Nitrogen carryover- Participate in our soil survey

By David G. Hallauer

District Extension Agent

Crops & Soils/Horticulture

During any year where stress limits yields, the question of leftover nutrients always arises. In many cases, the question is well founded --if the plant didn't attain yields supported by the fertilizer applied, then logic says there must be some left. To find it though, takes a little digging.

A profile N test is really the only way to accurately determine whether there's any carryover nitrogen left for the next crop--generally Wheat in the fall. Testing from across the state coordinated by KSU Extension soil fertility specialist, Dave Mengel has indicated that many fields do indeed have high carryover levels of available nitrogen. These carryover levels have in some cases shown enough N left over for this fall's Wheat crop to reduce nitrogen rates, sometimes by up to $20 per acre or more. McPherson County testing has revealed carryover nitrogen levels ranging from 0-125 pounds per acre.

Profile N tests must be taken to a depth of 2 feet. They must also be done before any N fertilizer is applied to keep results from being misleading. Despite the effort needed to pull 10 to15, 24 inch deep soil samples per field, the payoff could be great.

To encourage testing, Extension offices are now participating in a fertility survey. Each office has been offered the opportunity to submit samples from up to 10 fields being planted to Wheat in their county. If you are interested in participating, contact your local Extension unit for instructions. There are certain testing requirements we need to adhere to, to make the results most accurate. With the results we obtain this fall, we hope to get a better grasp of how we can best manage the nutrient resource that may yet be in the field. Contact us soon to participate.

Organic matter and the vegetable garden

One of the most common challenges for the gardener is the soil they have to work with. Some are blessed with deep, fertile, silt loam soils that will grow just about anything. Others are lucky to have a space large enough to plant anything without digging out enough rocks to fill a small canyon!

What can you do? We can't do much for extremely rocky soils, but for those with those marginal soil types, and even those with some good soils that could be better, consider the addition of organic matter. The benefits to inherent fertility, water retention, and thriving garden crops could be great.

Organic matter addition is accomplished in a couple of ways--mulching during the growing season and incorporating residues in the fall.

I hope you used some sort of mulch this summer to help conserve soil moisture and control weeds. In season mulching around crops with a generous quantity (a 4 to 6 inch layer) of material like straw, hay, old leaves, and chopped alfalfa (fresh manure is not a good choice for health reasons) can be a benefit to the garden for a number of reasons While they contribute to the soil's organic matter. Note: Wood chips may also be used, but tend to present challenges when it comes to preparing the garden for the next crop.

As we head now in to fall, we have to determine what to do with those mulches as well as decide whether additional organic matter is necessary.

If mulch is present, or more organic matter is being added, consider tilling crop residues and mulches into the soil so they have time to break down over the winter. Additional fall mulches could include up to a pound or two of leaves per square feet that can be added (its probably best to mow them first to speed decomposition) with good results.

Note: Avoid adding organic residues such as leaves in the spring because decomposition can deplete soil nitrogen available for plant growth. Manure is another option, but overdoing it can cause problems from excess nutrients and salts. Contact your local Extension unit for KSU publication MF 2320, Fertilizing Gardens in Kansas. It offers guidelines for application of different types of manure to gardens and discusses other aspects of garden fertilization.

If you choose not to till, you can leave mulch on the surface. Just plan to pull it back next spring to let soil warm. Be aware, though, that permanent mulch can provide an excellent habitat for slugs, which can be a nuisance in the garden.

Contact your Extension office for further information on organic matter addition to your garden soils.

Date: 9/19/06

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