In soil forming process, it is assumed that the velocity of soil chemical reactions is increased by three times with the temperature rising every 100C;the mean air temperature in ten-days, t, is changed linearly during a year;and when t<0℃, the soil forming velocity equals zero. Under these conditions, the temperature effect of soil forming process, T, may be expressed by the equation:

where t₁ and t₂ are the mean air temperature in the coldest and the hottest ten-days respectively.