Cropping Systems

Recall in module 5, we examined how soils, climate, and markets play major roles in determining which crops farmers cultivate. In many cases, farmers cultivate multiple crops of more than one life-cycle because the diversity provides multiple benefits, such as soil conservation, interruption of pest lifecycles, diverse nutritional household requirements, and reduced market risk. In this module, we examine some ways that farmers cultivate crops in sequence and define some of the terms for this crop sequencing.

A sole crop refers to planting one crop in a field at a time. Recall from Module 5, the seasonal crop types (Figure 7.1.1) and note that different seasonal crops could be planted in succession. A monoculture refers to planting the same crop year after year in sequence (See Figure 7.1.2). By contrast in a crop rotation, different crops are planted in sequence within a year or over a number of years, such as shown in Figures 7.1.3a and 7.1.3b. When two crops are planted and harvested in one season or slightly more than one season, the system is referred to as double cropping, as illustrated in Figure 7.1.4. Where growing seasons are long and/or crop life cycles are short (ex. leafy greens), three crops may be planted in sequence within a season, as a triple-crop.

Figure 7.1.1: Crop Term: Seasonal Types and Example Crops

Credit: Heather Karsten

Figure 7.1.2: Monoculture

Credit: Heather Karsten

Figure 7.1.3a: Simple Summer Annual Crop Rotation

Credit: Heather Karsten

Figure 7.1.3b: Dairy Perennial - Annual Crop Rotation

Credit: Heather Karsten

Figure 7.1.4: Double-cropped annual crops

Credit: Heather Karsten

Crop rotations and double cropping can provide many soil conservation and soil health benefits that are discussed in the reading assignment at the end of this page, and in Module 7.2. Crop rotations can provide additional pest control benefits particularly when crops from different plant families are rotated, as different families typically are not hosts of the same insect pest species and crop pathogens. Integrating crops of different seasonal types and life cycles in a crop rotation also interrupts weed life cycles by alternating the time when crops are germinating and vulnerable to weed competition. Rotating annual crops with perennial forage crops that are harvested a couple of times in a growing season also interrupts annual weed life cycles, because most annual weeds don't survive the frequent forage crop harvests.

When all or most of a crop is grazed or harvested for feed for ruminant livestock, such as dairy and beef cattle or sheep, the crop is referred to as a forage crop. Examples of forage crops include hay and pasture crops, as well as silage that can be produced from perennial crops and most grain crops. For instance, silage from alfalfa, perennial grass species, corn, oat, and rye is made when most of the aboveground plant material (leaves, stems and grain in the case of grain crops) is harvested and fermented in a storage structure called a silo or airtight structure. To preserve the silage, air is precluded from the storage structure and microbes on the plant material initially feed on the crop tissues, deplete oxygen in the storage structure, and produce acidic byproducts that decrease the pH of the forage. This acidic environment without oxygen prevents additional micro-organisms from growing, effectively "pickling", and preserving the forage.

Figure 7.1.5: Airtight upright silo

Credit: Heather Karsten

Figure 7.1.6: Bunker silos are packed tightly with heavy equipment and covered with plastic to keep out air and moisture.

The bunker silo on the right is uncovered because the silage is being removed to feed to dairy cattle.

Credit: Heather Karsten

Intercrops and Cover Crops

Intercrops are two or more crops that are planted together in a field at the same time or to be planted close in time and overlap for some or all of their life cycle. Intercrops may provide a range of benefits including: i. improving soil fertility, ii. increasing crop diversity and iii. reducing pest pressure. The mixtures also often produce higher yield and crop quality. There are multiple types of intercrops that vary in their spatial arrangement.

Strip intercrops are wide strips with multiple rows of one crop, that are alternated on the field with strips of one or more different crop(s). Strip intercrops are typically planted on the field contour with crops of different life cycles that protect soil from erosion throughout the year.  For instance, strips of corn may be alternated with strips of perennial forage grasses that can reduce soil erosion across the field when the corn isn't growing. Or, as in the photo below, winter wheat provided live plant coverage on portions of the field in spring, prior to corn and soybean were planted. In mid-summer, corn and soybean provide live coverage after wheat is harvested; and in fall, winter wheat will be growing on some strips after corn and soybean are harvested. Having strips of different crop species can also reduce the spread of insect pests and crop pathogens compared to cultivating one crop on the entire field. 

