The efficiency of many intercropping research programmes could be improved if research workers made fuller use of modern statistical knowledge about experimental design. Important statistical considerations for experimental design and plot sampling are reviewed and their relevance to intercropping research assessed. The general philosophy of factorial structure and blocking, and specific ideas on the use of systematic designs and monocrop plots, are discussed.

Data from 94 experiments on sorghum/pigeonpea intercropping were examined for evidence that the stability of yield is greater with intercropping than sole cropping. Stability of the major component (sorghum) was examined by calculating the distribution of yields; stability of the overall intercropping system was examined by calculating coefficients of variation, by computing regressions of yield against an environmental index, and by estimating the probability of monetary returns falling below given ‘disaster’ levels. All these approaches have some merit; taking the last as an example, it was found that for a particular ‘disaster’ level quoted, sole pigeonpea would fail one year in five, sole sorghum one year in eight, but intercropping only one year in thirty-six. Intercropping gave yield advantages under a wide range of environmental conditions and there was no significant evidence that advantages were greater under stress. This is discussed in relation to possible mechanisms contributing to greater yield stability.

Criteria for evaluating different intercropping situations are suggested, and the Land Equivalent Ratio (LER) concept is considered for situations where intercropping must be compared with growing each crop sole. The need to use different standardizing sole crop yields in forming LERs is discussed, and a method of calculating an ‘effective LER’ is proposed to evaluate situations where the yield proportions achieved in intercropping are different from those that might be required by a farmer. The possible importance of effective LERs in indicating the proportions of crops likely to give biggest yield advantages is discussed.

The implementation of a ‘Green Revolution’ programme in Nigeria, known as the National Accelerated Food Production Project, was linked with earlier programmes in other countries derived from CIMMYT and IRRI and with a previous FAO Fertilizer Programme in Nigeria. The methodology was based on ‘minikit’ demonstration trials on farmers' fields. Details are given of the the forms used in the field and plot size, number and choice of treatments and subsequent package demonstrations, and production kits are discussed.

A simple competitive ratio (CR) is proposed as a measure of intercrop competition, to indicate the number of times by which one component crop is more competitive than the other. Intercropping data show that this CR term could be useful in (i) comparing the competitive ability of different crops, (ii) measuring competitive changes within a given combination, (iii) identifying which plant characters are associated with competitive ability, and (iv) determining what competitive balance between components is most likely to give maximum yield advantages.

Photosynthetic rates of coffee plants grown under the full sun and shade were compared. The saturating irradiance of 300 μE−1 m s−1 of shade plants shifted to near 600 μE in sungrown plants, but shade plants possessed substantially higher photosynthetic rates. Photosynthetic rates decreased above 25°C, which was apparently due to a decline in the mesophyll conductance, as stomatal conductance remained more or less unchanged between 25° and 35°C. Most of these measurements were made on seedlings in plastic bags. It is concluded that coffee is more suited to high density plantings where mutual shading, resulting in low light intensities and lower leaf temperatures, are likely to produce a favourable environment for efficient photosynthesis and growth.

A technique has been developed and tested for successfully grafting large, leafy cowpea shoots onto roots, which may be nodulated or not. Grafting per se had no significant effect on either the production or distribution of vegetative or reproductive dry matter compared with control plants left intact throughout growth. Furthermore, numerical components of yield and the concentration (%) and content (mg) of nitrogen in respective plant components were remarkably invariant. Examples are discussed of the variations in nitrogen nutrition which can be achieved and the potentials of the technique in general.

Effectively nodulated plants of 3 cultivars of chickpea, classified as early, mid-late and late-maturing, were grown to reproductive maturity in 12 factorial combinations of simulated tropical environments in growth cabinets. Cultivars varied in sensitivity but all responded as quantitative long-day plants and flowered earlier in longer photoperiods. Differences in temperature had important consequences, especially on the duration of the reproductive phase and overall crop longevity; they also induced plants to flower at the same time in different photo-periods. Early flowering plants did not necessarily mature early; others taking twice as long to come into flower had short reproductive periods and came to maturity at the same time. Relations between phenology, morphology and seed yield are described and compared with similar data for field-grown plants. Screening for ‘adaptation to environment’ in chickpeas is discussed.

Trials carried out at a range of locations in northern Nigeria showed that gross cash returns from mixtures were never less than those from sole groundnuts, confirming results from the main research station at Samaru. In many cases they were considerably higher and in the Northern Guinea Savanna, where the system is most widely practised, showed a high probability of returns greater than the sole crop median. Increasing attention is being paid to haulm yield and the possibility that sole groundnut may be more profitable near large towns because of haulm value.

On the basis of a preliminary experiment with 20-day-old Cicer seedlings, wherein the values obtained by integrating the in vivo nitrate reductase (NR) activity with the duration closely approximated the actual reduced N, a field experiment was conducted with cv BG 203 (indeterminate type) to ascertain the extent to which the nitrate assimilated via the enzyme NR contributed to the total reduced N. Soil-derived N accounted for 15.1, 8.3 and 7.2% of the total reduced N at pre-flowering (I), profuse flowering (II) and seed filling (III) stages respectively. Out of the total soil-derived N, 10.1, 59.3 and 30.6% was reduced during stages I, II and III respectively.

