Groundnuts (Arachis hypogaea L.) are generally considered to be self-pollinated, but natural hybrids due to outcrossing have been observed in cv. Robut 33-1. Selections in segregating generations of these natural hybrids identified stable lines with large yield potentials in more than one environment. The role of natural hybrids in generating useful additonal variability is discussed.

Five varieties of French bean of contrasting growth habit were grown at a range of plant densities. Most varieties yielded best at 30 plants m−2, but the bush type variety Contender yielded best at 50 plants m−5. The best yield was obtained from the semi-spreading variety Rufus.

As zinc (Zn) fertilizer and water management affect the expression of Zn-enriched grain traits in rice, we studied the effect of Zn fertilizer and water management on Zn uptake and grain yield of different biofortification breeding lines and the possible biases in selection for high grain Zn content. The first field experiment showed that longer duration genotypes had higher grain Zn uptake rate than shorter duration genotypes during grain filling. In the first greenhouse experiment, neither application of Zn fertilizer at mid-tillering nor application at flowering significantly increased the grain Zn concentration. In the second greenhouse experiment, application of alternate wetting and drying (AWD) significantly increased the available soil Zn and plant Zn uptake but not grain Zn concentration. Terminal drying (TD) did not increase the available soil Zn or grain Zn contents. The second field experiment confirmed that differences in TD were not important in understanding differences between genotypes. Zn application is not always necessary to breeding trials unless there is a severe Zn deficiency and there is no need to carefully regulate TD prior to harvest.

Monthly partitioning of dry matter (DM) and nutrient contents of polybag oil palm nursery seedlings, planted at three spacings, showed that leaves and petioles accounted for about half of the DM up to 11 months. There was no spacing effect on the nutrient contents of seedlings, K being always higher than other nutrients followed by N, Ca, Mg and P in that order. Most of the nutrients were in the leaves and petioles, with a dramatic increase in the amount of nutrient taken up by the seedlings in November. Fertilizer rates and frequencies were deduced for an oil palm nursery based on the nutrient contents of seedlings.

The variation in number and yield of tubers from three commercial fields of sweet potato was measured over three seasons. Sources of variation were attributed to factors external to the plant, such as soil, management and climatic differences, and to inherent plant factors, including type of planting material. It is suggested that a reduction in variability could lead to increases in productivity, and may also increase the precision of field experimentation.

This paper offers guidelines for successful crop rotation trials derived from experience at ICARDA in the period 1980–1990. Emphasis is placed on the need to determine realistically the likelihood of the long-term, successful completion of the trial and the importance of considering carefully experimental design criteria prior to trial establishment. This involves assessment of what primary and secondary information to collect for the trial, and over what duration, in order to ensure an appropriate return for the large investment generally undertaken in any crop rotation trial.

Principios para ensayos con rotación de cultivos

Three different saffron strains (Crocus sativus, C. sativus var. ‘cashmerianus’ and C. cartwrightianus) were tested for two years in field experiments to study their red stigma yield and quality. The experiments were performed at a high-elevation (rainfed or irrigated) site and a coastal site in Lebanon. On average, the two C. sativus strains gave more flowers and stigma yield than C. cartwrightianus. The former was more productive in the more favourable environments, especially at the warmer coastal site, than the latter. C. sativus ‘cashmerianus’, which yielded better at the coastal site in 2004 and gave a stronger colour strength and aroma, appeared to be the better choice for the area. Mean yield at the coastal site was twice that at the non-irrigated high-elevation site. On average, saffron produced at the coastal site had more colouring strength and bitterness than that produced at the high-elevation site. Nevertheless, viable commercial saffron production may still be possible in the semi-arid, high-elevation Bekaa Valley if irrigation can be provided.

Field experiments during the winter seasons of 1986–7 and 1987–8 studied the effect of three sub-surface drain spacings and three levels of phosphorus on the yield, chemical composition and uptake of nutrients by Indian mustard (Brassica juncea). The number of siliquae m-2 and seed yield decreased with increasing drain spacing. Application of phosphorus increased seed yield and yield attributes. The concentrations of nitrogen, phosphorus and potassium in the seed and stalks decreased and those of sodium, calcium and magnesium increased with increasing drain spacing, but application of phosphorus increased the concentration of these nutrients in the seed and stalks. Absence of phosphorus in the drain water effluent and the level of available phosphorus in the soil profile after crop harvest indicated very slow movement of phosphorus, most of which was retained in the top 30 cm of soil.