Figure 7.1.7. Strip intercrop: Alternating strips of corn, soybean and winter wheat planted on the contour.

Credit: Heather Karsten

Row intercrops alternate rows of different crop species, usually every other row or every two rows.

Figure 7.1.8. Row intercrop: Alternating rows of onion and hairy vetch. Hairy vetch is a winter annual legume that is mowed frequently to reduce competition with the onions.

In this system, hairy vetch is planted to provide soil protection, suppress weeds, and add nitrogen to the soil.

Credit: Heather Karsten

Mixture intercrops tend to be combined randomly when planted; such as grass and legume forage mixtures. Intercrops of different crop species (ex. native tuber mixtures) or different varieties of a crop species (ex. rice) are sometimes planted to reduce pathogen and insect pest infestations. Crop rotation and intercropping increase agrobiodiversity across an agricultural landscape, providing multiple potential agroecosystem benefits, such as i. reducing the risk of crop loss to pests and climatic stresses (ex. frosts, floods, and drought), ii. providing habitat for beneficial organisms such as pollinators and pest predators, and iii. enhancing the diversity of nutritional crops for farmers and markets. Further, integrating crops from the grass family tends to promote soil structure, while legumes enhance soil nitrogen, and integrating perennial crops protects the soil from erosion and builds soil organic matter and soil biological activity because perennials allocate a high proportion of their growth to storage organs. For instance, the photos below illustrate how both intercropping and crop rotation enhance agrobiodiversity in the high Andes of Peru.

Figure 7.1.9. Pasture intercrop of four perennial forage crops: tall fescue, orchardgrass, Kentucky bluegrass, and white clover.

Credit: Heather Karsten

Figure 7.1.10. Four major native tuber crops: Maca, Oca, Ulluco, and Mashua at the CIP International Potato Center [3] in Lima, Peru.

Credit: Heather Karsten

Figure 7.1.11. Example High Altitude Andean Crop Rotation from Peru

Credit: Heather Karsten

Figure 7.1.12: Sheep grazing perennial pastures that are typically rotated to annual crops: potato, native tuber crops, legumes, and small grains before rotating back to perennial pasture.

Credit: Heather Karsten

Figure 7.1.13. Agrobiodiversity is high across the high altitude Andean landscape due to crop rotation and genotypic diversity within fields.

Credit: Heather Karsten

Figure 7.1.14. Diversity of potato and native tuber crops in a grocery store in Lima, Peru

Credit: Heather Karsten

Cover Crop: A cover crop is planted after a crop that is harvested and is terminated before the subsequent crop is planted. Cover crops tend to be annual crops that they can quickly establish after a harvested crop to protect the soil from erosion and provide other benefits including i. to add organic matter to the soil; ii. to scavenge nutrients and prevent nutrients from leaching out of the topsoil (also called a catch crop); iii. to support soil organisms in the root zone, iv. to suppress weeds, and v. to provide habitat for aboveground beneficial organisms, such as insects that predate on crop pests or weed seeds. Leguminous cover crops also add nitrogen to the soil when they are terminated and returned to the soil and are therefore often referred to as green manure crops. Cover crops are also sometimes referred to as "catch crops" because they can take up and retain nitrogen and other nutrients that might otherwise leach out of the rooting zone and be lost to deeper soil profiles, and potentially to groundwater.

Cover Crop Intercrops

Because cover crop species have different plant traits that provide different cropping system benefits, often two or more species of cover crops are planted together as a cover crop intercrop or cover crop mixture. For instance, small grains that scavenge nitrogen well and have fibrous roots that bind soil particles and promote soil structure are often mixed with tap-rooted legumes that fix nitrogen. Some cover crop mixtures combine plant species that establish quickly in the late summer or early fall but don't typically survive the winter, such as oats or deep-rooted radish species. Non-winter hardy species are sometimes combined with winter-hardy species such as hairy vetch, cereal rye or annual ryegrass that survive the winter and provide cover in early spring.

