Irrespective of the size of seed yam used, removal of mother tubers (‘milking’) from yam stands after 4 weeks of growth drastically reduced final yield, but removal after 7 weeks or more did not affect yields of individual plants of Dioscorea rotundata. If yam stands are milked after 4 weeks and the milked tuber replanted, the cumulative yield from both milked and replanted stands was significantly lower than from the control plants. However, milking and replanting mother tubers after 7 weeks or more gave cumulative yields which did not differ from the control.

Repeatability estimates of milk yield and length of lactation of local, ½ Anglo-Nubian × local and ¾ Anglo-Nubian × local cross-bred goats were calculated. There were highly significant differences in the effect of dams on milk yields for the third, fourth and fifth lactations for local goats, when considered together. No significant differences were found for the first two lactations. For the ½ Anglo-Nubian cross-bred goats significant differences were also found for the first and second lactations, but not for the third lactation. No significant differences were found for the two lactations in the case of the ¾ Anglo-Nubian cross-bred goats. The effect of lactation periods were not significant for the three types of goats. The mean repeatability estimates for local goats were 0·47, 0·42 for ½ Anglo-Nubian and 0·54 for ¾ Anglo-Nubian cross-bred goats, which were comparable to those reported for cattle. The between-dam effect was highly significant when three lengths of lactations were combined in local goats, and the interval between lactations were also significant, but these two effects were not significant for the ½ Anglo-Nubian and ¾ Anglo-Nubian cross-bred goats. The estimates of repeatability for length of lactation averaged 0·29 for local goats, 0·17 for ½ Anglo-Nubian and 0·53 for ¾ Anglo-Nubian cross-bred goats. The correlation coefficients between milk yield and length of lactation were positive and statistically significant for all the three types of goats, ranging from 0·59 to 0·93. The similarity of the genetics of goats to those of cattle and sheep is mentioned.

This paper summarizes a study initiated by the Turkish General Directorate of Agricultural Research and ICARDA/CIMMYT Wheat Improvement Program on the adoption of five new winter and spring wheat varieties developed and released by the Turkish national breeding program and through international collaboration in the past 10 years. The study results are based on a survey of 781 households selected randomly in the Adana, Ankara, Diyarbakir, Edirne, and Konya provinces of Turkey. The five new wheat varieties are compared to old improved varieties released prior to 1995 that are also still grown by farmers. Technical and biological indicators of impacts including crop productivity are measured to determine the impact of these varieties. Yield stability is assessed by comparing average yields in normal, good and dry years and by comparing the coefficients of variation of yields by variety. Profitability is measured by the gross margin generated per unit of land. Household income from wheat and for all economic activities are estimated and compared between adopters and non-adopters. Adopters of the new varieties have higher per-capita income than non-adopters as compared to the same group using old varieties. However, the overall impact of the improved varieties is generally low, mainly due to their low adoption levels. Farmers’ knowledge and perception of certain variety characteristics and unavailability of adequate and timely seed are the main reasons. Increasing adoption has the potential to improve household income and this requires revising wheat impact pathway to achieve the expected impact.

In cotton (Gossypium hirsutum), it is hard to determine the exact date when reproductive growth ceases on the basis of field observations, as compared to more visible factors such as the onset of flowering or boll opening. It is, however, essential to characterize the growth cycle in order to determine what varieties are suitable for planting in different climatic and local cropping conditions. We estimated the end of the effective flowering period on the basis of the opening date of the last flower giving rise to a first-position boll on fruiting branches (LFP1), and propose a simple method for estimating this date. This study, conducted in 2002 and 2003 at Okpara, Benin, involved a comparison of six cotton varieties planted at two different dates (June and July). Plants were monitored to determine the dates when flowers opened at each position on fruiting branches. The LFP1 indicator made a clear distinction between varieties. This highly heritable trait, which was found to be closely correlated with other earliness criteria, could be used to characterize the length of the growth cycle in cotton varieties.

The native rhizobia capable of symbiosis with potential pasture legume crops for the west Asian highlands were surveyed and estimates made of the numbers and nitrogen fixing efficiency of isolates of Rhizobium meliloti with a range of annual Medicago species. Soils were collected from 105 sites at elevations between 500 and 2200 m. Numbers of bacteria were generally adequate to permit efficient nodulation but the nitrogen fixing efficiency of three of the four host species with the indigenous rhizobia was often low. In contrast, nitrogen fixation in M. aculeata was generally highly efficient. No overall geographic pattern in either numbers or efficiency of nitrogen fixation was evident. Substantial further research is required before annual medic crops can be successfully introduced into highland crop/livestock systems in Turkey and elsewhere in the west Asian highlands.

Biodiversidad en el Rhizobium meliloti

Methods of recording experimental data in the laboratory and field are discussed. Use of specially designed record sheets, punch cards and punched paper tape in conjunction with an electronic computer extends the scope of experimental work and leads to improved efficiency and accuracy.

