… generally, the type of soil management that gives the greatest immediate return leads to a deterioration of soil productivity, whereas the type that provides the highest income over the period of a generation leads to the maintenance or improvement of productivity.
—Charles Kellogg, 1936
In this chapter, we’ll provide some guidance on promoting high-quality soils through practices that maintain or increase organic matter, develop and maintain optimal physical and biological conditions, and promote top-notch nutrient management. In Part 3, we discussed many different ways to manage soils, crops and residues, but we looked at each one as a separate strategy. In the real world, you need to combine a number of these approaches and use them together. In fact, each practice is related to, or affects, other practices that promote soil health. The key is to modify and combine them in ways that make sense for your farm. In our discussion of the topics, we generally focused on farms, but the same principles apply to gardens large and small.
We hope that you don’t feel as confused as the person on the left in Figure 24.1. If the thought of making changes on your farm is overwhelming, you can start with just one or two practices that improve soil health. Not all of the suggestions in this book are meant to be used in every situation. Also, a learning period is probably needed to make new management practices work. Experiment on one or two selected fields and permit yourself to make a few mistakes.
Ultimately your decisions need to support the bottom line. Research shows that the practices that improve soil health generally also improve the economics of the farm, in some cases dramatically. Higher soil health tends to provide higher yields and more yield stability, while allowing for reduced crop inputs. However, you need to consider the fact that the increased returns may not be immediate. After you implement new practices, soil health may improve slowly, and it may take a few years to see improved yields or changes in the soil itself. Similarly for other businesses like landscaping, your initial investments in soil health may be more expensive but will result in better outcomes for your clients in the long run, like more aesthetic parks and gardens that are more resilient and less expensive to maintain.
The bottom line therefore may not improve immediately. Changing management practices may involve an investment in new equipment; for example, changing tillage systems requires new tillage tools and planters. For many farmers, these short-term limitations may keep them from making changes, even though they are hurting the long-term viability of the farm. Big changes are probably best implemented at strategic times. For example, when you are ready to buy a new planter, consider a whole new approach to tillage as well. Also, take advantage of flush times—for example, when you receive high prices for products—to invest in new management approaches. However, don’t wait until that time to make decisions. Plan ahead, so you are ready to make the move at the right time. If you establish a new orchard, vineyard or landscaped area, it’s best to do whatever is possible to improve the soil before you put your plants into the ground. When switching to no-till it likewise makes sense to try to add extra organic matter, take care of subsoil compaction and correct any nutrient deficiencies. Remember that soil health management is a long-term commitment. There are no silver bullets or snake oils that will work to build soil health; it requires integrating the concepts of physical, biological and chemical processes we have discussed in this book.
General Approaches
The ultimate purpose of ecological soil management is to create a healthy habitat belowground, with good soil structure, thriving and diverse soil organisms, and nutrients in sufficient supply for high crop yields while not in excess and, as a result, causing off-site pollution. When this is combined with healthy above ground habitat, in the field and around its perimeter, plants are provided with optimal conditions for their growth and protection against pests. Soil health can be improved through six main approaches:
- reducing tillage
- avoiding soil compaction
- growing cover crops
- using better crop rotations
- applying organic amendments in appropriate quantities
- applying inorganic amendments in appropriate quantities, timing and locations
There are many options for making soil management changes in different types of farming systems. We have discussed these in the previous chapters with respect to helping remedy specific problems. A good analogy is to think of your soil as a bank account with credits and debits. The credits are management practices that improve soil health, like manure additions, reduced tillage and cover crops. The debits are the ones that degrade the soil, like compaction from field traffic and intensive tillage (Table 24.1). One farming system may result in a different balance sheet than another due to specific constraints. For example, a daily harvest schedule means that you cannot avoid traffic on wet soils, and small-seeded crops require intensive tillage (at least in the planting row) in order to prepare a seedbed. Still, strive to optimize the system: If a “bad” practice, such as harvesting in a wet field that contains spoilable crops, is unavoidable, try to balance it with a “good” practice, thereby making your soil health account flush. Also, you may have options to reduce the impacts of a bad practice, like controlling traffic to certain lanes to reduce unavoidable soil compaction.
If at all possible, use rotations that use grass or legume forage crops (or a combination of the two), or crops with large amounts of residue as important parts of the system. Leave residues from annual crops in the field, or, if you remove them for feed, composting or bedding, return them to the soil as manure or compost. Use cover crops when soils would otherwise be bare to add organic matter and maintain soil biological health, capture residual plant nutrients, keep the soil protected and reduce erosion. Cover crops also help maintain soil organic matter in resource-scarce regions that lack possible substitutes for using crop residues for fuel or building materials.
