Two pigeonpea (Cajanus cajan) cultivars GT-100 (determinate type) and BDN-2 (indeterminate type) were planted on three sowing dates (30 June, 20 July and 9 August) in 1993 and 1994. Pigeonpea sown on the earliest date attained the highest leaf area index (LAI), absorbed the largest amount of photosynthetically active radiation (PAR) and produced the highest total dry matter (DM). The differences in biomass and seed yield among sowing dates were largely ascribed to totals of PAR absorbed and dry matter produced, especially in the reproductive phase. The high LAI persistence and PAR interception, coinciding with the podding phase, appeared to be mainly responsible for the increased yield in early sowings. Radiation use efficiency decreased as sowing was delayed, but did not have much effect on DM accumulation in various phases nor on final yields. Although the extinction coefficient was not influenced by sowing dates, it was inversely related to leaf area index in both cultivars. Between the cultivars, the differences in biomass reflected the differences in PAR absorbed and DM accumulation, depending upon leaf area development and growth duration. The cultivar GT-100 had a higher seed yield and harvest index than BDN-2 due to more of the DM produced being partitioned into pods during the reproductive phase on account of its determinate growth habit. Early sowings of determinate cultivars could maximize both vegetative and reproductive growth, capture more light and produce more seed yields under rainfed conditions.

High temperature is a major problem in groundnut (Arachis hypogaea) producing areas of arid and semi-arid tropics whether rainfed or irrigated. Knowledge of the maximum air temperature that plants can tolerate will help in selecting genotypes adapted to high temperature. The objectives of this study were to evaluate the growth, development, yield and yield components of different groundnut genotypes grown under elevated temperatures. Five groundnut cultivars and lines were grown in the field from 1984 to 1986 in Vertisols. Measurements on flowering, growth and development were carried out frequently. Thermal units required for groundnut cultivars to reach maturity were 2247 °C days. Larger kernel size, higher pod:total growth ratio and longer pod-filling period were the most important parameters for yield increase in heat-stressed environments. Early Bunch gave a stable yield across environments and was found to be more tolerant of high temperature. Cultivars differed in their pod:total growth ratio and Early Bunch had the highest ratio.

Isolation of Colletotrichum gloeosporioides (causal agent of yam anthracnose) from soil is difficult because of the presence of fast growing micro-organisms like Rhizoctonia spp., Rhizopus spp., Penicillium spp. and bacteria. Therefore, a semi-selective medium consisting of antimicrobial agents such as pencycuron 50 mg L−1, tolclofos-methyl 10 mg L−1, streptomycin sulphate 100 mg L−1, chloramphenicol 100 mg L−1 and chlortetracycline 100 mg L−1 was developed using potato dextrose agar as the basal medium. The procedure involved screening of candidate fungicides, developing a suitable combination of antimicrobial agents, assessing the proposed semi-selective medium and adjustment of pH of the medium to 5. The effectiveness of the medium is due to selective inhibition of micro-organisms by the antimicrobial agents and the development of distinct salmon-pink colonies of C. gloeosporioides.

As cassava is grown mostly by small resource-limited farmers throughout the tropics on low-fertility soils with little fertilization and, due to the large potassium (K) export in harvested roots, genotypes that tolerate low-K soils and respond to K fertilization are warranted. The objective of this study was to evaluate cassava germplasm and identify such genotypes.

Fourteen cultivars of cassava (Manihot esculenta) selected from the core germplasm at CIAT were grown under rainfed conditions for ten months over five consecutive seasons in Inceptisols either with no K application or with 50, 100 or 200 kg K ha−1 applied annually together with adequate nitrogen and phosphorus. All cultivars responded to K application both in terms of root and shoot biomass with the highest yields obtained by CM 507-37 and M Ven 25 in the absence of K application and at high K levels. These cultivars had the highest adaptation indices to low K and the highest K use efficiency for total biomass production. CM 507-37 had the highest K use efficiency for root production at all K levels. Thus, it is desirable to use this material for breeding cassava which is adapted to low-K soils and is able to respond to fertilizer application. However, because of the high hydrocyanic acid (HCN) content in their roots, these cultivars should be crossed with genotypes that are low in HCN, such as HMC-1 and M Cub 74, in order to select lines with both high K use efficiency and low HCN for fresh cassava consumption. Root HCN contents were significantly reduced by application of K across all cultivars. Application of K fertilizer to low-K soils is warranted to minimize health hazards when fresh cassava is used for human consumption.

Field plots of sesame (Sesamum indicum) with six different levels of seed infection with Alternaria sesami were monitored for Alternaria leaf spot severity at Kibwezi, eastern Kenya. The aim of the study was to determine the effect of seed transmission of the pathogen on yield and tolerance level of the fungus in sesame seed. Increase in percentage leaf area diseased and percentage defoliation fitted the Gompertz model more closely than the logistic model. Areas under disease progress curves (AUDPC), infection and defoliation rates varied among the six infection levels. Disease severity increased with increase in seed infection and was least and most severe in plots established with seeds with 0 and 8% infection levels respectively. Yields ranged from 234.9 to 300.1 kg ha−1 compared with 312.5 kg ha−1 for the control, and losses due to seed infection ranged from 4% to 25%. Disease severity was negatively correlated with seed yield, 1000-seed weight and seeds per capsule. Alternaria leaf spot severity had a major effect on the seed weight component of yield. Tolerance level of A. sesami in sesame seed was determined to be less than 2%.

