Soil Testing, Fertilizer, And Liming Advice To Keep Your Vegetable Crops Healthy

To sustain profitability, growers’ approach to fertilizer and lime management must be based on the unique needs of the farm.

Dr. Matt Kleinhenz, associate professor at The Ohio State University, presented information on the topic of plant nutrition at the Ohio Produce Growers and Marketers Congress in January. He encouraged growers to be proactive in managing soils, fertilizer, and lime, reminding them of how critical it is to get quality input from soil testing labs and then develop a cohesive soil management plan that will increase profitability.

“At minimum,” he explained, “it is required [by growers] to maximize the return on ever increasing investments in soil, fertilizer, and lime,” he said. By having a cohesive plan in place that is designed specifically for an individual operation, growers will be able to remain compliant with the mounting number of regulations set up to keep nutrients on the farm and keep the nutrients with the plants.

pH And Overall Plant Health

For example, Kleinhenz said a soil pH of 6 to 7 is important for a number of reasons. First, pH itself affects plant health. Too low or high lowers plant health. Second, pH affects nutrient availability. A pH significantly different from 6 to 7 wastes fertilizer because nutrients are present — and show up on a soil test — but are mostly barred from entering the plant, he explains.

How much of a difference is significant? Kleinhenz told growers to keep in mind that pH is measured on a log scale. So, every change of one whole unit, such as 6 to 7, is a 10-fold change in hydrogen ion concentration. Therefore, a difference of even a fraction of a unit is meaningful.

“Soil pH tends to decrease naturally and with fertilizer application,” he explained. “[Soil pH] can be maintained in the optimal range with a variety of liming materials which vary in particle size, neutralizing power, and cost.”

Nutrient Management Goals

By maintaining soil pH in the proper range, growers can then focus on balancing nutrient supplies with crop demand. Three nutrients — nitrogen (N), phosphorus (P), and potassium (K) — stand out among the six nutrients that are managed most aggressively in production.

“These three elements,” Kleinhenz explained, “command about 99% of everyone’s collective attention in developing and implementing fertilizer programs.” Despite the fact that N, P, and K have a tremendous impact on crop health, other nutrients should not be ignored, he added.

“The goal is balance,” he continued. “The path is using the right fertilizer, at the right time, at the right rate, and delivered to the right place.” As mentioned previously, the “right” program will be tailored to the individual cropping situation.

“Each operation targets a specific market, relies on specific varieties, employs specially designed irrigation systems and application equipment, is bound by specific soil types, and works with particular rotations,” he said. “These and other factors influence fertilizer use.”

Fertilizers Versus Crop Protectants

There is more to the story, though, as fertilizer costs are high and volatile. Kleinhenz noted that growers can spend more money on fertilizers than any other input besides labor — and fertilizer costs continue to rise.

Unlike controlling insects, weeds, and disease, maintaining a fertilization program is much less predictable. “Insects, pathogens, and weeds possess biochemical pathways that are well-known by pesticide developers,” Kleinhenz explained. “[Suppliers of] crop protectants take advantage of the fact that these pathways — and the problems caused by pathogens, weeds, and insects — can be disrupted with chemical applications, much like derailing a train with a penny on the track. As pathogens, pests and weeds adapt, new products, hopefully, become available. This is a ‘target and switch-out’ process.”

It is not the same process for crop fertility management. “Soil fertility goes through boom and bust cycles,” he said. “Nutrient release fluctuates with season, temperature, rotation, and other factors. And, fertilizer availability is affected by soil type.”

Just how many soil types are there? The short answer is “a lot.” According to Kleinhenz, for example, there are more than 1,000 soil types in Pennsylvania and about 400 in Ohio.

“Ultimately,” he concluded, “fertilizer programs may be prescriptive but the prescription can be written only when the farmer’s operation and goals are well known.”