Feb 22, 2017
Container grown tomatoes preserve soil

Judson Reid is a go-to guy when it comes to commercial vegetable production in high tunnels.

Reid, Cornell Cooperative Extension vegetable specialist, made several presentations at the recent Great Lakes Fruit, Vegetable & Farm Market EXPO in Grand Rapids, Michigan.

One topic focused on container grown tomatoes as an alternative to in-ground for high tunnels.

“A common question in our high tunnel classes is ‘what can I do to keep my soil healthy if I want to grow tomatoes every year?’” Reid said. “The unstated problem is that soil health in tunnels degrades over time as pH, alkalinity, salinity, nutrients and diseases enter unsustainable levels. The balancing act of adding compost, cover crops and fertilizers is like juggling chain saws while walking a tight rope. With considerable skill it can be done. Otherwise a falling chainsaw may cut the rope.”

Reid said an alternative to the “slow motion juggling act” of growing tomatoes in the same ground year-after-year is to grow in containers.

“This allows the use of fresh potting soil every year to preclude alkalinity, salinity and nematodes. How do yield and inputs compare to growing in the ground? To find out we conducted a container trial to analyze the labor, water and nutrition inputs of tomatoes grown in several different sizes of containers as well as in the ground.”

Researchers sought to evaluate the potential of three container types and three container sizes for high tunnel tomato production as an alternative to in-ground production.

A trial to evaluate the potential of container production of tomatoes was established in a cooperating high tunnel in Penn Yan, New York, in March 2014. Grown on-farm from seed, tomato transplants (varieties Primo Red Harris Seeds) in three-inch pots were set in three types of containers: poly bags, soft felt pots and rigid plastic; each with three volumes (or container size); 5, 7 and 10 gallons; creating a total of nine treatments.

Plots were laid out in a randomized complete-block design, with three plants per plot, replicated three times. A single plot of in-ground tomatoes (nine plants total) was established to compare yield data. All plants were arranged in a single row with a 16-inch spacing. High tunnel soil was a Lima Silt Loam with two previous years’ history of tomatoes. Potting soil was a peat/perlite blend with an organic starter nutrient charge (Jeff ’s Organic, Lambert). Cultural practices including trellis, pruning, irrigation, fertility and pest management were followed to grower standards.

Single-point temperature readings were taken from the center of one container for each treatment on June 25 and Aug. 4. Tomatoes were harvested multiple times per week from June 7 to Oct. 2. Total weight of and number of fruit per block was recorded at each harvest. Data analysis was conducted using the statistical software Analysis of Variance (ANOVA) procedure, with significance groupings determined using Fisher’s Protected Least Significant Difference test.

Trial results

Yield as measured by both fruit number and total pounds per plant were not significantly different between any of the treatments, Reid said.

“Larger containers within each type yielded both more fruit and pounds per plant when compared to the 5-gallon containers,” Reid said. “The highest yielding treatment in weight was the 7-gallon poly bag with 29.8 pounds. The highest number of fruit came from the 10-gallon rigid plastic, with 65.1. All treatments were superior to in-ground production which averaged 24.3 pounds per plant and 43.4 fruit.”

Reid said the container type did not significantly impact yield when averaged across container size.

When container size is averaged across type, however, 10-gallon containers consistently increased yield in fruit number and weight in pounds over 5-gallon containers. Yield is affected by container size.

“Yield as measured by weight was similar across all treatments while fruit number varied,” Reid said. “A clear trend was significantly higher yield in larger volume containers. However, yield does not always translate to profitability. Given the increased input costs of potting soil, containers, ground cover, etc., we found that in-ground production still had the highest return-on- investment when compared to all but one of the container treatments.”

He said the 7-gallon poly bag exceeded the economic performance of in-ground tomatoes through the combination of higher yields and the lowest container cost.

“This represents an opportunity for high tunnel growers to continue in the same site over longer periods of time,” Reid said. “However, the container treatments required greater fertility inputs due to the low nutrient holding capacity and limited volume of the media. They also require increased management than growing in the soil. Finding the balance between increased inputs with container culture and the limitations of growing in a poor soil becomes an economic and risk management question.”

Grower Nelson Hoover, left, consults with Cornell University’s Judson Reid. Photos: R.J. Anderson/Cornell Cooperative Extension

Grafting study

Reid also reported on studies looking at grafting high tunnel tomatoes and how yield, rootstock and price influence profitability.

“Tomatoes grown in soil based greenhouse and high tunnel systems have proven profitable in wholesale auction settings as well as farmer’s markets and CSAs,”Reid said. “However,as production continues in the same soil, risk of root- zone diseases, nematodes and soil nutrient deficiencies increase. Grafting, the combination of two separate cultivars into one plant, is one management approach to these challenges.”

Reid said previous Cornell research has demonstrated the ability of grafted plants to increase tomato yields by 5 pounds per plant compared with ungrafted control plots. This can increase net revenue by $1.50 per square foot of greenhouse space; or $62,500 per acre.

