A function for describing nitrogen uptake and dry matter production by winter barley crops

Abstract

The quantityY, of dry matter produced,Yd, and nitrogen taken up,Yn, during the growth of winter barley, was shown to be a function of thermal time,x, $$Y = (A^{ - 1/n} + \exp ( - kx))^{ - n} $$ wheren is a shape factor,k a rate constant andA the ultimate maximum of the curve. The value ofn was 1.2 for N-uptake and 1.0 for dry matter. The rate constantskN andkd for N-uptake and dry matter production respectively were well related to the date of sowing of the crop as expressed as the number of days after August 31st. The maximum N-uptakeAN was related to sowing date and to rainfall during March preceding harvest;Ad, the maximum dry matter, was related to the time between sowing and the return of the soil to field capacity. These relationships and the function itself were tested by examining the fits of the function to the measured datasets. The relationships may be site specific and their similarity to those derived for winter wheat is discussed.