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A field study was established in 1986 on a Viborg silty clay loam (fine‐silty, mixed, mesic Pachic Haplustoll) soil in eastern South Dakota. The objectives were to quantify the influence of crop rotation, tillage, and residual P (254 kg P ha−1 applied in fall 1985) on the incidence of vesicular‐arbuscular mycorrhizae (VAM) of corn (Zea mays L.) and to define the relationship between VAM colonization, early growth response to P, and early P uptake of corn. Plant and root samples were collected periodically from plots that varied in tillage and previous crop. Crop rotation and tillage influenced the early growth and P uptake of corn. Large differences in early growth response to P were observed among cropping systems. Average relative growth response as compared with the check during both years ranged from 360% for the moldboard (MP) corn‐fallow rotation to 7% for the ridge‐plant (RP) corn‐soybean (Glycine max [L.] Merr.) rotation. Early dry‐matter production and P uptake in the check plots were highest in the RP corn‐soybean system and lowest in the MP corn‐fallow system. Generally, VAM colonization rates were significantly higher (P ≤ 0.10) in the RP systems than in the MP systems. Considerable reduction in VAM colonization rates were found with P fertilization (P ≤ 0.01) in all cropping systems. An inverse relationship was measured between VAM colonization and relative early growth response to P (Y = 647.0 − 49.4X + 0.97X2; R2 = 0.92; Y = growth response in percent, X = percent root length colonized). Considering early dry‐matter production, P uptake, and mycorrhizal association the RP corn‐soybean system appears to provide a good environment for P nutrition of corn during early vegetative growth.

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