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Summary

This literature review presents a global overview of the current level of knowledge and the state of play of compost use in viticulture, drawing on research results mainly from Europe and to some extend from North America.

Only a limited amount of information was available that related directly to the use of compost derived from source separated organic waste in viticulture. Therefore the report was complemented with results obtained in related research. It appeared that the organic vine growing industry had a leading role in developing and researching the use of compost in viticulture.

A wide range of municipal and commercial/industrial organic waste materials can be composted with source separated green and food waste being the most common input materials. Biosolids can be co-composted relatively easily with green waste. However this is not common practice in Europe, mainly due to high heavy metal densities in biosolids and potential marketing problems. Most European countries have compost quality standards, which prescribe among a wide range of criteria maximum permissible heavy metal densities. Broadly speaking they are similar to the NSW EPA Grade A Biosolids Standards, except for cadmium which is considerably higher in the NSW Standards.

The use of compost in viticulture can, as in other agricultural/horticultural applications result in a wide range of positive effects. However, there is also scope for potentially detrimental effects.

The use of compost replenishes soil humus, which is reduced particularly in cultivated soils; in Germany for example at a rate of approximately 4 t/ha per year. Long-term compost use has been shown to increase organic matter levels and it is assumed that compost dressings of 8 – 10 t dry matter (dm) are sufficient to maintain or increase soil organic matter levels.

Compost contains all macro- and micronutrients essential for plant growth. However, not all nutrients are readily available in mineral forms for plant uptake. Considerable amounts of nitrogen and phosphorus are organically bound in the compost and are released only once the organic matter is mineralised through microbial activity. The level of readily available mineral nitrogen contained in compost and the degree of nitrogen release due to the mineralisation process following compost application are of particular interest since nitrogen is such an important nutrient for plant production.

Several research projects focused on this aspect but found inconsistent results. In one trial it was established that the use of immature compost provided relatively little additional nitrogen, also during the second year after application while the use of mature compost delivered a flush of soil nitrate, which decreased over time. This positive effect of using mature compost was confirmed by another experiment in vineyards while two others showed that even the use of mature compost provided little additional nitrogen for plant uptake.

In order to reconcile conflicting research results and to solve many open questions related to nitrogen availability and the mineralisation of organic matter, which is important both from a plant nutritional and environmental point of view, a 10 year long-term, co-operative research project was established in Germany. It aims to provide a better understanding of the long-term dynamics of mineralisation and nitrogen supply potential of compost.

In many experiments it was shown that compost use can substantially improve soil physical, chemical and biological properties, which are often important factors in determining its fertility status. The improvement of these soil properties results often in indirect benefits such as reduced erosion, ease of cultivation, increased fertiliser efficiency du to a higher cation exchange capacity or a reduced disease incidence.

Compost use showed inconsistent effects on grape yields, depending on the type of compost used, the vineyard soil and the control it was compared against. A 3-year trial in an organic production system started to show beneficial long-term effects of compost use in the last year of the experiment.

According to the available results, compost use on grapevine makes relatively little difference to the quality of the must or wine generated from these grapes.

Particularly nitrogen and phosphorus have the potential of causing detrimental environmental effects if compost is used inappropriately. Generally compost does not have high nutrient densities and only a limited amount of the total nutrients contained in compost is immediately plant available. However, if large quantities of compost are used or if compost is applied to soils with high organic matter levels, nitrate leaching can occur. This is a potential problem particularly in viticulture since grapes have relatively little nutrient requirements and, as a survey in Germany has shown, many vineyard soils are already very well supplied with phosphorus.

In Germany the agricultural/horticultural use of compost is limited to a maximum of 10 t dm/ha per year (30 t dm/ha every three years) by way of federal legislation (Compost Decree). In addition, several voluntary schemes operate in various vine-growing regions, which limit the use of organic inputs on the basis of the total nitrogen content of the organic materials or of the soil phosphorus levels.

Grapevines take up very little heavy metals and very little is deposited in the grapes. Any potential residues are filtered out in wine production, which is why heavy metals do not pose a problem for wine drinkers.

However, high levels of heavy metals can have detrimental effects on plant growth and microbial activity. Heavy metals are, therefore, in a vineyard situation more of concern with regard to the long-term protection and stewardship of the soil. It was shown that sources other than compost can contribute significantly to the heavy metal load received by a vineyard.

Compost use is not only governed by legal regulations. The German Federal Association for Compost Quality, a self-regulating industry body published detailed recommendations that specify compost use in wine growing according to the primary objective of using the compost as well as the soil type, humus content and frequency of application.

It has to be realised that both the soil and the compost represent biological systems whose interaction depends on a range of factors, many of which are not as well understood as previously thought. Compost use tends to show its full potential only after prolonged use. Therefore, many new research projects, which assess the effects of compost use in viticulture, are long-term, running for 5 – 10 years.

To date, Australian research into the use of compost in viticulture has focused on important issues such as water conservation and weed suppression. However, future research into the use of compost should also investigate aspects such as nitrogen mineralisation from compost in various Australian climatic conditions and the release of nitrogen from compost to assess potential detrimental environmental effects if used inappropriately. In this respect it may be helpful to develop recommendations for the appropriate use of compost for various industries. The potential of compost to redress the common phosphorus and mineral deficiency in Australian soils should also be investigated.