A. H. Bunting was born in Johannesburg, South Africa on 7 September 1917 and died peacefully in his sleep at his home in Berkshire, UK on 8 May 2002.

An experiment conducted from 1988 to 1997 to determine the effects of the timing of application and nutrient supply (particularly of phosphorus) is reported. The sources of applied nutrients that were compared were farmyard manure, pre-rice green-manuring with Sesbania aculeata and fertilizer application in a rice-wheat rotation on a typic ustifluvent. The application of seven tonnes farmyard manure per hectare to both the rice and the wheat crops over eight years increased organic carbon levels from 1.4 to 1.6% but had no yield effect on either crop. Phosphorus application through farmyard manure was not adequate for rice, whilst an application of 34 kg P ha−1 to the rotation gave an economic yield increase only in rice and then only in the first four years of the experiment. From the third year, green manuring was able to replace the effects of the recommended nitrogen, phosphorus and potassium fertilizer applications in increasing rice yield. Green manuring had no effect on the wheat yield but the recommended fertilizer application increased yield. Green manuring increased soil total nitrogen and available potassium levels and reduced base saturation. After adjusting rice yields for variation in transplanting date between years there was no statistical evidence of a yield trend in either crop over the period of the experiment. Farmers' practice of applying seven tonnes farmyard manure per hectare appears adequate to produce stable rice paddy yields of 4–6 t ha−1 a−1.

A modified technique for measurement of nitrogen fixation by blue green algae and Azolla sp. using intact, moist soil cores was developed for use in field studies in which chemical fertilizers, blue green algae and Azolla biofertilizers had been used in association with a rice crop. This method involves collection of fresh and moist soil cores (0–30 mm) using a soil auger, incubation with 10% acetylene in airtight glass vials under field conditions for three hours, and measurement of the ethylene produced using a gas chromatograph. Experiments carried out over a period of three consecutive years revealed that the estimates of nitrogen fixation were comparable with data of other researchers obtained through the use of soil water columns, sophisticated chambers and automated sampling devices. This simplified technique, therefore, can provide rapid and reliable measurements of nitrogen fixation in field experiments.

Spatial variability in field trials is a reality. A proportion of this is accounted for as inter-block variability by using block (complete or incomplete) designs. A large amount of spatial variability still remains unaccounted for, however, and this may lead to erroneous conclusions. To capture this inexplicable variation (which is mainly due to intra-block variation), yield data from a series of variety yield trials, using cereals and legumes, were analysed using various spatial models. The most suitable of these, selected on the basis of the Akaike Information Criterion, were used to assess the relative performance of genotypes. Although incomplete-block designs have been found to be effective in variety trials, spatial models have added considerable value to trials with legumes and cereals. The ‘best’ spatial models gave efficiency values of over 330% in winter-sown chickpea (Cicer arietinum), 140% in lentil (Lens esculenta), and 150% in barley (Hordeum spp.) trials. Furthermore, the use of these best models resulted in a change in the ranking of genotypes (on the basis of mean yield), which resulted, therefore, in a different set of genotypes being selected for high yield. It is recommended that: (i) incomplete block designs be used in variety trials; (ii) the Akaike Information Criterion be used to select the best spatial model; and (iii) genotypes be selected after the use of this model. The selected model would account most effectively for spatial variability in the field trials, improve selection of the most desirable genotypes and, therefore, improve the efficiency of breeding programmes.

The effect of Ethrel on the yield and sugar content of coconut (Cocos nucifera) inflorescence sap and sustainability of productivity was investigated on forty-year-old tall coconut palms (var. typica) at Bandirippuwa Estate, Lunuwila, Sri Lanka. Ethrel was applied at a concentration of 2.5% and the volume and sugar content of the sap were measured. Application of Ethrel consistently increased the yield per day, yield per spadix, yield per palm per annum and sugar content in the sap for a period of four years. The removal of carbon, nitrogen, phosphorus, potassium and magnesium with the sap was greater from Ethrel-treated than from untreated palms, and this was attributed mainly to the enhanced sap yields and sugar concentrations.

Cassava, a crop widely adapted in the tropics, has the important attribute of withstanding adverse environmental conditions better than do many other staple crops. The performance of an individual genotype, however, is influenced by the environment in which it grows. In Malawi, the heterogeneity of agro-ecologies requires the cumbersome and costly assessment of new cassava genotypes at many sites. This study was conducted, therefore, to test the feasibility of selecting only a few locations for cassava evaluation that would be representative of all the agro-ecologies in which cassava is grown in Malawi. Enormous environmental effects, largely contributed by the interaction between season and location, were manifested. Genotype×environment interaction, due largely to a third level interaction (genotype×season×location), was highly significant for all the traits studied. A principal component analysis scatter plot showed no particular grouping of environments, but a pair-wise comparison showed that some of the locations had limited genotype×environment interaction, indicating that it would be sufficient to use one of these sites for evaluating these traits. The value of the residual was often large, probably as an effect of environmental heterogeneity in the test sites. The authors conclude that cassava genetic improvement will continue to be slow if Malawi is used as a single breeding zone. They recommend a much finer grouping of the locations and the use of smaller plot sizes to allow more clones to be tested at more sites for the same cost. Locations may be selected for intensive cassava breeding work from those that give the best discrimination between genotypes while having insignificant genotype×environment interactions in a relatively large number of environments.

