One of the great innovations of winemaking in State of São Paulo, Brazil, is occurring in the municipality of Espírito Santo do Pinhal (latitude 22º11'27 "S, longitude 46º44'27" W, altitude 870 m), close to the border with the State of Minas Gerais. It is the transfer of wine grape harvesting to the winter season (June-August), when the thermal amplitude, insolation and absence of rainfall are better for harvesting, similar to the great wine regions of the world. Harvesting in winter is possible due to the management of double pruning, that is, instead of a single pruning, a pruning is done immediately after harvesting for the plant formation, and the second pruning is performed in January-February to start the grape production season. The exact date of its start is defined only at the last moment, based on laboratory analyses, field team observation and weather forecasts. The different terroirs that compose the vineyard are divided into plots, which are harvested separately. Only the best bunches are selected and harvested manually. The grapes are then transported carefully so that they arrive in perfect condition to the winery. In that growing area, altitude ranges between 1,000 m and 1,300 m, nights are cool and optimal sunshine during the day provides an air temperature range between 10°C and 12°C at harvesting time, similar to that of large European regions. Additionally, soil is developed from granite rock, with good drainage, which is especially suitable for grapes destined to the production of high quality wines.
The application of water by an irrigation system depends on crop, weather and soil. Therefore, the water management of irrigated systems must take into account, at least, criteria of one of these factors. Even with the availability of several criteria and procedures for the performance of irrigation management, its adoption by the farmers is still small. Occasionally irrigation is based on only the experience of the grower, on the visualization of the wet soil surface or even on the perception of visual symptoms of plant water deficit, which, when identified late, can affect yield and product quality. The lack of knowledge about irrigation management criteria and procedures can lead to the failure of this water application practice, even if there is a system properly designed for a specific cropping area. The determination of the crop evapotranspiration (ETc, mm) has its application in the irrigation management increased and enhanced as the use of automatic weather stations has been used to determine the reference evapotranspiration (ETo, mm). Based on specific crop coefficients for each phenological phase of the crop (kc), ETc can be easily estimated. However, irrigation management based on climatic parameters does not take into account the soil physical-water attributes. One of the peculiarities of irrigation management in wine grape cultivation is the reduction of soil water availability in certain phenological phases to obtain desirable characteristics in grape berries destined to winemaking. Thus, it is of concern to the grower / irrigation technician to know: 1) How much and at what soil depth the amount of water is being reduced? 2) If after this soil water reduction, the irrigation depth applied and estimated based on ETc is increasing the water storage capacity throughout the root zone? 3) When a rainfall occurs, at how much and at what soil depth the moisture has been increased ? 4) When the irrigation should be restarted?
The field experiment will be carried out in the municipality of Espírito Santo do Pinhal, State of São Paulo, Brazil, at Guaspari Winery. In one of their vineyards, the cv. Chardonnay, grafted on the Paulsen 1103 rootstock, was planted in 2008 in the 2.5 m x 1 m spacing, in a trellis system, and with plant conduction in the unilateral Royat cord system. The irrigation system is drip irrigation, with single hose and emitters spaced at 0.5 m, and measured flow of 1.9 L h-1. The experimental area has 1.1 ha (Figure 1).
Soil texture and soil water retention curves are already know, as well as their spatial variability over the area. An automatic weather station installed in the winery provides information for irrigation management based on evapotranspiration. Soil water content has been measured by tensiometers and capacitive sensor. Data has been manually collected, but not in all vineyards. Calculation for decision making on irrigation water application has been performed by an Excel spreadsheet.
Some objectives of the Guaspari Winery Pilot are:
- To perform automatic measuring of soil water content at different soil depths and in several vineyards inside the winery´s growing area;
- To transmit information about soil water content into a base (“cloud”) to be jointly processed with weather and crop information;
- To provide quick and accurate irrigation management information by a software developed specifically for the area.
The field operation for collecting data about soil water content in the several vineyards is laborious and time consuming. Moreover, some vineyards are far from others in a mountainous topography. That is a great difficulty to enhance irrigation water management based on soil water content in winery's growing area. Hence, it is expected an automatic soil water measuring, data transmission to the cloud for data processing, and a quickly and accurate decision making about irrigation management in the growing area.