Improve Your Tomato Fertility Plan

Packable tomato yields of 20-plus pounds per plant are readily attainable if you’re 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.

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A number of cultural practices can be implemented 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.

The Advantages Of Protected Agriculture
While weather is a factor that remains beyond your control, shelters such as high tunnels have been shown in trials to be highly 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. Furthermore, keeping rain off the foliage all but eliminates a number of fungal and bacterial diseases caused by the movement of spores from splashing.

Spider mites, aphids, thrips, leaf mold and powdery mildew remain common pest challenges for shelter-grown tomato plants.

7 Key Elements For High-Quality Tomatoes
In order to produce the greatest quantity of the highest quality tomatoes you 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 your 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 water demands as growing conditions change.
  5. Plan and implement a regular and consistent program to test soil and plant tissue to meet your changing plant demands.
  6. Have a well-designed, easy to maintain nutrient-injection system. Most injectors require a rebuilding every other year in order to maintain accurate proportioning. This is especially important with acid-injection systems as even minor changes due to wear can have a great impact on nutrient availability.
  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 from the soil, 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 in Nitrogen (N), Phosphorous (P), and Potassium (K) versus conventional powdered concentrates.

Slower release fertilizers such as green sand, green potash, and burnt potash as potassium sources, aragonite as a calcium source, and magnesium sulfate (Epsom salts) applied at plow down have demonstrated high potential to further reduce blossom end rot and yellow shoulder.

Monitor Water, pH, And Alkalinity
Tomatoes have the best nutrient uptake at a soil solution pH of 6.2-6.5. When pH is maintained at this level, it will maximize potassium uptake and allow all other nutrients to remain in the high end of the “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.

When 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 per 100 gallons of irrigation water will reduce the pH of most water by about one full point on the pH scale.

Most tomato growers who have adopted acid injection find that their crop quality improves dramatically as their potassium utilization improves.

Conventional growers can use the AlkCalc alkalinity calculator to get extremely close to a proper dose. However, 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.

You can purchase a high-quality digital pH meter that self-temperature adjusts. Be sure to read the directions carefully, change the batteries at least annually, and use fresh pH 4 and 7 calibration solutions, replacing calibration solutions at least once a year. If you notice crystallization around the lid of the solutions, it’s time to replace them.

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Best Application Of Injected Nutrients
The K/N ratio deserves careful consideration for growing quality tomato plants. Tomatoes require substantial N available to rapidly grow a strong plant, however N demands change during the plant’s lifespan.

Prior to flowering, dry matter tissue levels of 5%-6% N are recommended. At flowering and during subsequent fruit fill, the ratio between K and N becomes critical. Experiments in Southwest Michigan indicate that a 2 to 1 ratio of K and N is necessary to produce quality fruit during fruit filling. This ratio will tend to enhance fruit firmness as well as reduce yellow shoulder.

K plays a key role in water relations and epidermis (skin) elasticity. Sites that are very poor in fertility may benefit from a 3 to 1 ratio of K and N. While tissue N levels of up to 6% are advisable as plants are growing out from a transplant, those levels need to be brought down to 3.5%-4.5% once fruit set and maturation get underway or suffer the likelihood of soft fruit and yellow shoulder.

Growers need to be cautious in applying micronutrients such as boron (B) as excessive amounts can result in fruit defects and phytotoxic damage to skin and leaves.

Once tomato plants are fruiting, look for the following tissue nutrient levels (by dry matter):

  • Nitrogen (N): 3.5%-4%
  • Phosphorus (P): .8%-1%
  • Potassium (K): 3+%
  • Calcium (Ca): 2.5%-3%
  • Magnesium (Mg): .5%-.9%
  • Sulfur (S): .3%-1.2%
  • Manganese (Mn): 40-500ppm
  • Zinc (Zn): 20-50ppm
  • Boron (B): 25-75ppm
  • Copper (Cu): 5-20ppm

One of the most effective ways to develop a nutrient application program is to base your initial applications on general plant population requirements. For example, an acre of tomatoes needs approximately .5 pounds of N per day. From this starting point, you can adjust your program as necessary based on soil and tissue analysis.

It’s recommended to start with a balanced fertilizer such as 20-20-20 (1-1-1 ratio) of N-P-K, or 20-10-20 N-P-K until the first flowers appear. When the first flowers appear, switch to a high K, low N fertilizer, such as 9-15-30, and adjust other nutrients based on tissue results.

Research is available to support moving to a high potassium program two weeks prior to flowering, as this is when the higher consumption begins. This may explain why growers who begin to increase K at flowering or shortly after find it so difficult to restore plant tissue levels.

Ca does not move from older plant leaves, so plants need it regularly for reduced cracking, firmness, and to prevent blossom end rot. Tissue testing will reveal whether you need to adjust this nutrient. It is not uncommon to have to regularly tweak levels of Mg and Ca. Note that testing for tissue Ca and Mg is always measuring past uptake, however, measuring these levels is useful in adjusting your regular feeding program.

Foliarly Applied Nutrients
Be sure to carefully follow the label directions and double check your math, as there is always the potential to burn leaves and fruit through wrongly applied foliar materials. Avoid applications during the hottest part of the day once temperatures reach 85o F to greatly reduce the potential for phytotoxic reactions from spray materials. Materials that are blended specifically for foliar application have adjuvants that increase the uptake of nutrients through leaf tissue.