by Stephen Wagner
Fred Hulme, with the Technical Services division of ICL Fertilizers, opened the Greenhouse Growers Day at Shady Maple Smorgasbord earlier this year by saying that he wanted to talk about fertilizer and nutrition in a broader context – “in terms of your growing systems … intertwined with your cultural practices.
“Our plant nutrition goal is to supply enough nutrients to meet plant needs at the correct ratios and at the right time throughout the crop cycle to maximize crop growth, quality and value,” said Hulme. “In some nutrients, if there is too much of a good thing, there can be problems.”
Generally, nitrogen is not a problem, he said. “Too much nitrogen is just wasteful. Certainly there are situations where ammoniacal or urea nitrogen too high in the right environment can cause problems,” Hulme said. If any nutrient is lacking or excessive, plant growth can suffer.
Fertilizer is added to supply missing needs. “However,” he said, “real life comes into play. All the other things you’re doing like propagating, shipping, ordering, pulling orders, spraying – sometimes fertilizer gets shifted to the back.”
If you don’t have enough fertilizer, it’s tough to grow a perfect plant. As you increase rate, growth goes up. At some point you will meet the minimum needs of your crop. Beyond that point, you are doing one of two things: either wasting fertilizer (putting on more than you need) or building up toxicities.
If plant nutrition is not optimized, you might see any or all of a variety of deficiencies such as stunting, yellowing, delayed growth, wilting, edge burn, necrotic spots and even death. Besides the wrong amount of fertilizers, most nutritional problems are the wrong fertilizers and pH issues. Economically, said Hulme, “I would say it’s penny wise and dollar foolish to cut your fertilizer budget too much. The implications on plant growth and quality are huge. If you’re not growing a high quality plant, you might save a few pennies on fertilizer-per-unit plant, but the value of the crop goes down. Fertilizer is one of the lowest direct costs to a plant’s production. Labor, energy, container, seed – all that other stuff – costs a lot more.” There is no universal panacea for all fertilizer-based concerns.
“There’s a couple of things in water you should look at,” Hulme advised, because water is so vital to this equation. Consider the chemistry of the water, alkalinity, nutrients, harmful ions (which can be done by testing) and water quantity.
When things go drastically wrong, the plant tells you. It can turn yellow, wilt, grow slowly or die. A bunch of things can cause those symptoms. Sometimes you have to play detective to figure out the cause. “What’s causing that mum to be yellow on the top, for example? From a nutritional standpoint, it’s pretty simple – the wrong fertilizer; not enough of the right fertilizer; too much of the right fertilizer, and pH issues.” Hulme said those issues constitute about 98% of the concern (if nutritional). “It isn’t just the bag of fertilizer. I develop fertilizers and we test those. I cannot make the perfect fertilizer for everybody at once because conditions are so different – how you water, the growing media, the crops, the environment, et cetera. So when we look at nutrition we have to look at it as a complex of water, media and fertilizer all coming together in terms of influencing pH, nutrition and the root zone.”
How much water is going through that container? Everything that’s happening in a container is in the soil solution. Pouring excess water through can prove counter-productive. “One key parameter is pH. pH is acidity – basically a measure of hydrogen ions in a solution,” Hulme stated. “If there are more hydrogen ions in water, the pH is lower. One thing I want to emphasize is to test your water and look at the alkalinity. Don’t look at the pH on the value. If you have a pH-8 in your water, that does not mean it’s going to turn your growing media root zone into 8.” High water pH does not affect media pH. Focus on alkalinity if the goal is to provide optimal nutrition and a stable media pH.
Regarding media BMPs, Hulme endorsed going with a quality producer of growing media, with consistency and well processed raw materials. Water soluble fertilizers have been standard practice in the greenhouse industry for more than half a century. Among the pluses for use of WSFs are concentrated readily availability and rapid injection into the irrigation system. On the minus side, WSFs can be costly, and nutrients can easily be leached from soilless media.
There’s only a readily available supply of phosphates in the world, Hulme said. “In China, the U.S., India, Canada and Brazil is where those reserves are. Once those get played out, there’s a big issue for mankind. I suspect technology will change. So we should use our resources wisely.”