Modification of root properties with phosphate solubilizing bacteria and arbuscular mycorrhiza to reduce rock phosphate application in soybean-wheat cropping system

Inoculation of phosphate solubilizing bacteria (PSB) and phosphorus mobilizing arbuscular mycorrhiza (AM) with low quality rock phosphate (RP) can be an alternative source to one of the costliest phosphatic fertilizers in India, i.e. single superphosphate, by enhancing phosphorus influx and modification of root properties. Co-inoculation of PSB and AM may play a pivotal role to reduce phosphorus application through RP. Root properties and grain yield of irrigated soybean-wheat cropping system were evaluated with two levels of RP {100 and 50% recommended P (1.0 RP and 0.5 RP)} and different combinations of PSB and AM with 0.5 RP (0.5 RP + PSB, 0.5 RP + AM and 0.5 RP + PSB + AM) versus 100% recommended P application through soluble single superphosphate (1.0 SP) in the Indo-Gangetic plains. The P influx under 0.5 RP + PSB + AM and 1.0 SP were statistically at par with each other and the former treatment provided 0.6 and 3.2% higher value than the later in soybean and wheat, respectively. The root surface area density (RSAD) of soybean and wheat under 0.5 RP + PSB + AM (13.71 and 6.16 m2 m−3, respectively) and 1.0 SP (13.70 and 6.37 m2 m−3, respectively) were non-significant and almost equal with each other. The values of root cation exchange capacity and other root properties under 0.5 RP + PSB + AM and 1.0 SP were also non-significant. The improved root properties under 0.5 RP + PSB + AM provided statistically at par grain yield with 1.0 SP for both soybean and wheat crops. The yield under 0.5 RP + PSB + AM of soybean crop was 3.4% higher than 1.0 SP. The net returns US$−1 invested was significantly higher under 0.5 RP + PSB + AM compared to 1.0 SP for both soybean and wheat crops. Co-inoculation of PSB and AM with 50% of recommended P through RP could be recommended for better root properties and profitable grain yield of soybean-wheat cropping system in the Indo-Gangetic alluvial plains.