Raising animals or having access to animal wastes from nearby farms gives you a wider choice of economically sound rotations. Those that include perennial forages make hay or pasture available to dairy and beef cows, sheep and goats—and nowadays even poultry. In addition, on mixed crop-livestock farms, animal manures can be applied to cropland. It’s easier to maintain organic matter on a diversified crop-and-livestock farm, where sod crops are fed to animals and manures are returned to the soil. Compared to crop farms, fewer nutrients leave farms when livestock products are the main economic output. However, growing crops with high quantities of residues, plus frequent use of green manures and composts, helps maintain soil organic matter and soil health even without animals. In many situations you may have opportunities to bring in organic resources. Perhaps there is a lot of municipal compost available in your area, or maybe a nearby dairy farm sells well-composted manure that can help you grow vegetables or improve an orchard or landscaped area.
You can maintain or increase soil organic matter more easily when you use reduced-tillage systems, especially no-till and strip-till. The decreased soil disturbance keeps biological activity and organic matter decomposition near the surface and helps maintain a soil structure that allows rainfall to infiltrate rapidly. Leaving residue on the surface, or applying mulches, has a dramatic impact on soil biological activity. It encourages the development of earthworm populations, maintains soil moisture and moderates temperature extremes. Adding mulch can be very helpful after you plant perennial trees to control weeds and conserve soil moisture.
Compared with conventional tillage, soil erosion is greatly reduced under minimum-tillage systems, which help keep organic matter and rich topsoil in place. Any other practices that reduce soil erosion, such as contour tillage, strip cropping along the contours and terracing, also help maintain soil organic matter. Even if you use minimum-tillage systems, you also should use sound crop rotations. In fact, it may be more important to rotate crops when large amounts of residue remain on the surface, as they may harbor insect and disease organisms. These problems may be worse in monoculture with no-till practices than with conventional tillage.
| Table 24.1 Balance Sheet for Soil Health Management* | ||
|---|---|---|
| Practice or condition | Improves soil health | Reduces soil health |
| Tillage moldboard plowing chisel plowing disking harrowing conservation tillage | X | XX X X X |
| Compaction light severe | X XX | |
| Organic matter additions bedded manure liquid manure compost mulch | XX X XX XX | |
| Cover crops winter grain winter legume summer grain summer legume | XX X XX XX | |
| Rotation crops 3-year sod 1-year sod | XX X | |
| *X = a moderate effect; XX = a greater effect. | ||
What Makes Sense for Your Situation?
We strongly advocate a holistic management approach designed to prevent problems from developing, as preventive medicine approaches do. And, as with human health, we have the ability to diagnose problems through observations and testing. If problems are identified, the patient and physician develop strategies to address them. This may include a change in diet, exercise, a pill or even surgery. There are often multiple ways and combinations to reach the same goal, depending on personal preferences and circumstances. Similarly for soil health, what makes sense for any individual operation depends on the soils, the climate, the nature of the enterprise, the surrounding region, potential markets and your goals. The tests and observations provide useful guidance to help target constraints, but there is rarely a simple recipe. We wish it was that easy. Holistic soil health management based on ecological principles requires an integrative understanding of the processes, which is basically the purpose behind this book.
Start with regularly testing your soils, preferably using comprehensive soil health analyses, and applying amendments only when they are needed. Testing soils on each field every two to three years is one of the best investments you can make. If you keep the report forms, or record the results, you will be able to follow soil health changes over the years. Monitoring soil test changes will help you fine-tune your practices. Also, maintaining your pest scouting efforts and keeping records of those over the years will allow you to evaluate improvements in that area.
Practices to Help Remedy Specific Constraints
Building soil health can help prevent problems from affecting the environment and plant growth. However, as good a job as you might do, specific problems may arise that require some sort of remedial action. The choice of a practice or combination of practices depends largely on specific soil health problems and possible constraints imposed by the farming system. We discussed in Chapter 21 how traditional (chemical) soil tests are used to provide quantitative nutrient and lime recommendations. As discussed in Chapter 23, newly available soil health tests, as well as careful attention to your soils and crops, can help target management practices related to specific limitations. We cannot be quite as precise for making recommendations regarding physical and biological constraints as we can be for nutrient problems because these systems are more complex and we don’t have as strong a research base.
