20 ref.; Summary (En)

Root parameters of three corn (Zea mays L.) genotypes influencing P and K uptake were investigated in solution culture and field experiments. The data for these parameters were used to simulate P and K uptake by plants grown in the field using the Claassen-Barber model. Root characteristics for ion influx, maximum rate of influx, Imax; Michaelis-Menten constant, Km; and minimum concentration of solution below which no further net influx occurs, Cmin, were determined in solution culture. These kinetic parameters varied 2 to 3 fold among genotypes. Variations among genotypes were different for K than for P. Three corn genotypes were grown in the field and harvested 47, 54 and 68 days after emergence. Yield and root surface per plant increased about 3 fold during this time. At 47 days, 2/3 of the total root surface was in the top soil whereas 3 weeks later, it was less than 50 per cent. Genotypes differed in distribution of roots between the topsoil and subsoil as well as in root surface per unit of shoot . K uptake predicted by the Claassen-Barber model was 2 to 3 times the observed. The overprediction could be related to high root density (length of root per unit soil volume) which indicated that competition between roots occurred that was not considered in the simulation model. The predicted P uptake (y) was correlated (r = 0.91) to observed uptake (x) by y=0.98 + 0.67x, indicating underprediction of P uptake. The presence of root hairs may have been the cause of the underprediction. The calculated contribution of the subsoil to the observed uptake was 10 per cent for K and 1 per cent in the case of P. It was concluded that the plant parameters used to simulate nutrient uptake were rated accurately when allowance was made for root competition and presence of root hairs

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