Importance of Nitrogen and Phosphorus for Production of Grasses Established with No-Till and Conventional Planting Systems

Abstract

High stocking rates and season-long grazing practices have produced excessively grazed pastures in northeastern and eastern Nebraska dominated by smooth bromegrass (Bromus inermis Leyss.) that are in need of renovation. There is a void of high-quality forage in midsummer that can be filled by either warm-season species or cool-season species that mature later than smooth bromegrass. Intermediate wheatgrass [Agropyron intermedium (Host) Beauv.] or switchgrass (Panicum virgatum L.) was seeded by either no-till or conventional seeding practices in the spring of 1978, following a fall application of a mixture of atrazine [2-chloro-4-(ethylamino)-6-(isopropyl-amino)-s-triazine] and glyphosate [N-(phosphonomethyl) glycine] at 1.0 and 2.0 lb/acre, respectively. Established stands were fertilized with N (0, 40, 80, and 120 lb/acre) and P (0, 40, and 80 lb/acre). A complete factorial design with three replications was used. Fertilizer treatments were repeated each year through the 1982 growing season. Forage yields were consistently increased by the application of both N and P, and there was a consistent N × P interaction. The response to N and P rate was curvilinear for both methods of grass establishment. Conventional seeding techniques produced higher yields of intermediate wheatgrass, but yields of switchgrass were not affected by method of establishment. Nitrogen fertilization increased the protein content of both species. Protein concentration decreased with rate of applied P due primarily to plant dilution.