A field experiment will sometimes give data so unexpected that their correctness is doubted. It would be wrong to discard them because they go against the experimenter's preconceptions but sometimes enquiry will reveal why they are aberrant. Sometimes no reason can be found but they still raise doubts. The problem is approached using a published body of data.

The calculation of residuals and total residuals is commended as a means of enquiry. Exclusion of data is to be avoided if possible. It can have serious consequences and methods are given for assessing them. It is important to seek alternative approaches and one possibility is the use of covariance adjustments on fertility trends shown by study of the residuals. It is shown also that extreme values sometimes arise from unsuitable data and can be eliminated by a suitable transformation, but it must be meaningful and not just a statistical expedient to avoid difficulties.

Relative palatability and some agronomic traits were studied for nine legumes including Aeschynomene histrix, Centrosema brasilianum (two accessions), Centrosema pascuorum, Chamaecrista rotundifolia, Stylosanthes guianensis (two accessions) and Stylosanthes hamata (two accessions). All species were consumed by cattle but the relative palatability varied according to season. Only the two S. guianensis accessions were positively selected throughout the year. A positive relationship was established between the ability to retain green leaves in the dry season and palatability. Once established, the two C. brasilianum accessions out-performed the other legumes in their ability to stay green and retain leaves in the dry season; related to the ability to retain green leaves under drought conditions, C. brasilianum ILRI 155 was among the most palatable legumes in the dry season. S. guianensis accessions had the highest dry matter (DM) yields and one of them (ILRI 15557) had the highest nutritive value. In contrast with earlier results in the same environment, C. rotundifolia and A. histrix performed poorly in terms of DM productivity. The implications of the agronomic characteristics of the legumes for the management of legume-based pastures in crop/livestock systems are discussed and the concept of legume–legume mixtures, composed of several compatible species, is advocated.

This study, quantifying variation in flower and pod production in lentil (Lens culinaris), aimed to answer the question: Will selection for more pods per inflorescence increase seed yield? In Season 1 (1992–93) all open flowers were tracked to maturity in a field experiment with two lentil genotypes sown on two dates. Genotype Talia 2 had a higher rate of flower abortion than pod abortion, in contrast to genotype ILL 2581 which showed the reverse. Flower abortion accounted for 15% of flowers opened in early sowing and increased to 22% in the late sowing. Pod abortion was 19% (of flowers opened) in early sowing and 23% in the late sowing. These are the first quantitative estimates of flower and pod abortion in lentil. From the data, a rapid sampling method was developed to estimate the average number of pods per inflorescence at maturity. In Season 2 (1993–94) an experiment was conducted at two locations to estimate the average number of pods per inflorescence of 81 genotypes and to relate this to seed yield. Although the broad-sense heritability (h2) of the number of pods per inflorescence was 0.68 and its phenotypic correlation with seed yield was r = 0.71, the highest-yielding genotypes were not those with the most pods per inflorescence. Selection for the number of pods per inflorescence cannot be recommended for increasing seed yield in lentil.

Three alternate-row intercrop experiments of sorghum (Sorghum bicolor)–cowpea (Vigna unguiculata) and/or millet (Pennisetum glaucum)–cowpea were grown at plant densities of 20 000 to 80 000 plants ha−1 at two locations in northern Nigeria between 1990 and 1992 to examine relations between yield and plant density. These relations were examined using the reciprocals of yield per plant to determine effects of environment, species and genotype on the theoretical maximum yield and optimum plant density. The intercrops were dominated by cereals, and cowpea biomass (BY) and seed yield (SY) were <10% of cereal BY and SY. Cowpea yields decreased as cereal plant density (D) increased, whereas cereal and total intercrop yields increased asymptotically with increasing D. Biomass yield of all intercrops responded to increasing D in a similar manner and the theoretical maximum intercrop BY was 12 290 kg ha−1 in all experiments. The response of SY to D varied among intercrops and was greatest and least with early and late maturing cereals respectively. The optimum D required to produce 90% maximum intercrop BY and SY varied between 15 600 and 30 000 plants ha−1, and 0 (no response to D) and 120 000 plants ha−1 respectively, and was higher for sorghum than for millet intercrops. The implications of these responses for agronomic management and germplasm improvement of cereal–cowpea intercrops are discussed.

In many highly weathered soils of the humid tropics, crop exploitation of the subsoil environment is limited through acid soil infertility. Since the use of mechanical profile modification is often prohibitive, surface incorporation of soil amendments is often the only means available to rectify this problem. A field trial was established with sugarcane on a strongly Acidic Dystrophic Brown Dermosol (Oxic Humitropept) in 1978 to evaluate the effects of surface incorporated lime additions on yield and performance of sugarcane. Eighteen years after the establishment of this trial, significant responses in cane yield were still evident following a single application of 5 t lime ha−1 made in 1978, as well as repeated applications of 5 t ha−1 on three occasions over the past 18 years. Progressive reductions in exchangeable acidity were accompanied by increases in subsoil Ca2+ and Mg2+. Soil pH increased significantly to a depth of 100 cm, this being attributed to the formation of ion pairs with NO3 in the surface soil, the subsequent leaching of these complexes and the differential uptake of NO3 at depth by roots. The results from this long-term study indicate that surface incorporation of lime is an economically viable approach to the remediation of subsoil acidity on soils such as those studied, namely, those with a low inherent cation exchange capacity and anion exchange capacity.