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.

Experiments involving N, P, and K fertilization, and height and frequency of cutting, were carried out on a mixed pasture of giant stargrass (Cynodon plectostachyus) and centro (Centrosema pubescens) at the University of Ibadan during the growing seasons 1951–61. For the first cut after fertilization yield responses of 17 and 24 per cent resulted from applications of 50 and 100 lb N per acre respectively in various experiments but the effect was transient and recovery of fertilizer nitrogen probably did not exceed 30 per cent. Nitrogen fertilization of sown pastures is unlikely to be an economic practice in Nigeria in the forseeable future. Yield responses of 30 per cent resulted from applications of 2½ and 5 cwt superphosphate per acre with a marked residual effect two years after application. Significantly higher concentrations of extractable inorganic soil P at the higher P fertilization rate after 2 years were largely a reflection of the levels of the iron phosphate fraction, but similar trends were evident in the aluminium and calcium phosphate fractions. No differences were found in total, organic, or residual P. The proportion of centro in one 1959 cut for the 0 and 5 cwt rates of superphosphate were 46 and 38 per cent whereas N had no effect, the reverse of the response normally encountered in a temperate mixed pasture. No response to K was obtained. Increased frequency and height of cutting both resulted in decreased yields of dry matter but cutting at 2–4 inches at 8-weekly intervals appears to be the most satisfactory method of managing this pasture for hay production, with yields of approximately 2¼ tons dry matter per acre.

The application of molybdenum, as ammonium molybdate at 40 gm./ha. as a foliar spray, alone or in combination with 400 kg./ha. of N, as ammonium sulphate, significantly increased total and soluble nitrogen in the leaves, stem and grains of the high-yielding rice cultivar IR8. The significant increase in protein content of grains was associated with a corresponding increase in most of the protein-bound amino acids, viz. leucine, phenylalanine, methionine and valine, alanine, threonine, glutamic acid, serine and glycine, aspartic acid, lysine, arginine and histidine, asparagine and proline. Nitrogen itself considerably increased the protein content, but nitrogen in combination with molybdenum was more effective.

The most important objective of lentil breeding programs is to develop new genotypes that are genetically more productive. Besides, it is necessary that the varieties obtained have short flowering cycles to allow the later sowing of summer crops. Selection is based through phenotypic means; however, we argue it should be based on genetic or breeding values because quantitative traits are often influenced by environments and genotype–environment interactions. The objectives of this study were to: (i) identify genotypes with the highest merit; (ii) estimate genetic parameters to know the genetic control of morphological traits in macrosperma and microsperma lentil types using best linear unbiased prediction (BLUP). Twenty-five recombinant inbred lines (RILs) from six F4 families selected on the basis of precocity and high yields were tested in four environments for important quantitative traits. The analysis of variance showed significant differences between genotypes, environments, and genotype–environment interactions for all the traits. Seven macrosperma- and two microsperma-type RILs were selected. Based on average ranking from breeding values and molecular data obtained with sequence-related amplified polymorphism (SRAP), the same genotypes were selected. Genotypic coefficients of variation, heritability across and by environment, and genetic correlation coefficients using BLUP were obtained. According to our results BLUP could replace molecular analysis methods because the selection process was simpler, more cost-effective, and more accurate. The breeding value of parents would give a better ranking of their genetic value than would their phenotypic value; therefore, the selection efficiency would be enhanced and the genetic gain would be more predictable. The selected genotypes could become potential commercial varieties or be used as parental lines in future hybridization programs.

Visual symptoms of deficiencies of manganese, copper, zinc, iron, molybdenum and boron on sisal are described, and compared with those observed previously with deficiencies of macronutrients. The diagnostic value of symptoms is discussed, and tentative suggestions made for micronutrient concentrations in leaves for adequacy and deficiency.

The agroclimatic potential of the forest–savanna transition zone of Nigeria for the cultivation of sorghum (Sorghum bicolor) was investigated. Five phenological stages of the crop formed the basic unit of time for the investigation. Selected agroclimatological thermal and moisture indices were measured daily and processed into ten-day (decadal) averages for the 1993 and 1994 cropping seasons. The thermal indices, temperature and photoperiods were optimal for sorghum growth but, on the basis of the distribution of rainfall and actual water availability in relation to the crop's water consumption, the moisture indices were above optimum. However by relating effective water availability to the indices of moisture adequacy for the growth of the crop, it was found that the agroclimatological moisture indices were optimum during the moisture sensitive stages. A comparison of the vegetative growth and grain yield of sorghum in the study area and elsewhere in the savanna region confirmed the agroclimatic potential of the forest–savanna transition zone for sorghum production.

