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.

Photosynthetic rates (Pn) of China-type high quality tea (Camellia sinensis), clone T78, 44–68 months after field planting, were monitored during the different seasons of 1996 and 1997. The maximum value of Pn (11.9 μmol m−2 s−1) was recorded in October when humidity was very high, temperature, sunshine hours and soil moisture were moderate and photosynthetic photon flux density (PPFD) was highest. Low temperature accompanied by low soil moisture reduced Pn during the winter (February). An important limiting factor for Pn was observed to be moisture stress. An apparent relationship between Pn and relative humidity was observed. In general, higher rates of Pn were recorded during periods of low evaporative demand (low VPD).

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.

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’.

Rice is widely grown in rainfed lowlands during the wet season in the Mekong region. Limited nutrient availability is a common constraint on crop yield, and the optimal rate of fertilizer application depends on the soil type. The objective of our study was to evaluate rice productivity and the economic feasibility of various nutrient management regimes in Cambodia. We conducted field experiments on three soil types (Prey Khmer, Prateah Lang, and Toul Samroung, equivalent to Psamments, Plinthustalfs, and Endoaqualfs, respectively) in four provinces (Battambang, Kampong Thom, Pursat, and Siem Reap) during the 2016 and 2017 wet seasons to compare nine (2016) and seven (2017) N–P–K combinations. Grain yield ranged from 0.9 to 4.8 t ha−1 in 2016 and from 1.0 to 5.2 t ha−1 in 2017, depending on soil type and nutrient management. The Prey Khmer soil contained around 80% sand, and rice yield responded most weakly to nutrient management. The moderate fertilizer input in the current soil-specific recommendation was effective on this soil type. However, on more fertile soils with a higher clay content and a higher cation-exchange capacity (Toul Samroung and Prateah Lang), an additional 20 kg N ha−1 combined with adding 15 kg ha−1 of P2O5 or 20 kg ha−1 of K2O significantly increased yield and economic return. Although P and K use during Cambodia’s wet season is uncommon, our results demonstrate the importance of these nutrients in improving the country’s rice production.

This paper seeks to make an exploratory investigation regarding farmers who have been using an innovation for a relatively long period (established users), compared to farmers who have only recently started (recent users). Therefore, the aims of this research were to identify (i) the extent to which intentions, attitudes and social pressure are similar or different between these two groups and (ii) whether comparison of the groups can improve academic understanding and provide insights into what is influencing the uptake of innovations. The study was conducted with 80 farmers who are already engaged with the use of improved grassland. In order to develop an understanding of the differences in drivers of the adoption of new technology, the sample was divided into established users and recent users of the innovation. To identify differences between groups regarding farmer and farm characteristics, 11 quantitative variables were analysed through a dependent t-test. The theory of reasoned action (TRA) was used as a theoretical framework and the Spearman rank-order correlation was used in data analyses. To identify differences in farmers’ perceptions of the components of the TRA, we used the Mann–Whitney U test. The results showed that established users had stronger intention to use improved grassland in the next 12 months, which would be attributed to activity based on milk production as a main source of family income. Advantages of improved grassland included lower animal feeding expenses; increases in quantity, quality and availability of fodder production and increases in milk production. We concluded that established and recent users’ intention to use improved grassland over the 12 months was influenced in different ways. Established users’ intention to adopt was strongly influenced by normative beliefs, i.e. social pressure from salient referents, where the father, uncle and veterinarian played the most important role, whereas recent users’ intention was mainly influenced by behavioural beliefs (positive and negative beliefs regarding the innovation) and the variables that describe the farm characteristics, i.e. the advantages and disadvantages that farmers perceive of the use of improved grassland on their farms, which were also considered as drivers of adoption.

Though bitter white lupin (Lupinus albus L.) is a traditional crop in Ethiopia, sweet lupins are new to the country. As a result, the nutritional value of low-alkaloid lupins has not been evaluated under Ethiopian conditions. Crude protein, amino acid and alkaloid contents of 16 cultivars of three annual lupin species grown in four lupin growing locations (Merawi, Finoteselam, Kossober-1 and Kossober-2) of Ethiopia were evaluated. Location × cultivar interaction was a significant source of variation for all traits (p < 0.0001). In all locations, blue entries had either similar (p ≥ 0.0584) or higher (p ≤ 0.0235) forage crude protein content than the Local Landrace, white group and yellow entry. Compared with the Local Landrace, white and blue entries, the sole yellow entry had higher (p ≤ 0.0148) seed crude protein content at all locations except at Kossober-2, where it had similar (p = 0.8460) crude protein content as white entries. The Local Landrace had the highest forage and seed alkaloid contents. However, sweet blue Vitabor and Sanabor entries had the lowest forage and seed alkaloid contents, respectively. Low alkaloid and higher crude protein contents of sweet lupins grown in Ethiopia show the possibility to use sweet lupin forage and seeds as cheap home-grown protein source for livestock feed and human food in the country. However, for more reliable information, the laboratory results need to be verified by animal and human evaluations of the crop.