Figure 7.1.15. Annual crimson clover and winter wheat cover crop intercrop photographed in spring.

Credit: Heather Karsten

Figure 7.1.16. Cover crop intercrop of annual cereal rye and hairy vetch (a legume) photographed in spring.

Credit: Heather Karsten

Soil Quality, Soil Health

As discussed in Module 5, soil is a complex matrix of minerals, air, water, organic matter, and living organisms. Historically, the emphasis in agriculture has been on reducing soil erosion. But since the 1990s, soil scientists and conservationists have recognized and described multiple valuable properties and ecosystem functions of soil that are referred to as indicators of soil quality or soil health. In 1997, the Soil Science Society of America's Ad Hoc Committee on Soil Quality (S-581) defined Soil Quality as:

"the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation" (Karlen et al., 1997).

Indicators or measures of soil quality describe a soil's biological, chemical and physical properties. In addition to the soil chemical properties such as nutrient content and pH, additional indicators of soil quality include a soil’s:

• Organic matter content. Organic matter stores carbon can release nutrients, support soil biological activity, buffer soil pH, hold plant nutrients, and increase a soil's water-holding capacity
• Biological activity in the soil. Soil organisms can provide multiple benefits such as nutrient cycling, secreting sticky polysaccharides that help bind together soil particles and increase soil porosity and predation, and suppression of plant pests such as plant pathogens and weed seeds.
• Soil structure and porosity. Soils with good structure and porosity can support water and air infiltration and resist compaction. Water stable aggregates are an important physical indicator of soil health. Water stable aggregates contain soil mineral particles such as sand, silt, and clay that are typically held together by a combination of binding materials including fine root hairs, soil fungal hyphae (fungal filaments), and sticky polysaccharides that are exuded from soil microorganisms. Because they are stable when wet (during or after a precipitation event) they maintain soil pores that can contain and allow air and water to infiltrate the soil, reducing water and soil run-off. Water stable aggregates can also protect organic matter from degradation and soil microorganisms from predatory micro-organisms.

Figure 7.1.17: Plant roots, fungal hyphae, and microbial polysaccharide exudates contribute to binding soil mineral particles together into soil macroaggregates, creating macropores between them.

Credit: Illustration by Heather Karsten

Read

Chapter 1 (Healthy Soil) and Chapter 2 (Organic Matter: What it is and Why it’s so important?) from the book that you downloaded: Building Soils for Better Crops. Edition 3 [1]. Sustainable Agriculture Network, USDA. Beltsville, MD.

Then watch the following video about soil biology and list four kinds of soil organisms and how they influence soil.: The Living Kingdoms Beneath our Feet. (USDA NRCS) [5].

Video: International Year of Soils July: The Living Kingdoms Beneath Our Feet (2:08)

Tillage Impacts on Soil Health

In addition to exposing soil to wind and water erosion, tillage can alter the physical structure, distribution of organic matter, and biological activity of soil. At the depth where the plow impacts the soil, a layer of soil compaction can develop (a plow pan), limiting water infiltration and plant rooting depth. Under tillage, crop residues, roots and root hairs, and their associated fungal hyphae are disturbed and more decomposed in the plow layer. By contrast, when roots, fine roots, and fungal hyphae are not disturbed and decomposed as rapidly, there are more channels that water, air, earthworms, and roots can move through, and soil aggregation is enhanced. Below is a schematic comparing the root zone profile of a conventionally tilled soil to a no-till soil.

Figure 7.2.1: Steps Toward a Successful Transition to No-Till.

Credit: S. W. Duiker and J.C. Myers. 2005 Penn State University.

Watch the three videos below, from USDA NRCS about soil tillage and soil health.

1. Video: The Science of Soil Health: What Happens When You Till? USDA NRCS (3:05)

   Click for a transcript of the What Happens When You Till video.

