Grain Sorghum Response to Arbuscular Mycorrhiza and Phosphorus Fertilizer under Deficit Irrigation

Deficit irrigation systems have been considered as practical strategies to overcome shortage of irrigation water in arid and semiarid regions. To assess the response of grain sorghum [Sorghum bicolor (L.) Moench] to deficit irrigation and whether arbuscular mycorrhizal fungi (AMF) can moderate drought stress influence on grain yield, a 2-yr field experiment was conducted using split-split lay out on a randomized complete block (RCB) design. Irrigation (full and deficit) was assigned to the main plots. Subplots were allocated to two genotypes (Kimiya and Speedeh) and P sources viz: no fertilizer, sole chemical P fertilizer, seed inoculation with AMF and combined fertilizer (50% of the chemical P fertilizer + AMF) were assigned to the sub-subplots. Results indicated that deficit irrigation reduced grain yield of Kimia and Speedeh by 16 and 26%, respectively, while improving their irrigation water use efficiency (IWUE). Grain yield adjustment by sorghum to water stress was mainly through reducing the number of grains per panicle rather than grain mass. Application of all forms of P fertilizer improved grain yield of sorghum; however, under drought stress, plants were more responsive to combined fertilizer and used irrigation water more efficiently. The root colonization percentage was greater in Kimiya than Speedeh under full and deficit irrigation, however, both genotypes showed a lower degree of root colonization under drought conditions. Application of combined fertilizer could be considered as an alternative to chemical P fertilizer when irrigation water is limited.