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On top of Brush Mountain, Pa.

I have been looking into what growers think we should be doing regarding phosphorus and sulfur levels in our soil. It seems that many believe that after you have calculated you calcium, magnesium, potassium and sodium levels based on your your cation exchange content that you should try to get your phosphorus to equal your potassium level in pounds per acre and your sulfur level to be 1/2 of your potassium level in pounds per acre. That means that if you potassium target level was 200 pounds per acre, your phosphorus target should be 200 pounds per acre and your sulfur target 100 pounds per acre. I am wondering what the growers here think and if they disagree, why? I have asked similar questions before but the answers did not really satisfy me. Joe, I have read your booklet and loved it. Maybe you can clarify your targets and and state again how you arrived at them.

3/7/2020 2:33:34 PM

On top of Brush Mountain, Pa.

Here is the thread from the last time I brought this up. Has anyone changed their thoughts? Joe has his thoughts on the matter clearly expressed in his posts. If interested review that thread. I grow tomatoes now and am wondering how all of this applies to them since most here are geared toward pumpkins.

3/7/2020 2:41:52 PM

On top of Brush Mountain, Pa.

http://www.bigpumpkins.com/msgboard/ViewThread.asp?b=20&p=660046

oops

3/7/2020 2:42:10 PM

Colorado

I'm curious about this. Just saw a soil test with crazy high sulfur and crazy growth on the fruit. Wondering if sulfur/available phos. were a factor.

3/7/2020 4:11:57 PM

Deer Park, WI

Always eager to re-engage in discussions like these, Marv. My position on both of these nutrients remains unchanged from last winter’s dialog. I’d like to have a look at the sources for the P:K ratios. I’ve yet to encounter any info that suggests there’s a meaningful relationship here. A point to consider....the ability of a soil to hold K is dependent upon its CEC. Therefore, optimal K values will float with CEC. If there is indeed an optimal P:K ratio, then P must also float with CEC. This doesn’t jive with what I’ve learned about soil nutrients...CEC is not a primary factor in P holding capacity, as Soil P is held in organic and anion forms. In sum, this implies a P:K ratio may not make sense. I’m open to learning new facts if they exist tho!

3/7/2020 6:04:52 PM

Deer Park, WI

Regarding sulfur and ratios...as stated previously, soil testing for sulfur is of little to no value and therefore no ratios for optimal sulfur values relative to any other nutrient have any meaning. If ratios for sulfur are to have meaning, then it must be from a plant need/fertilizer application standpoint. Because sulfur dynamics in the soil are so similar to nitrogen, a fertility ratio has been established and relatively well accepted by agronomists in the corn production world. See last years post for details.

3/7/2020 6:11:44 PM

Deer Park, WI

As far as sources and methodology go for drawing the conclusions I have here and in previous posts, a google search can provide multiple sources of university data that provide nutrient composition of pumpkins, from which simple math allows extrapolation to crop need. These calcs are then further substantiated by additional sources regarding soil fertility. If one is interested in diving deeper into the nuance of crop/soil fertility, I recommend Neil Kinsey’s “hands on agronomy”. Fair warning...it’s pretty heavy on biochemistry of soil nutrients...written more at the collegiate level than 3rd grade...

3/7/2020 6:20:58 PM

Deer Park, WI

Marv, I can sympathize with your desire to find and optimize for meaningful nutrient ratios. Tomato growers are less concerned with absolute nutrient levels because “crop removal” is of little relevance. The amount of biomass per unit area for a tomato is magnitudes of order less than a giant pumpkin. As such, fine tuning the nutrient ratio dials becomes the biggest bang for the buck. Tuning dials is important for every crop, tho, so hopefully we can unearth more useful information to raise the soil fertility bar.

3/7/2020 6:32:35 PM

On top of Brush Mountain, Pa.

I have several souces that support the target values I have mentioned. Michael Astera in his book "The Ideal Soil" recommends that the minimum for sulfur be 100 pounds per acre up to 600 pounds per acre using the formula S = 1/2 the ideal K based on TCEC. Solomon and Reinheimer in their book "The Intelligent Gardener" are recommending higher levels using the formula S=1/3 ideal Magnesium target level. McKibben in his book recommends 60 to 80 pounds per acre of sulfur. These are all respected agronomists which I am not and I am wondering how there can be such a discrepancy in opinions. Phosphorus goes along these same lines. Help me out here. Also these authors feel strongly that a decision to add nutrients to the soil must be based on soil tests. Is their thinking out of date?

3/7/2020 9:03:03 PM

Guelph, Ontario

I read review of "The Ideal soil" by someone who knows soil science. He says not a good source, as lot of errors.

3/8/2020 8:19:32 AM

Deer Park, WI

I was able to find Solomon and Reinheimer's worksheets online. Their sulfur reqs were not based on soil testing and they even admit in the sheets that sulfur's mobility makes it a challenging nutrient to manage. Thus, the ranges they give are a function of crop need, not soil analysis.

I cannot speak for Astera's work, as I haven't read it. But like Irischap, I've had others tell me his approach is not rooted in the most robust science.

Discrepancy in opinion on these matters is to be expected. There are no absolutes in biology. Its not that these authors are outdated in their thinking, its that there happens to be more ways to skin the proverbial cat due to a lack of scientific rigor that has defined an elusive absolute.

3/8/2020 9:32:28 AM

On top of Brush Mountain, Pa.

So, it is like so many things, a matter of choice. I asked the question here because there were so many different opinions. I was looking for more consensus on something so widely used as values for phosphorus and sulfur in soil. And, the targets are general and not even specific to plants grown. Thanks Joe.

3/8/2020 11:08:27 AM

On top of Brush Mountain, Pa.

Thank you Joe. I respect and value your opinion and appreciate your response. Marv

3/8/2020 11:40:20 AM