Integrated pest management (IPM) in rice has been mainly applied to irrigated, lowland paddy rice ecosystems which generally use more inputs and have higher yields ha−1 than rainfed ecosystems. Large scale implementation of IPM was stimulated in the 1970s in several Asian countries by pest resurgences resulting from indiscriminate insecticide use. Legislation has been enacted in at least five countries to support IPM and by 1992, approximately 0.05% of Asian farmers had received training in IPM. In at least two countries, adoption of IPM as national policy has resulted in large savings from reduced importation of pesticides with no reduction in total rice output or productivity. The inter-country programme on rice IPM of the Food and Agriculture Organization (FAO), the United Nations, the International Rice Research Institute and national programmes have all contributed to promoting rice IPM. Host plant resistance, deployed with location-specific cultural practices that conserve natural enemies, remains the basis for sustainable, low-cost rice IPM. Thresholds, monitoring and forecasting systems have little or no impact on farmer practice in the tropics; farmer group learning appears to be the most effective way towards IPM adoption.

Manejo integrado de plagas en el arroz

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.

Stomatal conductances (g) and photosynthetic rates (A) were monitored in six tea clones planted in a clone X irrigation experiment in the Southern Highlands of Tanzania. Measurements were made during the warm dry seasons of 1989 and 1990. There was no genotype X treatment interaction in the response in A or g of the various clones to irrigation. Irrigation increased A more than it increased g. Irrigation also increased the temperature optimum for photosynthesis and decreased photo-inhibition at high illuminance. Clones differed in g and A, and in the relationship between leaf temperature and A. The implications of these findings for clone selection are discussed.

Four genotypes of ‘desi’ and two of ‘kabuli’ chickpea (Cicer arietinum) were sown at six locations in Australia on various dates between 1986 and 1988, giving 22 combinations of site and sowing date with diverse photothermal environments. Times from sowing to first flowering (f) varied from 30 to 162 d, mean pre-flowering temperatures from 10.8° to 29.3°C and mean photoperiods from 11.3 to 15.6 h d−1. There was no evidence that any observation had been obtained in photoperiods shorter than the ceiling photoperiod (Pcc) or longer than the critical photoperiod (Pc). This suggests that, in typical agricultural environments, chickpea crops experience photoperiods (P) which should satisfy the condition Pcce < P < Pc. In one ‘kabuli’ and two ‘desi’ genotypes, 1/f was influenced by both temperature and photoperiod. The coefficient of determination (R2) for a linear, additive rate of development model ranged from 0.74 to 0.80, with no significant difference in either temperature sensitivity or photoperiod sensitivity among these three genotypes. In the remaining three genotypes, no significant response to temperature was detected between 10.8° and 29.2°C, so rate of progress to flowering was influenced solely by photoperiod. There was no significant difference in the sensitivity of 1/f to P among these three genotypes. The linear, additive rate model found here to be so satisfactory as a predictive tool for phenology, is also shown to have much wider general application.

Predicción del liempo de floración

Commercial cassava production from true cassava seeds (TCS) appears to be a promising option for reducing or eliminating several of the production constraints associated with vegetative propagation. The most important contribution of TCS would be to reduce virus build-up in vegetative material and to resolve the problems of stake storage, low multiplication rate and the long growth cycle. Preliminary results suggest that the root yield potential of TCS is comparable with that of traditional vegetative propagation. Improvements in the capacity of true seed progenies to germinate and establish in the field can be achieved either genetically or through pre-planting seed treatments such as coating the seed with rock phosphate. Development of a successful TCS technology will require a multidisciplinary approach, involving basic studies in cassava breeding, physiology, agronomy, socio-economics and other fields.

Changes in seed quality were monitored during seed development and maturation in three genotypes of soyabean (Glycine max), the USA cv. Bossier, the Indonesian line TGm 737p, and their cross TGx 536–02D in a controlled environment of 30°/20°C (day/night temperatures). The capacity of seeds to germinate following desiccation and their potential longevity increased after the end of the seed-filling phase. Potential longevity reached a maximum close to harvest maturity (that is, when seed moisture content had declined naturally to 14–15%). The subsequent decline in potential longevity in all three genotypes was quantitatively similar to that predicted in post-harvest air-dry seed storage in similar environments, but was far less in TGm 737p than in the other two genotypes as a consequence of the lower moisture content of its mature seeds. These findings contradict the previously well-established hypotheses that seed quality in soyabean is maximal at the end of the seed-filling phase and that viability and vigour begin to decline immediately thereafter. They also infer that the desirable seed longevity characteristics of the Indonesian line TGm 737p may not have been successfully incorporated into the cross TGx 536–02D.

