In this article we will discuss about:- 1. Characteristics of Green Manure 2. Suitable Crops for Green Manuring 3. Benefits of Green Manuring 4. Limitations of Green Manure Crops 5. Green Manure Crops in Rotation 6. Pest Management Benefits of Green Manure Crops.
Contents:
- Characteristics of Green Manure
- Suitable Crops for Green Manuring
- Benefits of Green Manuring
- Limitations of Green Manure Crops
- Green Manure Crops in Rotation
- Pest Management Benefits of Green Manure Crops
1. Characteristics of Green Manure:
The green manure crops should have profuse leaves and rapid growth early in its life cycle and have abundance and succulent tops. It should be capable of making a good stand on poor and exhausted soils, have a deep root system and be legume with good nodular growth habit. Use of leguminous green manure crop is more useful in comparison to non- legumes, as more nitrogen is added by legumes. This will be advantageous for the soils and crops grown after green manuring.
2. Suitable Crops for Green Manuring:
i. The Non-Legumes Crops:
They are used as green manuring crops provide only organic matter to the soil. The non-legumes are used for green manuring to a limited extent. Examples: Mustard (Brassica Sp), Wheat (Triticum Sp), Radish (Raphanus sativas), Carrot (Dancus carota), Jowar (Sorghum vulgare) Maize (Zea mays), Sunflower (Hellanthus annus), etc.
ii. Legumes or Leguminous Crops:
The legumes used as green manuring crops provide nitrogen as well as organic matter to the soils. Legumes have the ability of acquiring nitrogen from the air with the help of its nodule bacteria. The legumes are most commonly used as green manuring crops. Examples- Sannhemp (Crotalaira juncea), Djainach (Seshania aculata) Mung (Phaseolus aureus), Cowpea (Vigna catjung), Lentil (Lens esculenta), Senji (Melilotus alba), Berseem (Phaseolus aureus) Guar (Cyamposis tetragonolaba).
Type of Green Manure According to Season:
i. Winter Cover Crop:
A winter cover crop is planted in late summer or fall to provide soil cover during the winter. Often a legume is chosen for the added benefit of nitrogen fixation. In northern states, the plant selected needs to possess enough cold tolerance to survive hard winters. Hairy vetch and rye are among the few selections that meet this need.
They are sometimes planted in a mix with winter cereal grains such as oats, rye, or wheat. Winter cover crops can be established by aerial seeding into maturing cash crops in the fall, as well as by drilling or broadcasting seed immediately following harvest.
ii. Summer Green Manure Crop:
A summer green manure occupies the land for a portion of the summer growing season. These warm-season cover crops can be used to fill a niche in crop rotations, to improve the conditions of poor soils, or to prepare land for a perennial crop.
Legumes such as cowpeas, soybeans, and annual sweet clover, sesbania, guar, crotalaria, or velvet beans may be grown as summer green manure crops to add nitrogen along with organic matter. Non- legumes such as sorghum-sudangrass, millet, forage sorghum, or buckwheat are grown to provide biomass, smother weeds, and improve soil tilth.
iii. Living Mulch:
A living mulch is a cover crop that is interplanted with an annual or perennial cash crop. Living mulches suppress weeds, reduce soil erosion, enhance soil fertility, and improve water infiltration. Examples of living mulches in annual cropping systems include over seeding hairy vetch into corn at the last cultivation, no-till planting of vegetables into sub clover, sweet clover drilled into small grains, and annual ryegrass broadcast into vegetables.
Living mulches in perennial cropping systems are simply the grasses or legumes planted in the alleyways between rows in orchards, vineyards, Christmas trees, berries, windbreaks, and field nursery trees to control erosion and provide traction.
iv. Catch Crop:
A catch crop is a cover crop established after harvesting the main crop and is used primarily to reduce nutrient leaching from the soil profile. For example, planting cereal rye following corn harvest helps to scavenge residual nitrogen, thus reducing the possibility of groundwater contamination. In this instance, the rye catch crop also functions as a winter cover crop. Short-term cover crops that fill a niche within a crop rotation are also commonly known as catch crops.
v. Forage Crop:
Short-rotation forage crops function both as cover crops when they occupy land for pasturage or haying, and as green manures when they are eventually incorporated or killed for a no-till mulch. Examples include legume sods of alfalfa, sweet clover, trefoil, red clover, and white clover, as well as grass-legume sods like fescue-clover pastures. For maximum soil-improving benefits, the forage should not be grazed or cut for hay during its last growth period, to allow time for biomass to accumulate prior to killing.
