Organic high tunnel vegetables

Super Fantastic tomatoes  were used for the fertilizer trial.

Windy Meadow Produce was created as an extension of the nursery to improve year-round labor and facility utilization, and to extend brand promotion by providing Whatcom County (Ferndale, Wash.) residents with high-quality, sustainably grown produce.

A fertilizer trial was conducted to compare yields of Super Fantastic Tomato and Carmen English Cucumber using Feather meal, Fish meal or a combination of the two as a slow-release nitrogen source. The trial started on June 15, 2012, in Northwest Washington. An unheated high tunnel was constructed on sandy loam soil where an organic corn crop grew the previous year. After an unusually cold spring, night temperatures remained in the mid 40’s the first two weeks of the trial. Fresh water was used for all irrigations.

The options available for sources of organic nutrition in high tunnel and greenhouse vegetable production vary widely, from various manures to expensive complete granular formulations tailored to specific crops. Applied at rates suitable for improving soil texture, manure poses the problem of supplying an overabundance of immediately available nutrients to young crops.

The 4 R Nutrient Stewardship proposed by the International Plant Nutrition Institute states that applying nutrients from the right source at the right rate and at the right time and in the right place are interrelated considerations for achieving best management practices. Precise placement of nutrients increases Fertilizer Use Efficiency (FUE) by reducing nitrogen volatization, nutrient runoff and leaching loss, and potential long-term implications of environmental contamination. Using soil analysis to determine crop needs and sourcing nutrients from feed-grade agricultural bi-products can improve sustainable crop production.

The right source
Feather meal 13-0-0 and Fish meal 10-6-2 are two organic sources of nitrogen with long release rates and were chosen to determine if either one alone, or both in combination, is suitable for supplying nitrogen to long-term vegetable crops. Synchronizing nutrient release with plant demand is a challenge with organic materials. The structural protein keratin found in Feather meal is very resistant to microbial decomposition in cold soils.

High tunnels help elevate soil temperature and accelerate nitrogen release from protein based amendments. Feed-grade agricultural bi-products can supply nutrients over the course of the season and may save the grower labor costs for additional mid-season fertilizer applications.

The right rate of fertilizer was determined by a soil test that indicated an adequate pH of 6.4 and low levels of nitrogen, with moderate levels of phosphorus and potassium. Considering the previous crop grown, soil organic matter of seven percent, and a yield target of 80 percent of maximum due to the late start date, the following fertilizers were formulated.

Fertilizer was formulated with blood meal supplying 30 percent quick-release nitrogen and approximately 70 percent slow-release nitrogen from Fish meal and/or Feather meal. Other nutrient sources included Potassium Sulfate, Potassium Magnesium Sulfate, Bone meal and Wood Ash.

Super Fantastic Tomato and Carmen English Cucumber received 5 lb./100 sq. ft. incorporated into planting bed and 2 ounces placed in bands 2 inches under and to the side of each 4-inch starter plant.
 

The right time and place
Prior to planting, the broadcast application was worked into the top two inches of soil. Two ounces of each formula was applied in two bands. The first located two inches below the 4-inch transplant, and the second band was incorporated with the backfill soil surrounding the new transplant. In the case of the tomatoes, the deep band was placed 10 inches below the soil surface.

Placing fertilizer in the zone of depletion (area where roots will expand into) at the time of transplanting boosts yields by ensuring early and more complete nutrient uptake by the expanding root system and reduces runoff and leaching loss commonly associated with surface applications. Fish and Feather meal have low salt indexes that favor close band placement to the transplant with reduced risk of salt injury and root necrosis, compared to synthetic fertilizers. Applications made to the depletion zone help conserve water and increase FUE by restricting access of nutrients to competing weeds.

Conclusion
All treatments using Feather meal alone or in combination with Fish Meal had slightly higher yields than Fish meal alone. The difference in fertilizer grades is useful to illustrate that the Feather meal formula supplied 25 percent more nitrogen than an equal weight of Fish meal, which resulted in a 12 percent increase in production of tomatoes and 29 percent more cucumbers. The cost of nitrogen supplied by Feather meal is $5.38/lb. versus $9.00/lb. for Fish meal, making Feather meal the obvious choice for supplying slow-release nitrogen to long-term crops in warm greenhouse and high tunnel soil.

Scott Titus is the owner of Windy Meadow Nursery in Ferndale, Wash., and a member of Greenhouse Management magazine’s Grower Advisory Panel.