J.K. Ng'ang'a

Wind protection in a hedged agroforestry system in semiarid Kenya

In semiarid Laikipia (Kenya) severe crop damage and loss of mulch material may be caused by south to south-easterly winds from June to September. Demonstration agroforestry systems which surround farms with live fences had some success in protecting crops, mulch and soil, but great care must be taken, because air may be channelled through or over them. For demonstration purposes, a deliberate gap was made in a two meter high Coleus barbatus live fence to study its effect on wind speed and damage to crops. The effectiveness of protection given by this hedge together with intercropped Grevillea robusta trees was quantified using electrical cup anemometers. The combination of hedges and trees gave protection to a maize/bean intercrop but the biomass distribution was not the most suitable one. This picture was complicated by variable wind direction and interactions between wind and the biomass of hedges and trees. The lowest efficiency of wind reduction occurred closest to the deliberate gap, where also the lowest protection by the Grevillea trees was found. South to south-easterly winds increased the gap effect and caused gradients in tree protection perpendicular to the southern hedge. This gave at times wind speeds even higher than outside the system. Only visually wind effects could be detected. Trees and hedges strongly competed with the crops if not root pruned.

New Approach in Research Education to Solve Problems of Dryland Farming in Africa

For quite some time now, Africa has faced food shortages that are largely due to deterioration of agricultural environments and high population growth rates, leading to a combination of production pressures. The agricultural problems are particularly pronounced in dryland farming, and the means to mitigate them have to be mainly of a low external input nature. A case study from Kenya of an integrated research education approach holds much promise for contributions to solve such food production problems in the drylands of Africa and other low external input sustainable agriculture (LEISA). The approach emphasizes interdisciplinary research education of local scientists by problem‐oriented research in tackling environmental hazards facing the farmers. Six primary sequential steps, from problem identification via field quantification to the contributions to solutions, are distinguished as essential. In the Kenyan example, it was possible to give a “weather advisory,”; that is, an extension message with stron...

The “Picnic” model for research training at African universities: Evaluation and preliminary comparison

Abstract What distinguishes the “Picnic” model for research training at African universities from more classical models is reviewed and it is shown how the “Picnic” model deals with remaining drawbacks from the now popular “Sandwich” model. Starting with managerial experiences, criteria guiding this evaluation are used as sub-headings: realistic planning; adequate resource provision; partnership instead of aid; long term impact; high quality supervision; quality and quantity of student input; open and interactive communication; willingness to adapt to local circumstances; ongoing critical reflection; gradual expatriate withdrawal. The training output of the “Picnic” model tests in the four TTMI-countries is assessed after the actual and prospective jobs of its former students. The on-farm quantification of protecting systems/structures led in many TTMI PhD-research cases to improved design criteria for such systems/structures, with direct increases of yield or its preservation. In comparison with the “San...

Some aspects of frequency and stability wind roses in a tropical region

The frequency wind roses and stability wind roses based on meteorological data at Nairobi International Airport are calculated. The stability is estimated using a Pasquill-Gifford Scheme. The results show that in the tropics the winds have generally high speeds and are highly constant in direction throughout the year. The high wind speed in these regions has a great influence on the stability estimation scheme that is used.The high wind speeds and persistence in the tropics are viewed as favorable factors in the air pollution problem since the dispersive ability of the atmosphere is enhanced and, in terms of long term planning, the wind variability is much less than is the case with middle latitudes.

Some features of aitken nuclei in Nairobi

Abstract Measurements of Aitken nuclei in Nairobi were made using the small particle detector from November 1981 to July 1982 in the industrial area and four stations at varying distances from the centre of the industrial area. The industrial area had a concentration that was on average a factor of two higher than of the residential estates. The concentration was found to decrease with increasing distance from the industrial area. Concentration values depict a monthly variation with dry months recording a higher concentration than the wet months. The Aitken nuclei were found to be a good indicator of industrial pollution in the city, as a good correlation was found between the Aitken concentrations and total suspended particulate concentration values in the industrial area over the same period. The monthly variation of the Aitken nuclei were found to follow closely the annual wind and stability patterns.