Farmer-managed tests of Striga hermonthica-resistant maize varieties were conducted in 1994 in a moderately intensified zone in the northern Guinea savanna of Nigeria. Field history, soil properties, current season fertility management, and crop management observations were recorded for 37 farmer-managed trials. Site averages for maize grain yield varied from 300 to 4000 kg grain ha−1. In spite of the tremendous variability observed, the grain yield was significantly higher for the striga-resistant hybrid 8321-18 compared with an improved open-pollinated variety, STR Syn-W, and the farmers' current variety. Correlation analysis and stepwise regression analysis of grain yield on measured variables suggested that maize yield was a function of plant density for all three varieties. The rate of nitrogen fertilizer application was an important variable only for the hybrid, while the day of first weeding was most important for the improved varieties. The yield of the local varieties and STR Syn-W was related to the number of emerged striga at harvest in the stepwise regression, and the yield of the local varieties was highly correlated with the striga-damage score on maize. The striga-damage score was significantly lower on 8321-18 than on the other varieties, suggesting some degree of resistance in the hybrid. The number of emerged striga was lower for the hybrid but not significantly different. Farmers were almost unanimous in ranking the hybrid as least damaged by striga and highest yielding. Besides being related to maize variety, striga-damage score was lower if crop residue was observed on the field at the time of site confirmation. Highest yields (approximately 4 t ha−1) were recorded on fields near the homestead (compound fields) where soil organic carbon values were 2.0–2.5%. Realization of maize yield potential in the absence of manure or fertilizer will only be possible on long-term compound fields. Striga-resistant maize can maintain high yields under S. hermonthica infestation.

Soil quality indicators (SQI) can be used as a synthetic tool for the assessment of the sustainability of agricultural systems. In this study, we developed SQI using minimum data set (MDS) and determined the response of SQI to long-term tillage systems. Field pea (Pisum sativum L.) and spring wheat (Triticum aestivum L.) were grown in alternate years at northwestern China, and soil attributes and crop productivity were measured 6 years after the initiation of the experiment. The MDS used to develop the SQI included soil physical (aggregate, bulk density, capillary porosity, field capacity), chemical (soil organic matter, total nitrogen, available phosphorus, available potassium) and biological (microbial count, microbial biomass, and the activities of catalase, urease, alkaline phosphatase, and invertase) properties. All the property variables were measured in each of the 0–5, 5–10 and 10–30 cm depths and those variables that contributed significantly to the SQI were selected to be included in the MDS. Amongst the measured variables, bulk density and microbial counts occurred in the MDS of all the three depths, suggesting that these two properties are highly affected by the tillage treatments. In the long-term field experiment, the no-till with stubble covering the soil surface treatment received the greatest SQI score and achieved the highest crop yield. Soil quality under tillage systems can be assessed adequately using MDS measured at the top soil (0–5 cm) layer in rainfed agro-ecosystems.

In order to assess the response of cocoa trees to drought, changes in water status, gas exchange, leaf carbon isotopic ratio (δ13C), photochemical activity, and leaf N and chlorophyll content during the rainy and dry season were measured in 31 Venezuelan cocoa clones (17 Trinitarios, 6 Criollos, and 8 Modern Criollos) grown in a common garden. Drought caused a 40% decrease in water potential (ψ) in all but the Modern Criollos, and a reduction in net photosynthetic rate (A) and stomatal conductance (gs) without an increase in instantaneous water use efficiency (WUE) in 93% of clones, and an increase in δ13C (long-term WUE) in 74% of clones; these responses suggest differences in tolerance to drought among clones. A positive correlation between A and both gs and leaf N content was found for all genotypes. Leaf N content, chlorophyll content, and photochemical activity were reduced during drought, suggesting that metabolism was also inhibited. The best performance during drought was shown by Modern Criollos with the highest WUE, while five Trinitario clones seemed to be less sensitive to drought, since neither chlorophyll, N, total soluble protein concentration, nor gs changed with drought, indicating that those Trinitario clones, with lower A, have a conservative water use. Modern Criollos showed no reductions in either ψ or gs; A remained unchanged, as did WUE, which was the highest, suggesting that these clones would be more successful in environments with low water availability. Our results indicate large variation in physiological response to drought over a range of parameters, suggesting possible differences in tolerance among clones.

