Understanding Soil Tests: If a Pound of Nitrogen Falls to the Ground and It Isn’t Utilized, Did It Really Get Applied?

Okay, so maybe my title this morning is a bit Zen for a Tuesday. But it does bring up a very valid question. We head out each year and apply pound after pound of fertilizer, but is it doing us any good?  The answer lies in your soil test. So we are going to begina  three part series on attaining and understanding soil tests. Let’s begin.

Combine one-hundred pounds of N, thirty-five pounds of P, and 62 pounds of K. Mix thoroughly. Add a pinch of manganese, a dash of copper, zinc, and boron. Once items are combined, spread liberally over one acre of soil. It sounds like a gourmet concoction, something to rival Martha Stewart. It is for lawn and garden enthusiasts, the Holy Grail; a one-size fits all formula for row crops nationwide. It, also like the Holy Grail, probably does not exist. We would even settle for a formula, by region, if someone would just create one. Even if you tried to create such a formula, it would likely only serve as a recipe for disaster.

However, most gardeners tend to operate as if just such a recipe does exist. At the local garden center or at a table at the local breakfast nook or wherever gardeners gather, you can overhear conversations about what is working on one particular lawn or another. The following morning you can track the participants to the local big-box-store door as they try to order the same formulation, assuming it will work on their lawn or garden as it did on the county leader’s property.

The main problem with this theory is that land is a living organism, and far from being the static expanse we sometimes assume, there is a vibrant and delicately balanced network of nutrients, chemicals, and organisms that extends from the top soil through to the bedrock. Because of the way they are interlaced, you cannot change one without impacting another. The end result is soil from one side of your field to the other may be as vastly different as soil from Montana is from Alabama.

We recognize the differences between states and maybe even within regions but we tend to treat similar plants under our care as if they all need the same ingredients. This, according the Paul Leeds, a soil specialist and farmer from Ontario, Canada just is not the case. The way the land has been used historically, the strata within the soil profile, topography, weather, and cultivation practices all work to determine what surpluses and shortages are contained within each section of land.

Leeds recommends that all farmers begin to know their soils by conducting a soil sample, then sending the sample to a reputable lab for analysis. Dr. Tony Provin with Texas A&M extension provides the following guidelines:

  • 1)      In fields up to 40 acres, collect at least 10 to 15 cores or slices of soil, from evenly distributed locations across the region being sampled, per composite sample. Because soils are variable, it is important to obtain enough sub-samples to ensure a representative composite sample. The greater the number of cores in your sample the more representative or reliable the results will be of your total landscape.
  • 2)      Unusual problem areas should be omitted or sampled separately. To properly diagnose the causes of poor crop production, collect separate composite samples from the good and poor growth areas. Do not include soil from the row where a fertilizer band has been applied.

  • 3)      Traditionally, soil samples are collected to a depth of 6 inches from the soil surface (after non-decomposed plant materials are pushed aside). Surface accumulation (stratification) of phosphorus and lime (calcium) from prior surface applications can dramatically alter soil test data. Stratification is of particular concern in parts of the landscape that are not generally tilled or disturbed (such as lawns) or in areas that receive limited rainfall or supplemental water. In these instances, sampling depths need to increase from 3 to 9 inches.

Once samples have been gathered, combine them in a large, clean tub and stir until all samples are thoroughly combined. Fill the sample bag or other suitable container with approximately 1-2 pints of a composite soil sample. Any suitable container can be used for the sample, but it is important to complete the information sheet and follow the instructions for collecting and mailing samples.

Once an adequate sample has been gathered, then you need to select a lab to analyze your soils, and to provide you with comprehensive results. Leeds advises that when you are selecting a lab you consider the following:

  •  History and Reputation
  •  Variety of Tests Available
  •  Reports are Clear, Concise, Easy to Interpret
  •  Lab has Staff Qualified to Make Recommendations Based on Report
  • Familiarity with Your Particular Type Of Soil

 Most Land Grant Universities offer testing services and you can obtain additional information through your local county extension office. Additionally, there are many national and regional private labs that will survey your soils, even some fertilizer and nutrient companies have working relationships with particular laboratories if you consult with your company representative. (Expect to spend at least $15 per sample) All soil tests and all reports are not created equally, in our next installment we will analyze the different types of tests and reports commonly available.

 The goal is to bring your soils in balance so that they have the proper nutrition to maximize your production and quality while lowering your input costs. Calcium is great, but without enough manganese to metabolize it, any calcium you amend may be wasted. Similar statements can be made about any fertility product, macro- or micro-nutrient which you may add. Worse than not adding any amendments to your field is to add them, at times at considerable expense, only to find out later that they were unnecessary or under-utilized by the plants. The important thing is to realize that all soils are different, state-to-state, yard-to-yard, even year-to-year within the same lawn and without an accurate snapshot of your field’s condition you cannot make the best decisions about your Lawn or Garden.

It is possible to return, or increase, fertility to your landscape. But before you can improve the environment in which your plants will be grown, you must first know where you are beginning. Once you are armed with the knowledge of your fertility needs you can make the best, and most economical, decisions to promote healthier, stronger, and more productive vegetation.

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