The systematic rather than random entry arrangement of honeycomb designs (HDs) has been deployed to sample the spatial heterogeneity. This hypothesis was studied in fairly homogeneous populations, assuming that their phenotypic variability stemmed absolutely from spatial rather than genetic heterogeneity. It was based on single plant performance in two separate trials of a maize hybrid and a wheat cultivar reflecting different level of spatial heterogeneity. In general, the HDs counteracted spatial heterogeneity well, particularly when the number of evaluated entries was limited. There was a suggestion that they do well even in a high number of entries with many replicates per entry. Distribution and layout of spatial heterogeneity across the experimental area did not affect the precision of the HDs. Standardized configuration, which ensures implementation of essential principles met in other experimental models such as blocking, replication and nearest-neighbour (NN) adjustment on the same baseline, renders the honeycomb experimental pattern advantageous over the classical experimental designs like the randomized complete block (RCB), the NN method and the lattice model.

A large body of evidence demonstrates the agronomic superiority of maize hybrids over open-pollinated varieties (OPVs) in intensive monoculture. However, comparisons of the performance of hybrids and OPVs in agroforestry systems are scarce. In this study, the performance of four maize hybrids and four OPVs is compared in sole crop and under mature trees. Experiments were conducted on-farm during four seasons in Bugesera, Rwanda and two seasons in Meki, Ethiopia. Two tree species were selected in Bugesera (Grevillea robusta and Senna spectabilis) and one in Meki (Acacia tortilis), and three farms were selected for each tree species, each including two plots with almost identical trees in their centre and two plots without tree. In Bugusera, grain yield was higher for hybrids (2 Mg ha−1) than for OPVs (1.5 Mg ha−1), and the presence of trees reduced the harvest index more in OPVs than in hybrids. In this region, the estimated reduction in grain yield due to the presence of trees was 0.9 and 1.1 Mg ha−1 in hybrids and OPVs, respectively, while estimated reduction in biomass was 1.5 and 1.7 Mg ha−1, respectively. In Meki, the grain yield of OPVs (2.08 Mg ha−1) and hybrids (2.04 Mg ha−1) did not differ and the presence of trees reduced their grain yields in the same manner. Our results showed that hybrids yielded more than OPVs under G. robusta and S. spectabilis in Bugesera but performed equally well under A. tortilis in Meki. We conclude that agroforestry farmers could benefit from growing hybrids in the equatorial savannahs of Rwanda, but that the choice between hybrid and OPV in equatorial savannahs of Ethiopia can simply be based on other factors such as seed costs and availability.

We aimed to evaluate aluminium (Al) effects on the photosynthetic apparatus of two rice cultivars with contrasting tolerances to Al. Nine-days-old seedlings were exposed to 0 or 1 mM Al for 10 days, and then dry mass, Al and chloroplastidic pigment contents and photosynthetic parameters were determined. Al accumulated mainly in the roots of the Al-treated plants. In the leaves, Al increased only in the sensitive cultivar, but there was no difference between the cultivars in Al-treated plants. The root and leaf dry mass, the net carbon assimilation rate, stomatal conductance and internal CO2 concentration were all reduced in response to Al application, but only in the sensitive cultivar. Both the initial fluorescence and potential photochemical efficiency of photosystem II were unresponsive to the Al treatments, regardless of the cultivar. In the Al-sensitive cultivar, Al provoked significant decreases in the photochemical quenching coefficient, quantum yield of photosystem II electron transport and apparent electron transport rate, in parallel to an unaltered non-photochemical quenching coefficient. All of these parameters remained at the control levels in the tolerant cultivar. The chloroplastidic pigment content increased only in the Al-tolerant cultivar, whereas it remained unaltered after Al treatment in the sensitive cultivar. In conclusion, Al induced stomatal and (most likely) photochemical constraints on photosynthesis but with no apparent signs of photoinhibition in the Al-sensitive cultivar. Despite the similar Al levels of the cultivars, unchanging biomass accumulation or photosynthetic performance in the tolerant cultivar challenged with Al highlights its higher intrinsic ability to cope with Al stress.

