ORGANIC GREENHOUSE VEGETABLE PRODUCTION

J. A. Miles and M.M. Peet, Department of Horticultural Science

Box 7609, North Carolina State University, Raleigh, N.C. 27695-7609

 

 

Production of greenhouse tomatoes is increasing dramatically throughout the US[1]. Many greenhouse complexes consist of 100-acre ranges, which are adding on 20 or more acres each year. Imports of tomatoes from Canada, Mexico, Europe, and Israel have also increased dramatically. Large US greenhouses have already been hurt by price declines resulting from a saturated market, but so far smaller operations, at least in the Southeastern US, have been less affected. Organically certified greenhouse tomatoes are seen by many as a hedge against price competition since organic produce generally commands higher prices. According to the Organic Trade Association (OTA), a nationwide industry group based in Greenfield, Massachusetts, national organic sales for fresh fruits and vegetables increased at an average annual rate of 24 percent between 1991 and 1996. OTA estimates annual sales of organic foods at $4.7 billion and predicts annual average growth at 24 percent over the three years.

 

Organic greenhouse production is also attractive because many greenhouses are already virtually pesticide free. However, developing fertility practices acceptable to certifying agencies, while at the same time maintaining current yields is a major obstacle. Table 1 summarizes restrictions on construction, substrates, containers, fertilization, and pest control for organically certified production. Information in this table was abstracted from all certifying groups in North America that we could contact. For most of these groups, there are no specific standards for greenhouse production, but Table 1 is an extrapolation from restrictions on transplant and field production. The material in Table 1 should be used only as a general guide to the type of restrictions likely to be encountered, not as a definitive ‘Materials List.’

This paper describes some of the work we have done in developing organic fertilization regimes for greenhouse tomatoes. The purpose of our research, which was funded by the Southern Region IPM Program, was two-fold. One aspect was to study the use of Eretmocerus eremicus (also known as E. californicus to control silverleaf (Bemisia argentifolii) and greenhouse (Trialuerides vaporariorum) whiteflies. The other aspect was to develop an organic fertilization regime. There are a number of soil-based organically certified greenhouse tomato growers, mostly in Quebec and in New England. In these systems, growers usually must graft onto resistant rootstocks to avoid problems with buildup of nematodes and soil diseases. Grafting is an expensive and labor-intensive add-on to the other costs of greenhouse production, and temporarily retards plant growth. Because soil-borne diseases and nematodes are found throughout North Carolina, we concentrated on developing organic fertilization practices for soilless media. Most certifying groups require organic mixes or composts, so we decided to work with peat bags rather than water culture or inert substrates such as rockwool and perlite.

Materials and Methods

General: 'Grace' tomatoes were grown in three greenhouses in upright plastic bags utilizing three different growing methods: organic, conventional, and biorational. The biorational treatment consisted of IPM and use of reduced-risk pesticides. There was one treatment in each greenhouse in each growing season, and treatments were rotated to different greenhouses between crops. All inputs for the organic system were allowable according to the Carolina Farm Stewardship Materials List for organic certification and/or were approved by the Organic Material Review Institute (OMRI) at least at the start of the study. Restrictions on transition periods from and proximity to conventional greenhouses were not followed, however, because of the experimental design, so we did not seek formal certification. By the end of the project (fall 1999), organic methods will have been compared to conventional and biorational methods in two spring and two fall crops. The mixes reported here were used in all years.

Substrates:

Organic Substrates:

85 % Fafard’s Special Organic Mix[2]: Ingredients: Canadian sphagnum peat moss, vermiculite, perlite, gypsum, dolomitic lime, pine bark

15 % Vermicycle (commercial worm compost)

J.H. Biotech[3] "Natural Wet" 2T. /gal.

1.25 lbs./cu.yd. each, blood meal, bone meal, and potassium sulfate

1/2 lbs. / cu.yd. elemental Sulfur

Conventional and Biorational Substrates:

50% Southland SI-1: Canadian sphagnum peat moss, perlite, and vermiculite

50% processed pine bark

Transplant Production: The organic transplants were grown in Fafard’s Special Organic Mix and fertilized with organic fertilizers. The conventional and biorational transplants were grown in Southland’s SI-1 medium and fertilized with a commercial 20-20-20 fertilizer.

