Improved feasibility of sustainable salad production

[The full project report with figures is available from the Northeast SARE office in Burlington, VT]

Project Contact:

Barry Landers
Aquaculture Unlimited
Route 2
Box 190
Point Pleasant, WV 25550
304-675-2377
barrvllanders@yahoo.com

Goals

This project experimented with different levels of ammonia for watercress, which can contribute to crayfish, goldfish, and koi diets while providing inexpensive biofiltration. In addition, lettuce and other salads work well for hydroponics greenhouse production using anaerobic digester (AD) liquids without ammonia toxicity problems, but experience large price variations with limited shelf life and little salvage value. This project evaluated the potential of lettuce and other salad plants as aquaculture feed to recover production costs when market variations or culture problems would otherwise bring a complete loss.

Farm Profile

Barry Landers has been active in the operation of family farms for forty-five years, and has owned and operated a 150 acre beef cattle farm since 1976. In addition, Barry Landers has thirty years experience as a mechanical engineer (Registered Professional Engineer in the State of West Virginia) with mechanical and electrical design of dc servomotors and gear motors, with stress, vibration, and acoustics issues and most recently with hypervelocity guns and projectiles for the Navy. He designed, built and operated a commercially successful crayfish shedding system using LSD style up-flow sand filters and grow-out ponds for bait crayfish and minnows, as well as building a commercially successful greenhouse business from scratch.

Present products include crayfish, bait fish, greenhouse plants, beef cattle, hay for use on the farm, and timber from a woodlot on a five year re-growth basis (part of American Tree Farm System). Recently, the decision was made to integrate the greenhouse and aquaculture businesses into a multifunctional structure similar in some ways to aquaponics systems, but layered with higher profit margin products and including biofilters to increase the aquaculture potential. The past twelve months included the full life cycle production of crayfish in a recirculation system within the integrated facility.

Participants

Barry Landers designed and constructed the research system, handled routine operation and finalized the conclusions and report. John Bombardiere, digester researcher at West Virginia State University, supplied digester liquid for the tests, provided advice on analysis techniques and interpretation of results and helped with resolving problems in the use of AD liquid for greenhouse plants. Ann Goodlin, consultant, assisted in setting up and operating the research system, provided water analysis and data collection, and helped organize and interpret results. Rodney Wallbrown, West Virginia University Extension Agent, assisted with greenhouse horticulture issues and outreach. Annette Landers provided financial management as a CPA.

Project Activities

Each tray of watercress had its own flowing water source from a separate holding tank with a 2 gallon per minute pump in a greenhouse environment. Overhead shade fabric simulated the effects of overhead hydroponics trays or a vertical grow arrangement for herbs, strawberries or other plants needing full sun. The holding tank contained nine gallons of water, an appropriate amount of AD liquid for the desired concentration and the necessary phosphoric acid to adjust pH and to add the required phosphorous. The AD liquid came from an anaerobic digester at West Virginia State University that processes chicken litter. All AD liquid used in this research came from a single batch. Because the AD liquid contains solids which provide desirable nutrients, it was poured directly into each growing tray instead of into the holding tank. The solids generally stayed in the growing tray and therefore remained available for the plants. Most micronutrients came from the solids. The five growing trays were thus arranged so that watercress could be cultured at four different concentrations of digester liquid and compared to a control hydroponics solution (Peters Excel 21-5-20). Each tray system received fresh solutions every two weeks to minimize the uncontrolled variables from selective nutrient loss. Upon solution replacement, pH, conductivity and temperature were measured. These measures were repeated at the end of each two week period before the growing trays and tanks were drained and refilled. Final growing tray concentrations of AD liquid were 5%, 10%, 15%, 20%, while the fifth tray provided the control. A 3% concentration of AD liquid was chosen initially but since extensive, rapid chlorosis indicated insufficient nutrients, the tray was changed to 20% AD liquid with a new watercress tray.

