Cover and Green Manure Crop Benefits to Soil Quality

Soil Quality and Resource Management

Soil is one of the five resources—soil, water, air, plants, and animals—that NRCS deals with in resource planning. Soil is intimately related to the other four resources, and its condition can either negatively or positively impact the other resources. For example, if the soil surface is functioning adequately, the soil will allow water to infiltrate, thus reducing the potential for erosion and increasing the amount of water stored for plant use. This function of soil affects water quality, plant growth, and the health of animals. In addition, protection of the surface layer resists wind erosion, thus protecting the air resource. Soil Quality is a critical factor in the management of natural resources, and the protection or enhancement of soil quality is the key component of all resource management assistance activities in the NRCS.

What is Soil Quality?

Soil quality is 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

* support human health and habitation.

As defined, the terms soil quality, soil health, and soil condition are interchangeable.

Effects of Conservation Practices

One of the goals of conservation planning is to consider the effects of conservation practices and systems on soil quality. This is the first technical note in a series on how conservation practices affect soil quality. This technical note is designed to compliment local or regional information on the specific nature of cover crops. Cover and Green Manure Crop Benefits to Soil Quality

1. EROSION – Cover crops increase vegetative and residue cover during periods when erosion energy is high, especially when main crops do not furnish adequate cover. Innovative planting methods such as aerial seeding, interseeding with cyclone seeder, or other equipment may be needed, when main crop harvest, delays conventional planting of cover crops during recommended planting dates.

2. DEPOSITION OF SEDIMENT – Increase of cover reduces upland erosion, which in turn reduces sediment from floodwaters and wind.

3. COMPACTION – Increased biomass, when decomposed, increases organic matter promoting increased microbial activity and aggregation of soil particles. This increases soil porosity and reduces bulk density. Caution: plant cover crops when soils are not wet, or use other methods such as aerial seeding.

4. SOIL AGGREGATION AT THE SURFACE – Aggregate stability will increase with the addition of and the decomposition of organic material by microorganisms.

5. INFILTRATION – Surface cover reduces erosion and run-off. Cover crop root channels and animal activities, such as earthworms, form macropores that increase aggregate stability and improve infiltration. Caution: Macropores can result in an increase in leaching of highly soluble pesticides if a heavy rain occurs immediately after application. However, if only sufficient rainfall occurs to move the pesticide into the surface soil after application, the risks for preferential flow are minimal. Cover crops, especially small grains, utilize excess nitrogen.

6. SOIL CRUSTING – Cover crops will provide cover prior to planting the main crop. If conservation tillage is used, benefits will continue after planting of main crop. Increases of organic matter, improved infiltration, and increased aggregate stability reduce soil crusting.

7. NUTRIENT LOSS OR IMBALANCE – Decomposition of increased biomass provides a slow release of nutrients to the root zone. Legume cover crops fix atmospheric nitrogen and provide nitrogen for the main crop. Legumes utilize a higher amount of phosphorus than grass or small grains. This is useful in animal waste utilization and management. Small grains are useful as catch crops to utilize excess nitrogen, which reduces the potential for nitrogen leaching. Caution: To prevent nutrient tie ups, cover crops should be killed 2-3 weeks prior to planting main crop. Tillage tools are used to kill and bury cover crops in conventional tillage systems. However, with conservation tillage systems, cover crops are killed with chemicals and left on or partially incorporated in the soil.

Caution: Research has shown that incorporation of legume cover crops results in more rapid mineralization. However, due to delay in availability of nitrogen from legume cover crop in conservation tillage, a starter fertilizer should be applied at planting. (Reeves, 1994). An ARS study done in Morris, Minnesota reported dramatically higher carbon losses through C02 remissions under moldboard plow plots as compared to no-till. It was reported that carbon was lost as C02 in 19 days following moldboard plowing of wheat stubble that was equal to the total amount of carbon synthesized into crop residues and roots during the growing season. Long-term studies indicate that up to 2 percent of the residual organic matter in soils are oxidized per year by moldboard plowing” (Schertz and Kemper, 1994).

8. PESTICIDE CARRYOVER – Cover crops reduce run-off resulting in reduced nutrient and pesticide losses from surface runoff and erosion. Increased organic matter improves the environment for soil biological activity that will increase the breakdown of pesticides.

9. ORGANIC MATTER – Decomposition of increased biomass results in more organic matter. Research shows cover crops killed 2-3 weeks prior to planting main crop, results in adequate biomass and reduces the risk of crop losses from soil moisture depletion and tie up of nutrients.

10. BIOLOGICAL ACTIVITY – Cover and green manure crops increase the available food supply for microorganisms resulting in increased biological activity.

