Pools and distributions of soil phosphorus in China

We have investigated the pools and distributions of soil phosphorus ( P) in the top 50 cm of soil in China by using a combination of total and available P information from more than 2400 soil profiles and a map of soil types at a resolution of 1: 1,000,000. Our estimates indicate that the average total P density and available P density in China are about 8.3 X 10(2) g/ m(3) and 5.4 g/m(3), respectively. The total national soil P pool in the surface half meter is 3.5 Pg ( 10(15) g). The available P density ranges from 0.7 g/m(3) in the Lithosols to 16.7 g/ m(3) in the Irrigated Silting Soils. The total P density ranges from 1.2 X 10(2) g/m(3) in the Lithosols to 19 X 10(2) g/m(3) in the Frigid Desert Soils. The ratio of available P to total P density ranges from 0.6 X 10(-3) in Aeolian Soils to 21.6 X 10(-3) in Coastal Solonchaks. The available P content and its vertical distribution show a complex pattern among soil orders of different development stages, possibly indicating the important role of biota's control over soil available P content. There are large variations of P content in different climatic regions. The tropical and subtropical region has the lowest available P density ( 4.8 g/m(3)) and the second lowest total P density ( 8.2 X 10(2) g/m(3)) among all climatic regions. The large variation in the soil P content suggests that further study is needed to investigate climatic and land- use controls over the soil P content