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Soil Test Science - Part 1
The importance of testing your soil before planting food plots has been stressed in many previous articles in Quality Whitetails. The process is quick, inexpensive, and makes a world of difference in the quality and productivity of your plots.
Most serious food plot planters test their soil before planting. However, once they receive the soil analysis back from the lab, many are left scratching their heads trying to make sense of the report and calculate appropriate lime and fertilizer requirements. This article will detail how
to read a soil sample and implement the recommendations in the field.
Before outlining how to interpret a soil analysis, some background information is needed. Plants can be thought of as nutrient transfer agents to get nutrients from the soil into the deer. The condition and quality of the soil affects how well plants can transfer nutrients. Managing soil fertility impacts how well plants grow, and how nutritious they are.
In brief, collect six or more samples from each plot to be planted and mix these in a plastic or glass container. Then collect a single subsample from this mixture. The samples should be collected diagonally across the plot to ensure all soil variability is accounted for. Records should be kept for reference when collecting future samples from the same plot.
Sampling depth is one of the most important aspects of soil testing. Soil levels can vary greatly between three and six inches deep. A core sampler which collects 4-inch samples is the most commonly-used sampling tool, although a shovel or hand spade can do the job. After each food plot has been representatively sampled, the sample should be labeled with location and type(s) of seed or seed mix to be planted. The samples are usually sent to a Cooperative Extension Service, university, or private agronomic laboratory for analysis. Some fertilizer companies offer free analysis to their customers, while most other labs charge a nominal fee of $5 to $12 per sample.
It is important to remember that different plants have different nutrient needs. This is especially important when planting mixes containing both broadleaf plants like clover, and grasses like wheat. With a little experience or professional advice, you will soon learn which plants have the highest lime and fertilizer requirements.
Soil tests are performed on subsamples to estimate soil acidity (pH) and the amount of available nutrients in soil. The results are then summarized and printed. The difference between the available nutrients and the amount needed by the plants for optimum production is then recommended. Lime and fertilizer amendments are generally grouped for food plots with similar soil test results.
SOME SIMPLE SOIL FERTILITY CONCEPTS
Some soils can retain and transfer nutrients better than others. Lime and fertilizer applications are the most efficient in the best soils, so selecting high quality sites for food plots is important. Two important soil
fertility characteristics are 1) how much total nutrition the soil can hold and, 2) how much of that nutrition is actually available. Soil nutrients may be lost or made unavailable through leaching, plant uptake, browsing (physical removal), volatilization, denitrification (loss of nitrogen), acidification, microbial uptake, and erosion.
Soil scientists use the term "cation exchange capacity" to explain how much transferable nutrition soils can sustain. Organic matter and soil texture are two important determinants of cation exchange capacity. Decomposed organic material in the soil increases the soilıs ability to hold water and nutrients. Though it may be beneficial in the long run, putting large amounts of fresh organic matter (e.g., manure) on the soil can decrease the available nutrients, especially nitrogen, in the short term as microbe populations break down the complex carbon molecules. This short-term utilization of available nutrients by decomposer organisms is why organic gardeners compost material before adding it to the soil.
Soil texture (size of particles) is important because it determines the surface area available to hold soil water through surface tension. Size also controls the sites that available nutrient ions can be held onto the soil. Clays are the finest textured particles, sands are the largest, and silts are intermediate. To help envision the impact of particle size, think about sand as double 00 buckshot (9 pellets in a standard 12 gauge shell) and clay as number 8 shot with 238 pellets in a comparable load. A cubic foot of sandy soil can have a surface area of 0.9 acre, while soils with more silt and clay can have three acres or more of surface area in a cubic foot. In brief, the greater the surface area of the soil, the more nutrients and water it can hold.
While a soil such as clay may contain a large amount of nutrients, if the nutrients are not available for plant uptake, neither plants nor wildlife benefit. For nutrients to be available, there needs to be 1) adequate soil moisture, 2) good soil tilth (fluffy but firm), 3) a soil
microbe population in balance with organic matter, 4 )suitable pore space and aeration, and most importantly, 5) a proper pH for the crop being grown.
Please continue at Soil Test Science - Part 2
By: Robert N. Smith
Hits: 946
Posted : 02/12/2006
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