Fertility and foliar feeding for Ohio vegetable crops

Your soil test comes back with a number, and the number tells you something. What it does not tell you is when the plant will get it, or whether the roots can reach it at all. That gap is where sidedressing earns its keep, and where foliar feeding looks tempting. This piece walks through what each practice actually delivers in Ohio vegetable ground, and where the money is best spent.

The details cited in this entry were checked on Ohioline factsheet on oilseed radish.

What a soil test can and cannot promise you

A soil test measures what is sitting in the soil, not what the crop has taken up. Between those two things sit root depth, soil moisture, compaction, and temperature. Cabbage grown for a fall crop wants a pH window between 6.0 and 6.8, and the Ohioline cabbage page states plainly that this range maximizes nutrient availability while discouraging clubroot, which shows up most often below pH 6.0. Push pH outside that band and you can have a perfectly adequate phosphorus reading that the plant still struggles to use.

The same page notes that fertiliser and lime are best applied using the results of a soil test as a guide, and that a grower can contact a local OSU Extension office for soil testing information. For small plantings the cabbage page suggests 2 to 3 pounds of 8-16-16 over 100 square feet where no test exists, worked into the soil about two weeks before transplanting. That is a garden-scale figure, not a field prescription, and the page treats it that way.

Where sidedressing fits the crop calendar

Sidedressing exists because nitrogen does not sit still. On cabbage, the Ohioline page recommends about 0.75 pounds of urea (46-0-0) per 100 feet of row once plants are well established, two to three weeks after transplanting, applied alongside the row rather than over the top. The logic is timing: the plant is actively expanding leaf, and the nitrogen goes in when roots are there to take it.

The warning attached to that recommendation matters as much as the rate. Do not fertilize late in the season, the page says, because late nitrogen can lead to head splitting. A grower who front-loads everything at transplant and then chases the crop in September is working against the plant, not for it.

There is a second reason to keep nitrogen on a schedule rather than a wish list. Cabbage has a shallow root system, and the page warns that tilling near plants may cause harm. If you are working fertilizer into the top few inches late in the season, you are also working the roots that have to feed the head.

How do you keep nitrogen from leaving the field?

This is where a cover crop stops being a soil-health talking point and starts being a nutrient budget line. Oilseed radish, described on the Ohio muck soils side of the rotation as much as anywhere else, is a fast, cool-season brassica that captures excess soil nutrients in its biomass. When planted after manure, sludge, or fertilizer application, it may prevent water quality problems by storing nutrients in its tissue rather than letting them leach or run off.

The numbers on this are not small. Averaged across soils and manure application types, oilseed radish took up soil nitrate substantially and decreased nitrate concentration in manure-amended soil by more than 70 percent compared with control soil. For a grower who spread manure in the fall and then watched a spring rain, that is the difference between a nutrient and a loss.

As a cool season cover crop, oilseed radish is best suited for early fall growth, and it wants 60 days or more of development to give maximum return on the seed investment. It fits after small grain harvest such as wheat, after vegetable or sweet corn harvest, after corn silage, and after early maturity soybean.

What happens when the biomass breaks down

Oilseed radish has a fleshy composition and a low carbon to nitrogen ratio, which means the plant decomposes easily and the nutrients become available for the crop planted the following spring. The Ohioline factsheet on oilseed radish illustrates this with a worked assumption: if 10 percent of the biomass nutrients are available after decomposition to the following crop, those values would be utilized. That is an example, not a guarantee, and the page presents it as an illustration.

The taproot does physical work too. The Daikon type grows a large, fleshy taproot that can reach 2 to 3 inches in diameter and a foot or more in length, not counting the fine root hairs spreading from it. Those taproots generally help break up compacted soil layers over time, and they break down easily over winter, leaving holes that aid water infiltration and rooting of the next crop. Above ground, the foliage reaches one to two feet in height in a semi-erect stature, and it is soft and moist. Leaf stems break easily from the main root, so traffic or grazing will destroy the stand.

Does foliar feeding replace a soil application?

Nothing in the Ohioline cabbage page treats a spray over the leaves as a substitute for feeding the soil. The cabbage page covers liquid starter fertilizer at transplanting, applied as 1 cup of starter solution per plant and prepared according to label directions, which is a root-zone practice with a foliar convenience. It also notes that most gardens do not require the addition of micronutrients such as boron, manganese or zinc unless deficiency symptoms are observed.

Read that the other way round and it is a restraint: applying micronutrients on a calendar rather than a symptom is spending without a target. The same page defers disease and insect identification and control recommendations to a local OSU Extension office, and adds the standing line about always reading and following all label precautions and directions.

Where a cover crop can go wrong

Two problems are named. The first is smell: decaying oilseed radish gives off a sulfur-like odor that may take a few days to dissipate. The second is seed set. If allowed to set for seeding, oilseed radish can become a weed pest, and if late fall temperatures remain mild, a mowing or tillage may be necessary to prevent viable seed set.

There is also a hard stop built into the plant. Freezing temperatures of 20 to 25 degrees F will kill oilseed radish, and the Ohioline factsheet notes that Ohio conditions will winterkill this cover crop without any requirement of additional spring time management. That same fact is what allows successful no-till spring planting of the following crop: the cover is gone, the holes are there, and you plant into them.

Getting the seed and getting the rate right

Seed production is difficult in the Eastern United States, and humid conditions there give poor seed quality. Most seed is produced in the Northwest, such as Idaho, and the recommendation is to check with local seed suppliers who may be able to acquire it from production areas. The two Ohio retailers named are Mid-Wood Inc. in Bowling Green and Gries Seed Farms Inc. in Fremont.

Rate depends on method and date. Drilling before August 15 in Northern Ohio, 8 to 10 pounds per acre is sufficient. Between August 15 and early September when drill seeding, increase to 10 to 12 pounds per acre. Broadcast application may require an increase of 2 pounds per acre over drilling rates. The Ohioline factsheet also reports that several studies found lower rates, 6 pounds per acre, were successful where soil moisture and available nutrients were ample and planting happened before August 15. Seed goes in at one-half inch. Seed size is similar to alfalfa, so a small seeder attachment is necessary on a drill, and broadcast seed needs light tillage incorporation to work. Leaving the soil level after planting is what allows the no-till pass next spring.

Oilseed radish can also smother weeds through vigorous growth under cool conditions, which may eliminate a fall herbicide application. It has the potential to produce a total of 9.8 tons per acre of dry biomass when planted by September 1, according to the chart on the Ohioline factsheet, which is where the seeding-rate tables and biomass and nitrate charts live for anyone who wants the underlying figures. Take a soil test first, put the nitrogen where the roots are, and let a September-planted radish hold what is left until spring.

Ohioline is the fact sheet publishing arm of Ohio State University Extension, cataloguing numbered titles like SAG-5 and HYG-1611 across horticulture, agronomy and food preservation. Its pages carry seeding rates, cultivar lists, biomass and nitrate charts, and references to university and provincial trials, written for growers and advisers rather than for a general audience.