Conservation tillage systems (described below) can be an important part of a sustainable agricultural system, in that they can be used to decrease soil erosion losses ordinarily associated with typical US agricultural practices. It is important to remember that anything that is done to decrease erosion losses also decreases the need to add as much fertilizer and water to soils, given that top soil generally contains the most organic matter. Other ways to decrease soil losses are discussed in the next section, which includes coverage of the Conservation Reserve Program.
Conservation tillage also, ideally, decreases water pollution (via decreasing soil erosion) and saves fossil fuel energy and thus decreases CO2 emissions, compared to conventional tillage systems. Because soil organic matter tends to increase under conservation tillage, as compared to conventional plowing, the soils are also more effective at storing carbon.
Conservation tillage systems include a variety of techniques, including "no-till" "minimum till" "ridge till" "chisel plow" and "mulch till." The Soil Conservation Service (now called the Natural Resources Service) refers to these systems as "residue management."
Conservation tillage is basically any system of cultivating that reduces soil or water loss when compared to conventional moldboard plowing, which turns over the soil completely. Most definitions specify that at least 30% of the crop residue must remain on the soil surface at the time of planting.
It is designed to conserve soil, water, energy (as originally conceived), and protect water quality (again, as originally conceived).
Why do farmers till in the first place?
If farmers reduce their use of tillage, they must find alternative ways of accomplishing each of these goals, of course.
Except for drying, conventional tillage in nonirrigated systems requires more energy than any other direct activity on the farm (direct activity excludes things like the energy required to manufacture fertilizers).
How does conservation tillage conserve soil, and how effective is it?
With conventional tillage (complete turning over of the soil), the bare soil is exposed to the erosive action of water, which, in many areas is the major route of soil loss. Under conservation tillage, the crop residue buffers the raindrops' energy, so water has less erosive force when it reaches the soil. This protection by residue, along with the rougher surface provided by the residue facilitates infiltration and decreases runoff -- runoff that carries soil and nutrients with it. In addition, macropores, which are the major route for water movement through soil, get disrupted in the surface 15-20 cm of soil by conventional tillage, but remain intact under conservation tillage. Improved macropore development also enhances water infiltration and decreases water runoff. Conservation tillage thus can also conserve water and fertilizers.
In the midwestern US, farmers get consistent reductions of about 75% in soil loss when corn residue is left on the surface compared to losses under conventional tillage.
In drier areas, such as eastern Washington, wind rather than water is the primary erosive force. For wheat growers in eastern Washington, soil loss by wind averages about 32 metric tons/ha with conventional till versus 2 metric tons/ha for conservation till. That is, only about 6% as much soil is lost with conservation till as with conventional tillage.
As with so many things, conservation tillage is not a panacea -- there are some concerns about it, particularly concerning impacts on water quality and on pests.
1) Water quality. Originally, it was thought that conservation tillage would protect water quality. Why would that be?
Typical runoff water contains sediment, dissolved nutrients, and pesticides. If water runoff is decreased with conservation tillage (as it is) the thought was that these would decrease too. In some cases, this does seem to be the situation. However:
If the fertilizer is broadcast over the surface and not incorporated into the soil under conservation tillage, the runoff that does occur is heavily enriched. (With conventional tillage, fertilizer is often incorporated into the soil when it is tilled.) Thus, even though runoff is decreased, contamination of water may increase because the fertilizer is on top and vulnerable to removal.
This potential problem can be avoided by injecting fertilizer or by applying it in the row at planting time -- i.e. not broadcasting it.
As we just saw, conservation tillage generally increases infiltration of water. A potential downside associated with this improved infiltration involves impacts on groundwater quality. If more water moves back to the groundwater under conservation till, there is more potential for groundwater contamination with mobile anions such as nitrate and chloride and with pesticides. Results of various studies on impacts of conservation till on groundwater quality conflict; some find increased contamination while others do not. For example, an article in Journal of Environmental Quality from 1993 reported that there was actually less leaching of pesticides to groundwater under no till corn than with conventional tillage. The authors suggested that maybe the increased organic matter in the soil under no till enhanced microbial populations and thus enhanced degradation of pesticides.
