Agronomy Questions

Post your questions for the BFA Agronomy team to answer.

Submitted by TFabian on

What are the target numbers for the Saturated Paste Test?
When should the test be performed?
What do the results of the Saturated paste test tell you in regard to; soil conductivity, leaf tissue analysis, and soluble amandments?

Hi. I have really high phosphorous numbers, 500 ppm according to Mehlich lll. I read on your mineral descriptions that Zinc should be high if P is high. I also read that Zi should be 1/10th of P, which is consistent. However, what is the max levels of zi I should add per year? Is it more important to keep the P:Zi ratio 10:1 or to hav them misaligned but adhere to max levels? Thanks

Also, is there anything about the Mehlich III test that can be misleading about my P number?


Submitted by kclgarden on


According to a Mehlich III soil test done in June 2015, our garden here in Barnet, VT is low in Zinc. How and when would I apply Zinc? Would I broadcast Zinc sulfate? Dilute and spray? Can I apply this spring or would you recommend re-testing in the fall and applying before the winter?

In response to farmer_frank, according to Steve Solomon's worksheets, the max yearly application of Zi is 14ppa (10ppa if your soil is calcareous).


I am interested in trying Jerry Brunetti's chicken soup for the soil recipe as found in his latest book "Farm as Ecosystem." (which I gratefully recieved from the BFA). He suggests replacing sodium nitrate for the calcium nitrate but the calcium nitrate is in liquid form (2 gallons) while sodium nitrate is dry and must be put into solution. How much sodium nitrate by weight should be used for this recipe? Also there is a soluble soy based nitrogen on the market that is a 13-0-0. this seems like a nice option for nitrogen without the sodium and that is also sold in a powder. How much of that product could be used? And lastly, Jerry does give a basic recommendation regarding application rate for pasture but what would be a good rate to use this as a regular soil drench for vegetables? This recipe seems to have great potential as a less expensive DIY soil drench, but I just need some info. thanks. Dan

Submitted by farmershaun on


Damping off in the field? This happens to me mostly in the fall to my spinach, lettuce, turnips, beets and rutabagas. I cover the plants with row cover and when I come back to thin, sometimes half or all of my crop is gone. Is there something I can amend the soil with? I practice regenerative farming and am constantly adding nutrients to the soil.

Submitted by RPotwin on

Hi, How can I arrange a phone consultation session to interpret my Logan Lab soil report for my backyard garden?

Submitted by devima9 on

Hi, other than Spring Mix, what would be the best option(s) of how to generally mineralize our garden soils? we will be getting all soil tested, however would like to have some things on hand now.
am thinking about greensand and humates. thoughts?

Submitted by bfaagronomy on

Spring mix is a good one. Especially if you are in an area typically low in calcium. There is no one-size-fits-all recommendation, but using many different rock powders is a good way to spur microbial activity and diversity, and will also provide slow-release broad-spectrum minerals.

Greensand and humates are both good. Greensand is now in extremely short supply due to the closure of the only operating quarry in NJ. New sources are becoming available (slowly).

Also, everyone east of the rocky mountains who haven't been aggressively adding it for years are deficient in sulfur (please prove me wrong if you have a sample indicating you aren't), so elemental sulfur is a nearly universally necessary amendment (as is boron, granular calcium borate is my favorite source).

We did not get a soil test this year, but from our 2015 test we are low in calcium,potassium, phosphorus, zinc, boron, and manganese. we are also high in Magnesium. I know that amending in the fall is best practice, but since we were unable to do so this past fall, what can we do now, or in the spring to correct these issues for the up coming seasons?(we are located in south east Wisconsin going into our second season of growing on the property)

Submitted by bfaagronomy on

Best thing is to add what you're low in. And in the case of high Mg, you need to add even more Ca than normal to address that excess. Since you are low in Ca and high in Mg, Potassium is also critical, so add potassium. Potassium Sulfate is best. Depending on your calcium base saturation % you would want to use either gypsum or high-calcium limestone (or both) for calcium. All these things, and the trace elements, can be added any time of year (but if added when the ground is frozen, there is increased risk of early spring rains washing them away).

