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All Washed Out? Foliar Nutrient Resorption and Leaching in Senescing Switchgrass

Ruth H. Burke, Kenneth J. Moore, Martin J. Shipitalo, Fernando E. Miguez, Emily A. Heaton
BioEnergy research 2017 v.10 no.2 pp. 305-316
Panicum virgatum, bioenergy, calcium, canopy, feedstocks, frost, grasses, leaching, leaves, magnesium, nitrogen, nutrient content, nutrients, perennials, phosphorus, potassium, rain, rainfall simulation, resorption, winter
Ideal bioenergy feedstocks are low in nutrients that act as anti-quality factors during conversion processes. Research has shown that delaying harvest of temperate perennial grasses until late winter reduces nutrient content, primarily due to end-season resorption, but also indicates a role for foliar nutrient leaching. While end-season resorption has been estimated, foliar nutrient leaching has not, and is a factor that could refine harvest recommendations. Additionally, establishing a baseline of mineral loss during switchgrass senescence will improve our understanding of leaf-level nutrient resorption. Therefore, we applied simulated rainfall to replicated (n = 5) plots within a previously established switchgrass stand to determine if heavy precipitation can induce nutrient leaching in senescing, unharvested foliage. Hour-long simulated rainfalls of ∼120 mm were applied every 2 weeks from early September to a killing frost in 2014 and 2015. Leaf samples were taken from the upper and lower canopy before and after simulated rainfalls and from no-rain controls and analyzed for elemental N, P, K, S, Mg, and Ca. Nutrient resorption estimates ranged from 33 to 82% in control plots. Comparison of rainfall plots to controls indicated that lower canopy leaves, upon reaching ≥50% senescence, were slightly susceptible to foliar nutrient leaching, with losses ranging from 0.3 to 2.8 g kg⁻¹ dry matter for K, P, and Mg. Nitrogen, Ca, and S were not susceptible to foliar leaching. Although statistically significant (P ≤ 0.05), these values suggested that foliar leaching was not a strong driver of nutrient loss during senescence.