A simple hand-held reflectometer was used to estimate the shoot dry matter of pearl millet (Pennisetum glaucum), groundnut (Arachis hypogaea), cowpea (Vigna unguiculata), weeds and grass swards non-destructively. While the instrument was able to predict shoot dry matter well for single, standing millet and cowpea plants and proved useful for a growth analysis of millet, its reliability was unsatisfactory for groundnut. For millet, the slope of two separate regressions between the difference of reflectance ratios and shoot dry matter, taken 10 days apart, was almost identical. This suggests a possible simplification in future crop growth models. The usefulness of the instrument for estimating dry matter in natural species mixtures such as weeds and grasses depended on the homogeneity of the mixture and the uniformity of their physiological state.

Medición de la biomasa utilizando la reflexión

The dry matter yield, nutritive value and persistence of three legume species (Stylosanthes hamata Taub., S. capitata Vog. and Centrosema pascuorum Mart. ex. Benth.) cut at different frequencies during the growing season or only once at the end of the growing season were compared. The shorter cutting intervals enhanced regrowth, but very frequent cutting reduced total dry matter and seed yields. A defoliation interval of three to six weeks is recommended. Generally, S. hamata gave the best performance.

Efecto del deshoje en tres legumbres

The effects of phosphorus enrichment of Azolla inoculum and phosphorus fertilization during intercropping on the growth, nitrogen fixation and phosphorus content of Azolla caroliniana and the grain yield, straw yield and nitrogen uptake of rice were studied for four consecutive seasons. The phosphorus-enriched Azolla maintained a higher plant phosphorus content and produced a greater biomass and nitrogen yield than the unenriched Azolla. Application of phosphorus during intercropping significantly increased the dry weight, nitrogen yield and phosphorus content of both unenriched and phosphorus-enriched Azolla. The differences between the enriched and unenriched Azolla declined as increasing levels of phosphorus were applied during intercropping. The grain and straw yields and nitrogen uptake of rice were increased both by phosphorus-enrichment of Azolla inoculum and by phosphorus fertilization during intercropping.

La gestión de fósforos para la siembra simultánea del Azolla y el arroz

Surveys and on-farm trials are frequently used to facilitate farmer participation in agricultural research. This paper reports on a less common method-farmer involvement in on-station trials. Thirty-nine farmers were invited to multipurpose-tree screening trials in Burundi. Three different methods were used to determine which species the farmers wanted to test on their own farms. Private interviews and voting by a show of hands in plenary sessions gave very similar results whereas focus group interviews produced different and contradictory results. Researchers also learned what criteria farmers used to evaluate trees and the reasons for their choices. A supplementary survey of farmers’ preferences for trees grown on their own farms confirmed the findings and more clearly defined their criteria. In this survey, farmers used a local board game, Bao, to rate tree species across criteria they considered important. Overall, the visit to the trials and follow-up survey proved to be a useful and cost-effective method for getting farmer input and applying it in the screening process.

La participación de los agricultores en la selección de especies de árboles

Chickpea yields in Israel are usually considerably lower than wheat yields under comparable conditions. This study aimed to examine the possible yield limiting factors in chickpeas. Increasing the availability of nitrogen during seed development by a pre-sowing application of nitrate or by nitrogen top dressing at the onset of flowering led to an increase in the percentage of nitrogen in the straw but had no significant effect on seed yield. Growth analysis of chickpeas and wheat grown in two adjacent field experiments revealed that during the fruiting period these crops accumulated similar amounts of dry matter. However, the proportion of total wheat dry matter accumulated in the wheat grains was twice the proportion of total chickpea dry matter accumulated in the chickpea seeds. It was concluded that the main intrinisic factor limiting the seed yield of chickpeas is the continuation of vegetative growth during the period of seed development, which reduces the amount of assimilate allocated to the seeds.