Dry matter production and yield of tea were recorded in a genotype × environment interaction experiment with four tea clones planted at four sites at a range of altitudes in Kericho, Kenya. Large responses to environment in dry matter production and yield were found. After 34 months from planting, the total plant dry matter production ranged from 18 to 22 t ha−1 across the sites. One clone, TN14-3, produced the most dry matter, reaching 29 t ha−1 at the lowest altitude, while clone S15/10 produced the least (15 t ha−1). Analysis of genotype × environment inter actions showed that clone TN14-3 was above average stability in dry matter production across the four sites, but below average in yield. Clone S15/10 showed above average stability for tea yield, but was below average in dry matter production.

This review paper deals with some of the general statistical principles of crop rotation experiments. The basic terminology of the subject is defined. Attention is paid to the fundamental design principle that each phase of a rotation should each year be present in an experiment involving that rotation. The inclusion of ‘auxiliary’ treatments - usually fertilizer treatments - is discussed. Consideration is given to matters influencing the choice of size and shape of plots. The statistician's role in planning a rotation experiment is portrayed as onerous. Emphasis is put on the importance of care and good practice in the management of a long-term agricultural experiment. Complications arising in the statistical analysis of data from a rotation trial are sketched.

A field experiment in an alluvial sandy loam saline soil was conducted during the winter (rabi) season from 1997–98 to 1999–2000 at the Central Institute for Research on Buffaloes, Hisar, to study the effect of saline drainage water (EC=3.6 –7.4) on five (rabi) forage crops: oat (Avena sativa), rye grass (Lolium rigidum), senji (Indian clover) (Melilotus indica) berseem (Egyptian clover) (Trifolium alexandrinum) and shaftal (Persian clover) (Trifolium resupinatum). All the crops were established using canal water as pre-sowing irrigation and the various irrigation strategies were imposed subsequently. Irrigation with canal water resulted in a 115% increase in forage yield compared with the saline drainage water. The results suggested that alternate irrigation with saline drainage water increased the yields of all the forage crops compared with using saline drainage water only. Further, alternate irrigation, starting with canal water, was superior to alternate irrigation starting with saline drainage water because less salt was added in total. Oat produced the largest green-forage yield (32.3 t ha-1) in the first year while rye grass gave its maximum in the second (34.6 t ha-1) and third years (37.0 t ha-1). Persian clover performed better than did Egyptian clover in all the three years. Interaction between species and irrigation treatments was significant. In comparison with canal irrigation water, there was a 36 %, 42 %, 54 %, 68 %, and 85 % yield reduction in rye grass, oat, Persian clover, Egyptian clover and senji, respectively when only saline drainage water was used for irrigation reflecting their relative tolerances of salinity. Yields declined linearly for all crops with increases in the quantity of salt applied.

Two field experiments were conducted to evaluate the effectiveness of several pelleting materials in increasing the yields of cowpea (Vigna unguiculata (L.) Walp.) and soyabean (Glycine max (L.) Merr.) on acid soils in Sierra Leone. The results demonstrated the beneficial effect of molybdenum, applied either alone or in combination with rock phosphate, in improving growth and yield of cowpea. The beneficial effect of molybdenum was comparable (Exp. 1) or greater (Exp. 2) than the effect of liming with 3 t/ha basic slag. However, none of the coating materials had any effect on soyabean growth and yield, although molybdenum significantly increased nodules/plant. Calcium carbonate and basic slag pelletings were ineffective in both crops.

Ninety five cocoa clones were tested in Sabah, Malaysia at planting densities of 1096 and 3333 plants ha−1. Analysis of dry bean yields up to 60 months after planting showed that vigorous clones performed better at the lower planting density, some clones of intermediate vigour performed well at both planting densities and some weak clones performed well at high planting density. The conclusion that optimal planting densities are highly variable has significant implications for procedures in clone selection and suggests that the relation between the yield of a clone and its general combining ability will become clearer once planting density is taken into account.

