Crop News and Notes

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

Potential for Nitrogen Carryover in 2003 

        Given the low amount of precipitation during the past growing season and current winter, there exists the potential for above average nitrogen carryover in area crop fields.  The only method to confirm carryover status is to sample soils this spring with the pre-plant soil nitrogen test or early summer with the pre-sidedress soil nitrogen test.  The latter is by far the most popular but requires that producers be prepared to make sidedress nitrogen applications to corn.  For you cyber-geeks, a Nitrogen Carryover Calculator will be made available at http://www.soils.wisc.edu, then click on WI-MN Nitrogen Carryover.  The calculator takes into account site-specific factors such as previous N applied, soil moisture status in August of the previous year, over-winter percolation, soil type, and crop N removal to estimate potential N carryover.  It is not a substitute for soil sampling.   

Looking for Fame and Fortune? 

        Glyphosate, the active ingredient in Roundup and Touchdown herbicides, is widely used.  Currently, about 75% of the soybeans grown in the U.S. are glyphosate resistant.  As Roundup-ready corn hybrids hit the market and more options become available, the amount of glyphosate used will no doubt increase.  This of course leads to the real concern of weeds becoming resistant to glyphosate applications because of repeated use on the same fields.  Currently, glyphosate resistance has been confirmed for rigid ryegrass, Italian ryegrass, goosegrass, and horseweed.  Don't have any of those you say?  OK, how about waterhemp?  Yes, reports from Illinois, Iowa, and Missouri point to glyphosate resistance (or at least strong tolerance) developing in this nasty weed specie.  In some cases, waterhemp plants are surviving 6 to 8 times the labeled rate of glyphosate application. 

        So, if you're looking for fame and fortune (well maybe just fame, fortune was just a cheap trick to get you to read this), keep pounding the glyphosate applications to corn and soybeans year after year and you could own the very first farm in Wisconsin to have glyphosate resistant weeds.  If you're one who likes to avoid notoriety, use glyphosate in the crop rotation where it has the greatest value  and use different chemistries to control weeds for other rotation crops.  By not adhering to such a practice, the question will no longer be "if resistance will develop" but rather one of "WHEN resistance will develop".

Moving Silage from Structure to Structure

Controlled research studies have not been conducted to determine the amount of dry matter (DM) or nutritive value lost during the movement of silage from one storage structure to another.  However, we know that silage transfer is done on farms with both good and bad results.  If it's going to be done, NOW is the time to make it happen.  Silage is less prone to heating during transfer and feed-out in cold weather.  Limiting silage transfer and the feeding of transferred silage to the late fall, winter, and early spring months helps reduce the risks associated with transferring silage. 

        There are a number of propionic acid based additives that reduce the growth of yeast and molds when added to silage and thereby lessen the risk associated with transferring silage.  These products often contain some acetic acid or benzoic acid to make them more effective against yeast.  Even where used, remember that unstable silage that is prone to heating upon exposure to oxygen is not a good candidate for transfer.  Trying to transfer poorly fermented silage will only make it worse.  Make the transfer as quickly as possible to minimize the time that the silage is exposed to oxygen.  There should be less oxygen introduced into the silage mass if transferred to a bunker silo or bag than if blown into an upright silo.  Pack the re-ensiled material well to exclude as much oxygen from the silage as possible. 

Wheel Traffic on Alfalfa Reduces Yields

        You can't harvest alfalfa without driving over the field (Duh!).  However, a recent research project is showing that depending on when wheel traffic occurs after cutting has a large impact on yield loss.  Alfalfa plots were driven over with a 100-HP tractor either 2 or 5 days after cutting and compared to those with no wheel traffic.  Studies were conducted in six different states (including Wisconsin).  Total season yield loss ranged from 0 to 11 percent for plots driven-over 2 days after cutting and from 0 to 30 percent 5 days after cutting (both 0 percent losses came from Nebraska).  Additionally, there were varietal differences for being able to withstand wheel traffic after cutting.  This is probably explained by differences in plant crown architecture and speed of regrowth.  The significantly higher losses incurred 5 days after cutting were attributed to breakage of new growth shoots.  The bottom line on this study is evident:  when possible, don't drive on alfalfa fields 5 or more days after cutting.  If you do, expect significant losses under the wheel track.