So, while it appears that conservation tillage may decrease contamination of surface water (when accompanied by appropriate methods of applying fertilizer and pesticide), the answer for ground water contamination is not yet clear.
As with so many ecological phenomena, you can't change just one thing. If techniques of tillage are changed, then probably the methods of applying chemicals, and amounts applied, must be changed to avoid creating a new problem in the attempt to avoid another problem.
(2) Pests are currently the major problem with conservation till now -- from both farmers' and ecologists' perspectives.
For pathogens, such as fungi and bacteria conventional till buries crop residue which destroys many fungal and bacterial pathogens. Many pathogens use residue as an overwintering place, but are destroyed (or rendered incapable of causing damage) when they are buried. Hence, under conservation tillage, severity of some diseases can increase, potentially requiring more use of chemicals.
Here, however, is another potential advantage to wider use of crop rotation. Crop rotation may help decrease this disease problem if the crop planted in one year is different than that planted the previous year, such that the pathogen on the residue isn't matched to the current season's crop.
Just to show you how complex this system is, and how many factors must be considered and analyzed: There is concern that rotation with legumes (which "fix" atmospheric nitrogen) may lead to increased water contamination by nitrates. Much of the fixed nitrogen is initially in less readily leached forms (bound up in organic forms) than is inorganic nitrogen fertilizer, but it is taken up by plants less rapidly, hence may contribute as much or more nitrate to water as would chemical inputs! Again, the answer not in on this, yet
Conservation tillage has variable effects on insects. Deep plowing destroys many overwintering insects by exposing them to birds and weather, and can physically hinder their emergence; this doesn't happen under conservation tillage. More research is needed on conservation till's effects on insect pests.
Tillage is widely used to control weeds directly and by burying their seeds. (Germination of many weed seeds is stimulated by exposure to light. Maybe you've noticed this in your own garden -- you go out and hoe vigorously, turning up lots of soil in the process -- and within a few days thousands of weed seedlings appear? This because they were exposed to light during your hoeing....) There is particular concern about perennial weeds becoming a problem after a few years of conservation tillage. In addition, there are concerns that more of the herbicide will be adsorbed on the crop residue, rather than reaching the soil where it is effective at killing weeds. With some conservation tillage systems, growers often find that they have to use 14 - 37% more herbicides than they did with conventional tillage.
However, in Canada, growers aren't finding weeds to be a problem. They report that:
In Sweden, after 14 yrs of ploughless tillage farmers did find increases in weeds, but not to the point where they were viewed as a problem.
Further, there are some methods of conservation tillage that allow some tilling to control weeds, as we'll see below. Iowa corn and soy growers are getting good success at weed control by making one cultivation pass along the ridges ("ridge till" -- see below), and by banding herbicide on the crop rows rather than broadcasting, they can decrease its use.
Again, the answers about conservation tillage and weed control are not in yet! Initially (in the first few years after conservation tillage was adopted) it looked as if these problems with it might outweigh its benefits. However, after more years of its use, and as organic matter builds up in soil as a consequence, it begins to seem that these problems with pests, diseases, and weeds diminish over time.
We should also remember that herbicdes may have a short life anyway, because of resistance problems, so there may be a need to develop alternative weed control strategies anyway! There is a need to develop weed and pest control systems that are effective with conservation tillage. Such techniques will include those discussed later (under IPM; see link just above) as well as techniques such as spot treating with post-emergence herbicides rather than broadcasting herbicides over the entire field before the weeds emerge.
(Incidentally, despite the possible short life of herbicides, owing to resistance problems, about 41% of approved field trials for genetically altered crops in the US are for herbicide-resistant crops!)
