– Rory Lewandowski, Extension Educator, Athens County
One of the major agricultural limestone providers in Athens County recently announced a big increase in the cost of delivering/spreading limestone. At $50/ton the price has doubled compared to a year ago. Comments from several farmers regarding the economics of lime application prompted me to read through the liming section of the Ohio Agronomy Guide, and to send some questions off to Dr. Robert Mullen, OSU Extension soils specialist, about soil testing and lime application in pastures and hayfields.
Before I get to the questions I posed to Dr. Mullen and his response, let’s review some of the basics about soil sampling and lime recommendations. From the onset we need to understand that soil testing is not an exact science, but it’s the best tool we have available to give us some information related to soil fertility and soil pH. Soil test information can be made more reliable by doing a good job of soil sampling. Good soil sampling involves taking numerous sub-samples within a given pasture/hayfield that are each sampled at a consistent depth. A representative soil sample is then pulled from the combined sub-samples. Ideally, soil samples in any given pasture or hay field will be taken at the same time of year each time a soil test is done. Fall and spring are both good times to sample soil, just make sure that a field sampled in the fall continues to be sampled in the fall across years and that fields sampled in the spring continue to be sampled in the spring across years.
The soil pH is a measure of the active soil acidity or alkalinity based on a scale from 1 to 14. A simple explanation of soil pH is that it is a measure of the concentration of hydrogen ions in the soil. The higher the concentration, the more acidic the soil is. On the pH scale, 1 is very acidic and 14 is very alkaline. Many of you have seen the chart that shows the availability of elements essential to plant growth at different soil pH levels. Some of the macro elements such as nitrogen, potassium, sulfur, and calcium, don’t become fully available to the plant until the soil pH is 6.0. Some elements such as phosphorus and magnesium need a soil pH of 6.5 before they are fully available. Most of the grass species found in pasture and hay fields do best in a soil that is above 6.0 on the pH scale. Legumes prefer a soil pH closer to 6.5.
The lime requirement is based not on the actual soil pH, but rather on the buffer pH or the lime test index. Lime neutralizes hydrogen ions, causing soil pH to increase. Not all soils respond to a given lime application in the same way. Some soils have the ability to buffer (or resist) changes in soil pH by releasing hydrogen ions that are held on soil particles. Other soils have a lower capacity to release hydrogen ions. Soils that have a higher buffering capacity require more lime to reach a certain, desired, soil pH level as compared to soils with a lower buffering capacity. All lime recommendations are given in terms of agricultural limestone needed in tons/acre to increase soil pH to some desired level or soil pH goal. The tons/acre recommendation is based on a limestone material with an effective neutralizing power (ENP) of 2000 lbs/ton. This recommendation is also based on an 8-inch depth soil sample.
All limestone materials are not equal. Some limestone materials have a higher ENP than others. Some limestone materials are dolomitic, meaning that they also contain magnesium. In Athens County, since our soils tend to be low in magnesium, a dolomitic limestone material should be applied. Do not assume that the limestone material you are applying has an ENP of 2000. It is common that limestone materials have lower ENP values. This means more of the material will have to be applied to satisfy the lime recommendation. Your lime supplier should be able to provide you with a tag that contains the ENP value. Sometimes they will provide a total neutralizing power (TNP) value along with a fineness grade that provides a percentage of the limestone material passing various mesh sizes. The ENP can be calculated from the TNP and fineness grades. Remember, the TNP does NOT equal the ENP. A material could have a TNP of 100 and be equal to an ENP of 2000 or less. There are limestone materials that have a TNP of 105 with an ENP of less than 2000.
Let’s consider an example of 2 limestone suppliers in the Athens County area. Both can provide dolomitic limestone materials. Supplier A provided me with a tag that stated a TNP value of 105 and fineness grades of 97% passing an 8 mesh screen, 85% passing a 20 mesh screen and 60% passing a 60 mesh screen. From this tag information, I calculated the ENP at 1620. This is 81% of a 2000 value ENP. Supplier B provided me with tags from 2 different dolomitic limestone materials that had TNP and ENP values. Both materials had TNP values of 100, but the ENP value of the coarser material was 1088, while the ENP value of the finer material was 1450. The material with an ENP value of 1450 is 72.5% of a 2000 value ENP and the material with an ENP of 1088 is 54.4% of a 2000 value ENP. Suppose we had a lime recommendation for 2.0 tons/acre. Remember that the recommendation is based on a material with an ENP value of 2000. To meet this recommendation it would take 2.47 tons/acre of the limestone from supplier A and 2.76 tons/acre of the finer limestone material from supplier B. If the coarser limestone material from supplier B were used it would take 3.68 tons/acre to meet the lime recommendation. Once the cost of limestone materials are calculated on a per pound basis and multiplied by the actual application rate, it might turn out that cheaper materials are not the best bargain.
All right, now it is time to get back to the questions I posed to Dr. Mullen that I mentioned at the beginning of this article. When I read the section on liming in the Ohio Agronomy Guide, I noticed that the section that dealt with no-till fields said to take two separate soil samples. One sample should be at a 0 to 4 inch depth for the lime requirement and the other sample at the 0 to 8 inch depth for the phosphorus and potassium recommendation. I asked, in an email to Dr. Mullen, if soil sampling from pastures and hayfields should follow this same guideline. Specifically, should each pasture paddock or hayfield be represented by a soil sample from the 0 to 4 inch depth to reflect soil pH and provide a lime recommendation, as well as include a soil sample from a 0 to 8 inch depth to reflect soil phosphorus and soil potassium levels? Dr. Mullen’s response back to me was:
“Absolutely. Treat pastures and hay fields just like a no-till production soil.”
On one hand this means more work and expense to properly soil sample. On the other hand, this will provide soil test information that is better suited to pasture and hay fields. Also, since the soil pH sample will be from the 0 to 4 inch depth, the lime recommendation will be one-half of the lime recommendation chart contained in the Ohio Agronomy Guide, which will result in some economic advantage.
In these challenging economic times, with increasing input costs, beef producers need to get the best possible production from pasture paddocks and hay fields. Rethinking how soil samples are gathered and how recommendations are made will allow good economic decisions to be made regarding limestone applications.