A field experiment was conducted to study the effect of irrigation with brackish water on the growth and composition of millet and corn, fertilized with various combinations of N and P. Millet irrigated with water of EC 3.30 mmho/cm. produced yields 79 to 93 per cent of the control (tap water of 0.61 mmho/cm.), depending on the N and P treatment applied. With water of EC 5.05 mmho/cm. yields equivalent to 52–72 per cent were obtained. Corn yields were 78–90 per cent of the control with irrigation water of 4.60 mmho/cm., and 55–64 per cent when irrigated with water of 7.06 mmho/cm. The N and P contents were mostly higher in plants grown on plots irrigated with brackish water.

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.

Yields of maize were increased when they followed successfully established pasture legumes in two rotation experiments. The largest increases were obtained after silverleaf and were equivalent in one experiment to the effects of about 30 kg N ha−1 a−1 over four years and in the other experiment to those of 40 kg N ha−1 a−1 over three years. The largest beneficial effect of some of the legumes was on the first crop of maize but in others did not occur until the third or fourth crop. The possible reasons for the different patterns of residual effect are discussed in relation to the nature of the legume residues, the quality of the seedbed following the legumes, and rainfall

Pea is a self-pollinated, diploid (2n = 14), annual crop produced worldwide for human consumption and animal feed. The exploitation of maximum genetic potential from available pea resources implies the knowledge of genetic parameters of yield components. Hence, the present study was conducted in a cross between two pea varieties, namely DDR14 and Explorer, its F2 progeny and F3 families to find out transgressive segregants and to determine the magnitude of narrow sense heritability and heterosis. The high narrow sense heritability values obtained indicated that rapid gain could be achieved through selection for the different traits; however, the presence of genotype x environment interaction could limit the correspondence of these estimated values with the observed ones. The selection of lines through their phenotypic values is influenced by environmental and error effects. Best linear unbiased prediction (BLUP) was used for the prediction of genotypic values using morphological data from different years, allowing the correction for environmental effects. These estimates were used for genetic analysis of the traits. Heterosis was observed for number of pods (27.1%) and number of seeds (23.3%), characters that have a direct effect on yield. The cross also showed high frequency of transgressive segregation for these characters in F3 generation (15.5% and 13.6%, respectively). There were 12.73% families transgressive for two or more characters, with genotypic values of 49.82–64.41 for number of pods and 153.75–189.59 for seed number. The crossing between Explorer and DDR14 provided a base for the selection of superior progeny.

A computer technique for predicting the yields of the component crops in intercropping systems is described. Predictions using this procedure showed reasonable agreement with results obtained in an experiment using tomatoes and dry beans. Reasons for the discrepancies observed and limitations to the applications of the technique are discussed.

With a focus on eastern Africa, the results of research on the ecophysiology and water relations of tea are reviewed. In particular, work undertaken at the Ngwazi Tea Research Station (formerly Unit) in southern Tanzania is synthesized and interpreted in relation to work reported from elsewhere in Africa (and beyond where appropriate). Topics covered include factors influencing: the components of yield, yield distribution, root growth, stomatal behaviour, photosynthesis, transpiration, xylem water potential and how cultivars vary in their responses to water stress. A companion paper (Carr, 2010) reviews the results of research on the irrigation of tea, water productivity, and its practical significance to the tea industry and the wider scientific community.

The production potential of three arbuscular mycorrhizal fungi (AMF), AM-1004 (Glomus intraradices), AM-1209 (mixed indigenous AMF) and AM-1207 (Mycorise, commercial inocula), were examined separately in three fractions/forms (root-based, soil-based and mixture of roots + soil) at 40, 60, 80 and 105 days in raised beds. The beds were amended with organic matter to develop regression equations for predicting optimal AM production vis-à-vis time required for particular inocula using infectious propagules (IP) as the independent variable. The IP production observed in the system was found to vary among the different inocula used. AM-1004 and AM-1207 produced significantly higher propagule counts in root or soil-based samples and a mixture of both at 105 days as compared to AM-1209. Based on two-way ANOVA, irrespective of time, AM-1004 (root/soil-based) produced a significantly larger number of propagules, whereas propagules in the crude inoculum (roots + soil) of all three inocula were not significantly different. On the other hand, irrespective of AMF, significantly more propagules (in all forms) were observed at 105 days. Similarly, irrespective of time, AM-1004 produced significantly higher root colonization (MCP, mycorrhizal colonization percentage) in all three forms (roots: 65.95%; soil: 24.32; soil + roots: 58.03%). The MCP in roots was increased significantly with time of multiplication. However, there was not much improvement in the MCP of soil or in soil + roots fractions beyond 80 days. Further, prediction of the number of IP for the three AM inocula was mathematically derived separately from the Mitscherlish-Bray equation (Y = a – b*exp (–cD). Based on the maximum yield of propagules of the three inocula observed and fitted into equations, root-based AM-1004 and AM-1209 inocula were found to be more efficient in producing propagules in 65 days as compared to AM-1207, which produced propagules in 76 days. While comparing the overall combinations, AM-1004 and AM-1209 inocula used either as roots, soil or a mixture of both and have greater potential in producing more propagules in the shortest span of time. While taking into account the predicted values of AM-1209 crude inoculum, about 12 IP g−1 substrate can be achieved in 72 days. Therefore, if a farmer uses crude inocula (having zero time IP of about 0.8/g substrate) of AM 1209, a total production of about 12.12 million IP/m3 can be achieved in 72 days. These can be used for on-farm production.

