Part 1, Section 1: Soil Management

Table of Contents

Soil Health

Improving Soil Health

Soil Organic Matter

Soil organic matter content is considered one of the most important indicators of soil health. To maintain or increase organic matter content one needs to maximize inputs or additions of organic materials, and minimize outputs or losses. Inputs can be increased by growing crops that produce large amounts of residue and fine roots (species such as corn, small grains, grasses), leaving crop residue in the field, growing cover crops during otherwise bare fallow periods and adding compost and manure (especially bedded manure). How much organic material should be returned to the soil to maintain organic matter contents? This question is receiving increased attention because of the interest to harvest crop residue to produce biofuels. A recent review suggests that in a no-till system 4500 lbs/A/yr of crop residues need to be returned to maintain organic matter content under conditions pertaining to the Corn Belt, and with tillage this number needs to be a lot higher. To meet this goal will be very challenging because most annual crops don’t produce that much crop residue, even if no residue removal is allowed (Table 1.1-3 ). This takes us to the output or loss side of the organic matter question. Losses include removal or crop residue (such as hay, straw or silage harvest), burning and tillage. If crop residue or silage is harvested, one needs to give thought to how to supplant the removed organic material, for example by adding manure, or compost, or planting a cover crop that is allowed sufficient time to accumulate biomass to compensate for the removal. Soil tillage increases losses of organic matter, so eliminating tillage will help improve soil health. The type of tillage also matters; the moldboard plow tends to cause the largest losses of organic matter, while the chisel plow and disk harrow cause smaller organic matter losses. The distribution of soil organic matter in the topsoil is also dramatically influenced by tillage. With moldboard plowing, soil organic matter content is uniform throughout the plow layer. In long-term no-tillage or sod, on the other hand, soil organic matter content will be high at the soil surface and decrease rapidly below the 2–3" depth. Chisel plows and disks tend to lead to soil organic matter distribution that is intermediate between moldboard and no-tillage. From an agronomic point of view, organic matter gives the largest benefits if it is found close to the soil surface because of its effect on aggregate stability and soil tilth. The improved soil tilth observed in the top 1–2 inches of the soil in long-term no-tillage increases aeration and infiltration and leads to improved seed-to-soil contact when planting. The surface soil also becomes more resistant to compaction and will facilitate root development.

Table 1.1-3. Crop residue production of different crops in rotation.
  Yield (bu/A) Bushel weight (lbs/bu) Yield (lbs/A) Moisture content (ratio) Dry matter (ratio) Grain dry matter yield (lbs/A) Residue: grain ratio Residue dry matter yield (lbs DM/A) Tons/A
To calculate crop residue yield, multiply crop grain yield (bu/A) and dry matter content (ratio) and residue:grain ratio.
Barley 70 48 3360 0.120 0.880 2957 1.5 4435 2.2
Wheat 55 60 3300 0.120 0.880 2904 1.5 4356 2.2
Soybeans 40 60 2400 0.130 0.870 2088 1.0 2088 1.0
Sorghum 90 56 5040 0.135 0.865 4360 1.5 6539 3.3
Rye 50 56 2800 0.120 0.880 2464 1.5 3696 1.8
Oats 60 32 1920 0.120 0.880 1690 1.0 1690 0.8
Corn 130 56 7280 0.155 0.845 6152 1.0 6152 3.1