Extension Communications
Extension 4-H Youth Building
Ames, Iowa 50011-3630
(515) 294-9915
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Extension Communications |
7/8/04
Contacts:
Mahdi Al-Kaisi, Agronomy, (515) 294-1923, malkaisi@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Frequent Tillage Affects Soil Quality
(AMES, IA) -- Iowa State University Extension agronomist Mahdi Al-Kaisi says that improving soil quality and sustainability should be a main priority for Iowa farmers. "There are many characteristics and indicators of soil quality," said Al-Kaisi. "Good bulk density, abundant soil pores, good infiltration rates and water-holding capacity, overall tilth, high levels of organic matter, and beneficial soil organisms -- all are indications of good soil quality."
Al-Kaisi cautions that frequent tillage has a negative effect on almost all of those characteristics, and that sustained, frequent tillage translates into an even greater impact. Even in-season tillage can have a short-term effect, and every growing season is different, according to Al-Kaisi. So how should farmers make tillage decisions when managing their soils?
"Good soil managers make decisions based on frequent scouting and knowledge of soil conservation. A good example can be cited from an experience that occurred a couple years ago, when drought resulted in low crop residue levels. In the following season, managing for soil quality would have meant at least a temporary conversion to no-till or reducing 'in-season' tillage and cultivation. Those who chose to use conventional in-season tillage create conditions for serious degradation of the soil quality on their land."
Unnecessary tillage over a couple seasons generates more serious soil quality problems. "Without a break from tillage, a total break down of soil structure is possible," says Al-Kaisi. "The number of beneficial soil organisms decline, bringing microbial activity to a minimum and degrading soil structure, which results in severe limitations of water infiltration, increasing surface runoff."
"If moderate erosion occurs, there may even be some initial loss of productivity. Farmers putting themselves in this position are in danger of yield setbacks due to organic matter and nutrient loss, as well as the damage done to the soil's physical properties."
"When frequent and unnecessary tillage is sustained over many seasons, the deterioration of soil quality becomes even more severe. Hardpan develops, effectively cutting off root elongation, crop development and yield."
Al-Kaisi says that at this point, many farmers experience high rates of erosion and topsoil degradation. "Erosion contributes to a loss of inherent soil fertility levels because nearly all organic matter and plant-available potassium is located in the topsoil, as well as plant-available phosphorus. And while farmers can supply needed crop nutrients to offset the loss of inherent fertility, the productivity of eroded soils can be restored by adding inputs only when favorable subsoil material is present. Where unfavorable subsoils exist, such as limited rooting depth, coarse sand and gravel and high soil densities, there is little or no ability to recover yield losses. The impact on soil quality and productivity is devastating and final."
Al-Kaisi also says that the impact goes beyond the farm. Erosion and runoff resulting from frequent tillage can contribute to deterioration in overall surface water quality. Sediment from soil erosion is a major water quality pollutant, and sediment also transports nitrogen and phosphorus from fields into lakes and streams, causing serious surface water quality problems.
Unnecessary or frequent tillage can be costly in terms of soil quality, soil productivity and surface water quality, as well as extra wear on machinery and extra labor requirements.
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Funding support provided by USDA Natural Resource Conservation Service through Cooperative Agreement No. 74-6114-10-03.
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