ABSTRACT
Summary Aspects of the production of rhodesgrass (Chloris gayana Kunth) and green panic (Panicum maximum var. trichoglume) as roughage for high-grade dairy cattle when land and water resources are limited are described. Results from some 10 years of research are highlighted. The height of the canopy to which grasses should be allowed to regrow for maximum production is above the height that can be utilized efficiently when harvested in situ by cattle. Mechanical harvesting and indoor feeding provided 20%-25% more digestible dry matter/unit area of land (with a parallel increase in water-use efficiency) than strip grazing, almost without affecting the level of milk production. The efficiency of a single application of N fertilizer after cutting sharply decreased when the interval between irrigations was long, apparently due to leaching below the relatively shallow root system. Frequent irrigation and nitrogen application resulted in optimum uptake of nitrogen and high sustained yields during the season and over the years. Sewage effluent (containing about 50 ppm N) is an excellent source of water and of plant nutrients. The rate of initial regrowth after cutting was inversely related to the length of the period before cutting, particularly during stem elongation and flowering, which is promoted by high temperature. Relatively long cutting intervals in spring are permissiable and result in high dry-matter yields of relatively high digestibility. During summer, shorter cutting intervals are necessary in order to obtain comparable yields of digestible nutrients. Yields of 25 and 35 metric tons (t)/ha/season of rhodesgrass and green panic, respectively, were recorded from commercial fields. In-vitro digestibility of green panic was approximately 10% higher than that of rhodesgrass.
