Many types of weeds occur in cassava fields causing enormous yield losses due to competition for nutrients, light and space. The purpose of this study was to evaluate the growth and yield of four traditional varieties of cassava (Bonoua Blanc, Tambou, Yassé and Six mois) produced in Côte d'Ivoire and select the highest tolerant variety to weed competition. Six treatments were induced by varying the period in which cassava varieties were grown with weeds. Varieties and exposure time to competition with weeds significantly affected the productivity of cassava. The number of leaves per plant (NLP), the number of tuberous roots per plant (NTRP) and the weight of tuberous roots per plant (WTRP) declined with increasing duration of weed presence. After an initial period of weeding, the first four months of grassing proved critical for the four varieties. Despite the presence of weeds, Bonoua Blanc has higher growth and yield than Tambou, Yasse and Six mois. This suggests that Bonoua Blanc was more tolerant to weed competition than the others from planting to harvest, being a suitable variety in intercropping systems.

Linear covariance analysis of crop yield data using plot stand as the covariate is not satisfactory when the missing plants are eliminated before maturity. This is because the resulting relationship between yield and plot stand is non-linear. In this paper, a transformation of plot yield data to adjust for sub-optimal stands in circumstances involving interplant competition is examined. A biomathematical derivation and interpretation of the proposed model is provided. An experiment involving two varieties of maize (Zea mays) grown at three locations provided the data used to validate the model. Adjusted genotype mean yield values obtained using the proposed exponential transformation were in agreement with observed values.

Different methods of undersowing maize with a mixture of Rhodes grass and silverleaf desmodium were compared, together with the effects of applied nitrogen, in an experiment on the Lilongwe Plain. Drilling the legume on the ridge or in the furrow was superior to broadcasting, and caused no substantial reductions in maize yield. Nitrogen application increased all aspects of maize production but slightly reduced legume yield. The data generally confirm previous findings that undersowing causes no appreciable and consistent reduction in maize yield, and results in the establishment of mixed swards with a high legume content.

In a 20 plot experiment with central composite second-order rotatable design, basal non-chlorophyllous sections of “D” leaves of Sugarloaf pineapples were sampled at harvest and analysed for N, P, K. Maximum yield of 17·8 tons per acre of good quality Sugarloaf pineapples and maximum fruit length of 27·4 cm. were associated with the nutrient combination of 36–42–32 lb/acre N P K applied at 4, 6, 11 and 12 months. The nutrient levels in the basal sections of “D” leaves corresponding to maximum fruit yield were 0·35–0·40% N; 0·04% P; 0·44% K; K/P 11·2–11·5: 1. K/P ratio for maximum fruit length was 10·4–11·5: 1. N/K ratio was associated with lodging.

The participatory approach of Farmer Research Groups (FRGs) was used in Farmer Adaptation of Starter Technology (FAST) with small-scale farmers in Luapula Province, Zambia. The introduction of a starter technology proved to be a suitable method to induce self-help initiatives with farmers. Their first move in FAST related to the improvement of food security and income generation by the cultivation and marketing of new maize (Zea mays) varieties in wetlands during the dry and early rainy seasons. By informal on-farm seed multiplication the expenditure on external agricultural inputs was reduced. The technical aspects of the starter technology began with the integration of pasture legumes as a pioneer crop for green manuring purposes in maize production. In this respect, FRGs developed individual risk-aversion strategies to ensure early planting of the maize with the onset of the rains. The groups made adaptations such as biomass transfer, intercropping and crop rotations in order to integrate pasture legumes into current cropping systems for green manuring purposes.

Employing data from an intercropping field experiment which measured the yields achieved by a surviving crop when the other crop failed at 0, 6 or 10 weeks after sowing, the use of a simple computer model to study the long-term yield effects of compensation in intercropping is described. Assuming different probabilities of crop failure for one or both of the crops, the model provided a comparison of long-term intercrop and sole crop yields from intercropping systems of oat–mustard, mustard–bean and oat–bean. It showed that if failure was restricted to only one of the crop species, intercropping suffered less yield decline with increasing probability of failure than did sole cropping only if there was a sufficiently high yield of the surviving crop. However, in the more realistic situation where each crop was subjected to the possibility of failure, this decline in yield was less in intercropping than sole cropping for all three combinations because poor yields when one species was the surviving crop were offset by good yields when the other species was the survivor. Mustard–oat and mustard–bean gave no yield advantage in the absence of failure (Land Equivalent Ratios less than 1) but they outyielded sole cropping for failure probabilities above about 5% and 15%, respectively. All combinations gave large intercropping advantages at high probabilities of failure. Oat–bean always had a strong yield advantage, even with no failure.

The model is very simplistic but it illustrates the potential for modelling long-term effects from field data. Limitations of the model are discussed and it is emphasized that these can be overcome if information to make the underlying assumptions more realistic is available.

