Familiarity with fertilizers

Having an idea of how a healthy plant should look at each stage of development will give you a better understanding of what adjustments need to be made to fertilizer levels. ISTOCKPHOTO.COM

Plants require many of the same mineral elements that humans do to grow healthy and strong. But many vegetable greenhouse operations use hydroponic methods or peat-like growing mediums for vegetable production which lack these essential elements, while those that use soil still lack the necessary amount and range. As a result, the use of fertilizers is essential to achieve maximum productivity.

“It takes a certain quantity of these mineral elements for a plant to complete its lifecycle,” says Richard McAvoy, professor and head of the department of Plant Science and Landscape Architecture at the University of Connecticut. “You can usually estimate those and make adjustments as needed, with experience.”

Knowing the basic fertilizer needs of your particular vegetable crop, as well as how to adjust levels based on these needs, is key to getting the most yield for your efforts.

What to look for
Most prepackaged fertilizer products advertise their N-P-K ratio, the percentage the product contains by volume of the three key nutrients necessary for plant production: nitrogen, phosphorus and potassium. Other minerals necessary for healthy plant growth include calcium, magnesium, sulfur, and in more minor amounts, iron, zinc, copper and others.

Testing your growth medium first and foremost will indicate what levels of existing minerals may already be present, and thus what levels you’ll need of each.

Many bagged options come preformulated for ease of use, but growers should look to manipulate these ratios depending on growth stage and time of year to achieve maximum results.

“We adjust that depending on that balance between fruit production and flowering, and that’s one of the more tricky things for growers to manage,” McAvoy says. “You have to adjust that depending on how the plant looks.”

When to adjust
One factor affecting fertilizer is where your crop is at in its production cycle.

McAvoy, who advises regional greenhouse growers in tomato production, recommends keeping levels fairly even at the seedling stage. Adjustments are then made as development continues — such as increasing the potassium levels as the plant nears first flower, and then even more as it approaches fruit development.

Having an idea of how a healthy plant should look at each stage of development will give you a better understanding of when and what adjustments need to be made during development.

For example, with tomatoes, you’d look for leaf development to expand rapidly, a thick stem and eventually flowers that pollenate and set fruit regularly.

“If one or several of those things start getting off … then you would have to push the plant toward more of a vegetative type of growth for a period of time,” McAvoy says. “But if you push it that way too much, you’ll get poor-quality fruit. You’re constantly looking at the plant, evaluating it, and then making some adjustments.”

Light levels within your operation are another factor that will affect fertilizer needs. When lighting is lower, particularly in winter, more fertilizer is recommended — particularly at higher salt levels. Conversely, reduce levels during high-light seasons.

“When light levels are lower, plants take up less water, so uptake of mineral elements will be a lot slower,” McAvoy says. “And when light levels are high, they’ll take up a lot of water on a regular basis, so we can actually lower the concentration and get the same amount of mineral element into the plant.”
 

Knowing the basic fertilizer needs of your particular greenhouse vegetable crop, as well as how to adjust levels based on these needs, is key to getting the most yield for your efforts. DREAMSTIME.COM

Synthetic versus organic
Preference between synthetic fertilizers — those manufactured in a laboratory — and organic fertilizers — those derived from natural sources — vary across the industry. Each has advantages as well as disadvantages.

Synthetic fertilizers, which McAvoy works with, are typically cheaper and supply plants with nutrients at a faster rate than organic options. A variety of application methods are available, from dry to liquid concentrates, and some companies market fertilizers preformulated for specific vegetable crops.

Organic fertilizers are a slower option, as they typically don’t dissolve in water. They provide nutrients as they decompose within your growth medium. A benefit of this slower pace, however, is that it’s harder to overfertilize crops, which with synthetic options can result in plant death. Organic options are also popular with natural-minded consumers and enable you to charge a premium for your vegetables.

Fertilizer innovation
One organic fertilizer gaining more and more support may surprise you: fish and seaweed emulsions. According to VeggieGardener.com, they come in a liquid form and are mixed with water and sprayed directly on plant leaves, enabling faster absorption than typical organic methods. Claims by retailers of kelp fertilizers include improved root development, stronger plant growth and even extended shelf life of fruits and vegetables.

Across both traditional synthetic and organic fertilizers, however, options remain fairly standard. Most current substantial fertilizer products were developed more than 50 years ago, according to the International Fertilizer Development Center (IFDC). But organizations such as the IFDC are focusing on fertilizer research and development in the hope of increasing agricultural productivity — and thus food security — across the globe. These efforts show promise that could potentially benefit all vegetable growers.

One such example was reported in March of this year by the United States Agency for International Development (USAID). The Accelerating Agricultural Productivity Improvement (AAPI) project, funded by the USAID and implemented by the IFDC, reported yield increases for soil-grown vegetables and rice crops in Bangladesh with the use of deep placement of nitrogen, phosphorus and potassium fertilizer briquettes versus conventional broadcast application of fertilizer.

Increased yields included almost 11 percent for bitter gourd, 26 percent for taro, 29 percent for cucumber and between 4 and 36 percent for rice, depending on the type and location.

Another advancement closer to home is the introduction of grafted rootstock into the industry, with particular success among tomatoes in conveying both disease resistance and added vigor, says McAvoy.

“You can really get very dramatic increases under certain circumstances in fruit yield,” he says. “That requires some adjustment in fertilizer, because you need to keep up with the productive potential of the plants with those advanced root stocks.”

Regardless of which fertilizer and application method you choose, what’s key is to make sure you keep a close eye on plants and a careful record of growth progress. Knowing what’s healthy development for your crop and how to make fertilizer adjustments if that healthy development strays will ensure your operation continues to produce the best vegetable yield possible.

Jessica Hanna is a regular contributor to Produce Grower magazine.