Table Grape (Vitis vinifera L.) is the main exporting horticultural crop in Chile, with the country being one of the top exporters at the world level.

Commonly, grape producers perform trials of different commercial products which are not evaluated in an objective way. On the other hand they do not have the tools to easily identify areas within the field that may have some limiting factor. The use of active ground sensors that pass under the canopy several times during the season may be a suitable tool to solve these problems. In this regard, in an average field, producers go under the canopy > 20 times during the season to perform different managements, occasions that could be used to monitor it.

In order to assess the use of active ground sensors to evaluate commercial treatments and to define areas with potential limiting factors, two field studies were carried out in the Central Region of Chile during the 2014/2015 season.

In the first study three table grape fields var. Red Globe with a commercial treatment and two with a control treatment (producer) were evaluated. Fields had an average area of 3 ha. After application of the treatments, the canopy of each field was evaluated through the use of the OptRx sensor (AgLeader Technologies, Inc.) which was operated about one meter from the canopy, from an ATV, below the grapevine. The OptRx is an active three-band sensor, Red, Red Edge and near infrared (NIR), from which the NDVI was calculated. Evaluations were carried out on October 9, October 30, November 10, and December 5 2014; and January 12 and 28 2015. Within each field a systematic grid of 20 points was established; at each sampling point the number of clusters / plant and weight of bunches in four evaluation dates were determined: 12/5/2014, 1/12/2015, 1/29/2015 and 3/3/2015, the latter date to harvest. At harvest, the grapes collected at each point were assessed for: number of berries / bunch, berry weight, pH and Brix. Regression models using NDVI as an independent variable were developed to evaluate treatment effects.

In the second study, several fields of two table grape varieties (Thompson Seedless and Red Globe) were evaluated using the OptRx sensor in January 2015.  With sensor data NDVI was estimated for each field. Fields were classified in three vigor zones (low, medium, and high NDVI). Each zone was sampled using composited soil samples and several chemical, microbiological and biochemical (enzymatic activity) were determined at 0-30 cm depth. Zones of low vigor of the Thompson Seedless variety were amended using compost and fields evaluated again one year later. Analysis of variance was used to evaluate the effect of zones on selected soil properties.

Results indicated that OptRx sensor is a simple and useful tool to study canopy changes in table grapes. The NDVI from the sensor is a good variable to incorporate in regression models to evaluate modest treatment effects. Stratified sampling using NDVI allowed identifying few soil properties that may explain plant vigor.