Whether it is a wildlife food plot, garden spot, lawn, pasture, hayfield or commercial row crop field, determining the fertility level of the soil through a soil test is the first step in planning a sound lime and fertilization program. Knowing exactly the nutrient level of the soil and how much supplemental lime and fertilizer is needed helps insure optimum crop growth and quality is achieved.
A soil test is no better than the sample submitted for analysis. The following steps can be followed to insure a representative and meaningful soil sample:
- Obtain soil sample bags from your local university ag extension office, garden supply store or farm supply dealer.
- Use a soil sampling tube, auger, spade, trowel or other tool to take a thin vertical slice of soil from the soil surface down to the desired depth. When sampling, soil should be dry enough to crumble easily in your hand. Avoid taking excessively wet samples.
- Take at least 15 to 20 cores or thin slices randomly over the field or area to be tested. Each core/slice should be taken at the recommended sampling depth. Fifteen acres should be the maximum size area represented by a single composite sample. Place the cores/slices in a clean plastic bucket or non-metal container and thoroughly mix the soil. Fill the soil sample bag to the "fill line" marked on the bag. Fold the top of the bag and fasten the metal flaps securely to avoid possible spillage during shipment.
Plowed fields - plow depth
No-till fields - 4 “es
Pastures - 4 - 6 “es
Orchards - 8 - 12 “es
Lawns - 4 “es
Gardens - 6 “es
When collecting samples, avoid taking cores/slices from small areas where the soil type and condition is obviously different than the rest of the field or area. Avoid cores from wet areas, burn pile sites, fence rows, eroded areas, etc. If a field contains more than one soil type, separate composite samples should be collected from each soil type area.
When to Sample
Soil samples can be taken anytime of the year, but fall is the most desirable time.This is when soil pH and nutrient levels are at or near their lowest points. Since nutrient levels change during the year, it is important to sample at or near the same time each year. Note: It may take 1 - 3 weeks or longer for the analysis to be completed and returned. Therefore, plan accordingly to insure sample results are returned prior to fertilizer application and planting time.
How Often to Sample
Soils should be sampled every year until a soil fertility record is established (usually 2-4 years). Once this is established, soil testing every two or three years is sufficient for most pasture, wildlife, food plot, garden and lawn situations. Annual sampling is recommended on areas where high value, high input cash crops are grown or where large amounts of nutrients are removed by whole plant harvests such as silage or hay production.
Soil test results should be recorded in such a manner for easy access. This will allow the user to observe increasing or decreasing fertility trends over an extended period of time.
Selecting Nutrient Analysis
For most applications, a soil test that determines pH, phosphorus, potassium,calcium and magnesium levels and provides a lime recommendation is sufficient.Many labs also provide manganese, zinc and cation exchange capacity in their routine tests. Some specialty crops may require certain micronutrient analysis.Your local university ag extension office, garden or farm supplier can offer valuable assistance in determining which soil nutrient analysis to have completed for your area and intended crop.
(Information for this article was adapted from University of Georgia Extension Leaflet 99 "Soil Testing" by C. Owen Plank, Extension Agronomist.)