- Pellic Vertisols: 70%
|Chance||Depth||Drainage||Texture Reaction - pH||Organic Carbon Conductivity - Electrical||Subsoil Cation Exchange||Clay Cation Exchange||Calcium Carbonate - Lime||Gypsum Sodium - Exchangeable|
Soil Triangle - Pellic Vertisols
Definition - Pellic Vertisols
- Pellic indicates having in the upper 30 cm of the soil matrix a Munsell value, moist, of 3.5 or less and a chrome of 1.5 or less (in Vertisols only). Vertisols are churning, heavy clay soils with a high proportion of swelling clays. These soils form deep wide cracks from the surface downward when they dry out, which happens in most years. The name Vertisols (from Latin vertere, to turn) refers to the constant internal turnover of soil material. Common local names for many Vertisols are: black cotton soils, regur (India), black turf soils (South Africa), margalites (Indonesia), Vertosols (Australia), Vertissolos (Brazil), and Vertisols (United States of America). Vertisols are found in depressions and level to undulating areas, mainly in tropical, subtropical, semi-arid to subhumid and humid climates with an alternation of distinct wet and dry seasons. The climax vegetation is savannah, natural grassland and/or woodland. Most Vertisols occur in the semi-arid tropics, with an average annual rainfall of 500–1 000 mm, but Vertisols are also found in the wet tropics, e.g. Trinidad (where the annual rainfall sum amounts to 3 000 mm). The largest Vertisol areas are on sediments that have a high content of smectitic clays or that produce such clays upon post-depositional weathering (e.g. in the Sudan), and on extensive basalt plateaus (e.g. in India and Ethiopia). Vertisols are also prominent in South Africa, Australia, the southwest of the United States of America (Texas), Uruguay, Paraguay and Argentina. Vertisols are typically found in lower landscape positions such as dry lake bottoms, river basins, lower river terraces, and other lowlands that are periodically wet in their natural state
Description - Clay - Light
- Clay contains 40% or more clay, less than 45% sand, and less than 40% silt. Clay drains poorly, has few air spaces, warms slowly in spring, and is heavy to cultivate. If drainage is improved, plants grow well as it holds more nutrients than many other soils. Extreme caution should be used in plowing and tilling clay soils. If plowed when too wet they become cloddy. There is a certain point between wetness and dryness when a clay soil crumbles quite readily; it should be tilled only at this time, so far as is possible. The texture of a clay soil may be ruined for several years by one injudicious plowing, when it was too wet. Unless the soil is very tenacious, and "runs together" or "puddles" if left bare over winter, clay land may be fall-plowed to advantage, leaving it rough and exposed to the mellowing action of freezing and thawing. The crust that forms so easily over the surface of clay soil in summer should be prevented by frequent shallow tillage. Something may also be done to improve the texture of clay soils, in certain cases, by liming them. This causes many of the fine grains to stick together, forming larger grains, thereby making the soil looser and more porous. The farm crops that succeed most generally on clay soils are the cereals, grasses and some tree fruits. Clay land is especially valuable for hay. The fine particles of clay may be separated from each other and the soil loosened and lightened by mixing them with particles of humus or sand. It is rarely practicable to haul sand upon a clay soil and plow it under, because of the expense, but if this can be done expediently the result will be gratifying
|Soil reference depth||100 mm|
|Calcium carbonate CaCO3 - Lime||0.2% weight|
|Organic carbon||1.2% weight|
|Cation exchange capacity - clay||68 cmol/kg|
|Cation exchange capacity - soil||42 cmol/kg|
|Clay - percent - weight||56% weight|
|Gravel - percent - volume||2% weight|
|Sand - percent - weight||20% weight|
|Silt - percent - weight||24% weight|
|Electrical conductivity||0.1 dS/m|
|Gypsum content CaSO4||0% volume|
|Soil reaction - pH||6.8 -log H+|
|Reference bulk density||1.31 kg/dm3|
Conservation tillage systems such as zero tillage cause minimum disturbance to the soil after the previous crop has been harvested. In zero tillage, the ideal is to plant direct into the soil, without hoeing or plowing. Tillage is reduced to ripping planting lines or making holes for planting with a hoe. Crop residues are left in the field to reduce soil erosion, conserve moisture, inhibit weed growth, and act as green manure. Zero tillage is not recommended when disease is present. To manage disease, crop residues must be either removed from the field and destroyed or deeply ploughed to reduce sources of disease infection and spread.
