There have been conflicting reports of the effects of different plucking (harvesting) policies on yields of tea in Malawi. An experiment is reported which separates the effects of plucking round length from those of plucking standard, and is compared with the results of simulating those plucking policies. Between the experiment and the simulation the conflict is resolved, and the validity of the experiment and simulation model are thereby enhanced. The immediate practical implications of the work are limited because of the unquantified relations between plucking standard and quality and grade out-turn of made tea.

Farmers hosted on-farm trials and demonstrations involving three new groundnut (Arachis hypogaea) varieties in Malawi to assess their acceptability and adoption potential. Patterns of seed diffusion among trial farmers were examined as well as among non-trial farmers who were members of seed banks. The study showed that trial follow-up surveys provide a cost-effective approach for assessing early adoption and providing feedback to researchers. While useful, however, such studies are not an end in themselves. Rather they need to be perceived and designed as one of several studies that help researchers understand the complexity of farmers' adoption decisions.

Long-term field experiments were conducted at six different sites (representing dryland and irrigated environments) with wheat (Triticum aestivum) on sandy loam soils to generate a database relating available water supply and fertilizer nitrogen (N) rate to grain yield. Step-wise multiple regression analysis showed that water supply and fertilizer N at more than 53 cm a−1 and 103 kg ha−1 a−1 were unproductive. A method, based on the principle of equi-marginal productivity of water in different periods of crop growth, has been used to estimate the optimum allocation of the variable amounts of water supply over the growing season. The optimized quantities of water in different periods of crop growth were then employed to compute fertilizer N requirement to achieve a given yield target. For medium grain yield targets (4–5 t ha−1), the range of substitution between fertilizer N and water for efficient resource use was quite wide.

Two sets of experiments examined the effects of weeds on maize yields using weeding methods typical of small farms in Zambia where oxen are used for cultivation. Maize yield losses of 30% due to weeds were evident with common weeding practices. A critical period of competition, during which the crop should be kept clean, was demonstrated from 10 to 30 days after emergence. This is a period of peak labour demand and the prospect of using chemical weed control to ease the situation is considered. The value of weed competition data, given its variability between sites, is discussed.

The ‘banjhi’ or dormancy cycle in free-growing tea trees appears to be the result of an endogenous rhythm. However, in harvested tea apical dominance causes dormant shoots to be produced under conditions favourable to growth, and the synchronized flushing cycle causes periods of apical shoot (active terminal bud) and secondary shoot (dormant terminal bud) production.

Root traits, such as depth and root biomass, have been identified as the most promising plant traits in chickpea for terminal drought tolerance. With this objective, five contrasting genotypes of chickpea, viz. ICCV-4958, H-208, HC-5, RSG-931 and CSJ-379, having wide adaptability to drought prone areas at national level were assessed for various root characteristics under two environments, i.e. irrigated and rain-fed. The sampling was done at full bloom stage and there were significant differences in the rooting depth among the genotypes both under irrigated and rain-fed conditions. The chickpea roots penetrated to a minimum depth of 92 cm in CSJ-379 and maximum of 122 cm in ICCV-4958 under rain-fed conditions. The rooting depth remained higher under rain-fed than irrigated environment. Under irrigated conditions, the chickpea roots were able to grow to a maximum depth of 99 and 97 cm in HC-5 and ICCV-4958, respectively. Among the genotypes, biomass per plant of the root was higher in ICCV-4958 (6.7 g) and HC-5 (5.6 g) under rain-fed conditions. Similar observations were recorded for root/shoot ratio, dry weights of stem, leaf, nodules and total dry weight per plant. The moisture stress increased the biomass partitioning towards the roots. The water potential (ψw), osmotic potential (ψs) and relative water content (RWC %) of leaf were –0.98 MPa, –1.82 MPa and 60%, respectively, in the genotype HC-5, and –1.02 MPa, –1.72 MPa and 64%, respectively, in ICCV-4958 under rain-fed conditions. The rates of photosynthesis, and transpiration, values of the stomatal conductance and photochemical efficiency/quantum yield as indicated by Fv/Fm ratio were in the range of 6.7 to 10.6 (μmol m−2 s−1), 1.27 to 2.38 (mmol m−2 s−1), 0.23 to 0.48 (mol m−2 s−1) and 0.457 to 0.584, respectively, under rain-fed conditions. Genotypes HC-5 and ICCV-4958 also maintained higher photosynthetic and transpiration rates and Fv/Fm ratio than others. The maximum Fv/Fm values in these genotypes were correlated with the higher photosynthetic rate and dry matter yield per plant. Relative stress injury (RSI %) values in HC-5 and ICCV-4958 noticed were 25.3% and 23.7%, respectively. The results of this study indicate that under rain-fed conditions, genotypes ICCV-4958 and HC-5 had higher dry weight of stem, leaves, roots, nodules and total dry weight per plant, rooting depth, root/shoot ratio, photosynthetic and transpiration rates, photochemical efficiency and better plant water status but lower stomatal conductance than other genotypes. These traits are directly associated with maximum seed yield per plant, i.e. 15.6 g and 14.7 g per plant, respectively, in these genotypes. Therefore, both the genotypes in future can be used in crop improvement programme of chickpea breeding for drought tolerance.

