University of Minnesota Extension

WW-07399     2000  

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Publications to help you get more from your soil

A Year in the Life of Your Soil

Dates are approximate for Minnesota and vary each year.

  Spring
(Late April through early June)		 Summer
(June through August)		 Fall
(Late August through September)
Structure & Temp. Saturated soils have a weak structure and are prone to compaction. Spring soil is highly susceptible to wind and water erosion, because soil is often bare and soil structure is weak. By late spring, bacterial and fungal activity will help stabilize soil aggregates, and plant growth will begin to protect the soil surface. Even healthy soil is difficult to penetrate when it gets very dry. Risk of soil compaction increases again as soil moisture levels rise and heavy harvest equipment enters the fields.
Nutrients Bacteria and fungi are becoming active, but not necessarily enough to provide nutrients to young plants. Side-dressing of nutrients may be useful. If a young (high N) forage is plowed down, soil organisms quickly release N and other nutrients to the next crop. A low-N amendment, such as straw, may trigger N deficiency in a crop, as soil organisms use soil nitrate to decompose the high carbon amendment. Fall is a good time to test soil - leaving all winter to use test results for planning the next cropping season. Cool season cover crops can take advantage of nutrients (and water and sunlight) not being used by the main-season crop, and can prevent nitrogen losses.
Water Compacted soils drain slowly. The loose, rough surface of newly tilled soil readily allows rain water to infiltrate into the soil - unless a crust forms. High temperatures in July and August cause high water loss through evaporation and transpiration from plants. Soil water stores are at their lowest. Soil water levels begin to recharge as temperatures drop and evaporation and transpiration slow.
Organisms Warming temperatures, air from tillage, and food from a plowed-down crop trigger a high level of activity. Organisms give off heat, carbon dioxide, and nutrients as they consume residue. Any change in environment - new food, hot spell, heavy rain - will change microbial activity. In late summer, organisms from bacteria to earthworms are less active and reproduce less because of the lack of water. Microbial activity increases in response to greater soil moisture and new food in the form of roots and residue from harvested crops.
Plants Tillage triggers weeds to sprout. As crop roots begin to grow, they continually contribute organic matter to the soil. They exude organic compounds and slough off dying cells. Root growth slows as plants produce flowers and other reproductive growth. By this time, roots may have extended deep into subsoil in search of water and nutrients. Warm season plants such as corn and some grasses flourish in the heat (if they have enough water). Over the course of the year, 40% of the photosynthetic energy captured by a plant is used by the roots, and enters the soil system. Most of this carbon is released from the roots as CO2.

A Year in the Life of Your Soil (continued)

  Freezing
(October through mid-November)		 Winter
(Mid Nov. through February)		 Thawing
(March and April)
Structure & Temp. Both surface residue and the irregular surface left by rough fall tillage protect the soil from winter wind erosion and spring water erosion. A January thaw affects the structure of the top inch or so of soil. Bare soils warm more quickly than residue-covered soils.
Nutrients In late fall nitrate leaching increases as plant uptake and microbial activity decline. Few changes occur in nutrients during the winter. Freezing temperatures prevent biological and chemical activity, or water movement. Microbes and plants are not active and using nitrate, so soil nitrate is prone to leaching in early spring. Cool temperatures prevent denitrification losses.
Water If an early heavy snow insulates the soil, the ground may not freeze deeply. Surface soil may freeze and thaw several times each winter, but subsoil only freezes once. Any water from thawed snow or surface-applied manure cannot soak in and will run off. Soil ice does not thaw evenly. Cracks and openings in the ice begin to allow water to flow down into subsoil and recharge water supplies.
Organisms If it is warm, fall plowing triggers a final flush of microbial activity and organic matter decay. There is little or no biological activity, except from a few species adapted to living in snow and cold soil. A few organisms are becoming active. Root nodules on some perennial legumes have survived the winter and begin to fix nitrogen. When the soil fully thaws, some arthropods and earthworms move toward the surface from deep in the soil where they have been dormant.
Plants As perennials "harden off" they send energy down to the roots for storage. If perennials such as alfalfa are protected by a continuous snow cover, they may stay green and perform some photosynthesis well into winter. The soil environment is steeply stratified: Little or no root activity occurs near the frozen surface, while deep down, temperatures may be in the 40°s. Even when all above-ground growth is dead, deep perennial roots are alive and growing. They get energy from stores in the thicker roots. Root activity (growth and uptake of water and nutrients) gradually increases as soil warms, but does not become very active until soil temperatures pass 50 degrees. Perennials such as alfalfa take energy from the roots to start growth of a new crown.

Soil Management Sections:
Introduction | Soil Manager | Soil Scientist | Soil Life | What's Next | Acknowledgments
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