Interactive effect of phosphorus and nitrogen on leaf anthocyanins, tissue nutrient concentrations, and dry-matter yield of floralta limpograss during short day length

A field trial was conducted during the short-day period of 2004-2005 at Ona, Fl., to study the factorial effect of nitrogen (67, 90, and 134 kg N ha(-1)) and phosphorus (0, 5, 10, 20, and 40 kg P ha(-1)) rates on forage dry-matter yield, quality, nutrient uptake, and leaf pigment concentration of limpograss (Hemarthria altissima). The N and P fertilizers were applied 45 days before each of two harvests. There was no interaction between N and P rates on any of the measured variables. Cool-season forage yield increased curvilinearly from 137 to 350 kg ha(-1) in winter and 237 to 1389 kg ha(-1) in early spring, whereas crude protein (CP) concentration increased from 145 to 158 g kg(-1), as P was increased from 0 to 40 kg ha(-1), but yield and CP were not affected by N rate. There was a decreasing linear relationship between leaf concentration of anthocyanins and P rate of application such that forage obtained with 0 kg P ha(-1) had 61% more leaf anthocyanins and purple pigmentation than with 40 kg P ha(-1). There was no effect of N on anthocyanins content. It was concluded that increased level of leaf anthocyanins was due to the cumulative stress from cool weather and lower plant-tissue P levels, which resulted in reduced growth and yield of limpograss. In cool weather, P played a critical role in controlling leaf purple pigmentation and forage yield.