Post-Planting Fertilization: Conventional and biorational post-transplant fertigation began two weeks after transplanting. The organic plants were fertilized once by hand at this time. Since the EC levels from pour-through measurements were still high in the organic methods greenhouse, post-transplant fertigation did not begin in the organic greenhouse until four weeks after transplanting. At that time two different organic fertilizers were used: EarthJuice and Magna-Gro. Formulations were developed to approximate the concentrations of nutrients used in the conventional/biorational formulation. Fertilizers were applied with every watering, except in the organic house, where on weekends plants were fed only water to flush the emitter and drip lines. Mixes were as follows:

Organic:

1.      Earth Juice[4]: Formulated to make one gal. of stock injected at a ratio of 50:1

 Grow - analysis 2-1-1  ingredients: bat guano, Norwegian Sea Kelp, natural sulfate of potash, feather meal, oat bran, blood meal, and steamed bone meal

Bloom - analysis 0-3-1 ingredients: bat guano, Chilean sea bird guano, Norwegian sea kelp, natural sulfate of potash, steamed bone meal, oat bran, and rock phosphate

Catalyst - analysis 0.03-0.01-0.10 ingredients: oat bran, kelp, wheat malt, molasses, and yeast

Stage 1: Transplanting to first fruit set:1 qt. Grow;1 qt. Catalyst; 2 c. Bloom;                       1 1/2 c. 10% K₂O

Stage 2: First fruit set to topping:1 qt. + 1 1/4 c. Grow; 1 qt. + 1 1/4 c. Catalyst;                       1 1/4 c. Bloom; 1 1/4 c. K2O;1/2 c. Microburst Three

Stage 3: Topping to end of crop:  qt. + 3 c. Grow;1 qt. + 3 c. Catalyst; 3/4 c. Bloom; 2 1/4 c. K₂O;1/2 c. MicroBurst Three

2.  Magna Gro[5]: formulated to make 1 gal. of stock injected at a ratio of 70:1

Hydroponic Base Mix (HBM) - analysis 2-3-6 ingredients: poultry compost tea, pasteurized blood meal, calcium phosphate, and seaweed. This also contains trace minerals with fermented molasses in the form of Zn SO4, Mg SO4, and Fe SO4.

19%N  from poultry compost tea and pasteurized blood meal

 K-9 - 9% K₂O from seaweed

Stage 1: Transplanting to first fruit set: 1 qt. + 1/4 c. HBM; 1/2 TBS. 19% N;1/4 c. 9% K₂O (K-9)

Stage 2: Harvest to topping: 1 qt. + 1/4 c. HBM; 1/3 c.19% N;1/4 c 9% K₂0

Stage 3: Topping to end of crop: 1 qt. + 1/4 c. HBM; 1 c. 19% N; 2 c. 9% K₂0

 

Conventional: Plants grown using biorational and conventional methods were fertigated using “Chem-Gro” fertilizers from HydroGardens and supplemented with Ca(NO₃)₂, CaCl₂, KNO₃, and MgSO₄ so that N-P-K concentrations were 115 ppm N, 45 ppm P, 195 ppm K for stage 1, 125 ppm N, 45 ppm P, 195 ppm K for stage 2, and 165 ppm N, 45 ppm P, 310 ppm K for stage 3 of plant development.

Data Collection: Data was collected on plant development, whitefly populations, success of parasitism, yield, fruit quality, and nutrient status of tissue, substrates, and leachate,. Rate of plant development was measured by the number of days to first flower. Nutrient status was measured by: 1) weekly pour-throughs; 2) beginning and end of season substrate analyses; and 3) periodic leaf tissue analysis.

