Inorganic phosphorus and manure effects on bahiagrass production on a Spodosol

Bahiagrass (Paspalum notatum Flugge) pasture fertilization recommendations have traditionally been based upon clipping studies. Inclusion of P from ma nure, not originally considered when P recommendations were developed for p astures, may minimize the need for P fertilization without reducing bahiagr ass production or P uptake. The objective of this research was to determine if manure contributes greatly to the P crop nutrient requirement. A 2-year field study utilized a factorial arrangement of 0 and 6.9 Mg air-dried man ure ha(-1) with 0, 17, 34, 51, and 68 kg inorganic P ha(-1) from triple sup erphosphate to evaluate bahiagrass yield, root distribution, and P uptake r esponse on a Myakka fine sand (sandy, siliceous, hyperthermic Aeric Alaquod ). Because air-dried manure was used in the field study, a greenhouse study was employed to confirm that there were no differences in bahiagrass yield or P uptake from either air-dried or fresh cattle (Bos spp.) manure source s. There were no manure or manure by P interaction effects on yield or P up take of bahiagrass indicating that manure source did not effect grass produ ction in the greenhouse. In the field study, bahiagrass roots were distribu ted into the Bh horizon, and the Bh horizon had at least four times more Me hlich-1 extractable P than that of the Ap horizon. This horizon was most li kely acting as a main source for P-uptake by the grass. This observation wa s further confirmed by no yield response to levels of inorganic P applicati on in 1989. A linear-response-and-plateau (R-2=0.196) relationship with a c ritical point of 15.4 kg P ha(-)1 was found in 1990. Bahiagrass yield and P uptake were not dependent on P fertilization, either from manure or inorga nic P, due to the availability of P from the Bh horizon.