Differences in the net photosynthetic rates of two classes of Hevea clonal seedlings are explained in terms of resistances to carbon dioxide diffusion from the outside air into the carboxylation sites. The residual resistance, the sum of the mesophyll and the carboxylation resistances, is apparently related to photosynthetic rates.

The yields of four potato varieties (two old and two new) in trials and in agriculture were compared. The six possible paired comparisons of means and of variety-on-variety regressions showed genotype–environment interactions. Trials and agricultural data agreed rather poorly as to both means and regressions, suggesting that further studies are desirable, in diverse crops, of the ability of trials to predict agricultural yields.

Gypsum application and irrigation increased yield in early maturing groundnut genotypes in experiments using line source and conventional irrigation. Response to gypsum varied with genotype; with some gypsum increased yields at all water application rates, in some genotypes there was no response, while with others gypsum increased yield in drought conditions.

In a separate study of the effect of gypsum and drought on pod initiation and development in three groundnut genotypes, gypsum did not greatly influence pod initiation when adequate irrigation was applied, but was beneficial when water was withheld during pod set and again during pod filling. Crops where the combination of gypsum and genotype were most advantageous in the first drought period subsequently grew more slowly so that there were no final differences in response to gypsum. Cultivar EC 76446(292) had a higher requirement for gypsum and was more susceptible to drought than the other two genotypes.

Gibberellic acid (GA) at 1500 ppm, applied as foliar spray or pre-plant soak, effectively promoted flowering in Nigerian clones of the cocoyams Xanthosoma and Colocasia. A foliar spray (technical grade GA) applied with 0.25% surfactant gave better results than with 0.01% surfactant or than a foliar spray of Pro-Gibb Plus (commercial GA formulation). A pre-plant soak of Pro-Gibb Plus was least effective but could be useful in poorly equipped research stations.

Prolonged moisture stress and high vapour pressure deficits reduced the shoot water potential, shoot population density, rate of shoot extension and yield of clonal tea. The more drought susceptible Clone 6/8 had a lower shoot water potential, rate of shoot extension, number of shoots per unit area, rate of shoot regeneration and yield than the more tolerant Clones 31/8, 57/15 and 15/10 during the periods of low soil moisture, which coincided with high vapour pressure deficits. The changes in the shoot growth components could be used as an index of the suitability of different clones for different regimes of soil moisture and vapour pressure deficits.

Factores ambientales que afectan el rendimiento del té

With the exception of leafy and daylength-sensitive cultivars, cowpea (Vigna unguiculata (L.) Walp), produced larger yields in the first season (April-July) than in the second season (September-November) at Ibadan, Western Nigeria, whether or not the crop was protected by insecticide. The populations of major cowpea pests were low at the start of the rainy season and reached their peaks in September or October. The implications of these results in insect control strategy are discussed.

The main axis of a Principal Components Analysis, based on measurements of width and depth of canopy of two cocoa progenies was shown to be an index of canopy size and the second axis an index of shape. Mean scores of the progenies T85/799×T17/359 and E1:C43/291×T63/967 (Series IIB hybrid) on these axes showed that their canopies did not differ significantly in shape, but that the canopy size of Series IIB trees was on average greater than that of T85/799×T17/359. Regression lines of log numbers per tree of Planococcus citri Risso against canopy size of the two progenies were parallel, indicating that for a given canopy size P. citri was 2·3 times more prevalent in trees of Series IIB than in T85/799×T17/359. A similar analysis with the combined numbers per tree of seven mealybug species showed that they were 1·9 times more prevalent in Series IIB than in T85/799×T17/359 trees of the same size.

In a field experiment to estimate water needs of intercropped sorghum and soyabeans, leaf water potential (LWP) and canopy light transmission were measured. Sorghum had 8–11% lower LWP when grown in mixture than alone, but soyabeans, shaded by sorghum had a higher LWP than in monoculture. Absolute LWP values suggest that only about 10% additional water would be required by the mixture compared with individual requirements of the aggressor species in a two-species mixture of this nature.

Three experiments testing the effects of nitrogen on melon showed significant varietal differences. Nitrogen increased yields by increasing fruits/plant, seeds/fruit and seed weight, had no effect on fruit weight, size and husk, and increased leaf area through leaf number and leaf size. Fruit growth coincided with a rapid decline in leaf area, indicating that the mottled green fruits contributed appreciable assimilates towards their own growth. The implications of the findings, and the inefficiency of the crop in seed formation, are discussed.