A late-maturing, high-yielding maize released for the Burundi highlands was rejected by subsistence farmers. Analysis of this variety in terms of the local cropping system shows that it offers no advantage over earlier maturing varieties when whole-system biological and economic yield and Land Equivalent Ratios are examined, while farmer risk is apparently substantially increased. The value of incorporating a ‘farming systems’ approach into national commodity research programmes in developing countries is demonstrated.

In field trials a population of 61,700 maize plants/ha produced higher total dry matter and grain yields than the conventional 36,000 plants/ha. There was no difference in yields with inter-row spacings of 45, 60 or 90 cm, regardless of population levels. Weed suppression was increased by the higher population even though the entire experimental area was treated with herbicides. In one of three years perennial sedge and annual weed growth started 4–5 weeks after herbicide application, under which conditions row spacing had a greater effect and weed growth was significantly less with 45 or 60 cm maize rows than at 90 cm.

Attention is drawn to the large annual fluctuations of clove yields in Zanzibar and Pemba which appear to result from a synchronization of clove production by trees. Linear regression analyses are presented which show that in years of peak production tree yield is often correlated with tree canopy area and that when trees yield in two consecutive years, yield in the second year is usually negatively correlated with yield in the first year; equations including both variables often leave considerable variation in yield unaccounted for. It is suggested that some of the year to year variation in tree yield may result from an environmental stimulus affecting clove bud differentiation.

A breeding programme involving the progeny testing of small East African Zebu cattle for improved growth rates is described and an assessment made of environmental and genetic improvements which have occurred over a ten-year period. Evidence is presented to justify continuing the programme, but suggestions are made to modify it in order to speed up the testing period and also to make more use of genetically superior stock.

Two early maturing semi-tall (120–130 cm) rice varieties, Kalinga-3 (85 days duration) and Banaprabha (95 days duration), were compared in pure and mixed crop stands under intermediate deepwater conditions (15–50 cm) with a modern late maturing (170 days duration) semi-dwarf (100 cm) variety, CR 1016. Parallel line seeding of CR 1016 and Kalinga-3 or Banaprabha in alternate rows (1:1 ratio) 20 cm apart yielded 19% more grain than a pure crop of CR 1016 alone. Mixed crop planting in a 1:2 or 2:1 ratio or with reduced inter-rovv spacing gave no additional yield advantage. Mixed row cropping prevented lodging in early varieties, whereas monocrops of the same varieties were partially lodged and showed some premature seed germination. The better and more stable yields obtained from such mixed cropping could be beneficial to resource poor farmers growing rice in conditions of excess water.

A split-plot field experiment was conducted to investigate the influence of planting dates on the formation of nodules in a variety of cowpea (Paraguay 6). Results indicated that the principal factor influencing both nodulation and yield was day-length, the highest number of effective nodules being produced from the June planting.

Two tropical and one temperate genotypes of maize were grown during the cool dry winter seasons in northern Nigeria. The tall tropical genotypes produced a greater leaf area index and more above-ground dry matter, and so had a higher crop growth rate, than the dwarf temperate genotype. However, the early flowering temperate genotype yielded more grain than the late flowering tropical genotypes. Although the initial low winter temperatures prolonged the preflowering growth period in the tropical genotypes, the terminal high temperatures hastened maturity and were associated with poor grain filling.

Maíz de temporada seca en Nigeria

The developmental and scientific impacts of research carried out intermittently over a thirty year period on the tea crop (Camellia sinensis) in southern Tanzania are reported. It is an attempt to demonstrate to questioning donors that research can contribute, in many ways, to the alleviation of poverty in developing countries. During Phase I (1966–1972) the work was funded in large part by the UK Department for International Development (DFID), as it is now known, with the support of the tea industry in East Africa. During Phase II (1985–1991) a regional study in eastern Africa was largely funded by DFID with local field experimentation in Tanzania paid for by tea growers. In Phase III (1992–1997) the work was funded almost entirely by a consortium of commercial producers.

Throughout this period, despite political and economic uncertainties in Tanzania, the close contact with industry meant that the results of the research were exploited to commercial advantage whenever circumstances allowed. These interventions enabled productivity on a unit area basis to rise over time and companies to remain profitable. More recently major investments in new projects have taken place in southern Tanzania, again supported by the results of the research. All of this has led to the creation of new jobs and to continuity of employment in rural areas that have few other sources of paid work. The financial return on the research investment, although very difficult to quantify with precision, has been immense.

The science has not been neglected either. Over the same period more than 30 refereed papers have been published in the international scientific literature. These cover such topics as the responses of tea to climate and weather, including drought and irrigation. Scientists have also been trained in modern research techniques. In addition there have been ancillary benefits including the introduction of technical and management training programmes for staff in the tea industry. Frustration has been caused by the lack of continuity in funding due to changes in policies, and in the priority research topics, even within one donor organization, which have often put the work at risk. Ingenuity, patience and commitment have all been pre-requisites to ensure that the research continued.

