Economics of Lime and Phosphorus Application for Dual-Purpose Winter Wheat Production in Low-pH Soils

After decades of continuous cropping, the pH of many soils used to produce continuous winter wheat (Triticum aestivum L.) in the southern plains of Oklahoma has declined to levels that limit wheat grain and forage yield. Data from a 3-yr study were used to determine the effect of lime and diammonium phosphate (DAP) application on fall-winter forage yield and grain yield of winter wheat grown in extremely add soil and to determine the economically optimal strategy for dual-purpose (forage plus grain) wheat production. A split-split plot with sub-subplot treatments arranged in a randomized complete block design was used, with lime in the main plots, variety in the subplots, and DAP in the sub-subplots. Grain yield significantly increased (α = 0.05) with lime at 2800 kg ha -1 effective calcium carbonate equivalent (ECCE), DAP at 73 kg ha -1 applied in seed furrows, or DAP at 146 kg ha -1 broadcast. Forage yields were greatest when DAP was applied at 146 kg ha -1 in seed furrows (a = 0.05). When lime costs were fully assessed in the year of application, the strategy of applying 73 kg ha -1 DAP in seed furrows and zero lime generated the greatest expected returns across all forage value estimates and grain prices. With lime costs amortized over a 5-yr period, the optimal strategy included both the application of lime before the initial season and 73 kg ha -1 DAP in seed furrows in each season.