General management guidelines for specific constraints that may have been identified from soil health tests or field observations are presented in Table 24.2. They are listed in terms of two timelines: short term or intermittent, and long term. The short-term recommendations provide relatively quick responses to soil health problems, and they may need to be repeated to prevent recurrence of the problem. The long-term approaches focus on management practices that don’t provide quick fixes but that address the concern more sustainably. You will probably note that the same practices are often recommended for different constraints because they address multiple concerns at the same time.
| Table 24.2 Linking Some Soil Health Measurements to General Management Solutions | ||
|---|---|---|
| Suggested management practices | ||
| Physical concerns | Short term or intermittent | Long term |
| Low aggregate stability | Fresh organic materials (shallow-rooted cover/rotation crops, manure, green clippings) | Reduced tillage, surface mulch, rotation with sod crops |
| Low available water capacity | Stable organic materials (compost, crop residues high in lignin, biochar) | Reduced tillage, rotation with sod crops |
| High surface density | Limited mechanical soil loosening (e.g., strip tillage, aerators), shallow-rooted cover crops, bio-drilling cover crops, fresh organic matter | Shallow-rooted cover/rotation crops, avoiding traffic on wet soils, controlled traffic, physical decompaction— loosening |
| High subsurface density | Targeted deep tillage (zone building, etc.), deep-rooted cover crops | Avoiding plows/disks that create pans, reducing equipment loads and traffic on wet soils, deep tillage |
| Biological concerns | ||
| Low organic matter content | Stable organic matter (compost, crop residues with high lignin, biochar), cover and rotation crops | Reduced tillage, rotation with sod crops, mulch |
| Low active carbon | Fresh organic matter (shallow-rooted cover/rotation crops, manure, green clippings) | Reduced tillage, rotation |
| Low organic forms of nitrogen | N-rich organic matter (leguminous cover crops, manure, green clippings) | Cover crops, manure, rotations with forage legume crop, reduced tillage |
| High root-rot rating | Disease-suppressive cover crops, disease-breaking rotations | Disease-suppressive cover crops, disease-breaking rotations, IPM practices |
| Chemical Concerns | ||
| Low CEC | Stable organic matter (compost, lignaceous/cellulosic crop residues, biochar), cover and rotation crops | Reduced tillage, rotation |
| Unfavorable pH | Liming materials or acidifier (such as sulfur) | Repeated applications based on soil tests |
| Low P, K | Fertilizer, manure, compost, P-mining cover crops, mycorrhizae promotion | Repeated application of P, K materials based on soil tests; increased application of sources of organic matter; reduced tillage |
| High salinity | Subsurface drainage and leaching | Reduced irrigation rates, low-salinity water source, water table management |
| High sodium | Gypsum, subsurface drainage, leaching | Reduced irrigation rates, water table management |
Note that many of the management solutions listed in Table 24.2 involve improving organic matter. As you probably realize at this stage of the book, we believe that improved organic matter management is key to sustainable soil management. But keep in mind that simply bringing in any type of organic material in any amount is not necessarily the solution. For one thing, organic additions that are too large may create problems with nutrient surpluses. Second, some organic materials reduce disease levels, but others can increase them (see Chapter 11 on rotations and Chapter 13 on composting). Third, some constraints like acidity, sodicity and extremely low nutrient levels are often more effectively approached with chemical amendments. Fourth, there are important considerations relating to the type of organic materials that are used. In chapters 9, 10 and 12 we discussed different organic residues and manures, and their effects on soil health. One important distinction is whether the material is mostly “fresh” and easily decomposable or contains more stable compounds. Fresh materials like manure, cover crops and green clippings are high in sugars, cellulose and proteins, and have relatively high N content (low C:N ratios). They immediately stimulate soil biological activity, especially bacteria, and provide a lot of available N for crops. The organic materials that are dominated by stable materials high in lignin, like the residues of mature crops, and those that contain humic material, like composts, are critical to building soil health in the long term. Biochar and other heat-treated organic materials decompose slowly and are much more stable materials, sometimes remaining for hundreds of years. If, for example, aggregate stability or active carbon levels are low, the application of easily decomposable materials will be beneficial in the short term. However, these materials disappear quickly and need to be added regularly to maintain good aggregation. For longer-term effects it is recommended to include more stable organic compounds and use reduced tillage.
What is the role of fertilizers? The emphasis on organic matter should not be interpreted as a complete condemnation of synthetic fertilizers. It is true that the sole dependence on synthetic chemicals without consideration of organic matter and biology in the soil is a primary source of soil health degradation. But not supplying adequate nutrients where they are needed will make matters more dire. There are situations where organic crop production is possible and makes sense, but for better or worse, the current structure of agriculture leaves many areas without adequate options for carbon and nutrient cycling. There the emphasis should be on using conservation practices and supplemental fertilizer to reduce nutrient losses, maintain crop yields and enhance biomass cycling. Otherwise, soil health will deteriorate further and yield reductions will result in food shortages or will necessitate more agricultural expansion into natural areas.
