
%0 Journal Article
%A Spencer, K 
%A Chan, CW 
%T Critical phosphorus levels in sunflower plants
%J Australian Journal of Experimental Agriculture
%D 1981/02/01
%V 21
%N 108
%P 91-97
%K 
%R https://doi.org/10.1071/EA9810091
%U https://www.publish.csiro.au/paper/EA9810091 
%X To provide a basis for a tissue test for the diagnosis of P deficiency in sunflower crops, the influence of plant part and age on the critical P percentage (P concentration in tissues required to sustain 90% of maximum yield) was examined. In a glasshouse experiment, the known mobility of phosphate within the plant was reflected in the occurrence of the highest P concentration in the youngest leaves. Laminae contained more P than petioles on a dry-weight basis. Stem internodes contained less P than the adjoining petiole near the base ofthe plant but more near the apex. Three field experiments indicated that the lamina of the youngest fully-expanded leaf was a suitable plant part for diagnosis. Critical P concentrations for this tissue decreased from about 0.35% at the fourth week from sowing to 0.20% at the tenth week. 