The most important technological needs and farmers' problems in agricultural entomology were identified by analysis of data collected from farmers in Tamil Nadu, India. This showed that damage due to leaf hoppers in rice was the most important research need and that due to brown plant hoppers in rice was the most important extension problem.

The intercropping objective of the subsistence fanner in Botswana was identified as a need to secure some cowpea production without reducing the yield of the staple crop, sorghum. Field experiments in which sorghum and cowpea were intercropped in several different environments over three years met this objective on most occasions, but cowpea yields were low compared with their sole crop performance. Although intercropping out-performed monocropping by producing some cowpea yield, land equivalent ratios greater than one and higher gross income and cash returns to draught-power (but not returns to labour) the differences were never large and seldom statistically significant.

An experiment was conducted during the 1978/79 summer at the Central Cotton Research Institute, Multan-Pakistan to evaluate the crop production patterns of two cultivars of cotton (G. hirsutum L.) differing in their reaction to heat-induced sterility. Boll set in variety ST3 amounted to 7.7% of the total fruiting points, from flowers opening during the hottest months of June, July and early August, while almost all the fruiting points produced by cultivar B557 during the same period were shed and no bolls were set. Of the flowers examined during July, 83.3% in B557 contained non-dehiscent anthers against 6.7% in ST3.

Twelve varieties of sugar-cane grown in Barbados, West Indies, during the past 40 years are compared with respect to cane yield performance in trials and in agriculture. Comparisons are based on data-pairs matched for site, season and crop, using both means and variety-on-variety regressions. Conclusions are that: trials greatly over-estimate mean agricultural differences between varieties; variety-on-variety regressions reveal numerous GE effects and account for much variance, but agree poorly as between trials and agriculture and are not useful in improving prediction; in view of the universal use of trials for prediction and decision-making, it is a matter of some practical importance that their validity should be tested in other crops.

Rates of shoot extension and development (the unfolding of leaves) were recorded in an irrigation × fertilizer experiment on Clone 6/8 at Ngwazi Tea Research Unit in southern Tanzania. The wide range of mean temperatures (from 15–20°C) meant that the duration of the shoot replacement cycle (the time taken for an axillary bud released from apical dominance to develop three leaves and a terminal bud), in fully irrigated tea receiving 450 kg N ha-l, varied from 65 d in the warm wet season to 95 d in the cool dry season, compared with 75 to 180 d for unirrigated and unfertilized tea. Regression analysis indicated that the base temperature for extension, for Clone 6/8 in high-input plots, was about 10°C, some 2–3°C more than that for development. As a result of these differences in base temperature, the length of shoots with three leaves and a bud varied considerably between treatments and seasons, ranging from 15 mm in the unirrigated plots (at the end of the dry season) to 130 mm in the high-input plots at the start of the rains. Shoots from well fertilized tea were always longer (at a given stage of development) than those from unfertilized tea. The results are discussed in terms of the possible mechanisms responsible for the observed responses (changes in partitioning between roots and shoots), commercial harvesting practices and yield modelling.

Extensión y desarrollo de broies en el té

The centre of origin of cashew is believed to be Brazil, from where it has spread since the 16th century throughout the tropics. In recent years, Vietnam has surpassed India to become the world's largest producer of cashew nut. Most of the research on the water relations of cashew has been done in Brazil, where it is both a large-scale commercial and a smallholder crop, and in Australia, where cashew is a possible emerging new crop. There are two ‘types’ of cashew: ‘talls’ and ‘dwarfs’. Both are evergreen trees in which vegetative growth occurs in a series of flushes. Flowers form annually on the end of branches in the dry season, and flowering continues for two to four months. It then takes about two months from pollination for the nut to mature. Roots can extend to great depths (>5 m), while cashew's wide-spreading rooting habit is critical to its successful adaptation to semi-arid/dry conditions. The optimum temperature for CO2 assimilation is in the range 25–35 °C. Progressive closure of the stomata occurs at saturation deficits of the air >1.5 kPa. In the field, differences in rates of gas exchange between irrigated and unirrigated cashew trees only become apparent three or four months after the end of the rains, the stomata playing an important role in maintaining a favourable leaf water status in dry conditions. Sap flow measurements indicate transpiration rates of 20–28 L d−1 tree−1. Irrigation can be beneficial during the period from flowering to the start of harvest, but reliable estimates of water productivity have yet to be established. The best/only estimate is 0.26 kg (nut in shell) m−3 (irrigation water). There is a continuing need to develop a method to estimate the water requirements of cashew, to identify where and when irrigation of cashew is likely to be justified and to develop a practical irrigation schedule.

