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Deer Park, WI

Hi folks- Its that time of year when soil tests are completed and its time to amend the patch with this year's nutrients. In the last two weeks, i've reviewed more soil test reports than I can count. It is both exciting and humbling to help growers balance their soils in pursuit of maximized patch performance.

A reminder for those who are newer and/or less experienced at the soil test and pumpkin fertility game- I've published a 10 page booklet on soil test interpretation and fertilizer application suggestions. Many have reported that this guide helped them achieve personal best pumpkins in their patches. You can purchase the guide from the SCGA website for a measly $12. https://www.stcroixgrowers.org/collections/how-to-guides/products/giant-pumpkin-growers-guide-to-interpreting-soil-tests-managing-fertility

I will also include a personalized interp of your soil test if you purchase the guide, my way of saying thanks for making the investment.

4/13/2019 9:43:01 AM

Deer Park, WI

For those of you who already own it and are here to learn more, here's a few more insights-

Manganese is a tough nutrient to manage. 40ppm is the target value on a soil test. However, after poring over 100's of tests from all over North America, soils are generally very low in this nutrient (<5ppm is very common)

Conceivably, one could apply the full prescribed amount of manganese sulfate to reach the target value. however, applying more than 12ppm per year is not recommended. Too much too fast can lead to other problems and it is wise to spread out the application over a couple of seasons. 2 pounds of product per 1000sq ft gets you 12ppm per year.

Part of the reason I hammer on a slightly acidic pH target (6.2-6.5) is because of all the nutrients, manganese requires the most acidity to be plant available. Look at the chart on this link: https://andersonsplantnutrient.com/agriculture/market-feed/524

Find manganese and determine what pH range it is maximally available...slightly acidic.

So, because soils are so generally low in Mn, and because its such are hard nutrient to move, dialing in pH 6.2-6.5 means you've done what you can to maximize availability of this nutrient while also maintaining optimal availability of the other nutrients. Happy fertilizing!

4/13/2019 9:43:07 AM

Massachusetts

Thanks for sharing your knowledge with us (and I bought the guide). For my pre-amendment soil test this year I carefully mixed and split the sample in two. I sent half to Western Lab and the other to Spectrum Analytics. Very interested to see what each recommended for amendments but that's another post. I realize that different labs use different extraction methods and tests that make it often difficult to compare absolute results. On Manganese, one lab says 53 ppm and another says 9 ppm...same sample. So can you really say that 40 ppm is the target value for Manganese? Or do I assume that 40 ppm is the target value on a Western Lab soil test? I notice people using other labs this year since Western is now $55.

4/13/2019 11:38:21 AM

Deer Park, WI

Tom- lots to unpack on your post. Target values reported in my guide or anywhere else for that matter are lab-agnostic, unless otherwise specified by the author of the recommendations. Indeed, it is frustrating and confusing that two credible labs report very different levels.

Micronutrients are challenging to assess with great accuracy. Present in such small amounts and likely not evenly distributed in any given sample, the variances can be staggering. Had you not split the sample, the recommendations would be polar opposite. That's troubling. So what to do?

The only way to get to the truth is increasing test sample number over time. The more tests you have, the more data becomes reliable. In your circumstance, I'd consider averaging to two values. I'd also reference prior tests (if they were sampled in same patch) and account for any amendments. I'd also continue testing routinely in the future and use the sum-average of data over time to get a feel for what is true in your soil.

Lastly, I wouldn't hesitate to call the lab and ask to retest the parameter in question.

4/13/2019 12:45:11 PM

Massachusetts

Segal's law. "A man with a watch knows what time it is. A man with two watches is never sure."

4/13/2019 1:27:09 PM

Grittyville, WA

I think these tests have about a 90-95% accuracy rate. Pretty good, but two tests each testing for 10 nutrients... one result is likely to be off. This is how I see it now: fork out the money. Always be prepared to run three different labs spend a total of $150. Most are less than $55.

I think the easiest thing is just to accept this. Its probably worth it when you really think about it. Idk...

4/13/2019 5:20:36 PM

Bethlehem CT

Joze those are very interesting comments about pH . I have been keeping my soil at a slightly acidic pH now for several years. I started doing that because I was concerned about micronurtrient absorption, (like you mention) And if you look at the chart of nutrient availability. The low 6's seems to be a good compromise for good micronutrient availability, but not too acid.
Also I felt that it is quite unnatural in a climate with my sandy granite based soil to have a pH at 7. I don't want to add a bunch of expensive micros(metals) that get my soil in the proper range when I grow at 7 but become too high or toxic when the soil is allowed to revert to a more natural pH of 6-6.5.
The analogy that comes to my mind with this is a body builder that puts on tremendous size and mass while training as a young man and as that person ages and backs off on the training and special high calorie diet etc. his body returns to a more natural balance. ( i.e. less jacked) He may now have all kinds of extra skin and other health problems from losing all that mass. And if he tries to eat the same way he did when he was training it just isn't going to work. Maybe that makes sense to someone, you can take it or leave it.
Thank you for mentioning your thoughts on pH, it gives me some confidence that my thinking isn't that out of whack.

5/4/2019 8:10:40 AM

Bethlehem CT

Tom K That is so true. The more we know, the less we can be sure of things we thought we knew! LOL

5/4/2019 8:12:48 AM