Should I Soil Sample?

Sep 04, 2019

By Sarah Reiger

Producing a high yielding crop requires significant investment in the form of crop inputs. More often than not, investment in fertility will result in the highest ROI. As much as 30 – 50% of today’s crop production can come directly from nutrition. As yield targets continue to increase, the gap between native soil fertility and crop nutrient requirements will also increase. Each additional year of cropping depletes nutrients that are not replaced through fertilization. Think of your soil as a bank account; you cannot keep pulling out nutrients without putting a sufficient amount back in or eventually you are going to run into problems.

Soil sampling is a recommended practice that, simply put, helps you understand what is in your soil. This information can help in the production of higher yields and higher quality crops and leads to the most efficient and environmentally responsible use of fertilizer. Without an actual measure of your soil nutrient levels now and again, estimating crop removal rates could lead to some wrecks; wet, dry or ideal conditions impact removal or losses of nutrients differently, skewing those estimates. For example, this year was particularly dry. As a result, targeted yields may not have been reached and therefore you may be able to credit some of the nutrients applied this year to next year’s crop. Soil tests take out the guess work and let you know exactly what you’re working with.

Soil test results must be analyzed and interpreted, taking into account many elements such as targeted yield versus current nutrient levels, organic matter content, soil pH and cation exchange capacity (CEC). You always want to apply fertilizer based on a targeted yield. This starts with an evaluation of the macronutrients (N, P, K and S), but don’t forget to look at micronutrients as well. Next you want to look at your organic matter. This is a source of nutrients and can increase soil water and nutrient holding capacity. As a general rule in the G-Mac’s trade area, you can expect an additional 7 lbs of nitrogen released per percent organic matter annually, but this number can vary based on environmental conditions. The pH and CEC tells you a bit more about your soil. Soil pH indicates if your soil is more or less acidic. This is important information, as nutrients become more or less available to plants at different pH levels (Figure 1). For example, phosphorus becomes less available in soils with a pH of 8.5 than soils with a pH of 7.5. CEC tells you whether you have a light or sandy soil versus a heavy or clay soil. This is important in determining safe rates of seed-placed fertilizer; a clay soil can have more seed-placed fertilizer than a sandy soil.

Figure 1. Availability of nutrients at differing pH levels.

At the end of the day, a soil test that has been properly analyzed can help you make those important decisions when it comes to fertilization. If you are interested in soil sampling this season, talk to a G-Mac’s rep and they will get you signed up!

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