A study was undertaken to find out the nitrogen requirement of wheat (WH-157) when grown after various grain legumes on the sandy loam soils at Hissar (NW India). Yields of wheat were significantly increased when grown after black gram (110%), green gram (108%) and soyabean (41%) compared with those after pigeonpea. Preceding crops of green gram and black gram reduced the nitrogen requirement of a succeeding wheat crop by 30–60 kg ha−1, compared with only 30 kg ha−1 after pigeonpea or soyabean. Pigeonpea was least beneficial in this regard but a pigeonpea-wheat cropping sequence produced the maximum net profit.

Fairfield Smith's variance law is extended to study simultaneously the effect of plot size and its rectangularity (which quantifies shape) on variance. This model is fitted to two seasons' data on sorghum grain yield generated from uniformity trials under rainfed conditions. Some implications of the fitted model are discussed.

Low and unreliable rainfall, combined with high summer evaporation rates, frequently lead to poor yields and crop failure in Botswana agriculture. Over three test years it has been shown that the soil can store up to 100 mm. of available moisture at planting time, which represents about half the water requirement of a crop of sorghum, and the balance is likely to be met (P = 0.05) during the current growing season. Sorghum grain yields have been doubled (2007 kg./ha.) after fallow compared with 1028 kg./ha. after non-fallowed pre-treatments. The advantages of a farming system based on a bare summer fallow are discussed, and reference is made to the implications of its wider adoption.

The best time to plant Calliandra calothyrsus in association with Pennisetum purpureum and the appropriate in-row spacing of Calliandra for fodder and fuelwood production when grown on contour bunds were investigated. Main plot treatments were Pennisetum planted in November 1988 and associated with Calliandra in February 1989, Calliandra planted in November 1988 and associated with Pennisetum in February 1989, and both species planted simultaneously in November 1988. Sub-plot treatments were three within-row spacings of Calliandra. Survival of neither species was affected by time of planting. Total treatment yields of the second and third years were not influenced by time of planting but lower yields of leaf and wood were obtained from the later-planted Calliandra. Total yields were not significantly influenced by the spacing, but leaf and wood yields of the Calliandra at the 25 cm spacing were greater than those at the 100 cm spacing although not significantly different from those at the 50 cm spacing. Neither the time of planting nor the spacing of Calliandra affected the yield of maize or beans grown in the interbund areas. Simultaneous planting of Calliandra and Pennisetum is recommended.

This paper describes an attempt to develop and evaluate agricultural extension materials that support farmers' use of flexible management strategies. On the basis of experiment station and on-farm research results relating to millet and cowpea intercropping in Niger, a series of recommendations was developed, taking the form of a decision tree. The process of testing this format at the level of field extension agents and the implications of this experience for both research and extension workers are described.

The results are reported of an experiment on the Lilongwe Plain to investigate the effects of under-sowing maize with a mixture of Rhodes grass and silverleaf desmodium. Undersowing caused no significant reduction in any component of maize yield, and mixed swards with a good legume content were established. Nitrogen application had no significant effect on yields of grain or pasture, but in the following year undersown swards outyielded those directly seeded. Some practical advantages of undersowing are discussed.

Crop production surveys, which integrate the collection of data on both agronomic and economic variables, are increasingly common in on-farm research. A conceptual framework for designing and analysing such surveys is provided. Methodological issues in conducting crop production surveys are reviewed with respect to type of information collected, level of field observation, degree of quantification, frequency of observation, sampling, measurement of yields and yield components, and analysis of yield limiting factors. It is concluded that, while better integration of agronomic and economic perspectives in diagnosis may increase costs, the information and analysis obtained have considerable potential to improve the efficiency of experimentation.

Manure and chemical fertilizers have different effects on soil properties, the nitrogen cycle, and crop yield. This study aimed to investigate the effects of different fertilizer applications under the same N input on soil physicochemical properties and soil bacterial communities and to explain the contributions of soil properties to grain yield. Manure substitution of chemical fertilizer was conducted in leaching monitoring systems. The study began in 2009 and sampling was carried out in 2014 and 2016. Three fertilizer treatments with the same total N, P, and K application rates and one control treatment were designed as follows: (1) CK, without nitrogen fertilizer; (2) 100%U, whole nitrogen coming from urea; (3) 100%M, whole nitrogen coming from composted cattle manure; and (4) 50%U + 50%M, half nitrogen from composted cattle manure and half nitrogen from urea. Soil organic carbon (SOC) content was positively correlated with total N (TN), NO3−–N, and NH4+–N contents, the mean weight diameter of soil aggregates, and the Shannon diversity index of bacteria, whereas SOC content was not significantly correlated with grain yield. NO3−–N content was positively correlated with grain yield. Substituting half the amount of chemical fertilizer with manure as a nitrogen source improved soil stability, increased bacterial diversity, and enhanced nitrogen supply, while reducing nitrogen loss from ammonia volatilization and nitrogen leaching. Substituting half the amount of chemical fertilizer with manure as a nitrogen source was a more sustainable way to increase grain yield through a sustainable nitrate supply and to reduce N loss.