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.

Thirty Dorset Horn ewes were put to the ram four times in two years; four ewes lambed four times to produce 22 lambs, and 21 ewes lambed three times, producing 100 lambs with satisfactory birthweights. The minimum interval from parturition to conception was 32 days and there was no decline in the liveweight of the ewes. Another 37 ewes were run with a teaser ram from 1 January to 1 August 1964 (when it was replaced by a fertile ram) and from 15 April to 31 August 1965 when it was again replaced by a fertile ram. There was a marked decline in oestrual activity in Flock 2 from the middle of March until the middle of July.

The suitability of charcoal and filter mud as carriers for the survival of Rhizobium isolates at low and high temperatures was investigated. Both carriers were found to be suitable and maintained high rhizobia populations (1.0 × 108 rhizobia g−1). In Sudan, inoculants can safely be stored for 6–10 weeks in the ambient temperature (up to 37°C).

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.

Trials on ferrallitic soils in Uganda showed that crops responded to lime after the first year of cropping on soils which had a pH up to 6·0, and to potassium on soils which had an extractable K level up to 18 mg 100 g−1. Soil and leaf analyses indicated that responses to lime on soils of pH above 5·2 were due to an increase in phosphate availability. Low yields at several sites in the first year were apparently due to immobilization of nutrients during rapid mineralization of soil organic matter. In later years soil organic matter did not decline appreciably, and yields dropped only at sites where potassium or minor element deficiencies apparently developed.

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.

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.

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

Field experiments were conducted for two years to evaluate the effects of combinations of saline irrigation (ECw 14.0 ds m-1) and nitrogen levels on the yield, seasonal water use and nitrogen use efficiencies of mustard. These showed that the use of saline water can boost the growth and yield of dryland mustard and that, within certain limits, a non-saline water supply can be substituted by applying nitrogen and saline water. It is suggested that fertilizer nitrogen rates should be adjusted in relation to the supply of water and its predicted salinity.

Irrigación salina y los efectos del nitrógeno en la mostaza sembrada en las tierras de secano

In three field experiments studying the liming needs of cassava on peat, optimum tuber DM was obtained at pH 3.8 and optimum top DM at pH 4.2; liming to higher pH values decreased tuber DM while maintaining top DM. Consequently, the Harvest Index decreased over the whole range of soil pH studied (3.49–5.50). Increases in tuber DM per hectare with liming, and with an increasing growth period, were associated with mean tuber weight (r = 0.86) and with Harvest Index (r = 0.65) rather than with tuber number (r = 0.37).

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.

The shallot is a common crop in tropical areas where daylength and temperature conditions do not permit the growing of onions. Shallots are dormant for 70 days from the time of harvest to sprouting in bulbs stored at room temperature (75 to 95°F), during which period about 40 per cent of the bulbs are lost due to drying out and disease. Bulbs stored at lower temperatures (40 to 60°F) sprout more rapidly, with an optimum of about 50°F. Cool storage enables the farmer to use the previous season's crop for planting within 30 days of harvest.

The short term nutrient supply of Leucaena leucocephala, Calliandra calothyrsus, Acacia angustissima and Acacia karoo prunings with or without supplemental inorganic nitrogen were tested using rape (Brassica napus L.) in a field trial. Prunings were applied at a rate of 5 t ha−1 to soil, alone or with supplemental N at 37.5 kg N ha−1 (¼ of recommended N). The respective decomposition and N release constants of the prunings were 9.15 and 9.70% for L. leucocephala; 6.15 and 6.40 for A. angustissima; 4.50 and 4.90 for C. calothyrsus; and 2.20 and 2.10 for A. karoo. These constants were best described by the (lignin+polyphenol)-to-nitrogen ratio of the prunings. Total biomass over the two seasons ranged from 1.40 to 17.28 t DM ha−1 and total growth rates ranged from 2.34–26.70 g plant−1 week−1. The cumulative N recovery at week 9 ranged from 21.1–66.1 %. Legume tree leaves can be used as a source of N for vegetable production. Farmers who use high tannin leaf litter are recommended to supplement with mineral N in order to assure adequate N availability during plant growth.

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