Grain Crop Farms
Most grain crop farms export a lot of nutrients and are managed with a net loss of organic matter. Nevertheless, these farms provide a great deal of flexibility in adopting alternative soil management systems because a wide range of equipment is available for grain production systems. You can promote soil health easily with reduced-tillage systems, especially no-till and strip-till. Well-drained, coarse-textured soils are especially well adapted to no-till systems, and finer-textured soils do well with strip-till or zone-till systems. Regardless of the tillage system that is used, travel on soils only when they’re dry enough to resist compaction. However, managing no-till cropping on soils that are easily compacted is quite a challenge because there are few options to relieve compaction once it occurs. Controlled-traffic farming is a very promising approach, especially for such situations, although it may require adjustments of equipment and investment in a GPS guidance system. Incorporating these innovations into a conventional grain farm often requires an investment in new equipment and creatively looking for new markets for your products. There also are many opportunities to use cover crops on grain farms, even in reduced-tillage systems.
Even if you use minimum-tillage systems that leave significant quantities of residue on the surface and decrease the severity of erosion, you also should use sound crop rotations. Consider ones that use grass or legume perennial forage crops, or a combination of the two. Even bringing small grains into a row crop system (like corn and soybeans) can improve soil health and open up opportunities for cover crops. Raising animals on what previously were exclusively crop farms, cooperating on rotations and manure management with a nearby livestock farm, or growing forage crops for sale gives you a wider choice of economically sound rotations and at the same time helps to cycle nutrients better.
Organic grain crop farms do not have the flexibility in soil management that conventional farms have. Their main challenges are providing adequate nitrogen and controlling weeds. Tillage choices are limited because of the reliance on mechanical methods, instead of herbicides, to control weeds. On the positive side, organic farms already rely heavily on organic inputs through green or animal manures and composts to provide adequate nutrients to their crops. So their balance sheet (Table 24.1) is often very good despite the tillage. A well-managed organic farm usually uses many aspects of ecological soil management. However, erosion may remain a concern when you use clean and intensive tillage. It is important to think about reducing tillage intensity; using strips, ridges or beds; controlling traffic; and perhaps investing in a good planter. New mechanical cultivators can generally handle higher residue and mulch levels, and may still provide adequate weed control. Look into ways to increase surface cover, although this is a challenge without the use of chemical weed control. Alternatively, consider more traditional erosion control practices, such as strip cropping, as they work well with rotations involving sod and cover crops.
Crop-Livestock Farms
Diversified crop-and-livestock farms have an inherent advantage for improving soil health. Crops can be fed to animals, and manures can be returned to the soil, thereby providing a continuous supply of organic materials. For many livestock operations, perennial forage crops and management intensive grazing are an integral part of the cropping system, thereby reducing erosion potential and improving soil physical and biological properties. Nevertheless, integrated crop-livestock farms have challenges. Corn silage harvests do not leave much crop residue, which needs to be compensated for with manure applications or cover crops. Minimizing tillage is also important and can be done by injecting the manure or gently incorporating it with aerators, disks or harrows rather than plowing it under. Soil pulverization can be minimized by reducing secondary tillage, using strip or zone tillage, and establishing the crops with no-tillage planters and seeders.
Preventing soil compaction is important on many livestock-based farms. Manure spreaders are typically heavy and frequently go over the land at unfavorable times, doing a lot of compaction damage. Think about ways to minimize this. Livestock farms require special attention to nutrient management, including making sure that organic nutrient sources are optimally used around the farm and that no negative environmental impacts occur. This requires a comprehensive look at all nutrient flows on the farm, finding ways to most efficiently use them, and preventing problems with excesses. Finally, management-intensive grazing systems are very efficient and are similar to how herds of wild animals naturally graze. Harvesting and fertilizing are done by the animals, but be aware that it is important to match stocking rates to the productivity of pastures.
Vegetable Farms
Soil health management is especially challenging on vegetable farms. Many vegetable crops are sensitive to soil compaction and often pose greater challenges in pest management. Vegetable lands have generally been worked hard over many years and have a long way to go toward improved soil health. Most vegetable farms are not integrated with livestock production, and it is difficult to maintain a continuous supply of fresh organic matter. Bringing manure, compost or other locally available sources of organic materials to the farm should be seriously considered. In some cases, vegetable farms can economically use manure from nearby livestock operations or swap land with them in a rotation. Farms near urban areas may benefit from leaves and grass clippings, and municipal or food waste composts, which are increasingly available. In such cases, care should be taken to ensure that the compost does not contain contaminants. Contrary to large commercial vegetable operations, we found that many smaller organic vegetable farms are often on the other end of the spectrum for soil health. They typically use good rotations and cover crops to provide nitrogen and to reduce pest problems, and they import manure or compost to maintain fertility.
