The performance of a cassava clone susceptible to cassava mosaic disease (CMD) was tested over two successive years for CMD development, plant vigour and yield of fresh tuberous roots. Cuttings from plants with different CMD infection levels were used. There was a significant increase in mosaic incidence, severity and proportion of leaves showing symptoms of the disease in the subsequent crop as the levels of CMD primary infection in planting material increased. Plant height and stem diameter were also adversely affected and the yield of plants from severely affected cuttings was reduced by 60–70%.

The influence of a growth regulator, chlorocholine chloride (commercial name Cycocel 75) on plant growth, (yield) and quality of late-seeded (mid-December) cotton (Gossypium hirsutum) was studied in the Río Dulce Irrigation Area, northwest Argentina, during three growth cycles (1998–2001). Cycocel 75 reduced plant height and node number as well as the total production of aerial biomass, thus increasing the harvest index. Due to an increase in the boll weight and boll number per plant, the yield of treated plots increased by an average of 35% in comparison with the control. Cycocel 75 improved fibre strength significantly, although other parameters of fibre quality, such as length, uniformity, elongation, and micronaire index were not affected. This study indicated that late-planted cotton responds favourably to the application of Cycocel 75, especially when its development cycle is extended due to low air temperatures during the latter part of the growing season.

Univariate analyses of variance of mineral nutrient contents of samples of first and third leaves from seven fertilizer experiments in East Africa gave only limited information. Principal component analyses were then carried out on the nutrient contents of the third leaves. The most important component represented a balance between nitrogen and the basic nutrients potassium, calcium and magnesium, the variation of which was often related to yield. The results suggest that yield responses are likely to follow fertilizer applications only when the ratio of nitrogen to basic nutrients is within a defined range.

A rapid, simple method is described for estimating the area of rubber leaves from two measurements on the middle and one of the side leaflets. The relationship between the area of a leaflet (A) and its length × breadth (LB), described by the expression A = 0.654 LB, does not vary between the three leaflets or between leaves of different ages, and clonal differences are slight.

Prime lamb live weight response to lime application on pasture was measured in a grazing experiment in the high rainfall zone of the southwestern slopes of New South Wales, Australia. The pastures were limed every 6 years over 15 years. First cross South African Meat Merino lambs were used as test animals. Pre- and post-grazing pasture dry matter (DM) yield, botanical composition, feed quality and lamb live weight were monitored over 12 weeks in 2007. Results showed that liming significantly increased pasture DM yield of high quality species and improved overall pasture quality due to increased digestibility and metabolic energy content. As a result, the limed perennial and annual pastures carried 24.0% (3.6 lambs ha−1) and 29.0% (4.4 lambs ha−1) more stock than the unlimed perennial and annual pastures, respectively. Averaged across pasture types, the limed pastures produced 30.6% (131 kg ha−1) more lamb live weight gain than the unlimed pastures over 12 weeks. The live weight gain varied between grazing cycles depending on the availability of feed-on-offer and feed quality, which were closely related to the rainfall pattern. The perennial pastures did not show any advantage in animal production over annual pastures during the experimental period due to lack of moisture in the deep soil profile because of severe drought in the previous year. More seasons with normal or above average rainfall are needed to compare animal production on perennial pastures and annual pastures to investigate the advantage of perennial pastures in animal production.

A continuous daily rainfall record provides much information for agriculturalists but initial questions are imprecise and are modified in the light of experience. In order to match this uncertainty the program ‘Rainfall Statistics’ is designed as a simple interactive procedure for studying quantity probabilities, dry spell frequencies and a simple soil-moisture budget. The program has various functions depending upon user requirements. Use of the program is illustrated with rainfall records from northern Thailand.

Artificial defoliation was used to simulate grazing by cutting-grass or cane-rat (Thryonomys swinderianus), on three rices with durations of 110–115, 130–135 and 140–145 days respectively, defoliated before, during and soon after tillering by removing leaves to half, two-thirds and the total height of the plants. All varieties showed marked compensatory growth, resulting in increased tillering and yield, especially when defoliated during tillering, but yield fell when foliage was removed after tillering, especially with shorter duration rice. Defoliation to half the height of the plant during tillering had the most beneficial effect, whereas removal of all leaves to soil level after the tillering stage had the most adverse effect.

