Trunk growth rate frequencies as water stress indicator in almond trees

Abstract

The continuous monitoring of water stress will increase the accuracy of the deficit irrigation scheduling. Almonds are very sensitive to water stress conditions and an important water consumer. Recently, a novel approach to the use of trunk growth rate (TGR) data has been proposed for olive trees. These works suggested the use of TGR frequencies to evaluate water status of the trees. The aim of the current work was to compare the seasonal pattern of three different indicators derived from the daily curves of trunk diameter fluctuations with midday stem water potential. During three consecutive seasons (2017–2019), an irrigation experiment was carried out in a mature almond orchard (cv Vairo) at Dos Hermanas (Seville, Spain). Four irrigation treatments replicated in four blocks were evaluated using the daily curves of midday stem water potential and trunk diameter fluctuations. The different irrigation treatments were: Control, full irrigated conditions; RDI-1 (irrigation scheduling based on midday stem water potential with a deficit irrigation during kernel filling [values around − 1.2 MPa]); RDI-2 (similar to RDI-1 but with a more severe water stress [− 2 MPa]) and incomplete recovery after harvest due to limitation of the seasonal amount of water (around 100 mm); SDI, sustained deficit irrigation with a seasonal applied water equal to RDI-2. Trunk diameter fluctuations were measured with a wireless band dendrometer. The daily curves were processed to obtain three different indicators. Maximum daily shrinkage (MDS) was the difference between the daily maximum and minimum. Trunk growth rate (TGR) was the difference between two consecutive daily maximums. The frequencies of several ranges of TGR were compared with the midday stem water potential. Weekly frequencies of values greater than 0.3 mm day− 1 decreased with the reduction of midday stem water potential, but the pattern changed greatly in different seasons. The weekly frequency of values between − 0.1 and 0 and between 0 and 0.1 mm day− 1 were steadier in different seasons. Differences between seasons were related to growth pattern and yield.