The aim of this work was to test the performance of a shrimp-tomato culture system (STCS) in an arid-semiarid region (Sonora, Mexico) and to evaluate the water quality variables and phytoplankton variation of shrimp effluent and that water returning from the tomato module culture. The field study was conducted using groundwater and consisted of three circular tanks that were used for shrimp (Litopenaeus vannamei) farming and were coupled to one culture module of tomato plants (Lycopersicon esculentum). The shrimp effluent was used to irrigate the tomato plants. The yield was 11.1±0.2 kg shrimp per tank (3.9±2.0 ton ha−1) and 33.3 kg tomatoes per 45 plants (36.1±2.3 ton ha−1). During the culture, the concentrations of nutrients were (mg L−1): total N-ammonia, <0.001–0.848; N-nitrite, <0.001–1.45; N-nitrate, 5.2–172.2; dissolved reactive-P, <0.005–0.343. A total of 35 taxa belonging to three different algal classes were observed: Chlorophyta (87 to 98%), Bacilliariophyta (2 to 9%) and Cyanophyta (0–3%). This STCS allowed us to harvest the equivalent of 3.9 ton ha−1 of shrimp and 36.3 ton ha−1 of tomatoes, with a water consumption of 2.1 m3 per kg harvested of both products.

High-yielding short-duration cultivars are required due to the development of mechanized large-scale double-season rice (i.e. early- and late-season rice) production in China. The objective of this study was to identify whether existing early-season rice cultivars can be used as resources to select high-yielding, short-duration (less than 115 days) cultivars of machine-transplanted late-season rice. Field experiments were conducted in Yongan, Hunan Province, China in the early and late rice-growing seasons in 2015 and 2016. Eight early-season rice cultivars (Liangyou 6, Lingliangyou 211, Lingliangyou 268, Xiangzaoxian 32, Xiangzaoxian 42, Zhongjiazao 17, Zhongzao 39, and Zhuliangyou 819) with growth durations of less than 115 days were used in 2015, and four cultivars (Lingliangyou 268, Zhongjiazao 17, Zhongzao 39, and Zhuliangyou 819) with good yield performance in the late season in 2015 were grown in 2016. All cultivars had a growth duration of less than 110 days when grown in the late season in both years. Zhongjiazao 17 produced the maximum grain yield of 9.61 Mg ha−1 with a daily grain yield of 108 kg ha−1 d−1 in the late season in 2015. Averaged across both years, Lingliangyou 268 had the highest grain yield of 8.57 Mg ha−1 with a daily grain yield of 95 kg ha−1 d−1 in the late season. The good yield performance of the early-season rice cultivars grown in the late season was mainly attributable to higher apparent radiation use efficiency. Growth duration and grain yield of early-season rice cultivars grown in the late season were not significantly related to those grown in the early season. Our study suggests that it is feasible to select high-yielding short-duration cultivars from existing early-season rice cultivars for machine-transplanted late-season rice production. Special tests by growing alternative early-season rice cultivars in the late season should be done to determine their growth duration and grain yield for such selection.

Intensity of harvest in tea can be defined in terms of the number of leaves or axillary buds left behind after a shoot is harvested; we describe a simple method for measuring it. Application of the method in trials confirms that yield increases with more intense (harder) harvesting. Differences in intensity of harvest explain much of the variation in yield between different harvesting treatments, including semi-mechanical and mechanical harvesting methods. We recommend that measurements of intensity of harvest should be made routinely in experiments with tea.

Amorphophallus paeoniifolius, popularly known as elephant foot yam, is an important tropical tuber crop in India. Its modified stem (corm) is consumed as a vegetable after boiling, baking or frying. Mealybug (Rhizoecus amorphophalli), a soft-bodied insect, infests the corms both in storage and in the field. Though pesticides are effective in controlling mealybugs, they can be hazardous to human health and the environment. Two experiments, one in storage followed by one in the field, were conducted during 2009 and 2010 at the Regional Centre of Central Tuber Crops Research Institute, Dumuduma, Bhubaneswar, India, to determine the effect of six low cost and environmentally safe management practices on mealybug. In the absence of mealybug control measures, mealybug numbers increased by 4–5 times during the storage period. The pest affected the quality of the corms and reduced subsequent field establishment and crop growth. Salt (NaCl) solution (1000 ppm), cow urine, cow dung slurry (2 kg of cow dung in 1 litre of water) and clay slurry (1 kg of clay in 1 litre of water) treatments were effective in reducing mealybug numbers and the associated corm damage. However, availability of cow urine, cow dung and clay slurry limit their usage. Common salt is cheap, widely available and easy to use in treating the corms prior to storage. Relative to untreated corms, those treated with salt solution recorded greater emergence when field planted as well as producing plants with more vigorous growth.

