Manasah S. Mkhabela

Simulating ammonia loss from surface applied manure

The land spreading of manure can result in significant nitrogen (N) losses to the atmosphere through ammonia (NH3) volatilization. It is estimated that agricultural activities, including manure spreading contribute approximately 50% of the total global NH3 emissions. Computer simulation models have been developed in an attempt to predict NH3 losses resulting from manure spreading. Few models have been validated with success and no validation has been completed for conditions found in eastern Canada. The mechanistic model Volt’Air was implemented and tested to estimate NH3 emissions using field-based wind tunnel data from three field locations in eastern Canada. The model was validated using data from 27 wind tunnel trials, which measured NH3 loss over 5-19 d. Sensitivity analysis revealed that Volt’Air was most sensitive to pH. Good overall agreement was observed between measured results and model simulations over 5-19 d (R2 = 0.91, RMSE = 2.9 kg ha-1). Short-term flux simulations (kg ha-1 h-1) within the...

Improvements to the accuracy of modelled soil water content from the Second Generation Prairie Agrometeorological Model

The direct measurement of soil water on a regional scale is often not practical due to large instrumental and labour requirements. Alternatively, soil water estimates can be derived using models. The Second Generation Prairie Agrometeorological Model (PAMII) models soil water, crop development and evapotranspiration (ET) in order to derive an estimate of crop water use. The objective of this study was to validate, and if necessary modify, the soil water component of PAMII using weather and soil water data collected from several spring wheat trials in Saskatchewan and Manitoba during the 2003 though 2006 growing seasons. Comparison of modelled and measured soil water values yielded a RMSE of 62 mm. For most site-years, PAMII overestimated soil water during the second half of the growing season, which was caused by an increase in modelled canopy resistance (rc) before the crop experienced water stress. The rc function was thus modified so that rc would not increase until the soil water content was < 0.5 of ...