   Interviewer: When we use tillage, the soil ecosystem is disturbed on a massive scale. Purdue's Dr. Eileen Kladivko contrasted natural ecosystems with tilled systems, and what we stand to lose when soils are tilled. Eileen: If you think about natural ecosystems, they don't have a tillage implement running through them once a year or a couple of times a year, but nutrients get recycled and trees grow or grasses grow and what's recycling the nutrients are the organisms. And so, part of what we're saying with a with a no-till system, is that if you don't take an implement through there, and you allow the system to kind of come back, that there will be organisms that will do that job for you. They do it differently, obviously than a piece of metal would do it, but they can be very effective. And besides loosening the soil or making burrows, they do some of these other things, like convert nutrients, ok, recycle nutrients, have pathways where roots can grow and then those pathways stay there. You know, if you think about a tillage implement, any root channel from last year in the topsoil, is going to be totally broken up by a tillage implement the next year. If you have a nightcrawler channel, or even if you have a red worm channel, that's part of the red worm channel, it's there and then the roots can follow that and so you can have channel built upon channel, built upon channel. And the nightcrawler channel, you know, maybe a root, maybe a corn root, maybe a cover crop root, will go down that, and the next year another nightcrawler, and so on. So it builds upon itself. Interviewer: Will you explain to us why organic matter decomposes faster because of tillage? Eileen: A tillage operation does a couple things, number one is it opens up aggregates that were otherwise protected. So you're opening up more surfaces for the bacteria to decompose the organic material faster. That's probably the main reason. Sometimes people say well you're putting oxygen in the soil. It's not really so much that, as by breaking up aggregates, you expose the organic matter in the soil to decomposition. Whereas when it's in an aggregated state in the soil, some of that's protected and the bacteria that decompose that organic matter can't get to it. Interviewer: So the tillage actually favors then, say bacteria, that would live in that environment. And that may be what causes the flush of carbon dioxide and nitrates into the soil as well. Eileen: Oh yes, yes, the flush of carbon dioxide is very much related to the tillage, right.

2. Video: The Science of Soil Health: Nightcrawlers and Soil Water Flow. USDA NRCS (3:05)

   Click for a transcript of the Nightcrawlers and Soil Water Flow video.

   Interviewer: When we get to those dry summer months, good soil hydrologic function is critical. We visited with Purdue University's Dr. Eilieen Kladviko to talk about the remarkable effect that nightcrawlers have on aiding water flow into and through soils. Interviewer: Well you’re a soil physicist Eileen, so we better talk about. Eileen: We better talk about water flow. Interviewer: Let’s talk about that water flow, because obviously water is a free resource to the farmer. Eileen: Right, in general our soils are excessively wet in the spring and that's more of our issue and that's why we use tile drainage (yes) and things like that. But what I'm getting at really is that the nightcrawlers, in particular, can be very important for getting infiltration of water into the soil during the growing season. So when we get those quick thunderstorms in the middle of the summer, we usually want all that water to go in, because that's not when we have excess water. So we want the water to go into the soil, but, but especially with soils that are high silt, sometimes you can get crusting (yes). You have less crusting of course, if you're in no-till (yes). But if you have a lot of nightcrawlers, those deep channels that the night crawlers make can really help get water into the soil profile, where you have a chance for your crop to use it, as opposed to having it run off. You know an extra inch or two of water in a lot of our summers makes a big difference (okay) in yield (yes, yes). And I happen to have a few demonstrations of some night crawlers, if you'd like to see, nightcrawler channels, if you'd like to see. Interviewer: I would love to see. Eileen: So this is, my technician a number of years ago, went out and poured the liquid rubber, latex basically, that you use in in biology classes, on an area where there were some nightcrawler middens (yes). And then he came back a couple days later, after it had hardened, and he carefully dug it out. And you can see, these were nightcrawler channels, all in in this one square foot area Interviewer: one square foot, yeah. Eileen: And you can see that basically those channels are going down, they've broken a little bit now in the meantime, but some of these channels were down three feet deep (okay). And just imagine water flowing across the surface and into these channels, how much water can flow down those big and deep channels (right), and they're very vertical. You can see that there, Interviewer: So you’ve got the vertical flow and then they have the chance to flow laterally as well? Eileen: Oh yes, yes, right. Once the water is down in the soil, it's going to move out from those. Interviewer: This is a fantastic illustration and this was taken on a farm field? Eileen: Yes Interviewer: WelI, I love this, it’s great. Eileen: Yeah right, yes, I think it's a great demonstration of nightcrawler channels.