Fonio millet (Digitaria exilis), a small-grained cereal, plays an important role in food security in West Africa. As part of efforts to increase its productivity, we studied the effects of moderate levels of nitrogen (0, 15.0 and 30.0 kg N ha−1), phosphorus (0, 6.6 and 13.2 kg P ha−1) and potash (0, 12.5 and 25.0 kg K ha−1) fertilizers under varying climatic conditions. The three experimental sites at Bareng and Bordo in Guinea, and Cinzana in Mali, are representative of the distribution of fonio millet in West Africa. The average recorded grain yields were 1.51 ± 0.229, 1.08 ± 0.141 and 0.47 ± 0.182 t ha−1 in Bareng, Bordo and Cinzana, respectively. We observed a marginal to significant impact of N fertilization coupled, in Bordo, with a significant interaction with the P and K response. This interaction was highlighted by the limited effect of N without P or K fertilization or with the application of only one of these two major elements. Overall, N application as low as 15 kg ha−1 led to a 12–22% increase in production if the P and K applications were not limited. For better control over the risks associated with poor soil fertility and limited rainfall, it appeared to be more effective to apply moderate levels of N, P and K fertilizers to the fonio millet crop than a large amount of one of these nutrients.

Four surface sterilization agents and two hot-water treatments were evaluated with a view to eliminating bacterial contamination in sugarcane (Saccharum hybrids) buds used for in vitro initiation. None of the treatments achieved total elimination of contaminants. Disinfection in either a 2.7% solution of sodium hypochlorite (pH 6) or 1% mercuric chloride were equally good, resulting in 46.8% and 56.3% clean cultures respectively. However, sterilization with 2.7% sodium hypochlorite (pH 6) was most phytotoxic and 100% tissue necrosis and bud death were recorded. The Australian cold-soak hot-water treatment (consisting of a 48-h soak in running water followed by hot-water treatment at 50 °C for 3 h on the following day) reduced contamination from 70% to 25%. With the dual hot-water treatment (setts immersed in water at 52 °C for 20 min and then at 50 °C for 3 h on the following day) a decrease to 45% was observed. Bacterial contaminants were identified by fatty acid profiling and were found to belong mainly either to the Enterobacteriaceae family or the genus Bacillus.

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.

In a genotype × environment experiment at four sites with four tea (Camellia sinensis) clones in Kericho, Kenya, differences in ground cover and total dry matter production and partitioning were found between clones and between sites. The major contributor to these differences was the daily intercepted solar radiation that differed by as much as 30% between sites. Differences in radiation use efficiency (RUE) between the sites were small, but varied from 0.3 to 0.45 g MJ−1 between the clones. The rate of dry matter production was affected by the prevailing weather conditions. During the dry seasons the rate of dry matter production differed between the sites and clones by a maximum of 2 g m−2 d−1. Harvest indices were found to vary between the sites and increased with time. Partitioning to harvested shoots ranged from 10% for clone TN14-3 to a maximum of 19% in clone S15/10 at site 4. Partitioning to roots showed distinct differences between clones, being least in clone S15/10 (10–20%) compared with 15–32% in other clones. Rooting depths were greatly influenced by the prevailing temperatures.

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.

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.

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%.

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.

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.

A technique is described that allows neutron meter access tubes to be reinstated in tilled soil without disturbance below the depth of ploughing or tine cultivation. In a test there was no evidence of greater water movement to depth around reinstated access tubes compared with newly inserted ones.

Six products possessing suitable physical properties as fluid carriers for pre-germinated seed were assessed for their effects on seedling emergence. Both glasshouse and field experiments measured the carriers' performance on eight crop species at varying extrusion rates and under different environmental conditions. Synthetic clay or polyacrylate increased seedling emergence by 10% compared with the sodium alginate control. Seedling emergence was least affected by moisture stress when synthetic clay was used as the carrier.

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

Modification of the existing cropping practice is needed to maintain rice (Oryza sativa L.) productivity and reduce irrigation water input. A 2-year field experiment was conducted during the dry rice growing season of 2016 and 2017 at the Asian Institute of Technology, Pathum Thani, Thailand, to investigate the effects of establishment method and irrigation level on growth, yield, and water productivity of irrigated lowland rice. The treatments consisted of two Thai rice cultivars (Pathumthani 1 and RD57), two establishment methods (dry direct seeding [DDS] and transplanting [TP]), and three irrigation levels (continuous flooding [CF], 15 cm threshold water level below the soil surface for irrigation [AWD15], and 30 cm threshold water level below the soil surface for irrigation [AWD30]). Overall, the performance of RD57 was better than Pathumthani 1 under DDS with 50% higher grain yield and 90% higher water productivity at AWD15. RD57 also had higher shoot dry matter, number of tiller m–2, and number of panicle m–2 across establishment methods and irrigation levels. Grain yield and water productivity of RD57 were similar under two establishment methods across irrigation levels, whereas the performance of TP was better than DDS for Pathumthani 1 irrespective of irrigation levels. The highest grain yield and water productivity of Pathumthani 1 was observed at AWD15 under TP and that of RD57 under both establishment methods at the same irrigation level. AWD15 saved 26 and 32% irrigation water under TP and DDS, respectively, compared with TP-CF treatment combination. AWD15 irrigation level could be recommended for greater water productivity without compromising yield when Pathumthani 1 is cultivated through TP and RD57 is cultivated through either DDS or TP. Although water-saving potential was higher compared with CF, AWD30 is not recommended for irrigated lowland rice cultivation due to significant yield reduction.

