By Brad Turner
Cover cropping and composting in Florida citrus production are not new concepts. Our ancestors understood the basic principles and implemented these practices just a couple of generations ago.
YESTERDAY AND TODAY
As a boy, I can remember an old citrus grower telling me how beggarweed and crotalaria, both native nitrogen-fixing legumes, growing wild in neighboring fields would be mowed and baled. This hay and seed combination would then be broadcast across the groves and chopped into the soil. He told me this was done for seed cultivation and additional “tree food.”
Other legume species propagated in groves since the early 1900s included Japanese clover (lespedeza), cow pea, velvet bean, vetch and lupine. Early growers also increased diversity by utilizing buckwheat, rye, oats and rape.
Combining today’s science and technology with an understanding of the effect biology has on nutrition, we can look to cultural practices from the past with a clearer understanding of what our ancestors were doing right and where we can improve. These cover crops were providing more than the future formation of humus.
- Buckwheat makes phosphorous and zinc more available.
- Rye and oats are excellent for extracting silicon from the soil and making it more available to trees.
- Rape captures highly leachable sulfate and then releases it in a more stable form.
While there are a multitude of additional cover crop species that perform these tasks and more, cover crops are not extracting elements directly from the soil. Their roots secrete organic acids and carbohydrates to feed specific biology, enabling microorganisms to convert needed elements into plant-available forms. H. Harold Hume, former University of Florida dean of agriculture, said in his 1911 edition of “Citrus Fruits and Their Culture,” “Clean culture cannot produce good results indefinitely, and the sooner cover crops are given attention the better for the future of the citrus industry.”
Historically, composting was essentially mulching. We are reminded in Hume’s “Cultivation of Citrus Fruits” published in 1954 that citrus growers not utilizing cover crops would “cover the ground with a liberal coating of leaves, leaf mold from adjoining woods, straw, hay, grass or similar humus providing material.” Benefits of this included shielding soil from excessive heat and evaporation while adding plant-available nutrients and organic material.
Today, a quality, fully matured composted product has the additional benefit of adding a diverse array of soil microorganisms. These microbes will release additional locked up or unavailable nutrients from the soil. The high volume of carbon will provide these nutrient cyclers with a food source and habitat.
“Clean cultivation and no attention to the vegetable (vegetative) matter of the soil in the citrus grove inevitably leads to disastrous results,” stated Hume in “The Cultivation of Citrus Fruits.”
COVER CROPS AND INSECTS
In my lifetime, citrus cultivation, just as the rest of modern agriculture, has moved to a more monoculture/reduction approach. Growers need to make use of natural enemies. For every pest insect, there are at least 1,700 insects that are either neutral, beneficial or necessary.
When a grower has a pest problem, something is out of balance. From a beneficial insect perspective, growers can receive immediate results from establishing diverse cover crop plantings. Insecticides, fungicides and herbicides will be necessary at times. Some are harder than others on the soil and foliar populations of beneficial microorganisms and insects. All “cides” will be reduced over time.
Keep in mind that it is a complex system. When you intervene, you disrupt the system. Anything you do as an external intervention should only be short term as a temporary fix while you get the natural system back in balance.
UNLOCKING SOIL ELEMENTS
Given the current fertilizer situation, it is now time to take advantage of the “free gift” of atmospheric nitrogen and the abundant supply of locked up phosphorus in Florida soils. This requires a highly functioning biological system.
There are numerous research and white papers proving the importance of elements in the soil previously not thought of as essential for plants to grow and reproduce. Many of these elements are only needed by plants in trace amounts and are often in sufficient quantities in the soil. Some of these elements include silicon, cobalt, nickel, tin, selenium, iodine and a multitude of others. The issue is that it takes diverse soil biology to process these trace elements into plant-available forms.
Many of these elements are necessary catalysts and cofactors for plants and microbes that enable the production of necessary enzymes. Silicon is actually mentioned as an essential element in early citrus culture texts such as H.J. Wheeler’s 1923 “Citrus Culture in Florida.” Some research today suggests silicon plays an important role in regulating the movement of other elements within the xylem and phloem of plants. It is also well documented that sufficient levels of this nutrient in a plant aid in protection from pests and pathogens.
Agriculture as a whole has been utilizing rescue chemistry for decades rather than focusing on root causes. The Florida citrus industry is now at a tipping point, and it is time for “biological resuscitation.”
When citrus trees are weak and stressed, they cannot afford to sacrifice any of their root exudates (organic acids and carbohydrates) to feed the soil biology that is needed to convert the surrounding minerals into plant-available form. Microbes eat first; they must satisfy their own needs before helping any crop. With extremely low organic matter in most citrus-growing Florida soils, this biological workforce needs a constant food source.
In the short run, applications of diverse microbial inoculants and biostimulants to the soil and the trees are needed to jumpstart this process of restoring grove health. Historically, cover crops and compost aided in this dynamic process in citrus production. With today’s research, there is a better understanding of why these tools should be reintegrated into citrus culture to promote grove health and profitability.
As a 40-year conventional citrus grower and caretaker devoting the past five years to better understanding these principles and processes, I believe the health of any grove can be brought back to that of the early 1900s with a much-needed paradigm shift. This involves diverse cover crop cultivation, balanced fertilizer supplementation and biological resuscitation to accomplish.
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