This way, the canopy begins to open just as the legumes need more light. Legumes combined with grains or grasses provide excellent green manures. The legumes can be overseeded or broadcast with the grasses. The grasses or grains control weeds, add organic matter and can provide structure for viny legumes e. After the green manure is turned under, the carbon in the grains or grasses will tie up some of the fixed nitrogen, preventing it from being leached.
After trying a number of green manure combinations, I was most impressed by crimson clover mixed with annual ryegrass, and oats mixed with common vetch.
Ideally, the legume seedbed is kept moist for several weeks after planting. Many legume seeds are close to the surface and take a couple of weeks to emerge. Consequently, the seeds are quite susceptible to drying. Also, the bacteria in the inoculant will die if the inoculant dries out. For these reasons, legumes are often planted in the spring or overseeded or planted just before rain is expected. So, now the legume is growing, but is it fixing nitrogen? If you are curious, carefully dig up the roots of a few legumes that are about to flower weeks old.
Look for round or oblong growths on the roots: these are nodules, the site of nitrogen fixation. Their presence indicates that the legume was successfully inoculated and probably is or was fixing nitrogen. Ideally there should be a few large nodules or many small nodules.
For example, a hundred small nodules on a clover plant or two dozen large faba bean nodules is excellent. To see if the plant is actively fixing nitrogen, break a few nodules in half. Active nodules are red or pink inside; inactive ones are green or black. You might want to pull up some leguminous weeds to see what their nodules look like; weeds often provide excellent examples of nodulation.
If there is a considerable amount of nitrogen in the soil, the legumes will simply use the soil nitrogen rather than fix nitrogen. Legumes fix the most nitrogen when no nitrogen source has been added to the soil for the last two years. Nitrogen fixation in legumes peaks at flowering. After that, the nitrogen moves to the seeds. In the seeds, the nitrogen is converted into amino acids, the building blocks of protein. This explains why the dried seeds of legumes such as beans are high in protein.
When the beans or peas are removed, most of the fixed nitrogen is harvested as well. Penetration by roots of perennial legumes will also improve the internal soil drainage.
Thus, fields after alfalfa will drain more quickly in spring, allowing field operations to begin earlier. A study at Outlook with irrigated alfalfa plowed-down in late fall or early spring indicated that the following cereal crop required little nitrogen fertilizer, while the second cereal required two-thirds of its usual amount Table 6. Although not indicated in the table, the third cereal crop would require the full recommended rate of nitrogen.
Source: J. Henry, University of Saskatchewan, Saskatoon. Biennial legumes, like sweetclover, can also markedly increase grain production. In a long-term experiment on a thin Black soil at Indian Head, wheat yields in a 3-year rotation with sweetclover green manure were consistently higher than in a comparable rotation with fallow and similar to those of a well fertilized rotation.
During the first 18 years of this study the unfertilized green manure-wheat-wheat rotation also provided, by far the highest. Source: re Yields: R. Zentner et al. Annual legumes that are capable of fixing large amounts of nitrogen under good moisture conditions, can significantly improve the nitrogen supply for succeeding crops. This confirms that benefits from use crops are not only due to the added nitrogen they provide to succeeding cereal crops but also to positive 'rotational effects' due to disease suppression, improved tilth and other enhancements of soil quality.
Legume green manures offer several advantages over conventional summerfallow as they tend to improve, enrich and protect the soil.
Sweetclover green manure can be ineffective fallow replacement on Dark Brown soils, provided it is turned under early in the second year to reduce moisture depletion. In the more drought-prone Brown soil zone, however, deep-rooted biennial and perennial legumes are not suitable for green manuring, as their excessive soil moisture depletion will depress the yield of subsequent wheat crops for several years.
The recent introduction and evaluation of high nitrogen fixing and water use-efficient annual legumes has made it feasible to develop a legume green manure system that is more compatible with the short cereal rotations commonly used on Brown soils. In a study on a Brown loam, 4 annual legumes were seeded into wheat stubble with tall stubble strips for overwinter snow trapping. At bloom they were either disced under or desiccated. Figure 10 shows some of the fertility benefits only 3 months after incorporation of the green manures.
