Fall Tillage and Soil Compaction


Agricultural field practices seem to be like our national politics, very much divided. Maybe 25% more fields planted to cover crop due to H20 Ohio funds. On the other hand, there appears to be more vertical tillage, chisel plowing and plowing. Green fields surrounded by bare fields. The wet fall weather, soggy soils, and tillage has created hard pans and poor soil structure. Perhaps winter freezing and thawing will mellow out our soils but tilling soils wet almost always creates more problems; especially with soil compaction, drainage, and soil structure.

Farmers have many reasons for fall tillage. Eliminating ruts, burying diseased plant residue, and burying weed seed are common explanations. Stale seed beds (light fall tillage) create spring soil conditions for good seed to soil contact and slightly warmer soils which allow plants (especially corn) to germinate quickly. Corn is a warm season plant that also benefits from nutrients released during tillage. Soybeans and even wheat are more forgiving and these crops tolerate no-tilled or cover crop fields better than corn.

Many no-till and cover crop farmers have found ways to heal the soil so that they can get the same or sometimes even better yields by leaving the soil undisturbed. Improving soil health reduces pests (weed seed, diseases and insects) once beneficial organisms return. However, it may take 3-7 years, sometimes longer to make this transition to get the same yields. When crop prices are high and profit margins are tight, very few farmers will make this transition. When crop prices decline and/or fertilizer and fuel prices are high, interest in no-till and cover crops rise. Farming is a big gamble and most farmers try to minimize their risks on farming practices that appear risky. While soil health may be better long-term for the environment and even eventually higher crop yields; most agricultural decisions on made on a short-term basis.

There are two ways to deal with soil compaction and poor soil structure. Mechanical solutions are short-lived, lasting one year and contribute to long-term soil compaction and poor soil structure. A ripper or subsoiler will increase water infiltration 18 inches but it burns up soil organic matter (SOM) and increases soil erosion. The biological approach may be slower (takes 2-3 years, roots penetrate about 1 foot/year) but it is longer lasting. Increasing SOM levels creates a major storehouse for soil nutrient while reducing soil erosion. Cover crop roots may increase water infiltration down 3 feet or deeper to improve water drainage. Maintaining or increasing SOM should be every farmer’s goal if they want to improve soil structure, purchase the least commercial fertilizer, and optimize crop yields. 

Dr. Sjoerd Duikert, Penn State documented changes in soil structure once tillage was eliminated. A loaded grain truck was transported across 4 fields: conventional tilled field, one, two, and multiple years in no-till. The conventional tilled field had 6-12 inch ruts, the one year no-till 3-6 inch ruts, two year no-till 1-2 inch ruts, with minimal ruts in the long-term no-till field. The improved soil structure increased soil structural stability in the no-till fields over time.

To improve soil stability, farmers should limit or totally reduce tillage to improve soil structure and reduce soil compaction. Avoid subsoiling or deep tilling wet saturated soils which cause smearing and sidewall compaction. Second, plant cover crops yearly to maximize active SOM, root exudates, and beneficial mycorrhizal fungi glomalin which forms macro-aggregates critical for good soil structure. Plant a mixture of legumes, grasses and brassica cover crops. Grass roots (sorghum, annual ryegrass, cereal rye, oats) have fibrous roots and supply carbon and phosphorus. Legume roots (clovers: Balansa, crimson, red; hairy vetch; winter peas; Sunn hemp, cowpeas) have deeper tap roots and supply nitrogen. Brassica’s (daikon radish, kale, rape seed) reduce weeds and promote beneficial microbial populations. Sunflowers have deep roots while buckwheat has shallow roots, great for reducing soil compaction. 

Third, keep the soil surface covered with crop residue. Surface crop residue reduces heavy rainfall impact and cushions the weight of wheel and implement traffic. Crop residue also reduces soil erosion, improves water infiltration, and regulates oxygen and soil carbon levels. Removing residue, is like removing the roof on your house. The house will soon rot out and collapse just like our soils tend to break down and collapse with excess tillage and lack of live roots. Heavy wheel axle loads from loaded combines, grain carts, and large tractors along with excessive tillage are major causes of soil compaction and poor soil structure, but it takes live roots and microbes or Biology to improve your soil structure and build SOM!