The hydraulic press was compared with the dew point psychrometer and the pressure chamber methods for measuring leaf water potential (Ψ) in groundnuts (Arachis hypogaea L.). For measurements on the same leaf, regression analysis revealed that the slopes did not differ significantly from unity. An analysis of functional relations between measurements made by the press and the dew point psychrometer or the press and the pressure chamber showed that the error variance of the press was similar to those of the two other methods. Therefore, we conclude that for groundnuts the performance of the press, the dew point psychrometer and the pressure chamber are similar.

A technique for observing the effects of soil physical and other factors on root growth was evaluated, using glass tubes packed with soil. The number of root intersections observed on a grid at the interface between the soil and glass was correlated with the number of root ends counted within the soil core. Comparatively small differences in the dry bulk density of a structureless sandy loam (1.25 and 1.50 g cm−3) had much larger effects than differential watering treatments on the pattern of root growth of lettuces (Lactuca sativa). Loosening the soil to depth (with additional fertilizer) increased the availability of water, under both wet and dry conditions, and improved water use efficiency, primarily through effects on root activity.

The first number of the Empire Journal of Experimental Agriculture, of which this journal is the immediate successor, appeared in April 1933. It was part of a significant collaborative trend which included the Empire Marketing Board, the Commonwealth Agricultural Bureaux, and the International Wheat Pool, and led in time to the Commonwealth Secretariat and, indirectly, to FAO. The new journal was intended to serve agricultural progress in all the countries of the world which were connected with Britain, including South Africa and the Sudan. In the subsequent half-century of great change many new general and specialist journals have arisen, particularly in the more developed countries, in the Commonwealth and elsewhere; and this journal has come to be concerned mainly with production-oriented agricultural research in tropical, sub-tropical and winter-rainfall environments.

Most scientists now own, or have access to, an electronic calculator and appear to have absolute faith in the answers it gives. However, these calculators have design limitations which for some data sets will affect the accuracy of the calculations and so produce incorrect results. In statistics work, corrected sums of squares and products, needed for Analyses of Variance and Regression Analyses, can be affected. The first two sections of this paper describe these limitations and illustrate how they can affect the result of calculating the variance of a particular data set. A simple procedure is then described that will help overcome the problem. Finally, in anticipaion that the micro-computer will eventually replace the calculator as the main mathematical tool, a more general procedure is given for calculating the sums of squares and products.

Shifting agriculture is an ancient basis for maintaining soil fertility but pressures of population have caused it to give place in most countries to rotations and bare fallows which, in turn, have had to be reduced or modified. Research on various measures to shorten the duration of fallows and increase their effectiveness is reviewed. These measures include the use of organic manures and inorganic fertilizers, green manuring, mulches and the growing of legumes and grasses, which are discussed in relation to their effects on the soil and on crop yields. The increasing use of the factorially-designed experiment is recognized as a major contributor to this research.

Field experiments during 1979 and 1980 on a Vertisol soil at ICRISAT Centre, Hyderabad, India, examined the residual effect of pigeonpea (Cajanus cajan) on growth and yield of a following maize crop. Pigeonpea was grown alone or as an intercrop with sorghum fertilized or not with 80 kg N ha−1. Sorghum alone and fallow treatments were included for comparison. In the first year, the sorghum/pigeonpea intercrop produced the largest grain and dry matter yields, but the yield of intercropped pigeonpea was about 50% less than that produced by the sole crop. Pigeonpea alone had a large residual effect on maize, increasing grain yield by 57% and total plant dry matter by 32% compared with corresponding values after fallow. In comparison, intercrop pigeonpea had little residual effect. Maize following either fallow, sorghum grown alone, with or without N, or the sorghum/pigeonpea intercrop, again with or without N, required fertilizer equivalent to 38–49 kg N ha−1 in order to attain yields similar to that of unfertilized maize following sole crop pigeonpea.

A fluorescent-dye technique has been developed to measure root length of field crops. Roots are washed from soil samples, stained for about 30 min in a solution of fluorescein diacetate in acetone, washed, spread out on a tension table and photographed under UV light. Lengths of fluorescent roots recorded on the photograph are estimated by line intersection. The method is quick, simple, inexpensive and largely eliminates the usual time-consuming, tedious process of hand-sorting live roots from organic debris. Whereas all the roots of young laboratory-grown plants take up the dye, some older roots of field-grown crops do not fluoresce. Data indicate that the method may also give information on root diameter.

Large yields and dry matter production rates have been recorded for tropical perennial crops, despite the fact that little research has been done on most of them. Considerable increases in productivity should still be possible, since the potential energy fixation rate for such crops is estimated to be about 1.2 TJ ha−1 a−1. The dry matter equivalent of this energy varies between species; the oil crops and rubber, in particular, have large energy contents in their respective economic products. Hot leaf temperatures appear to limit productivity in some crops, while unfavourable partitioning of assimilates limits yield at the large leaf area indices necessary to maximize dry matter production. Respiratory losses are large in these crops and selection for smaller respiration rates could lead to considerable improvements in their net productivity.

A study was undertaken to find out the nitrogen requirement of wheat (WH-157) when grown after various grain legumes on the sandy loam soils at Hissar (NW India). Yields of wheat were significantly increased when grown after black gram (110%), green gram (108%) and soyabean (41%) compared with those after pigeonpea. Preceding crops of green gram and black gram reduced the nitrogen requirement of a succeeding wheat crop by 30–60 kg ha−1, compared with only 30 kg ha−1 after pigeonpea or soyabean. Pigeonpea was least beneficial in this regard but a pigeonpea-wheat cropping sequence produced the maximum net profit.

