Maize/cassava and maize/cowpea intercrops were evaluated in southern Ghana, over a 5-year period to determine the optimum combination of component crop varieties and component plant population densities to optimize productivity of maize-based intercropping systems. Results indicated that some cowpea varieties which perform well under sole cropping tend to climb under intercropping and may not be adapted for intercropping. Selection of improved cowpea lines under intercropping might, therefore, be necessary. Full-season maize intercropped with short-duration cassava (LER=1.5), and medium-maturing cowpea intercropped with early-maturing or full-season maize (LER=1.4-1.53) resulted in high productivity of the intercrops. The optimum plant population density of the intercropped maize (50,000 to 58,000 plants ha-1) was similar to the recommended optimum sole crop maize plant population density. It is recommended that intercropped cassava population density should not exceed 15,000 plants ha-1 to obtain marketable sizes of cassava roots. Planting double rows of cowpea between two rows of maize was a better alternative (LER=1.60-1.62) to sole cropping.

Original scientific paper. Received 30 Jun 98; revised 2 Aug 99.

Yield stability of 12 groundnut accessions mainly developed by ICRISAT and two check varieties were tested in multilocational trials covering four locations in northern Ghana during the 1994, 1996, and 1997 cropping seasons. The trial for each year was arranged in a randomized complete block design with four replications and analyzed following a factorial design of 14 genotypes W 3 years W 4 locations. Significant differences were obtained (a#0.05) for the main effects of genotypes, years, and locations as well as the first and second order interactions; 33 per cent of the variability in kernel yield was accounted for by genotype W year W location interaction whilst 26 per cent by genotype W location interaction. Proportions of the total variance due to yield differences between genotypes and genotype W year interaction were negligible. Yield stability as

indicated by the regression coefficient, among-location variance, and the value of mean yield suggested that JL 24, an early-maturing variety, was the most adapted to marginal environments whereas the check variety, F-mix, maintained its superiority in adapting to favourable environments.

Original scientific paper. Received 10 Oct 98; accepted without revision 13 Aug 99.

Studies were carried out on Citrus limon explants in vitro to determine the effect of applied pressure on callus formation, cell differentiation and its importance in grafting. Callus was formed earlier in pressure-free explants. The importance of applied pressure in graft formation was indicated by the fusion of callus cells in capped explant experiments. Where callus grew from the edges, a cambium eventually formed within it from the old cambium. The new cambium always curved towards the phloem side, suggesting that a nutrient gradient may be responsible for its location.

Original scientific paper. Received 17 Jun 98; accepted without revision 13 Aug 99.

The study investigated the effects of three 5-year-old cropping systems comprising Leucaena hedgerows with cowpea (Vigna unguiculata), maize (Zea mays L.), and groundnut (Arachis hypogaea) on the accumulation of soil organic carbon, bulk density, porosity, and aggregate stability; and compared these with soils under a Leucaena woodlot of similar age in a forest-savanna transition zone of Ghana. The woodlot soils had the highest accumulation of organic carbon and total porosity. The aggregate stability in this system was more than twice the values for the alley cropping systems. Furthermore, the aggregate stability correlated well with the soil organic matter (r = 0.77**), suggesting that it can be well estimated from organic matter content. Among the three alley cropping systems, the accumulation of organic carbon was in the order cowpea> maize > groundnut, but the aggregate stability did not show any consistent pattern with organic matter content in these systems. The results indicated that despite the periodic

addition of organic matter from pruned Leucaena hedgerows to the soil, the alley system did not improve the aggregate stability as much as the woodlot system.

Original scientific paper. Received 7 Jan 98; revised 23 Aug 99.

Original scientific paper. Received 14 Oct 98; revised 3 Sep 99.

Original scientific paper. Received 3 Sep 98; revised 3 Sep 99.

The study, which was carried out at the Crops Research Institute, Kumasi, Ghana, from April 1992 to March 1995, aimed at determining (i) the optimum plant density of False horn plantain for maximum yield, and (ii) the optimum frequency of handweeding for economic returns. Results indicated that the optimum plant density for False horn was 1667 plants per hectare. At this density, the significantly highest bunch weight was 8.0 kg per plant. In Ghana, plantain is mostly sold as bunches and, therefore, bunch weight per plant rather than yield per hectare is of paramount importance. Handweeding, as weed control measure, proved to result in high economic returns. Keeping the field weedfree for the first 4 weeks followed by slashing every 12 weeks (4-IWP W 12-FUS) produced the highest economic returns of 71.5 per cent over the farmer's practice of weeding at only 12-week intervals from planting.

Original scientific paper. Received 18 Sep 98; revised 15 Oct 99.

Anchovis spp. is of great importance in non-industrial feed formulation in Ghana as the main protein ingredient. Many microbial diseases found in poultry/livestock in Ghana are suspected to be due to contaminants on the fish in feed. Results from this survey suggest high levels of microbial contamination on the Anchovis fish. Seventeen genera of bacteria were isolated from Anchovis spp. samples taken along the coastal towns and markets in Ghana. The genera of bacteria isolated included Coliforms, Staphylococcus, Salmonella, Streptococcus, Pasteurella, Escheriachia, Shigela, and Pseudomanas. These organisms are known to cause various diseases in man and animals, resulting in economic losses. Caution should, therefore, be taken in the use of Anchovis spp. in human food and animal feed, since it can be a source of bacterial infection.

