Abstract
The objective of the study was to compare forage yield and quality responses of 'Redalta', 'Floralta', and 'Bigalta' limpograsses (Hemarthria altissima (Poir.) Stapf et C.E. Hubb.) to cutting frequency (CF) and nitrogen (N) fertilization. The grasses were grown near Gainesville. Florida, on a poorly-drained siliceous hyperthermic Ultic Haplaquod soil. Grasses were cut at 3-, 6-, 9-, 12- or 18-week CF and fertilized with 0. 60, 120, 240 or 480 kg N ha yr Thirteen combinations of the five CF and five N rates were arranged in a modified central composite design with treatments replicated three times. Dry matter (DM) yield, crude protein (CP) and in vitro organic matter digestibility (IVOMD) of 6-week regrowth were compared for the three cultivars. Mean values of CP (g CP kg-1 DM) and IVOMD (g digestible organic matter (DOM) kg-1 OM) for all cultivars were 50 and 470 in a mid-summer cut, as opposed to 90 and 550 g kg-1 for late-autumn forage. The CP and IVOMD were compared among cultivars and seasons for 27 July and 30 November cuttings using response surfaces. On 27 July, 3-week regrowth of Bigalta had IVOMD 120 and 240 g kg 1 higher than Floralta and Redalta respectively, and the most mature Bigalta herbage (18-weeks) had IVOMD 60 and 150 g kg-1 higher than Floralta and Redalta, respectively. In nearly all cases, the quality of grass of similar age was higher on 30 November than 27 July. The CP concentrations dropped below 70 g kg-1 for 6-week regrowth in summer, but sustained similar levels until 9 weeks in autumn. Total non-structural carbohydrate that accumulated in herbage during cool seasons partially explained increases in herbage quality. Optimum combinations of yield and quality would be obtained with adequate N fertilization (60-100 kg N ha-1), 4-5 week cutting intervals in the summer and 6-8 week cutting intervals in the spring and autumn.
