April (No. 495)
Soil assessment and management an essential component of business plans for established vineyards
John Rasic , JR's Soil Management Services
As vineyards mature and reach the stage the grower may have expected would be “full production,” it often becomes apparent that variation in winegrape yield and quality exists across single blocks. Further it may become apparent that groups of blocks which enjoyed healthy growth whilst reaching maturity, are suffering from a steady decline in health. This decline affects grape production, and may well be the cause of the grower’s dampened expectations.
Techniques to gauge the performance of operations at block level are widely applied and there has been strong promotion of Precision Viticulture as a means for measuring variability within individual blocks. However, less attention has been given to practical steps that the grapegrower can take to exploit this growing body of information and increase vineyard returns.
In essence, a grower might think: “you have told me I must measure it, and I have learnt how to measure it, but what do I do now?”
The importance of expert advice about soil quality
The key element of any agricultural pursuit is the resource that hosts the crop: the soil. An understanding of the soil and its variability across a property is critical if successful decisions are to be made and management strategies implemented.
As a crop grows, its interaction with the soil changes Over time, the medium itself is being continuously modified. The vineyard manager must at least have a general appreciation of these soil-related processes so that expert advice can be sought.
In capital intensive, high-value agriculture, where incremental improvements in yield and quality can return significant benefits in terms of return per hectare, the advice of consultants should be regarded as a normal part of running a business. It needs to be part of an established management routine, rather than an avenue of last resort. Financial analysis demonstrates clearly that the cost of this advice usually is quickly recovered through minor improvements in soil management.
How to deal with declining vineyard performance?
Most vineyard managers are familiar with the scenario of initial production being high but yields then either declining or becoming widely variable over time despite management practices that have remained unchanged. Variable growth and declines in production are related to a highly intricate and very complex interaction of local climatic and soil factors, including soil degradation and inappropriate irrigation system design. These interactions can be difficult to identify and modify because of the complexity of the factors involved.
One of the major factors is the response of grapevines to physical soil conditions. For example, roots of non-irrigated vines may routinely extract all available water to a depth of two metres or more in favourable soils, but when root systems are restricted to shallow depth, the soil may dry below wilting point within a few days after rain. Even in irrigated areas, compacted or otherwise restrictive layers reduce production because a considerable portion of the total supply of water and nutrients is concentrated within or below the pan and is unavailable to the roots.
Other factors include irrigation with poor quality water and the resulting build-up of salts in surface layers with limited leaching capacity. Surface sealing then leads to increased run-off, erosion, waterlogging, soil and root diseases, weed invasion and poor plant response to fertilisers. Physical, chemical, biological, and thermal degradation of the soil occurs and the vines struggle to survive under multiple stressors.
When previously productive soils have become degraded, increased yields and sustainability cannot be achieved without substantial changes to the current soil condition, followed by radical changes in soil and irrigation management practices. The important question to answer is: “what measures should be undertaken to improve the soils while the degradation is still reversible?”
The first step is to correctly identify the problems.
The second step is to determine the corrective measures for soil improvement to achieve the best possible yields.
A third step, which will be familiar to those pursing Precision Viticulture practices, is to ask: “how can I use the maps that I have been making and that describe the spatial arrangement of the problem to implement a property-scale strategy?”
There are many options for improving the performance of soil although it cannot be assumed one method can be universally applied. Opportunities for optimisation exist through varying the degree of intervention. For optimum yields and quality, irrigation and soil management practices should be adjusted to create harmony between local climatic factors and the inherent properties of the soils. Ideally, consideration should be given to modifying the soil to create a uniform growing medium providing the opportunity for consistent yields. This may require use of specific implements, combined with incorporation of various chemical and biological soil ameliorants to stabilise the newly-produced structure.
In addition to well known ameliorants such as lime, gypsum, compost, peat, manures and crop residues, a wide variety of waste organic materials, such as slurry, sewage sludge, tannery waste, industrial organic liquids, and food processing wastes can be incorporated into the soil, however, EPA regulations require consideration. In addition to these organic materials, an ever-increasing range of polymers is becoming available that can be introduced to modify specific soil properties.
It is important to select an appropriate ameliorant for the soil, for example, an acid peat can worsen an already low soil pH, and likewise, lime and gypsum should only be applied if soil analyses indicate the need for these materials.
The effects of amelioration can be dramatic and the improvement on performance both rapid and prolonged.
Sustainable production can be achieved only if ongoing attention is given to soil maintenance and if irrigation and management practices are adjusted to match the patterns of soil variability. The adoption of a soil management program that includes regular monitoring is therefore as important as the amelioration process itself for the long-term success and sustainability of the vineyard.
For maximum effect, the integration of soil management with the other property management programs is essential.
The addition of soil information to property information systems in a compatible format should be considered a medium-term goal. A strong message grapegrowers could take from this is that an explanation of the variability seen across many blocks is likely to be related to the condition of the soil.
Implementing an optimisation program requires a thorough understanding of the soil and therefore, an ongoing relationship with a soil consultant should be an integral part of your vineyard business plan.
The author thanks Rod Davies, David McKenzie and numerous vineyard managers for useful discussions regarding the contents of this article.
JR’s Soil Management Services is an Adelaide-based company which provides a wide range of specilised services including soil surveys, land evaluation and amelioration. John Rasic is a Chartered Civil Engineer and Certified Professional Soil Scientist and can be contacted on (08) 8326 0522 or 0419 671 655, or by email: firstname.lastname@example.org