Soil temperature effects of mulching including a review of mulch use in Tanzanian farming and an example of soil temperature under mulched tea in Kericho-Kenya

dc.contributor.authorMwampaja, Abell Royrald
dc.description.abstractOur main aim has been to study quantitatively aspects of a microclimate management techniques applied by traditional farmers in the third world. Such studies are important before one tries to improve such techniques or introduces new ones. Mulch application is one of such techniques used widely by both traditional and more modern farmers in the tropics. A general review of the types of mulches commonly used by traditional farmers in the third world is given in the first chapter. In the same chapter, a review of the effects of mulches on soil temperature, soil moisture, soil erosion potential, weed control, post and disease control, soil nutrient conditions, soil micro-organism activities and soil physical and chemical properties and conditions is briefly given. We also review the use of mulches in Tanzania from information largely obtained in a public contest. Details on which this review is based are given in Appendix 1. Having chosen thermal aspects of mulches as our subject, in the second chapter the background theory on heat transfer in soil and air is discussed. Taking appropriate assumptions the relationship between reflectivity of surfaces and their surface temperature amplitudes is established. Proof of the validity of the theory under dry conditions is shown and discussed in Appendix 2. In chapter 3, application of the theory is further outlined and used to analyze in detail monthly averaged diurnal soil temperature patterns under mulched tea from Kericho-Kenya. The average temperature calculated at each depth was shown to be constant or linear with depth. Hence the derived theory could be used. Two methods of finding the damping depth D, which may prove the homogeneity of the soil are discussed and used to show that the Kericho soils were indeed homogeneous both in time and space. Conservativeness of D-value indicated that the tea canopy acted as a supplementary shade only and not as a supplementary mulch. The theory is used to explain temperature patterns under thin mulches under tea with a shade cover less than 25%. A simple shade correction on temperature fluctuations appears allowed. To this end we use a temperature fluctuation reduction power ratio, now known as Stigler’s ratio. The use of this ratio as a measure of the thermal efficiency of grass mulches is also demonstrated and found to be more powerful than using average temperatures. From this ratio also an apparent reflectivity of such surfaces can be defined from which follows how much (radiation) energy is effectively absorbed by the soil surface. We finally end up in chapter 4 with our own soil temperature measurements under three types of mulches (Thick grass, Residue grass and Black Plastic) and Bare Soil. Temperatures at the surface were measured by a Stoutjesdijk infrared radiometer and thermistor thermometers. The two surface temperatures were found to be different. However, they had the same trend in the sense that their maximum occurred at the same time. Extrapolated surface temperatures. This shows that soil surface temperatures on a diurnal basis cannot accurately be predicted from sub-surface soil temperature with the simple model used. To the other hand, surface temperature measurements by contact sensors can only give an accurate guide towards the determination of the times of maximum temperature at the surface. Surface temperature results have also shown that remotely sensed temperature is no indication of what happens below the surface. They were in our three different cases hardly different during periods of maximum temperatures though sub-surface temperatures were quite different. This is of high importance in the interpretation of the consequences of remotely sensed surface temperatures. Stoutjesdijk temperature measurements also led to the detection of Black Plastic transmission of part of the infrared radiation. The apparent reflectivity of our local grass was compared to that used at Kericho. It was found for thick grass to be 90% while that of the Kenya grasses was at maximum 65%. Hence our local grass had a higher thermal efficiency than that of Kericho according to the definition given earlier. This was mainly due to its dryness, composition and density. Simultaneously done transmission measurements (Kainkwa, 1983) revealed that only 5% of the solar radiation was transmitted through the Thick grass. Therefore the 10% of the thermal energy which contributes to the sub-surface temperature fluctuations (as a consequence of the apparent reflectivity of 90%) has a contribution of 5% transmitted radiation and the other 5% must be due to the insulation properties of the mulch. For the Residue grass, an apparent reflectivity of 50% was calculated. Therefore the same amount of energy could be due to transmitted radiation. Hence the other 14% must be due to the insulating properties of the mulch and not to the shading properties. These data show the relative importance of the shading character of mulches which hitherto was not well recognized and could not be separately calculated. Our new micrometeorological look at shading has made this character better knownen_US
dc.identifier.citationMwampaja, A. R. (1983) Soil temperature effects of mulching including a review of mulch use in Tanzanian farming and an example of soil temperatures under mulched tea in Kericho-Kenya, Masters dissertation, University of Dar es Salaam. Available at (
dc.publisherUniversity of Dar es Salaamen_US
dc.subjectSoil temperatureen_US
dc.titleSoil temperature effects of mulching including a review of mulch use in Tanzanian farming and an example of soil temperature under mulched tea in Kericho-Kenyaen_US