MORE ABOUT SOILS

September 11, 2013

&

September 18, 2013

Web Soil Survey

• http://websoilsurvey.nrcs.usda.gov/app/ • Uses:

• General management decisions• Land use decisions• Required for Concentrated Animal Feeding Operations

(CAFO) siting

• Soil Survey: • Soil map for a land area plus soil descriptions plus

predicted use and limitations

Soil limitations for a CAFO (example)

• High seasonal water table

• Slow permeability

• Low bearing strength

• High shrink/swell capacity

• Corrosive to metal and concrete

Creating a Soil Survey

Soil Properties

• Horizons• Color• Texture• Structure • Other physical, chemical and

mineralogical characteristics

Landscape Features• Vegetation• Rocks• Slopes• Streams• Drainage-ways• Lakes• roads,• Dams• Gravel pits

Soil Scientists compare and classify soils, analyze how the soils will support different uses, and plot the soil location on aerial photographs.

SoilWeb – WSS App• New, free smartphone App

(http://casoilresource.lawr.ucdavis.edu/drupal/node/902)

• Gives users access soil survey information on iPhones and Androids

• Combines online soil survey information with the GPS capabilities of smartphones

• Particularly useful for those working in the field

Soil Testing After a Dry Growing Season

• Yield is the most important factor impacting P and K removal rates

• Corn and soybean return about 1/4 to 1/3 of the total P, and about 2/3 of the total K, to the soil

• Grain yields and nutrient removal levels are lower than normal after a drought

• But, do not assume that lower removal rates and lower yields will result in greater P and K levels in the soil next year

• Soil testing for P, K, and pH should be used to determine the need for fertilization or lime applications

Soil Testing• Certified commercial laboratories offer plant and soil

testing analysis services for growers in Indiana

• Purdue Agronomy list: www.ag.purdue.edu/agry/extension/Pages/soil-testing-labs.aspx

Biology of Soil Compaction

• Soil compaction: soil particles are pressed together, limiting the space for air and water

• Soil compaction can reduce farm yields (and profits)

• Factors that contribute to compaction:

• Farm machinery weight and traffic

• Rain, especially heavy rains

• Tillage

• Low organic matter (OM) (makes soil more susceptible to compaction)

Biology of Soil Compaction

• Soil compaction causes:

• Restricted root growth

• Poor root zone aeration

• Poor drainage, which causes

• Reduced oxygen in the root zone

• Increased loss of nitrogen

Soil Compaction

• Sub-soil tillage to break up a compacted layer

• Used to reduce compaction and related problems (lack of water infiltration and aeration)

• Soil is generally disturbed 12-18 inches deep

• Expensive, requires: fuel, labor, equipment and time

• Note: additional compaction can occur if the soil is sub-soiled when wet

Soil Compaction

Sub-soiling • Usually helps, but effects are often temporary unless

management changes

• Re-compaction of soil is caused by the same forces that cause compaction in the first place:• Equipment traffic• Rainfall (especially heavy rains)• Gravity• Low organic matter (OM)

Organic Matter & Soil Compaction

• Organic residues on the soil surface cushion the soil from compaction because they can be compressed and regain their shape

• OM that is attached to soil particles (esp. clay) reduces soil compacting

• OM binds microaggregates and macroaggregates in soil (macroaggreates improve soil tilth)

• Excessive traffic breaks up organic residues

Soil Carbon

• Tillage has decreased soil organic levels, and therefore, soil organic carbon by 60% in the last hundred years

• Carbon provides energy for soil microbes, stores nutrients, and recycles nutrients in the soil

• Types: active carbon and humus• Humus (old carbon, >1,000 years old) is the most stable

carbon

Humus

• Binds soil microparticles together to form microaggregates

• Not water soluble • Not readily consumed by microorganisms• More resistant to tillage and degradation than active carbon

Active Carbon

• Plant sugars, polysaccharides, and glomalin • Consumed by microbes for energy• Reduced with tillage • Stabilized under natural vegetation and no-till systems using a continuous living cover

• Part of the “glue” that binds microaggregates into macroaggregates• Macroaggregation improves soil structure and lowers bulk density, helping to keep soils from compacting

Soil Clods

• Clods are made by humans

• Clods do not exist in the natural world

• Tilling exposes clay to sunlight, heating and drying which forms clods (as bricks and clay tile are formed by heating and drying wet clay)