Field experiments conducted in two localities in two growing seasons on the effect of inoculating haricot bean showed that a local strain of Rhizobium significantly improved nodulation and usually increased the nitrogen content of plants. In three out of four experiments, increases in seed yield were obtained ranging from 20–145 Per cent (significant in two cases). Inoculation was better than 43 kg. N/ha. of combined nitrogen but not better than 86 kg. N. Soil inoculation gave better early nodulation than seed inoculation, but the difference diminished in the later stages of plant growth.

The possibility of using seasonal changes in leaf nitrate reductase activity (NRA) as a reliable and sensitive indicator of plant nitrogen (N) status has been investigated in field-grown cotton. These changes were compared with those in nitrate concentration in petioles and variations in soil-N concentration. We conclude that NRA in the uppermost, fully-expanded sympodial leaves may provide a more convenient, sensitive and reliable indicator of plant-N status than measurements of nitrate concentrations in petioles.

Bean yield at two sites in Costa Rica was affected by the interactions of maize and bush bean cultivars with cropping system (relay, row intercropping and sole cropping). The maize culti-vars were grouped according to leaf area index (LAI) and plant height. At a site with a severe weed problem, leafy maize of intermediate height allowed the most bean yield in relay but the least in intercropping. Tall, leafy maize allowed as much yield of intercropped beans as short, less leafy cultivars. In intercrops, tall maize plants shaded the beans less, while in relay crops leafy plants of intermediate height shaded and suppressed weed growth so benefiting the following bean crop. At the other site, all maize groups had the same effect on beans whether grown in relay or intercropped. Leafy maize cultivars of medium height are preferable for sole crops and for relay cropping of beans at physiological maturity when weeds are a problem, but less leafy types are better for bean intercropping or for relay crops where the beans are planted before maize maturity. Plant types selected for sole cropping are not necessarily best for poly-cultures and one crop may affect another even when their periods of active growth do not overlap.

Agricultural development projects frequently promote new crop production technologies for adoption at scale on the basis of research and pilot studies in a limited number of contexts. The performance of these production technologies is often variable and dependent on context. Using an example from the Agroforestry for Food Security Project in Malawi, that promoted agroforestry technologies for soil fertility enhancement, we explore the nature and implications of variation in performance across farmers. Mean effects of these technologies, measured by differences in maize yield between agroforestry and sole maize plots, were modest but positive. However, there was large variation in those differences, some explained by altitude, plot management and fertilizer use but with much unexplained. This represents risk to farmers. Those communicating with farmers need to be honest and clear about this risk. It can be reduced by explanation in terms of contextual factors. This should be an aim of research that can often be embedded in scaling up the promotion of agronomic innovations.

In trials conducted over five years, data on pest (insect, disease, bird) attack and yield of sorghum cultivar 65D were accumulated. A modified analytical method of damage assessment is described, which includes consideration of all pest occurrences and different levels and timing of pest attack. There was a positive correlation between crop yield and rainfall. The selective infestation of stronger plants, or the ability of those plants to support pest populations, is shown; thus, in most cases, yield reductions are masked. The importance of the tillering habit of 65D on yield, and its ability to compensate for pest damage by further tillering, are shown. A cultivar which does not normally tiller was tested in the final year. Effects on yield of all the pests encountered in the five years are discussed.

Stomatal conductances (g) and photosynthetic rates (A) were monitored in six tea clones planted in a clone X irrigation experiment in the Southern Highlands of Tanzania. Measurements were made during the warm dry seasons of 1989 and 1990. There was no genotype X treatment interaction in the response in A or g of the various clones to irrigation. Irrigation increased A more than it increased g. Irrigation also increased the temperature optimum for photosynthesis and decreased photo-inhibition at high illuminance. Clones differed in g and A, and in the relationship between leaf temperature and A. The implications of these findings for clone selection are discussed.

