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Prunings of Calliandra calothyrsus, Grevillea robusta, Leucaena diversifolia and farm yard manure were applied each cropping season at 3 and 6 t dry matter ha-1 to an Oxisol in Burundi. The field plots also received basal applications of nitrogen (N), phosphorus (P) and potassium (K). Application of the tree prunings or farm yard manure decreased the concentration of monomeric inorganic aluminium (A1) in soil solution from 2.92 mg A1 din-3 in the control plots to 0.75 mg A1 dm-3 in the plots receiving 6 t ha-l Calliandra prunings. The other organic materials also decreased the concentration of monomeric inorganic aluminium in the soil solution. The lowered A1 concentration led to a corresponding decrease in the percentage A1 saturation of the 0-10 cm soil layer from 80% to 68%. Grain yields of maize and beans were strongly inversely related to the percentage A1 saturation of the soil. This confirms that soil acidity was the main constraint to maize and beans production. The yield improvement was mainly attributed to the ameliorating effects of the organic matter application on A1 toxicity. The nutrient content had less effect presumably because of fertilizer use. In the best treatments, the yield of maize increased from 0.9 to 2.2 t ha-1 and the corresponding beans yield increased from 0.2 to 1.2 t ha-1.

Surveys and on-farm trials are frequently used to facilitate farmer participation in agricultural research. This paper reports on a less common method-farmer involvement in on-station trials. Thirty-nine farmers were invited to multipurpose-tree screening trials in Burundi. Three different methods were used to determine which species the farmers wanted to test on their own farms. Private interviews and voting by a show of hands in plenary sessions gave very similar results whereas focus group interviews produced different and contradictory results. Researchers also learned what criteria farmers used to evaluate trees and the reasons for their choices. A supplementary survey of farmers' preferences for trees grown on their own farms confirmed the findings and more clearly defined their criteria. In this survey, farmers used a local board game, Bao, to rate tree species across criteria they considered important. Overall, the visit to the trials and follow-up survey proved to be a useful and cost-effective method for getting farmer input and applying it in the screening process.La participation de los agricultores en la selection de especies de arboles RESUMEN A menudo se usan los estudios y ensayos en explotaciones agrfcolas para facilitar la participation del agricultor en la investigation agricola. Este documento informa sobre un metodo menos comun-la participacion del agricultor en las pruebasin situ. Se invitoa treinta y nueve agricultores a los ensayos multiproposito en Burundi. Se utilizaron tres metodos diferentes para determinar que especies querfan probar los agricultores en sus propias explotaciones agrfcolas. Las entrevistas personales y la votacion a mano en sesiones plenarias tuvieron resultados muy parecidos, mientras que las entrevistas a grupos dieron resultados contradictorios y diferentes. Los investigadores descubrieron tambien que criterios utilizan los agricultores para evaluar arboles y los motivos de sus elecciones. Un estudio suplementario sobre las preferencias de los agricultores en cuanto a arboles crecidos en sus propias explotaciones agrfcolas confirmo estos hallazgos y definio mas claramente sus criterios. En este estudio, los agricultores utilizaron un juego de mesa autoctono, Bao, para puntuar las especies de arboles de acuerdo con los criterios que consideraban importantes. En general, la visita a las pruebas y el consiguiente informe probaron ser un metodo de obtener la participacion de los agricultores util y con una buena relation coste-resultados para aplicarlo asf en el proceso de cribacion.

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Some agronomic, economic and ecological aspects of an agroforestry system combining Grevillea robusta trees, bananas (Musa spp.) and beans (Phaseolus vulgaris) were studied in the subhumid highlands of Burundi. Three densities of G. robusta, 208, 313 and 625 trees ha 71 were interplanted in plots of bananas, beans and a banana±bean mixture. When G. robusta was interplanted with bananas, the tree had a positive eect on banana yield with maximum yield occurring at 300 trees ha 71 . In the presence of beans, banana yield was not in¯uenced by the densities of the tree. Under low fertility regimes, the yields of beans interplanted with G. robusta were equal to or greater than those of the no-tree plots. Maximum bean yields were observed at between 283 and 295 trees ha 71 , representing a 25±135% yield increase above the no-tree control. When soil fertility was raised by the application of fertilizers, bean yields declined with an increasing density of G. robusta. Three years after planting, the growth of G. robusta was not aected by tree density. Mean height and mean basal diameter were 7.1 m and 13.2 cm respectively. Below ground competition between beans on the one hand, and bananas or bananas and G. robusta on the other, was more important than competition for light. Compared with the crops alone treatments, cumulative net present values of tree plots improved from being negative in the ®rst year to being positive in the third year. Net present value was highest in two of three instances when the density of G. robusta was 625 trees ha 71 . A multistrata arrangement of bananas and beans with G. robusta is viable for the low input agriculture system of the highlands of Burundi.

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In a survey of farmers' attitudes to four Musa hybrids, the majority (84%) considered them superior to the landraces in terms of plant establishment, plant growth, vigour and fruit yield. The hybrids had more green leaves at harvest, an added advantage as they provided shade for the young cocoa plants grown as an intercrop. Copyright © 2006 John Wiley & Sons, Ltd

Although alley cropping has been shown elsewhere to permit continuous cropping, it has not been widely tested in the highlands of east and central Africa where it has the additional potential of controlling soil erosion. The effect of four rates (0, 30, 60 and 90 kg N ha -~) of inorganic N on the performance of alley cropping using Leucaena diversifolia as the hedgerow species was studied in the central highlands of Burundi. Significant increase in maize yield (average of 26%) due to alley cropping was only first realised in 1992, three years after the commencement of the trial. In 1993, the average yield advantage of the alley cropping plots was 21%. The prunings augmented the response of maize yield to inorganic N in 1992 and 1993. Compared with the control, economic benefits over the five-year period for all the treatments were negative.