Development of an Automatic Irrigation Method Using an Image-Based Irrigation System for High-Quality Tomato Production

Fei Zhao,Eiji Goto,Hideo Yoshida,Shoko Hikosaka

doi:10.3390/agronomy12010106

Abstract

In this study, we developed an automatic irrigation method using an image-based irrigation system for high-quality tomato production in a greenhouse by investigating effects of a diurnal periodic cycle of irrigation on the photosynthesis, growth, yield, and fruit quality of tomatoes. The diurnal periodic cycle in a moderate wilting–full recovery treatment (MR) with a medium threshold value was more frequent than that in a severe wilting–full recovery treatment (SR) with a high threshold value. Mean daily maximum wilting ratios for MR and SR were 7.2% and 11.3%, respectively, when wilting ratios were set to threshold values of 7% and 14%, respectively. Total irrigation amounts in MR and SR were similar and lower than that in the untreated control. Net photosynthetic rate decreased under water stress, with values in MR being higher than that in SR, and recovered rapidly to more than 90% of its maximum value following irrigation. Plant growth and fruit yield per plant in MR and SR were lower than that in the control. Water stress treatment could improve fruit quality when it commenced at the anthesis stage or early fruit development stage. Total irrigation amount was a more important parameter than the threshold value for controlling the growth, yield, and fruit quality of tomatoes.

Highlights

Compared with standard cultivated tomatoes in a greenhouse, high-quality tomatoes have higher Brix and acidity values [1,2], and the demand for these superior fruits is growing concomitant with ongoing increase in living standards
We found that commencing water stress treatment from anthesis stage or the early fruit development stage was an effective strategy for improving fruit quality, whereas commencing treatment at the fruit ripening to mature stage was ineffective
We demonstrated the usefulness of the automatic irrigation method based on a diurnal periodic cycle of wilting–full recovery, which controls the wilting level and irrigation amount per time in the production of high-quality tomatoes in a greenhouse

Summary

Introduction

Compared with standard cultivated tomatoes in a greenhouse, high-quality tomatoes have higher Brix and acidity values [1,2], and the demand for these superior fruits is growing concomitant with ongoing increase in living standards. Recent studies have reported that wilting conditions in tomato plants can be digitized based on real-time monitoring of factors such as stem diameter [12], leaf temperatures using infrared thermometry [13], plant weight [14], projected leaf area using photo-image analysis [15] and artificial intelligence [16,17], for high-quality tomato production. In a number of these studies, researchers have monitored diurnal periodic cycles of wilting–recovery and irrigated when wilting conditions reached a certain threshold value. Few of these studies have sought to investigate the optimal irrigation amount per time and the set point of the threshold value for starting irrigation (hereafter, referred as ‘threshold value’) as the wilting level

Objectives

Methods

Results

Discussion

Conclusion