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 7.1.8.: 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(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.
- 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.
- 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.
Check Your Understanding (short answer)
Describe two or three practices that are components of the conservation system or agroecological approach of soil conservation and health.
(need a text box)
- Click for answer
Reduced soil disturbance through reduced tillage, particularly no-till or zone/strip tillage; Continuous plant cover through the integration of perennials, double crops, and cover crops. Returning organic matter to the soil through the application of animal manure, compost, and the integration of green manure and cover crops that are returned to the soil.