Each growing tray included a plastic greenhouse tray of watercress with holes in the sides of the plastic tray to permit good water flow through the watercress. After draining the liquid for 15 minutes, the watercress tray weight was measured both prior to placement in the growing tray and after a two week period in order to determine the growth based on weight increase. The drained, watercress-filled tray was weighed on a legal-for-trade scale. One month into the tests the trays suffered excess algae growth. The extent of the damage was so great that all five trays of watercress were replaced with new trays (this data was discarded). The algae problem was eliminated for the remainder of the test with the weekly addition of 3 ml of barley straw concentrated extract and by removing the standpipes in the trays to allow surface algae to drain into the dark holding tanks before it could multiply. The trays were tilted to retain water in case of a pump failure to minimize the risk of plant damage.

In a separate area of the greenhouse segregated groups of crayfish within a common recirculation system allowed comparison of the crayfish growth for three salad plant materials and a formulated feed control (floating catfish food). The sections were separated in a manner that allowed water flow through the sections. Each of three sections contained one salad food (spinach leaves, lettuce, or watercress) and control feed. The fourth section contained only control feed. Since there was no place for the crayfish to hide with formulated feed, an AquaMat was placed over the tray to guard against cannibalism.

Crayfish stocking throughout the project stayed between 5 and 10% of normal production densities to minimize uncontrolled variables from water quality problems such as ammonia and nitrite spikes. Formulated feed, weighed on a gram scale, was supplied at the same feed rate to each group (grams of feed/grams total weight for each specific group). The test groups received as much as they could eat of the salad materials in addition to as much formulated feed as they would consume. The control group received as much as it could eat of only formulated feed. Each crayfish group was weighed periodically to provide a good comparison for each plant type versus the control group. Wasted feed that had disintegrated in the water went out the drain to a juvenile crayfish culture system that included solid filters and biofilters. The filtered water was then returned to the test tray.

Results

The crayfish groups for spinach, lettuce and watercress shown in Figure 1 all consumed primarily salad instead of feed. In addition, prior experiments with mixed salad types revealed that crayfish will feed on the most tender leaves regardless of the salad variety. However, the crayfish group feeding preferentially on spinach appeared more lethargic and seemed to go off their feed fairly often (both salad and formulated). Furthermore, the spinach deteriorated in water much more quickly than lettuce. The watercress generally did not deteriorate at all, but instead grew faster than that crayfish group could consume it. Efforts to replace spinach more frequently and to use fresher spinach brought some improvement but failed to overcome the loss of appetite of the spinach group.

Figure 2 illustrates that spinach and feed together resulted in only 22% of the weight gain of formulated feed by itself. Lettuce and feed provided 166% of the weight gain of feed alone versus a 155% improvement for watercress and feed versus feed alone. In the process of growing during the test, watercress tended to raise the most tender leaves out of the water. While some species would have crawled up on the stems to reach the tips, the Orconectes virilis crayfish used in this experiment did not do so. As a result, the crayfish growth rate on watercress was not as good as lettuce, since the crayfish did not utilize it as fully. A potential advantage of this fact is that the premium tops of the watercress could be harvested while utilizing the less valuable part of the plant for a controlled population of crayfish.

AD solutions were tested with a hydroponics test kit and West Virginia State University also provided some analysis results. The dark suspended solids made analysis difficult, but the results revealed that the nutrients in a 15 - 20% AD liquid solution compared favorably to the control solution and met the hydroponics nutrient requirements for the plants grown in the test. The higher concentrations had a darker color that reduced light levels to submerged leaves and retarded the underwater growth. For this reason, a 15 - 20% concentration seemed to provide the best overall growth. A 25% solution was dark enough to greatly inhibit underwater growth and was not chosen for the full test period, since it appeared to have reached the point of diminishing returns. However, for plants with only submerged roots, the 25% solution could provide faster growth under good cultural conditions. Prior experience with AD liquids revealed that the accumulation of solids in the trays from repeated additions of AD liquid (between solution replacements) became a major source of nutrients and allowed good growth even for progressively reduced concentrations of AD liquid.

The ratio of the weight gains for the different AD liquid concentrations versus the control weight gain (Figure 3) clearly shows the largest increase between 10 and 15%. It also shows the beginning of diminishing returns at 20%. These conclusions agree with the nutrient analyses of the AD liquid solutions and the comparisons to recommended levels. This agreement proves that no ammonia toxicity occurred up to the 20% level at which underwater growth began to be significantly inhibited by suspended solids light absorption.