The partnership with industry has been beneficial to all the stakeholders. It has led directly to the creation of the new, commercially managed Tea Research Institute of Tanzania serving both small- and large-scale producers throughout the country. Researchers, with the support of the tea industry and in partnership with the Tanzanian Government and DFID, can continue to play a significant role in the fight against poverty. Research for development is a continuing process: it can be successful.

This research sought to link Andean soil knowledge and farmer categorization of soil fertility to soil science characterization of soils, and use these to understand the impacts of phosphorus (P) fertilization of legumes using rock phosphate and soluble P fertilizer in 17 smallholder-managed sites with varying soil properties. We found that farmer high/low categorization of soils corresponded to soil P fertility and distance from farmer dwellings. Measures of soil P fertility also were inversely related to mycorrhizal colonization of vetch roots and directly related to the potential for P release by legume residues (C:P ratio). However, particular soil properties (texture and calcium phosphate pools) were better in explaining the response of legume biological nitrogen fixation to P addition, with maximal impacts in low-clay soils and soils with low calcium phosphates, as assessed with a dilute HCl extraction. In these conducive contexts, legume BNF increased 67 and 150% for RP and TSP, respectively (p < 0.05), with similar increases in biomass P stocks that showed promise for soil regeneration. In low-P fields, added P increased potential P release from legume residues via lower C:P ratios (p < 0.05). Percent cover of soil increased from 35% in the control to 45 and 55% with RP and TSP (p < 0.05), which shows potential for reduced erosion risk under P fertilization of legumes. We discuss results with respect to the integration of local farmer knowledge systems with exogenous scientific knowledge.

In Coffea arabica, there is a small genetic distance between wild and bred genotypes. However, coffee genotypes express differential acclimation to multiple drought cycles, allowing them to successfully deal with water-limiting conditions. We hypothesized that bred coffee cultivars have a plant structure less sensitive to drought than wild genotypes. Plant and leaf architecture were analyzed over the coffee strata of two cultivars (Iapar 59 and Catuaí 99) and two wild Ethiopia accessions (‘E083’ and ‘E027’) grown under rainfed conditions and irrigation. During two consecutive productive years, evaluations were taken at leaf and berry expansion (BE1 and BE2) and harvest (BH1 and BH2) phenophases. The plant canopy was divided into up to four strata of 40 cm of thickness. Topological and geometric coding of coffee trees was performed in three botanical scales – metamers, branches, and plants in multiscale tree graphs (MTGs), following the VPlants modeling platform. Leaf and branch area per plant increased with tree structure development, being always significantly higher in irrigated than in rainfed plants over all phenophases. The individual leaf area was the least sensitive to water regime in Catuaí 99, while the 2nd order axis elevation – angle in relation to horizontal plane, ranging from 0° to 90° – of bred cultivars was less sensitive to drought than in ‘E083’. This finding partially corroborated our hypothesis that orchestrated reprograming of leaf/branch responses over the vertical plant profile were less sensitive to water availability in cultivars than in wild accessions. Leaves of 2nd to 4th-order branching were roughly plagiophile, while the 1st-order leaves were classified as extremophiles. When the coffee leaves were planophile, irrespective of genotype, this pattern was found at the lowest, 1st plant stratum, and the newest developed 4th stratum. Such responses were not obligatorily related to water regime, similar to branch elevation – with exception of ‘E083’, very sensitive to drought. Taken together, our data suggest that the leaf and branch elevations in C. arabica were more influenced by light distribution through the canopy profile – i.e., self-shading – than by water availability.

Considering straw resource utilization and air pollution prevention, straw return has been commonly practiced in China. However, the practicability of plenty straw return in an emerging maize–rice rotation and their effects on soil C and N pools have not been extensively investigated. This study has been conducted to examine the effects of straw return on soil nutrients, soil functional C and N fractions, and then to figure out their relationships with yield and N use efficiency. Two treatments of straw return (S2Nck) and without straw return (S0Nck) were compared in 3-year field experiment, and subplots without N application were added in their respective plots in the third year. The results showed that, relative to the control (S0Nck), straw return significantly increased soil mineralized nitrogen (Nmin), available P, and exchange K content by 11.7%, 41.1%, and 17.4% averaged across 3-year experiments, respectively. Straw return substantially increased soil dissolved organic C, microbial biomass C, and microbial biomass N content by 73.0%, 25.2%, and 36.8%, respectively. Furthermore, straw return markedly increased C and N retention in particulate organic matter in microaggregates (iPOM) and mineral associated organic matter within microaggregates (intra-SC), but significantly reduced in free mineral associated organic matter (free-SC) fraction. The structural equation modeling analysis showed that yield and the partial factor productivity of N were positively correlated with labile and slow soil C and N fractions. Consequently, straw incorporation significantly increased grain yields of maize by 14.7% and rice by 15.1%. The annual potential reduction proportion in fertilizer-N induced by straw return was estimated to be 25.7% in the third year. This study suggests that the incorporation of straws is an effective way to enhance soil nutrients and regulate soil C and N pools to improve crop production and has the potential to reduce N fertilizer application under maize–rice rotation in subtropical regions.