The economics of conservation tillage aren't clear. On the one hand, it can be more expensive than conventional tillage for growers because of increased chemical use. On the other hand, it can be less expensive because of decreased fuel and heavy equipment costs. The verdict depends on the balance between these opposing cost trends. (As described below, if farmers can sell CO2 sequestration credits on the land, that helps make conservation tillage financially attractive too!)
Various degrees of conservation tillage have various problems. Some forms have fewer problems than does absolute no till. You can read about various methods in the National Research Council volume cited on the supplementary reading list for this unit, if you wish.
For example, ridge till shows promise. In ridge till systems, the grower forms fields into parallel ridges and then tills only the ridge tops for planting in spring. Weeds emerging later in season tend to be between the ridges (because there is competition from the crop on ridge tops) so if needed, the farmer can till once between ridges to control them, and to decrease problems with soil compaction in rows between ridges.
Ridge till has significant erosion control benefits, because the residue is still there between ridges, but it overcomes some problems associated with strict no till:
Very widely! Because of its benefits in decreased soil erosion, the US government has encouraged its adoption. It was predicted that some form of conservation till would be in use on over 50% of US crop land by the year 2000. Percentages vary by crop and region, as opportunities for and constraints on farmers vary regionally. It was adopted very rapidly in some regions. For example, in Indiana in 1971, only 8.5% of corn and soy acreage was conservation till, whereas by 1988 the percentage was 51%.
Interestingly, it is reported that US soybean farmers who plant herbicide-resistant soy, a genetically modified crop, are much more likely to use conservation tillage than are farmers who do not plant the herbicide resistant varieties, presumably because the latter still use tillage as part of their weed control strategy, while the former can spray easily, since the crop is resistant to the herbicide (Science 25 May '07). More about genetically modified crops later!
The major resistance to adopting it comes from pest control problems, as discussed above.
Conservation tillage has additional advantages beyond conserving soil. These advantages lie in terms of global climate change prospects. As we'll see later this term, carbon dioxide (CO2) is one of the important "greenhouse gases," and soils store an abundance of carbon; even three times more than is stored in live vegetation and maybe as much as twice as much as is held in the atmosphere. Under conventional till, agricultural soils are net sources of CO2 to the atmosphere. With conventional tillage, the soil is mixed and aerated, and decomposition of organic matter is speeded, releasing CO2 to the atmosphere. By contrast, under conservation tillage, soils store much more carbon than under conventional till, and may actually be net sinks for CO2 rather than sources of it.
In fact, farmers who use conservation tillage were able to sell "credits" for the CO2 that the practice saves (by sequestering it in the soil) on the Chicago Climate Exchange; members bought such credits to offset their own emissions. (I write this in the past tense, as the Chicago Climate Exchange has basically been defunct sine Dec. 31, 2010). For example, one farmer in CO used conservation tillage on his 5,000 acres and earned $5,000 per year selling CO2 credits for that acreage. Ranchers were able to do the same thing by decreasing the number of AUM's and rotating the cattle frequently, allowing perennial grasses to build up root systems that store abundant carbon. From a global CO2 perspective, though, there's a "catch" to selling such credits; basically they don't accomplish a net decrease in emissions in cases where the farmers were carrying out these practices anyway -- net decreases will be accomplished only if farmers newly adopt these carbon-sequestering practices. Most people believe that payments per ton of CO2 sequestered will have to be higher than they are at present if we hope to encourage farmers to switch to such practices. There are also challenges with scientifically verifying how much carbon is actually sequestered compared to conventional tillage.
I said above that the US government has encouraged farmers to use conservation tillage. How does the US government "encourage" farmers one way or another?
Through Farm Bills, which have been enacted every 5 yrs or so since the Dust Bowl. Farm Bills set agricultural policies, including the basis for various crop subsidies. Historically, Farm Bills focused on farm income objectives + int'l trade + decreasing soil erosion. Income objectives have been met largely through subsidies paid to farmers on a yield basis -- the more yield, the more the money, so Farm Bills often encouraged unsustainable practices with the only goal being maximizing yields.
