By Brian Hefty
See if you agree with this statement: If I am going to spend millions of dollars on something in my farm business, I should know a lot about it. That makes a lot of sense, doesn’t it? Over the next 10 years, how many dollars will you invest in fertilizer? How much do you really know about fertilizer and just as importantly, can you read a soil test?
Your response may be, “I just ask my fertilizer guy” or “I have a crop consultant who tells me what fertilizer I should apply.” Look, I understand you may rely on people today for advice, and I would expect that to continue, but I come back to the fact that you will probably invest millions of dollars during your farming career in fertilizer. Don’t you think that if you knew a little more about fertilizer and your soils you would gain more yield or perhaps even save money, or if nothing else at least know what questions to ask of the person who makes your fertility recommendations?
During our Ag PhD Winter Workshops, we will discuss soils, fertility, and a host of other great and pertinent topics for your farm. At some of our workshops, we will spend some time talking through soil tests, where in 1 hour, we can teach you pretty much everything you need to know about reading a soil test. Here are 3 key points about soil tests that most people don’t look at closely enough (if they even get these things on their soil tests), but if you want us to help you raise better crops, YOU HAVE TO GET THESE 3 TESTS DONE ON YOUR SOILS THIS FALL!
- Soil pH – This should always be the first thing you look at on a soil test. 6.8 is ideal for most crops. If you have low pH (below 6.3), add lime. If you have high pH, odds are high that drainage is your issue, so add tile and consider adding elemental sulfur.
- Base saturation – This is the ratio of 5 nutrients to each other: potassium, magnesium, calcium, hydrogen, and sodium. The readings are given in percentages. If someone tells you base saturation isn’t important, don’t listen. Here’s an example of why. With potassium, you may have what’s considered a high level of parts per million, but if you also have extremely high levels of magnesium, calcium, and hydrogen, there may not be enough potassium getting into the plant, and we can prove that with plant tissue analysis. The key is to understand base saturation and use it along with other information on the soil test. If your base saturation test doesn’t add up to 100%, switch soil labs. The ideal ranges you are looking for are:
- Potassium – 4% to 8%
- Magnesium – 12% to 25%
- Calcium – 65% to 80%
- Hydrogen – less than 10%
- Sodium – less than 1%
- Cation Exchange Capacity (CEC) – This measures the holding capacity of your soil. The higher the number, the more water, nutrients, and pesticides your soil can hold. Here’s a simple thing we use CEC for: nitrogen capacity. Simply multiply 10 times your CEC. That will tell you roughly how much nitrogen your soil can hold at any one time. Let’s say your CEC is 15. That means your soil can hold about 150 pounds of N. However, you want to apply 200 pounds of N in order to get top yields. Should you do it all at once? No way! You will need to split-apply your nitrogen. You should also consider controlled-release nitrogen and/or a nitrogen stabilizer to prevent nitrogen loss when you are bumping up against your soil’s threshold.
Please get these 3 tests done on your soils. In our opinion, they are just as important as finding out your parts per million on N, P, and K. With commodity prices where they are and the opportunity for high farm income next year, a small investment in good soil tests should really pay off.