Effect of weed management practices and nitrogen application on seedling emergence, growth and yield of dry bean (phaseolus vulgaris l.)
One of the major constraints to bean production is the high labor requirements that farmers face in land preparation, planting and weed control. The conventional methods of weed control in many parts of Kenya and Africa is using a hoe and a machete, which is tedious and time consuming. A field experiment was therefore conducted during the 2009 long rains and short rains seasons at the University of Nairobi's Kabete Campus Field Station to determine the effectiveness of various weed management options and nitrogen fertilizer application in improving the performance of a dry bean crop. The following weed management options were evaluated: 1) mowing the weeds at the ground level and planting without hoeing the plot., 2) hoeing the plots removing all the weeds; 3) hoeing the plots and then incorporating the weeds into the soil; 4) hoeing the plots and then leaving the weeds on the ground to act as mulch; 5) spraying the plots with a herbicide and then leaving the weeds on the ground to decompose and planting without hoeing the field. Emerging weeds were controlled by hoeing; 6) spraying the plots with a herbicide and then leaving the weeds on the ground to decompose and planting without hoeing the field. Emerging weeds were controlled by mowing. The N treatments consisted of 0 kgN/ha and 30 kgN/ha. The treatments were laid out in a randomized complete block design with a factorial arrangement. Bean variety Mwezi moja was used as the test variety. Data collected included: percent emergence, plant height, number of nodules per plant, nodule dry matter, root dry matter, shoot dry matter, number of days to 50% flowering, number of seeds per pod, number of pods per plant, weight of 100 seeds, total seed weight, soil moisture content, weed population by species, total number of weeds and soil N before and after the experiment. All data were subjected to analysis of variance using General Statistics package (GENSTAT) for windows and means separated using the least significant difference (LSD) test at 5% level of significance. The results showed that use of mulch increased soil moisture content, bean nodulation, grain yield ar·.}y,.j,j components, delayed emergence and flowering and reduced weed population. Incorporating the weeds into the soil had similar effects as mulch although it did not increase the yield and yield cornponents relative to mulching. Relative to mulching, mowing and herbicide application resulted to reduced soil moisture, nodulation, yields and yield components and delayed emergence but hastened flowering. Hoeing the field resulted in reduced soil moisture content, weed population, yield and yield components but hastened germination and flowering. Application of N at the rate of 30 kg/ha did not significantly increase grain yield of bean relative to zero N. Jt '\JJ3.S cOD .eluded that mulching a bean crop is more effective in conserving soil moisture and hence having a geed crop performance and yield than conventionally opened plots, plots with weeds illcc-~porated in the soil or herbicide treated plots. The effectiveness was attributed to the high moisture content conserved in these plots. The evidence from the crop performance in terms cf height, flowering, nodulation, yield and yield components suggested that mulching is the iJ.IOS~promising weed management practice followed by incorporating the , weeds in the soil, hceing and herbicide application, especially to small scale farmers who cannot afford the high costs of herbicides and the expertise required in their application. It was also concluded that application of nitrogenous fertilizer at a rate more than 30 kgN/ha could Improve the bean crop growth and yield. It was therefore recommended that studies needed to be done to determine whether rates ofN fertilizer more than 30kg/ha are beneficial, hoeing the field and leaving the crops and weed residual in the field to decompose should be undertaken as a means of conserving moisture in a bean crop and hence improving overall yield and further investigations to be undertaken to determine the best mulching material for a bean crop and its cost implication, especially to a small scale farmer. Studies should be done to determine the weeds that leave a lot of weed seed on the field for farmers to avoid them as mulch.