PHOSPHATE SORPTION BY EGYPTIAN, ETHIOPIAN AND GERMAN SOILS AND P-UPTAKE BY RYE (SECALE-CEREALE L) SEEDLINGS

Phosphate sorption was studied in samples (0 - 20 cm depth) of five so ils from Egypt (pH 7.4 - 8.7), four soils from Ethiopia (pH 3.9 - 5.3) and six soils from Germany (pH 3.3 - 7.2). Sorption parameters were c alculated according to Pagel and Van Huay (1976) and according to Lang muir (Syers et al., 1973). Phosphate sorption parameters and oxalate e xtractable Fe and Al(Fe(ox), Al(ox)) were related to the phosphate upt ake by young rye plants in Neubauer pot experiments. P sorption parame ter after Pagel and Van Huay (A) correlated significantly positively w ith the Fe(ox), and Al(ox), content in acid (r = 0.73) as well as in c alcareous soils (r = 0.89) if the whole equilibrium concentration rang e (0 - 14 mg P/L) was considered. The relations calculated after Langm uir (B) were similar. P uptake by rye in acid soils was negatively cor related with the affinity constant n (r = -0.76, (A)). In calcareous s oils. a negative correlation between P uptake and affinity constant wa s calculated in the lower P equilibrium range (0 - 2.8 mg P/L) only fo r (B). Thus, P uptake decreased with increasing strength of P bonding to soil. From these results it is concluded that phosphate sorbed to F e/Al oxides is an important P source for plants in acid and calcareous soils.