3. Video: The Science of Soil Health: Compaction USDA NRCS (4:26)

   Click for a transcript of the Compaction USDA NRCS video.

   Interviewer: You know the plow seems to be symbolic of that can-do spirit that you find in American farmers. And so when you say that there may be better alternatives to tillage for compaction relief, that seems somehow counter-intuitive and almost un-American. I met two guys from Ohio State who use science to put conventional wisdom on its head. Alan Sundermeier: We're trying to tell the farmers that you cannot solve your problems with steel. You know, steel is shiny, you can put your hand on it. You can spend a lot of money on steel. And even with the subsoiler that may have minimal surface disturbance, it's really not solving the problem. You know, we're seeing that soil structure can be better solved by using natural rooting systems to their cover crops or continuous no-till from the cropping systems. And we have some other experiments here that are proving that. We have some compaction plots, comparing subsoil steel versus living cover crops. We're purposely compacting these plots in the fall, under moist soil conditions, by using a grain cart and going back and forth over the plots and forcing that compaction. And then the cover crops are planted, and then we're comparing that to using a subsoiler and our yields are showing better results with the cover crops. And of course, when you get some heavy rains, you can see standing water problems, you know, that show up between the compaction levels of the plots, also that way. And the cover crops are outdoing the steel. Interviewer: So what's the explanation for these rather surprising results? Jim Hoorman: When, when you look at a soil, you have to look at the components. And the major component of most soil is sand, silt, and clay. Now that makes up about 45% of a really good soil. The other part of the soil, what we tend to forget about, is it should be pore space. Almost 50 percent of a really good soil is pore space. But then the most important part of a soil is the organic matter, that's like your head and your brains. That controls most of the chemical reactions and most of the life is with that organic matter. You know when you start to till a soil, what you do is you burn up the organic matter. So in the last 100 to 150 years, through tillage, we've lost probably at least 60% of our organic matter. Some studies say as much as 80 percent of the organic matter is going right up into the atmosphere. And this is a good area because this was the black swamp in in Northwest Ohio. When the first settlers came here, they said our soil was as black as midnight. And when you look at the soil now, you'll see that it's not as black. It's actually kind of a brown. It's lost its color, so it's lost a lot of its organic matter. I like to tell farmers that a lot of times, when you till the soil, you turn it into cement mix, okay, and so the soil gets very hard and dense. And one of the things that we've learned is, that if I was going to drill into cement, I would start with a small drill and then use a bigger drill to go through it. And so that's what we do with the cover crops. The cover crops actually have very fine roots and they form a small hole and then we follow that with corn and soybeans and those corn and soybeans will follow those same channels down through the soil. And they also follow earthworm holes, because earthworms are fairly big and they're also enriched with nutrients. And so those roots just really proliferate around those earthworm holes and that's how we then can actually loosen the soil up. Is it's the roots that loosen the soil up and give that carbon to the soil and also is a storehouse for all the nutrients in the water. Alan Sundermeier: So a lot of innovation is happening It's really an exciting time because farmers are seeing that there's different ways we can improve our soils by adding cover crops, you know, by not going to steel, by reducing our tillage. A lot of good innovative thinking I think has happened.

Tillage Systems

Humans have developed many different ways to prepare the soil to plant crops, with the primary goal of achieving good seed to soil contact to keep seeds moist as they germinate and grow. There are some benefits of tillage. For instance, tillage enables the farmer to bury or mix-in crop residues that insulate the soil and keep it moist and cool which can delay crop seed germination in cool environments. By burying the insulating crop residues, solar radiation can warm the soil more quickly. Tillage can also terminate weeds, cover crops or perennials, and bury weed seeds and crop residues that may harbor pathogens and insect seeds; tillage also mixes in soil amendments, such as fertilizer and animal manures.