A survey was conducted of Indonesian cocoa farms to assess the extent of yield variation and factors associated with this variation. The survey of 120 farms during the course of 3 years encompassed four provinces in Sulawesi (South, South-East, West and Central), Western Sumatra, Lampung, East Java and West Papua. A high degree of yield variation was observed between farms, the average over 3 years ranged from 39 to 3586 kg ha−1. Overall, yields were greater on farms that were classified as ‘highly managed’, compared to ‘moderately’ and ‘less managed’. Seasonal variability in yields was generally greater in districts with a more pronounced dry season such as South Sulawesi and Lampung. Multiple regression analyses revealed particular husbandry practices that were linked with higher cocoa yields. Specifically, the use of inorganic fertilisers, application of fungicides against blackpod and weeding were all practices that were associated with higher yields. A positive association between rainfall and yield was observed for the years 2014/15 and 2015/16 but not 2016/17, which was a La Niña year (when rainfall totals were higher). Some of the farms surveyed were planted with cocoa at very low densities implying an opportunity for yield improvement through gap filling or replanting at higher densities (although it was noted that some farmers maintained lower planting densities due to the cultivation of companion crops). Given the smallholder status of most cocoa farms in Indonesia (mean area in this study was 0.71 ha) it is important that farmers are able to maximise returns from their land in order to maintain a livelihood. This study illustrated the potential for yield improvement on Indonesian cocoa farms through adoption of best agronomic practice.

A diallel cross study on Indian mustard revealed a preponderance of additive gene action for seven characters out of the nine studied. Plant height and seeds per siliqua seemed to be controlled by both additive and non-additive gene action. Days to flower, number of secondary branches, length of main branch, number of siliquae on the main branch, length of siliqua and yield per plant were mainly controlled by additive gene action, whereas oil content was determined mainly by non-additive gene action. Heterosis was prevalent and the maternal effect was not generally apparent in the crosses. Rank correlations established a positive correlation between performance per se and GCA, and between heterosis and SCA.

Plants of the photoperiod-sensitive, late-maturing pigeonpea (Cajanus cajan) cv. KAT777 were grown in pots in modified field environments at Katumani, Kenya. They were transferred at different durations after emergence from natural short days (SD, 12.6 h d−1) to artificially-extended long days (LD, 15.0 h d−1), and vice versa, under both ambient (19 °C) and warmer (26 °C) temperatures created beneath p olythene enclosures. All plants at 19 °C flowered within 106–160 d after emergence whereas only those transferred from LD to SD flowered at 26 °C during the investigation (202 d). A well-defined photoperiod-insens itive pre-inductive phase (a1) was detected after emergence; it lasted for 26 d at 19 °C but increased to 49 d at 26 °C. Thereafter, SD hastened and LD delayed progress to flowering until a third pha se, the photoperiod-insensitive post-inductive phase (a3) of pre-flowering development. At 19 °C, a3 was 66 d while the duration of the inductive phase in SD (IS) was 25  d and in LD (IL) it was 72 d. Plants were also moved from ambient to warmer temperatures and vice versa within either SD or LD at different durations after emergence. In SD all plants flowered during the investigation ( 250 d) whereas in LD only the plants transferred from the warmer to the ambient temperature regime flowered. During the initial stages of development plants were less sensitive to supra-optimal temperatures so that developmental progress from emerg ence to first flowering was the same whether plants were held at warmer or ambient temperatures during the first 35 d from emergence. Furthermore, plants transferred from the ambient to the warmer temperature in SD at any time from 49 to 77  d from emergence flowered at similar times to those kept at ambient temperature from emergence. Since a1 = 26 d and a1 + IS = 51 d, we sugg est that these results imply that exposure to supra-optimal temperature in SD during the latter 60% of the photoperiod-sensitive inductive phase (IS) of pre-flowering development delayed progress to flowering. In contrast, expos ing plants to supra-optimal temperature during either the photoperiod-insensitive pre-inductive phase (a1) or part of the photoperiod-insensitive post-inductive phase (a3) or during the first 40% of the photo period-sensitive inductive phase did not delay progress to flowering.

Data from three cocoa (Theobroma cacao) clonal selection trials are used to investigate the genetic and environmental components of variation in yield and the percentage of total pods affected by black pod disease (Phytophtora pod rot). Simulations based on these estimated components of variation are then used to discuss the best choice in future of numbers of clones, replicates and years of harvest to maximise selection advances in the traits measured. The three main conclusions are the need to increase the number of clones at the expense of the number of replicates of each clone, the diminishing returns from additional years of harvesting and the importance of widening the genetic base of the clones chosen to be tested.

A method is described for estimating boron requirements of the oil palm, and factors influencing leaf boron concentration of the palm are discussed.