In 2004 and 2005 through field trials in over 2500 locations in several agroecological zones, 40 new cassava varieties were introduced in Nigeria. The trials were managed by scientists, extension workers and farmers. The aim in introducing these new varieties was to pre-emptively manage cassava mosaic disease, to avert an imminent threat from the Ugandan strain of the pathogen and prevent damage to the Nigerian cassava economy. From these trials, 10 new varieties were selected and officially released for high root yield, high dry matter content and acceptability for food, industry and livestock. Cassava root rot is a major source of yield loss in Nigeria, especially where farmers practice late harvest because they wait for a good price from the market before harvest and sales. This paper investigated how the 40 varieties together with three old improved varieties currently in farmers' fields during the formal trials responded to root rot disease. No absolutely resistant variety was found, indicating that early harvest (9–11 months after planting) is still the best way to reduce losses from root rot. Root rot is also significantly (p ≤ 0.05) influenced by genotype and environment interaction. Most root rot was recorded in the humid forest and the least was in the Sudan savanna agroecological zone. Using a rank-sum method, the 43 varieties were separated into highly resistant, resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible classes.

Little bag silage (LBS) is seen as a low-cost alternative suitable for resource-poor smallholders to alleviate dry-season feed constraints. Within a research project carried out by the International Center for Tropical Agriculture and partners in Honduras, LBS was tested and its use encouraged during farmer training and field days. The present study highlights the most relevant technological and socio-economic potential and constraints of LBS. Surveys and experimental results revealed great vulnerability of plastic bags to pests, particularly rodents, accompanied by high spoilage losses. The main constraints to wider adoption include availability of i) suitable and affordable plastic bags, and ii) appropriate chopping equipment and storage facilities on smallholder farms. LBS proved to be useful and could play an important role in participatory research and extension activities, as a demonstration, experimentation and learning tool that can be used to get small-scale silage novices started with a low-risk technology.

Shortened fallow periods lead to a decline in crop yields in traditional mixed-food crop fields in southern Cameroon. Farmers use no inputs such as fertilizers for crop production in these field types. Planted fallows with adapted tree species might sustain or increase crop production under those conditions, as found in other parts of Africa. Two-year-old calliandra tree fallows, with trees planted in alleys, clusters, equidistantly or around plot borders, were compared with two- and four to five-year-old natural fallows for their effect on groundnut, maize and cassava yields on eighteen farmer fields in southern Cameroon. Trial fields covered a wide range of soil and environmental conditions. The tree fallows had no significant effects on the yields of maize and cassava with the exception of the border planting, in which trees were not rigorously pruned back prior to cropping. Here, cassava tuber yields were reduced. Cassava tuber yields declined generally with decreasing planting distance to trees. The yield of groundnut, the most important crop in this field type, was adversely affected. However, maize grain yields were positively related to biomass produced by calliandra trees, notably on soils with pH over about 5.3. The data indicated that yields of all crops could be increased with higher plant densities, irrespective of fallow type. The tree fallows, with the exception of border planting, showed less adaptability than four to five-year-old natural fallows to sites with low crop yields, whereas no difference compared with two-year-old natural fallows was found.

The genotype × environment (GE) interaction analysis is fundamental in crop breeding programs to guide selection and for recommendation of high performing and stable genotypes for breeding objectives. This study aimed at quantifying the GE interaction effects and determines grain yield stability among winter bread wheat genotypes under rainfed conditions of Iran. Twenty-four winter wheat genotypes were evaluated under nine test locations using a randomized complete blocks design with four replications during three cropping seasons (2019–21). The additive main effects and multiplicative interaction (AMMI) model and several parametric and nonparametric stability statistics were applied for analysis of grain yield data collected from the experiments. AMMI analysis of variance for grain yield revealed significant effects (p < 0.01) for genotype, environment, and GE interaction. The environment was the main source of variation and accounted for 83.5% of the total yield variation, followed by GE (6.5%) and genotype (1.0%) effects. The AMMI biplot analysis indicated the genotypes G3, G23, G22, G10, and G19 as high yielding with stability performance across environments. Genotypes G14, G13, G20, and G9 showed large positive interaction with the environments featuring the highest rainfall during growing season, while genotypes G7, G6, and G21 had a large positive interaction with environments with low rainfall. Spearman’s rank correlation analysis revealed that the AMMI stability value, Shukla’s stability variance (σ2i), Wricke’s ecovalence (W2i), coefficient of determination (R2i), variance in regression deviations (S2di), and nonparametric statistic of S2(i) were not correlated with mean yield in tested genotypes, showing they are related to static/biological concept of stability. In contrast, the genotypic superiority index (Pi) and regression coefficient (bi) were significantly correlated (p < 0.01) with mean yield and corresponded to dynamic/agronomic concept of stability. These findings suggest that selection of genotypes should be considered based on selection objectives of using the various stability parameters described here. In conclusion, the selected genotypes in this study should be recommended as new cultivars or parental lines for grain yield and stability improvement under rainfed conditions of Iran or similar agro-ecologies.

