College of Agriculture

Comparative Tomato Yields: Organic Systems vs. Conventional Production

Steven A. Gaddini


In today’s health conscious society, there is increasing demand for organically produced commodities. Organic produce commands a higher price than non-organic produce. The premium for the organic commodities typically runs from thirty percent higher to as much as double the going rate for regular produce. Organic farming can be an aspect of a large conventional farming enterprise or it can present an economically viable niche for the small producer or family farmer.

Steffen, et al. (1995) discussed comparative yields of four systems of tomato production: high and low input conventional production versus a high and low input organic system. My experiment was similar to the research conducted by Steffen and his associates in that both studies used organic soil building amendments to improve rooting environment and provide fertility. However, the organic soil amendments used by Steffen were much more complex (his mixture included horse and chicken manure, hay, ground corncobs and gypsum) than those used in this study. Also, the pesticides used in Steffen's research differed markedly from mine. His study used rotenone and diazinon, along with botanical oils and biological agents (insects and pathogenic bacteria). The study conducted by Steffen and his associates was also much larger in scope, with elements as diverse as root hair count and percent defoliation due to summer blight. My research was much narrower in focus, emphasizing low costs and techniques practical for use by a small-scale operator.

Objectives for this project were:

  1. Determine if the yields achieved under organic fertilizer systems could at least approach levels achieved under the conventional system.
  2. Determine efficacy of organic means of insect control as compared to conventional pesticide control, as measured by yield. These objectives would allow a researcher to ascertain if it would be worthwhile for a producer, (particularly a small operator or family farmer) to attempt organic production. If the yields produced by the organic systems were meager in comparison to the conventional, it would not be a viable commercial enterprise even with the increased price commanded by the organically produced fruit.

Materials and Methods

The area used to conduct this study was the backyard of my residence, 56 St. Francis Drive, Chico, Ca. Soil composition throughout the experimental area was clay loam. The experimental area was thickly overgrown with weeds. No vegetable gardening had been done in the area for at least several years prior to the experiment.

I used a split plot design, with 6' x 4' blocks, each divided into three 16" wide main plots.  I divided the main plots into three subplots.  Each of the six blocks contained nine plants, one plant representing each treatment combination of main plot factor and subplot factor.

Main plots contained a particular soil treatment. I used two organic soil amendments and one conventional fertilizer as a control. The organic soil amendments were decomposed peat moss and rotted steer manure. The conventional fertilizer was Osmocote 10-10-10, a commonly used sustained release, general-purpose fertilizer. After rototilling the strips, the soil amendments were applied to the strips. A wooden frame having inside dimensions of 16" by 4' by 6" high was laid in place and filled to level surface with the soil amendment, which was then incorporated to a depth of six inches with a shovel. The conventional fertilizer (40 grams per plant) was incorporated to a depth of one-inch using a rake. Soil preparation was completed by the end of March 1998.

The subplots were two organic and one conventional insecticide. The organic insecticides were diatomaceous earth and a hot pepper spray. The diatomaceous earth was originally intended as media for swimming pool water filters and was applied using a plastic squeeze bottle. The pepper spray was four ounces of pureed Habanero pepper mixed into one quart of water. The conventional control was Sevin dust, a common pesticide. Concentration was 27% active ingredient.

Nine to twelve inch specimens of Early Girl, a high yielding, flavorful, indeterminate hybrid tomato variety were transplanted into the blocks using a trowel. Planting was finished by the second week of April.

Rainfall was above average for the area and temperatures were unseasonably cool and overcast throughout the months of April and May. Rainfall returned to normal levels by late May but temperatures remained unseasonably cool into mid June.

As a result of the cool, overcast weather conditions which prevailed through the early part of the growing season, the onset of fruit production was delayed until early July, approximately five weeks behind schedule. As fruit ripened, it was harvested, bagged, then tagged. Harvest and data recording ran through mid September 1998.


There was no interaction between soil amendment and pesticides (p> 0.9) so I compared soil amendments across all levels of pesticides and pesticides across all levels of soil amendments. Soil amendments did not differ in terms of yield (p>0.3) and pesticides did not differ in terms of yield –p>0.9.


The results of the experiment indicate yields produced under the organic systems are very similar to yields produced by the conventional control. Is organic production more profitable than conventional production?  Many factors other than yield enter into the profitability of any business enterprise. A sustainable system using organic soil amendments would have higher labor costs due to the work inherent in soil preparation. Weed control would also be more costly in an organic system. The growing season got off to a late start due to the unfavorable weather conditions associated with the 1998 El Nino weather phenomenon. A normal season would have produced greater overall yields due to more favorable temperatures. With higher yields, the organic fertilizer's cost per pound of fruit would be reduced. In this case, the cost differential for producing organic versus conventional tomatoes would also be reduced. Also snails caused damage to some plants. Several plants succumbed to snail damage, while others may have been set back or stunted, thus reducing yield.

My results were similar to the results of the study conducted by Steffen.  Steffen observed significant increases in yield only when combining his high input organic system (incorporated soil amendments, drip irrigation, mulch, and trellising) with the use of synthetic pesticides and fungicides. His other systems (low input organic, low input conventional and high input conventional) all produced yields which were statistically similar.

Other research could be performed as a follow up to my experiment.  Other methods of organic fertilization could be tested and compared against the methods used in this experiment and against a conventional control.  Soil amendments such as chicken manure or incorporated green manure crops such as vetch, along with organic based fertilizers such as fish emulsion are possibilities.  This subsequent research might suggest means of maximizing yield under organic conditions.  To perform this follow up research, I would increase the overall magnitude of the experiment, adding more and larger blocks with greater numbers of replicates.  Also, I would use a determinate variety rather than the indeterminate variety I used for the experiment.  While a determinate variety would have made for an enormous amount of labor when ready to harvest, all could be accomplished in one fell stroke, rather than the season long harvesting and data logging which I performed.  By expanding the overall scale of the experiment, influences of local factors such as the less than optimal level of solar exposure prevalent in my experimental area could be mitigated.  In summation, my research suggested that organic systems of production can produce yields comparable to conventional production, and coupled with the premium price commanded by organic produce, can be an economically viable means of production agriculture.

Literature Cited

Steffen,-K.L.; M.S. Dann, J.K. Harper, S.J. Fleischer, S.S. Mkhize, D.W. Grenoble, A.A. MacNab, K. Fager, and J.M. Russo. 1995. Evaluation of the initial season for implementation of four tomato production systems. J-Am-Soc-Hortic-Sci. 120 (2) p. 148-156.