In conventional tillage systems, primary tillage equipment such as the moldboard plow or a rototiller inverts the soil. A second tillage event or plow is often used afterward to break up large soil clods into smaller particles, with the goal of improving seed to soil contact. See photos below.

Figure 7.2.2: Moldboard plow

Credit: Heather Karsten

Figure 7.2.3: Soil inverted and crop residue buried by a moldboard plow.

Credit: Heather Karsten

Figure 7.2.4. Disk plow breaking up soil clods in a secondary tillage operation

Credit: Heather Karsten

Removing or mixing-in crop residue leaves the soil exposed and prone to wind and water erosion, as well as soil moisture loss. Tilling crop residue into the soil also makes residues more accessible to soil organisms and incorporates oxygen into the soil, increasing the decomposition rate of the residues and decreasing organic matter content at the soil surface and plow layers. Tillage also disrupts soil organisms, particularly mycorrhizal fungi, and soil physical properties such as water stable aggregates.

Conservation tillage or minimum tillage is another soil preparation method designed to reduce soil erosion by reducing disturbance and leaving some plant residue (at least 30%) on the surface. The soil is not inverted, but the surface is disturbed and often a high proportion of crop residues are mixed in with tillage equipment such as a disk plow or a chisel plow.

No-till or Direct-seeding is designed to eliminate tillage, by cutting a slit in the surface and placing the seed in the slit. In addition to minimizing crop residue disturbance, the crop is planted in one pass across the field, thereby reducing erosion, labor, and fuel needed to prepare a field and plant the crop.

Figure 7.2.5. No-till drill. A coulter wheel cuts a slit in the ground, a tube drops the seed into the slit and press wheels follow behind to cover the slit with soil.

Credit: Heather Karsten

Figure 7.2.6. The no-till drill causes very little disturbance of the soil and crop residue.

Credit: Heather Karsten

Some hurdles to no-till adoption As discussed earlier, there are a number of reasons that farmers till the soil. For instance, conventional tillage can terminate perennials, cover crops, and weeds prior to planting the subsequent crop. Without conventional tillage, farmers typically use herbicides to terminate the previous perennial or cover crop and control weeds. In cool environments, crop residues can harbor pathogen and insect pests, and insulate soil, which can slow soil warming in spring and delay crop emergence. These factors can reduce crop yield, particularly if farmers don't rotate crops to interrupt pest life cycles. In addition, although farmers typically need less tillage equipment to plant with no-till, there is an initial cost associated with purchasing no-till equipment for farmers who use conventional or conservation tillage equipment. And with new equipment, farmers need to learn how to adjust no-till planters to ensure that seed is planted at the optimal depth. Consequently, no-till planters are typically heavier to cut through crop residues and place seeds at a sufficient depth for good seed to soil contact.

Zone or strip tillage When soils have high crop residue and/or are high in organic matter, or are not well-drained, soils can remain cool and delay seed germination. Zone tillage or strip tillage incorporates the insulating crop residue in a narrow zone or strip of soil where the seed is placed. Residue between the seed planting zones is not disturbed or removed. Removing the soil insulating layer increases the rate of soil drying and warming in close proximity to the seed, promoting earlier seed germination compared to soil with residue left intact.

Figure 7.2.7: A field prepared with zone tillage or strip tillage that removes residue in a narrow zone where the seed is planted.

Credit: Heather Karsten

Continuous Cover Through Crop Management

Soil conservation practices are most effective when they reduce soil disturbance or tillage and also maintain live plants in the soil.

As discussed in Module 5, perennials provide year-round live plant cover that protects soil from erosion; and their live and large root systems support rhizosphere activity and return organic matter to the soil all year. To provide continuous live roots for soil conservation and soil health, perennial crops can be rotated with annual crops, and double crops and cover crops can be integrated into annual cropping systems. Recall that in Module 7.1, a dairy crop rotation of corn-alfalfa was shown in Fig. 7.1.3b, and double cropping in Fig.7.1.4. The photos below also illustrate examples of how year-round cropping provides multiple agroecosystem benefits.

