Aug 31, 2015

Better tomato nutrition for improved packouts

Packable tomato yields of 20-plus pounds per plant are readily attainable by growers willing to focus on production details. However, fruit cracks, shoulder checks, radial cracking, yellow shoulder, and blossom-end rot are all serious defects in tomato fruit which in turn will result in losses in the quantity of marketable fruit. There are a number of cultural practices that growers can implement to dramatically decrease these problems. Proper irrigation management, careful attention to balancing specific nutrients, and the use of either plastic or organic mulches have all been proven in field trials to significantly increase fruit quality.

While weather is a factor that remains beyond growers control, shelters such as high tunnels have been shown in trials to be “unusually effective” at increasing fruit quality through reducing rain splash on fruit and even improving light quality when using ‘diffusion-type’ plastic films. Episodes of fruit cracking often follow rain especially in larger fruit. In addition, keeping rain off the foliage all but eliminates a number of fungal and bacterial diseases by keeping the leaves dry and preventing rain drop splashing-caused movement of plant disease spores. Spider mites, Aphids, Thrips, Fulvia leaf mold and Powdery mildew remain common pest challenges for shelter-grown tomato plants.

In order to produce the greatest quantity of the highest quality tomatoes (peppers too) growers must:

1. Pay careful attention to soil preparation prior to planting. In the case of soilless media, the selection of the appropriate media has long term consequences for the management of plant nutrition.

2. Select only those varieties that perform well and meet individual grower market requirements.

3. Understand their water resources thoroughly as pH and alkalinity have direct implications in water treatment and the selection of nutrients.

4. Use moisture sensing soil appliances such as tensiometers in order to meet plant demands as growing conditions change.

5. Be prepared to test both the soil and plant tissue as part of a concerted program to meet changing plant demands.

6. Have a well designed, easy to maintain, well maintained, nutrient injection system.

7. Be prepared to apply nutrients on a regular basis to meet plant demands. This includes foliarly applied nutrients.

Preplant soil preparation

The first step in creating a high yielding, high packout tomato crop is preplant soil testing. Vegetable crops such as tomatoes remove substantial quantities of nutrients, so test annually in order to use the best information in applying the coming years’ nutrients. Based on soil analysis results, conventional growers will need to incorporate at least 30-50% of nutrient requirements at soil preparation. Organic growers will want to incorporate 70-80% as organic fertilizers for injection post planting are substantially lower analysis in N, P, & K versus conventional powdered concentrates. Slower release fertilizers such as greensand as a potassium source and aragonite as a calcium source applied at plow down have demonstrated high potential to further reduce Blossom End Rot and Yellow Shoulder.

Variety selection

Perhaps no other issue is as open to argument as is variety selection. Most important in this selection: Is what do your customers expect from you? Then comes: What can you produce profitably to meet their expectations? Penn State Extension at the Southeast Agriculture Research and Extension Center has been trialing tomato varieties in both fields and high tunnels since 2008. Reports are available by contacting the author or from the Pennsylvania Vegetable Growers Association as the Pennsylvania Vegetable Marketing and Research Program grants have supported this work.

Currently the varieties that meet most growers’ needs for determinate, red, slicing tomatoes are: BHN 589, Scarlet Red, Primo Red, Rocky Top, Charger, Red Bounty, and Mountain Fresh Plus. Indeterminate varieties that have done well in our program include: Conestoga, BrandyBoy, Big Dena, Big Beef, and Arbason. There are many hundreds of tomato varieties available today with new ones coming to the market every year. Consider yield, flavor, fruit appearance, disease resistance, and training / pruning needs when selecting.

Water resources, pH and alkalinity

Tomatoes and peppers have the best nutrient uptake at a soil solution pH of 6.2-6.5. This will maximize potassium uptake as well as create a situation where it is possible to keep all of the other nutrients in the high end of ‘sufficient’ zone. Regular testing of your irrigation source for pH and alkalinity will provide you with the information to adjust your pH through the addition of acids.

Note: low pH is seldom a problem, but where the irrigation solution pH is below 5.8, the use of alkaline fertilizers is indicated. The injection of alkaline materials specifically for pH adjustments such as calcium carbonate is only recommended where the pH is below 5.5.

Sulfuric acid is the most common material used to reduce pH and alkalinity. Organic growers have had good success with citric acid for pH reduction. Nine ounces of powdered citric acid will reduce the pH of most water by about 1 full point on the pH scale. Conventional growers can use the NC State / Purdue alkalinity calculator to get extremely close to a proper dose.

The use of a calibrated pH meter is highly recommended to test the irrigation stream regularly as the online calculator and citric acid recommendation are simply tools to get close to the target pH. Water pH often changes during the growing season based on rainfall and source. Limestone aquifers will experience an increase in pH and alkalinity in a dry season as the underground storage area decreases. Surface waters will change with every rain event as rainwater combines with runoff.

Note on the pH scale: Even small incremental changes in pH mean a lot for soil solution chemistry. This is because the scale is logarithmic. The difference between a pH of 6 and 7 is ten-fold. Going from a pH of 6 to 8 is 10 x 10 or 100 fold. Most tomato growers that have adopted acid injection find that their crop quality improves dramatically as their potassium utilization improves.

Note on pH meters and litmus paper: Litmus paper is nearly useless for accurate water testing as it will age rapidly once the package is opened and is only designed to get within ½ of a pH point. The author regularly finds litmus paper tests to be off by 1-2 points. Purchase a high quality pH meter that self temperature adjusts, read the directions carefully, change the batteries at least annually and use fresh pH 4 and 7 calibration solutions weekly. Replace calibration solutions at least annually. If you notice crystallization around the lid of the solutions, it’s time to replace them. Your test results are only as good as the solutions that you use to calibrate your meter.

This article is an abbreviated version of the full length article: Refining Tomato Nutrition: Better Nutrition for Improved Packouts which can be found in the Vegetable, Small Fruit, and Mushroom Production Fact Sheets section of this website.

— Penn State University