Unique laboratory test chambers with attendant procedures are described, and the results of a comprehensive test protocol are discussed in terms of the mechanical, chemical and biological factors contributing to NO flux from agricultural soil to the lower levels of the troposphere. Soil moisture content, pH, and temperature are investigated to determine the effects of these important variables on NO flux. The flux is seen to increase with temperature and is greatest at pH8 for the ranges studied. Further, NO flux is seen to decrease as soil moisture content is 45% water filled pore space. Mechanical, chemical, and biological factors in the soil which contribute to these observed fluxes are addressed. ¿ 1999 American Geophysical Union