Although plant nematodes are ubiquitous and pathogenic to a wide range of crops, research into these pests in the tropics has been concentrated on commodity crops. While modern intensive tropical agriculture has become unsustainable and often relies on the use of toxic nematicides to control damaging populations of plant nematodes, many traditional subsistence farmers have been able to suppress nematodes by promoting crop diversity and selecting for tolerance and resistance. This paper gives examples of sustainable systems which suppress nematodes. Other examples of once sustainable systems in which nematode problems now occur are discussed and reasons for this instability suggested. The need for farmers to retain responsibility for the development of sustainable systems is stressed. Nematologists and other plant protectionists are encouraged to take a wider view of the complex issues that affect the sustainability of agriculture in the tropics.

Los nemátodos de las plantas y la agricultura continua

The radical concept of potato production from true potato seed (TPS) was adopted as a component of their farming system within three seasons by 23 farmers from Cibodas, West Java. The farmers showed an ability to conceptualize and experiment and desired concepts from which they could develop, through research, appropriate principles and field techniques. Information received solely as detailed practices or techniques hindered their progress, since they first needed to repeat the technique in order to understand the concepts and principles involved. Farmer experimentation resembled closely that of experimental station researchers, with the use of replication in space, often neighbouring farmers' plots, and time. Initial experiments covered a wide range of factors but within three seasons farmers had identified similar areas of concern which coincided with those of experiment station researchers worldwide. Farmer experimentation and the role of the researcher in this methodology for technology development are discussed.

Rice varieties were compared for their response to infestation by the stalk-eyed fly, Diopsis thoracica (West), both when a choice of varieties was available to the pest and when there was no choice. The fly significantly decreased the number of panicles produced (both total and mature), the percentage of tillers with panicles, grain weight and total yield of unprotected plants, and increased the number of immature panicles and time to 50% flowering. Reductions in grain yield of between 2 and 97% were recorded but these losses were unrelated to the percentage of damaged tillers. Production of new tillers did not fully compensate for damaged ones in most varieties. However, photoperiod-sensitive rice varieties were better able to compen- sate for pest damage than most.

Non-destructive methods are described for estimating annual above-ground dry matter production by the coconut palm, Cocos nucifera. Leaf dry weight is estimated from the cross-sectional area of the petiole. Trunk dry weight increment is estimated from the volume increment, and a function relating trunk density to palm age. Husk and shell dry weights are estimated from air-dry weights; copra dry weight is measured after oven drying. The weight of inflorescence stalks is small, and is ignored. Leaf area can be estimated from measurement of the length and width of a sample of leaflets. These methods have been applied to two coconut variety trials, and show significant differences between varieties in crop growth rate and harvest index. The trend of leaf area with palm age is described for two varieties and the hybrid between them.

Medida de la producción de materia seca en el cocotero

The relation between source potentials and sink capacities of four cassava (Manihot esculenta Crantz) varieties with different characteristics was investigated by means of reciprocal grafts. There were marked differences in the sink capacities (average stock effects) and source potentials (average scion effects) of the varieties.

The nitrate–N profile of soil was studied in sole and parallel multiple-cropping systems of pigeonpea and maize and of sugarcane and blackgram. In sole cropping there was more nitrate–N in the deeper horizons because of leaching from the inter-row spaces of row crops, whereas the nitrate content was drastically reduced in parallel cropping at more than 30 cm deep as N in the inter-row spaces was better utilized by the crops. The yield of two crops, when combined, was more in parallel cropping than the sum of crops grown separately, and the Land Equivalent Ratio was higher in parallel-cropping systems than in sole cropping.

The unit is a greatly simplified screw expeller, modified so that the crop is thoroughly rubbed to liberate juice before the charge moves into the part of the unit in which pressure is applied. The throughput of the model described here is 2 kg of crop per minute; power consumption is about 400 W. The unit weighs 40 kg, but larger ones, operating on the same principles, could be made.

The performance of three tropical grasses and three legumes (buffel grass, rhodes grass, green panic, butterfly pea, phillipesara and alfalfa), grown in pure stand and in legume–grass mixtures, was evaluated over two seasons when cut monthly at 0, 7 or 14 cm high. Harvesting at 7 cm favoured total dry matter and crude protein production in all cases, with highest yields from butterfly pea grown alone. Buffel grass was the best dry matter producer among grasses in pure stand, while rhodes grass–butterfly pea mixture was the best legume–grass mixture. Forage of these low-protein tropical grasses could be significantly improved by growing them in mixture with legumes.

