The effects of a straw mulch, applied either uniformly or in strips, on the surface energy balance and soil thermal regimes are investigated using a numerical solution to the two-dimensional soil heat transfer equation. The numerical technique used is an extended version of Barakat and Clark's (1966) alternating direction explicit method. The modified technique can solve problems that are periodic in time and/or space, on either rectangular domains or domains with a curvilinear upper boundary, and in which the soil thermal properties may vary with position, time, or temperature. The method also incorporates non-uniform grid spacings to reduce computation time and to increase efficiency.
The straw mulch is represented as a single layer of constant shortwave and longwave transmissivities and reflectivities. Vertical transport of heat and water vapour through the mulch is evaluated by bulk transfer equations. Shading of the bare strip and reflection of radiation onto it by the sides of the mulch strip, as well as the reduction of the sky-view factor seen by the bare strip, are included. Solar irradiance, air temperature and water vapour density, wind speed, soil thermal properties and mulch parameters are the required inputs. Evaporation is estimated using a surface resistance model to vapour flow.
The model is compared with micrometeorological measurements made in soils covered with barley straw, either uniformly at rates of 2, 10 or 20 t/ha or in 0.30 m wide mulch strips (10 t/ha rate) alternating with 0.10 m wide bare strips, with the strips oriented in north-south, northeast-southwest, or east-west directions. The results show that for the uniformly applied mulch soil temperatures can be adequately predicted but evaporation is underestimated. Both soil temperatures and evaporation are underestimated in the bare strip. The differences are attributed to the penetration of wind eddies into the straw mulch and the microscale advection from the warm straw strips onto the relatively cold bare strips. / Land and Food Systems, Faculty of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/28837 |
| Date | January 1988 |
| Creators | Hares, Mohammad Abu |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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