Phosphorus placement and microbial inoculation effects on potato yield and phosphorus recovery

Potatoes (Solanum tuberosum L.) have been shown in previous studies to respond to P fertilizer on high-P testing soils. Response to P under these conditions may be due in part to their shallow root systems and poor associations with mycorrhizal fungi due to the use of fumigation to control soilborne diseases. This study evaluated the effects of P placement and microbial inoculation on tuber yield and P recovery in high-P soil. A field study with a split–split-plot randomized complete block design was conducted over 2 years, with whole plots defined by fumigation treatment (no fumigant or metam sodium) and subplots defined by cultivar (Ivory Russet or Russet Burbank). Each subplot was divided into seven sub-subplots by P treatment. Four treatments were used to evaluate banded versus broadcast P placement at 37 and 73 kg P ha⁻¹ without inoculant. Four treatments were used to evaluate the effect of broadcast P at 0 and 73 kg P ha⁻¹ with or without an inoculant. At equivalent P rates, banded P placement produced 4.8% greater tuber yield, 4.8% greater P uptake, and 5.0% greater P recovery efficiency (PRE) than broadcast placement. However, microbial inoculation had no effect on tuber yield, P uptake, or PRE with or without fumigation. High soil P or control of foliar fungi may have inhibited mycorrhizae. Overall, at equivalent P rates, banded P placement increased tuber yield even under high soil P conditions, but inoculation with arbuscular mycorrhizal fungi and other beneficial microbes had no effect.