Growth and physiologic response of rapeseed (Brassica napus L.) to deficit irrigation, water salinity and planting method

Salinity and water stress reduces the ability of plant to take up water and decrease
growth rate, photosynthesis rate (An) and stomatal conductance (gs) of plants. In this
study, effects of deficit irrigation with different salinity levels and planting method
(in-furrow and on-ridge) as strategies for coping with water and salinity stress on
physiologic properties of rapeseed was investigated in a two years experiment.
Irrigation treatments consisted of full irrigation (FI) and 0.75FI and 0.50FI in first
year and 0.65FI and 0.35FI in second year and salinity treatments of irrigation water
were 0.6 (well water), 4.0, 7.0 m and 10.0 dS-1 in first year and 0.6, 4.0, 8.0 and 12.0
dSm-1 in second year. Planting in-furrow increased seasonal dry matter by 8.4 and
9.6%, respectively at first and second year (with frost occurrence in dormant period
in second year) relative to on-ridge planting. In-furrow planting increased maximum
leaf area index compared with on-ridge planting by 12.8% for second year. Deficit
irrigation and salinity decreased dry matter, leaf area index and had no significant
effect on crop growth rate (CGR) and relative growth rate (RGR). Decrease in
applied water resulted in lower stomatal conductance (gs) and photosynthesis rate
(An) and salinity had no significant effect on these traits. Ratio of photosynthesis rate
to transpiration rate (leaf scale transpiration efficiency, An/T) decreased when leaf
vapor pressure deficit (VPD) increased and in water and salinity stress conditions,
transpiration efficiency of rapeseed decreased. A linear function between An/T and
VPD with negative slope indicated that in higher VPD, An/T decreased, therefore in
water stress condition or in arid and semi-arid region in comparison with humid
region An/T of rapeseed decreased. There was no significant difference between the
effects of water salinity levels (up to 12 dS m-1) and planting method on slopes of the
relationships between An and gs and VPD. As forage plant, rapeseed can be
cultivated in soils with salinity of 3.4 dS m-1 and 11.7% deficit irrigation can be
imposed without dry matter reduction and in-furrow planting method was proposed
in salinity and water stress conditions in comparison with on-ridge planting.