In addition, consider how managing crops and soils for soil conservation and health can enhance agricultural resilience and adaption to climate change. For instance, by increasing soil organic matter content, agricultural soil can: i. contribute to carbon sequestration (removing carbon dioxide from the atmosphere and storing it in soil), ii. improve soil structure and porosity and enhance water infiltration and water content in soil, and iii. store and cycle nutrients. Perennial crop production and double-cropping can utilize potentially longer growing seasons; provide more year-round protection of soil from erosion, and planting and harvesting crops at multiple times of the year can reduce the risk of extreme weather events or irregular weather interfering with cropping activities.

Figure 7.2.8: When annual crops such as corn and soybeans have completed their lifecycle in autumn, perennial forages such as alfalfa

and perennial grasses and winter annuals such as winter wheat are alive, protecting the soil and supporting soil organisms in their root zones.

Credit: Heather Karsten

Figure 7.2.9: Double-cropped winter canola provides live soil cover in fall and early spring.

Credit: Heather Karsten

Figure 7.2.10: Winter rye cover crop in March protects the soil from erosion, produces organic matter to return to the soil, takes up soil nutrients such as

Nitrogen, suppresses weeds and provides habitat for below ground and aboveground organisms such as beetles that eat weed seeds and crop insect pests.

Credit: Heather Karsten

For more discussion of a crop-soil system management approach, watch the three short videos below from NRCS about the benefits of cover crops on soil health.

1. Video: The Science of Soil Health: Using Cover Crops to Soak up Nutrients for the Next Crop USDA NRCS [7] (3:08)

   Click for a transcript of the using crops to soak up nutrients video.

   Interviewer: No farmer wants to lose precious nutrients in the cool season, but this is exactly what happens when a field is left fallow. We've visited with Penn State's Dr. Sjoerd Duiker to talk about how they use cover crops to ensure that those nutrients stay where they belong. Sjoerd: You know in Pennsylvania a special characteristic of our state is that we are very heavily reliant on the dairy sector. And our farms, they spread manure, and they spread it at times when there might not be living vegetation in the field. So the water-soluble portion of the nutrients can easily be lost. And we, being a large part of our state is in the Chesapeake Bay watershed, so we are under scrutiny. There's a lot of concern about nutrient losses to the rivers, to the streams, and eventually to the Chesapeake Bay. There are basically two periods during the year that we lose a lot of nutrients. One is in the fall, there's a little peak. And then most of the, especially nitrogen loss, occurs in the spring. That time, April, May, when we come out of the winter. The soil starts to thaw, the soil is saturated, mineralization is taking place, and now we get leaching through the soil profile. A lot of nitrogen is then lost through groundwater and eventually then, through lateral flow, ends up in the streams. So what we are trying to do is to have living cover crops that take up all those nutrients, the water-soluble nutrients, nitrogen primarily, is made available and is then absorbed by the roots. It's like a sponge, a continuous sponge, that is there. We have evaluated the nutrient uptake and what we can find in the above-ground biomass, depending on growing conditions and the type of cover crop, but it can be even 200 pounds of nitrogen per acre into the above-ground vegetation only. So that makes up typically perhaps 80 percent of the total plant biomass. The rest is underground. All that would otherwise have been liable to loss. So what we are normally considering when we grow a full corn crop, we might assume that that corn crop needs 150 pounds of nitrogen, perhaps 200 pounds of nitrogen per acre. So we are trying to really stimulate that cycling of those nutrients and avoiding them from being lost from the system. We would like to see every acre of corn silage in the state be followed with cover crops, no more fallow after corn silage.

2. Video: The Science of Soil Health: Without Carrot or Stick USDA NRCS [8] (2:39)

   Click for a transcript of the without carrot or stick video.

