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The development of irrigated pastures in the Sudan is still at its infancy. The present study determined the influence of 2 cutting heights (2.5 and 5.0 cm) and 4 cutting frequencies (4-, 6-, 8-, and 10-week) on forage yield as dry matter and forage sucrose of Rhodes grass (Chloris gayana Kunth. cv. Massaba) and Ruzi grass (Brachiaria ruziziensis Germain et Everard cv. Congo Signal) under irrigated conditions. Forage yield interactions involving species X cutting height X cutting frequency were significant. These yield interactions were attributed to differences in growth period and growth rhythm of the two species. On average, Rhodes exhibited a short growth period (13 months) compared to Ruzi grass (20 months). Forage yield and forage sucrose were, on average, superior in Ruzi compared to Rhodes grass. Forage yield and forage sucrose averaged 5.2 t ha−1 and 7.2 % fw sucrose in Ruzi compared to 2.8 t ha−1 and 6.9 % fw sucrose in Rhodes grass. Forage yield and forage sucrose of both species were negatively correlated with cutting frequency. The highest forage yield may be obtained at an 8-week cutting frequency in Rhodes (45.6 t ha−1 yr−1) compared to a 10-week cutting frequency in Ruzi grass (88 t ha−1 yr−1). Results suggest that very high forage yields as dry matter and forage sucrose of Rhodes and Ruzi grass may be possible under irrigated conditions in the Sudan at a cutting frequency of between 8 to 10 weeks.

Careful cultural management of field crops has become imperative in countries where chemical measures are not economically feasible. The occurrence of the endemic parasitic witchweed [Striga hermonthica (Del.) Benth] in production fields of sorghum-sundangrass hybrid [Sorghum bicolor (L.) Moench×S. sudanense Stapf. cv. Piper], Pioneer brand hybrid 988 (coded P988), is one example that requires such procedures. Study objectives were to relate : (i) P988 seed size (large and small) to witchweed germination, P988 root and shoot length, and weight and (ii) P988 seed size and harvest growth stage to P988 greenchop yield and sucrose content at three initial and subsequent P988 harvests at boot stage, late bloom stage, and maturity in witchweed-infested fields (...)

Delaying harvest of P988 from the boot stage to the maturity stage significantly reduced 1) forage greenchop yield of P988 grown on Striga- infested soil at 1st and 3rd harvest of July sowing and at 3rd harvest of October sowing, 2) root dry weight of P988 grown on Striga-infested soil at 3rd harvest of July and October sowing, and 3) forage sucrose of P988 grown on Striga-infested soil at 3rd harvest of July sowing and at 1st and 3rd harvest of October sowing. Reductions in forage greenchop yield of P988 with successive harvests were accelerated by Striga infestations. The root dry weight was significantly greater from P988 plants grown from small compared to large seed. Delaying harvest of P988 to the maturity stage was associated with significant increases in number of open Striga flowers at 1st and 2nd harvest from October planting and in Striga shoot dry weight at 1st harvest of July and 1st and 2nd harvest of October planting. These increases were positively correlated with forage sucrose of P988. Results suggest that optimal forage greenchop yield on Striga-infested soil may be obtained from P988 plants grown from small seed and harvested at the boot stage.

Little is known about forage sorghum [ (L.) Moench] and forage sorghum-sudangrass [ × ] hybrid production in soil infested with witchweed [ (Del.) Benth]. The objective of the present study was to evaluate the immediate effects (first harvest) and aftereffects (second and third harvest) of two cutting heights (0.1 and 0.3 m) and five N treatments (0,60 + 60,120,120 + 120, and 240 kg N ha−) on witchweed management in forage sorghum (cv. Abu Sabeen) and forage sorghum-sudangrass (cv. Pioneer 988) hybrid. Field studies were conducted at Shambat, Sudan, in 1984 and 1985 on a heavy alluvial clay soil (montmorillonitic, isohyperthermic Vertic Camborthid) heavily infested with witchweed. Pioneer 988 was more tolerant of witchweed than Abu Sabeen at first harvest, but less tolerant of witchweed at later harvests. The shorter cutting height resulted indirectly in a larger number of tillers (26%) and a higher forage greenchop yield (37%) at first harvest. Nitrogen increased forage tiller density approximately twofold and forage greenchop yield by approximately ten-fold at the first harvest. There was a concurrent, approximately fivefold reduction in witchweed shoot weight. At second harvest, forage tiller density, forage greenchop yield, and witchweed shoot weight were increased with N. Both forage sorghum and witchweed were dead in the zero N plots at third harvest. No differences were detected between single and split applications of N, or between low (120 kg N ha−) and high (240 g N ha−) rates of N. Forage tiller density, forage greenchop yield and witchweed shoot weight were reduced at the second and third harvests compared to the first harvest.

SUMMARY Four experiments were conducted to compare the yield, and stability of yield of oats and barley grown separately and in an equiproportional mixture (w/w). The cultivars used were Maris Mink and Karin, chosen to synchronize, as far as possible, their maturity dates. In general, the mixtures marginally overyielded the more productive species but not significantly so. When barley was sown at half field density, grain yield did not drop. In contrast, the yield of oats was lower when plots were sown at lower density. Barley was generally more unstable in its yield than oats, which it outyielded on good sites but underyielded on poor sites. Mixtures were much more stable than barley, and almost as stable as oats, but were never the most stable type of plot.

In two species mixtures over all nutrient levels and harvests, mixtures of cocksfoot and timothy invariably gave relative yield total (RYT) values well above 10 thus implying a synergistic relationship, while mixtures of cocksfoot and perennial rye grass (PRO) consistently gave RYT values well below 1-0 thus indicating a mutually antagonistic relationship. However, mixtures of PRO and timothy generally gave RYT values approaching 10. Similarly mixtures of cocksfoot and timothy overyielded their respective highest yielding pure stands and mixtures of cocksfoot and PRG underyielded their respective lowest yielding pure stands. PRG and timothy generally gave intermediate yields between those of their highest and lowest pure stands. Relative yield values over all nutrient levels and harvests revealed that PRG is more aggressive than cocksfoot, which in turn is more aggressive than timothy. In a three species mixture this trend in order of aggressiveness was also maintained. The yields of the three species mixtures invariably exceeded those of their highest yielding pure stand. In both experiments pure stands of cocksfoot gave the highest yields and timothy the lowest. Nitrogen fertilization significantly affected herbage yield maximizing it at high nutrient level. There were also significant differences in yield between harvests over all nutrient levels. However, the particular combination of species in a mixture affected the mixture behaviour and yield, though generally the behaviour of a component in a mixture was not predictable from a knowledge of its behaviour in pure stands. The present findings also suggest that the hypothesis that mixtures yield more than pure stands is untenable as a general statement about all mixtures.