Impact of regulated deficit irrigation on the physiological characteristics of two rapeseed varieties as affected by different potassium rates

Abstract

A field trial was conducted at experimental field of Qazvin region, Iran (36° 18´ N and 49° 57´ E) in 2008/2009 and 2009/2010 growing seasons to determine the physiological properties of rapeseed varieties (Zarfam and Opera) subjected to drought stress condition under different potassium sulphate levels. The trial was laid out in a factorial experiment based on a randomized complete block design with three replications. Irrigation regimes included I₁, irrigation after 40% (control); I₂, irrigation after 60% and I₃, irrigation after 80% soil water depletion (SWD). However, the applied potassium rates were K₁, non-application, K₂, 100 kg ha^-1 and K₃, 200 kg ha^-1 of K₂SO₄. Physiological indices including relative water content (RWC), stomatal resistance (RS), canopy temperature (T_c), and the difference between canopy and air temperature (ΔT) were measured at three stages. Both varieties regarding physiological indices in all sampling stages showed a significant difference. Higher relative water content (RWC) and lower stomatal resistance (RS) and canopy temperature (T_c) in Opera variety under limited moisture condition indicated its salient drought tolerant over Zarfam variety. Results show that with increasing stress severity in all growing stages, the decrease in RWC and increase in RS and T_c was higher when compared with the control which asserts their susceptibility to soil water condition and leaf water potential. Potassium application, in both stressed/non-stressed conditions caused a lower RS and T_c, but increased RWC. To sum up, K₂SO₄ could ameliorate negative effects of water stress on physiological properties and consequently improve them. RWC, RS, T_c and ΔT, are beneficial indices for screening large numbers of drought-tolerant rapeseed varieties in a short time at critical stages of crop growth.

Key words: Brassica napus L., canopy temperature, potassium fertilizer, relative water content, stomatal resistance, water deficit stress.