Pollen vitality

** The following page is very much a work in progress.
The following page will be better organized as more data and information are compiled and made available. **

A brief discussion about fertilization from TACF's Staff Pathologist, Fred Hebard

Getting annual soil tests and implementing their recommendations can avoid many problems.

TACF's network of growers and Regional Coordinators can help you go over your soil fertility report. Be sure to contact them before starting an orchard, particularly one of a large amount of material. Many Chapters have extensive experience with local soil testing laboratories, and the Regional Coordinators can help you track those down.

Usually, if you say you're growing azaleas or blueberries, you can get a commercial-type recommendation back with your fertility
report. If you tell them you're growing chestnut trees, the recommendation usually will be useless. Recommendations usually take the form of pounds of material per unit area, usually either per 1000 square feet or per acre. It's pretty easy to convert between the two remembering that there are 43560 square feet per acre. Your local agricultural extension agent probably could help you calibrate your fertilizer spreader to deliver the appropriate pounds of material per unit area.

For growers with less than an acre, one of the spreaders that hangs over the shoulder and is operated with a hand crank might be best, as they go easily over uneven ground, being carried. The push spreaders tend to get stuck, etc, when being pushed or pulled, and the handles break; they're OK for lawns but not fields. For smaller areas, a coffee can dipped in the fertilizer also works. It helps to wear gloves when handling fertilizer, which can burn the skin.

Granular fertilizer also can burn the foliage if it gets on wet leaves. It's important to not apply it while the foliage is wet, especially on small trees. Often, a formulation such as 30-10-10 or 20-6-6 is appropriate, especially on sweeter soils (higher pH, 6-6.5). We typically put down 200 lbs per acre of N and 60 lbs of P & K. At 20-6-6, this would be 1000 pounds of material per acre (200 divided by 0.2). At 30-10-10, it would be 667 pounds of material (200 divided by 0.3). I divided by 0.3 because that's equal to 30 percent. The numbers in the 30-10-10 refer to the percent of the weight of material that is Nitrogen, then Phosphorous, then Potassium.

Assuming 1000 lb per acre, a one-inch dbh tree might have a drip area of 50 square feet. So you might want to put down around 1 lb of fertilizer in that area. A pint of fertilizer would weigh about one pound, so a coffee can would be an appropriate amount. Using the shoulder-carried spreader, for a row of 1-in dbh chestnuts 100 feet long, assume the spreader is putting out a band 5 feet wide. That's 500 square feet. So 1000 lb/acre multiplied by 500 sq ft divided by 43560 sq ft/acre gives 12 pounds per 500 sq ft down the 100 foot row. You calibrate the spreader by adjusting it to deliver that amount of material while walking at a steady pace down the row. Our soils are not highly deficient in phosphorous, so 60 lbs per acre usually brings them up to snuff. You might need more; the soil sample should give a clear indication. Also, on soils with a lower pH, chestnut usually does not need such heavy doses of nitrogen; 10-10-10 might be more appropriate.

Some can get bagged urea and 10-10-10. I'm sure there are farm/fertilizer stores in most rural counties where urea, 10-10-10, ammonium nitrate, etc, can be bought in bags for $5-10 per bag. In suburban and urban areas, one tends to get organic formulations, such as bone meal, etc. If you buy a fair amount of fertilizer from a store, they usually will run soil samples for free. I hardly want to put myself up as a fertilizer expert; I'm just another farmer when it comes to soil nutrition. I think there can be a lot of hand waving about the relative merits of ammonium nitrate, ammonium sulfate, calcium nitrate and urea. I shy away from calcium nitrate for chestnut. Usually, we use ammonium nitrate, sometimes urea. In general, the two ammonium salts will acidify soil, with the ammonium sulfate acidifying more strongly than ammonium nitrate. Urea will sweeten (make it less acidic) a soil, as will calcium nitrate or, alternatively, lime. Changes in pH can have strong effects on the availability of mineral nutrients, some of which, such as manganese, can be toxic to plants in high concentrations.

This is just a brief look at the nutritional requirements for chestnuts. For a more in depth look for your orchard or tree establishment, be sure to contact your local Chapter, growers, and Regional Coordinators.

The effect of Boron and Calcium on Pollen Vitality

There has been some discussion about how to increase seed set in an orchard situation. Harvey Correia of Correia Chestnut Farm in central California tested the effect of boron and calcium on the vitality of pollen from selected trees on his farm. The results follow.

The almond industry is quite large in California and almonds are a big part of this lab’s business.  Still, I don’t know how practical this information is, though it did seem to provide useful information in my case.  I’d be very interested into the thoughts of some of you who work in the research/science fields.  I loved soil science courses in college but never had any courses that covered anything like this.

Thanks,Harvey Correia
Correia Chestnut Farm  

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Click here for a copy of the Excel spreadsheet documenting the pollen vitality samples and their responses to increases in boron and calcium (right-click to download, XLS file, ~200KB)

We completed analysis of the samples you sent us. I've attached results for your examination. My interpretation of results are as follows:

 1.    Pollen vitality increased in 17 of 19 samples when calcium was added to test media (avg. = 19%). This means the mother plants which produced the pollen were deficient. The orchard should receive a boost of calcium. Nut development is occurring now and their growth would improve as a result.

>Nine samples increased less than 10%, which is pretty close to optimum and I   define them as "slightly deficient."
>Vitality decreased in 2 samples, but less than 10%, which is also close to optimum.
> Eight were "moderately deficient" (+10-80%) 
>One was "very deficient" (+98%)
> None were "severely deficient." (+>100%)

2.    Pollen vitality increased in 16 of 19 samples when boron was added to test media (avg. = 13%). This means the mother plants which produced the pollen were deficient. Again, nut growth would benefit following a light application of boron to the orchard.

> Seven samples increased less than 10%, which is close to optimum.
> One sample decreased when boron was added to the medium, but less than 10%, which is also close to optimum.
> Two samples decreased -19% and -27%, which is moderately excessive.
> Nine samples increased from 10 to 80%, which is moderately deficient.
> None were very deficient or severely deficient.

Attached are graphs which allow you to compare differences between samples. Error bars on the Pollen Quality graph (first graph) allow you to determine when significant differences between samples occur. When they overlap, no statistical difference exists (95% confidence level). Vitality is a relative measure of pollen quality.

There are three graphs which are included which are standard curves which relate to viable pollens per gram and relative vitality: ignore them. Sample graphs and related tables are somewhat self explaining. Sample number 7 was dead for unknown reasons.

Tom Ferrari