Root interactions and tomato growth in tomato/potato onion companion-cropping system under different phosphorus levels

When two plants interact, changes in plant growth are usually related to variations in root distribution and phosphorus (P) levels. However, root distributions and root tendencies are difficult to study because root systems grow beneath the soil surface. In this study, a transparent root box was used to observe interactions between root systems in situ, and the relation between tomato growth and root proliferation at different depths and distance from the rows at no P added and 120?mg kg^-1 P added levels were also tested. We found that tomato shoot and total biomass increased and roots grew deeper when companion cropped with potato onion under both P levels. Moreover, tomato roots tended to grow away from the potato onion roots. Our results suggest that a deeper and more evasive root distribution may be related to the increased plant growth of tomato when companion cropped with potato onion.