Nutrient Removals by Pinestraw Harvesting in Slash Pine Plantations in Florida

Pinestraw harvesting is an important industry in the southeastern United States. There is a need to understand how fertilization can be used efficiently to sustain or increase long-term pinestraw yields and avoid adverse environmental consequences. The effects of fertilization on needlefall nutrient concentrations, pinestraw yields, and nutrient removals on soils with contrasting soil nutrient sorption potential (Entisol vs. Ultisol) were compared using two midrotation slash pine plantations in North Florida. Diammonium phosphate was applied at 0, 144, 430, or 718 kg ha(-1) in the spring of 2009 and 2010. Pinestraw was harvested annually in 2009-12. Needlefall mass, pinestraw yields, total Kjeldahl nitrogen concentrations in needlefall and pinestraw, and total Kjeldahl nitrogen, P, K, Ca, and Mg removals increased with fertilization. Diammonium phosphate at 718 kg ha(-1) year(-1) increased pinestraw yield over the control by 37 and 35 percent 2 years after the second fertilization, and by 11 percent (from 21.5 to 23.8 Mg ha(-1)) and 12 percent (from 25.0 to 28.1 Mg ha(-1)) over the 4-year control totals, at Entisol and Ultisol sites, respectively. Differences between sites were larger than fertilization response for most variables. Yields, nutrient concentrations, and removals were higher at the more fertile Ultisol than Entisol and, at both sites, higher than most reported in the literature. Study Implications: Results from this study provide guidelines for efficient fertilization of slash pine stands managed for annual pinestraw harvesting, to mitigate nutrient depletion and avoid excessive fertilization. Study sites with contrasting nutrient holding capacity and drainage class provide experimental data to support site-specific best management practices for pinestraw production. Pinestraw yields and nutrient removals are greater from higher-productivity sites, therefore requiring greater fertilizer inputs. Mineral fertilization can increase pinestraw yields on sites with adequate nutrient and water-holding capacity, given sufficient precipitation and competing vegetation control. Some yield increase is also possible on deep sandy sites, but the modest benefit may be outweighed by the potential for negative environmental impact. Pinestraw yield responds positively to additions of deficient nutrients; therefore, fertilization should be based on foliar nutrient analyses. Pinestraw harvests remove considerably more nitrogen than any other nutrient. High pinestraw yields on fertile sites, similar to our Ultisol, can be sustained with application of approximately 40 kg N ha(-1) annually or 80 kg N ha(-1) biennially. P applications depend on inherent soil P content, but a one-time application of 25-30 kg P ha(-1) at midrotation should support pinestraw yields for the following 5-7 years if P status is adequate prior to onset of raking.