by Tamara Scully
“Feed the soil to help feed the crops that you want to grow,” Neil Kinsey, soil fertility specialist, advised. “If you just put down what the plants need, you aren’t feeding the soil.”
Feeding the plants does not feed the soil. Growing plants remove essential elements from the soil. If those elements aren’t replaced, and aren’t in balance, then soil fertility is compromised, and crop health and yields will be impacted, Kinsey cautioned.
Just getting the pH right is not nearly enough. The result of the interactions of soil chemistry is pH, and a target pH can be achieved even when the chemistry is out of balance. But when the chemistry is unbalanced, important elements are not available to the plants.
“Ideal pH is only ‘6’ if all elements that effect pH are there in the right amounts. If you have too much of something, you have too little of something else. pH does not tell you whether or not you have the right elements,” he said. “Not all elements affect pH at the same rate. Anytime we have a soil that isn’t balanced,” the plant suffers.
Four main elements determine pH, the positively charged cations of calcium, magnesium, potassium and sodium. These bases — or alkaline cations — are held in the soil by negatively-charged sites. The cation exchange capacity of the soil is the measure of how many negatively charged bonding sites are available to hold these nutrients. Increasing organic matter adds to the cation exchange capacity.
The percentage of the cation exchange capacity that any given cation occupies is known as the base saturation percentage. While there are standards for the optimal levels of cation base saturation, the key is balancing the elements proportionately.
For example, the proportions of calcium and magnesium impact the soil’s ability to absorb water. Calcium creates porosity, while magnesium tightens up the soil particles. In heavy clay, increased percentages of calcium can be beneficial. These elevated levels would be harmful to sandy soil. But together, the two elements of calcium and magnesium should make up about 80 percent of the base saturation, no matter the situation.
Kinsey does not recommend automatically pushing the soil pH down if it is too high. High pH levels are often seen in soils where calcium levels are high. But it isn’t calcium levels alone that cause issues, but rather the proportion of calcium related to the percentage of other elements. Instead, he recommends balancing the elements, so that they are available as required even with the higher soil pH.
“We have clients that grow excellent crops on 80 percent calcium,” Kinsey said. “The key is…do you have enough of everything else to grow that crop?”
“You can’t manage what you can’t measure,” Kinsey said. To get ideal soil, you need “to correct chemistry, not chemicals, but chemistry.”
Kinsey, the keynote speaker at the recent Northeast Organic Farmers Association of New York (NOFA-NY) Organic Dairy and Field Crop Conference, held in Liverpool, NY in early March, shared with farmers the information needed to achieve a healthy soil, and examined how a healthy soil translates into healthy crops.
Right after harvest, the soil has the lowest amount of nutrients, as they were utilized by the growing crop. In the spring, soil nutrient level is maximized. Soil samples, therefore, need to be taken at the same time each year in order to offer any meaningful data for year-to-year management. They should be taken yearly, both to chart the impact of any fertility program implemented — which may not be noticeable for several years — as well as to assure that the elements remain balanced, and excesses are not a concern.
Because too much of a good thing can definitely be a bad thing where soil fertility and crop yield is concerned. Adding manure or compost year after year without knowing if it is providing the balance of nutrients the soil needs can block essential elements. Dairy manure, for example, can be high in manganese, depending on whether the cows were heifers or not, and cause problems if this is not measured. Compost, too, differs in composition.
“How much is too much? Every soil has a different answer,” Kinsey explained. “A good, moderate amount of manure can go a long, long way without causing a problem. The key is in moderation; a balance between all the elements.”
When soil chemistry is out of balance, problems result. Excess NPK limits a plant’s ability to fight off disease. In soils without enough calcium, squash and cucumbers will have a bitter taste. Other nutrients, including copper, boron, phosphorous and sulphur are also important. Too much potassium will limit boron, and boron helps fight disease.
Chemical, physical, biological
Building life into the soil depends upon balancing the soil chemistry.
“The chemical structure determines the physical structure,” Kinsey said.
Creating a balanced soil chemistry will help create an aerobic zone where microbes can thrive, as can the crops. While soil biology is important, microbes will take what they need first, leaving the plant with whatever nutrients remain, so having adequate and balanced soil fertility is of primary importance.
The top five inches of soil is the aerobic zone, and functions as the “plant’s stomach.” The key is to keep nutrients in this zone. The aerobic zone is comprised of 25 percent air, and 25 percent water.
“The roots are going to grow where you put the nutrients,” Kinsey said. “A plant is smart enough to go where the nutrients are.”
Humus determines the nutrient-holding ability of the soil. Humus is found in the top two inches of the soil, not eight or nine inches down, he said. Organic matter is all residue, not only that which is decomposed, while humus is all organic residues, fully broken down. With sufficient humus, plants could even grow in toxic soils, Kinsey said.
“When you start taking bigger yields out, you have to put back what you’re taking” from the soil, Kinsey reminded growers. “Learn what the fertility does in your soil, and learn how to put it there and learn how to keep it there.”
Organic growers need to observe their fields. Observe the crops. Track yields. Use GPS sampling to map the fertility of the farm. Yield decreases mean there are soil imbalances. If organic growers concentrated on balancing their soil chemistry, their yields would increase beyond that of conventional fields.
“You get the nutrient levels right, and you can produce just as well as conventional growers,” Kinsey said.