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Plant Nutrition

Contributed by: Chip East

I talk with many people each year who are having problems with their plants. Usually insects, disease, weeds, and nutrition top the list. I recommend understanding the crops you grow as well as the problems associated with those crops as this would aid in scouting.

The Extension office will be happy to talk with anyone about potential pest problems with particular crops. Insects, disease, and even weed pressure can vary from year to year depending on the environmental conditions. Keep in mind that a pest that was a major problem last year, may or may not be a problem this season. However, providing plants with proper nutrition is something the grower is also responsible for every year and should be thought about in advance of planting. Once a nutrition problem is visible, it takes time to correct the problem, and production could be greatly reduced.

What can a grower do to reduce the chance of having nutrition problems? Organic matter increases the soil nutrient holding capacity of the soil, so the more organic matter, the better. Planting cover crops is a good way to increase the soil’s organic matter, but it does take time and should be something you work at each year. When you have decided what crop or crops you are planning to grow, you will need to soil test. We know what plants need. What we do not know is what elements are in your soil. A soil test simply analyzes the soil. A soil test analysis from our lab at Auburn costs $7 and provides valuable information for the grower. Once we know what is in the soil, we will know how much of what element or elements to add. I recommend the growers who market produce have their soil tested for each field on a yearly basis. A soil test can be done at any time of year, but I had rather test before planting.

At planting time, we would add half the recommended nitrogen, all the phosphorus, and half the potassium. Then two to three weeks after planting, we would apply another fourth of the recommended nitrogen and potassium. Two to three weeks after the second application, I would add the other fourth of the recommended nitrogen and potassium.  Of course this is just one example, and different growers apply fertilizer in different ways. Some will apply the fertilizer in only two applications, others will use drip irrigation, and it is easy to inject fertilizer through the drip on a weekly basis. I will be glad to help anyone calculate the needed fertilizer to inject in the drip.

In addition to soil testing, an analysis can be preformed on leaf samples at our lab. A deficiency would show up in an analysis long before it is visible in the field. Many growers do this regularly on crops such as strawberries, pecan, field tomatoes, greenhouse tomatoes, and others. This test costs $16 and gives the farmer valuable information.

Some plants that appear to be nutrient deficient may not always have a problem related to nutrients. Insects, disease, and other stresses can cause plants to look off color. Strawberries can develop a bronzing color due to a spider mite infestation and adding additional nitrogen will not solve the problem.

It is common for calcium deficient tomatoes to develop blossom end rot. It is caused from a lack of calcium in the plant, but adding additional calcium may not solve the problem. I have seen many times where the grower has sufficient calcium in the soil, but the plant is showing signs of a calcium deficiency. Plant stresses from things such as improper irrigation can cause the plant not to take up the needed calcium. In this case, mulching and irrigating the plants can help with nutrient uptake. It is hard to write an article about plant nutrition without mentioning pH. More elements are available for plant uptake at a pH of around 6.0 to 6.5, and we do not know the pH without a soil test. Calcium happens to be one to the elements that is not available for the plant at a low pH.

If you can visibly see that you have a nutrition problem, it will take time to correct, so it is important to scout fields regularly for any plant problems. If you have problems, just contact your local Extension office, and we will be glad to help.