Renewable Farming

Neal Kinsey’s most effective weedkillers: soil fertility and intensive management

Not many soil and crop consultants can show you 45 years of field experience based on consistently applying the proven principles of soil life and fertility pioneered by legendary University of Missouri scientist William Albrecht

Dec. 1, 2016  By Jerry Carlson — Neal Kinsey is the only agronomist we know with those credentials. So when he speaks, you’d expect a packed audience at his sessions at the ACRES conference underway today at Omaha.  Here are some raw notes from his presentation. All of these observations come from his own field experience and farmer cases of resolving weed issues by fine-tuning soil fertility to favor the crop and take away either nutrient deficiencies or excesses which favor the weeds versus the paying crop.

Kinsey repeated his “wish list” several times: “If U.S. agriculture invested as much time and intellect and money into managing weeds with benign fertility rather than toxic chemicals, We’d be a long way ahead of where we are now,” he stressed. “The biggest mistake in ag research is failing to look at what gives weeds an advantage.”

Dr. Neal Kinsey at ACRES

That’s particularly evident in recent years, with weed “resistance” to overused herbicides.

Here are just a few observations captured from Kinsey’s show-and-tell at ACRES Dec. 1. He has not reviewed these notes, so they’re of course abbreviated. (You can obtain the audio recording of his presentation from ACREs by calling the number at this link.)

Sourdock (and many other kinds of “dock.”) 

When sourdock moved into the alfalfa many years ago in Missouri, most farmers gave up raising alfalfa. They wouldn’t accept the Albrecht view that the soil simply didn’t have enough calcium, as shown in the Albrecht soil test. Farmers often looked at soil pH and said that a pH of 7 or higher had enough calcium. However, excess sodium, magnesium and some other elements can generate a high pH, even more than calcium does. If sourdock invades, don’t look at pH. Add high-calcium lime and the sourdock will recede.  A pH of 8 does not indicate calcium excess. 

Cocklebur (Xanthium strumarium)

We had a client who grew soybeans and didn’t use herbicides. He needed calcium, and also needed zinc. Cocklebur loves low zinc and low calcium. This Missouri farmer improved his soil test, and the cocklebur no longer took over. But the soybeans did better, and quickly shaded the cocklebur. Improving zinc and calcium in the soil took the advantage away from the cocklebur. 

Foxtail   (Setaria spp.)

We analyzed the soils of farmers who had serious foxtail, including giant foxtail.

This is the water-soluble test, which measures more closely what the roots see and are able to take up. In each case, the tests pointed to excessive magnesium. Foxtail loves high magnesium, low sulfur soil. We applied gypsum and the foxtail pressure declined.  We started with a ton of gypsum; calcium sulfate. Foxtail also shows up under excess nitrogen.

Broomsedge bluestem (Andropogon virginicus)

Presence of this weed signals low ph and a need for more calcium. When calcium is in the 60% saturation range, the broomsedge will stop growing.

Trumpet vine (Campsis radicans)

Generally, this means calcium deficiency.  In wet areas, water saturation reacts with nitrates in the soil, which converts the nitrogen to nitric acid. In turn that acid strips the calcium out of the soil. Adding two tons of high-calcium lime ended trumpet vine.

Canadian thistle (Cirsium arvense)

Severe phosphate deficiency is an indicator on Canadian thistle. Soil tests can be misleading in the pastures, because localized manure deposits by grazing livestock can kick up the phosphate reading in a soil sample. Get adequate phosphate in your soils and thistle problems will recede. We recommend 200-mesh soft rock phosphate, 500 pounds per acre, to stop the thistle and enhance pasture growth. 

Stinging nettle (Cnidoscolus Angustidens)

This weed is vicious. Try to eradicate it with tillage or chopping and it regrows from the roots. The roots go deep. One of our clients tried to dig out the roots of stinging nettles around the farmstead. He couldn’t find the bottom end of the roots, so he tried pouring salt over the roots that remained. Didn’t work. Tried kerosene to kill the roots, and the nettles regrew. Then he dumped both salt and kerosene together over the roots, but the nettles came back.  When he balanced out the soil fertility, the stinging nettle transitioned into history. 

Nutrient excesses also can favor certain weeds.

When your potassium goes above 7.5% saturation, you will have weed problems.

Spiny Amaranth is a case in point. It shows up where there is severe potassium excess in the soil.  

Peppercrest showed up in southern Missouri in the corn rows, where the farmer had strip fertilized with zinc. The soil around the roots showed extreme excess:  90 parts per million. The peppercrest thrived in that excess zinc. But it didn’t grow between the corn rows, in the middles, where there was low zinc. The weed looked like it had been planted, right along with the corn.


Apply calcium and reduce compaction. “Jim Martindale once showed me a photo of a pasture worked with an AerWay. Where the compaction was relieved, no dandelions. So it’s not always just fertility.”

Other comments by Kinsey:

Boron, which you can easily apply as Solubor, will kill certain weeds because of a phytoxic reaction to boron. 2 lbs. of actual boron. You can increase boron in the soil, and boron is often deficienct in Midwest soils.

There are weeds that like tight low-air soils. Compacting it wet leads to wild onion weeds. Soil tests may not look different, but the compaction level can change. If you press out the pore space, you give an advantage to wild onion.

Over the years we’ve bought books which link weed symptoms to soil fertiity relationships. Some of these are available from ACRES.