Available Soil Phosphorus Affects Herbage Yield and Stand Persistence in Forage Chicory

Low available soil P (ASP) may contribute to poor productivity of forage chicory (Cichorium intybus L.). The effect of ASP on forage yield and stand loss was evaluated over two harvest years for three chicory cultivars ('Puna', 'Forage Feast', 'Lacerta') at sites with low [West Virginia (WV), Gilpin silt loam (fine-loamy, mixed, mesic Typic Hapludults)] or high [Pennsylvania (PA), Hagerstown silt loam (fine, mixed, semiactive, mesic, Typic Hapludalfs)] ASP. Low (LP), medium (MP), and high (HP) ASP treatments averaged 6, 27, and 41 mg kg(-1) of Bray-P for LP, MP, and HP in WV, and 30 and 41 mg kg(-1) for MP and HP in PA. Across all data, critical soil P for 95% of maximum dry matter yield (DMY) was approximately 30 mg kg(-1) of Bray-P. Cumulative DMY of all cultivars increased with soil Bray-P in the first year after planting, but in the second year, only Forage Feast DMY increased with soil Bray-P. Cumulative DMY declined 45, 69, and 89% from the first to second year after planting for Puna, Forage Feast, and Lacerta, respectively. Across cultivars and time, stand density increased 12% as ASP increased from LP to MP, but medium to high ASP was associated with stand decline via increased bolting of Lacerta and frost heaving of Forage Feast. Across cultivars and sites, stand densities of less than 50 plants m(-2) in September predicted poor cumulative DMY in the following year. Phosphorus fertilization improved overall forage chicory DMY and persistence when ASP was low, but may contribute to bolting, heaving, and stand loss at high ASP.