s:850:"%T Root functions in agricultural systems 
%A De Willigen P 
%A van Noordwijk, M. 
%X Root research in agricultural systems is aimed at increasing the efficiency of using external inputs. Nutrient uptake efficiency is defined as the ration between uptake during a growing season and the size of the available pool in the soil. Part of the available pool is "unrestricted available", i.e. it can be taken up at the rate required for maximum crop growth: the remaining part is "restricted available" and its rate of transport to the root determines the uptake rate possible and hence crop growth. Root characteristics determine for a given soil-nutrient combination which part of the available pool is unrestricted available and how fast the restricted available pool can be depleted. A mathematical formulation of these effects is now available. 
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