Perspektief van het tropische grasland

Rede. Wageningen, 3 februari 196

Climate, nitrogen and grass. 6. Comparison of yield and chemical composition of some temperate and tropical grass species grown at different temperatures.

For part 5 see NAR 43, 148. 6. Lolium perenne, Festuca arundinacea and 2 tropical grasses, Axonopus compressus and Brachiaria ruziziensis, were grown in pots under day/night temperatures of 19 deg /12 deg , 24 deg /18 deg , 28 deg /23 deg and 34 deg /30 deg C and regrowth was cut after 18 and 35 days. The stemmy Brachiaria was much more productive than the others which remained vegetative. The optimum production temperature was 24 deg or less for the temperate grasses but >30 deg for the others. Yield was greatest after 35 days and with high N fertilization. Lolium had the highest average content of N, soluble carbohydrates and digestibility in vitro and Brachiaria the lowest. Digestibility declined with increase in temperature and age, most for Brachiaria. These effects were caused by an increase in content of cell-wall constituents and a decrease in their digestibility. N fertilization had no effect on digestibility. Results support the hypothesis that the low digestibility of tropical grasses is mainly due to the high temperature during growth but may be improved appreciably if stem formation is suppressed. ADDITIONAL ABSTRACT: Lolium perenne, Festuca arundinacea, Axonopus compressus and Brachiaria ruziziensis were grown in pots in a glasshouse under day/night temperatures of 19/12, 24/18, 28/23 or 34/30 deg C with intermediate or high N and regrowth was harvested after 18 and 35 days. Reproductive B. ruziziensis was much more productive than the other vegetative species. Optimum day temperature for production was 24 deg or lower for temperate grasses but >30 deg for tropical species. L. perenne had the highest contents of N and soluble carbohydrates and in vitro digestibility and B. ruziziensis the lowest, differences being smallest at the low temperature. There was a consistent decline in digestibility of all species with increase in temperature and age which was correlated with an increase in cell wall constituents but was not related to amount of N applied. [For Part 5 see HbA 43, 1557] (Abstract retrieved from CAB Abstracts by CABI’s permission

Climate, nitrogen and grass. 4. The influence of age on chemical composition and in vitro digestibility of maize (Zea mays L.) and tall fescue (Festuca arundinacea Schreb.).

In a field experiment with maize it was found that in vitro digestibility of leaves decreased somewhat during undisturbed growth, whereas digestibility of stems decreased appreciably. This decrease in leaf digestibility was caused by a lower digestibility of later-developed leaves and by a slight decrease in digestibility during ageing of each individual leaf. In a pot experiment with tall fescue grown at 15/10, 20/15 and 25/20 deg C, it was found that a higher temperature resulted in higher concentrations of cell-wall constituents and lower digestibility, whereas during ageing the percentage of cell-wall constituents remained constant or even decreased, digestibility decreasing slightly. Results suggested that in a constant climate the effect of age on digestibility would be small, and that the great effect of age on forage quality in spring is mainly due to rising temperature and stem formation. (Abstract retrieved from CAB Abstracts by CABI’s permission

The influence of defoliation and nitrogen on the regrowth of Rhodes grass (Chloris gayana Kunth). 2. Etiolated growth and non-structural carbohydrate, total-N and nitrate-N content.

Data are given on the chemical composition of Rhodes grass cv. Common grown in a heated glasshouse [see HbA 42, 1910]. Plants given high N (8.29 meq/100 g soil) contained about 30% less carbohydrate in the stubble and roots than those given low N (1.43 meq/100g). The carbohydrate content of plants cut every 28 days was generally lower than that of plants cut every 14 days. Amounts of etiolated growth in darkness after cutting were positively correlated with the carbohydrate level in the roots and in the stubble. The percentage of tillers exhibiting regrowth in darkness increased linearly up to about 60% with increase in the amount of etiolated growth. Contents of total N in roots and in stubble were almost double at the high rate of N. Amounts of nitrate as a proportion of total N were about 12% in low-N plants and up to 47% in high-N plants. The nitrate contents of shoots, stubble and roots were negatively correlated with the carbohydrate levels in each of these tissues. The overall difference in carbohydrate level between shoots, stubble and roots was relatively small. It was concluded that Rhodes grass had a limited capacity to accumulate reserve material when grown under conditions favouring rapid growth. (Abstract retrieved from CAB Abstracts by CABI’s permission

The influence of photoperiod on head formation in some Brachiaria species and Chloris gayana cv. Masaba.

The effect of the photoperiod on head formation was investigated in 5 Brachiaria spp. and selected ecotypes of C. gayana cv. Masaba. The experiments were conducted in the glasshouse with photoperiods of 10, 12 or 14 h in 1971 and 9, 10.25 or 12.5 h in 1973. The photoperiods comprised 9 h natural daylight in the summer, supplemented with 40 W incandescent lamps. It was concluded that B. mutica is a qualitative (obligate) short-day plant whereas B. ruziziensis and cv. Masaba are quantitative short-day plants. B. brizantha and B. decumbens were already flowering when exposed to 24-h photoperiods during the pre-experimental period in 1971. In Brachiaria introduction PI 299498, head formation in both experiments occurred a few days earlier under the short photoperiod treatment. In the later-formed heads of all grasses tested the number of racemes/head decreased, though the length of the racemes was not affected. During the 1971 experiment, culm branching was observed in most of the grasses. It was found that in Masaba "secondary" culms were mainly formed during photoperiods of 10 and 12 h but rarely in 14 h. "Tertiary" culms in B. ruziziensis were observed in photoperiods of 10 and 12 h. It is suggested that culm branching can be attributed to high RH. The low seed production of tropical grasses is mainly caused by the low number of heading tillers/unit area and the disynchronization of the flowering resulting from the long period of head production. It is suggested that more research on the photoperiodic response of these grasses would provide useful information on seed production. After selection of photosensitive cv. and seed production at lat. of approx. 15 deg N. and 15 deg S. the long period of heading would be reduced and the synchronization of the flowering would be improved. Some of the early heading types of Masaba are typical examples of photosensitive cv. (Abstract retrieved from CAB Abstracts by CABI’s permission