Submitted by bobcat230 on

What do you think is the max rate of manganese sulfate I can apply without harming my plants and microbes? Cobalt sulfate? Sodium molybdate? My ppm Mn is in the single digits and I would love to put down 100 lb/A elemental Mn to correct for a severe deficiency in my blueberries, but how much is too much? Depending on who I read, these values change. For example: In "Quantum Agriculture", Lovell says you shouldn't apply more than 25 lb/A/year manganese sulfate. On, citing , the max rate is 200 lb/A/year manganese sulfate. Significant difference. I'm having the same confusion with Co and Mo limits.

How do you account for amending 100 lb/A of sulfur deficiency on a soil that is receiving a substantial amount of sulfate from potash sulfate, manganese sulfate and gypsum? That is, can I apply the deficit as ag sulfur with the understanding that sulfates in these forms will not be readily available to my blackberries this year?

This same soil is very deficient in P, but perfect levels of Ca. What's the best OMRI certified option to amend for the P without using so much soft rock that excess Ca becomes a problem? Granted, I know we always need to promote the biology to make P available, but could there be an underlying cause of the deficiency? Perhaps the sulfur deficiency has something to do with it?

I just saw this... The max rate for GRANULAR manganese sulfate (~27%) is 200 lbs per acre. Granular is sometimes hard to find, so many recommendations list the max for powdered, water-soluble manganese sulfate, which would be MUCH lower, 25lbs per acre per year is probably about as high as I'd go for that.

For cobalt and molybdenum, see rates here:

Sulfates are readily available to plants (as sulfates are water soluble) and this is precisely why I always recommend elemental sulfur to fix a soil sulfur deficiency... sulfates leach too fast and don't address soil deficiency. Elemental sulfur takes 6 months to break down and offer many opportunities to become "attached" to the soil over that time. So if you have a sulfur deficiency in the soil, elemental sulfur is best. If you have an immediately sulfur deficiency in plants, sulfates will help more.

If you are very deficient in P, you'll likely have to add some to get the system working better (and deal with the extra Ca since I know of no organic P source that doesn't also have Ca). But the little bit of extra Ca will hurt you far less than a severe lack of P. As you know, work on your soil biology, so you may not have to add as much P as the test indicates, and definitely fix your S deficiency as adequate S is key to keeping the cations balanced (so the S will deal with any excess Ca).

I am looking at my soil report and my Al is quite high 574 ppm. What can I do about this in my raised beds for vegetables? Are there treatments I should avoid?
I am also quite low in Mn (15 ppm) and Boron (0.79 ppm) Are these connected in any way?

Despite what Logan Labs says about the desired Aluminum levels, I have actually never seen a soil test come back in their desired range (<200 ppm). 574 is actually right about the average for sample results I've seen, so I wouldn't worry. The best way to make sure Al isn't a problem is to move the soil toward balance.... if you're low in Ca, or Mg, or K, or S add them to get closer to the "ideal" level. I've certainly seen lower Mn and B levels, but you should address them. 20 lbs per acre of 10% granular Calcium Borate is my favorite Boron source, and 100 lbs per acre of granular Manganese Sulfate for the Mn deficiency (it'll take a few years of applications to bring it up to where you want it).

~ what is the composition of Spring Blend and of PlantSure and how do I know how much to apply?

~ do we have a call today 3/27? If so, what time?

~ since sulfhates are so soluble and don't contribute to the long-term soil balance improvement, should one apply both sulfhates and slower-release minerals at the same time - ie a quick shot in the arm plus long-term amendment?

Composition of spring blend:
Spring blend consists of (in 1,000 lbs, the recommended per-acre application rate):
150 lbs Humates, 100 alfalfa meal, 100 carbonatite, 100 ks plus, 100 tn rock phos, 100 sul-po-mag, 100 dynamin, 100 humus compost, 50 sea salt, 50 kelp, 50 zeolite.

Note that you should only apply Spring Blend if you need calcium... if you already have excessive calcium, either don't use it at all or use it at a much lower rate (250 lbs per acre or so).

The Agridynamics 'Plant Sure' product label info can be found here:

Sulfate forms of other elements do in fact contribute to mineral improvement... for instance Potassium Sulfate adds potassium, and Calcium Sulfate (gypsum) can add calcium. The thing that isn't improved by using sulfates is simply the sulfur levels (or at least not by much). For increasing the level of sulfur on a soil test, the only thing that has a big impact in the short term is elemental sulfur.

Submitted by Cindy on

I'd like to have a soil test done, but I need help with the Logan Test results. How can I get these interpreted with any amendments I need?

