The perfect (nutrient) solution

Finding a perfect fertilizer system can be tough. For a crop to reach its peak potential, it has to have the right nutrient solution or combination, yet there are many to choose from and a slew of factors that can affect the way your crops react to them. But technological advances like fertilizer injectors, electrical conductivity meters and commercial labs to test your make up water can help.

Sixteen nutrients are essential for plant growth, says Wilkerson, and because greenhouse growers don’t have soil to provide some of those nutrients, they have to come up with solutions to compensate for that difference in their hydroponic systems.

“But it’s not just enough to know that you need 16,” he says. “You have to know what rate to apply –– [which] can either be measured in terms of parts per million (ppm) or the overall salinity typically measured in terms of conductivity of the solution.”

Other considerations include application timing, temperature of the solution, what elements are in your make up water, and the temperature of your make up water.

When it comes to application, fertilizer injections are one option. The injectors can reduce labor time because concentrates can be diluted with each application.

Newer fertilizer injectors are advanced with in-line pH monitoring systems and acid injectors.

“If it senses that pH is rising, then it may inject phosphoric acid or sulfuric acid – it depends on how much buffer capacity the solution has. It’s sort of auto-correcting,” says Wilkerson.

But if fertilizer injectors are cost prohibitive, growers can also use applied strength fertilizers distributed through 100- to 300-gallon tanks of nutrient solutions growers create, which can be applied through a drip system, sub-irrigation or troughs.

Another important thing to do is study your makeup water. Wilkerson suggests getting a water test performed by sending it to a commercial lab. But there are a couple tips to keep in mind. “You need to let the water run for a good 30-45 minutes before you pull a sample. Don’t just turn on the tap and grab the first thing that comes out,” he says. Also, send a few samples over the course of time to get a fair reading.

Another challenge is finding the right salinity. Because nutrients are applied in the form of salts, salt factors in the solution itself and in the water you’re using are important to track. There’s a range of salt that’s conducive to plant growth, and if it’s not met, can result in evaporation and transpiration.

If you have the wrong salinity levels, salt can be separated from the solution, and once it is, it causes perspiration and the salt can’t be added back.

Wilkerson suggests monitoring total salinity using an electrical conductivity (EC) meter. Advanced hydroponic systems, he says, have inline EC meters that monitor electrical conductivity. With these in-line systems, you can set a targeted level and once it’s reached, fresh water is automatically added to the solution to bring salinity back down.

Although fertilizer applications can be challenging and complex, there is a bright side, Wilkerson says. When you find a solution and rhythm that works, you’re good to go.

“It’s not like it’s changing all the time,” he says. “Once you get your regime down, you can pretty much stick with it.”