Determination of a suitable indicator of tomato water content based on stem diameter variation

- The MDS has the advantages of sensitivity and signal intensity in diagnosing tomato water content.
- The critical soil water baseline is 75%FC below which the water stress could be diagnosed by the MDS.
- The prediction equation of MDS consisted of VPDm and Rmax could be used as the baseline equation.

This paper describes a study on stem diameter variations (SDV) of tomatoes planted in a greenhouse on the North China Plain in autumn. The results indicated that comparing full irrigation (T0) and water stress (T1) treatments, the indexes of MDS (maximum daily shrinkage), predawn leaf water potential and midday stem water potential were all able to diagnose tomato water stress in a timely manner, but the MDS had the advantages of sensitivity and signal intensity that the others lacked. The critical soil water baseline was 75%FC, below which the water stress inner tomato stem was able to be precisely diagnosed by MDS. Statistical analyses of the MDS under T0 and T1 treatments as well as the main meteorological factors showed that the treatments were correlated according to linear correlations and quadratic polynomials respectively, and the key meteorological factors influencing tomato SDV in a greenhouse were the daily mean vapor pressure deficit (VPDm) and daily maximum radiation (Rmax). The prediction equation for MDS consisted of VPDm and Rmax,was able to predict the values of MDS under full irrigation exactly, which could be used as the baseline of the tomato water content diagnosing and irrigation planning.