2012 Tomato & Sweet Potato Polyculture Trial

This is a demonstration project:  A single field without controls or replications for statistical analysis.  The purpose of this trial is to explore possibilities before launching a full-scale research program.

Experimental Location:  Butler County, Pennsylvania, United States of America.  40.8606 degrees North Latitude, 79.8947 degrees West Longitude.

Climate:  Butler County has a temperate climate with cold winters.  Average annual temperature = 48.75 degrees Fahrenheit = 9.3 degrees Centigrade.  Average yearly rainfall = 41.85 inches = 106.299 centimeters.  Average yearly snowfall = 37 inches = 93.98 centimeters.  Average Last Spring Frost (36 degrees Fahrenheit) = 26 May.  Average First Fall Frost (36 degrees Fahrenheit) = 23 September.  Frost Free Growing Season = 119 days (about 4 months).

Experimental Plot Size:  1 acre = 208 feet x 208 feet (approximately).

Soil Type:  Heavy Clay Loam

Crop Rotation:  Organic herbicide (vinegar & citric acid) applied spring 2011 followed by broadcast seeded buckwheat (Fagopyrum esculentum) cover crop mowed at first flower then over-seeded with Dutch white clover (Trifolium repens).

Organic Herbicide:  10% Glacial Acetic Acid (liquid) + 5% Citric Acid (powder) + 83% Pure Water (rain water) + 2% Wetting Agent (surfactant) = 100% by weight.

Tillage:  Field rotary mowed prior to planting with a no-till transplanter.

Plants Per Acre:  Tomato transplants set 4 feet apart in rows 4 feet apart = 52 plants per row x 52 rows per acre = 2,704 tomato transplants per acre.  1 sweet potato transplant set every 2 feet between tomato plants in the row = 50 plants per row x 52 rows per acre = 2,600 sweet potato transplants per acre.

Crop Varieties:  Determinate, open pollinated, “Stake-Less” tomatoes (with thick upright stems).  “O’Henry” yellow sweet potato variety.

Predominate Weed Varieties:  Pigweed (Amaranthus blitum), Lambs Quarters (Chenopodium album), Bull Thistle (Cirsium vulgare), Foxtail Millet (Setaria species), and Morning Glory (Ipomoeae species).

Weed Management:  Organic herbicide, buckwheat cover crop, and Dutch white clover provided approximately 80% weed-free field for this trial.

Weed Spacing:  Clumps of broadleaf weeds were hand thinned to 1 plant every 3 feet.  Hand pruning weeds took the local scout troop (14 boys) about 4 hours.  Approximate weed density = 5,000 weeds per acre.

Irrigation:  Overhead sprinkler irrigation, 1 to 2 inches per week as needed.

Fertilizer:  Soluble nitrogen (62 pounds), phosphorous (76 pounds), potash (359 pounds), and magnesium (38 pounds) applied with irrigation water according to soil test recommendations.  Clover living mulch supplies about 100 pounds of nitrogen per acre.  2 tons of agricultural gypsum applied in spring 2011 to provide adequate sulfur for Dutch white clover.

Tomato Yield:  Approximately 51,000 pounds = 25.5 tons of marketable fruit per acre = 19 pounds per plant (pick-your-own).  High yield = 37 pounds per plant (controlled harvest).  Low yield = 7 to 8 pounds per plant (destructive harvest).

Sweet Potato Yield:  Approximately 10,000 pounds = 5 tons of marketable, first-grade roots per acre = 3.8 pounds per plant.

Planting Cost:  $4,025 per acre (mostly for amortized irrigation system and deer fencing).

Harvest Cost:  $1,810 per acre.  Sweet potato harvest took the local
Scout troop (14 boys) three days or approximately 300 hours to lift and sort roots by hand.

Marketing Cost:  $2,900 per acre (mostly for sales labor, newspaper advertisements, and post card mailings to previous customers).

Total Production Costs:  $4,025 planting cost + $1,810 harvest cost + $2,900 marketing cost = $8,735 total cost to grow and sell vegetables.

Tomato Income:  Fruits sold for canning at $0.25 per pound pick-your-own x 51,000 pounds harvested = $12,750 gross income.

Sweet Potato Income:  Roots sold for $1.50 per 5-pound bag.  10,000 pounds of number 1 roots harvested / 5 pounds per bag = 2,000 bags x $1.50 per bag = $3,000 gross income.

Net Income:  $15,750 income from vegetable sales – $8,735 cost to grow and market vegetables = $7,015 net income per acre.  $7,015 net income / $15,750 gross income = 0.4453968 x 100 = 44.5% profit.  [$7,015 net income / $8,735 cost] x 100 = 80.30% return on investment.

Agronomy Notes:

>>>  Dutch white clover living mulch normally provides 90% to 95% weed-free fields.  This season’s relatively poor 80% control rate is unexplained but provided an opportunity to examine the effect of weed spacing on crop growth and yields.  Widely spaced weeds (3 feet apart) appeared to have little or no effect on crop yields but did lower tomato hornworm populations — insecticides were not needed for the 2012 crop year.

>>>  Sweet potato yields were 50% less than normal because of low plant density; transplants were set only within tomato rows, not between tomato rows.

>>>  Buckwheat (Fagopyrum esculentum) is an ideal cover crop for non-chemical weed control.  Buckwheat grows very quickly (8 inches per week) to a maximum height of approximately 50 inches (4 feet 2 inches) in 6 weeks.  Seeds ripen at 10 to 11 weeks.  (Buckwheat must be cut at flowering to prevent reseeding).  Buckwheat’s fast growth and dense shade eliminate most weeds.

>>>  Sweet potatoes (Ipomoea batatas) make good living mulch:  They thrive in poor soil, require no insecticides, and established plants overrun most weeds.

Would You Like To Know More?  Please contact the Author directly if you have any questions or need additional information about using living mulches for weed control in vegetable crops.

Eric Koperek = worldagriculturesolutions@gmail.com

About The Author:  Mr. Koperek is a plant breeder who farms in Pennsylvania during the summer and Florida during the winter.  (Growing 2 generations per year greatly speeds development of new crop varieties).

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