Table 8. Source: V. Biederbeck, p. Great Plains Conservation Tillage symp. The yield of wheat after these green manures was greatly affected by legume management but not by the type of annual legume. Wheat yields after legumes grown to maturity and also after uninoculated disced-in green manure were generally as low as those of well-fertilized continuous wheat because of increased moisture depletion and nitrogen deficiency.
The results from this and other recent green manure studies indicate that fallow replacement with annual legume green manure is feasible in the Brown and Dark Brown soil zones, but only in combination with some method of snow management and early incorporation of the legume, to enhance soil water recharge.
Annual legumes can also reduce soil erosion by improving aggregate stability. However, do not over-incorporate these crops. Severe instances of erosion have occurred after over-incorporation. Annual grain legumes are normally grown for grain production although some producers do use them as green manure crops. Choosing which grain legume i. Growing annual grain legumes can increase the yield of succeeding crops in the rotation. This benefit, called rotation effect , is due to more than an increase in high-N crop residue.
Thus, the rotation effect has been attributed to improved physical, chemical and biological characteristics of the soil, after resulting in reduced duration and severity of attacks by diseases and insect pests. Seed costs of most annual legumes are prohibitively high for their widespread use as a green manuring crop.
The full nitrogen supplying potential of an annual legume can be harnessed by partially incorporating the crop at the first pod stage.
Partial incorporation helps reduce volatilization losses of nitrogen directly from the decomposing plant material. Annual grain legumes are fairly tolerant of early spring frosts and thus can be seeded early. A severe frost may destroy the top growth, but regrowth will occur from one of the scale nodes at or below the soil surface.
Pea, lentil and fababean should be sown into firm, moist soil, at a depth of 1 to 3 inches to get below dry surface soil. Good soil fertility is required to achieve high yield and protein content. Placing phosphate fertilizer with or near the seed is particularly important due to the "pop up"" effect which results in a more vigorous seedling better able to compete with the weeds. Only a limited amount of phosphate fertilizer can be placed in a narrow band with the seed. Surpassing safe rates can lead to germination and seedling damage.
For more information on seed-placed fertilizer see the FarmFacts bulletin entitled Guidelines for safe rates of fertilizer applied with the seed. Legumes preferentially use available soil nitrogen rather than fix atmospheric nitrogen.
The only biennial forage legume grown on the Canadian prairies is sweetclover. Sweetclover is an upright, broadleaved legume with many stems and branches. In the seeding year plants develop to a height of inches. In the second year, flowers are produced and the crop grows feet tall at maturity.
The two common types are yellow-flowered and white-flowered. The yellow-flowered type is preferred by farmers. It is more drought-tolerant, shorter, and finer stemmed and leaved. These characteristics make it a more palatable livestock feed and easier to incorporate as green manure.
The yellow-flowered type also grows more rapidly early in the spring and can be harvested or incorporated earlier. This allows a longer period for recovery of soil moisture reserves. Where sweetclover is grown for feed, the variety Norgold should be grown. Norgold is a yellow-flowered variety that produces forage with a low coumarin content.
Low coumarin sweetclover poses no danger of causing "sweetclover or bleeding disease" of livestock. Sweetclover and most other forage legumes have small seeds, thus they will only emerge from shallow depth less than 1 inch.
Any preseeding tillage should be done as shallow as possible to conserve moisture near the surface and provide a firm seedbed. Economic conditions often dictate that the forage legume is seeded with a companion crop. The forage legume should then be sown preferably at right angles to the companion crop rows to reduce competition. The legume should be sown within a few days of the companion crop to improve its ability to compete and survive with the companion crop.
Cereals are the most suitable companion crops. Limited research with canola indicates that poor stands result, probably due to shading of the legume by the large canola leaves.