11.WEEDS AND PATHOGENS – Increased cover will reduce weeds. Caution: Research has shown reductions in yield are possible in conservation tillage cotton systems following winter cover crops. Reductions are attributed to interference from residue (poor seed/soil contact), cool soil temperatures at planting, increased soil borne pathogens, and increased insects and other pests. Harmful effects from the release of chemical compounds of one plant to another plant (allelopathic) are possible with crops like cotton, but losses can be reduced by killing the cover crop 2-3 weeks prior to planting main crop, and achieving good seed/soil contact with proper seed placement. Cover crops have shown some allelopathic effects on weeds reducing weed populations in conservation tillage (Reeves, 1994).

12. EXCESSIVE WETNESS – Cover and green manure crops may remove excess moisture from wet soils, resulting in reduction of “waterlogging” in poorly drained soils. Caution: transpiration of water can be a detriment in dry climates. Planners should adjust the kill date of cover crops to manage soil water.


Cover and Green Manure Crops as a conservation practice can improve soil health. Soil quality benefits such as increased organic matter, biological activity, aggregate stability, infiltration, and nutrient cycling accrue much faster under no-till than other tillage practices that partially incorporate the residue.

One example comes from the Jim Kinsella farming operation near Lexington, Illinois. He reports that organic matter levels have increased from 1.9 percent 6.2 percent after 19 years of continuous no-till (Schertz and Kemper, 1994). Future technical notes will deal with other conservation practice effects on soil quality. The goal of the Soil Quality Institute is to provide this information to field offices to enable them to assist landusers in making wise decisions when managing their natural resources.

(Sources –

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Green-manure crops

Green-manure crops – also known as cover crops – play an important part in field-crop production in both agriculture and horticulture.

They can be used to break up pest and disease life cycles, increase soil fertility and nutrient levels, suppress the growth of weeds and improve soil structure.

Green manures can be easily incorporated into a growing system either field-wide or inter-row depending on the crops being grown. They are particularly useful in tree production where plants are in place for a number of years and demand access to good levels of soil nutrients. Lifting and selling trees affects soil structure and green manures can help to stabilize these areas.

Some green manures are best sown in the autumn and can therefore be effectively fitted in between some crops. They can provide good control over any potential nitrate leaching, which can occur on bare soils, particularly over the winter months. For crops such as Sudan grass, tagetes or brassicas, planting should occur when the risk of frost has gone — during late spring and summer months.

1. Grazing rye

For the prevention of nitrate leaching over the winter months, grazing rye is one of the best green manures to sow. It establishes quickly and will grow year-round even in the cooler months. When rye is subsequently incorporated, it is important that the following crop is planted as soon as possible afterwards to maximize the available mineral nitrogen and prevent leaching.

2. Leguminous plants

Legumes, such as lupins and vetch, will produce nitrogen during their growing stages that results in significant levels of soil mineral N available to crops that follow. It is important, therefore, to time the sowing — and subsequent incorporation — of a legume crop to maximize on the amount of nitrogen that is produced.

3. Phacelia

Phacelia has vigorous and highly branched roots that penetrate the soil and help to break it down. It is a valuable green manure for soils with poor structure. Its roots quickly reach their maximum development when the plant is in flower, usually around two months after sowing.

It produces dense foliage that can reach about 45cm in height, which can protect the soil from the impact of rain and smother weeds. Damage by frost (at -5°C or below) results in foliage collapse that then provides good soil cover — particularly useful on capped soils.

As phacelia decomposes, it releases high levels of accessible forms of minerals, particularly phosphorus, calcium and magnesium, which are then available for the following crop. When incorporated into the soil, the foliage and stems quickly release high levels of nitrogen one or two months after decomposition begins. Planted in autumn, it can help to reduce nitrate leaching in mild winters, retaining up to as much as 50 per cent of nitrogen produced by cultivation.

The bright-blue flowers attract hoverflies, which will predate on aphids on nearby crops. Bees are also attracted to this crop. It can be sown on all soil types — March to September — and grows in most climate ranges in the UK.

4. Sudan grass (Sorghum spp.)

This crop is heat-tolerant, drought-resistant and can grow in a wide range of soils. It produces a deep, penetrating network of roots throughout its life. This can be increased further by cutting the top growth part-way through the growing season.

Sudan grass does not produce flowers but forms a large, dense canopy layer that suppresses weed growth and prevents erosion. Soil nematode populations and Verticillium wilt propagules may be reduced in an infested soil after growing this crop. The plant produces a harmless glucoside called dhurrin, which when the plant is damaged by cutting, frost or drought is converted into hydrogen cyanide.

During growth, roots will also exude dhurrin, providing some initial control. Young tissue produces the greater amount of hydrogen cyanide but it must be incorporated and sealed immediately after flail-cutting for maximum effect.

5. Marigolds (Tagetes spp.)

Tagetes species have the added benefit of being able to produce flowers and can be sown in between crops such as field-grown trees. The plant roots contain naturally-occurring broad-spectrum biocides that act as nematicides, fungicides and bacteriocides. Levels of organic matter incorporated into soils depend on the variety used.

