The layout of experiments for the study of the growth of four crops in the central rainlands of the Sudan in 1965 is described. The treatments, different levels of flooding prior to sowing, were replicated within blocks. Standard procedures for estimating within plot, between replicate plotswithin block and treatment x block components of error are set out and an example is given of the analysis employing data on kenaf. Using typical values for components of error found in these experiments, increases in precision obtainable by varying the number of plants sampled per plot, and the number of replicate plots per treatment, are considered in relation to their costs. It is concluded that excessive replication would be required to establish differences of interest and that attention should be given to sources of error variation when such large errors are found.

Dry weight, stem and branch length and node number, and flower and fruit number where appropriate, were recorded through the season on cotton, groundnuts, kenaf and sesame in the central rainlands of the Sudan in 1965. For each sampling date variation within plots and betweenreplicate plots within blocks and treatment x block interaction have been studied, together with the effect of these components on the magnitude of the residual root mean square in the analysis of treatments x blocks. The main components were usually within plot and between replicate plots within block errors. Uncontrolled variation was unacceptably great, and was thought to be in large part the result of irregular surface drainage conditions. It seems more likely to be useful to include surface drainage contrasts in field experiments subject to high intensity rainfall on this impermeable clay soil than to attempt to increase precision alone.

Effects of daylength and night temperature on the onset of flowering of selected cowpea cultivars have been investigated, using automatically controlled glasshouses at Reading. The results show close agreement with those from field trials in Nigeria, wherein low intensity incandescent lighting was used to extend the natural daylength. As the field technique has proved an effective screen for daylength insensitivity, future screening work in glasshouses can be for effects of night temperature on time to first flower and for day temperature on the rate of leaf senescence and components of seed yield. This integrated approach can accelerate the screening of cowpea cultivars for sensitivity to environmental factors over ranges characteristic of the low altitude, humid tropics.

The crude protein contents of four Nigerian edible leafy vegetables were high, with values ranging from ao to 30% on a dry weight basis and maximum yields of crude protein ranging from 428 to 602 kg/ha. The percentages of leaf protein extracted ranged from 41 to 70%, whilst the highest yields of extractable edible protein varied from 199 to 332 kg/ha. The crude protein levels, as well as yields of extractable proteins, were slightly affected by the season of growth, but greatly by the age and species of plants.

In experiments conducted in the Ord River Valley, North Western Australia, the extent of egg laying, larval numbers and grain damage from Heliothis armigera was studied with three sorghum varieties of different head densities. Total numbers of eggs laid were similar for each variety, larval infestation was highest on a very dense-headed variety Pickett 932045 and similar in the semi-dense headed RS610 and the open-headed E57 varieties. Greater losses per larva were estimated with varieties E57 and Pickett 932045 than for RS610, where lesser susceptibility was associated with ability to compensate, mainly by increased grain size, for grain loss. This paper reports the results of experiments at Kimberley Research Station to measure infestation and damage caused by H. armigera on three varieties of sorghum with head types ranging from dense to open, and the effectiveness of biological and chemical control practices are also discussed.

Methods of adjusting plots by their neighbours are discussed as a means of reducing experimental error independently of the blocking structure. Six cases are described, using from two to eight neighbouring trees with single and double covariance. The method was applied to trials of various perennial fruit crops from different parts of the world. Most trials have their experimental errors reduced, although there were exceptions. The technique was particularly successful with tea but unsuccessful with apples. Double covariance was superior to single covariance and generally the more trees used for adjustment the larger the reduction in error.

The effect of different soil temperatures on the development of young eggplants was examined at extreme seasonal air temperatures. In winter, rising soil temperatures accelerated growth, but lowering the soil temperature in summer had no effect and extremely high soil temperatures caused very poor plant development.

The effects of different soil temperature regimes on vegetative growth, symbiotic nitrogen fixation and seed yield of two cowpea cultivars (K 2809 and Prima) were investigated in experiments carried out in plastic houses during the UK summer. Mean maximum soil temperatures above 32°C significantly reduced vegetative growth of both cultivars, through their effects on branch, peduncle and root dry weight per plant and, to a lesser extent, leaf production. The warmest temperature regime (35.4°C) also reduced nodule activity, especially in cv. Prima. Seed yields were adversely affected, due largely to changes in the number of peduncles per plant, as mean maximum soil temperature increased from 25.8 to 35.4°C.

When several clones of tea were grown in neighbouring plots, the xylem water potential was lowest in clones which gave a higher yield. It is unlikely that differences of transpiration rate are involved. Although the physiological link between yield and water potential is still obscure, measurements of potential with a pressure chamber might be used to screen new clones for high productivity at an early stage of growth.

Fluid-drilling is the term used to describe sowing seed in a liquid carrier. Elliot (1966) used a tractor-mounted fluid drill designed by the National Institute of Agricultural Engineering to sow normal seed into killed grassland, and a similar but modified drill was subsequently used at the National Vegetable Research Station to sow pre-germinated vegetable seeds (Gurrah et al., 1974; Gurrah, 1975). It then became necessary for compact and economical experiments to be carried out, both on and off the Station, creating a requirement for a small, portable, easily operated, hand-powered drill of simple and robust construction (Gurrah, 1975). Such a drill was built in 1975 and is described in this paper.

Mean yields and average trends with time are given for cotton, finger millet and groundnuts grown in a rotational experiment during the period 1936–64. The experiment, which ran for five cycles, involved a five-year rotation with three different resting periods, five types of resting cover, and farmyard manure at three levels. Yield trends differed from crop to crop, and a critical level of total soil nitrogen is suggested in partial explanation. Responses to farmyard manure in most crops increased over die years, with increasingly marked negative curvature in a pattern that showed most strongly in cotton crops immediately following the application of manure.