Field measurements using 30-month-old grevillea trees indicated that the three main sources of error in sap flow estimation can be overcome by: estimating the temperature bias with the gauge heater switched off or covering the whole trunk with 20 mm thick styrofoam sheet and alumimium foil; or by inserting thermocouples in the stem and accounting for radial and conductive heat losses. These corrections reduce gauge error for tree trunks (50–90 mm diameter) from 10–47% to ±7%. In the absence of a large lysimeter, a comparison of sap flow rates was made by attaching gauges to the trunk and a single terminal branch on the same tree.

Calibrado del flujo de la savia en los árboles del género Grevillea

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

Phosphorus, followed by potassium, were the plant nutrients that most limited yields during the third decade of a long-term fertilizer experiment on groundnut, maize and cassava conducted on an Ultisol in Ghana. Application of sulphate of ammonia significantly decreased soil pH, thus reducing crop yields. Superphosphate or mulch applied alone consistently increased the yields of all three crops. Application of potash increased the yield of cassava throughout the cropping period, but the potash × mulch interaction depressed yields in two of the three cropping seasons. Use of crop rotation, grass mulch and fertilizer, including small amounts of lime, enabled crop yields and soil fertility to be maintained at a fairly high level under continuous cropping.

Defoliation affected inflorescence production by oil palms, causing a decrease in sex ratio (ratio of female inflorescences to total) and an increase in abortion rate. Clones differed in response to defoliation. One of seven clones showed no increase in abortion rate; in one clone there was a tendency for female inflorescences to abort in greater numbers than males. The change in sex ratio occurred much sooner after defoliation in some clones than in others, and comparison of flowering records with dissections done at the time of defoliation indicated that inflorescence sex was affected at more than one stage in development. This has important consequences for attempts to predict yields.

Field experiments are commonly designed in blocks and there are sound reasons for using them, for example, control of unwanted environmental differences and administrative convenience. If used, they should be chosen to correspond to perceived differences in the site or to simplify farm operations and not merely to conform to statistical desiderata. Thus, it is not essential that each must contain one plot for each treatment, though there are advantages if they do. Some of the consequences of using other block sizes are examined, it being borne in mind that modern computer packages will perform most of the tiresome arithmetic. The effectiveness of blocks is considered and it is noted that they sometimes do harm rather than good. The analysis of variance is explained in terms of strata as used in many modern computer programs and is extended to include the recovery of information and resolvability. Recommendations are made as to randomization.

The numbers of bacteria and the nitrogen fixing efficiency of isolates of Rhizobium leguminosarum, R. ciceri and R. meliloti with appropriate legume crop species were determined from soils collected from a wide range of locations in Turkey with elevations between 500 and 2200 m. For vetch and lentil nodulated by R. leguminosarum, many native rhizobia are present in most locations but they often have limited nitrogen fixation capacity. However, for chickpea nodulated by R. ciceri, relatively small numbers of bacteria and the almost universal ineffectiveness of fixation capacity point to a need for artificial seed inoculation of chickpea crops as a future agronomic priority. The wide range of bacterial numbers, considerable geographic inconsistency and generally low effectiveness of the indigenous rhizobia associated with the annual Medicago spp. suggest that inoculation would initially be a sensible precaution for all sowings.

Biodiversidad del rhizobium en Asia occidental

Nitrate-nitrogen was analysed over two cropping seasons in 57 farmers' fields in the northern Guinea savanna of Nigeria. Differences between fields were at least five-fold and often ten-fold irrespective of fertilization rates. Average concentrations were highest at the beginning of the rainy season. Loamy soils had a later peak for nitrate release and maintained high concentrations for a longer period after the start of the rains than the more sandy soils. Nitrate-N was not correlated with soil organic carbon or total nitrogen content. Grain yield of maize was closely associated with nitrate-N in the soil but not with organic carbon or total N. Four patterns of nitrate-N release over the season could he differentiated using cluster analysis. Soil texture, soil pH, soil organic carbon, stover management and cropping history contributed most to a differentiation of the four cluster groups in a discriminant model. There was wide variability in the inherent soil-nitrate level and in its importance in explaining differences in yield among farmers' fields. The development of technologies resulting in improved nitrogen availability or better nitrogen utilization should be based on research of inherent soil processes. For the transfer of such technologies, recommendation domains should be defined based on different native patterns of soil-nitrogen availability.

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

The implications of a novel system of seed production for tossa jute (Corchorus olitorius), involving late sowing and intercropping with vegetables, were studied in 1989 and 1990. The greatest jute seed yield was obtained from jute-radish intercropping, where radish yielded 12–13 t ha−1 roots and gave the highest average gross margin, although jute-amaranthus intercropping performed marginally better in 1989. This system of husbandry yielded 3–4 t ha−1 of jute stick for fuelwood, which is of great value to rural households, and proved to be a viable means of producing jute seed, vegetables and fuel.

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 native rhizobia capable of symbiosis with annually-sown food and forage legume crops in the Turkish highlands were surveyed and estimates made of the numbers and nitrogen fixing efficiency of native Rhizobium leguminosarum with Turkish cultivars of lentil (Lens culinaris Medik.) and vetch (Vicia sativa L.). Native rhizobia were present in medium to high numbers in most samples but the nitrogen fixation efficiency of at least half of the isolates was poor. Vetch was somewhat less specific in its rhizobial compatibility than lentil, suggesting a potential for artificial inoculation to improve the productivity and sustainability of cropping in both species especially in areas of central and eastern Anatolia where legumes are not traditionally grown.

