Soil Management

Introduction

Good gardening begins with good soil. The successful gardener needs a basic understanding of soil since soil conditions strongly influence how plants grow.

Healthy soil is a complex substance full of beneficial bacteria, fungi and animals.

These organisms help break down rock, plant, and animal matter and release their nutrients in forms that plants can use.

Soil Texture

Three different soil particles determine a soil’s texture. Sand particles are the largest, clay the smallest, and silt is in between. Medium-textured soils (loam, sandy loam, and silt loam) have a good mixture of sand, silt, and clay that is ideal for growing most plants. It is more difficult to grow plants in soils that contain an excessive amount of either clay, sand, or silt.

The easiest way to evaluate your soil’s texture is to lightly squeeze a handful of moist soil. If the clump crumbles apart, the soil is sandy. If it forms a sticky ball, it is clay. If the soil ends up as a spongy ball, you have loam.

Soil Structure
The combination of individual sand, silt, and clay particles into larger clumps called aggregates creates soil structure. Good garden soil is crumbly. Nutrients and water are held within the aggregates. The spaces between aggregates allow water and air to move easily though the soil and provide enough space for plant roots to grow.
Plants grow best when good soil structure is maintained. Do not walk on, work in, or drive machinery over wet soil. It is also important to refrain from excessive tilling. Any of these actions can damage soil structure, compacting the pores, which decreases the movement of air and water through the soil. 
 
Amendments
Amendments are materials which change the physical or chemical properties of the soil and indirectly improve plant growth. Reasons to change the properties of the soil with organic matter or chemical amendments include:
 
  • Make soil surface more water permeable , especially silty soils
  • Enlarge pore spaces so water and air move more freely, important in clay Soils
  • Prevent soil cracking; distribution of roots, water, and air are more uniform
  • Make soil easier to work, important for managing annual plants
  • Allow roots to grow easily and quickly from container soil into heavier native soil

Soil Amendments

A variety of amendments

Soil organic matter consists of all the dead plant and animal matter in various stages of decay. A soil rich with organic matter supports a thriving population of beneficial organisms from microscopic bacteria and fungi to larger life forms like earthworms.

Organic matter acts like a slow release fertilizer and also improves soil structure. Soil microorganisms feed on organic matter and release nitrogen and other nutrients it contains in a form that roots can absorb.
Compost is an excellent organic amendment. Good compost, either homemade or store bought, is the most beneficial all-purpose amendment for soil. In addition to compost, there are other amendments that may be helpful. Click here to go for information on specific amendments and their benefits. Amendments should be free of weed seeds, toxic materials, and disease organisms.
The top six to eight inches of garden soil should be amended with composted organic matter. If you spread two inches of compost on top of a previously cultivated soil and incorporate it to a depth of six inches, the soil will be amended 25 percent by volume.

Organic matter continually breaks down and decomposes, so you must periodically add new material. Good gardeners incorporate organic matter into their soil before each planting season.

Fertilizers

Vegetables and flowers usually grow better if fertilizer containing Nitrogen, Phosphorus and Potassium is mixed into the soil prior to planting. Organic fertilizers are derived from plant, animal, and mineral sources. They are not made with synthetic materials. Organic fertilizers feed microorganisms in the soil, which break down the organic matter and release nutrients in a form that plant roots can absorb. The advantage of using organic fertilizers is that they contain more than one nutrient. These nutrients are released slowly, in smaller quantities, making them available to the plant for a longer period of time. They are less likely to burn plants or be lost from the soil. Another advantage is that organic fertilizers may also act as soil Amendments.

Prior to planting apply fertilizer uniformly over the soil, then till it in to a depth of about six inches. Manure that is not mixed into the soil after it has been applied will lose some of its nitrogen content as ammonia gas. Phosphorous and potassium have very little mobility in the soil; they must be worked into the soil where plant roots can reach them.

During the growing season, most plants will periodically need additional applications of nitrogen fertilizer. A fertilizer containing nitrogen should be applied on direct-seeded crops when the plants have four to six true leaves. Fertilizer containing nitrogen should be applied to transplants about four or five weeks after planting

Additional applications of nitrogen fertilizer should be made at intervals of about four to six weeks depending upon the crop. In sandy soils, which require frequent irrigation, small amounts of fertilizer will be required at more frequent intervals.

Click here for more information on Post Planting Fertilizing.

Soil pH - Acidity or Alkalinity

Soil acidity or alkalinity is expressed as a pH number ranging from 1.0 (extremely acid) to 14.0 (extremely alkaline). A pH of 7.0 is neutral, neither acid nor alkaline. Most plants grow best in slightly acidic to neutral soil (a pH between 6.0 and 7.0).

Most of the soils that are cultivated tend to be alkaline because our irrigation water is alkaline. Soil pH affects the chemical form of some nutrients like phosphorus and iron. When the pH is too high or low, plants may suffer a nutrient deficiency even in a nutrient rich soil. When the pH is too high or low, some nutrients convert to a form that cannot be absorbed by plants. This can cause a nutrient deficiency in plants - even in nutrient rich soil.

Soil Testing

Soil testing can provide information on your soil’s texture, pH, salinity and the level of essential plant nutrients and fertility. This information may be very useful if you are starting a new garden in an area where plants have not been grown before.

Soil testing may also help you find out why plants are not growing well in an existing garden. A soil test is not always necessary, however, and it will not tell you if poor plant growth is caused by pests or diseases, improper irrigation or poor cultural practices, such as planting at the wrong time of year.

One of the most useful soil tests is the measurement of soil pH. The test will tell you if your soil is too alkaline or acidic and if corrective measures are needed. A lab can measure soil pH for you or you can do it yourself. A simple pH meter and test kit are available at local nurseries or from mail order companies.

You will only get good information from a soil test if you collect a good sample. To collect soil for testing, dig a small hole 6-8 inches deep with a trough and collect a thin slice of soil from one side of the hole. Put the soil in a bucket and collect more samples from several locations in the garden. Mix the samples together to produce a representative sample from your garden. If you use a commercial testing lab, ask if they will provide a report to help you interpret the results of your soil test. Also ask if they provide recommendations on how to correct soil problems