Factorial combinations of three daylengths (11, 12 and 15 h), warm and cool days (30° and 22° C) and warm and cool nights (18° and 10°C) were imposed on nodulated plants of three chickpea cultivars grown in pots in controlled environment growth cabinets. The treatments had large effects on growth, phenology and seed yield and no single environmental regime was optimal for all successive stages of development. Root growth and nodulation were extremely responsive to the environment experienced by the shoot. Conclusions are drawn on the potential contribution of these data to the development of empirical screening techniques suitable for large, segregating populations in field programmes devoted to the production of chickpea cultivars better adapted to their intended environments.

Experiments were carried out to relate soil moisture to leaf water potential (Ψ1), and to determine the effects of varying Ψ1, on leaf conductances and photosynthesis in coffee. Stomatal conductance was maximum at 0900 h, but plants growing in drier soil showed marked mid-day stomatal closure. After 1500 h, stomata began closing although plant water status improved. Photosynthesis in relation to changing Ψ1 appeared to exhibit roughly three different rates. At the fixed experimental temperature (25°C) low Ψ1 reduced photosynthesis throughits influence on stomata, but under field conditions low Ψ1 and an accompanying rise in temperature could lower the rate by lowering both mesophyll and stomatal conductances.

Various intercrops were examined in an alternate row pattern with pigeonpea or sorghum on both Alfisol (red soil) and Vertisol (black soil). The slow-establishing and later-maturing pigeonpea combined well with earlier cereals and legumes to give very large yield advantages as measured by the Land Equivalent Ratio. In the pigeonpea/cereal combinations, the earlier the cereal the bigger the yield advantage tended to be, attributed to improved use of resources over time as the difference in maturity periods of the component crops increased. Sorghum was generally more competitive than pigeonpea and intercropping advantages tended to be less. But even where there was little difference in maturity periods of the component crops, both sorghum/legume and sorghum/cereal combinations gave substantial and statistically significant advantages, suggesting that improved ‘spatial’ use of resources was also important.

Sesame was grown in four seasons in which differences in the distribution of the rains and treatments of pre-sowing flooding, irrigation during crop growth and surface drainage resulted in contrasts in soil water content and crop development. In wet years pre-sowing flooding, absence of surface drainage and premature irrigation gave 32–37% decreases in yield. In a season of low rainfall prevention of surface run-off and one later irrigation gave, in the absence of pre-sowing flooding, a 43% increase in yield over that from plots irrigated only at sowing and with surface drainage. Agronomic applications are discussed.

In a three-year field experiment on acid peat (pH 3.47) up to 12 t/ha lime increased peat pH (0–30 cm depth) by 0.061/t. Annual guinea grass dry matter increased in quadratic relation with liming up to pH 4.20 (12 t/ha lime) but there was no difference between the cvs Sigor and Colonoa. Liming decreased the N, P and K, but increased the Ca and Mg contents of the harvested grass. Liming also increased the uptake of all five nutrients investigated, either linearly or curvilinearly.

Experiments were carried out to examine the effects of agri-silviculture in three different ecological zones of Southern Nigeria. The four treatments considered were Gmelina arborea (forest tree crop) alone, Gmelina + maize, Gmelina + yam, and Gmelina + cassava, each treatment being replicated 8 times in each location. Composite soil samples, collected from two surface layers of each treatment plot, were analysed. Inter-planting young forest plantations with food crops usually increased soil N and P, at the slight expense of soil organic carbon. However, exchangeable Ca, Mg and K contents, pH, and soil N and P contents, were not statistically different among the treatment plots.

Growth and interception of Photosynthetically Active Radiation (PAR) in a maize/pigeonpea intercrop and sole maize and sole pigeonpea crops grown in large plots in an operational research watershed at ICRISAT research centre were compared. Growth and yield of the maize crop, in pure stands and in intercrop, were not significantly different. Efficiency of dry matter production, calculated from the relations between dry matter production and cumulative intercepted PAR, was highest for the maize/pigeonpea intercrop, followed by sole maize and sole pigeon-pea, proving the utility of such intercrops in making better use of resources in the Semi-Arid Tropics (SAT).

In a 4 × 4 × 4 NPK field experiment with coconut on a sandy soil, N increased girth, height and leaf production during the pre-bearing period, but phosphorus (up to 6½ years) and K (up to 3½ years) had no effect on any vegetative growth parameters. The rates of fertilizers for optimum copra and nut yield (13 to 16 years) were 0.35, 0.73 and 0.64 kg N, PO and KO/palm/ year respectively. The high P requirement was due to the low solubility of the saphos phosphate in these sandy soils. A positive N × P interaction was also observed.

Leaf area index is an important parameter in many agronomic and physiological studies, but its determination in cowpea (Vigna unguiculata) and soyabean (Glycine max) is difficult and time consuming. A simple and rapid method is described in which dry weights of the middle leaflets were used to predict leaf areas of cowpea and soyabean. This method was based on results which indicated that leaf dry weights were highly correlated to leaf areas and that the ratio between leaf area of the terminal leaflet and total area of a trifoliate leaf was constant, at least in some cultivars, giving ratios of 0.37 for cowpea and 0.33 for soyabean.

Twenty soyabean genotypes, grown in 12 environments, showed significant g × e interactions for grain yield and most of the other traits. The g × s interactions were unimportant, but the g × 1 and g × 1 × s were of considerable magnitude for most traits. The experiments provided estimates of genotypic, environmental and genotype-environmental variance. The presence of a high environmental variance for grain yield suggested the possibility of raising yield levels through improved management practices.