THE FLORIDA CATTLEMAN AND LIVESTOCK JOURNAL
SWFWMD Community Education Grant
Reyna Speckmann and Maria Silveira, Range Cattle REC
Soil and plant tissue testing are excellent tools for identifying lime and fertilizer requirements in bahiagrass pastures. The Range Cattle Research and Education Center in Ona provided free soil and tissue testing for the first 200 samples of established bahiagrass pastures received between April 1 and June 30, 2010 as part of a SWFWMD Community Education Grant. In addition to the testing results, participants received fertilizer recommendation and copies of education materials related to fertilization management.
One hundred and sixty nine paired soil and tissue samples collected from established bahiagrass pastures in the Alafia River, Peace River, and Manasota basins were submitted to a commercial laboratory for analysis. Soil samples were analyzed for pH, phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), zinc (Zn), and manganese (Mn) using the Melich-1 extraction procedure. Sulfur (S), boron (B), iron (Fe), and copper (Cu) results were also provided for most samples. Plant tissue samples were analyzed for nitrogen (N), P, K, Mg, Ca, S, B, Zn, Mn, Fe, and Cu.
Samples submitted for this extension effort were solicited from beef cattle producers through industry advertisement and word of mouth; as such, the results described herein do not represent all soils in the participating basins and are not intended to be indicative of average bahiagrass pasture nutrient loads in the Alafia River, Peace River, or Manasota water management basins. Nearly 65% of the samples received came from pastures in the Peace River basin; samples from the Alafia River and Manasota basins contributed 11 and 24%, respectively (Figure 1).
Soil and Tissue Results
As summarized in Table 1, soil acidity ranged from 4.2 to 8.0. The target pH for bahiagrass is 5.5; samples submitted for analysis averaged slightly higher than the target. Approximately 44% of the samples submitted fell between 5.1 and 5.9. Many of the high pH samples came from bahiagrass pastures treated with biosolids and reclaimed mine lands. Samples collected from reclaimed mine lands also account for the excessively high soil P values we observed. If reclaimed mine samples are excluded from calculation, the average is reduced drastically to approximately 20 ppm, within the range defined by UF-IFAS soil scientists as medium. Soil P was very low or low in 68% of the samples analyzed. Only three samples, however, also exhibited tissue P concentrations below the critical level of 0.15% to warrant P fertilization. Soil K was very low in 32% of samples, low in 40%, medium in 15%, and high in 13%. Only one sample returned a very high level of K.
Soil and tissue nutrient results were also summarized within pH ranges and soil P interpretation ranges (data not included). As expected, Ca and Mg increased with pH. Of the 19 samples with pH greater than 7.0, only 5 had very high P levels. Each of these five samples also had K levels in the low to medium range, suggesting that the soils received biosolid application. The remaining soils with pH greater than 7.0 exhibited predominately low or very low P, and K levels in the medium, low, or very low range, suggesting an overuse of lime in the absence of N-P-K fertilizer.
Fertilizer recommendations were provided in accordance with the IFAS recommendations set forth in “UF/IFAS Standardized Fertilization Recommendations for Agronomic Crops” (SL129). Low, medium, and high nitrogen options were provided for each pasture tested. This document instructs producers to choose the nitrogen option that best fits their fertilizer budget, management objectives, and land capability. It is also advised to consider the potential for economical return on the fertilizer investment before using the medium or high nitrogen options, as the added forage may not be worth the cost.
The Low option recommends 50-60 lb N with no additional K2O; application of 25 lb P2O5 is only recommended if soil P is low or very low and tissue P concentration is below 0.15%. The medium option advises 100 lb N per acre with 50 lb K2O if soil is very low or low in K. Application of 25 lb per acre of P2O5 is only recommended if soil P is low or very low and tissue P concentration is below 0.15%.
The high option is rarely cost-effective and seldom practiced by beef producers. Nitrogen is recommended in a split application totaling 180 lb per acre. Potassium, as K2O, is recommended at 80 lb for soils testing very low or low and 40 lb for soils testing medium. No K2O is recommended for soils high or very high in K. No P2O5 is recommended unless soil P concentration is very low or low and tissue P is below the critical level. If both criteria are met, 40 lb/A P2O5 is recommended.
Lime recommendations were provided for all samples below 5.3, to a target of 5.5. Slightly more than half the samples (52%) required lime to increase pH. Only three recommendations for P2O5 were made, despite very low or low soil P in 72% of samples, as a result of the critical level of 0.15% identified in plant tissue. Approximately 72% of samples fell in the very low or low K range to receive a recommendation for K2O under the low and medium N options. Approximately 15% of samples had medium levels of K and received a K2O recommendation under the high N option. Approximately 13% of samples were high or very high in K, and received a recommendation for no K2O at all N options.
Impact and Implications
One hundred and sixty nine pastures in the local agriculture community will receive fertilizer as determined by soil test. The potential impact of this may include a reduction in unnecessary phosphorus and potassium applications. Of the pastures sampled, only three had tissue P levels below the critical level to warrant P fertilization. This critical level is based on the level at which plants will respond to supplemental P. While the 0.15% critical level seems low, data from the Range Cattle Research and Education Center in Ona indicates that plants will not respond to supplemental P if tissue P is at or above 0.13% ± the standard error.
If you haven’t already…
Now is an excellent time to sample your pastures. Lime doesn’t become biologically active in the soil for three to six months. So, if you did not participate in the free program earlier this year, now is an excellent time to determine if your soil will need a fall lime application to correct pH before the spring growing season. A number of educational documents related to soil and tissue testing, liming, and fertilizer can be found on the UF IFAS ‘EDIS’ website (http://edis.ifas.ufl.edu) or by contacting your county’s livestock extension agent.