Pot experiments in which cowpea and hyacinth bean were grown at 15–45% soil moisture showed that nodulation, nitrogen fixation and plant growth were poor at 15%. The weights of nodules and plants were lower in January (winter) than in June (summer). In June cowpea was more tolerant of dry conditions giving good nodulation at 25–35% whereas hyacinth bean required 35–45%.

Under field conditions the number and dry weight of nodules were affected by the irrigation interval whereas plant growth was affected by the amount of water applied. Applying 75 mm depth of water every 7 days gave the best combination of nodulation and plant growth.

Cowpea and hyacinth bean nodulated and grew well at 11–14 h and poorly at 8 h light duration. Nodulation and plant growth increased with increase in light intensity from 1·4 to 17·1 W/m2 but the natural light intensity (228·3 W/m2) inhibited nodulation in July and plant growth in December.

Nodulation and growth of both crops were best at ‘moderate’ temperature and cowpea tolerated ‘warm’ more than ‘cool’ temperatures whereas hyacinth bean showed the reverse situation.

Inoculation improved nodulation of cowpea but not hyacinth bean. Application of nitrogen did not improve the growth of plants affected by light and temperature.

Aflatoxin was found in forty-one out of seventy-four samples of various pulses, whereas Aspergillus flavus occurred in all samples, and there was an apparent correlation between the occurrence of the fungus and the level of the toxin in haricot beans. There was evidence that the toxin was produced in haricot beans after harvest, and drying the pods immediately after harvest is therefore suggested as a method of controlling mould growth and the formation of aflatoxin.

Cross-inoculation tests among ten Acacia species and cowpea (Vigna sinensis) showed that eight Acacia spp were related to cowpea while two were independent and this agreed with the placement of Acacia in the cowpea group. The Acacia rhizobia showed certain cultural and physiological similarities to the cowpea Rhizobium and were resistant to high temperatures.

Field experiments conducted in two localities in two growing seasons on the effect of inoculating haricot bean showed that a local strain of Rhizobium significantly improved nodulation and usually increased the nitrogen content of plants. In three out of four experiments, increases in seed yield were obtained ranging from 20–145 Per cent (significant in two cases). Inoculation was better than 43 kg. N/ha. of combined nitrogen but not better than 86 kg. N. Soil inoculation gave better early nodulation than seed inoculation, but the difference diminished in the later stages of plant growth.

Cross-inoculation tests, based on nodule formation and nitrogen fixation, were made on 21 species of legumes commonly found in the Sudan. The results showed that they may be grouped according to the accepted system of classification, but there were some important inconsistencies in the cowpea group. For instance, Arachis hypogaea and Acacia spp. have their own strains of Rhizobium. The cultural and physiological characters of the rhizobia studied were generally similar to those known for other species of the organisms.