6. Mustards

There are several varieties on the market but the Caliente brand from Plant Solutions has shown significant promise abroad and in the UK. A wide range of soil diseases can be reduced including Verticillium wilt, silver scurf, Sclerotinia and nematode damage, onion pink root, Sclerotinia minor in lettuce, Pythium in carrots, Fusarium in tomatoes and Sclerotinia, Pythium and Fusarium in beans. A significant amount of organic matter is also produced that can be incorporated into the soil to release a similar product to the Sudan grass.

Flowering time and incorporation depend on variety and sowing date. A period of 21 days after incorporation is recommended prior to planting a new crop to prevent the risk of poor seed germination.

Caliente Brand Mustard 119 is a good all-round variety for sowing in spring or late summer for quick crops or mid autumn for overwintered crops in milder parts of the UK.

Caliente Brand Mustard 99 provides the best biofumigant action from its high glucosinolate levels (30 per cent more than 119). Requires good growing conditions including additional fertiliser and irrigation in dry periods.

Caliente Brand Mustard 61 is a large-leaved variety producing high levels of biomass under ideal conditions. Requires a longer season to grow and is the slowest to flower. It needs good warm weather and irrigation in dry conditions, so is suitable for midsummer UK growing.

7. Nemat (Eruca sativa)

A white-flowered rocket (pictured) that has shown similar biofumigant properties to the mustards. It can also be used as a trap crop for various nematodes including some root knot and cyst species. The roots contain the highest glucosinolate levels.

The dense foliage produced will provide a good level of biomass for incorporation. Mowing the crop before it flowers can extend the growing — and trapping — period. It is tolerant of a range of temperatures, can take a light frost and is relatively drought-tolerant once established.

(Source  –

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Winter Cover Crops

Cover crops are valuable tools in many kinds of agricultural production. They find there greatest use in horticultural and home garden practices but should be used any time the soil will be bare for more than a few weeks. The name “cover crop” suggests one of the functions of a cover crop but does not fully describe all its functions.

Any crop covering the soil protects it from erosion, moderates the temperature and inhibits weed seed germination and growth. Most West Virginia cropland is on sloping soils. It’s very important to keep it covered over winter to avoid the development of rills and small gullies and to prevent loss of nutrients by erosion. Grass winter cover crops also prevent leaching loss of nitrogen and other nutrients over the winter period. Prevention of nitrogen leaching is especially important. Well fertilized cropland may have a lot of valuable nitrogen left at the end of the growing season. If there is nothing growing over winter to use the nitrogen, it will likely be leached below the root zone before the spring planting season. A grass cover crop will capture this nitrogen, incorporate it in its tissues, and then release it when the cover crop is plowed under the following spring. This “left-over” nitrogen is saved for the next crop instead of allowing it to leach into the ground water.

Cover crops are helpful in maintaining soil organic matter. While they are in place they protect the soil from organic matter loss by erosion and exposure to high temperatures. When the cover crop is added to the soil it will be converted into soil organic matter. One-time use of a cover crop will not have much impact on soil organic matter content. Regular use over a period of years will slowly raise the organic matter level in the soil. Perhaps the most beneficial short-term effect of a cover crop is increased activity of soil organisms. Earthworms, fungi and a variety of organisms attack the freshly added organic material. Their by-products are in turn used by other organisms in the soil. This biological activity brings about increased soil aggregation and improved structure and tilth.

A range of species is available to use as cover crops. The most common crops used are winter small grains. These have the advantage of making rapid growth, have good winter hardiness and seed is readily available throughout the state. Some, particularly winter rye, may be somewhat difficult to manage in spring because, if turned under too late, they tend to decompose slowly and compete with planted crops for available nitrogen. Some legumes also may be used as winter cover crops. Their greatest disadvantages are they are less winter hardy than grasses. In addition, they are not as effective in preventing erosion and are not effective in reducing leaching loss of left-over nitrogen. Their primary advantages are that they add significant amounts of available nitrogen to the soil and have a more favorable effect on soil tilth than grasses.

The choice of the most suitable cover crop depends on many factors. On level land where the cover crop can be seeded early, crimson clover or hairy vetch plus a small grain would be good choices. Where later seedings are necessary, use the more cold-hardy species.

Triticale is a new crop which was developed by crossing wheat and rye and has characteristics intermediate between its parents. Varieties vary in the extent to which they resemble the wheat or rye parent. All of them tend to be more cold-tolerant and herbicide-tolerant than wheat… <more>


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Green Manures – Effects on Soil Nutrient Management and Soil Physical and Biological Properties

Both organic and conventional growers can gain many benefits from increased use of green manures. A wide range of plant species can be grown as green manures as different ones can bring a variety of benefits. Leguminous plants will fix nitrogen from the air whilst non-legumes will conserve nitrogen by preventing nitrate leaching. Green manures add organic matter to the soil, improving its physical and biological properties and they can assist with pest, disease and weed management. Some of the effects on soil physical properties may only become significant after several green manure crops have been grown over a period of perhaps five to ten years. Green manures are often categorised according to the time of year they are grown.