Advantages of conservation tillage include less machinery, labour and fuel, as well as reduced soil erosion and compaction. Disadvantages of conservation tillage include lower soil temperatures, slower germination and emergence when direct sowing is used, slower early growth, delayed competition with weeds, higher incidence of root diseases, heavier crop residue, the possibility of more difficult planter operation, weed spectrum changes, and potential increase of soil insect pests or insects that spend part of their life cycle in the soil (e.g. cutworms, thrips, leafmining flies, grubs). Cultivation exposes these pests to desiccation by the sun heat and to predation by natural enemies.
Green manure legumes create nitrogen in the soil by fixing it from the atmosphere.
Benefits of Green Manure Cover Crops
- Easy to grow
- Increases soil organic matter
- Reduce soil losses from wind and water erosion
- If it is a legume, it can fix nitrogen. When the legume is mature, chopped up and added to the soil, it will add nitrogen to the soil which will be used by later crops on the land.
- The roots of the green manure crops extract nutrients from deep in the soil.
- The deep roots work to break up and aerate the soil
- When the green manure is added to the soil, it works to lighten and loosen the soil to aerate and improve drainage, making the soil healthier for later crops. After tilling in a green manure crop, we see the soil level in the farm beds raise several inches. The soil is loose and no longer compacted.
- Green manure crops include jack beans, perennial peanut, and Mucuna.
- These plants help the main crop by increasing soil fertility by adding nitrogen to the soil by nitrogen fixation.
- They add biomass (organic matter) to the soil.
- As cover crops, they reduce soil loss.
Planting Green Manure Crops
Green manure crops can be planting using intercropping with the main crop or by using crop rotation in which the green manure crop is planted in-between plantings of the main crop. For intercropping, plant the legume seeds in rows between rows of the main crop. Plow the legumes into the soil at the start of the rainy season.
In crop rotation, plant legumes after the main crop has been harvested. The legumes will benefit the field as a cover crop and as green manure. At full biomass maturity, plow the legumes into the soil as green manure for the next crop.
For a source of green manure to the field, cut the legumes at full maturity, shred, and spread over the field.
Preventing Soil Erosion while Adding Nutrients to the Soil
The first step in soil management is preventing the loss, or erosion, of soil. Topsoil is particularly vulnerable to erosion if not protected by plants or mulch or by other measures. The soil that remains after the loss of topsoil is usually less productive, which can result in lower yields. The challenge is to protect soil while using the land for food production and other non-food activities.
Soil erosion is caused mainly by wind and water but also by incorrect cultivation practices. Rain and wind dislodge and then carry away soil particles. Where the soil is bare or the vegetation poor, rainwater does not seep into the soil; instead it runs off and carries with it loose topsoil. Sloping land and light soils with low organic matter content are both prone to erosion. Once eroded, the soil is lost forever.
Soil erosion is a problem in regions with little vegetation, particularly in the semi-arid and arid zones. In the humid tropics, erosion was not considered a problem when the land was in its natural state, because the variety of native plants kept the soils covered at all times. Now, people are clearing more land for agricultural purposes, and the situation has changed. Heavy rains coupled with poor soil management of cultivated areas are now common causes of soil erosion in the humid areas.