Gliricidia sepium is a leguminous tree native to Mexico and Central America, and is utilized for fuelwood, animal fodder and green manure in rural communities. It is widely distributed throughout the tropics, but many populations of the tree have arisen from haphazard introductions of unknown quality. Methods for determining the genetic structure and origin of populations are therefore required as a basis for genetic improvement. In order to test the effectiveness of various measures of genetic diversity, provenances of G. sepium from Panama, Guatemala, Mexico and Honduras were studied by electrophoresis of seed storage proteins and the enzymes leucine aminopeptidase (LAP) and acid phosphatase (ACP), and by measurement of plant morphological characteristics. Study of seed storage proteins and morphological characters was very informative, and there was some genetic variation for ACP, but LAP showed no clear variation. In the cases where genetic variation was present, the different methods of study showed a consistent pattern of variation: genetic diversity was greatest in the population from Honduras, and least in that from Panama. This was contrary to expectations on the basis of the locations of origin of the populations and the range in which G. sepium is believed to be native. Electrophoresis of the storage proteins of Gliricidia maculata confirmed the status of this species as a distinct taxon.

The main objective of this study was to quantify the genotypic variation of photosynthetic and gas exchange parameters of Hevea and to examine their relationships to dry rubber yield and its components. Canopy photosynthesis (Pc) of the genotype RRISL 211 was 20 % greater than that of RRIC 121. This was primarily due to RRISL 211's greater light-saturated leaf photosynthetic rates and a greater leaf area index in the top canopy stratum. Tapping significantly increased Pc in RRISL 211, but not in RRIC 121. The genotypic variation in photosynthetic capacity was not reflected in the overall dry rubber yield, which did not differ between the two genotypes. However, analysis of yield components showed that while RRISL 211 may have preferentially partitioned a greater proportion of its additional assimilates to increasing the latex volume and extending the root system, RRIC 121 partitioned more assimilates to increasing its dry rubber content through greater biosynthesis of rubber. The higher plugging index and the greater post-tapping girth increment of RRIC 121 were probably responsible for observed increases in its dark respiration following tapping. Although RRISL 211 had a greater transpiration efficiency, this did not provide a yield advantage as the trees were growing in an environment with adequate rainfall throughout the year.

A simple but reliable type of drainage lysimeter was used to measure evaporation rates from lucerne and wheat and these were compared with calculated estimates of evaporation. Plant height was found to have an important effect on the amount of water lost from a plant cover, which also varied between two different species of crop of similar heights. Using two different soil types, maintained at a high moisture status, the rate of water loss was not influenced by the type of soil in which the plants were grown.

Tea shoot development was measured by sequentially sampling shoots from seven clones growing at Nsuwadzi Research Station, Mulanje, Malawi. A Gompertz growth curve best described the increase in shoot length with time, an exponential curve described the relation between dry weight and shoot length, and a quadratic curve related dry weight to fresh weight. The parameters of these curves differed among clones and provide a basis for exploring genetic influences on tea yield. The most rapid elongation of shoots of all clones occurred about 42 days after plucking, considered the optimum age for harvest at Mulanje. Clones selected at Mulanje produced longer shoots with greater dry weight but slightly lower dry matter content per unit stem length than clones selected at Kericho, Kenya. The dry:fresh weight ratio of 0.22 used at Mulanje to calculate dry matter yields was too high for most clones.

