Archive for May, 2011

Fertilizing with Carbonized Limestone, Sea 90, and Micronutrients

We want soil that is dark and crumbly with a very healthy soil life population and luxurious amounts of minerals.  Soil like this will support our animals’ health and our future farm business.  We have a long way to go to get this soil, so to start off, we’re adding some minerals.

You can see our soil test results at this post.  We’ve done 3 soil tests over the past couple of years, and they all pretty much say the same thing.  We need a lot more organic matter and calcium, a little more potassium, and a lot more of almost all of the micronutrients (boron, zinc, copper, etc.)  Because our soil is sandy, with a very low cation exchange capacity (CEC), we are adding small amounts of fertilizer each time.  A low CEC means our soil doesn’t have much room for holding nutrients, and if we add more than we need, the soil gets unbalanced very easily.   So, we’re taking it slow.

Carbonized limestone (left), O-charger (top), Sea 90 (right)

The cool thing is, we’ve found fertilizers that are therapeutic for our soil!  I say “therapeutic” because these fertilizers do more than just supply nutrients – they also help soil life!  They come pelletized with humates and microbe food and compost.  Our soil needs all the help it can get in the microbe and organic matter department, so we’re happy to have found these.

The carbonized lime came from Fertilizer Brokerage.  It’s calcitic limestone pelletized with carbohydrates (food for microbes) and humates.  Humates are organic matter that has decomposed all the way, basically soft coal.  It’s very dark and has an extremely high CEC, exactly what our soil needs!  We spread about 150 pounds per acre, a tiny amount.  We’ll probably spread at least that much again this fall, depending on what the new soil test says. In sandy soil, calcium leaches easily, and calcium is very important for soil quality and animal health, so we’ll probably add carbonized lime every year.

To supply micronutrients, we bought a fertilizer called O-charger from Midwestern Bio Ag.  It’s borate, copper sulfate, manganese sulfate, and zinc sulfate pelletized with compost.  Our soil needs the compost of course, but the purpose of pelletizing it with lots of compost is to get a more even spread of tiny amounts of these micronutrients.   We spread 200 pounds per acre of O-charger.  Our soil is very low in boron, and boron is critical for getting calcium into plants.  Gary Zimmer of Midwestern Bio Ag says he rarely spreads calcium without spreading boron too, so the O-charger should work well with the carbonized lime.

We also broadcasted Sea 90 in our two fields with the lowest amounts of sodium.  I’ve read that you want sodium to be at least 40 pounds per acre.  Sea 90 is a good quality sea salt that contains nearly every element listed on the periodic table.  I actually look for opportunities to spread a product like Sea 90 because it’s a good way to get all the elements necessary for life into the soil.

Our West field is short on potassium, so we spread granular Potassium sulfate there.  Potassium sulfate is 50% potash, which is 41% potassium, so we spread 200 pounds of potassium sulfate per acre.  I know this field is extra hungry for potassium because we dumped a pile of low-quality aged horse manure (lots of potassium and not much else) in this field and the grass went nuts around the pile.  It’s still a deep, healthy green and much thicker and taller than the rest of the field.  We can’t wait for all of our grass to look this good!  Now we’ll wait for a nice warm rain to soak the fertilizers into the soil and watch for results.

Sorghum Sudangrass and Cowpeas Cover Crop

Planting sorghum sudangrass and cowpeas using St. Mary's County's drill

We’re trying out our first cover crop on our neighbor’s fields.  Like our fields, our neighbor’s land was farmed in roundup-ready soybeans for a good while (we think 10 years).  Organic matter is very low, around 1.5%, and the soil seems lifeless.  Instead of immediately planting perennial grasses like we did with our fields, we’re going to give our neighbor’s soil some extra TLC and a good dose of tough love (disturbance) to try to jump-start this soil into healing itself and becoming hospitable to soil life.

Because summer is approaching, we decided to plant sorghum sudangrass and cowpeas as a cover crop.  Both of these love the heat!  Sorghum sudangrass is a cross between sorghum (relative of corn) and an African grass.  Cowpeas are good ole’ black eyed peas.  We’re hoping the sorghum sudangrass will grow thick and tall and provide support for the climbing cowpeas.  Like corn, sorghum sudangrass loves nitrogen, and the cowpeas are a legume, so we want the cowpeas to fix nitrogen and provide it to the sorghum sudangrass.