Plantain hybrids and landraces, and banana cultivars (Musa spp. L.) were evaluated for three years in the plant and ratoon crops at three locations in the humid lowland forest (Mbalmayo and Onne) and derived savanna (Ibadan) agro-ecozones of sub-Saharan Africa. Additive main effects and multiplicative interaction (AMMI) models accounted for a significant percentage of the genotype × environment interaction (GE) affecting bunch weight (kg plant−1) and yield potential (t ha−1 a−1). Obino l'Ewai, a plantain landrace, showed little GE for bunch weight, whereas the exotic cooking banana cultivar Cardaba had the most stable yield potential as revealed by the biplots of the GE analysis (AMMI-2 biplots). Plantain hybrids achieved high yield potential due to their short growth cycle. The high yield potential of the cooking bananas was mainly the result of their fast sucker development.

The area of individual leaves in oil palm has been conventionally estimated from a regression equation that is based on the size and number of leaflets. The aim of the present study is to verify the accuracy of this equation, which became standard in oil palm research. Therefore, true leaf area, measured with a video camera, was estimated from the product of number of leaflets per leaf (n) with mean length (l) times mid-width (w) of six of the longest leaflets (nlw). The database was assembled, annually for the first 4 years after planting, from 2961 leaves of dura × pisifera testcrosses descending from six distinct pisifera origins. The regression coefficients of the regression lines of nlw plotted against true area did not show a trend with age of the palms or a difference among pisifera origins. The common regression equation fitted through all data of this study accurately estimated true leaf area of the testcrosses and also the areas of 2- to 3.5-year-old dura palms of three distinct origins as well as 18-year-old tenera palms. These outcomes are at odds with the conventional regression equation that overestimates the true leaf areas by about 24%. A more recently-developed variant underestimates true area of the young tenera and dura palms by 28%, while overestimating true area of old tenera palms by 19%. Possible causes for these deviations from true area are discussed. The paper argues that parameters depending on leaf area of previous physiological studies need to be reassessed.

The literature for the past seventy years describes a variety of methods of sampling tea leaves, in some of which analytical data from samples have been suggested as capable of widespread use as a measure of the nutritional status of tea plantations.

In their response to our paper on the problems of using on-farm trials in efforts to scale-out new crop production technologies and practices among smallholder farmers, Wall et al. (2019) focus on our descriptions of on-farm trials in just one of the three case studies of Agricultural Research for Development (AR4D) projects that were presented. They argue we did not understand the projects’ philosophy and that the biases in farmer and site selection we discussed, do not exist in the southern Africa case study.

Nepalese hillside terraces are classified into two broad groups, sloping or bari terraces which are only rainfed, and level or khet terraces which are commonly flood irrigated but may also be rainfed. Although such terraces may be adjacent, the process of irrigation by flooding and puddling changes the pattern of variability both within and between terraces. Data collected from Pakhribas Agricultural Centre, Dhankuta, Nepal, were used to describe this variability. The variability is manifest not only in the soil characteristics of the two terrace types, with khet terraces being more uniform than bari terraces both within and between terraces, but also in the variability of field experiments on the two terrace types. However, both terrace types exhibit similar patterns of variability which influence the design of experiments. These include the following: a gradient between the terrace riser and wall which is generally more important than gradients along the terrace, variability within terraces which can preclude the assumption that plots on the same terrace are similar, and variability between terraces which requires experimental units in the same block to be assigned to the same terrace.

Few references are available on collaborative monitoring and evaluation, that is, how diverse organizations promoting similar innovations can together assess their efforts. We examined the experience of 30 organizations in working together in western Kenya, from 1999 to 2003, assessing their impact in helping farmers to adapt and adopt two soil fertility practices. While the collaborative process improved the flow of information among organizations, it did not reduce monitoring costs, but rather increased them. The process increased participating organizations' awareness of farmer innovations and the number being promoted. The process also contributed to the formation of a consortium among the participating organizations. We viewed the benefits of the collaborative approach as greater than the costs, but recognize that the resources for implementing such exercises may often not be available.

The magnitude of heterosis for 15 characters was studied in ten sorghum hybrids, produced by crossing ten restorer varieties with male-sterile Combine Kafir 60 as a common female parent. The most evident expressions of heterosis were higher yield and increased vegetative growth, often associated with delay in flowering. The increase in yield of the hybrids over their superior parents, ranging from 35 to 238%, resulted mainly from an increase in number of grains per head, rather than from an increase in the weight of individual grains. The regressions of hybrids on male parents, and the correlations of yield with other characters were studied, and the prospects of producing adapted hybrids for the Sudan are briefly discussed.