Fertilizing Chestnut Trees

This section should be titled "Soil Management" instead of fertilizing because fertilizing emphasizes adding chemicals to the soil. Fertilizing should really be "Soil Amending". Exact terminology is not as important as having a good healthy soil. When the soil does not have the right amounts of plant nutrients available the plant suffers. Soil amendments are any materials applied to the soil to improve plant health and growth. The amendments used in modern farming can be broken down into 3 basic groups, soil structure modifiers, fertilizers, and inoculants. For chestnut orchards all three groups play an important role in nut production.

Let us start this section right by offering a little advice; no soil is in the perfect condition to produce chestnuts. Even if you are able to get the right everything, soils are to complex to say for certain the soil is at its best for chestnuts. Because of these complexities the best the experts can do is provide ball park guidance. When applying fertilizer always apply it to the soil surface, never cultivate the soil in and around chestnut trees. Cultivating near chestnut trees can cut roots allowing soil borne pathogens access to the tree.s internal plumbing.

Of all the parameters associated with soil nutrient levels chestnuts are most sensitive to soil pH, phosphorus and nitrogen. Soil pH for chestnuts is recommended to be between 5.0 and 6.0. Most crops like the soil pH to be around 6.5. The soil pH of 5.0 . 6.0 is slightly acid. With a lower pH the soil nutrients are not as available as compared to the normal pH of 6.5 for other crops. The lower availability of nutrients means the levels of nutrients chestnuts are dependent upon need to be at higher than normal levels. The levels for soil nutrients for chestnuts have not been determined by any experts. Because chestnuts are such a small part of all the crops grown in North America we do not expect any specific recommendations from the experts.

Of the nutrients chestnuts are dependent upon nitrogen (N) has some basic guidance from the experts. For a mature orchards, where the canopy covers the entire growing area, 125 lbs of actual N. For orchards with younger trees the recommended N is 0.2 lbs for each inch of caliper measured at the base of the tree. Nitrogen should be applied twice a year. The first time is once the leafs have budded out the the new growth is extending out. In northern states this is in April. The second application should be no later than the first week in July. Applying later than this date will cause the trees to delay going dormant. A hard freeze in late November or in early December could damage the trees including the death of the tree.

Appling fertilizer in the early years (1 - 7 years) is done with hand application. When hand applying fertilizer always place the fertilizer starting at the branch drip line out 12 - 18 inches. Root systems of trees often extend beyond the drip line (outer most point of the branches). By applying the fertilizer starting at the drip line helps place some of the fertilizer near the root zone. The chestnut trees need to extend their roots out to help anchor the tree. Extended roots help the tree from being uprooted in wind storms. Chestnut trees grow anywhere from 18 to 72 inches a year on any of the branches if good growing conditions exist. Distributing the fertilizer past the drip line encourages the trees roots to extend out beyond the drip line.

Applying fertilizer to orchards where the canopy is fully covering the entire area is done using the broadcasting method. This distributes the fertilizer evenly throughout the orchard. If the spreading equipment was left idle it may have left a small pile of fertilizer standing. Always remove these piles and redistribute the fertilizer. Excessively high concentrations of fertilizers damage the soil ecosystem, so always be careful of how much fertilizer is applied.

There is a lot of discussion of when to apply fertilizer. The easy part is to never apply fertilizer when the trees are dormant (there are some exceptions). Some components of the fertilizer will go away before the trees are ready to use them. It is best to time the application of fertilizer with the activity stage of the chestnut trees. Split the fertilizer evenly between the applications (if your are going to use 100 lbs of fertilizer for the year and you will use 2 applications then use 50 lbs per application) The first application of fertilizer should be applied just after the first leaves appear. The second application should be done about 1 month after the chestnut trees are done blossoming. Some orchardist use a third application after the nuts fall to give the trees a little something for the winter. This practice is no longer recommended.

So far this section has focused on fertilizers. Fertilizers are only part of the big picture of soil health management. The other two are soil structure modifiers and inoculants. Both of these aspects of soil health have to be given equal attention. If you do your own research into these you will find soil structure modifiers has had numerous studies resulting in demonstrating the benefits of improving soil structure. The soil inoculants are a different story. There are few research studies where the focus was soil inoculants. Soil inoculants and other soil organisms provide an important roll in breaking down soil particles into basic elements the plants can use for their nutritional needs.

A study performed in India by the Nation Bureau of Soil Survey and Land Use Planning on soil structure modifiers made this summary statement:

"Presence of gypsum and Ca-zeolites, on the other hand, prevented the rise of pH, decrease in Ca/Mg ratio of exchange sites and improved the hydraulic properties amidst an exchangeable sodium percentage..."
Geoderma, Volume 136, Issues 1-2, 1 December 2006, Pages 210-22

This is real fancy talk just trying to say, "Improving soil structure was able to help make more nutrients available to the plants". There are two conditions that help make soil nutrients available to plants. The most important is the amount of water in the soil. Water in the soil can be one of those things where too much or too little is not a good thing. Too much water in the soil causes the soil nutrients to be washed out below the plants root zone. Too little water and the soil dies with most everything in it. Good soil structure helps the water be in the right place at the right time. Water being in the right place means it can transport the soil nutrients released from the soil particles and organisms to the plant root system. This makes for healthier plants. Soil structure improvements are mostly based on adding calcium (Ca) to the soil. It takes 1500 lbs of applied gypsum to the acre to cause an overdose of Ca. Typical applications are between 200 and 600 lbs to the acre (for more details see the article Application of Ca in a Chestnut Orchard).

Soil inoculants have been applied to farm soils for many centuries. Long ago farmers would take a little soil from an existing farm or vineyard and place it around the plants in the new farm/vineyard. This was thought as a good luck kind of thing to do. What was actually happening was the soil in the existing farm had soil organisms already present that enhanced the soil health were being brought into the new farm. This practice is no longer used on modern farms. Now farmers apply the inoculants at planting time with the seeds. For plants propagated by other mean the inoculants are added to water and applied to the soil in the starting beds. For chestnuts the soil inoculants of importance is mycorrhizal. Mycorrhizal is a soil based fungi that forms a beneficial relationship between specialized soil fungi and the tree root system. It does the exact same thing that good soil structure does, that is improve the soil efficiency of transporting soil nutrients to the plant root system.

As the health of the soil improves the less fertilizer needed to compensate for the inefficiencies of poor soil structure and the lack of inoculants. Chestnut trees will always need fertilizer if the nuts are removed from the orchard.