ISSUE 15 August 11, 2005
HEAVY RAINS AND HARD SOIL
The talk around the eastern part of North Dakota late this summer has been the hardness of the ground. I do not hear this as much out west. The tilth of the soil around Dickinson last week seemed quite mellow. Tillage is conducted to manage weeds, bury residue so it decomposes faster, and incorporate fertilizers. It also can be rather disruptive to soil structure.
Soil particles naturally group together by chemical forces into aggregates. These aggregates have the beneficial result of being resistant to both compactive forces and environmental forces that sort clays from silts and sands and fill in pore spaces made by the activity of roots, wetting and drying cracks and cracks due to frost. I would be surprised even in the east if medium to heavy-textured long-term no-till fields were hard even this year, unless they were flooded and silted over.
Tilled fields, however, were broken up in the fall once and sometimes several times, then again once or twice this spring. These activities beat the aggregates apart, separating the natural cohesion that might have started to attract particles last summer. These loose particles are very susceptible to dispersion and sorting with medium to heavy rainfall, which in some years results in crusts and this year filled in many small to large pores several inches in depth.
With time, wetting and drying and growth of plants, the structure will gradually return to the soil. Tillage in dry soil will form new cracks, but these aggregates again will not be stable and will react just like they did this spring if the rain is heavy following tillage.
The key to minimizing these problems in the future is to minimize tillage, and rely more on residue managing equipment at seeding to form a good seedbed. Timing of field operations is more important than the number of trips.
Dr. Dave Franzen
NDSU Extension Soil Specialist