Figures for maximum crop growth rates, reviewed by Gifford (1974), suggest that the productivity of C3 and C4 species is almost indistinguishable. However, close inspection of these figures at source and correspondence with several authors revealed a number of errors. When all unreliable figures were discarded, the maximum growth rate for C3 stands fell in the range 34–39 g m−2 d−1 compared with 50–54 g m−2 d−1 for C4 stands. Maximum growth rates averaged over the whole growing season showed a similar difference: 13 g m−2 d−1 for C3 and 22 g m−2 d−1 for C4. These figures correspond to photosynthetic efficiencies of approximately 1·4 and 2·0%.

A glasshouse was built over an established tea crop in Malawi, and the internal air temperature was controlled by manual regulation of the heating, cooling and ventilation rates of two domestic air conditioners. When the inside environment was carefully matched to conditions outside, the glasshouse had only a minor influence on the tissue temperature, stomatal behaviour, leaf water potential and shoot growth of the bushes. The system could be a useful aid to experimentation on the temperature and water relations of field crops in the tropics.

A 4-year investigation of the effects of sowing date on three types of groundnut showed that the earlier the sowing date, the later was kernel initiation and kernel maturity. Early sowing resulted in a high pod yield, oil content and iodine number, but reduced the shelling percentage. The leaf area index ranged from 3·0 to 5·0, the highest value being obtained with early sowing and with non-upright bunch varieties.

The conventional method of inoculating Phaseolus vulgaris with Rhizobium phaseoli, using a peat carrier and dry seeds, was compared with a method using a slurry inoculation of germinating seeds, which were subsequently sown with a fluid drill. The mean number of nodules per plant 28 days after sowing was 0·64 (uninoculated control), 2·14 (dry seed), and 7·0 (fluid drill), differences between treatments being significant at P=0·01. Two varieties included in the experiment gave similar responses, and it is concluded that the fluid drill technique has a useful potential as a method of ensuring good inoculation of legume seedlings.

Broadsense heritability, and correlations of grain yield and related characters, were estimated in three crosses under two levels of soil fertility, which profoundly affected heritability of height and seed weight. Grain yield exhibited heritability of 51–81%, and in one cross significant heterosis in F2. Amongst yield-related characters only pods/plant and seeds/pod were both correlated to yield, and also lacked negative genotypic correlations with other economic characters. However, direct selection for grain yield was considered more efficient than indirect selection using yield-related characters.

In NPK experiments over three seasons additional N gave highly significant increases in total yield, average bulb size and doubles, and decreased bolting. P application gave similar results but responses to K were negligible. The increases in onion yield due to N and P fertilization were accompanied by significant increases in the N and P contents of the leaves.

Field and plant tissue tests under Sudan Kenana conditions revealed that rice does not respond to K but response to P was very clear, both from visual symptoms, tissue analyses and in yields. As early as the seedling stage, a concentration of leaf blade-P of about 1300 ppm is considered optimum. Yield, and level of soil application, corresponding to this value were 5000 kg/ha paddy rice and 42·8 kg/ha P2O5 respectively. A low yield (2400 kg/ha) was obtained from plants receiving no P2O5. Phosphate application reduced the grain protein.

Estimates of variety × environment interactions for grain yield were obtained from a study involving 16 sorghum varieties grown at the same three locations over a 3-year period. Whereas the variety × year interaction was small and not significant, the variety × location and the variety × location × year interactions were highly significant. Evidence was presented suggesting that the years of testing could be reduced by increasing the number of test locations. T.F.M.7 and Karkatib 4/1/1 were identified as desirable varieties, combining high yield and stability of performance, thereby deserving a place both in commercial production and future breeding programmes.

Assessment of the relative advantages or otherwise of inter-cropping compared with sole cropping needs to be done over a wide range of plant populations. Systematic spacing designs lend themselves to this, and the paper discusses the interpretation of the yield/plant population curves which can be so derived.

The experiment, designed to investigate the production of alfalfa in Saudi Arabia, was a factorial involving three irrigation rates and three cutting heights. The irrigation rates were sub-optimum, optimum and super-optimum, supplying 2730, 3850, and 5040 mm of water over the duration of the experiment respectively; cutting heights were low (2 cm), high (8 cm) and alternate (2 cm and 8 cm). The experiment ran for a year, with 14 harvests. Sub-optimum, optimum and super-optimum irrigation treatments produced 27·5, 31·4 and 31·9 tonnes of DM per hectare respectively. Proximate analysis of crude fibre, crude protein, and ash percentage were determined, and plant density and weed infestation recorded.

Formulae are given to calculate the efficiency of the split-plot design, in which whole-plot treatments are arranged in randomized complete blocks. Efficiency for each of the whole-plot and split-plot treatment comparisons is discussed relative to three simpler designs. Tables are given to facilitate calculations for experiments in which up to five whole-plot treatments and five split-plot treatments are tested, using four, six or eight blocks.

New productive variants (PV) with physiological and morphological characters distinctly different from their original counterparts (OR) were isolated under disruptive selection in Brassica campestris cv Brown Sarson. Two new breeding approaches were tested—mating (PV × OR) F1 lines with selected cultivars, and mating disruptive with two-directional selection lines. The resulting superior three- and two-way hybrid populations, when advanced through large-scale inter-mating, produced double the yield potential of the existing controls. The genetic principles behind these breeding approaches are discussed.

Forage production of common vetch in semi-arid Mediterranean regions can be increased by varietal improvement. Dry matter content and crude protein yield were affected by environment more than crude protein content and harvesting date. Forage produced in environments where plants grew quicker was of lower dry matter content, higher crude protein content but of similar weight as forage produced in late environments. Variations in annual rainfall explained 35 to 76% of the total variation in dry matter yield.

A method is described of inducing many ‘eyes’ on yam tubers to sprout, and of using the sprout-bearing segments as propagules for establishing yam fields. The number of such propagules obtainable from a tuber depends on its size, but the method greatly increases the rate of propagation and holds special promise for both breeding and commercial production of yam.

Leaf protein concentrate was prepared from the weed Parthenium hysterophorus L. and the nutritional properties of this preparation were studied in relation to its amino acid composition and digestibility. The product and the residual fibre closely resembled similar products made from conventional forage species.