Soil test finds nothing extreme in field of laminitic horses

December 4, 2012

Robin gets his left front foot soaked on Sept. 20, 2012.

Robin gets his left front foot soaked on Sept. 20, 2012. His problems over the summer pushed me to test the soil.

I tested the soil in one of my pastures in August 2012 as the heat wave was waning. I concentrated on the pasture where five of my six horses lived when they foundered over the years, even though Angel foundered in the middle of winter in a snowstorm.

I was looking for anything out of the ordinary, particularly since my gelding Robin Hood became sore July 4, 2012, and hadn’t improved much.

I took two samples to Missouri’s local extension office on Aug. 20, 2012: one from the grass surrounding my septic drain field, which sits in this pasture, and one from the roughly 2-acre pasture in general. I tested the soil around the septic area because I had been worried that the septic drain field was creating some sort of extreme situation, leading to the laminitis.

Note that I also tested this pasture in 2005 using the same testing lab, which had the same scientist at the helm.

In 2005, the field had a low pH level of 4.9 (compared to an optimum pH of 6 to 6.5). A 4.9 reading meant the pasture was too acidic, which would lead to the field being low in the macronutrients of nitrogen (N), phosphorus (P) and potassium (K).

The field as a whole still has a low pH level. It remains at 4.9. The area around the septic drain field is 5.8, and it might be worth noting that the horses spend more time there than on the fringes of this pasture.

The pH level affects growing conditions. The extension office’s website says that raising a pH of 4.5 to 6.0 using lime can increase soybean yields by 15 percent.

Increasing the yield of grass is not really my goal, but I’m trying to take this all in.

The field as a whole is now “low” in phosphorus as opposed to “very low” in 2005, meaning it’s improved in phosphorus, despite me refusing to fertilize it for 15 years. Nonetheless, the scientist referred to the current phosphorus level as “quite deficient.”

He said phosphorus is largely responsible as a component in stimulating growth. When plants grow, cells divide, and plants must have adequate phosphorus for that process to happen. He said phosphorus drives root growth as well as overall growth of a plant. Nitrogen does that, too.

I asked about the nitrogen level since I was worried that too much nitrogen may be causing the horses’ problems.

He said the nitrate was a little elevated, meaning that it probably reflects some sort of fertilization, as in from a manure source. He said it’s not a number that he would say is excessive. It is normal with respect to the fact that this field is a pasture. He added that nitrogen is extremely mobile. With rainfall, nitrate levels will drop. He left it there. He was not worried about the nitrate level.

All the other minerals near the septic area and in the field as a whole are in the high area, which the scientist explained was actually the upper end of normal.

The area around the septic drain field had elevated nutrients compared to the rest of the field, but the scientist said this elevation was not dramatic.

He said that, if my horses were having nutritional issues — and he prefaced this by saying he is not a horse person — he would have a difficult time pinning it on the soil nutrients in this field being out of whack. He said there must be other contributing factors.

However, the low pH level should not be overlooked, he said, because it’s lower than it would appear at first glance.

The numbers for pH are not on a linear scale.

The difference in pH from 7 to 6 is a factor of 10, as in soil with a pH of 6 is 10 times as acidic as soil with a pH of 7.

The difference from 7 to 5 is a factor of 100, as in soil with a pH of 5 is 100 times as acidic as soil with a pH of 7.

Acidic plants don’t grow optimally.

The quality of the grass is less than optimal, and overall growth is less than optimal.

I asked if a plant in acidic soil would have higher levels of sugar because it’s not growing.

He gave it some thought and then said that would seem the opposite of what he would expect.

He said when we refer to sugar, we’re talking about the carbs in plants.

Plants photosynthesize, or take sugar along with carbon dioxide and convert that to energy for the plant.

In a field that is less than optimal, it doesn’t make sense to him that there would be more sugar in the plant. If anything, it’s going to be the other way around, he said.

Plant scientist Kathryn Watts, a horse owner herself, has done studies that suggest that improved grasses have more sugar, allowing them to do well in less-than-ideal conditions, and, when this sugar is not used for growing, it accumulates in the grass. I didn’t go into this with the scientist, as I felt like I had used up enough of his time. But it’s interesting to me that this sugar theory is not well-known and runs opposite to conventional thinking by people working in this field for a long time.

At any rate, to move the pH more toward neutral, I would need to add lime.

For limestone to be effective, you need to know the rating of the limestone material in terms of corrective treatment. Limestone varies in quality. A common rating for a ton of limestone is 400 to 500 percent effective neutralizing material.

My test suggests that I should use 1,200 pounds of effective neutralizing material. If the limestone has an ENM of 400, then I need 3 tons of lime per acre to raise the pH to the proper level.

I asked about the iron in my field being on the line between high and very high.

He said my levels are still in the normal range or the slightly upper end of the normal range, not out of kilter.

He said manganese, iron and copper are micronutrients, and plants use these in very small quantities. All three are well within normal parameters.

He said he’d like to see the “medium” and “high” lab ratings say “satisfactory” instead. He said the high reading tends to make people get a false sense of a problem where none exists.

He also pointed out that the ratings were influenced by the specific “cropping option” I chose (I chose cool season grass, because cool season grass can produce fructan, particularly when stressed, and I wanted to evaluate the field with that in mind). If I had chosen grass or legumes, the ratings would have been lower.

Beyond the lime, the extension office is recommending I put down 60 pounds per acre of nitrogen, 30 pounds of phosphorus and 20 pounds of potassium. As I explained in my previous post on fertilizer, I won’t be doing that.

However, if the wallet allows, I’m willing to add the lime. I had to call him back to ask when to do so. He said I could add it any time as long as the ground is firm. I don’t need to worry about it washing off unless a torrential downpour is in the forecast.

He said to add the lime all at once, and once should correct the acidity for maybe five to six years. Acidic soil is the result of a natural process of soil development and weathering. It’s a chemical reaction of soil’s ongoing degradation. As plants die and leave behind debris over a long period of time, the soil becomes more acidic. He emphasized that, if acidity is identified, it should be corrected.

I have no tractor, so adding 3 tons of lime per acre is going to be no small feat.

The things we do for our horses.



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