The centre of origin of cashew is believed to be Brazil, from where it has spread since the 16th century throughout the tropics. In recent years, Vietnam has surpassed India to become the world's largest producer of cashew nut. Most of the research on the water relations of cashew has been done in Brazil, where it is both a large-scale commercial and a smallholder crop, and in Australia, where cashew is a possible emerging new crop. There are two ‘types’ of cashew: ‘talls’ and ‘dwarfs’. Both are evergreen trees in which vegetative growth occurs in a series of flushes. Flowers form annually on the end of branches in the dry season, and flowering continues for two to four months. It then takes about two months from pollination for the nut to mature. Roots can extend to great depths (>5 m), while cashew's wide-spreading rooting habit is critical to its successful adaptation to semi-arid/dry conditions. The optimum temperature for CO2 assimilation is in the range 25–35 °C. Progressive closure of the stomata occurs at saturation deficits of the air >1.5 kPa. In the field, differences in rates of gas exchange between irrigated and unirrigated cashew trees only become apparent three or four months after the end of the rains, the stomata playing an important role in maintaining a favourable leaf water status in dry conditions. Sap flow measurements indicate transpiration rates of 20–28 L d−1 tree−1. Irrigation can be beneficial during the period from flowering to the start of harvest, but reliable estimates of water productivity have yet to be established. The best/only estimate is 0.26 kg (nut in shell) m−3 (irrigation water). There is a continuing need to develop a method to estimate the water requirements of cashew, to identify where and when irrigation of cashew is likely to be justified and to develop a practical irrigation schedule.

Experiments were conducted across 2 years to determine the effect of harvesting methods – combine harvester and hand harvesting – and harvest time during ripening on milling quality of long grain rice grown in the rainfed lowland ecosystem in Cambodia. Head rice yield (HRY) was highest when rice was harvested 25 days after flowering and decreased with delay in harvesting at 35 and 45 days after flowering. This was accompanied by a general decline in grain moisture content at harvest, although it was still high at 24–25% at 35 days after flowering. The decline in HRY was associated with increases in fissured grain percentage observed immediately after harvest. Hand harvesting produced 2–6% higher HRY than combine harvesting. Fissured grain in hand harvested crops was lower in year 1, but was similar to combine harvested crops in year 2. Both hand and combine harvested crops were sun-dried but rough rice harvested by combine was dried on plastic sheet and this may have contributed to reduction in HRY. Maximum HRY percentage was only about 44% and the factors contributing to this low HRY were discussed. Harvesting time and methods had no significant effect on grain yield, but the field grain loss during the harvesting operation was 2–5% higher in combine than hand harvesting.

In the process of developing an improved fallow system based on forage legumes, the potential interest of crop-livestock farmers in enhancing soil fertility restoration and dry-season feed supply was assessed during a socio-economic study on 11 farms of settled agro-pastoralists in the subhumid zone of West Africa. Simultaneously, eight farmers in the group participated in simple and largely farmer-managed on-farm experiments testing the establishment of selected forage legumes on fallow land. In addition to agronomic parameters, the participatory approach included an evaluation of the technology by farmers both during farm visits and field days.

With cropping and dry-season feeding strategies increasingly being limited by land availability, the agronomic performance of some of the tested legume species, in particular Stylosanthes guianensis, promised substantial productivity gains once they could be integrated into the traditional fallow system. The major concerns of the farmers were animal health and labour supply for cropping activities, rather than soil fertility and feed constraints. The need for initial weed control within most of the legume species, therefore, limited their acceptability by farmers at this early stage of innovation testing. Nevertheless, farmers' interest grew remarkably in the course of the study. Options for the selection of appropriate species and management practices, which aimed at facilitating the establishment of legumes on fallow land, are discussed as a means of enhancing further adoption of the innovation.