Nearly two hundred years have elapsed since Robert Malthus published (anonymously) his first ‘Essay on the Principle of Population as it Affects the Future Improvement of Society …’. Population, he argued, will always grow faster than the means to sustain it, unless constraints to its growth arise naturally or are imposed artificially.

The proliferation of statistical methods and software increases the need for authors to state, unambiguously and informatively, the methods they have used. The reader of any paper should expect to learn precisely what the author has done, and to be able to adopt similar procedures in his or her own work.

This paper offers guidelines for the presentation of statistical material in scientific journals and project reports. Emphasis is given to the importance of planning a study so that the various components of statistical material can be linked to ensure the full efficiency of the work; if this is done well, the presentation of the results of the study, including the statistical components, can be achieved with greater ease.

Impact assessment is important to agricultural research. It quantifies benefits from both proposed and past research, and allows comparisons of the cost effectiveness of different research investments as a basis for priority setting. Though there are important economies of scale in the global and regional level research done by the international centres of the Consultative Group for International Agricultural Research (CGIAR), this research covers only one small sector in the sequence of research and development reaching down into farmers' fields. CGIAR impact thus depends on the rest of the research and development (R&D) sequence operating effectively, something largely beyond its control. In deciding a strategy for impact assessment, the international centres need to resolve two dilemmas: first, how much impact assessment they should do, for their own programme planning and monitoring, and to satisfy their stakeholder constituencies; and secondly, how sophisticated this assessment should be. Impact measurement is itself research and, like all research, is very much concerned with how much is gained from the extra costs of collecting further information.

Centros agrícolas internacionales

The effects of weeds on coffee productivity and the methods used for their control are discussed. The more common weeds are listed, together with the control methods that can be used at various phases of coffee production.

Malezas y control de las mismas en el café

Grain barley was grown either continually or in rotation with fallow in a 12-year experiment. Annual rainfall ranged from 120 to 297 mm. As the water requirement of the crop is 240 mm, growth in most seasons occurred under water stress. The amount of water conserved under fallow was only significant (75–100 mm) in three of the 12 years and only once did the water conserved increase barley yield in the following year. The total grain yield over the experimental period was twice as high in the barley–barley sequence as in the barley–fallow sequence.

Cultiuo continuo de cebada o después de barbecho

Crop simulation models have been proposed as tools for the transfer of technology in less developed countries. Using a validation exercise as a framework for evaluation, this study looked at the ease of use of a simulation model in a small African research station. Although the model did not accurately predict grain yield of the local maize hybrid, the procedure did highlight some of the problems involved in applying the model. The constraints to the use of such models at small research stations are discussed and improvements that could facilitate model use are suggested.

Uso de model de cultivo para la investigación en Africa

The effects of cropping system, nitrogen application and harvesting stage on the quantity and quality of the forage produced by Sudan grass-lablab mixtures were studied in central Sudan. Mixing increased the number of tillers plant-1 of Sudan grass and the plant dry weight of both crops. Application of nitrogen increased the number of tillers and dry weight plant-1 of Sudan grass but had no significant effect on the growth parameters of lablab. Growth parameters of both crops were appreciably increased by harvesting at the milk-ripe stage of Sudan grass. The largest total dry matter yield was obtained from a mixture of 20 kg Sudan grass and 40 kg lablab ha-l, but the largest protein yield was obtained from sole lablab.

Nitrógeno en combinaciones de sorgo sudanés y Lablab purpureus

The influence of liming and method of cultivation on the dry matter yield, botanical composition and seedling density of a rainfed pasture grown in a Mediterranean environment from a commercial seed mixture based on subterranean clover was investigated. Liming resulted in a 2.5-fold increase in pasture dry matter yield. Yields were greater when the soil was scarified before sowing than when it was ploughed, and when the lime was spread after cultivation rather than before. Liming and scarifying increased the proportion of sown species (subterranean clover, white clover and tall fescue) and reduced the proportion of native species and bare ground. Subterranean clover seedling density was higher after scarifying than after ploughing.

Uso de cal en pastos mediterráneos regados por precipitaciones

Yields of intercropped cotton and groundnuts grown on alternate ridges 75 cm apart were compared in areas of high (more than 1000 mm a year) and low (less than 800 mm a year) rainfall and in rainy seasons with a low and high frequency of drought periods. There was no advantage from intercropping in the low rainfall area but in the high rainfall area land equivalent ratios of about 1.4 were obtained, confirming that intercropping is more suited to wet conditions. These high land equivalent ratios were associated with enhanced yields per plant in the cotton and unsuppressed yields per plant in the groundnuts, suggesting that a crop such as cotton, which both tolerates a wide range of population density and has a late-developing leaf canopy, may be particularly well suited to intercropping.

Cultivo simultáneo de algodón y chufa en zonas con altas y bajas precipitaciones en el este de Zambia

Oil palm rachis length was determined on primordia dissected from palms planted at four densities. It started to increase rapidly in leaf–10, that is, about ten leaves younger than the spear leaf in all density treatments. The mean number of leaf primordia at the three higher palm densities was 47.7 compared with 51.5 at the lowest density of 56 palms ha-1. Some of the palms planted at the highest density were thinned to identify the stage at which the amount of light affected the rate of leaf opening. A sudden increment of light accelerated leaf production at both the rapid expansion stage and the preceding slow expansion stage. The greatest acceleration of leaf production began 24 months after thinning, probably because of the effect of the extra light on the rate of leaf initiation. The response of leaf production to thinning may apply to other related cultural practices.

Desarrollo de hojas en la palma aceitera (Elaeis guineensis) y determination de la tasa de apertura de las hojas

Irrigation responses of three locally adapted onion cultivars were studied in drainage type lysimeters and under field conditions on a deep sandy loam soil, free of salinity problems, at Maradi in Niger. Evapotranspiration (Et) was established by the water balance method, and used to establish the rate of water use. The peak rate of water use was 7.5 mm per day during the bulb formation stage. Irrigating onions when the available soil moisture to a depth of 20 cm had been depleted by 40% increased the yield more than irrigation at 60 or 80% depletion. The mean yield from plots receiving frequent irrigation was 33 t ha−1.

Evapotranspiratión de la cebolla en el sahel nigeriano

The possibility of growing dry peas in the semi-arid areas of Mediterranean countries was assessed by comparing dry pea (Pisum sativum L.) varieties with the highest yielding barley and durum wheat varieties under rainfed conditions and with supplementary irrigation in Cyprus. The yield of barley cv. Kantara was greater than that of the best pea variety selected, PS 210713, especially under the driest conditions, but the differences between cereals and dry pea varieties were smaller when grown in areas where there was more rain or where supplementary irrigation was supplied. The protein content of the dry seeds and straw of the peas was higher than those of the cereals. It is concluded that selected varieties of dry peas could be grown in dry Mediterranean areas, particularly in rotation with barley or wheat.

Pisum sativum L. para zonas mediterráneas