) replicates.

Generally, beds without compost treatment germinated only slightly better than those replicates that were treated.

After notation of the above, beet seedlings were thinned to the healthiest 14 plants per replicate (two rows of seven specimens).

Part Five: Measurement Guidelines for Harvest and Recording

The weight of edible parts of each plant was the guideline for measuring the experiment. Beet weights include root and leafy portions of the plant since both are edible and are regularly used for human consumption. Guidelines set to record zucchini specimens include any fruit measuring at least eight inches long from blossom end to base of stem and harvest occurred each Wednesday morning. To ensure consistency, the same individual harvested while another weighed and recorded.


Lettuce Harvest: (7/15/98)

Replicate Control (lbs) Treated (lbs)
1 6.1 6
2 3.5 5.4
3 9.2 8.2
4 7.9 8.5
Total 26.7 28.1

Note: Generally, lettuce specimens grown in replicates without compost possessed a thicker core, versus specimens grown with compost had thinner cores, but more leaves. Dense core weighs more than leaves. The treated replicates seemed to have facilitated more prolific leaf growth, the edible part of the plant.

Beet Harvest: (8/5/98)

Replicate Control (lbs) Treated (lbs)
1 4.3 7.0
2 9 3.6
3 10.6 9.1
4 12.5 11
total 28.3 30.7


Zucchini Harvests (summary 7/22/98, 7/29/98, 8/5/98, 8/12/98, 8/19/98, 8/26/98)

Replicate Control (lbs) Treated (lbs)
1 106.7 93.9
2 107.7 57
3 84.3 88.2
4 106.2 128.2
totals 404.9 367.3




Part Six: Conclusion

Sites containing compost in the lettuce and beet plots demonstrated that the amendment increased yields slightly whereas in the zucchini plot, compost apparently had an adverse affect. However, overall, replicates located within the southern areas bordering the existing pumpkin patch, which has been amended with compost previously, performed demonstrably better than replicates located within the newly tilled areas. We believe that composted dairy manure is not a "quick fix", but rather, when applied annually, is an amendment that will prove its worth over a period of several years.

Part Seven: Recommendations

With reference to the aforementioned conclusion, this group suggests that another study be conducted to experiment with composted dairy manure. We recommend that a minimum five year study, with replicates annually treated within that five years, be conducted and the results measured against controlled, untreated replicates. We believe that a study of this nature will conclude that the properties of composted dairy manure are, indeed, beneficial.


Report completed by Natali Asplund on 9/22/98 and submitted to Craig McConnell, WSU Cooperative Extension Agent, on 9/23/98.


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