Winter green manures or cover crops are usually sown in the autumn and incorporated in the following spring and may be legumes (e.g. vetch) or non-legumes (e.g. rye). Summer green manures are usually annual legumes (e.g. crimson clover) which are grown to provide a short term boost for fertility. However, they could also be nonlegumes (e.g. mustard).

Longer term green manures are usually pure clover or grass/clover leys grown for two or three years. They are common in organic stockless rotations where they form the main source of nitrogen. However, in conventional farming these rotations would be harder to justify unless there were animals to graze them.

Green manures may also be used in intercropping systems, although in vegetable cropping it is important to avoid too much competition with the cash crop. Protected cropping systems offer particular challenges and opportunities for green manuring whilst fertility building in orchards can be difficult as nitrogen must be provided at the right time to ensure good fruit set and crop quality. Green manures grown as an understory can also attract beneficial insects.

Green manures are often grown to add nitrogen to the soil. In organic systems this represents the main source of nitrogen, whilst for conventional growers, it can be a way of minimising fertiliser inputs. Almost all legumes use Rhizobia bacteria to fix nitrogen from the atmosphere.  Unfortunately finding out how much  nitrogen is actually fixed is not easy  and depends on many factors.  Firstly, the correct strain of bacteria  must be present. Different bacterial  species interact with different groups  of legumes (clovers, lucerne and trefoils, lupins, beans etc.). If the same types of plants are regularly grown then sufficient bacteria will usually be present to establish sufficient nodules. Sometimes it is worth inoculating the seeds with the correct type of bacteria. There are several types available commercially, at a modest cost.

Sometimes the nitrogen fixation still does not occur, even if the roots form a symbiosis with the bacteria. Some strains will infect the plant but not be very effective. They can even drain the plant of resources

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(Source: Horticulture Development Company –

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Green Class

State-of-the-art technologies use efficiency can not be unambiguously estimated. High-capacity productive tractors cause depth soil degradation caused by machines weight which can not be eliminated via no-till technology use as far as this problem requires larger technical efforts and deep tillage works lead to faster nutrients withdrawal. Chemical fertilizers cause soil depletion, while certain profitable crops growing leads to further higher production costs. It is rather questionable if we should replace machines with human labour, still we consider it helpful to remind about natural fertilizers to replace synthetic ones.

Some experts identify natural fertilizers as sideration – the process of ploughing under green mass from intentionally cultivated plants in order to enrich soil with nitrogen and organic nutrients. Still we can include the rests of current crop as natural fertilizer. For example we can gather, recycle and distribute the rests of straw as manure or utilize natural ashes. The ashes from only one sunflower top consist about 30 g of potassium which plants require to raise water circulation efficiency and apparently prevents from drought.

In fact “green fertilizers” use is capable in two ways: ploughing under mown crops on its cultivation field or transportation to the place use. In some cases it is possible to interplant the main crop on the field covered with green manure. Talking about the method drawbacks we must mention constrained delays in main crops cultivation provoked by green manure cultivation periods, diseases spreading and additional efforts aiming to plough under the green mass. Nevertheless the technology advantages significantly exceed the effect of the above-mentioned hardships. First of all we must mention fertilizers economy: for example green manure of legumes increases nitrogen receipts. Moreover 50% of synthetic nitrogen fertilizers quantity runs out within the first 3 month, while natural nitrogen withdraws much more slower. Secondly, natural fertilizers slow down soil degradation and even restore problem soil characteristics, while it supports natural humus generation. Thirdly, the crops with minimal chemicals content fit high quality standards and can be sold at a relatively higher price. Finally, this technology brings essential economical effect as far as it assures from fertilizers prices increase and problems with fertilizers long-term storage. Within 2009-2012 ammonia contract price has tripled (Middle East FOB, Yuzhnyy FOB).

“Green fertilizers” are particularly useful in cases of dung substitution in those countries which have problems with livestock population shortage.

There is no doubt that natural fertilizers can not be considered as the universal measure, while the resources scarcity and food deficit force agrarians to apply more and more extensive business measures. Not all agrarians are willing to wait until green manure grows to use it as fertilizer – it looks much more profitable to get two crops in a same time and to sell them at a reasonable price. But if we speak about long-term efficiency – it would be great to remind an old proverb “the miser pays twice” and look at “green fertilizers ” consumption increase all over the world.

Tags: fertilizers, green manure, wheat, sunflower, tractor, ammonia, no-till, “green fertilizers”

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