The effect of nitrogen and phosphorous application and spatial arrangement of maize intercrop on occurrence of common bacterial blight disease in beans

Abstract

Many factors affect crop production and hence the agronomical practices of farmers. Such factors are low soil fertility, disease, pests, and limited resources/land among others. Pests and diseases such as common bacterial blight affect farmer’s decision and production in many ways. Farmers may or may not use fertilizers, intercrop or mono-crop depending on level of production and resources available or other. Two studies aiming at identifying the relationship between Common Bacterial Blight (CBB) disease of beans and agronomic practices, such as fertilizer use and intercropping were conducted. The first study was to determine how the use of fertilizers (N and P) influences the occurrence of common bacterial blight disease of beans. The second study aimed at determining the effect of intercropping beans with maize on the occurrence of common bacterial blight disease.

In the first study treatments included four different levels of P and N fertilizers i.e. 0 & 0, 5 & 10, 10 & 20 and 15 & 40 kg ha-1 respectively. The second study composed of different spatial arrangements for the bean and maize crops. These were 1 maize row to 1 bean row, 1 maize row to 2 bean rows, 1 maize row to 4 bean rows 1 maize row to 6 bean rows and a sole bean crop. Then all treatments above were sprayed with CBB inoculums.

The experiments were carried out at Kabanyolo and a susceptible bean variety K131 was used. The crops were planted at the beginning of the rains for three seasons. The common bacterial blight (CBB) inoculums were prepared. This was then used to inoculate two weeks-old plants using a hand spray pump. Disease progress was observed and recorded as percentage infected leaf area at a weekly interval for seven weeks. The data collected also included; biomass of the bean plant at flowering, pods/plant, seeds/pod and weight/100 grains and yield/plot.

Phosphorous and nitrogen fertilizers had a significant effect (P = 0.05) on the yield components such as biomass at flowering, pods /plant, weight/100 grains but not on grains/pod. The effect of fertilizer level on yield was more pronounced at low fertilizer level (5:10 and 10:20). After these levels, addition of more fertilizers did not increase yield but led to increased vegetation cover and more tolerance to CBB. The plots where no fertilizers were used generally had highest disease incidence. Hence there is need to use N and P in bean production but low levels (5:10 and 10:20) should be used for reduced CBB occurrence and best yields hence economic advantage.

Intercropping affected the bean yield in two ways: the shading affected the potential yield of the bean crop to as much as 80% reduction. The shading also seemed to favour the occurrence of CBB causing more yield reductions. More CBB was experienced in plots with more maize plants. The results obtained showed that yields of the susceptible variety K131 were reduced significantly (P = 0.05) due to CBB infections. Hence intercropping and varying spatial arrangement had a pronounced effect on growth and yield of beans intercropped with maize except in the 1:4 and 1:6 arrangements. There was suppression of the bean crop by maize in 1:1 and 1:2 arrangements reducing biomass at flowering, pods/plant and grain yield in addition to increased CBB disease occurrence.

Intercropping of beans with maize in a ratio of 1:4 and 1:6 had less CBB occurrence, gave best yields and was recommended. However, the intercrop spacing depends on whether beans or maize is considered the major or minor crop. This varies from region to region and farmer to farmer for different reasons.

Weather conditions also influenced the CBB occurrence and crop yield. For both experiments, there was generally a higher disease incidence during the second season which had more rainfall compared to the first season which had less rainfall.