3. Benefits of Green Manuring:
i. Nitrogen Production:
Nitrogen production from legumes is a key benefit of growing cover crops and green manures. Nitrogen accumulations by leguminous cover crops range from 40 to 200 lbs. of nitrogen per acre. The amount of nitrogen available from legumes depends on the species of legume grown, the total biomass produced, and the percentage of nitrogen in the plant tissue.
Cultural and environmental conditions that limit legume growth such as a delayed planting date, poor stand establishment, and drought will reduce the amount of nitrogen produced. Conditions that encourage good nitrogen production include getting a good stand, optimum soil nutrient levels and soil pH, good nodulation, and adequate soil moisture.
The portion of green-manure nitrogen available to a following crop is usually about 40% to 60% of the total amount contained in the legume. For example, a hairy vetch crop that accumulated 180 lbs. N per acre prior to plowing down will contribute approximately 90 lbs. N per acre to the succeeding grain or vegetable crop.
ii. Soil Microbial Activity:
A rapid increase in soil microorganisms occurs after a young, relatively lush green manure crop is incorporated into the soil. The soil microbes multiply to attack the freshly incorporated plant material. During microbial breakdown, nutrients held within the plant tissues are released and made available to the following crop.
Factors that influence the ability of microorganisms to break down organic matter include soil temperature, soil moisture, and carbon to nitrogen (C : N) ratio of the plant material. The C : N ratio of plant tissue reflects the kind and age of the plants from which it was derived. As plants mature, fibrous (carbon) plant material increases and protein (nitrogen) content decreases. The optimum C : N ratio for rapid decomposition of organic matter is between 15:1 and 25:1.
C : N ratios above 25:1 can result in nitrogen being “tied up” by soil microbes in the breakdown of carbon-rich crop residues, thus pulling nitrogen away from crop plants. Adding some nitrogen fertilizer to aid the decomposition process may be advisable with these high carbon residues. The lower the C : N ratio, the more N will be released into the soil for immediate crop use.
iii. Green Manuring Increases Crop Yield:
Green manure increases the organic matter and nitrogen content (in case of leguminous green manuring crop) of the soil. It is proved that if green manuring is done properly, it always results in increased yields of the succeeding crops.
iv. Increases the Biochemical Activity:
The organic matter added to soil by way of green manure acts as food for microorganisms. The organic matter stimulates the activity of micro-organisms and they stimulate the biochemical changes accordingly.
v. Nutrient and Soil Conservation:
Green manuring crops act as cover crop. They protect the soil from erosion and nutrient loss by taking up soluble nutrients which might otherwise have been lost in drainage water or due to erosion. Green manuring crops make available phosphorous and other nutrients for the succeeding crops. Green manure has a marked residual effect also.
In addition to nitrogen from legumes, cover crops help recycle other nutrients on the farm. Nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), and other nutrients are accumulated by cover crops during a growing season. When the green manure is incorporated, or laid down as no-till mulch, these plant-essential nutrients become slowly available during decomposition.
Certain broad-leaved plants are noted for their ability to accumulate minerals at high concentrations in their tissue. For example, buckwheat, lupine, and sweet clover are noted for their ability to extract P from soils. Likewise, alfalfa and other deep-rooting green manures scavenge nutrients from the subsoil and translocate them upwards to the surface rooting zone, where they become available to the following crop.
vi. Supply of Organic Matter and Soil Structure:
A major benefit obtained from green manures is the addition of organic matter to the soil. During the breakdown of organic matter by microorganisms, compounds are formed that are resistant to decomposition, such as gums, waxes, and resins. These compounds and the mycelia, mucus, and slime produced by the microorganisms help bind together soil particles as granules, or aggregates.
