Irrigation Using a "phytomonitoring" System
Experiment in Pepper Plants of Lorca and Parker

Eviatar Itiel, Yoram Zvieli - Negev Extension Service, Ministry of Agriculture and Rural Development
Rivka Offenbach, Rami Golan - Arava R&D Center
Aharon Barda, Moshav Tzofar


Summary

Pepper plants of Lorca and Parker varieties were grown in a commercial 25 mesh net-house in Moshav Tzofar. Phytomonitoring system ('Phytech' Company, Yad Mordechai) was installed in two irrigation treatment plots in mid-September, 2002: a) the control "Commercial" treatment in which the grower, based on his experience, made the water application decisions, and b) the "Phytech" treatment in which application decisions were made based on the analysis of the readings of the system's various sensors.



Beginning mid-October one could detect, based on sensors' night readings, VPD values that caused transpiration during night hours. (VPD = vapor pressure deficit - the difference between vapor pressure under saturation and the one actually measured.) In fact, based on these findings, the "Phytech" treatment received only night irrigations from mid-October till mid-March.

The number and timing of irrigations in the "Phytech" plots was determined based on the stem diameter sensor fluctuation readings in the Parker pepper.
 

This increase in yield fits the results obtained in a similar trial carried out a year earlier in the Lorca variety. There was only slight increase in the exportable percentage, since most of the additional yield consisted of deformed fruit (reason unknown) disqualified for export. Aside from this problem, night irrigation had no negative effects on fruit quality parameters including cracking, and this contrary to the common opinion on the negative effect of night irrigation on fruit cracking.

Considering the big demand of irrigation water in the dry hot season and the insufficient supply of water during the day time, night irrigation can greatly ease day-time water supply and distribution "bottle-necks" common in summer days in Moshav Tzofar.


Introduction, and Trial Aims

Last season, the pepper area grown under net-houses in the Arava Valley and Kikar Sedom was 4,700 dunam (470 hectare), accounting for 60% of all pepper grown in the region.

The micro-climate pervading inside a net-house is different from that inside a plastic-film covered greenhouse. There are autumn and winter nights in the Arava in which the VPD values rise and the plant loses of its water. To the extent the plant enters the morning following with a water deficit, it loses growth ability (see diagram 1). Setting the irrigation timing based on the phytomonitoring system, enables detecting such a situation in the plants through sensing stem diameter response to morning irrigation: if response as measured in stem swelling is large, it means there was a noticeable night moisture deficit.

There is also a clear technical advantage to night irrigation related to the water distribution limitations in Moshav Tzofar, where the system is over-loaded during day-time. Moreover, there are growers without water-strorage capacity who are forced to irrigate partially at night. Studying the effects of night irrigations is therefore important.


Methods and Materials

Pepper plants of Parker and Lorca varieties were planted in a net-house on 2 August 2002 on the Barda farm in Moshav Tzofar. There were two irrigation treatments planned: a) the control "Commercial" treatment in which the grower, based on his best knowledge and experience, made the water application decisions, and b) the "Phytech" treatment in which application decisions were made based on the analysis of the readings of the system's various sensors. Forty five days after planting the Phytomonitoring sensors were put in place, showing no reason to change the irrigation regime at that time. Based on sensor readings, the "Phytech" treatment was split from the "Commercial" one mid-October. Two beds for each variety X treatment were designated making for a total of 8 beds.

Representative plants in each of the two Parker variety "Phytech" treatment plots were monitored by means of phytomonitoring sensors of "Phytech" Company of Yad Mordechai.

The plant sensors included a stem diameter monitor, a leaf-sap flow monitor, a leaf temperature monitor and a fruit diameter monitor. Environmental and soil sensors were also installed - measuring radiation, air temperature, relative humidity and soil moisture.

As discussed above, for each variety two beds were selected for the "Phytech" treatment, on which the exact same irrigation regime was applied. Two yield sampling plots were marked in each bed, making for a total of 16 harvest plots - four for each treatment x variety. The fruit harvested was sorted and weighed in nearby Yair research station. The plots in fact do not constitute true replications since they could not be designated randomly. Results are therefore presented as averages only, without analysis of variance.


Results and Discussion

In relatively dry nights in which vapor pressure deficit (VPD) values can rise to quite a high level, night transpiration can account for 10% of total 24-hour day transpiration (Moreshet et al. 1999). The same work showed that rising night VPD values stops small fruit growth.

The results obtained (table 1) show a definite trend of increased total yield and number of fruits in the "Phytech" treatment in both pepper varieties, compared to the control. This increase began with early December harvests (diagram 2) in Parker var, while only in late March in Lorca var. This increase in both total yield and fruit number did hardly at all, however, result in increased exportable fruit (actually lowering exportable fruit percentage). The reason for this decrease in exportable fruit percentage in both varieties was due to the increased (doubled) number of deformed fruit, a phenomenon which began with December pickings in Parker (see diagram 3) and with end January pickings in Lorca. An explanation for this phenomenon could not be found so far.

It is commonly thought that night irrigation induces fruit cracking in tomato and pepper (Moreshet et al., 1999). However, in two years of night irrigation no effect on fruit cracking was observed at all.


Diagram 1. Rate of change in stem diameter and VPD, in night- and day- irrigation regimes

Table 1. Yield components in irrigation regime trial for pepper using Phytech phytomonitoring system