Los factores restrictivos del rendimiento en el garbanzo

The intercropping of a young compact Arabica coffee hybrid with food crops was studied in three coffee growing areas in Kenya. Intercropping with Irish potatoes, dry beans, tomatoes, cabbages, kale, carrots, finger millet, sorghum or soyabeans was feasible in suitable coffee ecological zones. Intercropping with maize or sweet potatoes was not feasible because of their adverse effects on coffee growth in the early stages of coffee establishment, which led to substantial reductions in coffee yield.

Siembra simultánea de café arábica con cultivos de comestibles

Seeds of 50 sorghum genotypes were tested for emergence after imbibition in water for different times followed by up to 30 days of drying. The emergence of a large number of sorghum genotypes was then tested after 40 h imbibition in water followed by 10 h drying. Genotypes selected as resistant to 45 hours imbibition and 10 days drying regained turgor in the radicle and plumule when exposed to imbibition and drying injury. Genotypes showed significant difference both for emergence and seedling dry weight after exposure to this stress. The genotypes resistant to imbibition injury and drying had a specific protein of 33.0 KDa which was absent from those which were susceptible to such stress.

La adaptación del sorgo a la siembra seca

Dry matter and tuber yields of potato grown in a sub-tropical environment were estimated employing simple radiation-based models which require meteorological information on air temperature and solar radiation. Two versions of the MacKerron and Waister (1985) model, in which estimation of dry matter accumulation relies on a single composite parameter, radiation use efficiency (RUE), were compared with the Versteeg and Van Keulen (1986) model, which explicitly accounts for temperature and radiation effects on dry matter accumulation. In the original version of the MacKerron and Waister model, a linear change in the radiation interception factor with leaf area index is assumed; in the modified version an exponential change in the interception factor with leaf area index is considered. The accumulation of dry matter estimated from all three models was close to the measured values throughout the growing season, but estimates of tuber yield differed widely. Our analysis showed that the best agreement with measured values was obtained using the MacKerron and Waister linear model with RUE values adjusted according to the incident radiation level.

Estimatión del rendimiento del tubérculo de la patata

The literature on ‘stability analysis’, which is better called ‘sensitivity analysis’, leaves much to be desired. This paper attempts to clarify the issues, particularly the effect of the non-linearity of the standard model relating variety yields to mean yields over sites. The model is extended from its original applications in the analysis of crop yields to the analysis of measurements that cannot be considered Normally distributed, such as disease assessments expressed as percentages or proportions. Modern computer software offers a method that is theoretically sound and can be applied routinely to data of many different distributional types. Graphical methods of displaying the results of the analysis of non-Normal data are discussed.

Análisis de la sensibilidad de ensayos con variedades

Variation in time from sowing to flowering (f) was examined for 44 cultivars of soyabean, mungbean, black gram, ricebean, cowpea, chickpea, lentil and barley, when grown in up to 21 diverse environments obtained by making one or more sowings at each of six locations spanning tropical, sub-tropical and temperate climates in Australia. The utility of simple linear models, relating rate of development (l/f) towards flowering to mean photoperiod and temperature prevailing between sowing and flowering, was evaluated. The models were highly efficient, explaining most (86.7%) of the variation observed across species, cultivars and environments. They were particularly efficient in describing responses where cultivars were relatively well-adapted, in agronomic terms, and least efficient where cultivars were exposed to unfavourable temperature and, to a lesser extent, photoperiod. Opportunities for exploiting the models in applied crop improvement include their use in interpretation of G × E interaction, genotypic characterization and selection of parental genotypes, selection of test environments, designing screening procedures, and more efficiently matching genotypes to target environments. The main strengths of these linear, additive rate models in crop improvement are their wide applicability across species and genotypes, their relative simplicity, and the requirement for few genotype-specific response parameters. Their main weakness is their lack of precision in describing responses when plants are exposed to unfavourable photothermal extremes, albeit in circumstances that are sometimes unrealistic for cropping those particular genotypes.

Predicciones del tiempo que ha de transcurrir hanta la floración. VI.