Our Goals

sorghum sudangrass

Organic Matter:  Our primary goal for this cover crop is to provide tons of biomass to the soil.  According to this very useful handbook on covercrops, sorghum sudan is “unrivaled for adding organic matter to worn-out soils”.  It quickly grows 5 to 12 feet tall and usually results in at least 2 tons of biomass per acre.  We plan to kill and incorporate this biomass into the soil by rotovating.  With the help of soil life, this biomass will decompose and start to become organic matter in the soil.    Cowpeas grow quickly too and should provide another ton or so of biomass per acre.  Compared to the stiff, crunchy sorghum sudan biomass, cowpea biomass (vines and leaves) is softer and will break down quickly.  After going from year after year of soybeans, we think the soil life will like snacking on these two crops for a change. 

Weed Choker:  After many years of roundup-ready soybeans, the weed pressure in these fields, especially with round-up resistant weeds, is immense.  Both of these cover crops have been shown to out-compete weeds, but sorghum sudan is especially great at it.  This crop actually kills weeds by secreting allelopathic compounds from its seedlings, shoots, leaves, and roots.  The same handbook cited above, page 107, says this compound is strongly active at extremely low concentrations, comparable to synthetic herbicides.  Amazing! 

Iron and Clay cowpeas

Healthy Disturbance:  The tough love I mentioned above is all about disturbance.  This soil has been in no-till soybeans and sprayed with roundup for many years now.  It has gotten very little food in terms of plant matter.  By growing very strong and dense covers and incorporating all that plant matter in the soil by shallow tilling, we intend to shock the soil in a good way and jump start it into heading in the right direction.  Nature uses disturbance quite a bit to initiate renewal (think of forest fires or huge buffalo herds).  We’re convinced that our own fields would be better off if we planted successions of cover crops instead of perennial grasses.  This is the 3rd season we’ve had grass, and the grass gets a little better every year, but the soil seems stuck in a bad place in terms of soil life (crusty, dusty soil, very few earthworms, etc.). 

Method and Cost

We rented St. Marys County’s no-till drill (planter) and drilled about 30 lbs per acre of sorghum sudan and 15 lbs per acre of cowpeas (Iron and Clay variety) on April 30th.  We inoculated the cowpeas with the bacteria that help cowpea roots fix nitrogen.

Seed Cost = $1,175.  (15 bags of sorghum sudan at $30 per bag bought locally, 7 bags of cowpeas at $60 per bag + shipping, inoculant = $35)

Drill Rental = $200

Diesel = $30 (~ 7 gallons)

Labor = $160 (8 hours at $20 per hour)

Total = $1,565 or about $70 per acre (22 acres total)

This being our first cover crop, we have no basis on which to judge the cost, but the cost seems high to us.  In the future, we intend to lower the seed costs by only buying seed that’s available locally (no shipping costs).  We can also lower the diesel and labor costs by getting more experienced with planting different seeds and learning to use the drill.  We had a hard time adjusting the drill to spit out the seeds at the right rate – this took about an hour.  We were also moving the tractor very slowly in order to notice groundhog holes and dodge them in time. 

Our Plan for the Growing Season

Grow & Mow:  As long as the cover crops are out-competing all the weeds, we’ll let the sorghum sudan and cowpeas grow until they’re 3 or 4 feet tall and then mow them.  The cover crop handbook says this encourages the sorghum sudan to tiller and put down even deeper roots for regrowth.  Deeper roots are fantastic – they go into the subsoil, break up compaction, and bring up long-lost minerals and put them in the plant.  When we incorporate the plants into the soil, the minerals will be placed in the top soil and the roots will eventually turn into organic matter. 

Fertilize?:  We haven’t decided if we’ll fertilize or not.  We’ll watch the sorghum sudan, and if it’s starting to look wimpy and nitrogen deficient, we might spread some ammonium sulfate.  It’s $12 per 50 pound bag, and each bag has just over 10 pounds of nitrogen in it.  We’d probably spread at least 50 pounds of N per acre, so the cost could add up quickly.  However, ammonium sulfate also supplies nice amounts of sulfur, which this soil needs badly.  We’ll see – we might end up in a situation where it’s beneficial to “buy” more biomass by fertilizing with ammonium sulfate.     

Rotovate & Wait:  After a good re-growth, we’ll kill the cover crops by rotovating them into the soil, probably in early August.  A rotovator is like a very wide garden tiller for a tractor.  If the sorghum sudan does produce a lot of biomass, we will need to give the soil 2 to 3 weeks to start breaking all the biomass down.  By the end of August, we’ll plant the next round of cover crops for the fall/winter season.  We’ll look for crops that this soil hasn’t seen for a long time, probably cereal rye and hairy vetch. 

Updated June 23, 2011 here.


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