You can start by trying to do it yourself. You can listen to past lectures and S&N Conference talks to get some assistance, as well as reviewing our recommended targets for the minerals here:

If you want one-on-one assistance, it is available to members at a discount by contacting me here: agronomy @

Submitted by SharonS on

I attended Dan's 2-day workshop which was quite helpful. He had recommended The Ideal Soil by Michael Astera. That is also very good and helped me work through some of my remaining questions. If there is no workshop in your area some of the past workshops are up on the BFA site.

I have very small amounts to add to a 1000 sf plot: 4#Gypsum, 2# Biomin Copper (4% Cu), 11 oz Zinc (Zn) Sulfate, 7 oz Borax. Got any suggestions for how to distribute that evenly ;-)

Generally, for small plots like that, I'd recommend mixing the minerals with a carrier, like compost, as homogeneously as possible (sometimes I don't bother with the carrier, as sometimes that can create more problems). Then spread by hand (literally with your hands) out of a bucket. I find it's convenient to divide the space into equal size blocks (maybe 10, 100sq ft blocks), divide the material into that many buckets, and spread that way. When you do that, you have a very good, very apparent, visual cue if you are spreading at a rate that is too high or too low, and it allows you to tweak your technique so you get close to even coverage. If you're nervous, start by spreading at what you perceive as half, or even a quarter, of what you think the rate should be and adjust accordingly.

Looking at Claire's Logan soil test, she found base saturation of 80.64 Ca, 12.97% Mg, 1.77% K and and 0.82% Na. Exchange Capacity came in at 17.71 and pH at 7.6. Logan's table is not registering a ppa deficiency in magnesium, but my understanding is that 6:1 ratio of Ca:Mg is preferred and I'm not sure if that's by percent saturation or ppa, so I'm wondering what if anything needs to happen to adjust that critical Ca:Mg balance point. Sampling was done in December so I'm wondering also if that might have lowered the potassium levels. Sulfur was low at 24ppm.

Submitted by RPotwin on

Hi David,
I need some clarification regarding advice given during the consult call for my 16'x16' vegetable garden
Question #1: You had recommended 1/2 lb of elemental sulfur this year and 1/4 lb for the next 2 years. I bought Espoma Soil Acidifier which is 30% sulfur (a mixture of elemental sulfur and gypsum). Should I adjust the application amount?
Question #2: The copper sulfate (Bonide) which I bought, is in powder form. Your recommended application for a granular form was 1 ounce. Can I apply the powder all at once? Thanks!

Hello David,

Couple of questions about Azomite and Cobalt sulfate purity.

1. Azomite. It looks like a pretty good bang for your buck for micronutrients.

What are your thoughts on it? I see in the analysis that it has 11% Al2O3 or Alumina. Is that going to raise the Aluminum concentration too much? or will the Alumina leach out of the soil after a year or so?

Also will the 1.8% Calcium have a noticeable effect and possibly throw off the Ca, Mg base saturation ratio? So is it safe to use at the recommended rate by the manufacturer?

2. Cobalt Sulfate. I looked up buying Cobalt Sulfate from pottery supply online but the only stuff I can find for a reasonable price is around 99% purity. My soil test for my farm from Kinsey Ag calls for 8g/1000 sqft of 27% or something Cobalt Sulfate.

So my question here is how do I extrapolate their math on 27% to 99% without overdoing it? And what is a safe application rate for home garden use/1000 sqft with the 99%?

Thank you


Also, What organic matter percentage that shows up a soil test would support biological life in the soil the most? Do I want to see 5% or 6% etc.? And what is the best way to incorporate more organic matter without throwing off the cation ratios on a big area? Is it just cover cropping? or sending Kinsey a sample of the manure compost from my local beef farmer etc etc. We just don't generate a lot of compost nor do we have the time to tend it.

Thank you

Submitted by Greg Walsh on

Hi David! 2 questions...

1. Question on Sodiun Moldybate. I calculate it is 43.75% Mo. Looking at your yearly limit Applications (below), it seems to suggest a 5% concentration. This leads to a 10 lb/acre allowable limit. Where did I go wrong?