Some common forms of water erosion include:
- Sheet erosion: a thin top layer of soil is removed from the soil by the impact of rain. With sheet erosion, small heaps of loose material (e.g. grass) amass between fine lines of sand after a rainstorm. This erosion takes place across a whole garden or field.
- Rill erosion: water flows over minor depressions on the land's surface and cuts small channels into the soil. The erosion takes place along the length of these channels.
- Gully erosion: a gully forms along natural depressions on the soil's surface or on slopes. The head of a gully moves up the slope in the opposite direction of the flow of water. Gullies are symptoms of severe erosion.
This occurs mostly on light soils and bare land. High winds cause severe damage. Wind erosion is a common problem in dry and semi-arid areas, as well as in areas that get seasonal rains.
Unlike water which only erodes on slopes, wind can remove soil from flat land as well as from sloping land; it can also transport the soil particles through the air and deposit them far away. Soils vulnerable to wind erosion are dry, loose, light soils with little or no vegetative cover.
Plowing up and down a slope causes soil erosion. To prevent the loss of soils, certain measures must be taken.
- clearing only the land to be cultivated;
- planting along a contour and using grassed channels;
- establishing windbreaks and bench terraces;
- plowing along a contour;
- planting cover crops and mulching.
When clearing land for cultivation, the beneficial effects of certain trees and plants should be considered. Some trees should be left, since they may supply food, medicine, shade or, when they shed their leaves, organic matter.
Feeding the Soil
One of the main goals in growing crops is to make the soil fertile and well structured, so a wide range of useful crops can grow and produce well. In order to grow, plants require nutrients that are present in organic matter, such as nitrogen, calcium and phosphorus, as well as minerals and trace elements.
If the natural fertility or structure of the soil is poor, it must be continuously "fed" with organic matter, such as leaves and manure, in order to improve its productivity and water-holding capacity. As organic matter decomposes, it becomes food for plants. It also improves soil structure by loosening heavy clay and binding sandy soil.
Feeding the soil with organic matter is especially important in the early years of cultivating the land. Organic matter (i.e. waste from plants and livestock) can be collected and buried in the soil, where it will decompose. The organic matter also can be used to make compost, which can be applied to the soil to enrich its fertility.
The roots of legumes contain nitrogen-fixing bacteria. Therefore, intercropping or rotating legumes with other crops helps maintain or improve the nitrogen content of the soil, and this enhances the growth of other plants.
Healthy plants yield more and are better protected from insects and disease. The application of organic matter, such as compost, animal manure, green manure and soil from anthills, improves soil structure and adds nutrients to the soil.
Long-Term Soil Management
The ideal way to protect and feed the soil is to apply organic matter or compost regularly and to keep the soil covered with plants. A multilayer cropping system in which a mixture of trees and other plants with different maturity times are grown together will protect the soil and recycle nutrients. Leguminous plants such as cowpeas, groundnuts and beans are particularly useful in providing continuous nutrients for crops.
Apply Organic Matter to Soil to Improve the Crop
Plants can contain up to 90 percent water. The water is absorbed mainly through the root system of the plant. With the water, plant nutrients are absorbed. Healthy roots need air (aeration) for development. Excess water in the soil prevents air from penetrating and damages a plant's roots. Water management is therefore extremely important in regions with good water resources as well as in those where water is scarce.
The water-holding capacity of soil varies according to soil type. Soil with a high content of organic matter has better aeration, better structure and better water-holding capacity. Heavy, sticky soils are too dense to allow air in and water out, so roots cannot breathe and plants can have growth problems. When this kind of soil dries out, it sets like cement, and water takes a long time to soak into it. On the other hand, sandy, coarse-grained soils are too loose to hold water before it drains away. In this kind of soil, without a regular external water supply, a plant's roots cannot find enough water for growth. Regular application of organic matter will improve the ability of both these kinds of soil to hold and release enough water and air. During land preparation for planting, organic materials such as animal manure or compost should be applied to the land such that they are well incorporated into the soil.
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