Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
6/7/01
Contacts:
Mahdi Al-Kaisi, Extension Agronomy, (515) 294-1923,
malkaisi@iastate.edu
Mark Hanna, Extension Agricultural and Biosystems Engeering,
(515) 294-0468, hmhanna@iastate.edu
Wet Soils Vulnerable to Compaction
AMES, Iowa -- A stubborn pattern of wet weather has presented Iowa farmers with a number of challenges to accomplishing fieldwork. But Iowa State University Extension Agronomists soil management specialist Mahdi Al-Kaisi and Extension agricultural engineer Mark Hanna say farmers need to do a risk assessment before heading out to the field.
"The decision to be in the field should consider the possibility of damage to the soil, and when soil moisture exceeds field capacity, there is increased potential for creating soil compaction, particularly at topsoil depths," said Al-Kaisi. "The impact of soil compaction is significant because the soil's physical and chemical properties -- such as infiltration rate, bulk density and nutrient availability -- can be altered."
Farmers are tempted to work wet soil for the potential benefits. Planting has to be done, and cultivation helps break up crusted soils and "darkens" the soil's surfaceand (speeds warming and drying of the soil surface). But Al-Kaisi and Hanna say the potential for soil compaction is at its highest when the soil is just dry enough to work without getting stuck.
Checking soil moisture takes just a few secondsminutes. Probing the top 3 to 4 feet with a hand soil probe to assess the field's soil moisture conditions is time well spent. Or, Check the soil moisture status by try pushing a ribbon of soil from between the thumb and index finger. If it breaks off within an inch or two, the potential for creating compaction is less. However, if the ribbon stretches out to 4 or 5 inches, it's still too wet. Another method is to make a ball of soil 2 inches in diameter and toss it into the air. If it hangs together until it lands, it has a lot of cohesiveness, and is probably too wet to work.
Al-Kaisi and Hanna also have concerns about planting and replanting in wet soils.
"If conditions are too wet, producers could smear the seed furrow sidewall, a form of soil compaction that makes it difficult for root systems to move laterally," Hanna said. "Also check the planter's press wheels and keep the pressure slight by lightening the tension on the downspring mechanism."
Lighter tractor axle weights lessen the likelihood of soil compaction. Because field operations like planting, rotary hoeing and cultivating require less horsepower, if a choice in tractor size exists, now is the time to use the smaller tractor.
Farmers should watch the calendar, watch the weather and know the soil conditions. "Every day that passes makes it more tempting to get in the field and work at the first opportunity, but producers should consider implications for soil compaction as opposed to delayed field operations," said Al-Kaisi.
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