Original scientific paper. Received 16 Oct 98; revised 1 Nov 99.

Field strains of the cattle tick, Amblyomma variegatum, collected from 10 herds scattered in the western part of the coastal savanna zone of Ghana, were tested for resistance to acaricides, according to the FAO Acaricide Test kit. Discriminating doses were obtained from tests with a reference susceptible strain of Boophilus microplus. The LC50 values, where possible, were derived from fitted lines for graphs of mortality rates versus acaricide concentration for the various herds. Tick larvae from all the herds were completely susceptible to cypermethrin (0.025, 0.05, 0.10, 0.20, 0.40, and 0.80 %) and flumethrin (0.003, 0.006, 0.012, 0.015, 0.03, 0.06, 0.12, 0.25, and 0.50 %). However, eight herds had significant proportions of tick larvae showing resistance to diazinon at 0.2 per cent concentration, while three herds showed resistance to 0.2 per cent dieldrin. At the discriminating dose of 0. 2 per cent coumaphos, none of the ticks from the herds tested showed resistance. The results indicate possible resistance of field strains of A. variegatum to organophosphates, toxaphene, and/or lindane. The implications of this finding are important, if tick control measures should be effective in the coastal savanna zone of Ghana.

Original scientific paper. Received 26 Feb 99; revised 8 Nov 99.

Studies were conducted between 1994 and 1997 on the incidence, distribution, and control of the onion fly Delia antiqua in northern Ghana. Results showed that the insect is prevalent in most of the onion-growing areas and is capable of causing up to 33 per cent crop damage. It was also established that early transplanting (before mid-January) and transplanting of seedlings 6 weeks after emergence reduced D. antiqua infestation and crop damage. Neem seed powder and aqueous neem seed extract were as effective as Carbofuran for the control of the onion fly. Economic nalysis showed that the neem products were the most cost-effective and had the best returns.

Original scientific paper. Received 2 Feb 99; revised 9 Nov 99.

The study investigated the effect of including high amounts of wheat bran (WB) in finisher diets on growth performance and economy of gain of broiler chickens. The WB contained g kg-1 of dry matter, 894.3; crude protein, 193.5; ether extract, 42.1; crude fibre, 97.1; ash, 49.5; neutral detergent fibre, 503.8; acid detergent fibre, 167.2; hemicellulose, 336.6; Lignin, 29.3; starch, 197.0; and metabolizable energy of 6.72 MJ kg-1. In a feeding trial, four finisher diets containing maize, fishmeal, micro-ingredients and either 150, 250, 350 or 450 g of WB kg-1 diet and designated as dietary treatments WB150, WB250, WB350 and WB450, respectively, were fed ad libitum to 480 3-week-old commercial broiler chickens for 35 days. Birds had free access to water. As the dietary WB content was increased from 150 to 450 g kg-1, there was a significant (P< 0.01) increase in feed intake and a reduction in body weight gain and efficiency of feed utilization. The inclusion of high amounts of WB significantly influenced carcass dressing proportion and gizzard weight. However, there were neither health-related problems nor mortalities attributable to the amount of WB in the diet. There was a decrease in the cost of kg feed and feed cost kg-1 liveweight gain with increasing levels of dietary WB.

Original scientific paper. Received 19 Feb 98; revised 23 Dec 99.

The problem of land degradation resulting in insufficient food production for the ever-increasing population is recognized worldwide and some observations by scientists, administrators, and politicians on its threat to human existence, have been made and highlighted at scientific meetings, in newspapers, and other fora. The causes of land degradation are many and most of them are known and are being tackled for solutions. However, several of them have not received much attention but are grave. Plinthite and its hardened form, petroplinthite (ironpan), constitute the major forms of danger to land use. They are the results of unnoticed and gradual pedogenetic processes going on mostly in tropical soils. Scientists have worked for some time on the hardened form, petroplinthite, but the soft form, plinthite, has not received much attention. Over a third of the agricultural soils of Ghana have plinthic material and FAO reported that 96 920 km2 of land have already hardened and made the soil unproductive. The situation may be similar for other countries in the tropics. This paper attempts to review plinthite, its physical, chemical, mineralogical and micromorphological forms, and its importance for construction and agriculture. It also warns mankind about the danger ahead if solutions are not found for the prevention of its formation and subsequent hardening to form petroplinthite.

Subject review article. Received 17 Nov 98; revised 2 Aug 99.

Drought is an important climatic phenomenon which after soil infertility ranks as the second most severe limitation in the production of crops under rainfed, low input agriculture. Breeding of genotypes with greater drought tolerance is the best strategy for maintaining and/or increasing crop production in such systems. This paper reviews the concept of drought tolerance and discusses approaches that may be adapted to breed varieties of crops with tolerance to drought. What remains to be done is for breeders to use the available genetic variability with respect to mechanisms that aid the plant in adapting to drought in their breeding programmes. It is concluded that biotechnologies will prove quick and stable markers for identifying genes that confer drought resistance.

Subject review article. Received 3 Sep 98; revised 23 Dec 99.