Field experiments were conducted to determine the direct and residual contributions of legumes to the yield and nitrogen (N) uptake of maize during the wet seasons of 1994 and 1995 at the University Farm, Abubakar Tafawa Balewa University, Bauchi, Nigeria, located in the Northern Guinea savannah of Nigeria. Nodulating soybean, lablab, green gram and black gram contributed to the yield and N uptake of maize either intercropped with the legumes or grown after legumes as a sole crop. Direct transfer of N from the nodulating soybean, lablab, green gram and black gram to the intercropped maize was 24.9–28.1, 23.8–29.2, 19.7–22.1 and 18.4–18.6 kg N ha–1, respectively. However, the transfer of residual N from these legumes to the succeeding maize crop was 18.4–20.0, 19.5–29.9, 12.0–13.7 and 9.3–10.3 kg N ha–1, respectively. Four years of continuous lablab cropping resulted in yields and N uptake of the succeeding maize crop grown without fertilizer N that were comparable to the yields and N uptake of the succeeding maize crop supplied with 40–45 kg N ha–1 and grown after 4 years of continuous sorghum cropping. It may therefore be concluded that nodulating soybean, lablab, green gram and black gram may be either intercropped or grown in rotation with cereals in order to economize the use of fertilizer N for maize production in the Nigerian savannah.

In two similar experiments, Lablab purpureus was sown at dierent dates in July and August to evaluate the eects of sowing date on the yield and nutritive value of the plant and shed leaves. On each occasion, an interim harvest was performed on half of the plants sown at each date and the regrowth recorded. The interim harvest reduced the total yield, and in particular that of shed leaves. In one of the two experiments, late sowing resulted in a considerable reduction in yield, increased crude protein and reduced modi®ed acid-detergent ®bre concentrations. Ash concentrations were higher in plants sown later and their shed leaves. Sodium concentrations were inadequate for ruminants and, like phosphorus concentrations, tended to decrease with later sowing. However, both calcium and magnesium concentrations increased with later sowing and were sucient for ruminant production. Potassium concentrations were high and were little aected by sowing date. It is concluded that both an interim harvest and late sowing are disadvantageous when lablab is grown for ruminant livestock, the former because of yield reduction and the latter because of yield reduction, increases in ash concentration and reductions in sodium and phosphorus concentrations.

In two years the growth and composition of mixtures of sorghum with Lablab purpureus as strips, paired rows and alternate rows were compared with those of sorghum and lablab monocrops. In the first year, when sowing did not occur until 7 August, the sorghum yields were low in the monocrop and even less in the mixed crops. Lablab yield was also reduced in mixtures compared with the monocrop, but total forage yield was greater for the mixed crops compared with sorghum alone. Of the mixed cropping systems, a reduction in the yield of lablab plants and in the phosphorus and potassium content of shed lablab leaves in paired rows suggested that there was more competition for nutrients between lablab plants grown in this treatment. In the second year, earlier sowing increased sorghum growth at the expense of lablab yield in the mixed cropping systems, with the result that total forage yield was not increased when sorghum was intercropped with lablab. However, the crude protein content of sorghum stems and leaf yield were increased in mixed crops, particularly in paired and alternate rows rather than strips, demonstrating that close configuration of the legume and cereal are necessary for the cereal to obtain most benefit from nitrogen fixed by the legume. It is concluded that, when conditions are favourable for rapid sorghum and lablab growth, the sorghum will benefit more when it is grown in paired rows with lablab rather than in strips. However, the close spacing normally adopted for paired rows may encourage competition between lablab plants and increase the requirements for phosphorus and potassium fertilizer.

Lablab purpureus was grown in two ®eld experiments in consecutive years to evaluate the eects of the timing of an interim harvest on the yield and nutritive value of the harvested material and the subsequent regrowth, which was determined from the second and ®nal harvest. Delaying the ®rst harvest to 50±70 days post-sowing increased the total (®rst plus second harvests) dry matter (DM) yield, with a greater ®rst harvest and reduced second harvest DM yield. The delay also reduced the crude protein concentration of the ®rst harvest and tended to increase its modi®ed aciddetergent (MAD) ®bre concentrations. The delay increased the crude protein concentration and decreased the MAD ®bre concentration of the second harvest. The total crude protein yield of both harvests increased with late interim harvesting. The ®rst harvest plant calcium concentration increased and phosphorus concentration decreased with a delay in the interim harvest. It is concluded that, in the dicult growing conditions of the Sahelian zone of sub-Saharan Africa, delaying the interim harvest of Lablab purpureus until 50±70 days post-sowing will have bene®cial eects on total dry matter and crude protein yields.

A study was conducted to evaluate digestible nutrient intake, nitrogen balance and rumen metabolites in twenty growing Yankasa rams fed urea and /or sundried broiler litter (SDBL) as a partial or complete replacement for cotton seed cake (CSC) in diets for 90 days. The diets were: 1(CSC; control), 2(urea), 3(urea/SDBL), 4(CSC/urea) and 5(CSC/SDBL). The results indicated difference (P<0.05) in DM intake across diets, with animals fed CSC, urea and CSC/urea having the highest values (543.1, 523.4 and 483.6 g/day respectively), while those fed urea/SDBL and CSC/SDBL ((459.5 and 424.3g/day respectively) had the lowest feed intake. Mean digestible CP intake differed (P<0.001)across the diets and the values were higher for rams fed CSC and urea (75.7 and 72.7g/day) and lowest for those on CSC/SDBL (49.0g/day). However, mean digestible ADF intake was similar among the diets. A positive nitrogen balance was observed for all animals across the treatments, with significant (P<0.05) differences between treatments ranging from 4.3g/day for rams fed CSC/SDBL to 7.5g/day for those on urea. pH decreased with time after feeding. At 3 hrs post feeding, pH was highest (P<0.01) for rams fed CSC/SDBL and CSC/urea (6.9) and lowest for those on urea alone (6.1) and CSC (6.2). There was a gradual increase in the concentrations of both rumen ammonia-N (RAN) and total volatile fatty acids (VFA) after feeding. Rams fed urea and urea/SDBL (37.5 and 34.2mg/100ml respectively) had the highest (P<0.001) RAN concentration 3 hrs after feeding, while those on the other diets recorded the lowest. On the other hand, rams fed CSC/SDBL (13.1mmol/100ml) had the highest (P<0.001) VFA concentrations while those on urea the lowest (10.5mmol/100ml). It was concluded from this study that diets containing urea and CSC/urea fed to Yankasa sheep gave results comparable to those fed cotton seed cake (control), which are better than for those fed sundried broiler litterbased diets in terms of digestible nutrients intake, positive nitrogen balance and production of adequate rumen ammonia-N. However, rams fed CSC/SDBL had a better concentration of total volatile fatty acids of rumen fluid after feeding.