Effects of rate, placement, and frequency of P application on yield and P content of bromegrass-red clover herbage and soil P distribution
This study was conducted on a P-deficient Dark Grey Solod to compare the effects of the rate (0, 45, 90 kg P ha−1 cumulative), placement method (broadcast vs. banding), and frequency (preplant only vs. annually) of P fertilizer application on herbage production by a bromegrass (Bromus inermiss Leyss)–red clover (Trifolium pratense L.) mixture. The preplant broadcast application was incorporated by rototilling, and subsequent broadcast applications were topdressings. Annual applications continued for 3 yr only and dry matter (DM) yields were taken for 4 yr following the establishment year in 1991. Rate of P applied had the greatest effect on herbage yield, but its effect was influenced by the frequency of application. When P fertilizer was applied annually, herbage yields increased linearly with application rates. When P was applied preplant only, herbage yields reached a plateau with 45 or more kg P ha−1. Broadcasted P yielded slightly more than banded-in P in the first year harvest only. Annual application of 30 kg P ha−1 gave the highest cumulative herbage yield, suggesting decreasing P availability with time. This was supported by soil P analysis in 1994 and by herbage P concentrations. Herbage P concentration was significantly correlated with herbage yields of the second year and subsequent harvests. It is concluded that a preplant broadcast-incorporated application of 30 to 45 kg P ha–1, followed by at least one subsequent surface application of 30 kg P ha–1 was required for optimum herbage production by a legume-grass mixture. Key words: Application method, P fertilizer management, bromegrass-red clover, Grey Luvisol, soil P distribution