Phosphorus application affects root length distribution and water uptake of upland rice in a column experiment

Abstract

We investigated the effect of basal phosphorus application at 0–0.2 m depth (−P: 0 kg ha −1, +P: 120 kg P2O5 ha−1) on the root system development and water uptake pattern of upland rice (Oryza sativa L.). Applications were made toP-deficient soil, and plants were either irrigated or nonirrigated (subjected to short-term mild soil water stress) at the panicle initiation stage. P application enhanced the growth of nodal roots and medium-sized lateral roots (80–220 11-m in size). In the +P plants, root length per layer was longer in all the soil layers (p<0.01) and the percentage of the total root length located below 0.2 m depth was higher (−P: 18%, +P: 24% ). Under irrigated conditions, most of the water was extracted from 0–0.2 m depth regardless of the P level, and the water uptake rate from this layer and hence the total amount of water was higher in the +P than in the −P plants. Under water stress conditions, the water uptake at 0–0.2 m depth was lower than that under irrigated conditions, while the water uptake below 0.2 m depth was higher than that under irrigated conditions during the 0–2 d period after the imposition of stress in both −P and +P plants. Under water stress, since the water uptake from below 0.2 m depth was higher in the +P than in the −P plants, the total amount of water was higher in the +P plants. By promoting the development of deeper root systems and improving the water uptake below 0.2 m depth, basal P application at 0–0.2 m was found to be important for increasing the total water uptake by upland rice under mild soil water stress in phosphorus-deficient soils.