Impact of fall irrigation on phosphorus transportation & transformation in the agricultural irrigation area in Inner Mongolia
秋浇对内蒙古农业灌区磷元素迁移转化的影响

The impact of irrigation on phosphorus transportation and transformation in the agricultural irrigation area in inner Mongolia during the period of fall irrigation was analyzed by monitoring the soil water ratio, total phosphorus (TP), inorganic phosphorus (IP) and organic phosphorus (OP) concentration from farmland soil and water in both irrigation ditches and drainage streams. The fall irrigation uses the largest volume of irrigation water in the year. The research showed that the soil water ratio was greatly increased, which resulted in the dissolution of soil phosphorus. The irrigating water carried substantive particulate phosphorus (PP) which settled in the soil and became adsorbed, leading to a slight increase of TP in the soil and subsequently a large reduction in the drainage streams compared with that in the irrigation ditches. The inherent soil OP and calcium ion were adsorbed onto insoluble substances which shifted the chemical equilibrium in the direction of OP generation, which led to a large gain in OP. The wet soil became more anaerobic because of the long submersion time which promoted the utilization of soluble phosphorus by anaerobes and its transformation to OP, which explains the dramatic augmentation of OP in both soil and drainage streams.