ARE WE MANAGING THEM TOWARDS A QUALITY WINE OUTCOME?
Through our involvement with the wine industry, we are very aware of the limited use that is made of information that can be gained from soil and tissue testing. There appears to be considerable potential to improve soil and vine nutritional management in relation to vine health and crop quality in many vineyards by making better use of soil and tissue analytical data. Over the last ten years this has become even more pronounced, especially in light of our increasing understanding of soil fertility and biological process, and our improved understanding of vine nutrition issues and vine physiology. In the last few years we have started to actively try to integrate these different aspects of the vineyard. Discussions with viticulturists and consultants resulted in a request to put some thoughts on paper.
There is a considerable chasm between nutrient management in the vineyard and our aim to produce quality grapes. There appears to be insufficient recognition of the effects that soil management and fertilisers (can) have on quality.
Often the only recognised links between soil fertility and grape quality are the effects that nitrogen has on vigour/canopy/quality, and the effect of potassium application on juice potassium and pH.
Apart from that, soil and fertiliser management is often only reactive and not integrated with petiole/blade analytical data and juice parameters (desired and actual).
If soil samples show deficiencies, some fertiliser will be applied. If petiole samples show deficiencies a foliar spray may be applied. However, typically here is no coherent nutrient, soil and vine management system in place. Information from soil samples and petioles is not used to its full potential (effect on vine health and production, and grape quality) and is not properly retained/documented for easy future access.
In many cases there is little communication between the winemaker and the person making the fertiliser recommendations/decisions.
This is surprising, if one compares it with the way canopy management and irrigation management has been geared towards quality management in recent years.
One of the reasons for this lack of integration is probably poor understanding of soil fertility, it’s effects on vinegrowth, grape production and grape quality. In addition to fertiliser effects there are issues of soil structure/compaction, and the effects of soil biological activity on vine performance and crop parameters.
These are quite specialised areas, and availability of information in relation to many of these issues has been rather poor until recently. And indeed, there are still a significant number of such issues where our knowledge is lacking and further work is needed.
However in our opinion there is now considerable scope to integrate soil management and vine nutritional management in such a way that we can manage towards certain outcomes (crop quality).
Towards Integrated Management
Below we have identified some (potential) areas where we believe progress can be made in relation to soil/vine management. Some of these aspects can be implemented at little cost. Others involve significant commitment and investment of especially time. Some aspects need more research before that can be implemented fully. Gathering information to better understand relationships between soil, vine and grape is only possible when we have better systems documenting results and actions (fertiliser applications etc.). Consequently, some of these areas could be implemented almost immediately, others will need further finetuning based on closer monitoring of vineyard parameters.
- Improve soil and petiole/blade data collection. Reduce variability by taking samples from the same places (or vines) at certain times. Soil analyses should include more than just the basic analyses, include sulphur, sometimes a second phosphorus test (Olsen test has shortcomings in certain situations), add boron (and sometimes other trace elements) and of course organic matter. When setting up this system, additional baseline data may be considered like total nitrogen, total phosphorus, potassium and total and/or organic sulphur. It is important to know subsoil parameters (pH, major elements, and in some cases soluble salts and chlorides). These extra tests are not required on an annual basis. Formulate a testing program (what/where/when/how) so testing is consistent.\
- Integrate soil, petiole and blade analytical data in a database system. This should also include information regarding the vineyard block (variety/rootstock, fertiliser and foliar application made etc.). Very few vineyards have soil/petiole/blade analyses and fertiliser and foliar application data in (electronic) databases in such a way that they are easily retrievable per block/variety/rootstock/season. Integrating these data is the first step for better management. Not only does this provide a good tool for analysis of fertiliser practices, soil fertility trends etc, it may well become a requirement (need for better vineyard documentation systems and for full traceability). It is important these data are linked to variety and rootstock so that effects of both can be taken into account. SO4 rootstock effects on potassium and magnesium uptake are well known, but more information is now gathered regarding other rootstock nutrient uptake effects. There are also significant differences between varieties that need to be taken into account when interpreting petiole results for instance (pinot noir-phosphorus for instance). Use interpolation of desired values for petiole/blade samples collected outside the flowering or veraison standards.
- Increase (in house) knowledge and utilise external knowledge in relation to soil management, vine nutrient management and vine health, production and grape quality parameters. This includes better interpretation of soil and petiole/blade data. For instance understand relationships between (petiole and blade) nitrate N and total N. At first sight they often seem to contradict each other, understanding N metabolism often helps explain what is happening. Better understanding of which nutrients are best measured in petiole sample and which in a blade (mobile against less mobile nutrients). To name some other examples; the vines ability to defend against a number of pathogens can be enhanced by ensuring certain key nutritional elements are in place (for instance calcium to increase cell wall strength, making it harder for pathogens to breach the cell wall structure). The vine’s own “immune system” can be primed to further maximise defence capabilities by using natural elicitors which increase resveratrol levels. Another example is the role boron plays in carbohydrate metabolism and transport as well as flowering and fruitset, effects of phosphorus on acids and bouquet. Effects of magnesium on sugars and colours and tannin flavours. Nitrogen management in order to ensure good flowering/fruitset, yet control excessive vigour. There still are a number of areas that need further study, for instance possible relationship between low sulphur and “stuck” fermentations due to low levels of key amino-acids.
- Define primary desirable quality parameters (juice pH and potassium, juice nitrogen parameters, total acids etc.). Relate these back to soil/petiole nutrient status, and where needed, explore changes that lead to desirable outcomes. For instance high potassium can be managed in a number of ways using regular calcium and magnesium application to the soil. Boron also plays a potentially important role in managing effects of high soil potassium. Improving root activity will enhance calcium uptake. Soil moisture management may play a role; wet conditions after a long drought can release high levels of plant available potassium on soils containing certain clays. Promoting mycorrhizal fungi will help calcium, zinc and phosphorus uptake.
- Identify secondary issues which may respond to targeted soil/vine nutritional management. These include BSN, poor flowering, berry splitting, high incidence of fungal disease. Many of these have a nutritional component, such as nutritional imbalance, straight deficiency or excess of one or more elements. Apart from a straightforward soil nutrient imbalance, these could also be associated with soil conditions leading to poor or excessive uptake (waterlogged cold soils, compaction effects, root damage due to nematodes or phylloxera affecting nutrient uptake, effects of soil biological activity including effects of beneficial organisms like mycorrhizal fungi). Most vineyards will be confronted with at least one of these issues, understanding the effects on vine performance will help manage the problem.
Ongoing work is taking place in all of these areas, but there are some very exciting tools available now, that can be used to manage our crop better. Without a doubt the first steps would be to improve data collection (soil/petiole testing) and integrate the information in a database.
At the bottom of all management lies understanding and information. Understanding of the processes (soil/vine) and systems involved, and information in the form of measuring essential data (soil/petiole/blade/juice etc.) on which nutrient management decisions can be based.
The saying: ”There can be no management without measurement” certainly applies here.
AgConsult has provided soil and tissue test interpretation services to the wine industry for many years. Very few people would disagree with our observation that there is significant potential in better integrating soil/vine management with the oenological objectives. We felt it is time to do something about it, and have in the last few years been starting to work towards that goal.
Last year we started integrating test and vineyard data into a database format as a nutritional management tool. This year we have made this database nutrient management system available to a number of our clients, with full commercial release planned in 2004.
Ing, CPAg, mNZIAS, mNZSHS, mISHS
Senior Soil Consultant