One of the joys of summer, if not life, tomatoes hold sway over home gardeners and commercial producers alike. Everyone likes a plump, tasty tomato.
In Mississippi, the size of the tomato industry is steady, but not growing. “I hate to say it, but Mississippi’s overall commercial vegetable acreage has declined in the last 20 years,” says Rick Snyder, Mississippi State University Extension specialist for greenhouse and field vegetable crops.
“Unfortunately, that seems to have picked up some speed in the last five years. Farmers in general are an aging population and that extends to commercial tomato growers, as well. Growers get out of the business and no one takes their place.”
Whether for a home gardener or commercial grower, Snyder provides some common management advice. The one thing all tomato growers have in common “is a real need to soil test. Sometimes — especially with home gardeners — there’s a temptation to skip the soils tests. That’s not a good idea. However, soil tests are absolutely critical for commercial operations.”
To grow tomatoes properly, soil pH must be known. A soil test and subsequent fertilizer applications are “inexpensive corrections for the soil. If pH is below 6, just buy some ground limestone and put it out. Often, soil tests will show the pH is okay and there’s no need for that.”
Correcting pH actually saves money, insists Snyder. That’s because fertilizer put down will be taken up better by plants. “Again, by using a soil test, growers won’t put out an unneeded application and waste money by having excess leach away. The soil test might show the phosphorus is adequate and growers don’t need to apply it. The same can be true of potassium.”
For a home garden, a soil test every other year is probably enough. For commercial operations, “I’d spend the $6 for a soil test every year.”
To grow tomatoes, a rule of thumb is the crop needs 120 pounds per acre of N-P-K. “You don’t want to under- or overdo it. More commercial growers have a tendency to overdo fertilizing — sometime by 50 percent or even doubling what’s needed. They consider it insurance, but a lot of that insurance is a waste.”
Like all vegetables, tomatoes need N, P and K. All plants also need calcium but with tomatoes it’s more urgent. If there’s any shortage of calcium in the plant, it’s much more likely to produce fruit with blossom-end rot on the bottoms.
Once a fruit has blossom-end rot it isn’t marketable. “It’s still edible but isn’t pretty.
“Here’s the way I explain it to people: if the pH is low and lime is being added to the soil, the tomatoes are probably getting enough calcium. That’s because lime is calcium carbonate.”
If there’s any question about calcium availability, Snyder always recommends side-dressing with calcium nitrate instead of ammonium nitrate. That allows the plants to get needed nitrogen and, at the same time, have some calcium too.
“Whatever pounds per acre is recommended for ammonium nitrate, the grower can double the amount of calcium nitrate. That will provide the same amount of nitrogen. Ammonium is at about 33 percent and calcium is about 15.5 percent — so it’s pretty close.”
Another thing about blossom end rot: many times it occurs not because there isn’t enough calcium in the soil but because the plants dry out a bit between irrigations. That’s why it’s very important not to let the plants wilt. Anytime they wilt “the finest, microscopic roots die quickly — and those microscopic roots are the ones that take up calcium. They must stay healthy to get calcium into the plant.”
Snyder says sulfate of potash is also a good fertilizer. “We’ve used that more in greenhouse tomatoes to try and balance nutrients. The plants need potassium but we don’t always want to provide a fertilizer with multiple elements in it. With sulfate of potash, potassium can be adjusted easily and accurately. That’s also true of potassium chloride.”
For commercial production, if growers are using black mulch and drip irrigation, “they should probably consider fertigation for side-dressing. With black mulch, it’s hard to side-dress plants since the root zone is covered with plastic. However, with drip irrigation, fertilizer can be dissolved and injected straight into the irrigation system.”
There are advantages to that approach. Growers can put fertilizer “right where it’s needed in a soluble form. Just drip it in at the base of the plant and it’ll soak into the root zone.”
Another big advantage is the frequency of providing plants with nutrients. “Usually, side-dressing is done twice — once at bloom and again when the fruit are about the size of a quarter. With fertigation, though, plants can be provided fertilizer once per week.”
Tomato plants have a steady fertilizer demand through the season. So, with weekly fertigation, “you can put out small amounts of fertilizer. We have an entire schedule of fertigation — nitrogen and potassium — worked out. Phosphorus still needs to go down pre-plant because it doesn’t move very well in the soil.”
To access the fertigation scheduler mentioned above, go to http://msfruitandveg.com and click on “Vegetable crops handbook for Southeastern U.S.” Go to pages 96 and 97 for the fertigation information.