An on-farm trial was conducted in the northern Guinea savanna of Nigeria, over a period of five years, with the objectives of quantifying the effects on maize of applying cattle manure in combination with synthetic fertilizer with regard to soil characteristics, yield, plant nutrition and profitability. Maize grain yield was significantly increased by the annual application of cattle manure, compared to maize receiving an equal amount of N through synthetic fertilizer, but only from the third year of the experiment. The application of manure resulted in higher soil Kjel N, Bray-I P and exchangeable K values, and an increased N utilization efficiency by maize, suggesting that yield-limiting factors other than N deficiencies were of lesser importance than in the treatment receiving sole inorganic fertilizer. Nutrients other than N applied via the manure, particularly P, K and/or B, may have contributed to the higher grain yields in treatments receiving manure. A partial budgeting analysis revealed that, over a 5-year period, investments in the application of manure, in combination with synthetic fertilizer, resulted in higher margins than the application of fertilizer alone. However, analyses of marginal rates of return of changes from low urea N to high urea N or additional manure applications suggested that it was more profitable to invest in additional urea than in organic manure in the first two years of the experiment. The results suggested that manure applications, even when applied at relatively high rates, did not serve as a quick fix to on-farm soil fertility problems, but over a longer period, manure applied in combination with synthetic fertilizers did provide a significant and profitable contribution to enhanced cereal production.

The effects of temperature (14–19°C) and mean soil water deficit (up to 90 mm) on the shoot extension and development rates of six contrasting tea clones in southern Tanzania were studied 10–28 months after field-planting. An exponential function with two constants, an initial shoot length and a relative extension rate (r), provided a reliable description of the length of axillary shoots for the period from the release of apical dominance to the unfurling of three true leaves. Apparent base temperatures (Tbe) and thermal extension rates (ρe), derived from linear relations between r and the mean air temperature, were able to explain 85–92% of the seasonal variation in r for each fully irrigated clone. The mean soil water deficit was used to explain 80% of the remaining variation in r across three drought treatments.

Clonal differences in the values of Tbe (8.9–11.3°C) and ρe (7.8–11.8 × 10−3 mm mm−1 (°Cd)−1) can be used to explain differences in the seasonal distributions of yield. The apparent base temperatures for development (Tbd) were consistently 1.7–3.4°C below those for extension; an observation supported by the effects of temperature on the length of shoot internodes. The results are compared with those obtained in other studies and are discussed in terms of clonal selection, the choice of harvest intervals and the prediction of green-leaf quality.

The stomatal functioning of high, medium and low yielding clones of tapioca was examined to see whether yield could be associated with conductivity and/or resistance to moisture stress. A sensitive falling pressure porometer was used to measure stomatal conductivity to the viscous flow of air at small pressure differences. No marked differences were observed which could account for the large range in yields shown by the varieties, but stomatal functioning could be related to canopy type and to planting conditions. In general the conductivity values of all three varieties were very low compared to many other crop species, which suggests that increases in canopy efficiency and yield could be obtained in certain environments by an increase in leaf conductivity.

Trials carried out at a range of locations in northern Nigeria showed that gross cash returns from mixtures were never less than those from sole groundnuts, confirming results from the main research station at Samaru. In many cases they were considerably higher and in the Northern Guinea Savanna, where the system is most widely practised, showed a high probability of returns greater than the sole crop median. Increasing attention is being paid to haulm yield and the possibility that sole groundnut may be more profitable near large towns because of haulm value.

Climatic conditions affecting the development of CBD are assessed by measuring wetness within the tree canopy and air temperature. Saturation of the tree canopy, necessary for spore dispersal, occurs most frequently at the tops of trees and the duration of wetness permitting spore germination is most prolonged at night. Night air temperatures are closest to berry temperatures and are important in assessing infection periods. Disease development in 1968 and 1969 was related to the number of infection periods during the growing season. Polythene tree covers which kept trees sufficiently dry to stop disease development were used in determining infection at different times of the year.

The uptake of S followed a similar pattern to dry-matter production by groundnuts given enough fertilizer-S to prevent S-deficiency. The fastest rate at which dry matter was produced was 140 kg./ha./day. Of the 6857 kg./ha. at harvest, 3401 were in haulm, 967 in shells and 2489 in kernels. S was taken up fastest during the eighth week, when the daily average was 0·22 kg./ha.; at harvest, of the 11·6 kg./ha. in the plants, 5·4 was in the haulm, 0·8 in shells and 5·4 in the kernels. Of the 157 kg. N/ha. in the harvested crop 62 per cent was in shells and kernels and of the 13·5 kg. P/ha., 64 per cent was in shells and kernels.