A graphical method, based on bivariate analysis, is used to present yield data from intercropping experiments involving two crop species. The method is used to demonstrate two- and three-factor interactions in factorial experiments.

Mixed tree and food crop farming systems are being developed in the humid tropics. They offer one solution to the problems caused by population pressure and de-forestation, since they can provide a satisfactory income to the subsistence farmer, while adequately protecting the environment In seeking to develop optimal systems, examples and information can be drawn from traditional mixed cropping systems, from taungya systems of forestation, and from other systems developed within the commodity cropping sector. However, the full potential of mixtures involving perennials and food crops can only be realised within the limitations of local socio-economic and political circumstances.

Maturation of peas in cool temperatures (mean 17.5°C) at Dalang Maidan, Lahaul (in the Himalayas) led to the development of larger seeds in comparison to those of the same varieties which had matured in warmer temperatures (mean 24.5°C) at Delhi, India. The larger seeds from Lahaul, when sown at Delhi, gave rise to taller plants which came into flower earlier compared with those from the seeds matured at Delhi. Significant location ′ variety interactions were recorded for germination and plant height. Inherent variation in days to flowering could have been a major factor in these interactions. These data are of direct importance to breeders using seeds developed at more than a single location if environmental conditions differ appreciably.

Three levels of N were imposed on mature Indian hybrid tea and green leaves were harvested according to different plucking standards at either 7 or 14-day intervals throughout the main production period. Larger rates of N and less selective plucking standards improved the fresh weight of shoots harvested but dry matter yields were less and the proportions of waste fibre in the finished product were increased. Thus, saleable black tea production was less responsive to N and plucking standard and the order of combined treatment effects was altered. Plucking interval did not affect yield but it changed the distribution of the crop in time. A 7-day interval gave the most uniform crop. These data are discussed in relation to the economics of tea production in Central Africa.

The yields of eight grass species, Axonopus compressus, Brachiaria decumbens, B. humidicola, B. miliiformis, Dicanthium caricosum, Ischaemum aristatum, Paspalum conjugatum and Stenotaphrum secundatum, were compared at five sites under different coconut densities giving variations in shade. Light transmission (LT) values were approximimately 100 (adjacent open area), 70, 50, 40 and 20% of full sunlight. Soils were fertile, red-brown clays developed on uplifted coral limestone (typic arguidoll), with marginal K status. Brachiaria spp. yielded most in full sunlight, with B. decumbens giving 28 t ha−1 year−1. I. aristatum was less sensitive to shade than the Brachiaria spp., at least down to 40% LT. S. secundatum, although poor yielding at 100 and 70% LT, gave the best yield of all species at 20% LT. Shaded plants had thinner leaves and larger nitrogen concentrations than unshaded ones. B. decumbens and B. humidicola are recommended for open plantations (LT > 70%), I. aristatum for moderate shade (LT 45–70%) and S. secundatum for deeper shade (30–50%) on poor fertility soils.

A two year study on ‘Pusa Sawani’ okra grown during the summer in Rampur, Nepal (228 m OD; 27° 37′ N) has shown that spacing did not affect days to first harvest or pod length but that pod number plant−1 was affected significantly. Although individual plant yields at each harvest were maximum viith plants spaced 45 cm apart (a population of about 50,000 plants ha−1) pod yields ha−1 were maximum with plants spaced only 15 cm apart (about 150,000 ha−1). Applications of nitrogen fertilizer hastened the first harvest by 4–6 days compared to the unfertilized control plots. The greatest pod yield (9.3 t ha−1) was obtained from plots given 60 kg N ha−1.

Field experiments were done during the rainy seasons of 1980 and 1981 at Hissar, India; they studied the effects of time of weed removal on the yield of mung beans. Removing weeds at 10, 20 or 30 days after sowing led to significantly larger yields than that of the weedy check. Maximum seed yields in booth years were obtained when weeds were removed 20 days after sowing

Glasshouse studies have shown that nodulation and dinitrogen fixation in groundnuts grown in a sand/vermiculite mixture increased with an increase in Rhizobium numbers inoculated onto each seed. Cultivars Robut 33-1 and TMV 2 required 106 rhizobia seed−1 for maximum nodulation and dinitrogen fixation, while cv. Kadiri 71-1 required larger numbers.

The black teas produced from the field treatments described previously (Cloughley et al., 1983) were evaluated chemically and organoleptically. Increasing N application rates and harvesting larger shoots had adverse effects on the liquor quality as assessed by theaflavin (TF) analysis, and on the value of the product as assessed by tea tasters' sensory examination. There were also large, regular intraseasonal fluctuations in TF content, small values corresponding to occasions of crop peaks. Shoots predominantly of 2 or 3 leaves and a bud harvested from plots given 135 kg N ha−1 generated the largest total cash value. A total value index (TVI), involving yield and quality, is introduced and illustrated.

Four cultivars of cowpeas (Vigna unguiculata L. Walp.) were grown in 15 sets of conditions (environments) i.e. in several monthly plantings in each of three years. Data for seed yield were analysed to investigate the effectiveness of using planting dates in preliminary yield trials of new cultivars. Extremely significant environment mean squares and wide ranges of environmental indices (− 13.3 to 23.5) and seed yield (11.4 to 48.2 g plant−1) indicated real differences among environments. Stability analyses of the cultivar × environment interactions suggest that, where limited funds preclude the use of several locations, monthly plantings for two or more years could be used effectively in the preliminary evaluation of cultivars without losing much information on their relative ranking.