Citrus trees are often exposed to severe infectious diseases. Mal secco caused by Phoma tracheiphila (Petri) Kantschaveli and Gikashvili is one of the most destructive fungal diseases of lemons (Citrus limon Burm. F.). In the present study, antioxidant enzyme activity in different mal secco-resistant and susceptible citrus rootstocks including Cleopatra mandarin (C. reshni Tan.), sour orange (C. aurantium L.), rough lemon (C. jambhiri Lush.), Volkameriana (C. volkameriana Tan. and Pasq.), Carrizo citrange (Poncirus trifoliata L. Raf. X C. sinensis L. Osbeck) and trifoliate orange (P. trifoliata) was investigated. Possible differences in constitutive levels of these antioxidant enzymes and correlations between enzyme levels and mal secco caused by P. tracheiphila were examined. Among the rootstocks, Cleopatra mandarin was found to be resistant to mal secco, whereas rough lemon, sour orange and trifoliate orange were highly susceptible. Total peroxidase (TPX; EC: 1.11.1.7) activity increased in all infected rootstocks. Ascorbate peroxidase (APX; EC: 1.11.1.11) activity increased in most of the rootstocks and no correlation was found between catalase (CAT; EC: 1.11.1.6) activity and mal secco resistance. This study indicates that overall TPX activity is upregulated and APX activity is up- and down-regulated depending on the type of rootstock in response to P. tracheiphila infection.

The poor fertility of sandy Sahelian soils remains one of the major constraints to pearl millet (Pennisetum glaucum) production in West Africa. On-farm trials under farmers' management were conducted in two rainfall zones of Niger in 1996 and 1997 to evaluate the risk characteristics of six soil fertility restoration options. Stochastic dominance analysis was used to compare the fertilizer treatments tested. Results showed that the farmers' traditional method (no fertilizer control), Tahoua phosphate rock (PRT) alone applied at 13 kg P ha−1 broadcast, and a combination of PRT broadcast at 13 kg P ha−1 and single super phosphate (SSP) hill-placed at 4 kg P ha−1 had the most desirable risk characteristics and were acceptable to risk averse decision-makers in both rainfall zones. At current input–output price ratios, most fertilizer-using farmers would choose the combination of PRT broadcast and SSP hill-placed. If the availability of SSP was limited, some farmers would use PRT alone. The demand for risk efficient alternatives could significantly increase if farmers could bear less than half the fertilizer costs at the current output price, although further research is required to say if a fertilizer subsidy could be justified on broader economic or social grounds.

Dry matter production and partitioning in old clonal tea bushes pruned and maintained at different heights were investigated. New tissues (leaves, new branches and small roots) consti- tuted a small fraction of the total dry matter in all bushes pruned and initially maintained at 70, 40, 25 and 10 cm high, 36 months after pruning. Leaf/frame dry matter ratio was larger and the shoot/root and frame/root ratios were smaller in the bushes initially maintained at 10 cm than in the bushes maintained at other heights. Yields per unit area of the plucking surface were greatest in the smallest bushes initially maintained at 10 cm in 42 months of recording but on the basis of the available space they were greatest in the large bushes initially maintained at 70 cm.

Cocoa (Theobroma cacao) farmers in Sulawesi, Indonesia typically use subsidised, ammonium-based rice fertilisers that in combination with poor agricultural practices have resulted in soil acidification, loss of organic matter, aluminium toxicity and lower soil fertility. As a result, these soils are only marginally appropriate for replanting cocoa to boost production. A field experiment was performed to test alternative soil amendments for successful replanting of cocoa on these deficient soils. In a trial with a randomised block design, 6-month old seedlings, top-grafted with the local MCC02 clone, were planted under light Gliricidia sepium shade and after 3 months treated quarterly with two options of mineral fertilisers: either a customised fertiliser, consisting of Nitrabor (a combination of calcium nitrate and boron), dolomite, rock phosphate and KCl or a NPK/urea mix used by farmers, each supplied with or without ‘micronutrient’ rock salt, organic fertiliser and beneficial microorganisms or their culture medium, a mixture of chitin and amino acids (a total of 20 treatments). Over a 4-year period, the marginal mean rates of stem diameter increment and flowering score were higher in customised fertiliser than NPK/urea treatments. The average growth rate was highest in the first year and was increased by supplying organic fertiliser. A significant correlation (r = 0.22, p < 0.05) occurred between growth and available P, but concentrations of available P were higher in the NPK/urea plots, which also had lower mean growth rates. Combined supply of organic fertiliser and microbes increased available P, as well as growth rates, in both the customised and NPK/urea treatments. In contrast, NPK/urea-treated plots without these amendments demonstrated very low growth rates. The customised formulation was more effective with or without added organic fertiliser or inoculated microbes. Micronutrient supply stimulated flowering. Growth rates in trees supplied with NPK/urea were also promoted by micronutrients. Leaf flush production occurred in regular cycles and was unaffected by the nutrient amendments. After 3 years, the customised and organic fertiliser application increased soil pH and exchangeable Ca and Mg concentrations, although they remained below recommended levels for cocoa production. These treatments had little impact on soil C content (about 1.3%) which was also deficient. Exchangeable Al and total Zn concentrations were higher in soils amended with NPK/urea. The results of the trial provide evidence that utilisation of organic fertiliser in combination with customised nitrate-based formulations improves cocoa establishment, growth and soil properties and should be recommended as a replacement for the NPK/urea fertilisers traditionally used by farmers.