Improving water productivity depends on how local communal water and grazing resources are governed. This involves institutional and organizational issues. In the mixed farming systems of the Amhara Regional State, Ethiopia, non-participatory water users’ associations, neglect of traditional water rights, corruption, village power relations, inequitable allocation of irrigated land and free-grazing practice impact the governance of local common pool resources (CPR). Indigenous governance structures for CPR such as the kire are participatory and effective in terms of rule enforcement. Externally initiated governance structures lack acceptance by farmers and sufficient support from local government. In order to improve water productivity in the mixed farming systems, institutional deficiencies need attention and existing indigenous governance structures require recognition and support.

Seedling growth from sowing to emergence of two crust tolerant and two susceptible sorghum genotypes is described. Tolerant genotypes had longer mesocotyls with faster growth rates than the susceptible genotypes. The mechanism involved in crust tolerance appears to be that of avoidance by fast growth.

At doses of 75 mg./kg. given per os, Neguvon was ineffective against Sarcoples scabiei var. Auchenidae. Benzene hexachloride (BHC) per os was ineffective at doses of 20 mg./kg. and killed alpacas when the dose was increased. Spraying the lesions with BHC killed the acari and lesions quickly disappeared. Psoroptes communis, the cause of otitis in alpacas, was equally susceptible to spraying. Lesions and their location are described and attention is drawn to the possible role of acari in nostrils and perinea in the epidemiology of the disease. Dipping is, at present, the only method of cure worth using, but the search for systemic acaricides should be continued.

Plant water potential and leaf diffusive conductance, key features of plant responses to water stress in field experiments, can be estimated, respectively, by xylem pressure potential measured with the pressure chamber apparatus, and leaf permeability measured with the air flow porometer. This paper describes modifications to these two techniques in order to increase the rapidity of measurements in wheat to 60/h with the pressure chamber, and 200/h with the porometer. Rapid measurements are needed because of the large within-and between-plot errors encountered with daytime measurements in typical field experiments, examples of which are presented.

Scores of assessments of the impacts of agricultural research have been carried out over the years. However, few appear to have been used to improve decision making and the effectiveness of research programmes. The Institutional Learning and Change (ILAC) Initiative emerged within the Consultative Group on International Agricultural Research (CGIAR), with the goal of strengthening learning from experience and using lessons to improve pro-poor innovation. It is testing approaches for expanding the contributions of impact assessment and evaluation to learning, decision making and improvement.

The translocation of C and N in a maize-Striga hermonthica association was investigated at three rates of nitrogen application in a glasshouse experiment. The objectives were to measure the transfer of C and N from maize to S. hermonthica and to determine whether the amount of N in the growing medium affected the proportions of C and N transferred. Young plants of maize were labelled in a 13CO2 atmosphere and leaf tips were immersed in (15NH4)2SO4 solution. The Striga×N interaction was not significant for any of the responses measured. Total dry matter for infected maize was significantly smaller than for uninfected maize from 43 to 99 days after planting, but N application increased total dry matter at all sampling times. Infected maize plants partitioned 39–45% of their total dry matter to the roots compared with 28–31% for uninfected maize. Dry matter of S. hermonthica was not affected by the rate of N applied. S. hermonthica derived 100% of its carbon from maize before emergence, decreasing to 22–59% thereafter; the corresponding values for nitrogen were up to 59% pre-emergence and up to 100% after emergence. The relative proportions of nitrogen depleted from the host (up to 10%) were greater than those of carbon (maximum 1.2%) at all times of sampling after emergence of the parasite. The results show that the parasite was more dependent on the host for nitrogen than for carbon.

A field experiment was conducted on a highly alkaline soil (pH 10.6, exchangeable sodium 95%) to compare biological reclamation using Leptochloa fusca with chemical reclamation using gypsum. Rice gave satisfactory yields in the first year of gypsum application but sorghum and Sesbania gave extremely poor yields. The yield of Leptochloa was not affected by gypsum application. Trifolium resupinatum yielded more than T. alexandrinum when sown in the winter season. The green forage yield of sorghum was greatest when the sorghum followed Leptochloa grown for two years, with the harvested grass allowed to decompose on the site. The results show that biological reclamation with Leptochloa is a good substitute for chemical reclamation with gypsum.

In Kenya, coffee growing east of the Great Rift Valley has its main flowering either in February–March or in October–November. These flowerings are mainly initiated from approximately August to December and June to September, respectively. Changes from an early to a late flowering rhythm and vice versa can be caused by (a) pruning, (b) the condition of the tree, and (c) the weather pattern, but more information is needed for a complete understanding of this problem.