Parthenium weed is an invasive species in a growing number of countries where it infests numerous crop fields, including sorghum. Two field studies were conducted to quantify the effect of parthenium weed on the performance of grain sorghum at different weed densities (0, 5, 10, 15 and 20 plants m−2) and durations of weed-crop competition (season-long weed-free, weed-free after 2, 4, 6 or 8 weeks, and season-long weedy). Our aim was to identify the density threshold and ideal duration to control parthenium weed in sorghum fields. Both field experiments were planned in a randomised complete block design each with three replications in 2016 and were repeated in 2017. Parthenium weed biomass increased significantly with increasing density and competition duration. The increasing parthenium weed density had a linear negative effect on sorghum growth, yield and yield-contributing traits. The highest yield loss, of up to 66%, was recorded at the highest parthenium weed density of 20 plants m−2 when compared to weed-free treatment. In addition, the season-long competition of this weed with sorghum caused 81% reduction in grain yield over weed-free treatment. According to our results, parthenium weed should be managed below a density of 5 plants m−2 and throughout the crop growth duration in grain sorghum fields as it can cause serious yield losses even at low densities and through strong competition at early as well as late growth stages of the crop.

Norman Simmonds was an outstanding member of the group of British Tropical Agriculturalists who served overseas with great distinction during and immediately after the Second World War. He was then equally successful and influential in British academia and as an internationally respected researcher. He will be remembered as a plant breeder, a geneticist, a teacher and author, and as incisive commentator on current affairs in tropical agriculture. Simmonds had a long association with Experimental Agriculture, serving on its Editorial Board from 1978 to 1998, and as a Book Review Editor from 1978 to 1987.

This special issue brings together a selection of papers that not merely present agronomic research findings, but critically review orientations, methodologies and research practices in agronomy. The focus is on agronomic research as it conducted as component of rural development efforts in the global South or, in short, development-oriented agronomy. Aiming to contribute to development challenges like food security, human welfare and wellbeing, and environmental sustainability, a focus on development-oriented agronomy implies a step beyond a narrow understanding of agronomy as the science of crop production and soil management. Doing development-oriented agronomy forefronts the juggling with productivity enhancing, environmental and social developmental goals entailed when doing agronomy. What is more, development-oriented agronomy generally takes place within a complex environment of (inter)national research and development policy organisations, development donor-funded projects, governmental, NGO and private sector agencies and global professional networks and (public–private) partnerships. Consequently, development-oriented agronomy is a field where debate and contestations over goals and direction, research methodologies and findings of agronomic research are first likely to emerge and become apparent.

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.

Weedy rice species exhibit differential competitive ability and cause significant losses to rice yield. The present study was conducted to evaluate the competing ability of weedy rice accessions collected from foothills of eastern Himalayas and coastal Odisha grown in the presence of cultivated indica rice var. Swarna. The competitive ability of Swarna and weedy rices were estimated on the basis of (i) Swarna yield reduction under different durations of competition with weedy rice; and (ii) nutrient uptake by Swarna and weedy rice in competitive environment. There was significant yield reduction (18%) when competition was allowed until 6 weeks after emergence (WAE) compared to competition until 2 WAE, which was due to vigorous growth of weedy rice at early vegetative stage. The biomass accumulation and tiller number of weedy rice were significantly higher compared to Swarna. Odisha weedy rice accession recorded about 18, 57 and 24% higher N, P and K uptake, respectively, than Swarna. The highest yield reduction (22%) in Swarna was recorded when grown with OA1 and the lowest impact (7.7%) was recorded with AA2. As conclusion, management practices should be implemented within 2–4 weeks of emergence considering 5–10% acceptable yield loss of Swarna, and grain yield of cultivated rice was reduced significantly by high N and K uptake by weedy rice under a competitive environment.

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.

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.

Impact assessment is important to agricultural research. It quantifies benefits from both proposed and past research, and allows comparisons of the cost effectiveness of different research investments as a basis for priority setting. Though there are important economies of scale in the global and regional level research done by the international centres of the Consultative Group for International Agricultural Research (CGIAR), this research covers only one small sector in the sequence of research and development reaching down into farmers' fields. CGIAR impact thus depends on the rest of the research and development (R&D) sequence operating effectively, something largely beyond its control. In deciding a strategy for impact assessment, the international centres need to resolve two dilemmas: first, how much impact assessment they should do, for their own programme planning and monitoring, and to satisfy their stakeholder constituencies; and secondly, how sophisticated this assessment should be. Impact measurement is itself research and, like all research, is very much concerned with how much is gained from the extra costs of collecting further information.

Centros agrícolas internacionales

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.

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.

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.

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.

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.