Northwest Iowa Crop Update Newsletter
by Todd Vagts
ISU Extension Crops Specialist
Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.

In this issue
Take the soybean aphid “treated vs. non-treated” yield survey
Calculate grain weight losses from drying
Making the most from corn stalks
Managing soil compaction
Soil sampling dry soils

Example:  You plan to dry shelled corn from 25% to 15.5% moisture (a removal of 9.5 percentage points), the water shrink would be [9.5 * 1.183 (from table 1)], or 11.24% of the original grain weight.  Total shrink would be [11.24% + 0.5% (handling loss)], or 11.74%.  So if we started out with 1000 lbs of 25% moisture corn, we would end up with 882.6 lbs of grain dried to 15.5% moisture; [1000 lbs * 0.1174 (total shrink loss) = 117.4 lbs of lost weight; then 1000 lbs – 117.4 lbs (lost weight) = 882.6 lbs of dry grain]
Source:  Calculating grain weight shrinkage in corn due to mechanical drying, D.R. Hicks and H.A. Cloud, Univ. of MN.  NCH 61.  http://www.extension.iastate.edu/Publications/NCH61.pdf

Corn stalks have feed and $ value 
Cornstalks can be a great source of winter feed for cattle.  Cornstalks that are supplemented with protein, vitamins and minerals can supply the nutritional needs of cows that are in moderately good body condition.   Cornstalks are generally considered to have about 80 to 90 percent of the energy of mixed grass and legume hay per pound of dry matter, but only 20 to 30 percent as much protein.  Adding soybean meal can be a good way to increase protein content.  Bruce Anderson (Nebraska Extension Forage Specialist) recommends that if you plan to graze cornstalks, the stalks should be grazed as soon as possible after harvest. The nutrient value of stalks declines the longer they are exposed to weathering. Grazing stalks right after harvest will put more condition on cows and faster gains on young stock.  For information on estimating dollar value of cornstalks baled or in the field, obtain the October 6, 2003 ISU ICM newsletter, also found on-line at:  http://www.ipm.iastate.edu/ipm/icm/. 

Soil and Fertility Management
Minimize the effects of soil compaction  The impact on yield from soil compaction has been reported to be as much as 10 to 20 percent in unfavorable years. A major effect of soil compaction is the alteration of the soil's physical (bulk density, soil strength, and porosity) and the hydraulic (infiltration rate and movement of water within the soil profile) properties. Changes in the soil's physical properties alter the ratio of water to air in soil. Plant roots require air as well as water to develop a healthy root system.  The main cause of soil compaction is field traffic from machinery. Soil compaction is most likely to occur when soil moisture is at or near field capacity.  Under these conditions, aggregates can be "lubricated" by water and readily reposition themselves through the air spaces under heavy traffic.

Most soil compaction occurs from the first pass of the implement; therefore minimize field-wide compaction by using controlled traffic lanes. For example, avoid driving loaded grain carts randomly through the field.  Check wheel and tire size and pressure. Larger wheels and tires allow better flotation, and lower tire pressures reduce the load on the soil. Increase the tire's "footprint" with larger wheel diameters. Spend the extra time with your implement and tire dealer to obtain proper tire size and set tire pressure, the extra time this fall may pay off quickly next year through higher yield potential soil conditions.
Source:  Soil compaction may be cutting into your yield; ICM Newsletter 7/8/2002.  Mark Hanna, ISU Extension Agricultural Engineer, and Mahdi Al-Kaisi, ISU Extension Soil Specialist

Soil Sampling Dry Soils  When collecting samples this fall for soil testing, watch the soil sampling depth. It can be difficult to sample to the recommended 6-inch depth when soils are dry and hard. If you can't sample to the correct depth, don't take the samples. Shallow sampling will result in incorrect results and recommendations. If low rainfall persists after harvest, less K may be leached from remaining crop residues. This could impact soil test K results.  (Dr. John Sawyer, ISU Extension Soil Fertility Specialist in “Drought impacts on soil fertility management” (http://www.ipm.iastate.edu/ipm/icm/2003/10-6-2003/droughtsoilimpact.html)