PHYTOMONITORING TECHNIQUE FOR TUNING IRRIGATION OF FRUIT TREES

Transcription

1 PHYTOMONITORING TECHNIQUE FOR TUNING IRRIGATION OF FRUIT TREES Y.Ton, M.Kopyt, I.Zachs and Z.Ben-Ner PhyTech LTD., Yad Mordechai 79145, Israel Keywords: fruit trees, orchards, sensors, phytomonitoring, irrigation Abstract There are two standard techniques for scheduling irrigation of orchards: soil moisture monitoring and evaluation of evapotranspiration made with the use of standard pan or Penman-Montheich model. Limitations of these techniques are well known. Nowadays, the use of physiological indicators for assessing dynamics of plant water status has attracted attention of many growers and experts. The large-scale field tests of phytomonitoring technique and instrumentation were carried out in Israel in A few dozens phytomonitors were installed in apple, plum, peach, kiwi, mango, persimmon orchards and avocado, citrus, table grapes and banana plantations. Besides environmental factors, the trunk, shoot and fruit growth were subjects of monitoring. The phytomonitoring technique was used for fine-tuning irrigation scheduling according to two criteria: a good yield with less water. Encouraging results have been obtained in most cases. Many growers have reported substantial savings in water at due level of yield and quality. 1. Introduction All but most Israeli orchards are drip irrigated. In view of the growing limitations in use of water resources, farmers are looking for techniques, which enable them to minimize non-productive water losses and, at the same time, provide the expected yield and quality of fruits. Almost all modern irrigation-scheduling methods are based on the environmental factors such as soil moisture monitoring and calculation of water budget using Penman equation or standard pan. The phytomonitoring technique (Ton and Kleiman, 1987, Ton, 1997) was developed for early, objective detection of crop problems and on well-timed disclosing of crop response to measures, which a grower may undertake for improving irrigation. In the large-scale field tests of phytomonitoring technique and instrumentation were carried out in Israeli orchards and plantations under supervision of the Israeli Ministry of Agriculture. The present paper includes several application examples, which demonstrate a role of the phytomonitoring technique for tuning irrigation on commercial fruit trees plantations. 2. Materials and methods The standard phytomonitoring systems (Phytech Ltd., Yad Mordechai, Israel) were installed in apple, plum, peach, kiwi, mango, persimmon orchards and avocado, citrus, table grapes and banana plantations. A standard plant-related measurement set included four and more fruit growth sensors and two dendrometers. An environmental set consisted of soil moisture, solar radiation, air temperature, air humidity and wind speed sensors. All sensors were connected to a solar powered data logger with GSM modem for data transmission. In all cases, two adjacent visually representative plants located in the middle of a plot were selected for deploying replicated sensors. Standard allocation of sensors was used for providing data comparability. Dendrometers were settled on a base of trunk. Visually representative fruits were selected for monitoring growth. 127

2 The following main indications of plant status were used: trends of trunk and fruit daily maximums; response of the trends to variable environmental factors; trunk and fruit diurnal contraction (Ton, 1997; Kopyt et al., 2001; Y.Ton and M.Kopyt, submitted for publication). All indications were used both for short-term detection of physiological disorders (stresses) and for long-term analysis of plant water status and growth. 3. Results and discussion When to start irrigation season? This is one of the most important questions a grower should answer to. Presumably, it may be a time when plants begin to manifest considerable physiological response to developing water deficit. Negative deviation of trunk diameter trend in response to combined influence of gradually reducing soil moisture and cyclic daily variations of vapor pressure deficit (VPD) is a good indicator of soil water deficit. In Fig. 1a, a trunk was shrinking under growing drought conditions during May Next day (May 31) brought certain relief but water content had replenished only partially. The beginning of the irrigation season (June 1) induced positive turn of trunk diameter trend as well as acceleration of berry growth. Another example is shown in Fig.1b. In itself the negative trend of the trunk was a sign of water stress. On April 18, a beginning of irrigation led to a positive turn of trunk diameter trend and dramatic acceleration of fruit growth as well. Next example demonstrates a growth retardation effect of a water stress. The results of fruit size monitoring of two separately irrigated plots of avocado plantation are presented in Fig.2. The first treatment (NORM) was irrigated as usual. The second one (LOW) received less water (70% from NORM). The normally irrigated plants showed continual fruit growth during almost the whole observation period. Four days long air drought attack caused only temporary depression of fruit growth. Fruit growth of less irrigated plants was not uniform even in favorable conditions. Negative trend of fruit size was observed repeatedly. The trial-and-error phytomonitoring approach (Kopyt et al., 2001; Ton et al., submitted for publication) also demonstrated its efficiency in tuning irrigation scheduling. An example is shown in Fig.3. Higher volume of each irrigation pulse had good consequences in the trunk and fruit growth of apple tree. Similar effect was observed on pomelo in result of an extra daily watering (Fig.4) as well as on persimmon when daily watering has been applied after less frequent irrigation period with the same average daily irrigation norm (Fig.5). A successful attempt of saving water discharge is presented in Fig.6. An avocado grower changed twice-a-day irrigation regime to one daily watering with lower water norm. Because of no evident depression of trunk and fruit growth, it was concluded that preceding irrigation had been superfluous. An example of comparative examination of two irrigation techniques is shown in Fig.7. A regular daily watering and multiple pulses watering with the same water discharge were tested on persimmon trees. The second regime provided higher tolerance of fruit growth to drought attacks. Fruit daily contraction was also less pronounced for pulse irrigated plants. In this case even a short-term monitoring allowed distinguishing effect of different irrigation techniques. The trial applications described above confirmed effectiveness of the phytomonitoring technique for tuning irrigation in accordance with the local environmental conditions and plants peculiarities. Many growers reported substantial savings in water and improved fruit quality and size. The experts and growers have 128

3 gained beneficial expertise in using of phytomonitoring indicators, resulting in developments of application protocols applicable for most of irrigated orchards. Acknowledgements The study was supported by the Israeli Ministry of Agriculture. References Kopyt M., Ton Y., Ben-Ner Z. and Bachrach A., A trial of the phytomonitoring technique for roses. Acta Horticulture. 547: Ton Y. and Kleiman E., Phytomonitoring technique for investigating plant water status. In: M.Kushnirenko (ed.). Water relations of agricultural crops (rus.). Stiinta, Kishinev, Ton Y., Phytomonitoring system. IV International congress on new agricultural technologies. Puerto Vallarta. Jalisco. Mexico: a b Fig.1. Effect of beginnig irrigation season on trunk diameter and fruit growth. (a Table grapes, Lakhish, 2000; b Lemon, Yad Natan, 2001) 129

4 Fig.2. Effect of normal and reduced irrigation (70% of the norm) on fruit growth. (Avocado, Afikim, 2000) Fig.3. Effect of higher irrigation norm on trunk and fruit growth. (Apple, Manara, 2001) 130

5 Fig.4. Effect of higher irrigation frequency with the same daily norm on fruit growth. (Pomelo, Yad Mordechai, 2000) Fig.5. Effect of new irrigation schedule on trunk and fruit growth. (Persimmon, Mor Aviv, 2001) 131

6 Fig.6. Zero effect of reduced irrigation on trunk and fruit growth confirmed possibility of saving irrigation water. (Avocado, Maagan Mikhael, 2001) Fig.7. Examination of two irrigation techniques with the same daily irrigation norm. (Persimmon, Bizaron, 2000) 132