Use of flax as a companion crop usually results in weedy stands, as flax is not very competitive. Barley is very competitive with forage legumes and is not generally recommended as a companion crop. Wheat and oat are less competitive and alter maturing than barley. They are more useful as companion crop in the Brown and Dark Brown soil zones where rainfall is frequently inadequate for significant fall growth. Where the companion crop can be used as green feed, oat is preferred.
Early removal of the companion crop as forage is beneficial for establishment of a forage legume, particularly if the crop is weedy or suffers from lack of moisture. Letting the companion crop mature for grain significantly reduces the seedling vigour of the forage for 1 to 3 years after establishment. Seed sweetclover as early as possible in the spring. Early seeding takes advantage of favourable moisture conditions and allows the sweetclover seedlings to emerge and become established before weed growth begins.
Fall seeding of sweetclover is not recommended. Inoculate the seed immediately prior to seeding with the proper inoculant to ensure optimum nitrogen fixation. Refer to the latest "Guide to Crop Protection" for herbicides registered for use in sweetclover. Production of sweetclover should be planned well in advance to minimize weed populations prior to seeding. Several practices which have proven useful in reducing weed populations and competition are as follows.
An alternate method for use on stubble is to spray winter annual and biennial weeds in the fall and then spray a "burn off" herbicide and zero till seed the sweetclover and companion crop directly into the undisturbed stubble in spring. Wild oat and green foxtail can be controlled with herbicides; however, the herbicide selected must be compatible with both the companion crop and sweetclover.
Refer to the latest Guide to Crop Protection. Fertilizer applications should be based on soil test results. Where required, phosphorus, potassium and sulphur should be applied. Proper use of fertilizer aids in establishment of vigorous competitive stands of sweetclover, and may contribute to increased yields of the succeeding crop s.
Sulphur deficiency can severely depress sweetclover growth. Because the crop is a biennial, some consideration should be given to supplying enough of these nutrients to also meet the second year's needs. Sweetclover obtains its nitrogen requirements by nitrogen fixation in the root nodules.
Where the crop is grown on stubble with a companion crop, it may be desirable to use some nitrogen fertilizer for the companion crop. However, high rates of nitrogen should be avoided, as this will reduce nitrogen fixation.
The sweetclover weevil can cause significant damage significantly in an area. This crop and the pest become more abundant whenever sweetclover acreage is increased. Refer to the Guide to Crop Protection for registered insecticides and their use. Sweetclover is one of the most suitable crops for use as a green manure. In the second year it grows rapidly and can be incorporated early.
Incorporation should be done at the bud stage, as most of the N fixation has occurred by this time Table 4 and Figure This allows time for recovery of soil moisture reserves and residue decomposition during the partial fallow period. Later incorporation should only be considered in cases where it is desirable to incorporate the maximum amount of organic matter. Examples of such cases are on moderately saline soils or soils that have poor structure due to very low levels of organic matter.
However, excessive moisture depletion by alter growth may result in slower decomposition of the green manure and low moisture reserves for the succeeding crop. Sweetclover is most beneficial on Gray Wooded soils. Where sweetclover is growth as a regular part of rotations on such soils, succeeding grain crop yields are similar whether the crop is used as forage or as a green manure.
Where it is grown less frequently it may be more valuable as green manure than as hay. Where it is used as hay, care in harvesting is required to minimize leaf losses. Sweetclover production for seed usually increases the cash value of the crop. However, seed prices can fluctuate widely from year to year.
Sweetclover grown for seed reduces moisture available to succeeding crops, compared with sue as green manure or forage. Soil moisture recovery can be enhanced by leaving stubble as tall as possible or by leaving strips of standing crop to trap snow. Much of the nitrogen from the crop is removed with the seed, therefore reducing the amount available to succeeding crops. Sweetclover fits well into short rotations with grain crops because it is a biennial.
It is best adapted to use on problem soils such as degraded soils low in organic matter, soils where crusting is a problem or on saline soils. In many cases it fits well into rotations as a substitute for summerfallow.
