Tillage Affects Soil Nutrient Availability

By Crystal McNett, Assistant Editor
Thursday, April 5, 2007 4:24 PM CDT

"Tillage is probably the most profound thing we do to the soil and it is going to affect nutrient availability," said Dick Wolkowski of the UW-Madison soil science department at the recent soil nutrient workshops in Madison.

Tillage involves the mechanical manipulation of the soil surface to modify soil condition for crop production. Conventional tillage leaves 0 to 15 percent of crop residue, reduced tillage leaves 15 to 30 percent crop residue and mulch or conservation tillage leaves greater than 30 percent of crop residue. No-till, as the name implies, leaves all crop residue.

The eight Midwestern states of Ohio, Indiana, Michigan, Illinois, Wisconsin, Minnesota, Iowa and Missouri, in 2002, composed 106 million acres of cropland, which made up 37 percent of the total cropland in the United States. Wisconsin is behind the regional trend for minimal tillage practices because of the northern geography, but more importantly because of the great amount of forage produced in the state, Wolkowski explained. "There is room to improve conservation tillage management," he added.

Tillage has a measurable affect on soil's physical, chemical and biological characteristics. Residue modifies temperature and moisture. It also affects nutrient and pH stratification as well as carbon distribution and nitrogen transformation.

As tillage impacts soil erosion, conservation tillage can be utilized to reduce erosion. Chisel plowing is versatile and can leave more or less residue depending on the type of shovel used, Wolkowski explained. A twisted shovel will bury much of the crop residue, while a sweep will leave a significant portion.

Conservation tillage reduces soil erosion by up to 60 percent when 30 percent of the residue remains. It also improves water quality by improving water filtration. In addition, conservation tillage has the following benefits:

Maintains soil moisture.

However, conservation does have its down side, Wolkowski recognized. It can affect emergence, nutrient stratification, weed and pest management, fertilizer and manure application, cultivation and can increase the risk of field fires and yield loss.

Tillage affects soil and water relationships. No-till soils tend to have lower porosity and higher water content, but this varies considerably by soil type. Those continuous channels in no-till increase infiltration rate, Wolkowski explained. "Long-term tillage management allows for more continuous pores and greater potential for water movement," he added.

Traffic management is critical in reduced tillage soils. Growers should focus on where tractors are driven and how many times they are driven over that track. Driving areas should be designated to reduce soil compaction throughout the field where it is not necessary, Wolkowski recommended. A study regarding fertilizer placement, inter-row versus row, untracked soils allowed for nearly three times greater root growth than soils that had been driven over. Reduced tillage has long-term affects on soil characteristics including, lower penetration resistance compared to chisel and greater penetration resistance in the wheel track.

Tillage has a great effect on soil biological properties. No-till and reduced tillage affect nitrogen availability as it causes lower and slower mineralization, greater immobilization, volatilization of ammonia from urea, potential for increased denitrification and overall reduced availability.

 

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