Leaf osmotic potential as an indicator of crop water deficit and irrigation need in rapeseed (Brassica napus L.)

Leaf osmotic potentials (l_ψ0) of field-grown rapeseed Brassica napus L. were measured in 1975 and 1976 under rainfed conditions and at two levels of irrigation. Irrigations were scheduled on the basis of tensiometer measurements in 1975, and on the basis of l_ψ0 in 1976. The l_ψ0 of rainfed plants was lower (more negative) than that of irrigated plants. Leaf osmotic potential responded to changes in soil moisture caused by precipitation or irrigation. Tensiometers placed at 0.2 m depth in the high irrigation treatment were as responsive to soil moisture changes as l_ψ0. Tensiometers placed at 0.4 m depth in the low irrigation treatment were less responsive than l_ψ0. Scheduling of irrigations on the basis of l_ψ0 in 1976 produced yield differences between water regimes similar to those obtained in 1975. Leaf osmotic potential provides a satisfactory means for determining need for irrigation in B. napus.