The Real Cost of Cutting Lime
It's January. We've survived the holiday and calving seasons and need to start thinking about warm season pasture management. As the economy and high fertilizer prices continue to drive many of our pasture management decisions, we’re all looking for opportunities to maximize inputs or cut them all together. Cutting lime applications, however, may cost our pastures more than it saves. The fall is the most appropriate time to soil test and lime the pastures, however, it is never too late to perform soil tests and decide the liming and fertilization strategies to provide the desired forage yield and quality in the coming spring.
The pH index is a measure of hydrogen ions (acidity) in the soil. Most Florida soils are acidic and may require lime application to bring the pH to the optimum level for warm season grasses. Repeat applications of nitrogen fertilizers can further increase soil acidity by increasing the number of hydrogen ions. Some soils are better able to maintain pH following fertilization than other soils. This, termed buffering capacity, is largely dependent on a soil’s clay and organic matter components. Because of these inherent differences, the only way to accurately determine lime requirement is by performing a soil test.
pH and Nutrient Availability
Nutrient availability and soil pH are closely linked; optimal pH is requisite for root development and efficient uptake of soil nutrients. The IFAS recommended pH range for each pasture forage is the pH at which root growth and development, and water and nutrient uptake are maximized for that particular species. Outside of these ranges, roots are less able to efficiently utilize fertilizers and soil nutrients.
When soil pH is below 5, nitrogen, phosphorus, and potassium availability typically decrease, which may in turn limit the roots’ ability to take up macronutrients and ultimately reducing forage production.
The same principle applies to soil at high pH. Micronutrients (iron, manganese, zinc, copper, and cobalt) become less available in high pH soil, resulting in production failures similar to those associated with overly acidic soils.
As such, applying fertilizer to soil below its optimal pH range will not likely provide cost-appropriate increases in forage yield and quality. For instance, applying nitrogen without addressing lime can be detrimental, ultimately exacerbating damage caused by insects and diseases.
Lime recommendations are specific to the type of forage indicated on the soil test submission form. Recommended lime application rates are based on the soil sample’s pH and buffering capacity and the target pH for the forage species. A soil with high buffering capacity (high organic matter and contents) will likely require more lime to reach the target pH than will a soil of similar pH and low buffering capacity. In general, sandy soils of the flatwoods and central Florida have lower buffering capacities and thus require less lime to raise the pH than loamy soils. However, soils with lower buffering capacities will require more frequent lime applications to maintain pH. This is why you might have two different lime recommendations for pastures with the same pH; one has a higher buffering capacity than the other. The ‘rule of thumb’ that one ton of lime will raise the pH one unit is a generalized approximation and not always reliable due to these inherent differences in soil characteristics. It is well worth the time and money to test the soil to obtain a more reliable lime recommendation.
The Cost of Cutting Lime
Field trials conducted at the Range Cattle Research and Education Center in Ona between1998 and 2007 compared fertilizer application, with and without lime. A 30% decrease in forage yield resulted from fertilizer application in the absence of lime to one of the experimental sites. For each acre of this pasture receiving fertilizer without lime, a 30% reduction of forage yield translated to 2,700 pounds of lost dry matter and ultimately 1431 lbs of TDN, and 257 lbs of crude protein over one season. The replacement value of this yield reduction, per unit of TDN and CP, is considerable and illustrates the potential cost of skipping a recommended lime application. It would require approximately 32 bags of a 20% range cube to replace these nutrients. At $9 per bag, the cost of skipping lime in the above situation was approximately $288 per acre. While yield losses and subsequent nutrient replacement costs can vary significantly, the above situation, observed under research conditions, illustrates one potential result of skipping a necessary lime application.
Further confounding the issue, repeated fertilizer applications in the absence of lime also decrease root/stolon masses and create favorable conditions for mole cricket and weed infestations. Nematodes for mole cricket control will cost roughly $25 per acre, not including any costs associated with application. Common pasture herbicides range on average anywhere from $10-15 or more per acre and do not include any application related costs.
Half of the experimental pasture described above was treated with one ton per acre of dolomite every three years. When receiving lime, soil pH remained within the optimal range for bahiagrass, and yields were within expected ranges. The cost of lime and application in this example was $32 per acre per year.
The results of a soil test are only as reliable as the sample collected. Literature detailing proper sampling technique can be obtained through the UF-IFAS EDIS website (http://edis.ifas.ufl.edu/) or from your county’s IFAS Cooperative Extension Service. Soil samples can be analyzed by the IFAS Extension Soil Testing Laboratory or a private laboratory of your choosing. Because IFAS recommendations are based on the Melich-1 extraction and the adams-evans procedures, it is essential that the analyzing laboratory also uses these procedures. It is not possible to interpret or convert results from labs using alternative methods. Your county’s IFAS Extension Agent can assist you with the soil test interpretation and fertilizer recommendations.