Phosphorus Nutrition in Cropping Systems Through Arbuscular Mycorrhizal Management

Abstract

Improvement of phosphorus (P) uptake and plant growth by arbuscular mycorrhizae (AM), one of the most common symbiotic systems, is well known in many crops. Because AM fungi require living roots of the host to complete their life cycle, the number of AM fungal spores in the soil and subsequent AM colonization of crop roots were enhanced with the cultivation of mycorrhizal crops. This enhancement is affected by the degree of mycorrhizal association of crops grown in previous seasons. Thus, preceding crops influence growth and P uptake of succeeding mycorrhizal crops. Enhancements of the growth and P uptake of succeeding mycorrhizal crops are influenced by the degree of AM symbiosis of preceding crops. Because of the high cost of AM inoculum and the usual predominance of indigenous AM fungi over inoculated AM fungi, effective utilization of the indigenous AM fungi is desirable. This improving effect is also dependent on the degree of AM symbiosis of succeeding crops. The improving effect is especially clear on crops grown under dry weather conditions because the efficiency of AM colonization of crop roots and the diffusion of phosphorus in soil are decreased with the decrease of soil moisture. The improving effect of AM colonization on crop growth is also clear when crops are grown in soils of high P-fixing capacity such as Andosol. To establish cropping systems efficient in P utilization, arranging crop sequence from the point of view of AM symbiosis is important for environmentally sound and sustainable crop production. AM symbiosis, however, does not always improve the growth of mycorrhizal crops even though they are grown on soils of low P availability and high P-fixing capacity. Factors involved in this scarce enhancement of growth have to be well understood to further extend P-efficient cropping systems over wider areas. Effects of soil properties, agrochemicals, and agronomic practices on AM symbiosis also are not completely clear. Additional research is necessary to explore interactions among environmental factors, AM, and host plants, and their benefits in different cropping systems.