This study reports the results of model simulations of the potential yield of tea in north-east India. The CUPPA-Tea model, developed using data from a high-altitude site close to the equator in East Africa, was validated against the yield data from irrigation experiments conducted on contrasting soil types at Siliguri and Tezpur in the tea growing region of north-east India. The close correspondence between observed and predicted yield and yield distribution suggests that the model is applicable in north-east India. The model was used to simulate the yield response of tea to drought and irrigation using daily weather data for seven years (1983–89) at Siliguri and 14 years (1974–85) at Tezpur. On a clay loam soil at Siliguri, with an available water capacity of about 200 mm m−1, the predicted mean reduction in yield was 1.5 kg ha−1 for each 1 mm reduction in evapotranspiration. However, there appeared to be no reduction in evapotranspiration until the soil water deficit reached about 240 mm. By contrast, at Tezpur on loamy sand, with an available water capacity of about 100 mm m−1, evapotranspiration was reduced once soil water deficits exceeded about 85 mm. There was then a mean reduction in yield of 2.2 kg ha−1 for each 1 mm reduction in evapotranspiration. At both sites, even when soil water deficits were not limiting, the predicted year-to-year variation in yields was about 500 kg ha−1. The results highlight the soil-related differences in response to irrigation and the benefits of using process-based simulation models to investigate the potential yields over long periods.

India is the world's dominant producer of crude Mentha arvensis oil, and exporter of its processed derivative, natural menthol. This status has been achieved through superior product price competitiveness resulting from progressive agronomic improvements that include a transition from cultivation of this mint as a semi-perennial to an annual crop. This paper describes and analyses recent developments in Indian M. arvensis cultivation.

Observations were made during 1998/99 and 1999/2000 in the fields of 295 farmers in the central Indo-Gangetic plains area. The criteria recorded included: mint cultivars used; the planting, weeding, irrigation, pesticide application and harvesting schedules; crop health in relation to diseases and pests; yields of the harvested herb and the distilled essential oil; the oil menthol content; and the net income.

Most of the farmers used the cultivar, Kosi. The performance and returns of Kosi transplanted in April had proved superior to Kosi and Shivalik suckers and to transplanted Shivalik. The returns from late-transplanted Kosi were in the range of Rupees (Rs) 25 000 to Rs 40 000 ha−1 (Rs 50≈US$1), similar to those from Kosi suckers and much higher than for both transplanted and suckers of Shivalik. This survey revealed that rotations of rice (Oryza sativa) with chickpea (Cicer arietinum) and mint, and pigeonpea (Cajanus cajan) with wheat (Triticum aestivum) and mint could be profitable in the central Indo-Gangetic plains. They also conserved inputs and were preferable to the conventional rice-wheat rotation. A re-survey in the summer of 2002 confirmed that recommendations made to farmers have led to the adoption of the Kosi and Himalaya cultivars in 80% of the survey region and that 70% of mint cultivation in the area occurs in the summer season.

A reliable means to induce sprouting in dormant seed tubers of yams (Dioscorea species) is required to enhance flexibility in planting date and rate of propagation of the crop. Experiments were conducted to assess the potential of two gibberellin inhibitors, Uniconazole-P and Prohexadione-calcium, to induce sprouting in tubers from three varieties of D. rotundata and four of D. alata. Uniconazole-P and Prohexadione-calcium shortened the period of dormancy in tubers of some varieties. In others, they either had no effect or extended dormancy. The varietal responses were also influenced by whether the tubers were treated at harvest (before shoot senescence) or four weeks after harvest by which time shoots had senesced fully. Tubers stored in darkness at a constant temperature of 30 °C sprouted earlier but lost weight faster than did those stored under natural daylight and ambient temperature. The apparent slow action of Uniconazole-P and Prohexadione-calcium, and their variable effectiveness in relation to variety, would limit their usefulness in seed or breeding programmes, or in determining treatment timing and the best storage environment for the tubers after treatment.

ROOT CHARACTERISTICS IN THE COWPEA RELATED TO DROUGHT TOLERANCE AT THE SEEDLING STAGE

By MATSUI and SINGH