****************************************FARM BILL INFORMATION ***************************
Historically, Farm Bills focused on farm income objectives + international trade + decreasing soil erosion. They were created during the Depression to help farmers survive. Income objectives are met largely through subsidies paid to farmers on a yield basis -- the more yield, the more $$, so, as you can imagine, these subsidies encouraged unsustainable practices since the only goal was to maximize yields. There were major environmental impacts associated with the early Farm Bills (and with today's as well, unfortunately, despite the newer bills increased focus on environmental as well as income objectives). The financial incentives they provide influence what farmers plant, how much they irrigate, and to what extent they take steps to protect the environment.
When initiated, subsidies were intended to make up the difference between the costs of production and sales prices when commodity prices were low - regardless of environmental problems associated with that production. Unfortunately, the subsidy system has basically rewarded unsustainable farm practices and large corporate farm operations. The more you produce, the more money you get from the government -- you can imagine how this affects the competitive abilities of small-scale farmers? From 1997 - 2006, producers in the US received an average of 30% of their net farm income from direct government payments! (Science 15 June '07). It is estimated that about ½ of the annual income for US corn producers comes from government crop support programs (Sierra, Nov/Dec 06). Huge subsidies are provided for corn, wheat, rice, soy and cotton (by and large staples that are already overproduced) yet at the same time, 2/3 of the farmers who apply for conservation programs through the Farm Bill (see below) are turned away for lack of funds (EDF 2007).
Fewer than 10% of farmers benefit from the subsidies - those who do are mainly commercial outfits in the Midwestern and Southeastern US (EDF 2007). Subsidy payouts run as much as $20 billion per year! (In 2005 they were > $24 billion; Science 15 June 07).
Fruit, vegetables and livestock have historically been ineligible for subsidies. Thus, subsidies tend to hurt the little farmers and help a relatively few large operations. Sixty percent of US farmers get no subsidy payments at all and most of the rest receive less than $200 per month (EDF 2007).
In defense of Farm Bills, however, the relatively recent Bills (starting in about 1985) retained subsidies but were different from earlier Bills in their emphasis. The 1985, 1990, 1996, 2002 and 2008 Farm Bills put much more emphasis on sustainability of agriculture and environmental concerns than had previous pieces of farm legislation. The 2008 Farm Bill, also known as the Food, Conservation, and Energy Act of 2008, which was enacted into law in June 2008, will cover the subsequent 5 years. These bills have each included specific provisions for conserving soil.
As an example, the Conservation Title of the 1985 farm bill (the "Food Security Act") had a four-part strategy regarding soil conservation. The parts of the strategy are listed briefly below, and then elaborated below that:
Requiring soil conserving practices: Conservation Compliance Provisions of the 1985 Farm Bill: These provisions held that, if a farmer was farming highly erosion-prone land ("HEL"), and wished to retain eligibility for government benefits such as crop-price supports and subsidies, he/she had to have in place a Soil Conservation Service (now = Natural Resources Service) approved plan for conserving soil. These plans were to be approved by 1990 and to be followed through by 1995. (Since that time, subsequent Farm Bills have continued to support the Conservation Compliance Provisions.) How is HEL defined? Such lands must be eroding at rates at least 8 times the soil tolerance level, which varies from place to place but is the rate that can occur without causing declines in productivity. Plans for conserving soil must result in a "substantial reduction" in soil erosion, which is defined as a 75% reduction of the potential erodibility, not to exceed two times the soil loss tolerance level for that area and soil type.
By the summer of 1990, it was estimated that 1.5 million farmers had worked with NRCS to develop approved plans to stabilize soils on 134 mill acres. The 2002 Farm Bill contained a Conservation Security Program (renamed under the 2008 Farm Bill as the Conservation Stewardship Program) see more information about this program, below), which offered financial and technical assistance to farmers to implement soil (and other resource) conservation strategies. That is, in addition to penalizing farmers for not using soil conserving techniques (by denying farm benefits), this program also had provisions for incentives to use such techniques, such as sharing costs.
