Improved irrigation scheduling for pear-jujube trees based on trunk diameter sensing data
A suitable indicator for scheduling pear-jujube (Ziziphus jujuba Mill.) irrigation in China was developed based on trunk diameter fluctuations (TDF). Parameters derived from TDF responses to variations in soil matrix potential (Ψsoil) were compared under deficit and well irrigation. Maximum daily shrinkage (MDS) increased with higher Ψsoil, whereas daily maximum trunk diameter and daily growth decreased with lower Ψsoil. MDS signal intensity (actual MDS/reference MDS) to noise ratio was highest in response to higher and lower Ψsoil. The advantage of MDS in automatic irrigation scheduling compared with other TDF-derived parameters was its prompt reliable response to water deficit, with less effect of phenophase. Based on the MDS signal threshold values, the Ψsoil without irrigation-related stress was in the range of -40 to -25 kPa during anthesis and setting, and -53 to -35 kPa during fruit development. The MDS signal was around 1.30 when the Ψsoil ranged from -80 to -67 kPa during fruit development, indicating drought stress. In addition, leaf water use efficiency increased under these conditions, but photosynthetic rate and transpiration rate decreased. Vegetative growth was reduced, but individual fruit weight increased and compensated for yield losses caused by water deficit. These values can facilitate precise irrigation and deficit irrigation of pear-jujube in China.
Key words: Drought stress, trunk diameter fluctuations, soil matrix potential, jujube (Ziziphus jujuba Mill.), anthesis and fruit-setting periods, fruit development period