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 soils 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 calculated according to Pagel and Van Huay (1976) and according to Langmuir ( Syers et al., 1973). Phosphate sorption parameters and oxalate extractable Fe and Al (Fe ox , Al ox ) were related to the phosphate uptake by young rye plants in Neubauer pot experiments. P sorption parameter after Pagel and Van Huay (A) correlated significantly positively with the Fe ox and Al ox content in acid (r = 0.73) as well as in calcareous soils (r = 0.89) if the whole equilibrium concentration range (0 ‐ 14 mg P/L) was considered. The relations calculated after Langmuir (B) were similar. P uptake by rye in acid soils was negatively correlated with the affinity constant n (r = −0.76, (A)). In calcareous soils, a negative correlation between P uptake and affinity constant was calculated in the lower P equilibrium range (0 ‐ 2.8 mg P/L) only for (B). Thus, P uptake decreased with increasing strength of P bonding to soil. From these results it is concluded that phosphate sorbed to Fe/Al oxides is an important P source for plants in acid and calcareous soils.