Conditions

The crayfish tray in the basement area had an insulated recirculation tank that kept the water temperatures in a good range and water quality remained very high. The crayfish test therefore was not significantly affected by site conditions. However, initial test conditions were hot and dry in the greenhouse. Figures 4 and 6 show the floating algae that caused problems during the first month of the test. The same pictures show the effect of heat on the watercress. Since this greenhouse has been kept chemical free to allow future organic production, we used barley straw extract to attempt an organic control. The extract by itself did not reduce the algae sufficiently for this test, but by removing the standpipes the floating algae went down the drain into the dark reservoir before it could reproduce significantly. The extract and better Surface removal resulted in insignificant algae levels - especially with the darker 20% solution shown in Figure 5. The lighter 5% solution in Figure 7 had small amounts of algae on tray surfaces but not enough to significantly deplete nutrients or otherwise affect the watercress. The 10-15% concentration therefore also helps with algae control by limiting light to the submerged algae. It should be noted that since the algae came from a different aquaculture experiment within the greenhouse, algae control was far more difficult than in prior years when algae was not deliberately cultured within the same greenhouse. Manual misting each day resolved the problem with heat damage to the watercress until the conditions cooled to the point that it was no longer necessary.

Economics

The results indicate that the feed replacement value of lettuce is about $0.38 per pound versus $0.35 per pound for watercress. Furthermore, the crayfish will eat bolted lettuce, including flowers and small branches, regardless of bitterness. Insect infestations increase the feed value to the crayfish and no cultural problem so far has precluded this method of recovering value from otherwise worthless salads. The crayfish also consumed outer wilted leaves from lettuce heads as well as almost any form of trimmed materials from lettuce or watercress. Excess watercress placed in the shallow part of a crayfish pond provided habitat and food for these crayfish when quantities exceeded the needs for the recirculation system. In addition, the salad materials created less waste and far less impact on water quality than did formulated feed within a recirculation system - especially for watercress. This fact alone can significantly reduce cost for crayfish recirculation systems and potentially could also apply to goldfish and koi.

Assessment

Watercress in particular offers opportunities for providing habitat and a renewing food source for crayfish while still permitting harvest of upper stems. The next step is to explore the maximum formulated feed replacement that can occur with this approach and the possibility of supplementing with digester solids as well to replace the protein now provided by formulated feeds.

Adoption

The WVDNR is currently selecting species (including crayfish) for aquatic ecosystem restoration projects. After the DNR finalizes these plans later in 2005, Marshall University and Barry Landers intend to cooperate in the culture of these species and to use the methods developed in this project for crayfish production. I also intend to explore using goldfish for this approach.

Outreach

Barry Landers submitted an article for the "Extension Emphasis" newsletter and provided tours of the research setup for local farmers, 4H representatives and for Dr. Tom Jones' biology students from Marshall University. Barry Landers sent a poster and article on this SARE research project to Dr Ken Semmens of WVU for the extension website and for the West Virginia Aquaculture Association.

Report Summary

This project evaluated the feasibility of growing watercress with anaerobic digester (AD) liquid and the potential of using salad plants as aquaculture feed to recover production costs when market variations or culture problems would otherwise bring a complete loss. Four trays of watercress with different concentrations of AD liquid, as well as a control tray of watercress with hydroponics fertilizer, were monitored for weight increase over time. Four crayfish groups were fed spinach and feed, lettuce and feed, watercress and feed, and feed only. Each group of crayfish received the same amount of feed per pound and the same weight of salad per pound of crayfish.

The ratio of the watercress weight gains for the different AD liquid concentrations versus the control weight gain shows the largest increase between 10 and 15% and the beginning of diminishing returns at 20% - with no evidence of ammonia toxicity. Spinach and feed together resulted in only 22% of the weight gain of formulated feed by itself. Lettuce and feed provided 166% of the weight gain of feed alone versus a 155% improvement for watercress and feed as compared to feed alone. The next step is to explore the maximum formulated feed replacement that can occur with this approach and the possibility of supplementing with digester solids as well to replace protein now provided by formulated feeds.

Barry Landers
4/28/2005