A well-aggregated soil tills easily, is well aerated, and has a high water infiltration rate. Increased levels of organic matter also influence soil humus. Humus is the substance that results as the end product of the decay of plant and animal materials in the soil-provides a wide range of benefits to crop production.
Sod-forming grass or grass-legume mixtures are important in crop rotations because they help replenish organic matter lost during annual cultivation. However, several years of sod production are sometimes required before measurable changes in humus levels occur. In comparison, annual green manures have a negligible effect on humus levels, because tillage and cultivation are conducted each year. They do replenish the supply of active, rapidly decomposing organic matter.
vii. Rooting Action:
The extensive root system of some cover crop is highly effective in loosening and aerating the soil. When cover crops are planted after a sub-soiling treatment, they help extend the soil-loosening effects of the deep tillage treatment.
viii. Weed Suppression:
Weeds flourish on bare soil. Cover crops take up space and light, thereby shading the soil and reducing the opportunity for weeds to establish themselves. The soil-loosening effect of deep-rooting green manures also reduces weed populations that thrive in compacted soils.
The primary purpose of a non-legume green manure, such as rye, millet, or sudangrass, is to provide weed control, add organic matter, and improve soil tilth. They do not produce nitrogen. Thus, whenever possible, annual grain or vegetable crops should follow a legume green manure to derive the benefit of farm-produced nitrogen.
Providing weed suppression through the use of allelopathic cover crops and living mulches has become an important method of weed control in sustainable agriculture. Allelopathic plants are those that inhibit or slow the growth of other nearby plants by releasing natural toxins, or allelochemicals.
ix. Soil and Water Conservation:
Retention of soil moisture under cover crop mulches can be a significant advantage. When cover crops are planted solely for soil conservation, they should provide a high percentage of ground coverage as quickly as possible. Most grassy and non-legume cover crops, like buckwheat and rye, fulfill this need well. Of the winter legumes, hairy vetch provides the least autumn ground cover because it puts on most of its above-ground growth in the spring.
Consequently, it offers little ground cover during the erosion-prone fall and winter period. Sowing a mix of leguminous and grassy-type cover crops will increase the ground coverage, as well as provide some nitrogen to the following crop. The soil conservation benefits provided by a cover crop extend beyond protection of bare soil during non-crop periods.
x. Vegetation Management to Create a Cover Crop Mulch:
Herbicides are the most commonly used tools for cover crop suppression in conservation tillage systems. Non-chemical methods include propane flamers, mowing and mechanical tillage.
4. Limitations of Green Manure Crops:
1. The recognized benefits of green manuring and cover cropping the soil cover improves soil structure, nitrogen from legumes, and long- term value of sustained soil health. For the immediate growing season, seed and establishment costs need to be weighed against reduced nitrogen fertilizer requirements and the effect on cash crop yields.
2. Insect communities associated with cover crops work to the farmer’s advantage in some crops and create a disadvantage in others.
3. The winter legumes that harbor cat-facing insects such as the tarnished plant bug, stink bug, and plum curculio can pose problems for apple or peach orchardists.
5. Green Manure Crops in Rotation:
Green Manure crops can fit well into many different cropping systems during periods of the year when no cash crop is being grown. Even the simplest corn/soybean rotation can accommodate a rye cover crop following corn, which will scavenge residual nitrogen and provide ground cover in the fall and winter.
When spring-killed as a no-till mulch, the rye provides a water-conserving mulch and suppresses early- season weeds for the following soybean crop. Hairy vetch can be planted behind soybeans to provide nitrogen for corn the following spring. Many vegetable rotations can accommodate cover crops as well. Buckwheat can follow lettuce and still be tilled down in time for fall broccoli.
6. Pest Management Benefits of Green Manure Crops:
In addition to the soil improving benefits, Green Manure Crops can also enhance many pest management programs. Crop cover is a stable natural system, typically diverse, containing many different types of plants, arthropods, mammals, birds, and microorganisms. Growing cover crops adds diversity to a cropping system.
In stable systems, serious pest outbreaks are rare, because natural controls exist to automatically bring populations back into balance. Innovative farmers are paving the way by inter-planting cover crops with the main crop and realizing pest management benefits as a result.