Winter Cereal–Corn Double Crop Forage Production and Phosphorus Removal

Maximizing P removal with cropping can increase regulated P‐based manuring rates or reduce soil test P in manure‐enriched soils. The potential for increased P removal with winter forage–corn silage double cropping was evaluated in a 3‐yr study at Parma, ID. Winter barley ( Hordeum vulgare L.), and both winter and spring genotypes of wheat ( Triticum aestivum L.) and triticale (× Triticosecale Wittmack) were fall planted at three seeding rates (112, 168, or 224 kg ha −1 ) and followed with silage corn ( Zea mays L.). Corn alone and a noncropped treatment were included. Winter forages were harvested near boot stage. Seeding rates of 168 kg ha −1 were necessary for maximizing winter forage production but had little effect on P uptake. Winter forage production and P content were highly year dependent due largely to appreciable winterkill of spring wheat and winter barley in 1999. Winter forage P concentrations, unlike those for corn, decreased with successive harvests. Cumulative P uptake ranged as high as 65.7 kg ha −1 for winter triticale. Winter forages reduced corn yields in 2 of 3 yr and corn P uptake in 1 yr. Compared to corn alone, double cropping increased cumulative forage production from 8.4 to 15.9% and total P removal by 29.8 to 42.2%. Soil test P concentrations after 3 yr decreased more with double cropping than with corn alone. Half of the P decline was unrelated to P uptake and removal. Double cropping can increase total forage production, P removal, and hasten soil test P decline.