High temperature is a major problem in groundnut (Arachis hypogaea) producing areas of arid and semi-arid tropics whether rainfed or irrigated. Knowledge of the maximum air temperature that plants can tolerate will help in selecting genotypes adapted to high temperature. The objectives of this study were to evaluate the growth, development, yield and yield components of different groundnut genotypes grown under elevated temperatures. Five groundnut cultivars and lines were grown in the field from 1984 to 1986 in Vertisols. Measurements on flowering, growth and development were carried out frequently. Thermal units required for groundnut cultivars to reach maturity were 2247 °C days. Larger kernel size, higher pod:total growth ratio and longer pod-filling period were the most important parameters for yield increase in heat-stressed environments. Early Bunch gave a stable yield across environments and was found to be more tolerant of high temperature. Cultivars differed in their pod:total growth ratio and Early Bunch had the highest ratio.

Multiple comparison methods are described. It is noted that they have always been controversial, partly because they emphasize testing at the expense of estimation, partly because they pay no regard to the purpose of the investigation, partly because there are so many competing forms and, not least, because they can lead to illogical conclusions. There are many identified instances where they have been found misleading.

An alternative approach is to designate ‘contrasts of interest’ from the start and to concentrate estimation and testing upon them. In many experiments the approach is powerful and definite in use, but sometimes there is no reason to designate one contrast rather than another, for example, in the assessment of new strains or new chemicals. In such circumstances some have found multiple comparisons useful, especially when the problem is to ‘pick the winner’. Bayesian methods and cluster analysis are considered briefly as other alternatives.

The current over-use of multiple comparisons is deplored. It is thought to arise in part from bad teaching and in part from the general reluctance of non-statisticians to venture into the unknown territory of specifying contrasts. A bad situation is made worse by the availability of software that carries out multiple comparisons as a matter of course.

Grain maize in south-east England showed a markedly flat-topped curvilinear response between density and grain yield, maximum yields being obtained over a range of 80,000–120,000 plants/ha, but yields were reduced at less than 70,000 plants/ha. A general density recommendation of 80,000–90,000 plants/ha is suggested, or a seed rate of 95,000 seeds/ha to allow for germination losses. Yields of cv Anjou 210 and DeKalb 202 showed some decline when the density exceeded 100,000 plants/ha, whereas yields of Pioneer 131 increased above this value and 100,000 plants/ha can hence be recommended. Although planting above the optimum density markedly increased the incidence of stem lodging at harvest, only a minor delay in stage of maturity occurred.

Weeds are generally considered to be undesirable plants as they can cause yield losses but fodder weeds are traded as a valuable feed in Niger, Vest Africa. In vitro analyses of fodder weeds indicated that they are a suitable crude protein supplement to low quality millet stover, a major feed during the dry season. Dry matter production of fodder weeds increased with a crop residue mulch. When weeds are used as feed, farmers may generate additional income through an increased availability of energy for animal traction or for dairy and beef production. Species with the highest crude protein content, usually the most limiting factor in feed for animal production, had the highest market prices. The sale of fodder weeds may provide farmers with cash. Agricultural research programmes should be encouraged to consider the use of fodder weeds to improve both the quality and quantity of feed in the West African Sahel.

Tomato leaf curl virus disease (TLC) was checked by frequent and early applications of Anthio, Folimat, Malathion and Phosdrin against the aleyrodid vector, Bemisia tabaci. Conversely, up to two-fold increases of fruit yield resulted from such applications of the insecticides. Though seed-bed or field applications, separately, gave satisfactory results on occasions, treatments of the plants in the seed-bed and the field were often both essential. Field observations during the experimental period, over four consecutive seasons, showed peak infection rates within the first 8–12 weeks of tomato planting. There were marked inter-seasonal fluctuations of disease incidence, ranging from < 50 to 100 per cent. There was no clear correlation between spread of the disease and the wind direction. Epidemiological behaviour of the disease is discussed in relation to its chemical control.

Reducing soil evaporation by different agricultural practices is important not only for water saving but also for its applicability by farmers. In wheat fields, the goal of efficient water management is to save water and increase yield. At present, the combined effects of maize-straw mulching (M) and crop density (D) on soil evaporation and temperature, wheat performance, and water use efficiency (WUE) are not clear. A field experiment was conducted for winter wheat (Triticum aestivum L.) in the North China Plain (NCP). The two levels of crop density included high (HD) and normal density (ND), and the three levels of mulch included high (HM), low (LM), and no mulch (NM). The results indicated that both straw mulching and high crop density had significant inhibitory effects on soil evaporation. Normal crop density with high mulch gave the lowest yield among all treatments because high mulching reduced the soil temperature and hindered the soil temperature increase in early spring. Compared with normal crop density with no mulch, the yield and WUE of winter wheat for high crop density with low mulch (HDLM) were enhanced by 20.6% and 21.9%, respectively. Compared with other treatments, HDLM gave the higher WUE due to the higher soil temperature, leaf area index, and biomass. Therefore, HDLM was an effective way to maximize the WUE of winter wheat in the NCP.