A cereal crop should be grown following sweetclover. Oilseeds do not respond as well as cereals when grown immediately after sweetclover Table 9. When grown as a second crop after sweetclover, oilseeds frequently show yield responses on degraded, low organic matter soils or those that crust. Table 9. Source: S. Brandt, unpublished data. Sweetclover may be substituted for fallow on more productive soils.
Most soils will benefit from the additional organic matter and nitrogen added. However, it is difficult to document yield responses by crops following sweetclover on such soils. Frequently yield depression occurs in crops following sweetclover compared to those grown on fallow. This is particularly so in drier areas and in dry years. Such losses may be recovered in improved yields in other years of the rotation or reduced costs for nitrogen fertilizers.
Leaving strips of sweetclover standing over winter will trap snow Figure 13 and help soil moisture reserves to recover, however, they may cause problems tilling the field the following spring.
When perennial legumes are included in rotations, they fix nitrogen and add humus and nutrients to the soil. The choice of perennial legume will depend mostly on the soil zone and intended use of the crop. Alfalfa is a widely adapted high yielding forage legume. It has good drought tolerance, moderate salinity and flooding tolerance and is winter hardy. Sainfoin and birdsfoot trefoil are bloat-free alternatives.
Sainfoin is short-lived and not very drought tolerant and seed costs are generally high. Birdsfoot trefoil is lower yielding than alfalfa and not widely grown in Saskatchewan. Alsike or red clover are best suited to the Parkland or acidic soils, but will produce less dry matter than alfalfa. Alfalfa is the main perennial legume grown in western Canada. It is grown for hay, pasture, seed and in some areas as a major crop for the dehy industry. Alfalfa is adapted to a wide range of soil and climatic conditions.
Production and persistence is favoured when alfalfa is grown on neutral to slightly alkaline soils and is severely limited by acid conditions i. Alfalfa growth is best on well-drained soils. It is intolerant of flooding and does poorly on soils with inadequate internal drainage. However, alfalfa is quite drought tolerant due to its deep root system.
As with other perennial legumes, the best currently available varieties of alfalfa are listed in the latest Saskatchewan Forage Crop Production Guide. Alfalfa varieties are often characterized according to the nature of their root system, tap rooted or creeping rooted.
Creeping rooted plants develop horizontal roots from the tap root which are capable of giving rise to independent plants. Creeping rooted varieties are generally more persistent, stress tolerant and grazing tolerant than other types of alfalfa. However, creeping rooted varieties have slower regrowth potential after harvest as compared to tap rooted types.
Red clover is another common perennial legume grown for feed and seed. It is shorter-lived than alfalfa and fits well into short-term rotations. It is adapted to a wide range of soils in the moister areas of the province and is more tolerant to acidic soils than is alfalfa.
Red clover is not tolerant of salinity or extended periods of drought. Other perennial legumes are grown to a limited extent in Saskatchewan. Alsike clover is a short-lived perennial adapted to low lying moist areas. It withstands considerable spring flooding and has the capacity to propagate itself from seed. It is well suited to acidic, organic soil.
Birdsfoot trefoil is a potentially long-lived perennial forage which is very tolerant of waterlogged soils and can withstand several weeks of flooding and some acidity. It is not adapted to dryland areas. Although it can be used for hay in wetter areas, it is more commonly used as a pasture species because it does not cause bloat.
Birdsfoot trefoil is very sensitive to competition, particularly during establishment. Peanuts are legumes. Alfalfa is a legume. There are also many different kinds of trees that are legumes. As a food, beans are high in protein. Most beans also contain a lot of nutrients such as calcium, iron, phosphorus and niacin.
Some beans contain amino acids and lysine. The leaves of bean plants and other legumes also are high in nutrients. They are often fed to farm animals. Some farmers grow legumes especially for their animals. Cows, goats and other animals are permitted to eat the leaves on the plants in the fields. Many farmers around the world know the value of growing legumes along with their main crops, or between harvests.
The legumes replace nitrogen used by crops. They also provide a cover for the soil to help protect it from heavy rains and strong winds. The roots of the legume plants hold the soil in place. This keeps the soil from being blown away by the wind or washed away by rain.
0コメント