For Release December 10, 2006

The Current Thoughts on Crop Fertility

AGRI-VIEWS

by Chuck Otte, Geary County Extension Agent

It's that time of year when the current research reports start showing up. The 2006 test plots have been harvested, the figures have been run through the statistics programs, the researchers have scratched their heads and attempted to figure out what it all means. What it means at the field level is that the changing world of crop production has started to require some changes in how we handle soil nutrient management.

One of the hottest topics last year was manganese on glyphosate tolerant soybeans (Roundup Ready). Some early work was showing significant yield responses to low rates (two to five pounds per acre) of manganese. Additional work this year, in more locations across Kansas and the Midwest, is starting to refine when and where we might expect this response. Adding the 2006 results to the ongoing knowledge base, there is a general feeling that we would expect yield response on Roundup Ready soybeans in fields were the pH is higher than 7.2, organic matter is under 2% and the yield potential is 50 bushels per acre or higher. In Geary County that is going to restrict the area where we may want to consider some manganese to irrigated river bottom soils, especially those on the lighter or sandier fields.

K-State has also been tweaking their nitrogen fertilization recommendations. Probably the biggest change is in the area of wheat where we are now recommending 2.4 pounds of nitrogen per bushel of yield. This is an increase and is taking into account the higher yield genetics of the newer wheat varieties. It also really points out that we need to do a better job of taking good, representative profile nitrogen soil samples in our wheat fields. Nobody likes pulling a dozen 24 inch soil profiles, but if we don't, we may very well be over-fertilizing our wheat fields and that is an expense nobody can really afford! Remember that in our wheat nitrogen fertilization formula we need to take into account yield goal, soil organic matter, past manure applications or legume crops and residual profile nitrogen. What we aren't getting from the organic matter, manure, legumes and soil profile, we have to make up with applied fertilizer.

Some of the most intriguing studies right now are the ones being done in no-till fields. Because we have now taken tillage operations out of some of these fields for ten or fifteen years or longer, we are starting to see some interesting nutrient stratification in soils. This stratification isn't horizontal through the soil profile, but vertical, following planting rows.

In many no till fields and especially in ridge till or strip till production, we find that the rows are being continually planted in about the same zone. Without the residue incorporation and soil mixing, the nutrients in these row zones is being drawn down faster than in the furrow or between row zones. This really becomes a factor with seedling growth because the roots haven't grown over to the higher nutrient areas. Naturally, this is most obvious in early planted corn. You have a young plant, often in cold moist soils, with a limited root system. The cold reduces potassium uptake and for the first few weeks your crop is potassium deficient.

What we probably need to be doing is taking soil tests right in the zone where the row will be planted. If we have borderline potassium levels, we probably need to be adding potassium to our starter mix. We've also found some interesting results from surface applied lime, but that will have to wait for a future column!

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