Calidad y desarrollo de similla en la soja

Six genotypes of cowpea (Vigna unguiculata) of diverse origin were sown on various dates at five locations in Australia in order to provide a range of photothermal environments. Times from sowing to first flowering (f) ranged between 36 d and 145 d; pre-flowering temperature and photoperiod means varied from 15.7° to 29.2°C and from 11.6 to 15.5 h d−1. In five genotypes there was no effect of photoperiod on rate of progress towards flowering (1/f), but the relation between 1/f and mean temperature was always positive. The base temperatures (at which 1/f = 0) varied between 8.1° and 10.4°C. The rankings of parameter estimates among four photoperiod-insensitive genotypes common to this study and earlier research in controlled environments were almost identical, and there was generally good agreement between field observations and predictions from controlled environments once hourly temperatures were used to describe the natural environment. When cowpea plants were exposed to temperatures below 3°C, flowering was delayed beyond expected values, presumably as a result of chilling damage. In one genotype, rate of progress towards flowering was affected by both temperature and photoperiod, and relations between 1/f and the photothermal environment were described by a two-plane linear model of similar form to that determined in an earlier controlled environment study. These latest findings support the utility of such linear models for the prediction of crop phenology in the field and for the genetic characterization of photothermal flowering response in annual crops.

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.

Poor drainage of Vertisols in the Ethiopian mid-altitude highlands limits farming operations and cropping in the early rainy season (July–August). Traditional crops are grown on residual moisture late in the season (September–January) when waterlogging is less of a problem. Productivity is therefore below its potential. The recent introduction of a broadbed and furrow system for improved drainage on Vertisols allows full use of the growing period and provides scope for a wider variety of cropping systems and increased productivity. Trials using a sequential cropping system demonstrated that two crops a year can be grown when Vertisols are drained. The crops used in the trial were oats or an oat/vetch mixture forage in the early season followed by grasspea or chickpea food crops in the late season as the second crop. Further on-farm research on sequential cropping of forages and food crops in the mid-altitude highlands of Ethiopia is now needed.

Several parameters of seed vigour were monitored during seed development and maturation in three contrasting genotypes of soyabean (Glycine max)— the USA cv. Bossier, the Indonesian line TGM 737p, and the cross between these two parents TGx 536–02D—grown in three different temperature regimes. Evidence of a decline in seed quality in the pre-harvest environment was seldom detected until harvest maturity, when seed moisture content had declined naturally to 14–15%. Atypically, an increase in the susceptibility of freshly-harvested shelled seeds to imbibition damage was detected before harvest maturity for cv. Bossier in the two warmer regimes. Seeds of cv. Bossier were also far more vulnerable after harvest maturity to pre-harvest deterioration in the warmer environment than the other two genotypes. From these results and those from two earlier studies, it would appear that the main seed quality characteristic of TGm 737p that has been incorporated successfully into the cross is resistance to soaking damage, rather than enhanced air-dry seed storage longevity per se.

Desarrollo y vigor de la semilla en la soja

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.

Eight genotypes of cultivated mung bean, black gram and rice bean (Vigna mungo, Vigna radiata ssp. radiata and Vigna umbellata, respectively) were sown at six sites in Australia on various dates in order to provide a range of photothermal environments. In addition, four accessions of the related wild species Vigna radiata ssp. sublobata were sown on five occasions. Times from sowing to first flowering (f) varied between environments from 34 to 317 d; pre-flowering temperature and photoperiod means ranged from 12.7° to 29.1°C and from 11.8 to 15.5 h d−1. No effect of photoperiod was detected on rate of progress towards first flowering (1/f) in four genotypes, but in each case a significant positive relation was detected between 1/f and mean temperature. These simple thermal time relations did not differ significantly among these four genotypes; the common base temperature was 7.9°C. In two genotypes observations were well described by a thermal response plane when the mean photoperiod was less than 13 h d−1 (p < 0.01) but photoperiods greater than 14 h d−1 delayed flowering. In each of the remaining genotypes the observations were best described by photothermal planes, that is, 1/f was modulated by temperature and photoperiod. Predictions from the models based on our data were in good agreement with the times to first flowering observed in three genotypes in an earlier controlled environment study.