Biological Control: At the beginning of each experiment, yellow sticky traps were hung in all three greenhouses. When whitefly adults appeared on the traps, control measures commenced. The yellow sticky cards were removed from the organic methods greenhouse before the parasitoids were released, however. Since both Bemisia spp. and T. vaporariorum populations were present, both E. eremicus and E. formosa were released. E. eremicus were released by placing an equal amount of carrier (provided by Greenspot[6]) into distribution boxes that were hung in the upper 25% of each plant. E. formosa  were released by hanging the cards randomly throughout the greenhouse in the upper 25% of the plants. Malathion was applied on a regular spray schedule in the conventional practices treatment. BotaniGard, a wettable powder formulation of Beauvaria bassiana, was used in the biorational methods greenhouse. Sprays were applied four times in a five-week period. In all greenhouses, whitefly data was collected by examining leaflets from five plants under a 30x dissecting microscope to determine adult whitefly genus (Bemisia or Trialuerides), the number of immatures of each genus and the percentage and the type of parasitism, if any. Weekly samples were collected from 5 plants, chosen randomly throughout each greenhouse.

Conclusions and Lessons Learned to Date

The following represent some of our observations and concerns in our 4th season of experimentation. Statements should not be construed as product recommendations or lack thereof. This project was not designed to test particular products, but rather to develop general guidelines for the use of organic substrates and fertilizers, mycoinsecticides and biocontrols and to highlight directions for future research. Recommendations on fertilizer use in particular, are still being revised.

There are a number of obstacles to using organic substrates and fertilizers. An initial obstacle was locating suppliers. We have put together an on-line directory of organic suppliers, some national, but most located in the Carolinas. This directory can be accessed by selecting the databases option on the Organic Farming Systems Website: http://www.ncsu.edu/organic_farming_systems/. Overall, there is a dearth of good, soluble, organic fertilizers, and especially those that are locally available and affordable. Fishmeal products can be unpleasant in the closed working environment of the greenhouse, and were only used in the first season in this study. Two promising new materials[7][8][9] have come on the market since we started this project, but we were not able to test them. An ideal solution would be to use locally available animal wastes. However, most certification agencies do not allow the use of raw manure. Composts or manure teas would be allowable, but are not easy to produce or convenient in large-scale production. A guide (Compost Tea Manual 1.1) has recently been produced by Elaine Ingham and Michael Alms. This guide describes the production and use of compost teas and is available from the Organic Farming Research Foundation in Santa Cruz, CA (Phone 831-426-6606).

Another issue with organic fertilizers in soilless media is clogging. This was partially overcome by keeping the concentrate stirred, flushing out the irrigation lines weekly and checking emitters frequently for clogging. Other strategies to deal with the high particulate content could include using emitters with high flow rates, e.g. 2 gph instead of 0.5 gph, and lower dilution ratios in the injectors so the fertilizer solution would be less concentrated. We were satisfied with the overall performance of both fertilizers but growers would need to experiment on their own with concentrations, especially if using a different soilless media. Potassium levels in the leaves were lower than desirable in most of the experiments but this problem should be correctable with additional adjustment of fertilizer blends. This is straightforward with the Magna-Gro fertilizers, as most nutrients, including K, are available separately, but is not easy with blended fertilizers such as Earth Juice. Another problem with both organic fertilizers was avoiding high pH and salts levels in the substrate and leachate. Monitoring the leachate using the pour-through method was useful in tracking changes. It may be useful to substitute ingredients in the bag mixes that either lower, or at least do not raise, pH and salts.

Some difficulties with the organic system, such as poor quality transplants in the first two experiments, are common to all new growing situations. No commercial organic transplant substrates or fertilizer formulations are available, so we used the same materials as in the mature crop, which were probably not optimal for seedlings. Again, new products may make it easier to produce healthy transplants. Certifying groups may not require organically grown transplants because of the lack of good starter mixes and fertilizers. Another problem experienced early in the project was applying excess fertilizer to correct a nutrient deficiency, resulting in fertilizer burn. In subsequent crops, cycles of under and over fertilization have been avoided or at least minimized by daily or weekly injection of nutrient solution and monitoring of the leachate for EC and nutrient levels. 

Problems experienced in using the mycoinsecticides and biocontrols have mostly been overcome, and insect control was good in all three systems for as long as control measures were implemented.

In conclusion, Our experience suggests that all three systems give comparable yields of high-quality fruit, but further work needs to be done on organic methods of transplant production and fertigation. Another area requiring further study is the relative economics of the three systems, an issue not addressed in this project.

Table 1. Summary of general restrictions on greenhouse production for organic certification.

Construction and Operation

 

Substrates & Containers

 

 

Fertilization:

           

 

Pest Control