Nitrogen in the P Band for Forage Establishment

Band seeding, a recommended practice for forage establishment, increases seedling growth primarily because of early P uptake. Ammonium N (NH₄⁺) has been demonstrated to increase P uptake with several crop species. The objective of the experiments reported herein was to determine if the inclusion of N as NH₄⁺ in the P band would result in a further increase in the seedling weight of forage species. Five field experiments were conducted on a Typic Hapludalf soil using hand placement of the fertilizer band and seed in 1 m rows of alfalfa (Medicago sativa), bird'sfoot trefoil (Lotus corniculatus), and bromegrass (Bromus inermis). Monocalcium phosphate, labelled with ³²P, was placed in a band 5 cm directly below the surface placed seed with NO₃⁻ supplied as Ca(NO₃)₂ or NH₄⁺ supplied as (NH₄)₂ SO₄. Dry weight per plant, total up take of P and uptake of fertilizer P were measured 5 weeks after seeding. Band seeding up to 30 kg P/ha increased seedling growth as much as five-fold in all experiments regardless of species or soil test level for P. Consistent evidence that NH₄⁺ was increasing the concentration and/or up take of fertilizer P and hence the concentration and/or uptake of total P by forage species was not established. In one experiment, up to 52% greater seedling growth of alfalfa, in addition to that obtained with P alone, was obtained by including NH₄⁺ in the band in contrast to a 20% increase with NO₃⁻. In a second experiment, inclusion of N in the band increased growth by 11% without a preference for the form of N. Using ³²P techniques one of two experiments showed the increased growth associated with the N applications was due to enhanced fertilizer P concentration and uptake, and hence increased total P uptake resulting from including the NH₄⁺ nitrogen in the P band. It is concluded that NH₄⁺ in the P band is of minor importance for increasing early seedling growth of cool season forage species.