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

This paper describes an attempt to develop and evaluate agricultural extension materials that support farmers' use of flexible management strategies. On the basis of experiment station and on-farm research results relating to millet and cowpea intercropping in Niger, a series of recommendations was developed, taking the form of a decision tree. The process of testing this format at the level of field extension agents and the implications of this experience for both research and extension workers are described.

Farmer surveys have consistently shown maize storage losses to be of primary concern to farmers in the western highlands of Cameroon. Past attempts at evaluating these losses, however, have proved to be unsatisfactory, mainly because of failure to consider qualitative, as well as quantitative, losses or to take account of consumption patterns (that is, timing and end use). A simulation model is presented that overcomes these deficiencies while providing a reliable estimate of the economic value of storage losses to the farmer, albeit at the cost of requiring fairly exacting data. The model is used to estimate the value of storage losses to farmers in the North West Province of Cameroon.

Following a survey of fertilizer use on farmers' barley fields in northern Syria and very positive results from barley fertilizer trials on ICARDA research stations, a programme of researcher managed trials on farmers' fields indicated considerable potential for yield increase from the use of nitrogen and phosphorus fertilizers across a range of environments. It was then necessary to test and demonstrate the effectiveness of fertilizers in farmers' hands. A researcher managed trial (RMT) and a farmer managed trial (FMT), with similar fertilizer treatments, were compared over the winter cropping season on each of 10 on-farm sites in 1987/88 and 20 sites in 1988/1989. Despite large differences in rainfall between the two seasons (means across sites, 422 mm in 1987/88 and 174 mm in 1988/89), yield responses to fertilizer were similar in both seasons, with only marginal yield differences between researcher and farmer managed trials. Crop sequence had no effect on the pattern of fertilizer response in either type of trial. Once the effectiveness of fertilizers had been tested in farmers' hands, demonstration trials were conducted in the following two years to transfer the technology to farmers in the barley growing areas of northern Syria.

Ensayos conducidos por agricultores e investigadores en Siria

This paper addresses the issue of genotype by environment (G × E) interaction in relation to the distribution of germplasm from international to national breeding programmes. Theoretical aspects of G × E interaction and of the selection versus the test environment are reviewed. The importance of specific adaptation to maximize yield and yield stability under stress conditions is highlighted in barley and lentil. We conclude that repeated cycles of selection at a few sites have a high probability of reducing the frequency of genotypes specifically adapted to environmental and/or agronomic conditions not represented at those sites. Therefore a wider and earlier devolution of the selection work done by International Agricultural Research Centres (IARCs) to plant breeders in national programmes will increase the chances of exploiting positive G × E interactions. It will also address the needs of small, resource-poor, subsistence farmers and reduce the danger of narrowing genetic diversity within crops and regions. This is an efficient way of making breeding programmes in less developed countries more self-reliant, which is a major objective of International Agricultural Research Centres.

Programas internacionales de reproducción

Nitrogen deficiency severely limits production of the bean–maize association grown by small-scale farmers in upland Peru. Sixty-four bean Rhizobium isolates were evaluated for induction of a plant growth response in pots of soil from the area and 14 of the most promising strains of these were tested on farmers' fields in 13 trials over a three year period. Bean yields were increased by inoculation with at least one Rhizobium strain in seven of the trials, with increases ranging from 0.21 to 0.68 t ha−1. Bean yields were not increased by the application of 120 kg N ha−1 to the intercrop. Maize yields were increased by Rhizobium inoculation in nine of the 13 trials by between 0.34 and 1.85 t ha−1. Maize responded to nitrogen fertilizer on the same nine farms. This Rhizobium selection strategy, although laborious, was effective in identifying strains that can be recommended for use as inoculants by farmers in the region.

Tillage trials on sandy soils in Zimbabwe have shown that sheet erosion from arable fields under a no-till tied ridging treatment is negligible but that the system generates environmental conditions that have an adverse effect on crop potential. Tied ridging improves crop production by preventing waterlogging in high rainfall years and improving rooting depth when adequate water supply prevents soils from setting hard, but it causes high temperatures in the ridges and rapid drying during dry weather, resulting in poor or delayed emergence and thus in low and uneven crop stands. New strategies need to be developed to minimize these effects.

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