FINDING CREATIVE SOLUTIONS
Dairy farmers in Vermont were concerned about soil health on their corn fields. The state’s colder continental climate limits the time window for cover crop establishment before winter dormancy sets in. Working together with University of Vermont specialists, the farmers experimented with shorter-season corn varieties that both mature seven to 10 days earlier and increase the time window for cover crop establishment equivalently. They found that their corn yields were generally unaffected by the shorter growing season, but their ability to establish cover crops was greatly enhanced.
MORE IS NOT ALWAYS BETTER WITH GRAPEVINES
A good soil is needed in the early years in order to establish healthy grapevines. But the best wines generally come from soils that are not overly fertile and that allow for some water stress during the season. High organic matter and nitrogen contents in vineyard soils create overly abundant vegetative growth in grapevines, reducing fruit set and requiring repeated pruning. Also, important traits of wines are enhanced by the presence of the grapes’ anthocyanin pigments, which contribute to both the taste and to the color of wine. Mild water stress and reduced root growth during the early summer (between bloom and the beginning of the ripening stage) increase the content of these pigments. Poor drainage and aeration are bad for wine quality. Some of the world’s best wines are grown on soils that allow for deep rooting; are calcareous, sandy or gravelly; and are low in organic matter. The best climates experience water deficits during the growing season, which can be supplemented by irrigation if needed. This complex interaction between soil, climate and vine is referred to as terroir.
Vegetable cropping systems are often well adapted to the use of cover crops because the main cropping season is generally shorter than those for grain and forage crops. There is usually sufficient time for the growth of cover crops in the pre-, mid- or post-season to gain real benefits, even in colder climates, and vegetable growers often have a multitude of cover cropping options. Using them as a mulch (or importing mulch materials from off the farm) appears to be a good system for certain fresh market vegetables, as it keeps the crop from direct contact with the ground, thereby reducing the potential for rot or disease.
But many vegetable crops are highly susceptible to diseases, and selection of the right cover or rotation crop is critical. For example, according to Cornell plant pathologist George Abawi, bean root rot is suppressed by rapeseed, crown vetch, wheat and rye but is actually enhanced by white clover. Sudan grass can effectively remediate compaction, control pathogenic nematodes and allelopathically control weeds, but it requires a long time window for sufficient growth.
The immediate need to harvest crops during a very short period before quality declines, often a concern with vegetables, can result in severe compaction problems on vegetable farms. Controlled-traffic systems, including permanent beds, should be given serious consideration. Limiting compaction to narrow lanes and using other soil-building practices between them is the best way to avoid compaction damage under those conditions.
Fruit Farms and Landscaping
Many fruit crops, such as brambles, citrus, grapes, apples and stone fruits, are perennials that take several years to establish and may be harvested for 20 or more years. Similarly, landscaped areas in parks and gardens are intended to remain attractive for many years with minimal maintenance. This makes it especially important to address soil health concerns up front and to avoid mistakes during the establishment years, which can have negative impacts long into the future. Comprehensive soil health analyses and field surveys are worthwhile investments, considering the already high costs of establishing the crops. For tree and vine crops, these evaluative steps should pay attention to deeper soil layers, especially the presence of hard pans, subsoil acidity and shallow water tables, because the quality of the fruits is often strongly influenced by deep roots. It is often worthwhile to make one-time investments like drainage installation, in-row deep ripping and deep lime and compost incorporations, as these are difficult to perform after planting. For landscaped areas, future maintenance costs and watering are concerns that can be addressed by building up the soil before transplanting. Post-establishment, the emphasis should be on managing the surface layer. Avoiding compaction is important, and maintaining good surface mulches is generally also beneficial, depending on the crop type.
Some Final Thoughts
The old folk saying, “The farmer’s footprint is the best fertilizer” could be modified to “The farmer’s footprint is the best path to improved soil health.” If you don’t already do so, begin to regularly observe and record the variability in plant growth and yield across your fields. Take the time to track production from the various sections of your fields that seem different. Compare your observations with the results of your soil tests, so you can be sure that the various areas within a field are receiving optimum management. Each of the farming systems discussed above has its limitations and opportunities for building better soils, although the approaches and details may differ. Whatever crops you grow, when you creatively combine a reasonable number of practices that promote high-quality soils, most of your soil health problems should be solved along the way, and the yield and quality of your crops should improve. By concentrating on the practices that build high-quality soils, you also will leave a legacy of land stewardship for the next generations to inherit and follow.