The utility of phosphate sorption curves for transferring soil management information
AbstractPotato yield data from field experiments performed in Bangladesh (Noakhali), Canada (Ontario), Peru (Huancayo), and U.S.A. (Alaska, Hawaii and Idaho) were used to evaluate the P requirements of potatoes. Estimates of the concentration of P in soil solution were obtained from phosphate sorption curves plotted for soils from the various sites. The quantity of P required to establish solution P at standard concentration (0·2 p.p.m. P) ranged from 15 ?g/g (Ontario) to 1000 ?g/g (Alaska - Cryorthod). The concentration of P in a solution equilibrated with a soil to which no P had been added ranged from about 0·002 p.p.m. for a Gibbsihumox of Hawaii to 0·05 p.p.m. for soils from Bangladesh and Canada. Although rates of P applied were high, the Alaska site - a soil influenced by volcanic ash - gave no evidence that maximum yields were attained. Inadequacy of P fertilization was confirmed by foliar analysis. The P sorption curve for this location predicted that the P fertilizer requirement was much greater than that actually applied. This information is consistent with other information that P sorption by soils which contain weathered amorphous materials is in the range of 1000 to 3000 ?g P/g of soil. At one location -Wahiawa (Hawaii) - maximum yields were attained at levels of P in solution which were greatly in excess of that required for potato plant nutrition per se. Except for the highest P levels, these plants were severely affected by Rhizoctonia solani. Yield data from the remaining five locations were plotted against estimated P concentrations in solution to give a composite yield response curve. Phosphorous concentration of about 0.2 p.p.m. in soil solution was associated with approximately 95 per cent of maximum yield. This approach should have wide application as a means of utilizing existing field trial data for determining standard external P requirements for crops in areas where few data are now available. Phosphate sorption curves can then be used to transfer result of field experimentation from one location to another.