Vineyard water use – Adapting to change
The GWRDC/CSIRO project ‘Vineyard water use – adapting to change’ has been successful in developing innovative tools to assist in irrigation management. The project has addressed two critical issues, that of determining how much water a vineyard has used and the effects of poor distribution uniformity of irrigation water. The IrriGATEWAY system combines the use of satellite technology to determine individual block water use with text messaging to deliver the information in an easy to use format to the irrigator. This system has been successfully trialed with 70 irrigators in the Riverina region. Poor distribution uniformity of drip irrigation systems has been tackled by developing a system whereby field measurements can be taken and run through an online system to provide easy to understand information to the grower. These tools can be viewed at: http://www.irrigateway.net/tools/
Water scarcity is an acute problem for grape growers. The need to enhance their water use productivity, i.e. tonnes/ML and $/ML is of critical importance. However, there continues to be widespread uncertainty about how precisely to manage irrigation. This is evidenced by still less than 10% of the irrigation industry using any form of objective decision making regarding irrigation scheduling (Montagu et al., 2006). The situation maybe better in horticultural crops such as grapevines, but the uptake of the current best practice approach of irrigation scheduling by soil moisture monitoring and/or by water balance is still low. There remains to be developed a robust, cost effective and industry acceptable model for irrigation scheduling.
This project has undertaken fundamental research to determine vineyard water use in red and white varieties in the Riverina region. Using multiple measurement systems such as Bowen ratio (energy balance), water balance and sap flow sensing, it has been possible for the first time to establish the total water use and evaporative and transpiration components of vineyard water use in the Riverina region. This data has been used to derive crop factors (Kc) for use with the FAO56 approach of determining crop evapotranspiration as a function of potential evapotranspiration scaled by a crop factor. However, it is clear that the water use, evaporation:transpiration relationships and crop factors developed are only applicable to those particular vineyards with their particular layout, soils, varieties and management. Also the crop factor will vary from year to year depending upon the season, disease, age of crop, management etc. This has been the major hurdle for widespread adoption of the FAO56 approach. The approach itself is robust and well accepted worldwide.
The requirement for individualised (to block/vineyard) crop factors that also take into account year to year variation is unsurmountable when using traditional monitoring techniques. This project therefore explored the use of satellite data which is low cost, has complete spatial coverage and has the required time interval to provide relevant information. A relationship was developed between the field derived crop factors (Kc) and the satellite data derived normalised difference vegetation index (NDVI). This relationship was then tested against other vineyards in the region and was found to adequately predict vineyard water use.
Having developed the techniques to derive water use from satellite data, a delivery mechanism to provide that data in a timely and easy to understand format was required. The project determined that the most understandable format for the data was in terms of pump run times and the best method of delivery was by text message (SMS) to mobile phone. The combination of the satellite derived vineyard water use and text message information delivery was set up via the IrriGATEWAY server and tested with 70 growers in the Riverina region for season 2008/09. This trial was highly successful with the bulk of irrigators closely following the system and reporting high levels of productivity. See the system at http://www.irrigateway.net/tools/sms .
This satellite and SMS system shows great potential to provide a practical, affordable and widely applicable irrigation scheduling service. As such GWRDC has funded a follow up project (Vineyard Irrigation – delivering water savings through emerging technology) to expand trials in the Riverina and N.E. Victoria regions.
Non uniformity of growth in vineyards has been widely recognised. The impacts of this on yields and quality have been investigated. However, the impact of irrigation application variability and its’ management is less well understood. This project undertook numerous field analyses of the spatial variation of drip irrigated vineyards in the Riverina and N.E. Victoria region. The results were surprising in that the spatial variation was higher than would be expected under drip irrigation. The highest distribution uniformity measured was 85% and the lowest an extraordinarily poor 32%. These results indicate that there is a poor appreciation in the industry of the importance of distribution uniformity in achieving high water use productivity. This lack of appreciation is evident both when purchasing new drip systems and in the operation and maintenance of existing systems. Currently there is not an accepted practice of routine monitoring of drip irrigation systems, and especially there is no practice of field measurement of spatial variation in the output of drip systems. This lack of standard practice means that the full benefits of adopting drip irrigation are not being achieved. Due to high levels of both under and over watering leading to increased pumping and fertiliser costs and reduced water use productivity. This project demonstrated that simple maintenance of flushing a system could increase the distribution uniformity by 10%.
The lack of appreciation of the importance of a high distribution uniformity maybe associated with the terminology used. The expression of distribution uniformity as a single term, as a percentage, communicates little to the grower as to the importance of uniformity across a block or vineyard. This project has developed the use of maps to demonstrate the irrigation variability in a block and to also express this as the total application over a season in ML/ha. In this way a grower can easily understand that the distribution variability of 85% in their block actually leads to a variation in seasonal application of 2 ML/ha between the highest and lowest areas and an equivalent variation in nitrogen fertiliser application.
The project has developed an online tool that allows a grower to take their field readings of dripper output rates and have them automatically processed to produce a contour map of variation in instantaneous and seasonal irrigation application and a percentage distribution uniformity http://www.irrigateway.net/tools/du. This tool is ready for wider application and promotion.