Factorial treatment structure and, in particular, confounded designs are important methods of using experimental resources efficiently. Confounded experiments are not used, and possibly not understood, by experimenters. However, the construction and analysis of confounded designs is logically extremely simple, and can be expressed in terms of simple principles. Modern computing facilities can make confounded designs even more useful.

Pearl millet (Pennisetum typhoides) was grown on stored water at Niamey, Niger, using three row spacings (38, 75 and 150 cm), to determine the physiological basis of exploitation and conservation of water by crops during drought Between 18 and 32 days after sowing, roots grew rapidly beneath all crops reaching 140 cm in the narrow spacing, but there were differences between crops in the pattern of growth. Soil cores and trench profiles indicated that plants in wider rows had fewer, deeper roots. Substantial differences in both the amount and pattern of shoot growth were recorded in the different populations. Initially growth was fastest at the narrow spacing but stopped by day 45 and eventually the wide spacing produced most dry matter due mainly to greater survival of tillers. The partitioning of above ground dry matter into vegetative and reproductive fractions was similar at all three spacings and was consistent with figures for comparable crops elsewhere. The important role of tillers is discussed in relation to the development and maintenance of a canopy.

Pearl millet was grown on stored water at Niamey, Niger, using three row spacings. Water extraction based on neutron probe readings was compared with crop transpiration using a porometer and allied measurements. Between 23 and 52 days after sowing, plants at the narrow and medium spacings used about 77 and 100 mm of water, respectively, and those at the wide spacing used between 59 and 75 mm. Estimates of seasonal crop evaporation from leaf resistances and from the green leaf area index (GLAI) of the crops were 103, 130 and 123 mm for the narrow, medium and wide spacings, respectively. The water use per unit of dry weight produced was similar for both narrow and medium spacings but water was used more efficiently in the wide spacing. Dry weight increased in proportion to intercepted radiation with the same efficiency (1·3 g MJ−1) irrespective of spacing.

Rice varieties were compared for their response to infestation by the stalk-eyed fly, Diopsis thoracica (West), both when a choice of varieties was available to the pest and when there was no choice. The fly significantly decreased the number of panicles produced (both total and mature), the percentage of tillers with panicles, grain weight and total yield of unprotected plants, and increased the number of immature panicles and time to 50% flowering. Reductions in grain yield of between 2 and 97% were recorded but these losses were unrelated to the percentage of damaged tillers. Production of new tillers did not fully compensate for damaged ones in most varieties. However, photoperiod-sensitive rice varieties were better able to compen- sate for pest damage than most.

Differences in the water and air regime of the germination environment may cause variations of 30% and over in the yield of barley, wheat and oats.

Ramie (Boehmeria nivea Gaud.), which can provide fodder in addition to bast fibre, was supplied with nitrogen in three different forms: as neem cake coated urea (NCU), lac coated urea (LCU) and standard urea, at rates of 60, 120, 180, 240 and 300 kg N ha−1 annually in four equal applications. The ramie was cut four times a year for two years. NCU increased fresh weight, leaf dry matter yield and leaf protein at almost every cutting compared with the other forms of nitrogen, and there was an indication of increased residual nitrogen in the soil. Leaf dry matter and protein content increased with increasing levels of nitrogen up to 180 kg ha−1. It is suggested that coating urea with neem cake makes it a better source of nitrogen for ramie leaf production.

Six intercropping systems and four levels of nitrogen were compared at the Indian Agricultural Research Institute, New Delhi, in the summer rainy seasons (July-October) of 1978 and 1979. The maximum increase in sorghum yield was obtained when it was associated with fodder cowpea, followed by association with grain cowpea and greengram. The application of 40, 80 and 120 kg N ha−1 increased sorghum yield by 8.6, 16.1 and 18.2% in 1978 and by 2.9, 8.1 and 14.1% in 1979, respectively, compared with unfertilized sorghum. The nitrogen uptake by sorghum, and by the total system, was greater in sorghum-legume intercropping systems than in sole sorghum. Nitrogen application also increased the nitrogen uptake by sorghum and by the whole system.

Wheat yield was increased significantly when grown after sorghum intercropped with cowpeas (both for fodder and grain) or with groundnut compared with sole sorghum in the previous season. The nitrogen requirement for the target wheat yield of 4.0 t ha−1 was 108 kg ha−1 after sole sorghum and this was reduced by 87, 61, 83 and 38 kg ha−1 after intercrops of sorghum with fodder and grain cowpeas, groundnut and greengram, respectively. The different levels of nitrogen applied to the sorghum-legume intercropping systems also allowed savings of between 18 and 55 kg ha−1 of fertilizer nitrogen on wheat in the following season.