Studies on the effects of age on the elemental nutrients contained in Celosia argentea cultivars showed that calcium, phosphorus and potassium decreased with age, the highest content of those elements occurring in the leaves between 5 and 7 weeks after sowing. Other elements, notably manganese and magnesium, increased up to 15 weeks after sowing. An anthocyanin-pigmented cultivar contained more iron, sodium and copper than green cultivars. Breeding potentials of the cultivars in terms of elemental nutrients are discussed, and harvesting the leaves of all cultivars 5 to 9 weeks after sowing is recommended.

Monthly and annual totals for the Penman estimate of potential evaporation have been reliably determined, for periods varying from 7 to 11 years, at 14 East African observatories. At each site, these annual and monthly totals are normally distributed, with coefficients of variation of the order of 5 and 10 per cent, respectively. Meteorological stations established for the sole purpose of supporting evaporation surveys should therefore be relocated at 5- or 6-year intervals so as to derive maximum benefit from the valuable instruments. The results of these variability analyses were applied in the evaluation of confidence limits for monthly and annual potential evaporation rates, and reference is made to recent compilations of such limits for 137 sites in Kenya and Tanzania.

Nursery trials have shown that carbamate fungicides containing zinc or manganese are effective against Helminthosporium heveae. The addition of a wetting or sticking agent did not improve control, and in one test significantly reduced it.

Bud removal of the cuttings at underground level has been claimed by cassava growers in Thailand as a method to increase cassava yield. This practise should be tested experimentally to explain the reason for yield increase. The objective of this study was to investigate the effects of bud removal and cutting length on storage root yield and starch content of three cassava varieties. Field experiment was conducted in a split–split plot design with four replications in 2010 and 2011, under rainfed conditions. Three cassava varieties (KU50, RY9 and HB60) were assigned as main plot. Two cutting lengths (15 cm and 30 cm) were assigned as sub plots, and two treatments of buds (buds cut and not cut) were assigned as sub–sub plots. The buds on the cuttings that were inserted into the soil were removed. In 2010, the plants from 15-cm long cuttings subjected to bud removal had higher fresh storage root yield (88.4 Mg ha−1) than did plants from 30-cm long cuttings subjected to bud removal (75.8 Mg ha−1). Cutting of buds also had higher fresh storage root yield (89.1 Mg ha−1) than did non bud-cutting (75.0 Mg ha−1). KU50 had the highest fresh storage root yield (91.4 Mg ha−1), dry root yield (48.4 Mg ha−1) and starch yield (20.1 Mg ha−1). Cutting length of 15 cm had higher starch concentration in storage roots (25.6%) than did cutting length of 30 cm (24.2%). HB60 had the highest starch concentration (27.0%) among cassava varieties tested. The data in 2011 were similar to the data in 2010. The responses of varieties to bud removal and cutting length are discussed.

A wide variety of training activites has been carried out related to farming systems research (FSR). The majority have had one or more of the following objectives: to introduce the farming systems perspective, to teach new research methods, and to promote the institutionalization of FSR. Many of these objectives are important, but FSR training is not usefully seen as a separate field of endeavour. The goals of FSR training will be better served by reconsidering the roles of universities, national research institutions, and international institutions.

The response of germination and early seedling growth to levels of salinity (0, 50, 100, 150, 200 and 250 mM NaCl) were examined in single seed lots of ten modern rice genotypes. Unaged and deteriorated rice seeds were germinated in rolled paper towels and in Petri dishes. Initial seed quality, final germination, germination rate and early seedling growth were assessed. The samples of the rice genotypes differed in their initial seed quality (measured in terms of Ki). The effect of deterioration varied depending upon the initial seed quality and the severity of the treatment imposed. Ageing (using the technique of controlled deterioration, CD) for up to 24 h had no effect on final germination levels. Although CD for 30 h only reduced final germination slightly, ageing for 36 or 48 h reduced it greatly. Controlled deterioration for 36 h or longer reduced the final length and the rate of extension of both the plumule and radicle. Combining information about germination in salt solution with that about seed quality enabled a distinction to be made between varieties which performed poorly because they were genetically salt-susceptible from those which germinated poorly due to poor seed quality. It is argued that the seed vigour of seed lots used in genotype evaluation should be assessed in order to avoid discarding potentially useful genotypes because of poor physiological seed quality.