Abstract
Two trials with the combined effects of seeding density and application of DAP fertilizer on the yield of four biofortified bean varieties were carried out in Kashusha on the experimental site of the Université Evangélique en Afrique during the 2013-2014 agricultural long rains season (September-January) and short rains season (March-May). The overall objective was to investigate the response of biofortified common bean and its response to seeding density, mineral fertilizer application, and good agricultural practices. Four bean varieties were used (RWK-10, HM 21-7, CODMLB001 and RWR2245) and the experimental design was split-split plot whose main plot was occupied by varieties and sub-plots had DAP fertilizer crossed with two seeding spacing. Two seeding densities were considered, 250,000 plants ha-1 and 500,000 plants ha-1 respectively corresponding to the spacing between plants 40 cm x 20 cm (commonly used) and 20 cm x 20 cm. The plot was divided into 3 blocks (or repetitions), distant of 2 m and each comprising two sub-blocks separated by 1 m. A sub-block was treated with fertilizer (DAP) and the other was kept as control. The yield of bean seeds has varied from one season to another independently of varieties, which had no effect. It was better in long rains season (1725 kg ha-1) than in short rains season (1087.4 kg ha-1). The effect of fertilizer was also dependent on the season, no effect was observed in short rains season, with huge poorly distributed rains. However, in long rains season, the application of DAP has produced a high number of pods per plant and large grains leading to a higher yield of 1368.6 kg ha-1 when the fertilizer was applied compared to control which produced only 806.1 kg ha-1. During the same season, doubling the density, a yield of 1842.9 kg ha-1 was obtained compared to the density of 250,000 plants ha-1 that produced 1607.1 kg ha-1. The agronomic efficiency of fertilizer was low, ranging from 1.53 for the CODMLB001 variety to 5.64 for HM21-7 variety. Multi-local trials, in contrasting environments are needed to better understand the influence of the season on the bean behaviour in dissemination in South Kivu. It is also interesting to test other seeding densities, fertilizer types and doses for adequate recommendation of fertilization of this crop in Kabare territory. Due to low soil pH, it should be important for example to apply lime before applying the fertilizer. Key words: Bean, seedling density, Di-ammonium phosphate (DAP), variety, yield  
Highlights
Given their high protein content in the dry seed and their symbiotic fixation of atmospheric nitrogen capacity, food legumes are an essential component of cropping systems in the tropics
In long rains season (LRS) the number of pods per plant and number of grains per pod was high compared to the short rains season (SRS), which has seen uneven rainfall, which were abundant compared to the needs of the crop
The effect of fertilizer on common bean grain yield varied from season to season independently to variety, showing that the chemical fertilizer depends on soil water
Summary
Given their high protein content in the dry seed and their symbiotic fixation of atmospheric nitrogen capacity, food legumes are an essential component of cropping systems in the tropics. These plants are often characterized by low and unstable yields, because of their sensitivity to diseases, pests and low fertility of tropical soils on which they are grown in most of the cases (Baudouin, 2001). In South-Kivu, bean is often sown at 40 cm x 20 cm spacings, or 12 plants per m2, while densities of 15-40 plants per m2 are possible for bush beans (Carburet and Hekimian, 2009). The project recommends to seed-multipliers the use of 40 x 20 cm spacing and the yields range from 500 to 800 kg/ha depending on the cropping seasons without fertilizer. Carburet and Hekimian (2009) evoke yields of 1000-3000 kg/ha for growing beans in the US and Europe in intensive cropping system when fertilizers, pests control and improved varieties are used
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