Agricultural Soils

October 3, 2012

Computer Lab Question

» Schedule˃ Group A: Oct 5˃ Group AA: Oct 12˃ Group AAA: Oct 19

» Hourly Exam # 2: Oct 24

Computer Lab Answer

» Schedule˃ Group A: Oct 5 – optional, but must sign up & make

up one of the following days/times:+ Oct 12, 4:30 – 5:20 + Oct 19, 4:30 – 5:20

˃ Group AA: Oct 12 (as scheduled, 3:30 – 4:20) ˃ Group AAA: Oct 19 (as scheduled, 3:30 – 4:20)

» If there are openings people in groups AA & AAA may attend one of the later labs

Dr. Whitford, Pesticides

» Farm chemical inputs˃ Fuel˃ Pesticides˃ Fertilizer and manure˃ Oil, antifreeze and the like

» We need to protect water and soil» It matters, because

˃ Protect property values˃ Potential legal issues˃ Avoid regulatory fines˃ Protect the environment (humans, domestic animals, wildlife,

plants)

Pesticide Management

» Put all products in the right place» Follow the product (from delivery to use): think

about how the product is transported and used» Conduct inspections, follow proper

maintenance

Last Wednesday Lecture

» Re: articles we read & reported on in class» Answers in the PPT (“More About Soils.pptx)

˃ The Fate of our Nation's Soil Resource˃ World Food Prize Digs Deep for Hunger Relief

Conservation Practices Help Correct Erosion Issues & New Conservation Program Protects Most Highly Erodible Croplands

˃ No-till Practices Open Mississippi Hills to Crop Production & Gullies in Long-term No-till Fields can be Troublesome

SoilWeb – WSS App

» New, free smartphone App » 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 » Article: Smartphone app offers access to soil information

Soil Testing After a Dry Growing Season

» Yield is the most important factor impacting P and K removal rates» Grain yields and nutrient removal levels are lower than normal due to

the drought » Some fields were been baled or harvested for silage» Soil testing for P, K, and pH is used to determine the need for

fertilization or limestone applications.» Corn and soybean return approximately one-fourth to one-third of the

total P taken up, and about two-thirds of the total K taken up, to the soil. » It is not safe to assume that lower removal rates and lower yields will

result in greater P and K levels in the soil this year˃ Drought limits the equilibration of nutrients in the soil˃ Plants have extracted P and K during the growing season˃ The soil has not been able to replenish those nutrients as well as in

normal year

Illinois Ag Connection, www.croplife.com

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˃ Tillage

Hoorman, Carlos de Moraes Sá, and Reeder, Crops & Soils magazine, July-August, 2011

Biology of Soil Compaction

» Results of Soil Compaction˃ Restricted root growth˃ Poor root zone aeration˃ Poor drainage, which causes

+ Less oxygen in the root zone+ Increased loss of nitrogen (from denitrification)

Biology of Soil Compaction

» Sub soil tillage to break up a compacted layer˃ Expensive, requires: fuel, labor, equipment and time˃ Used to reduce compaction and related problems (lack

of water infiltration and aeration)˃ Soil is generally disturbed 12-18 inches deep ˃ Additional compaction can occur if the soil is subsoiled

when wet

Biology of Soil Compaction

» Usually helps but effects are often temporary unless management changes

» Re-compaction of soil is caused by ˃ Equipment traffic˃ Rainfall, especially heavy rains˃ Gravity˃ Low organic matter (OM) which makes soil more

susceptible to compaction

Biology of Soil Compaction

» Organic Matter ˃ 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 will break up organic residues

Biology of Soil Compaction

» Tillage has decreased soil organic levels and therefor soil organic carbon by 60% in the last hundred years

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

» Humus (old carbon, >1,000 years old) is the most stable carbon, and binds soil microparticles together to form microaggregates˃ Humus is not water soluble

+ Stabilizes microaggregates + Not readily consumed by microorganisms+ More resistant to tillage and degradation than active

carbon

Biology of Soil Compaction

» 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)

Biology of Soil Compaction

» What is a clod?˃ Made by humans – do not exist in the natural world˃ Tilling exposes clay to sunlight, heating and drying ˃ Clods are formed… just like 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

Biology of Soil Compaction

» 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 traffic2. Plant roots create voids and macropores in the soil that allow

air and water movement3. Plant roots supply food for microorganisms (esp. fungi)4. Organic residues (from decaying plants, animals, microbes)

are lighter and less dense5. Aids in combining microaggregates into macroaggregates

which improves soil structure

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.

Fyksen, AgriView.com

Ways to Evaluate, Avoid Compaction

» Check 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

Ways to Evaluate, Avoid Compaction» Shallow, Surface 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

˃ Conventional or reduced tillage systems: avoid during planting

˃ No-till system: avoid at all times

Ways to Evaluate, Avoid Compaction» 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 (use

minimum allowable tire pressure) may help

Ways to Evaluate, Avoid Compaction» 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?

Ways to Evaluate, Avoid Compaction» 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

» Sjoerd Duiker (quoted for this article):˃ “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.”

Ways to Evaluate, Avoid Compaction» Sjoerd Duiker: 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 compaction3. Remediate compaction only if needed

Herbicide-resistant Weeds Threaten Soil Conservation Gains

» The Flip Side: Herbicides & Conservation Tillage» 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

CAST* staff, Feb. 6, 2012

*CAST ~ Council for Ag Science and Technology (www.cast-science.org/)

Herbicide-resistant Weeds Threaten Soil Conservation Gains

» Mitigating the impact of herbicide-resistant weeds˃ A diversity of strategies is necessary

+ Alternative tillage, including mechanical + Alternative herbicides+ Crop rotation (depending on the crops and

management practices used)