Tuesday, October 27, 2009

Functions of Soils

Mineral soils perform at least four functions for plants:
1. They provide anchorage for plants.
2. They store plant food (nutrients) for plant use.
3. They hold water for plants.
4. They supply aeration (oxygen) for plant use.
5. They act as temperature regulators for plants.

These five soil functions should be kept in mind when working with or selecting a soil type, or when making an artificial soil media.

Some soils perform these functions better than other soils. For example: Clay soils do well with the first three functions, but on the fourth and fifth soil functions they do poorly. Sandy soils do well in the fourth and fifth soil functions, but fail, quite severely, on the first three functions. Clay loam and sandy loam soils
perform well on all five soil functions. Peat soils do well on functions 1, 3, 4, and 5, but in function 2 they fail.

These examples show that almost all types of soil fail to perform all the functions that the ideal soil is to perform.

In traveling one quickly realizes that crops are grown on many different types of soil. The crops appear to grow equally well regardless of the type of soil. Any and all kinds of soils and soil types that perform the above-mentioned five functions will grow satisfactory crops. This includes both natural soils and artificial soils.

Thus, clay soils can be improved by increasing the drainage and loosening them up, either through proper cultivation or by incorporating organic residues.

Sandy soils can be improved by incorporating peat moss, sawdust, organic residues, green manures, etc. These materials increase the water-holding capacity of sandy soils.

Since peat soils are low in fertility, they must be supplied with the proper fertilizers which the crops require.

High summer heat has an effect on the growth of many plants. Some plants are called heat-loving plants. Other plants are called cool-loving plants. These two words are used correctly in some places, but they do not tell the whole story in other places.

Almost everyone is acquainted with nurseries that deal with plants. Nurseries are divided into many groups, such as: tree nurseries, ball and burlap, container growers, flowering plant nurseries, potted plant nurseries and florists, indoor foliage plant growers, orchid growers, azalea growers, vegetable and bedding plant growers, and still others.

The bedding plant growers will be used to illustrate that plants can be grown out-of-season. Peppers, tomatoes, eggplants, sweet potatoes, etc. are heat-loving plants. They will freeze at 32°. But bedding plant growers (nurseries) grow these, and other heat-loving plants, during the coldest part of the winter season.

Pansies, stocks, calendulas, cabbage, lettuce, etc. are called cool-loving plants, and they are grown by the nurseries in July and August–the hottest part of the summer. Bedding plant nurseries must grow plants out-of-season to have them ready for sale, to the retail public, when the proper planting season arrives.

All will agree, at least in Southern California, that the plants that the nurseries grow out-of-season, for resale, are of the highest and finest quality. How can they do it?

It is really quite simple. They merely provide the ideal soil for the growing media, and the proper environment. In other words, for the cool-loving plants, which they grow in the hottest weather, they provide diffused sunlight, and a cool, light weight, porous soil media for the plants to grow in. For heat-loving plants they provide heated greenhouses and a lightweight, porous soil media. In both cases
the soil media is the important requisite.

In many places the soil is gray clay, red clay, brown clay, or black clay. Because of the universal shortage of organic materials, and the lack in using those that are available to improve clay soils, the heavy frequent rains pack the clay soils almost like concrete. They set up so hard that the plant roots have a very difficult task trying to penetrate the soil deeper than a few inches.

In the cooler season of the year the demands on plant roots to provide moisture and plant nutrients to the stems and leaves is much less demanding than in the heat of summer. Also, the soil temperature is more ideal for plant root growth. Other factors being favorable, vegetable crops can perform their normal functions in cool weather.
However, when the weather gets hot, both day and night, the clay soil
temperature rises. The rains are less frequent, and between rains the hard clay soil contracts and large cracks develop. These unfavorable growing conditions are usually more than many vegetable plants can cope with; thus they just do not mature the crop, if planted in the hard soil in the heat of summer.

Realizing that nurseries grow plants all through the year, many experiments have been conducted using a soil media similar to that used by nurseries–a lightweight, porous, organic and inorganic media.

The results were most impressive. Common vegetable crops were grown
successfully every month of the year, in areas where they were only grown seasonally before. The results of the experiments indicate conclusively that if plant roots can penetrate the soil with ease, to the depth that they can reach the soil temperature they prefer, then plants will grow and produce even though the temperature above the ground becomes much hotter than the soil root zone.

In other words, the root zone temperature in the soil (approximately 6" to 8"), is more the determining factor whether plants will grow in the heat of summer, than the temperature above the ground.

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Blogger David William said...

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Best Regards,

7:38 AM  

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