A comparative study of two lettuce varieties (Lactuca sativa: ‘Romaine’ and ‘Vista’) was conducted to understand the effect of iron deficiency on growth, biomass allocation, chlorophyll fluorescence and root and leaf enzymatic activity. After 15 days of growth in hydroponic solution under Fe-deficient and Fe-sufficient conditions, leaf chlorophyll concentration, activities of ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) in leaves extract, ferric chelate reductase (FCR) and phosphoenolpyruvate carboxylase (PEPC) in root extracts were measured. We found that there were significant differences in fresh matter accumulation and pigment concentration between the varieties. Fresh weight and total leaf area and leaf number were significantly reduced under iron deficiency. There was also a significant decrease in photosynthetic pigment concentration in both varieties. In response to Fe deficiency, ‘Vista’ variety showed higher FCR and PEPC activities compared to ‘Romaine’ variety. Moreover, this increase was accompanied by an enhanced accumulation of phenolic compound in roots of ‘Vista’ variety. These findings show that ‘Romaine’ was more affected by iron deficiency than ‘Vista’.

Four experiments were conducted in southern Taiwan to evaluate the yield and economic benefits of management practices aimed at alleviating the effects of high temperature and heavy rain on tomato production. Following tropical storms, waterlogging caused wilting which was more evident in tomatoes grown in beds 20 cm in height than in those grown in raised beds 40 cm in height. This indication of crop water stress induced by flooding was quantified by measurement of the difference between canopy surface and air temperature at a specified saturation vapour pressure deficit. Canopy heating was less on the raised beds, especially when straddled by rain shelters. Nevertheless, waterlogging stress for the low-bed treatment did not result in loss of stand. In crops which experienced heavy rain, application of a synthetic fruit-set hormone enhanced fruit numbers as did the simple transparent polyethylene rain shelters. While planting on raised beds was without yield benefit the use of fruit-set hormone improved yield by at least 10 t ha−1. A further 4–6 t ha−1 yield was gained through the additional use of rain shelters. Partial budget analysis showed positive returns to the use of fruit-set hormone (US$6600 ha−1) but, unless rain shelters could be constructed with cheaper frame material or used for two tomato crops throughout the summer, their use would be uneconomical. Using existing frame material, net returns to rainshelters reached US$8000 ha−1. The likelihood of high temperatures, tropical storms and typhoons will influence economic returns to summer tomato production. Data from this study may be subjected to economic analyses using values for inputs and tomato prices from other countries with similar climatic conditions.

Soybean–wheat systems are the major grain production systems on vertisols in Madhya Pradesh, India. A study on yield response to nutrients (N, P, K, S and Zn) and estimation of N2 fixation by soybean under different nutrient combinations was studied in a 33-year-old, long-term experiment on soybean–wheat–maize system. For estimation of N2 fixation, annual input–output N balance technique was used. The experiment was initiated in June 1972, comprising eight treatments, viz. control (no fertiliser and no manure), 100% N, 100% NP, 100% NPK, 150% NPK, 100% NPK + 15 t farmyard manure (FYM), 100% NPK + Zn and 100% NPK – S with four replications arranged in a randomised block design. The amount of N applied (100%) to each crop of soybean, wheat and maize was 20, 120 and 80 kg ha−1, P (100%) 35, 35 and 26 kg ha−1 and K (100%) 16, 32 and 16 kg ha−1, respectively. FYM was applied one week before the onset of monsoons. Both soybean and wheat yields responded to applied N and P during all these years. The yield response to K was observed after 10 years. The estimated amount of N2 fixed by soybean annually varied from 62.8 to 161.1 kg ha−1; however, the net gain of N in soil after offsetting the N derived by soybean from soil varied from 24.2 to 66.5 kg ha−1 annually. Maximum N gain was recorded on application of P. There was a linear relationship between the amount of harvestable biomass N and residual biomass N, whereas quantity of N added to soil has a curvilinear relationship with the harvestable biomass N. The highest percentage of N derived from the atmosphere (% Ndfa) was recorded in the control treatment, but the highest amount of N2 fixed was found in the 100% NPK treatment. Balanced use of nutrient is the best option to harness the N2 fixation potential of soybean.

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.