Effects of alfalfa root exudates on insoluble phosphorus in soil

The root exudates of 6 alfalfa cultivars including Zhongmu No.1, Target, TG3, Knight 2, Knight T and Adina growing in hydroponics with phosphorus or without phosphorus were collected to investigate their activation of insoluble phosphorus and effects on P effectiveness in soils. Compared with the soils without root exudates, the contents of effective P (OlsenP) increased, the contents of Ca2P extremely significantly decreased (P＜0.01), the contents of AlP、FeP and Ca8P significantly decreased (P＜0.05) and the contents of OP and Ca10P did not change in soils treated with root exudates（P＞0.05）. The activation of insoluble phosphorus of root exudates from plants without P was better than that of root exudates from plants with P. The contents of Ca2P had the largest decline in soil treated with TG3 root exudates with the highest P effectiveness. The contents of Ca8P had the largest decline in soil treated with Knight T root exudates with the secondly P effectiveness. Alfalfa root exudates have activation on AlP, FeP, Ca8P, Ca2P and especially for Ca2P which was the largest source of OlsenP under phosphorus deficiency condition.