A mobile sampling method was used to measure the amount of photosynthetically active radiation (PAR) transmitted through the canopies of coconut palms in two long term field trials. PAR transmissions were measured at approximately monthly intervals for one year. Fractional interception of light was found to vary considerably between months, and to be associated with frond shedding caused by dry season water stress. Palms receiving potassium fertilizer intercepted more light and replaced leaf area lost during the dry season more rapidly than those receiving no potassium. Palms planted at a higher density intercepted more light and carried more fronds per palm, but intercepted less light per frond than those planted at a lower density. The ratio of moles of carbohydrate yield to moles of intercepted PAR quanta was calculated for six plots of hybrid palms, giving a dimensionless light efficiency index (LEI) comparable to harvest index. Mean LEI for all plots was 1.275 × 10−4 and was found to increase with increased light interception, results suggesting that there is a basal level of light interception below which no yield is produced. The potential for using LEI in agronomic experimentation on sole cropping and multicropping and as a criterion for genetic selection of coconut palms is discussed.

The concept of an integrated pest management (IPM) strategy is explored using case-study evidence from smallholder agriculture in southern Malawi. The conventional concept of strategy as a ‘plan’ is contrasted with the use of strategy as a game, as a performance, and as an accident. This pluralistic view is echoed in recent literature on business strategy. A typology is developed that relates farmers' choice of IPM strategy to the predictability of crop losses, the stability of the crop environment, and farmers' knowledge of pests. Some implications for IPM are explored. Where conditions favour ‘adaptive’ rather than planned IPM strategies, formal experimentation to verify farmers' strategies may be an inefficient use of resources. Where the crop environment is volatile and several pests attack the crop simultaneously, there may be limited scope to increase the adoption of IPM strategies by improving farmer knowledge of pest biology. Addressing the interactions between pest and crop management is critical in making IPM relevant for resource-poor farmers. A deeper understanding of farmers' management strategies is required to frame meaningful recommendations.

Incorporation of dry matter of perennial soybean into the soil, alone or with mineral fertilization, resulted in improved vegetative growth of common beans. Fairly high LAI was observed at flowering time where dry organic matter had been added, causing leaf self-shading and decreased growth in the later states of development. In contrast, both the control and mineral fertilized plots showed slower but continuous growth up to 50 days from plant emergence. Only slight differences in grain yield were noticed despite remarkable increases of Crop Growth Rate, Relative Growth Rate, Net Assimilation Rate, and Efficiency of Solar Energy Conversion that resulted from the application of dry organic matter.

A phenol colour reaction test was found to be useful for classifying rice varieties. The degree of colouration varied between varieties and could be explained by differences in the enzyme activity, expressed as phenoloxidase and peroxidase. Light, temperature and aeration appeared to influence colour development, but age and crop location did not. A concentration of 1.5 per cent was found to be suitable.

Leaf area index is an important parameter in many agronomic and physiological studies, but its determination in cowpea (Vigna unguiculata) and soyabean (Glycine max) is difficult and time consuming. A simple and rapid method is described in which dry weights of the middle leaflets were used to predict leaf areas of cowpea and soyabean. This method was based on results which indicated that leaf dry weights were highly correlated to leaf areas and that the ratio between leaf area of the terminal leaflet and total area of a trifoliate leaf was constant, at least in some cultivars, giving ratios of 0.37 for cowpea and 0.33 for soyabean.

Crop simulation models have been proposed as tools for the transfer of technology in less developed countries. Using a validation exercise as a framework for evaluation, this study looked at the ease of use of a simulation model in a small African research station. Although the model did not accurately predict grain yield of the local maize hybrid, the procedure did highlight some of the problems involved in applying the model. The constraints to the use of such models at small research stations are discussed and improvements that could facilitate model use are suggested.

Uso de model de cultivo para la investigación en Africa

Eucalyptus spp. is the main tree used in cellulose production worldwide, cultivated mostly in extensive monocrop plantations. However, due to concerns on environmental impacts, fear on decrease of food production related to the size of cultivated area, its location near human settlements with few jobs generation, eucalypt cultivation is no longer encouraged in many places. At the same time, large plantations hold the opportunity to integrate eucalypt into agroforestry systems (AFS) in a variety of production systems with many social, economical and environmental advantages. In this study we studied canopy modifications of E. camaldulensis sprouts under different degrees of shade. The plants were located on a gradient of available solar irradiation ranging from 51 to 94%. E. camaldulensis showed canopy plasticity with modified radiation interception patterns under diverse irradiations. Most of these variations were of small amplitude with some important variables remaining almost unchanged (leaf density, canopy percentage, tree, trunk and canopy height) or increasing only slightly (leaf area index and canopy opening). The main changes presented by E. camaldulensis, with a steep increase towards full sun, were: foliage area, canopy surface, canopy volume and area of canopy projection. In order to design appropriate agroforestry systems with young eucalypt growing under the shade of other crops, it is necessary to determine at which point the observed variable changes can support reasonable production.