Relationship between root uptake-weighted mean soil water salinity and total leaf water potentials of alfalfa

Abstract

Alfalfa was grown in five laboratory soil columns and irrigated at a fixed average amount per day. One column received tapwater at 6-day intervals; the others saline water (h o=−12 m) at intervals of 4, 6, 8, and 12 days. The alfalfa was harvested at 24-day intervals. The resulting widely varying distributions of soil water content, pressure potential and osmotic potential were measured in detail. From these data variously weighted mean soil water potentials were calculated and correlated with measured total leaf water potentials. This indicated that in the moist, saline soil columns the alfalfa plants tended to maximize the root uptake-weighted mean total soil water potential and, since the pressure potentials were generally high compared with the osmotic potentials, also the uptake-weighted mean osmotic soil water potential (minimize the uptake-weighted mean salinity). For the drier nonsaline soil column the leaf water potentials were much lower than expected from the soil water retention function. This was attributed to dominant resistance for water flow through the soil and across the soil-root interface.