• Moisture and organic residues keep clay particles from chemically binding by keeping clay particles physically apart

Soil Cover & No-Till

A continuous living soil cover plus continuous long-term no-till protects the soil from compaction, because:

1. Covered soil surface acts like a sponge to help absorb the weight of heavy equipment traffic

2. Plant roots create voids and macropores in the soil that allow air and water movement

3. Plant roots supply food for microorganisms (esp. fungi)

4. Organic residues (from decaying plants, animals, microbes) are lighter and less dense

5. Aids in combining microaggregates into macroaggregates which improves soil structure

Soil Type & No-Till• No-Till works well on forest soils (historically) No-Till may

not work as well on flat black prairie soils • They tend to stay wetter and cooler in the spring when

covered with heavy no-till residue• Highly productive soils may have residue from 225

bushel corn which acts like a blanket: good to prevent erosion but will have a buffering effect (warming or drying)

• Where are these soils? • ISEE website/Bedrock Geology and Soil Properties/Dominant

Soil Parent Material

Ways to Evaluate & Avoid Compaction

• The amount of soil water present is a critical factor in soil compaction potential.

• Spring is the best time of the year to measure soil compaction when the whole profile has usually been thoroughly moistened during the winter.

• If the soil is too wet and muddy, compaction could be underestimated because the soil water acts as a lubricant.

• If the soil is too dry, compaction could be overestimated because roots will be able to penetrate the soil when it re-wets.

Ways to Evaluate & Avoid Compaction

Checking for soil compaction• Shovel – look for surface crust or platy soil structure

• Soil probe – insert slowly, feeling for increased resistance

• Soil pentrometer – push in (1 inch/sec.); resistance > 250-300 psi in moist soil is root-limiting

Shallow Soil Compaction

• Related to pressure on the soil surface• Normally removed by tillage operations • May be removed by freeze-thaw and wet-dry cycles

• Control:• Better load distribution (larger tire size or more tires)

• GPS can help maintain controlled traffic

Sub-surface Compaction

• Related to maximum axle load• Will not be reduced by distributing equipment weight

• Can only be avoided by limiting traffic with heavy axle loads • A maximum axle load of 10 tons is recommended (Note: a 1,000-bu grain cart can weigh more than 36 tons)

• Low-inflation tires with a large footprint may help (use minimum allowable tire pressure)

Sidewall Compaction

• Caused by planting when soil is too wet• Planter openers push on the side of the soil furrow, creating a compacted zone

• Avoid by not planting when the soil is too wet*• Spoke wheel seed slot closers can be helpful

• *Testing for moisture content – how?

Fall-Planted Cover Crops

• Provide support for livestock and/or manure spreaders over winter

• Plant cover crops right after harvest of annual crops to keep living roots in the soil year-round

“Living root systems are probably the best protection against compaction.” “Avoiding compaction is a lot more cost-effective than causing it and then having to repair it.”

• Dr. Duiker, Penn State soil mgmt. specialist

The Basics of Soil Compaction

1. Use no-till to help your soil resist and bounce back from compaction • Increased organic matter accumulation at the soil

surface • Permanent burrows of old root channels and

prolific activity of earthworms and fungi in permanent no-till fields also helps make the soil resist compaction

• Biological organisms also help alleviate compaction after it has been caused

2. Avoid causing compaction

3. Remediate compaction only if needed

No-till Challenge

• Herbicides were developed for weed control (conventional tillage)• Highly effective herbicides and herbicide-resistant crops (e.g.,

glyphosate) allowed the development of conservation tillage and less soil damage

• When any single herbicide mechanism is used repeatedly without alternative management, selection pressure becomes intense for plants that can tolerate the herbicide

• Several weed species exhibit resistance to glyphosate and many are resistant to other herbicide mechanisms

Herbicide-resistant Weeds Threaten Soil Conservation Gains, CAST paper, Feb. 6, 2012 (CAST ~ Council for Ag Science and Technology, www.cast-science.org/)

CAST Recommendations

Mitigating the impact of herbicide-resistant weeds (use a diversity of strategies):

• Alternative tillage, including mechanical

• Alternative herbicides

• Crop rotation (depending on the crops and management practices used)

In Class Assignment • Work in teams of 2 (assigned):

• Reader• Recorder

• Read: On-Farm Soil Monitoring for Water Resource Protection (WQ-43)

• Answer the questions • Hand in before leaving today

• Reminder – Lab 3 on Friday