Soil factors affecting plant performance of climbing beans (Phaseolus vulgaris L.) in south western Kenya

Abstract: The south west part of Kenya is the most densely populated part of Kenya. This part of Kenya has relatively fertile soils and a favorable environment for crop production, which is why it is a major food producing area. The high population results in land scarcity with the average farm size ranging from 0.8-1.8 ha. Climbing beans(Phaseolus vulgaris L.) have the potential for higher areal yield than common beans, because of their indeterminate growth habit and ability to climb if being supported mechanically. This is the reason why the project Legume CHOICE introduced them in this area. The aim of the study was to determine if certain soil factors in the area limit the performance of climbing beans. The soil factors studied were pH, penetrometer resistance, C and N concentration and CN ratio. The plant performance was measured by germination rate, plant height and growth stage at three occasions. The hypothesis was that a high pH, C and N concentration and CN ratio would have a positive effect on plant performance, and that a high penetrometer resistance, indicating soil compaction, would have a negative effect on plant performance. Data were collected from 30 on-farm trials on three sites in Kisii and Migori counties. Soil samples for pH were taken in each plot, using a soil auger, and analyzed at the ICRAF lab in Nairobi. Soil samples for C and N analysis were taken according to the LDSF sampling technique and analyzed at the University of Hohenheim, Germany. Soil samples were taken for topsoil (0-0.2 m) and subsoil (0.2-0.5 m). Penetrometer resistance was measured in five places in each plot. There was a difference in soil factors between the sites, and also a great variation within each site. The principal component analysis indicated that soil pH and penetrometer resistance affected germination and plant height. The most prominent result of the multiple regression was the negative correlation of penetrometer resistance and plant height at the second visit. The results show that pH and soil compaction in the topsoil affects the plant performance of climbing beans in this area, although the management, especially staking, also plays a crucial role in the plant performance.