“However, does grafting make sense horticulturally and/or economically in all situations?”

He said that on Feb. 21, 2012, seeds of tomato scion varieties Big Dena and Panzer (no longer commercially available) and rootstock varieties Maxifort and Arnold were sown in a soilless potting mix (Promix, Premier Horticulture) at a cooperating greenhouse in Penn Yan, New York.

Seeds of rootstock variety Colossus were sown on Feb. 22. All varieties were transplanted to 50-cell flats at first true leaf stage, on March 6. On March 23 grafts were made with the three rootstock varieties and two scions, for a total of six combinations, 40 finished plants per combination. Cuts were made with a double-edged razor blade on a 45 ̊-angle across the stem of both varieties, immediately above the cotyledons, the union was then joined with 2 mm silicon grafting clips. Grafted plants in 50-cell trays were placed immediately in a darkened healing-chamber with 100 percent relative humidity and temperature of 80-84 ̊ F.

Grafted plants were gradually re- acclimated to greenhouse bench conditions, with increasing intervals of time out of the healing chamber, until complete acclimation, approximately 12 days post-grafting. Grafted plants were transplanted into an unheated high tunnel with a Lima Silt Loam soil on April 18. Conventional fertilization was carried out per grower standards. Plants were grown on a vertical trellis and pruned to a single growing point. Graft survival was recorded with viable plants available on April 18.

The number of fruit per block and total weight per block was recorded at each harvest, beginning June 6 and ending Oct. 30. Data were analyzed using statistical software analysis of variance procedure, and treatment means were separated using Fisher’s Least Significant Difference (p<0.05).

More results

Survival of grafted plants was highest with Colossus rootstock, with an average of 94 percent, followed by Maxifort with 84 percent and Arnold 73 percent, Reid said.

When examining graft survival based on scion, Big Dena had an average 86 percent survival across the two rootstocks and Panzer 79 percent. Grafting significantly increased yield of both scion cultivars. The highest yielding combination as measured by pounds per plant was Big Dena X Maxifort with a value of 30.6. Panzer X Maxifort followed with 29.16 pounds per plant.

The graft survival rate is not likely related to cultivar compatibility, Reid said.

Two people conducted the grafting process and differences in technique may account for variability in survival, he said.

“It is critical however, to match the scion stem diameter as best as possible to rootstock stem diameter. Vigorous scions such as Panzer could be started several days after all of the rootstock used here. Grafting of Panzer scions onto all rootstock trialed here offered significantly higher production than the ungrafted controls.

“Big Dena yield was higher on all rootstock, but only significantly separate from ungrafted when grafted to Maxifort. It should be noted this trial took place in ‘fresh’ tunnel soil that had not seen vegetable production for several years.”

Reid said in other work by the Cornell Vegetable Program it has been noted that yield response to grafting is greater at sites that have a recent history of intensive tomato production.

“Yield as measured by pounds per plant, is perhaps the most important metric in this trial; however it is not the only one needed for selecting a scion/rootstock combination,” he said.

According to Reid, the grower noted a preference for Panzer fruit, based on color and shape. The three rootstock X Big Dena combinations gave the significantly heaviest fruit weight, creating their own grouping. Fruit size may be an important attribute for some markets.

“Unfortunately Panzer is no longer commercially available in the U.S.,” Reid said. “Yield precocity is also important for tomato marketing, as a price differential exists for early season fruit.”

Reid said the determination of whether grafting is the proper decision is based on the following factors:

  • scion and rootstock combination
  • transplant cost
  • soil conditions
  • market value of tomatoes

He used the economics of grafting Panzer onto Maxifort which are very favorable based on the yield increase in this trial. The grower estimated cost of a Maxifort X Panzer is $1.50 per plant vs. ungrafted Panzer at 36 cents per plant. With a mean increase of 4.7 pounds per plant, the break-even price required is 24 cents per pound.

“Indeed, all of the Panzer/rootstock combinations were significantly higher in yield than the ungrafted treatment at a level that justifies the investment,” he said. “However, Big Dena when grafted onto Arnold and Colossus shared a statistical grouping with the ungrafted treatment. This could indicate an economic negative performance, by increasing the cost of the transplant, without significant yield increase. Big Dena grafted onto Maxifort yielded significantly higher to justify the investment.”

Reid said if commercial grafted transplants cost $3 per plant, additional revenue of $2.64 per plant is required (based on the grower’s estimate).

“The lowest performing combination in this trial would have to be marketed at nearly $1 per pound to justify the grafting investment. Current USDA terminal price points are often below 5 cents per pound.”

Reid said his comments do not consider the impact of rootzone disease, which was not detected in this trial.

“Growers with infested soils would face greater losses from ungrafted production further justifying the investment,”he said. “As many tunnels have soil further compromised than this site, yield differences between grafted and non-grafted will likely be higher.”

In the future Cornell’s program plans to publish data on the relationship between grafting, spacing and economic returns, Reid said.

For more information, see “Tomato nutrients linked to pH, phosphorus management.”

— Gary Pullano, associate editor


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