Building Soils for Better Crops, Third Edition

Practices to Help Remedy Specific Constraints

Overview

Building soil health can help prevent problems from affecting the environment and the growth of plants. 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 combinations 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 22, newly available soil 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 23.2. They are listed in terms of two time lines: 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 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 23.2: Linking Soil Health Measurements to General Management Solutions
 Suggested Management Practices
Physical ConcernsShort-Term or IntermittentLong-Term
Low aggregate stabilityFresh organic materials (shallow-rooted cover/rotation crops, manure, green clippings)Reduced tillage, surface mulch, rotation with sod crops
Low available water capacityStable organic materials (compost, crop residues high in lignin, biochar)Reduced tillage, rotation with sod crops
High surface densityLimited mechanical soil loosening (e.g., strip tillage, aerators), shallow-rooted cover crops, biodrilling, fresh organic matterShallow-rooted cover/rotation crops, avoiding traffic on wet soils, controlled traffic
High subsurface densityTargeted deep tillage (zone building, etc.); deep-rooted cover cropsAvoiding plows/disks that create pans; reduced equipment loads and traffic on wet soils
Biological Concerns
Low organic matter contentStable organic matter (compost, crop residues high in lignin, biochar); cover and rotation cropsReduced tillage, rotation with sod crops
Low active carbonFresh organic matter (shallow-rooted cover/rotation crops, manure, green clippings)Reduced tillage, rotation
Low mineralizable NN-rich organic matter (leguminous cover crops, manure, green clippings)Cover crops, manure, rotations with forage legume sod crop, reduced tillage
High root rot ratingDisease-suppressive cover crops, disease-breaking rotationsDisease-suppressive cover crops, disease-breaking rotations, IPM practices
Chemical Concerns
Low CECStable organic matter (compost, lignaceous/cellulosic crop residues, biochar), cover and rotation cropsReduced tillage, rotation
Unfavorable pHLiming materials or acidifier (such as sulfur)Repeated applications based on soil tests
Low P, KFertilizer, manure, compost, P-mining cover crops, mycorrhizae promotionRepeated application of P, K materials based on soil tests; increased application of sources of organic matter; reduced tillage
High salinitySubsurface drainage and leachingReduced irrigation rates, low-salinity water source, water table management
High sodiumGypsum, subsurface drainage, and leachingReduced irrigation rates, water table management
graph illustrating combining practices that promote soil health

Note that many of the management solutions listed in table 23.2 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 problem 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 approachedwith 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 that are high in lignin, like the residues of mature crops, and those that contain humic material, like composts, are critical to the longterm building of soil health. Biochar, which decomposes slowly over hundreds of years, is perhaps the most stable material. 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.

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, strip-till, and zone-till. Well-drained, coarse-textured soils are especially well adapted to no-till systems, and the finer-textured soils do well with ridge-tillage or zone-tillage 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.

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 rotations that use grass, legume, or a combination of grass and legume perennial forage 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 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.

Organic grain crop farms do not have the flexibility in soil management that conventional farms have. Their main challenges are typically 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 23.1) 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 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 returned to the soil, thereby providing a continuous supply of organic materials. For many livestock operations, perennial forage crops are an integral part of the cropping system, thereby reducing erosion potential and improving soil physical and biological properties. Soil health tests conducted on dairy farms in New York consistently show good results for most soil health indicators, although compaction is still often a concern. Nevertheless, integrated crop-livestock farms have challenges. Silage harvests do not leave much crop residue, which needs to be compensated with manure application or cover crops. Minimizing tillage is also important and can be done by injecting the manure or gently incorporating it with aerators 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. In the spring, allow the fields to dry adequately (do the ball test) before taking spreaders out. If there is no manure storage, building a structure to hold it temporarily allows you to avoid the most damaging soil conditions. Frost manure injection completely avoids compacting the soil and, despite the generally narrow time window, should be considered in colder regions. Compaction can also result from animal grazing on wet soil, although it is generally limited to shallow depths. On pastures, regular aeration helps reduce this problem.

Livestock farms require special attention to nutrient management and making sure that organic nutrient sources are optimally used around the farm and 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.

Vegetable Farms

Soil quality 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 becoming available. In such cases, care should be taken to ensure that the compost does not contain contaminants.

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. Based on identified soil health constraints (see table 23.2) and growth windows, vegetable growers often have a multitude of cover cropping options. Using the cover crop 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 need to harvest crops during a very short period before quality declines regardless of soil conditions often results in severe compaction problems on large vegetable farms using large-scale equipment. 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.

FINDING CREATIVE SOLUTIONS

Dairy farmers in Vermont were concerned about soil health on their corn lands. The colder continental climate of the state limits the time window for cover crop establishment before winter dormancy sets in. Working together with University of Vermont specialists, the farmers experimented with shorterseason corn varieties that mature seven to ten 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.

Fruit Farms

Many fruit crops, such as bramble, citrus, grape, and stone fruits, are perennials that take several years to establish and may be harvested for twenty or more years. This means that mistakes made during the establishment years can have negative impacts on future years and places the emphasis on addressing soil health concerns in the establishment phase. Comprehensive soil health analyses and field surveys are worthwhile investments, considering the expense of establishing orchards and vineyards. For tree and vine crops, the reconnaissance should pay attention to deeper soil layers, especially the presence of hard pans, acidity, and shallow water tables, because the quality of the fruits is often strongly influenced by deep roots.

Any soil health concern should be addressed prior to transplanting. Depending on the results of tests and field analyses, it is often worthwhile to perform onetime investments like drainage installation, in-row deep ripping, and deep lime and compost incorporations, as these are difficult to perform after the establishment of trees, vines, or canes.

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.

MORE IS NOT ALWAYS BETTER WITH GRAPEVINES

To establish healthy grapevines a good soil is needed in the early years. But the best wines generally come from soils that are not overly fertile and 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 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.

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