2. I saw in another post that elemental sulfur is the only way to raise a low Su test. I had been relying on gypsum. Should I not count the Su in gypsum and just go for elemental Su to raise the levels. THANKS



Molybdenum: 0.5 lb/acre actual, up 0.25 ppm/yr

Sodium Molybdate (5%) 3.5 oz/ 1,000 sq ft, 10 lbs per acre

Submitted by esbest on

Hi David - Soil test question (I'm confused looking at my notes/results from consult w/you from autumn soil test...)
Potassium was tested as 3.57 Is it 100 lbs./acre? to determine quantity I need?
Is sulfur/sulfate the same as potassium? I have a note to add sulfate ... and another note to add sulfur over years...?
Thanks, Ellen Best

Hello, I am planning to start a new farm, the Logan labs soil report shows i have very poor soil. i have access to granite fine up to 15 tons, how much do i apply, if any to 2 ac of land. the soil is sandy loam. OM is 1 %, ph is 5%, total excahnge capacity is 1.90ME, sulfur is 6ppm, all other macro neutralists are low. Thanks

I recently attended a webinar with John Kempf and he mentioned that Micronutrient amendments are often in the wrong form, making them ineffective when added to the soil. What are the best forms of micro nutrients like Molybdenum, Cobalt, zinc etc? what are the best times and techniques to apply them? are liquid amendments (like those from Advancing Ecoag) superior, and do they have lasting affects in the soil?

Submitted by RPotwin on

After adding your recommended amendments last spring, along with seed innoculants, my garden had a very vigorous start. The disease resistance was noticeable. However, the beets and carrots had lush greens but stunted roots. Also, I had the best broccoli ever, yet the romansco did not head up. Any suggestions?

Submitted by agp613 on

My Logan Labs Soil Test show's an excess of Calcium, Magnesium and Potassium (all in excess of their recommendations by 1-5% and no exchangeable hydrogen). My PH is high (7.4) and my sulfer is low. I plan on adding sulfer following Ideal soil 2.0 recommendations - but I'm curious if I need a AA8.2 soil test and if there are any things I should not add until I have that test done.

An AA8.2 (ammonium acetate extraction) soil test would be helpful, but 7.4 isn't THAT high. More than likely, the story won't change, just the intensity. Meaning that your exchange capacity is probably reported higher than it actually is by 10% or so, and the %s are off by a small amount, but it likely won't change your approach anyway. Adding enough elemental sulfur to (theoretically) get you to 75ppm (100lbs is generally max, 200lbs max in high CEC soils) is likely the best approach. By the way, you won't get to 75ppm because a bunch of the sulfur will go toward dealing with your excesses, but just keep at it. Once they excesses start to approach target, your sulfur levels will more readily approach the 50-75ppm target.

Submitted by agp613 on

I just finished reading The Anatomy of Life and Energy in Agriculture by Arden Anderson and he recommends Calcium Carbonate and Rock Phosphate regardless of soil test, I was hoping you could shed some light on this? In a soil with adequate base saturation of Calcium and Phosphorus would these still be beneficial?

Additionally I've been adding Peat Moss to many of my beds and generally notice good results - although I am worried it my dehydrate the soil if not properly hydrated first. Could you talk about the benefits and drawbacks of adding Peat to boost carbon in the soil - I assume it will increase water holding capacity but does it effect CEC?

There are people out there who recommend this practice. I even know of some "consultants" in the midwest who tell their clients to "add 2 tons of hi-cal lime per acre per year, EVERY year"... That may work (for a while) in those specific areas (because they have CRAZY high exchange capacity, and outrageously excessive Mg), but as a generalized recommendation to apply everywhere, it is terrible.

There are many people who work in regions where general recommendations like this work out, and are easier to issue broad statements about... but unfortunately, then people outside those areas hear it and think it's going to work for them.

You can indeed add lots of rock phosphate, and in many areas, calcium carbonate to soil and, for years, not see a detrimental effect. BUT, that's assuming you have an unlimited budget too. If you don't need calcium and phosphorus, it's just not going to deliver the benefit.

Peat moss will dehydrate your soil if added dry, but only temporarily. Once it becomes wet, it will help to hold moisture. It would take a LOT of bone dry peat moss to cause a real issue, but it is one reason why you should moisten it prior to transplanting into a peat moss-rich soil. It will have basically zero impact on CEC, at least directly. It can provide a home, food, and moisture control that will make soil microbes "happy". As it decomposes, the carbon is available to soil life. The best way to add organic matter to soil is to grow healthy plants, but peat moss can make that easier when used appropriately.

My understanding is it is quite acidic as it has very low levels of cation elements so it can "suck up" cation ions at least temporarily. In this way it does add to CEC, but not a lot, and not for overly long, but it should be kept in mind, especially in soils that have a high percentage of peat moss added (which I generally don't recommend).

Help with Soil Test interpretation
Hi David,
I'm looking forward to the Agronomy Call March 6th. I would love some clarification in reading my Logan Labs Soil Test.
1) Exchangeable Cations shows Ca deficit at 3166#/A, High Mg @597#/A, and Potassium deficit at 291 #/A. Yet the Base Saturation %s look good: Ca 64.93, Mg 20.41, and Potassium 3.06%. Why the difference?,
(TEC is good-12.19, pH is 6.6)
2) I add lots of compost. OM is 7.12%. What should I aim for?
3) Sulfur is low- 20ppm. If I understand what I learned from your presentation at the S&N conference and reviewing the video, I should add about 80#/A/year for the next 3 years of Elemental Sulphur (66.5 + some to cover what is used to fix the excess of Mg, and Al?).
4) Phosphorous is 953#/A (477ppm?). From adding a lot of compost? So bring everything else up? How do I keep Ca high and available so it doesn't get tied up with the Phosphorous?
5) Aluminum is very high 1390ppm. But Saturated Paste Test says 1.5ppm. How is this? Anything to do about it?
6) Keys to understanding the Saturated Paste Test. What is it used for? What is it telling me?
Thank you!

Azomite calculations
Hi David, I hope you are feeling better. I've been looking at the mineral make-up of Azomite and thinking it would be a great way to cover a lot of the mineral needs of my soil. The recommendations I'm seeing are to add 100-500# per 1000sq, ft. What I'm not clear on is how to calculate the quantities of the different minerals that will give me. Here's the relevant mineral make-up:
Zn 64.3ppm
B 29ppm
Cu 13.5 ppm
Co 22.3 ppm
Mn 200ppm
Mo 12.6 ppm
Se 0.79 ppm
So, for example, if I want to increase manganese by 80 ppm how much Azomite would I add? Do I have to figure out what percentage of the Azomite is Manganese? How do I do that?

ppm is parts per million. So for instance zinc (Zn) at 64.3ppm. Divide by 1 million to give you pounds per pound of material. So, 64.3/1,000,000 = 0.0000643lbs/lb of Azomite. Multiply that by your application rate and you'll see why adding rock powders like Azomite is a much slower method of correcting mineral deficiencies!

Also - I generally recommend 100-500lbs per acre. Not per 1000sq ft. While it may not hurt at all at that higher rate, it's expensive to add that much, may not be your best bet, and may cause harm. The max I would add in most circumstances would be 2 tons per acre.

So, back to math... if you add 250lbs of Azomite per acre, you'll get 250 x 0.0000643 = 0.016075lbs of Zinc per acre. As you can see, this is why if you need to raise the level of an element in your soil, it's cheaper and more effective to do so with the concentrated mineral you need.

Azomite spurs microbial activity, and is a great way to get trace amounts of the micronutrients, but it should not be thought of as an alternative to adding the fertilizers you need to move your soil toward balance.

There's always "a risk" to applying anything... literally anything. Your footstep in the garden damages soil life, but sometimes it needs to be there. Same with any amendment, not just synthetic forms of nitrogen like you're asking about.

I actually very much appreciate having calcium nitrate available as a tool to manage crop nutrition. Obviously you can't use it in organic ag but it's one of the least damaging of the synthetic nitrogens. As with ANY form of nitrogen, including organic nitrogen sources, applying too much will shut down the nitrogen fixation processes (microbes) in the soil. So I very highly recommend that you stick well below the recommended application rates and only use it when you really think you have a nitrogen deficiency. I like it early in the year to deal with low nitrogen prior to microbes "waking up" in cold soil (if I have to plant into cold soil) and also for dealing with short term nitrogen issues during the growing season (like if I messed up and allowed soil to get too hot, dry, wet etc - impacting microbial nitrogen synthesis) and especially if I also see calcium deficiency issues at the same time (like blossom-end rot on tomatoes).

My other favorite synthetic nitrogen source is probably ammonium sulfate. In granular form it's slow release (taking about 90 days to fully breakdown and become available) and can be very useful for getting good crops (especially grain and fruiting crops) for farmers transitioning to regenerative ag (but who haven't yet got the organic matter and soil activity necessary to do away with nitrogen applications).