Biodiversidad en el Rhizobium leguminosarum

Hesperaloe funifera (Agavaceae) is an experimental fibre crop which produces strong, fine fibres with potential uses in the specialty-paper industry. Hesperaloe's agronomic potential was evaluated in two long-term studies. The plant is a perennial with a rosette habit. Growth occurred by production of new leaves from the primary rosette until Year 3 and from secondary rosettes from Year 3 on. Rates of biomass growth increased over the five years studied. High-density stands (27 000 plants ha-l) produced 190 t fresh weight ha-1 after five years. Plots harvested once, after Year 5, produced more biomass than plots harvested twice, after Years 3 and 5. Increased biomass production can be achieved by improved stand establishment and nutrient management.

A computer crop simulation model of the growth and development of maize was validated using data sets obtained from field experiments run at various sites in the mid-altitude maize zone of central Malawi between 1989 and 1992. The model was used to provide information concerning management options such as the timing and quantity of nitrogen fertilizer applications and to quantify the weather-related risks of maize production in the region. It was linked to a Geographic Information System to provide information at a regional level that could ultimately be of value to policy makers and research and extension personnel.

The native rhizobia capable of symbiosis with potential pasture legume crops for the west Asian highlands were surveyed and estimates made of the numbers and nitrogen fixing efficiency of isolates of Rhizobium meliloti with a range of annual Medicago species. Soils were collected from 105 sites at elevations between 500 and 2200 m. Numbers of bacteria were generally adequate to permit efficient nodulation but the nitrogen fixing efficiency of three of the four host species with the indigenous rhizobia was often low. In contrast, nitrogen fixation in M. aculeata was generally highly efficient. No overall geographic pattern in either numbers or efficiency of nitrogen fixation was evident. Substantial further research is required before annual medic crops can be successfully introduced into highland crop/livestock systems in Turkey and elsewhere in the west Asian highlands.

Biodiversidad en el Rhizobium meliloti

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

A field experiment was conducted from 1989 to 1992 to investigate the effect of sewage sludge applications on wheat yield under different irrigation regimes. The sewage sludge was applied at rates equivalent to 0, 20 or 60 t ha-1 whenever the available soil moisture reached 30 or 70%. The results showed a significant response in grain yield and its nutrient content with no significant differences between rates of sewage sludge applied. Much higher responses were obtained under the wet than under the dry regime.

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.

The native rhizobia capable of symbiosis with chickpea crops in the Turkish highlands were surveyed and estimates made of the numbers of bacteria and the nitrogen fixing efficiency of isolates of R. ciceri in symbiosis with an improved Turkish cultivar and a local landracc. Soils were collected from locations at elevations between 500 and 2200 m.

Native rhizobia specific to the local landrace were more abundant than those specific to the improved cultivar but nitrogen fixation efficiencies of all isolates were consistently poor. Agronomic research priorities must include the identification of strains of rhizobia symbiotically efficient and ecologically persistent in highland soils. Comprehensive trials with these strains as artificial inoculants on chickpeas are required throughout the region.

Biodiversidad en el Rhizobium ciceri

The possible use of tropical forage legumes in pastures based on Brachiaria decumbens and Andropogon gayanus pastures was tested on farms in the humid tropics region of Pucallpa, Perú. The pastures were established by farmers using manual labour. They were associated with maize in some cases and were normally grown without fertilizers. The pastures were established in areas where fallow regrowth was felled and burnt. These pastures, with grass-alone controls, were incorporated by farmers into their normal paddock rotation and were grazed by dual-purpose cows. Despite the variable terrain and soil conditions, all the pastures established and persisted well. Over a four year period under grazing, the legume contribution to the forage averaged 21% and ranged between 1 and 66%. Desmodium ovalifolium was the dominant legume in paddocks that were not burnt, whereas in pastures regularly burnt to control weeds it tended to disappear and Stylosanthes guianensis was the main legume present. It is concluded that where farmers ensure the maintenance of adequate levels of forage, grass-legume mixtures are a viable and persistent option even if the pasture is occasionally burnt.

Permanent pastures were successfully established with mixtures of bulks of crosses of Hordeum vulgare ssp. vulgare with ssp.spontaneum (given the name Mia Milia) and with mixtures of natural crosses involving H. vulgare ssp. agriocrithon (given the name Akhera).These crosses were made to exploit the brittle rachis gene of wild barley in order to develop self-reseeding pasture barley. No re-seeding of the pasture was necessary but a light cultivation to cover the seed in the first year of sowing improved plant establishment. No cultivation was necessary in the following years. Genotypes with a tough rachis were rapidly eliminated from the Milia pastures (F2 bulks) because of their poor seed dispersal. Nitrogen and phosphorus fertilizer increased dry matter yield. Levels of seed dormancy in the wild barley were adequate to provide a safeguard against extreme dry weather conditions and other natural hazards. Forage quality was very high, with a crude protein content of 18% and digestible organic matter of 80% in harvested dry matter. Permanent barley pastures that exploit the brittle-rachis gene of indigenous genetic material have considerable potential for increasing the animal-carrying capacity of permanent pastures and marginal cropped lands.