Abstract: A field mini-plot experiment was conducted on clay loamy oxisol using ³²P trace technique when P fertilizer was applied in three depth soil (15, 35 and 55 cm soil layer) to compare P absorption, distribution and translocation in plant organ and soil profile under soybean and citrus monoculture and intercropping at Taoyuan Experimental Station of Agroecosystem Research of Chinese Academy of Science. Total P uptake (PT) and P accumulation in different parts (PA) of soybean were remarkably decreased under intercropping. When ³²P was applied in topsoil (15 cm soil layer), ³²P uptake ( ³²PT) by soybean was significantly lower in intercropping than in monoculture. Whereas ³²PT uptake by soybean was significantly greater in intercropping than in monoculture when ³²P was applied in deep soil layer (35 cm or 55 cm soil layer). However, considerable difference was not observed for ³²P translocation and distribution among soybean organs. ³²PT uptake by citrus was much lower under intercropping than under monoculture. The P uptake by citrus newly could be transferred rapidly to aboveground and prior to active growing organ. Intercropping did not affect ³²P distribution in citrus organ, but when P was applied in deep soil layer, the speed of ³²P transferred to aboveground and active organ was slowed down. P mobility was strengthened in soil profile, and P of deep soil layer was promoted to move to topsoil in intercropping. The experimental results showed the optimal depth of applied P should be within 20 cm soil layer in soybean-citrus intercropping system.

Key words: Agroforestry ecosystem, ³²P, Distribution, Translocation