Flint on Crops: Lime Is Fertilizer Too – Commentary

    Spreading lime. Photo: John Deere

    As I have worked with growers through the years one of the ideas that has kept coming up is how to choose between applications of lime or “fertilizer”. There seems to be a great misunderstanding about the importance of these two kinds of soil amendments but this question should not be a big problem since both are essential to supplying nutrients to the crops we grow.

    Our predecessors in the field of agronomy have done a good job of stressing the importance of testing the soil to determine the amounts of plant nutrient elements that should be applied to support the growth of crops.

    We have all been taught the importance of being certain that the soil contains sufficient amounts of nitrogen, phosphorus, and potassium which are referred to as the “macro” nutrients.

    In recent years there has been increased awareness of a “secondary” set of elements which includes sulfur, zinc, and boron. Sulfur is essential for the formation of proteins since amino acids contain this element. Sulfur is essential for the best utilization of nitrogen while zinc is needed in many cases for corn as is boron for cotton.

    Application of these elements has become almost standard as a means to lessen the chance that yields might be reduced by inadequate amounts of these elements. Most recently we are learning about the importance of Silicon for plants in their ability to tolerate environmental challenges.

    Most of the elements I have mentioned are usually supplied in fertilizers that are applied according to soil test recommendations.

    Zinc, and boron may be applied to the leaves as foliar sprays since this may be the most direct and efficient way to make sure they are absorbed by plants rather than being bound in unavailable forms following soil application.

    In this region poultry litter is an important part of many soil fertility programs but it must be used carefully so as to avoid oversupplying some elements especially phosphorus.

    We have also been taught that soil pH should be kept within fairly well defined boundaries with the low end at something like 5.9 and the high end around 6.8. There are fringe areas that go as low as 5.5 or as high as 7.1 but we like to keep the soil slightly acid which ideally might be around 6.2 for most crops although there are a few grasses and horticultural crops that are exceptions.

    This is my opinion so hold me accountable if you disagree.

    Lime is normally thought of as a material to manage soil pH and this is absolutely true. However, lime has another role in actually supplying another essential element which is Calcium. Some kinds of lime also supply Magnesium which is also a vital element for plants.

    Both Calcium and Magnesium are needed for formation of cell walls and for the production of that all-important substance called chlorophyll which converts sunlight into matter that is then used to build the plant and form the seeds, fruit, and fiber we require for our own existence.

    This is especially important for cotton since the fiber we grow it for is little more than cell wall.

    There are issues with “balance” of elements which have been discussed and debated through the years, particularly the ratios of Calcium to Magnesium, Magnesium to Potassium, Phosphorus to Potassium, and others. There is not enough space here to get into all that but if you want to talk we can do that later. I will be on leave for a while so save a spot for me.

    Thanks for your time.

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