These soil conserving plans, if fully implemented, had potential to cut erosion losses by 700 mill tons/yr from cultivated lands. This is approximately equal to 1/3 of excessive soil loss from US agriculture ("excessive" meaning losses in excess of formation rates), and is an amount about equal to the decrease in erosion from Conservation Reserve Program lands (which we'll discuss soon; this 700 million tons/yr does NOT include Conservation Reserve Program lands that are pulled out of production) . (I should point out, however, that farmers and soils people are variously unhappy with the soils models used to predict their erosion losses under various circumstances, feeling that in some case the models overestimate and in others underestimate losses badly.)
Unfortunately, this program is unlikely to reach its full potential for decreasing erosion losses. The USDA (US Department of Agriculture) lowered the program's soil loss goals to permit erosion that is in excess of formation . The USDA justified this softening of standards by citing economic hardships faced by farmers.
Part of the strategy with Conservation Compliance has been to provide better education to farmers about conservation practices other than conservation tillage. These soil conserving practices include contouring, terracing, strip cropping (e.g., an alfalfa cover crop alternating rows with corn, in which the alfalfa slows the movement of water), mulching, and shelterbelts (planting trees as windbreaks). Conservation tillage can, of course, be a part of the Conservation Compliance Program as well.
As of the early 1990's, about 1/4 of US farmers were on some conservation compliance plan.
This concept about the government "forcing" farmers to use soil conserving practices may seem to conflict with our ideas about individual property rights. However, the idea is that farmers that receive federal payments or other subsidies should, in return, be conserving the nation's soil resources. These programs do not force farmers to participate; rather they say that if you do not participate, you will not be eligible for certain priviledges.
These Conservation Compliance Provisions differ from the history of soil conservation attempts in the US, which have relied on voluntary compliance and incentives such as availability of technical assistance, rather than on disincentives for not complying. (Incentives are still available, of course, but disincentives are a relatively recent addition.)
There are several other ways that farmers can decrease soil and water losses from their lands, with the major alternatives varying by geographic region. These can include changed land use practices, such as taking highly erodible land out of production. In the past, the government would occasionally pay farmers to idle good land to lessen price-depressing crop surpluses. (These payments were eliminated in the 1996 Farm Bill.) In contrast, the US government is now paying some farmers to take highly erodible land out of production in a program called the Conservation Reserve Program (CRP).
The 2002 Farm Bill included a Conservation Security Program (CSP) [renamed in the 2008 bill as the Conservation Stewardship Program] that offers financial and technical assistance to farmers to implement soil (and other resource) conservation strategies on working lands. Unlike Conservation Compliance which denies farm benefits unless one complies (e.g., no benefits if you convert a wetland into cropland or farm HEL without an approved conservation plan) - basically denial of benefits to encourage environmentally friendly practices - the CSP focuses on using cost-share and incentive payments to encourage adoption of environmentally friendly practices on actively working farms. These opportunities are available to further enhance operations that have already made steps to address environmental problems (e.g., soil or water quality issues, loss of wildlife habitat, invasive species domination). That is, they are intended to "reward the best and motivate the rest."
The CSP includes cropland, grassland, prairie land, improved pasture and range land as well as forested land that is an incidental part of an agricultural operation. $202 million was budgeted for this program in FY-2005. Contracts are for 5 - 10 years, depending on circumstance, and pay $20,000 - $45,000 per year.
Click ">>" at the bottom of the page to jump to a description of the CRP, "<<" to move to the preceeding section on trophic issues, or "CONTENTS" to return to the overall contents for the BI 301 home page. Click on "NAVIGATE" here for reminders on how to move about within and among these documents.
Page maintained by Patricia Muir at Oregon State University, and last updated Nov. 25, 2012.