Striga hermonthica infestation causes significant losses of maize yield in the Nigerian savannas and several technologies have been developed and promoted to control Striga in maize. However, since no single technology has been found to be effective against Striga, integrated management is needed to achieve satisfactory and sustainable Striga control. Both on-station and on-farm trials were undertaken from 2013 to 2015 in Bauchi and Kano States of Nigeria to evaluate the performance of integrated Striga control technologies. In the on-station trials, a soybean–maize rotation did not suppress Striga in maize in either location. However, nitrogen application suppressed and reduced Striga infection, except in Bauchi in 2014. The soybean–maize rotation accompanied by N application reduced Striga damage in both locations. On farmers’ fields, rotating soybean with maize significantly reduced Striga infection. At the same time, the use of maize varieties with a combined tolerance to drought and resistance to Striga parasitism also increased maize grain yield on farmers’ fields, probably due to three factors: a reduction in Striga infection, reduced effects of a mid-season moisture deficit, and increased uptake of nutrients from the soil. We concluded that the use of Striga-resistant maize varieties in combination with the application of N fertilizer and rotation with soybean could increase the productivity of maize in Striga-infested fields in the Nigerian savannas.

The effect of mixtures of cultivars on yield and risk distribution in four maize cultivars grown at four different population levels was studied in semi-arid environments in Ethiopia. Mixtures yielded between 2 and 29% more than the pure stands, but late maturing pure stands produced more biomass than mixtures. Mixtures of cultivars with similar flowering periods yielded 60% more than the pure stands in dry growing seasons, but only 30% more when there was more rain. Yield gain was associated mainly with varietal synchrony of anthesis and silking. Mixtures composed of cultivars with different flowering times were less at risk from yield loss in the case of end-of-season drought and yielded 100% more than their late flowering component in pure stand. But in long growing seasons, with an early dry spell, pure stands of the late cultivar outyielded the mixtures whereas pure stands of the early flowering cultivars yielded less than the mixtures, except in years with a serious end-of-season drought. The results indicate that it would be profitable to grow mixtures in semi-arid regions if cultivars with similar height and synchronized flowering time were grown at populations of between 65 000 and 90 000 plants ha−1.

Methods are described for releasing HCN from cassava leaves and tubers by organic solvents and its spectrophotometric estimation as the red complex formed with alkaline picrate. Chloroform was the most efficient solvent, with toluene an acceptable alternative, using enough solvent to wet samples thoroughly to maximize cyanide yield. Cyanide content was concentrated in the veins and towards the base of leaves and declined linearly with leaf age. Release of HCN with solvent compared favourably with traditional homogenization/steam distillation with leaves and parenchymal tissue, but was unsatisfactory for tuber peel. The effective removal of HCN from cooked cassava leaves depends chiefly on release of enzymes by efficiently chopping them before boiling, which only slowly destroyed potential cyanide content of unchopped leaves.

When the same cultivars of groundnuts (Arachis hypogaea) were grown under a wide range of environmental conditions, temperature and irradiance played a major role in determining crop duration and partitioning of dry matter to pods, the latter assessed by harvest index. Utilizing published data for the Virginia groundnut cultivar Early Bunch under non-limiting conditions, we show that accumulation of thermal time using three cardinal temperatures (Tb=9 °C, To=29 °C and Tm=39 °C) has considerable potential for predicting crop maturity. In sixteen sowings ranging from the wet tropics in Indonesia to the elevated subtropics in Australia, harvest date for Early Bunch corresponded to the accumulation of 1808 (±23) degree-days after sowing. In all sowings except one in the semi-arid tropics, this value of thermal time was within eight calendar days of actual harvest maturity. Harvest index varied greatly with both location and sowing date, ranging from 0.31 (Indonesia) to 0.58 (subtropical Australia). Using total short-wave solar radiation incident during the growing season and calculated values of thermal time, the growing season for each sowing in each location was described in terms of a photo-thermal quotient (PTQ, MJ m−2 degree-day−1). Values for PTQ ranged from 0.99 (Indonesia) to 2.11 (subtropical Australia). Variation in harvest index could be explained largely by a curvilinear function of PTQ (R2=0.98), provided data were not confounded by the effects of photoperiod. In the semi-arid tropical environment, decreases in photoperiod associated with delayed sowing were the dominant factor controlling harvest index.