Abstract: | An estimated 97 percent of the soils in Laos are characterized by low phosphorus (P). This characteristic, together with high acidity, constrains food crop production. The P status, sorption, and associated properties were evaluated for fifteen important agricultural soils from the uplands. Soil pH values ranged from 4.5 to 5.9. Soil organic carbon (C) varied from 7.0 to 22.9 g kg?1. Soil clay varied from 179 to 709 g kg?1. The cation exchange capacity (CEC) also varied from 4.30 to 32.1 cmolc kg?1. Extractable P levels of thirteen of the fifteen soils were P deficient with medium to very high P sorption, indicating substantial fertilizer P requirements. Dithionite and oxalate aluminum and iron predicted P sorbed at 0.2 mg P L?1. The extractable P increase per unit added P, P buffer coefficient (PBC), was low, also indicating high P sorption. Field studies are needed to confirm predictions of P requirements. |