   Interviewer: Planting cover crops enhance the soils ability to function as a nutrient recycler. Penn State's Dr. Sjoerd Duiker talks about how dairy farmers in his state are using cover crops to improve their businesses, without regulations or subsidies. Sjoerd: In my work, I have concentrated on helping farmers adopt no-tillage systems, diversify their crop rotations, and also to fill any fallow periods in the crop rotation with living vegetation. So our principles, our guiding philosophy, is basically to have a living vegetation and living roots systems in the soil 365 days a year. So I have a project that is actually called, without carrot or stick. Because we are trying to stimulate the farmers to adopt cover crops without a carrot of subsidies, without a stick of regulation. Usually, we have 10 dairy farmers all over Pennsylvania, and it is all focused on cover crops after corn silage. There is a good window for planting the cover crops and there is a good also opportunity for using the cover crops for forage. Instead of them buying feed from outside, they are cycling more nutrients on their own farm. It's going through the animal, they’re producing some products, they’re producing manure, the manure goes back on the field. If we can produce more feed on our own farm, and cycle more nutrients on our own farms, it is very beneficial. Interviewer: How's that make you feel? Sjoerd: Yeah, that is very satisfying. We've already seen an enormous increase in the adoption of no-tillage. But now we want to really emphasize, as part of that no-till system, we need to fill all those fallow periods with living crops. And so the cover crops are a big part of that and we see that now our farmers are actually starting to use those practices. So we think it will be very beneficial for soil quality, for nutrient management, the nutrient cycling. And the farmers are intensifying their production, so we hope they can produce more forage on their own farms, cycle more nutrients on their own farm.

3. Video: The Science of Soil Health: Cover Crops and Moisture USDA NRCS [9] (3:26)

   Click for a transcript of the cover crops and moisture video.

   No cropping system is drought proof, but there are things that farmers can do to mitigate the effects of a dry year. The road took us to NC State's Dr. Chris Reberg-Horton to discuss how cover crops affect water dynamics. Chris: Water, I think, is going to be real limiting factors over the next several decades and particularly here in the southeast. We tend to get most of our summer precipitation and these huge rain events. And one of the things that cover crops bring to the system is they slow the movement of water across our fields, and so we think that we have a lot of yield potential that we can garner from cover crop residues by allowing more water to soak into the soil Interviewer: Okay, okay. Well, tell us about some of the actual work that you've done. Chris: Sure, well we've worked both in corn and soybeans at this point. So we started with soybeans and there we use a rye cover crop. One of the ways that we're going to get more biomass into these systems is not treating the cover crop as an afterthought, thinking of it as a key part of the production philosophy of the field. We plant our rye cover crops early, which makes a big difference. We try to plant that in October, as opposed to throwing it in, you know, November December timeframe. That does tremendous amounts for us. It's interesting what that does for water dynamics. I think for one thing it makes it actually drier in the spring. If you think about it, if you're gonna plant a plant out there over the winter and we're going to grow it, we're gonna extract water out of the soil over the season. So as you plant, we can actually be a fair bit drier than we would be. Now that can be a plus or minus, depending on where you're farming. So in some areas, your traditional no-till agriculture without the cover crop, we can be a bit wet and cool later into the spring. And so getting into the field can be troublesome. Some drying can be a benefit on some soil types. On some soil types, it can be a greater concern. But then at some point in the season of that soybean, we then flop. The plot that had the cover crop now becomes the wetter one because we're soaking in. Again, those big rain events that come in, we're allowing greater water infiltration in those than we are in a conventional no-till setting where we don't have that residue to break up the water. Corn, of course, we stand even greater benefit. In our work with corn we've done, again, that side-by-side comparison, with and without the cover crop. And we can see that certainly by the time we get to silking, which can be a very important time for water dynamics, those two have flopped under our conditions. So now the one with the cover crop mulch is now wetter than the one without a cover crop mulch. Both of them done via no-till. We can actually score that. We go in and we look at our corn plots and we rate when in the morning, under drought conditions, does the leaf first start to curl. That's a powerful integrator, telling you what the water stress on that plant is. And the plants under normal no-till are rolling well before, hours before we see them rolling under a no-till with a massive cover crop under there. So we think that alone right there, gives you a longer period each day to grow the set carbohydrates, to build your yield.

Conservation Agriculture in Brazil Case Study

Activate Your Learning

Go to the FAO UN website and read their brief description of Conservation Agriculture. Then watch the short video “Conservation Agriculture in Southern Brazil [10]” (4:41).

After Watching the Video, Answer the Following Three Questions: