Archive for the ‘standard soil test’ Category

Standard Soil Test + Saturated Paste Test = Complete Soil Picture

Why Standard Soil Tests Only Show Part of the Picture

Logan Labs Standard Soil Results. Click to enlarge.

At the Acres USA eco-farming conference, we learned a lot about testing plant tissue to determine the health of our pasture grasses and specifically, what nutrients the grasses are picking up from the soil.  We learned that soil tests are usually poor predictors of what and how many nutrients will get into plants.  There’s a lot going on between soil and plants.  Soil biology must be hearty enough to help the plant’s roots absorb nutrients.  The soil is the plant’s digestive system, and if it’s not working at its full potential, plants won’t pick up the quality and quantity of nutrients they need.  It’s the same with us – we can eat all the healthy food in the world, but if our digestive systems are unhealthy, we’re not going to absorb the nutrition.  That’s why healthy soil with super robust biology is so important to plant health.

The Saturated Paste Test

Many conference speakers encouraged the audience to get a saturated paste soil test.   The saturated paste test shows what nutrients are immediately available in the soil’s water solution.  These are the easy access nutrients for plants, so this test better predicts what nutrients (and how many) will get into the plant.  Logan Labs describes the standard test as the soil’s “savings account” and the saturated paste test as the soil’s “checking account”.  Both show nutrients that are accessible, but the checking account nutrients are more easily available.

Logan Labs Saturated Paste Results

We came home from the conference and sent in four pasture samples to Logan Labs.  Each sample was a quart-sized ziploc bag full of soil.  You need to send in more soil than usual if you’re getting both tests.  The pictures show the results of our standard soil test, our saturated paste test, and Logan Lab’s guidelines.

What Both Tests Show Us

Comparing the two tests with the guidelines, it’s clear that magnesium and potassium are pushing out calcium.  On the standard test, it looks like we have enough calcium in proportion to our very sandy (very low) Total Exchange Capacity (CEC), but both magnesium and potassium are too high, especially in base saturation.  The saturated paste results confirm that plants don’t have enough easily accessible calcium.  Calcium is one of the most important plant nutrients, and excesses of magnesium and potassium spell trouble, so we need to figure out how to get this balanced.

Phosphorus is also interesting – the standard test shows we have plenty, but the saturated paste test shows we barely have any phosphorus that’s easily accessible.  This, combined with the low calcium availability, might explain why we have a constant broomsedge problem.  Phosphorus is an anion (negatively charged) that easily locks up with other nutrients.  Active, healthy soil biology is the key that unlocks it.  These two tests are confirming our soil’s biology is lacking.   Like we didn’t already know, thank you :)

Our Plan

Logan guidelines. click to enlarge.

Besides maybe some sulfur, zinc, and copper, we’re not going to add any fertilizers.  With our very sandy soil, we’ve learned that it takes very little fertilizer to throw things out of whack.  Take a look at our soil test from last year, for example.  Potassium was lacking, especially in the West field, at 2.6% base saturation.  In Spring 2011 we spread just 250 lbs/acre of potassium sulfate, which is 40% or 100 lbs of potassium, and the base saturation jumped to over 6.5%, way too high.  Perhaps the soil needs more time to straighten out, and December probably isn’t the best month to test.

We need calcium to come down closer to 60% base saturation on the standard test, but that’s probably not wise since it’s so deficient on the paste test.  We want magnesium to come down to maximum 20% base saturation (calcium plus magnesium should not total more than 80%), and we definitely want potassium to come back down under 5% base saturation.  We’re hoping the soil can do this on its own, especially with the fallow cover crops and biology inoculants we plan to introduce in Spring 2012.  More to come on that- thanks for reading!

Our Farm’s Soil: Where We Are and Where We Want to Be

Here’s where we are as of November 2010:

Soil Test Results

And here’s where we want to be:

a. Organic Matter:  at least 5%

b. Calcium: close to 3,000 pounds per acre

c. Magnesium: close 430 pounds per acre

d. Potassium: 150 to 200 pounds per acre

e. Sodium: 40 to 130 pounds per acre

f. Phosphate (P2O5): 400 pounds per acre

g. Sulfur: around 100 ppm

h. Boron: between 2 and 4 ppm

i. Iron: at least 150 ppm

j. Manganese: between 40 and 50 ppm

k. Copper: around 10 ppm

l. Zinc: around 20 ppm

Organic Matter

Our organic matter, currently less than 2%, needs to more than double to 5%.  We’re trying hard to protect our organic matter by mowing and mowing and leaving all clippings on the field.  We’ve done this for the past two summers, and we can see small but promising signs that soil microbes and earthworms are returning.  When we finally do get animals, our organic matter should start to climb sharply from the impact of hooves stomping plant matter into the soil and from the microbe-rich manure.  Can’t wait!

Calcium – Add Lots

Typical of soils in wet climates, our soil badly needs calcium.  Great pasture has at least 3,000 lbs of calcium per acre available to plants.  Our best field has under 1,400 lbs, so we have a long way to go.  We bought a fertilizer named TRIO, a.k.a. carbonized lime.  We’re going to spread it at a rate of 200 lbs per acre this spring and again this fall.  It has about 30% calcium, microbials and humic acid, which is nice carbon for the soil.  We’re excited to see what this can do for our land in terms of calcium, microbes and organic matter.  Because we don’t want to get outside the ideal base saturation range for calcium (more than 70%), we have to go a little slow.  I wrote about that here.

Magnesium – Add None

With sandy, low-organic matter soil, our exchange capacity is around 4 and 5.  This is really low and means the soil won’t hold many nutrients.  We want to eventually have close to 430 lbs per acre magnesium.  But our magnesium values, in the low 200s, are maxing out our base saturation percentages for magnesium.  We don’t want more than 20% base saturation for magnesium, or the soil gets unbalanced, and problems, such as magnesium locking up other needed nutrients and the soil getting too tight and non-porous, start to occur.  Because of this hazard, we’re not going to apply any magnesium.  We might never need to.  If our organic matter levels come up, it might make more magnesium available to plants.  Magnesium doesn’t leach out of soil in wet climates as badly as calcium does, so we might have plenty of magnesium anyway.  We just need more organics to make it available to plants.  We’re aiming for the ideal calcium to magnesium ratio of 7:1.  This ratio, with adequate organic matter, gives the soil nice tilth, meaning it’s neither too loose (compacts easily) nor too tight (water and air can’t get through).  So 430 lbs per acre with 3,000 lbs per acre calcium gives us this nice ratio.

Potassium – Add a Little, and be Careful

All fields except our Middle one are a little short (below 150 lbs per acre) on Potassium.  We plan to up the Potassium levels by spreading composted manure.  We’ve been getting free horse manure from nearby horse barns and composting it in big piles.  I know it has lots of potassium because I put a lot of it in our veggie garden and our potassium levels are now way too high (argh!).  The microbes in the composted manure will be good for our fields.  I’ll definitely get an analysis on the compost before I apply it so I don’t repeat the veggie garden mistake.

Sodium – Add a Little

We need at least 40 lbs per acre, and some of our fields are short.  There are wonderful sea salt fertilizers available out there.  Coming from the sea, they have nice amounts of all micronutrients along with 30% sodium.  We need massive help with micronutrients anyway, so we plan to apply one of these fertilizers.

Phosphate – Some Fields Need it

Two of our fields consistently show high amounts of phosphate while the other two don’t.  This might give a clue to our farm’s history.  The two fields with high levels are close to the house and outbuildings.  The previous farmers might have spread manure in these two fields so they wouldn’t have to transport it to the farther fields.  Who knows?  We’ll definitely need to apply soft rock phosphate to our East and West fields.

Micronutrients – Add a Lot

Boron, Copper and Zinc are in the worst shape, and some fields need iron and manganese too.  We plan to apply Boron, Copper Sulfate and Zinc Sulfate to our fields this summer.  These nutrients are needed in small quantities, but they’re essential for plant and animal health.  We’ll probably apply Iron Sulfate and Manganese Sulfate next year.  We’ll apply all of these very conservatively because with levels testing this low, they might just be tied up by something, such as lingering herbicides or mineral imbalances.

Why All the Trouble?

Our goal is to produce highly nutritious, very tasty food.  Taste and nutrition come from the soil.  We’re hoping that our current efforts and fertilizer expense will pay big dividends in the future such as little to no animal disease, fast-growing animals, high meat quality that attracts customers, and increased human health as well.


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