The stabilities of plant height and yield for rice varieties grown in Sri Lanka were calculated by regression analysis. High yields were produced by both stable and unstable varieties in the wet season, but in the dry season high-yielding varieties tended to be of above-average stability. The yield of the newer, shorter varieties exceeded those of older varieties except at low nitrogen levels, and the new varieties were of above-average stability.

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.

Forty different cultivars of cassava were grown in unreplicated plots at a plant population of 20,000 plants/ha in fertile soil. Harvests were taken at 4, 6, 8, 10 and 12 months after planting 18 varieties. The characteristics of the two highest yielding varieties, M Colombia 113 (66 t/ha) and M Colombia 22 (32 t/ha), were compared with the other types. M Colombia 22 is an early type (25 t/ha after 6 months) with a very high harvest index; M Colombia 113 yields little better than average 6 months after planting. High yield is associated with a balance between leaf production and root production, so that leaf area index does not decline excessively in the later growth stages. Changing canopy structure is unlikely to increase yields.

Four tomato varieties (Harvester, Pusa Early Dwarf, Ife No. 1 and Ibadan Local) were grown in three ecological zones of Western Nigeria, at a range of densities from 10,000 to 40,000 plants/ha. The highest yield of fruits was obtained at a plant population of 30,000 plants/ha. Pusa out-yielded the three other varieties. Fruit number per plant declined as plant density increased.

Annual applications of calcium, potassium and nitrogen (as urea) over three years caused significant differences in soil exchangeable cation ratios and in the yields of subsequent groundnut and maize crops. High rates of potassium and nitrogen, combined with low rates of calcium, lowered groundnut yields, and high rates of potassium, enhanced by ploughing in crop-residue ash, seriously reduced the exchangeable Mg: K cation ratio and maize magnesium status. Maize yields were significantly negatively correlated with soil potassium status. The balance between exchangeable cations in these soils is very easily upset by injudicious combinations of fertilizers and management practices.

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 efficiency of the randomized complete block design, relative to the completely randomized design, is linearly expressed as: Relative efficiency=A+CF, where A and C are constants determined by the number of treatments (t) and blocks (b) and F=calculated F value for blocks in the ANOVA table. For values of t and b ranging from 2 to 10 the constants A and C are estimated. Curves of relative efficiency are given when o≤F≤10 for t values ranging from 2 to 10 when b=4, 6 and 8.

The relations between sugar content and certain features of growth were followed in 16 sugarcane varieties during two crops. High sugar content was promoted by the absence of tillering during cane elongation, by a high leaf blade to joint weight ratio, by a long phyllochron, and perhaps slightly by a long life span of leaves. To combine high yield with high sugar content it is important to have a high tiller number early in growth, which appears to be promoted by delayed onset of cane elongation, small initial leaf size, and an upright leaf habit. To combine a small initial leaf size with a high leaf blade/joint weight ratio during elongation requires a large increase of leaf size during growth.

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.

The important interactions in a 2-year maize trial were population × location, location × year and population × year × location, and our analyses suggest that eight locations, two years and three replications will allow the detection of a 5% differential in yield. The most effective way of obtaining the true value of a variety is by increasing the number of years, and the least effective is by increasing the number of replications. Since locations can be effectively substituted for years, increasing the number of locations will expedite the release of improved cultivars.

Variety, spacing and harvesting date trials with fodder beet were carried out in Cyprus under rainfed conditions. The variety Polyrossa gave the highest dry matter (DM) yield, 12,906 kg/ha. Yield of DM increased linearly with population density to an optimum spacing of 45 × 20 cm. Yields of beet decreased slightly when harvested after 15 June and significantly when harvested after 29 August. Irrigation with saline water increased DM yields.

The design of field trials sometimes raises queries (which often go unanswered) about alternative designs and the best ways of allowing for environmental variation in the area allotted to the experiment. It is shown how recent developments in iterative methods for working out analyses of variance make possible the determination of error for systems of blocks other than the one actually used, and also for the row-and-column case. Some suggestions are also made for judging the error to be expected if plots were made larger.

Trials are described comparing the effects of applying four, eight and 12 sprays of various insecticides on control of Heliothis armigera Hub, and Earias biplaga Wlk., and the consequent effect on yield and quality of seed cotton produced. Yields of unsprayed cotton ranged from 300–900 kg/ha, while four sprays of DDT gave 1000–1200 kg/ha. Increasing the number of sprays to 12, using three insecticides (DDT, endosulfan and carbaryl) gave increments of 300–600 kg/ha over the standard four spray treatment. Eight sprays gave smaller but significant yield increases, and endosulfan, dicrotophos and carbaryl were particularly promising in such regimes. A mixed DDT/phenthoate spray was not superior to DDT used alone. Spraying reduced the percentage of stained cotton.

The growth and development of a short-season sweet potato (Nemagold) and a long-season cultivar (White Maltese) were compared quantitatively in sub-tropical Australia and also with growth data for Nemagold in a temperate environment. Total and storage root dry matter production (DMP) followed autocatalytic equations, with similar whole plant DMP from planting to week 25 for both cultivars but plateauing (at 90% of asymptotic weight) at week 23 for Nemagold (448 g) with favourable temperatures and at week 38 for White Maltese (813 g) when temperatures were unfavourable. Storage root DMP of Nemagold plateaued at week 23 (246 g) and at week 36 (219 g) for White Maltese. Data are given on other attributes and on phasic development.

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.

Changes in soil moisture and nitrate content in the top 75 cm of soil in bare and cropped plots were followed throughout the growing season in a Ferruginous savanna soil. A low leaching efficiency, of 0.38–0.66 cm/cm rainfall, was related to very slow wetting of the subsoil, a phenomenon which could be explained satisfactorily only by assuming that part of the rain passed through the profile relatively quickly in the larger pores. However, losses of fertilizer nitrate to deep drainage by this rapid percolation were only 25% of that applied, at most, the greater part remaining in the top 45 cm of soil for almost the whole growing season, thus explaining why only small responses have been obtained at this site to delayed or split applications of nitrogen.

Since 1970 the University College of North Wales, in co-operation with the Saudi Arabian Ministry of Agriculture and Water, has been investigating the potential for forage production in all-year-round irrigated conditions in Saudi Arabia, and the principal results of the first 4 years of field experiments are discussed. Both temperate and tropical annual forages as well as perennial species were tested, and generally produced high yields with high nutritional value. Fertilizer responses and different management practices were evaluated and their relevance to the development of systems of forage production are discussed.

Three systemic insecticide granules, viz. carbofuran, phorate and disulfoton, were applied at 1·0, 1·5 and 2·0 kg ai/ha on 16 January, 16 February and 16 March 1973 against Brevicoryne brassicae Linn. on Indian rape plants (Brassica campestris var. sarson) in the Kulu valley, Himachal Pradesh, India. The results showed that phorate at 2·0 kg/ha, followed by disulfoton, applied on 16 February, gave effective control of the pest and were reasonably persistent. None of the granules were phytotoxic but these treatments increased crop yields.

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.

Trials on leaf abscission of cassava led to the conclusion that the leaf lamina is necessary, and must receive light, to prevent abscission of the petiole. The abscission rate of old leaves is increased by the presence of an active apex, but is not affected by the carbohydrate requirements of the roots.