Taking an environmentally sensitive approach to pest management
The soil test is an excellent gauge of soil fertility. It is an inexpensive way to maintain good plant health and maximum productivity without polluting the environment by over application of nutrients
Soil fertility fluctuates throughout the growing season each year. The quantity and availability of nutrients in the soil are altered by the addition of fertilizers, manure, compost, mulch, lime or sulfur and by leaching. Furthermore, large quantities of nutrients are removed from soils as a result of plant uptake, growth and development, and by harvesting of crops. A soil test will determine the current nutrient/fertility status. It also provides the information needed to maintain optimum fertility year after year.
Some plants grow well over a wide range of soil pH, while others grow best within a narrow range of pH. Most turf grasses, flowers, ornamental shrubs, vegetables and fruits grow best in slightly acid soils (pH 6.1 to 6.9). Plants such as rhododendron, azalea, mountain laurel and blueberries require a more acidic soil to grow well. A soil test is the only precise way to determine whether the soil is acidic, neutral or alkaline.
A soil test takes the guesswork out of fertilization and is extremely cost effective. It not only eliminates the expense of unnecessary fertilizers but also eliminates overuse of fertilizers and helps to protect the environment.
When is the best time for a soil test? Soil samples can be taken in the spring or fall for established sites. For new sites, soil samples can be taken any time when the soil is workable. Most people conduct their soil tests in the spring. However, fall is a preferred time to take soil tests if one suspects a soil pH problem and wants to avoid the spring rush. Fall soil testing will allow you ample time to apply lime to raise the soil pH. Sulfur should be applied in the spring if the soil pH needs to be lowered.
How to take a soil sample? Most errors in soil testing occur when the sample is taken. Potential sources of errors include the following:
Taking a representative sample is important in soil testing. Use a trowel, spade and sampling tube/core samplers.
What soil sampling tools do I need? A soil sample is best taken with a soil probe or an auger. Samples should be collected in a clean plastic pail or box. These tools help ensure an equal amount of soil to a definite depth at the sampling site. However, a spade, knife, or trowel can also be used to take thin slices or sections of soil.
Push the tip of a spade deep into the soil and then cut a 1/2-inch to 1-inch slice of soil from the back of the hole. Be sure the slice goes 6 inches deep and is fairly even in width and thickness. Place this sample in the pail. Repeat five or six times at different spots over your garden. Thoroughly mix the soil slices in the pail. After mixing thoroughly, take out about 1-1/2 cup of soil and mail or, preferably, take it to your University Extension Center. You can also mail or deliver it to the MU Soil and Plant Testing Laboratory in Columbia or at the Delta Research Center in Portageville. It is important that you fill out the soil sample information form (Fig. 1) completely and submit it with your sample. By indicating on the form the crops you wish to grow, you can get specific recommendations. For additional information on submitting samples to the lab visit lab’s website at: http://soilplantlab.missouri.edu/soil/
How often should I test my soil? Soil should be tested every two to three years. In sandy soils, where rainfall and irrigation rates are high, samples should be taken annually.
What tests should be run? In general a regular fertility test is sufficient. This includes measurement of pH, neutralizable acidity (NA), phosphorus, potassium, calcium, magnesium, organic matter (OM) and cation exchange capacity (CEC).
What do the test result numbers mean? Some labs report soil test values as amounts of available plant nutrients, and others report extractable nutrients that will become available to the plants (Fig. 2). Fertilizer rates are given in pounds of actual nutrient (as distinct from pounds of fertilizer) to be applied per 1,000 square feet.
Apply fertilizers as recommended by soil test
All fertilizer recommendations given in a soil test report are based on the amount of nutrient (N, P2O5, and K2O) to apply for a given area. Lawn and garden recommendations are given in pounds per 1000 sq. ft. From the given recommendations it is necessary to select an appropriate fertilizer grade and determine how much of this fertilizer to apply to the garden area. Numbers on fertilizer bags indicate the exact percentages of nutrients by weight: 100 lb of 5-10-10 fertilizer contains 5 lb of nitrogen (N), 10 lb of phosphate (P2O5), and 10 lb of potash (K2O). Because it is difficult to
achieve the exact amount of all recommended nutrients from the garden fertilizer blends available in the market, it is important to match the nitrogen requirement.
Example
A soil test recommendation for your vegetable garden calls for 2 lb of N/1000 sq. ft, 0 lb of P2O5 /1000 sq. ft and 1 lb of K2O. The garden is 40 ft by 10 ft.
Note: The weight of 2 cups of dry fertilizer is approximately 1 pound. Therefore to meet the garden fertilizer recommendation, you will need about 6 cups of the fertilizer blend (25-0-12) material for the 400 sq. ft. area.
Never apply fertilizers directly on the plant. Ideally, you should apply it about three to four inches from the plant to let the roots absorb the nutrients.
Garden soil needs plenty of organic matter. In addition to applying commercial fertilizer, it is recommended to apply manure, compost and organic sources of fertilizers that would add considerable amount of organic matter to the soil. Calculating the fertilizer rates using organic sources is often difficult. However, some types of organic fertilizer can be purchased in bags that are labeled with their fertilizer grade. Fertilizer rates for these sources can be calculated in the same manner as for inorganic fertilizers
Recommended application rate for various granular fertilizers to apply one pound of nitrogen.
|
Application rate |
||
Per 1000 square feet |
Per 10 square feet |
||
Source |
Pounds |
Cups |
Tablespoons |
10-10-10 |
10 |
20 |
4 |
8-8-8 |
12.5 |
25 |
5 |
12-4-8 |
8 |
16 |
3 |
16-4-8 |
6 |
12 |
2 |
20-10-10 |
5 |
10 |
2 |
12-6-6 |
8 |
16 |
3 |
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REVISED: March 7, 2016