Oil palm rachis length was determined on primordia dissected from palms planted at four densities. It started to increase rapidly in leaf–10, that is, about ten leaves younger than the spear leaf in all density treatments. The mean number of leaf primordia at the three higher palm densities was 47.7 compared with 51.5 at the lowest density of 56 palms ha-1. Some of the palms planted at the highest density were thinned to identify the stage at which the amount of light affected the rate of leaf opening. A sudden increment of light accelerated leaf production at both the rapid expansion stage and the preceding slow expansion stage. The greatest acceleration of leaf production began 24 months after thinning, probably because of the effect of the extra light on the rate of leaf initiation. The response of leaf production to thinning may apply to other related cultural practices.

Desarrollo de hojas en la palma aceitera (Elaeis guineensis) y determination de la tasa de apertura de las hojas

The growing season in the semi-arid region of West Africa is drought prone and of irregular duration. Two experiments were conducted in 1986 and 1987 to test the effects of flat cultivation and tied ridge cultivation (TRC) on the yields of maize and the component crops of a maize and cowpea relay cropping system. The two research sites, with slopes of 0.05% and 3%, were near Sapu, The Gambia, on an Aridic Kandiustalf in the 700 mm rainfall zone.

Both growing seasons had above average rainfall. In both years, maize on level sites showed no response to tillage practices. On the sloped site in 1987, soil moisture 10 and 15 days after the last rain was greater with TRC than with flat cultivation and yields of sole cowpea and maize were 25% and 18% greater, respectively. On the level site, TRC had no effect on residual soil moisture or grain yield. When rainfall was well distributed, tied ridging did not appear to be a viable tillage alternative for maize-based systems on flat land in central Gambia but with modest slopes, tied ridges markedly increased soil water reserves in the 0.15 to 0.60 m depth after maize harvest.

The performance of two contrasting pearl millet (Pennisetum glaucum) genotypes was compared following five planting dates under rainfed conditions in deep sandy soils at Bengou, Niger in 1986 and 1987. The early and partially photo-sensitive cultivar HKB yielded more grain than the late and photo-sensitive cultivar Somno when planted with the first two seasonal rains. But after delayed planting, the crop growth rate and harvest index of cultivar HKB were reduced, leading to smaller grain yields even though the growth period, rainfall, radiation and temperature were similar at all the planting dates. In contrast, cultivar Somno maintained a small but stable harvest index over various planting dates, so that although its growth period and crop growth rate were reduced by delayed planting, the reduction in grain yield was less. Since agronomic manipulation, such as increased plant density and fertilizer application, can be used to increase crop growth rate, photo-sensitive millet genotypes such as cultivar Somno could be used for late July plantings in the Sudano-Sahelian zone.

There is a need to shorten the selection process for sugarcane (Saccharum hybrids) in Mauritius in order to improve the efficiency of the varietal improvement programme. On average six to seven ratoon crops are grown in Mauritius and selection for ratooning ability is of major importance. The current selection cycle lasts around 15 years and ratooning ability is tested on five occasions. Data (estimates of sucrose content, cane and sugar yields) from the Mauritius Sugar Industry Research Institute's selection trials planted in 1986–90, representing 85 trials (9680 genotypes) in Stage 3 (one-line stage) and 141 trials (2620 genotypes) in Stage 4 (two-line stage) were analysed. It was hypothesized that 1st ratoon (1R) data in Stage 3 and 2nd ratoon (2R) in Stage 4 were effectively redundant and that the cycle could be shortened by two years without loss of precision. Repeatability estimates, between plant cane (P) and the mean of P and 1R (P + 1R) in Stage 3, and between (P + 1R) and the mean of plant cane, 1st and 2nd ratoon (P + 1R + 2R) in Stage 4, were found to be positive and highly significant for all characters indicating that the extra ratoon data were unnecessary.

Present and proposed selection scenarios were studied further using differential-selection methodology. The coincidence indices (CI) obtained with the two scenarios were extremely high (63–82% in Stage 3 and 91–96% in Stage 4) again indicating that the additional ratoon data were not cost effective. Realized gains from selection in Stage 4 based on (P + 1R + 2R) as opposed to (P + 1R) were shown to be small or even negative. The results concur extremely well with published data from Australia and the USA. It was therefore recommended that the cycle be reduced by two years and that the resources be more usefully allocated to test genotypes over more sites and more replicates.