Introduction
Carefully planned vineyard nutrition helps growers manage vine performance, yield and fruit quality while making the most efficient use of fertiliser inputs. Maintaining appropriate nutrient levels supports vine health and helps manage susceptibility to pests and diseases.
Petiole testing is a practical tool for assessing vine nutrient status and making informed and targeted nutrition decisions.
Flowering is a key time to assess vine nutritional status and make decisions to support optimum fruit set. While the weather and other factors around flowering are outside a grower’s control, nutrition can be influenced and getting it right ensures deficiencies do not limit production targets.
Macronutrients, including nitrogen (N), phosphorus (P) and potassium (K), are consumed by plants in large amounts so can need substantial additions each season. Micronutrients, while just as important for plant health and grape quality, are applied and consumed at a smaller scale.
Soil and fertigation applications can provide much of the macro-nutrients a vine needs while foliar sprays can deliver micronutrients right where they’re needed, when they’re needed.
Why flowering nutrition matters
Nutrient status at flowering influences vine health, fruit set and yield potential. For example:
- Boron deficiency reduces fruit set
- Copper or zinc deficiency can stunt vine growth
- Nitrogen deficiency affects metabolic functions throughout the vine
Too much of a nutrient can also cause harm. For example, boron toxicity reduces shoot growth. Knowing the actual level of nutrients in a vine means growers can apply only the amount required to eliminate deficiencies without risking toxicity or wasting money on fertiliser above what is required.
How to assess nutrient status
Visual vine assessments are unreliable. Vigorous vines are not necessarily healthy vines while deficiency and toxicity symptoms can look similar to each other or to pest or disease damage.
Plant tissue analysis measures the nutrients inside the plant and involves sampling petioles (or leaf stalks) from the vineyard and testing at a laboratory.
Petiole testing is performed at flowering, specifically EL25 or 80% capfall, because plant nutrient levels vary throughout the growing season. Testing at this time ensures that the results can be compared with research on expected nutrient levels in plants of the same stage.
Plant tissue test results can be complex and difficult to review so it is recommended to have an agronomist analyse them. Agronomists can often assist with sampling and submitting samples to a laboratory if needed.
Flowering petiole testing isn’t the only way to test nutrient status. Other options include leaf blade testing at veraison, nitrogen testing (Yeast Available Nitrogen, or YAN) from winemakers at harvest, and/or soil testing.
A thorough testing program can optimise vine performance and save on fertiliser and application time/labour. More testing also means more time and cost, so starting with one or two measurements a year can be a good strategy.
Avoid common sampling pitfalls
The AWRI Petiole analysis fact sheet (PDF) provides detailed sampling instructions for growers ready to start sampling.
A few key tips for sampling:
- Since nutrient testing costs relatively little compared with fertiliser, it is often worthwhile to submit separate samples from areas that are likely to have different nutrient requirements. These may include different soil types, slopes or low-lying, areas of high or low vigour, or areas where vine growth appears abnormal. This allows fertiliser applications to be tailored to the specific needs of each part of the vineyard.
- When collecting one sample to represent an area, try to collect petioles from the whole area, for example, don’t sample just the bottom of the hill or the ends of the rows.
- Factors to look out for when collecting a representative sample are:
- Variety, rootstock and vine age
- Terrain
- Soil types
- Edges of vineyards – edge rows and the ends of rows experience less competition for nutrition meaning it may skew the result.
- Avoid unusually unhealthy or sick looking plants as these may have other issues affecting them that might skew the results. Consider taking a separate sample to assess if deficiencies are causing the problem.
- If foliar fertilisers have been used before sampling, the sample should be thoroughly washed so that fertiliser residues don’t affect the result. The following is an accepted protocol:
- Prepare a wash solution of 3 mL phosphate-free liquid laundry detergent per litre of distilled or reverse osmosis (RO) water.
- Wash freshly collected leaf blades or petioles within this solution for 30 seconds, gently agitating and rubbing each sample by hand.
- Avoid prolonged soaking, which can leach soluble nutrients from the tissue.
- Transfer samples to fresh distilled/RO water and rinse for 15 seconds.
- Repeat with a second fresh distilled/RO water rinse for another 15 seconds.Shake off excess water, blot dry with a clean paper towel and submit or dry samples according to laboratory instructions.
Making cost-effective nutrition decisions
The right nutrition decisions depend on plant tissue test results, the site, available infrastructure and equipment, and the costs vs likely benefit in yield/quality. Because of this complexity it is recommended that growers work with an agronomist to help make the best decision for the specific combination of factors.
Factors to discuss with an agronomist include:
What is the best method to apply the required nutrients?
- The three options for nutrient application are solid fertiliser spreading, fertigation and foliar sprays. An agronomist can recommend which option is right for the situation.
- Solid fertilisers (which can be applied quickly either by broadcasting or in a targeted band) have a slower response than other methods but can build longer-term soil health. Nitrogen can be lost to volatilisation (evaporating into the air) if not incorporated into the soil.
- Fertigation is efficient for nitrogen, phosphorus and potassium application and is directly applied to the root zone but requires infrastructure and, over time, can result in soils becoming more acidic.
- Foliar sprays are useful for applying micronutrients and have a fast response but they can’t be used to apply a full dose of macronutrients; they also need to be applied at the right time.
What factors should I consider in nutrition decisions?
- Infrastructure and equipment: Consider the equipment available in your vineyard. If the ideal application method isn't practical with your current setup, a method you are already equipped for may be a more suitable option.
- Compatibility: Foliar applications may be able to be carried out at the same time as disease or pest management sprays, saving time. It does depend on compatibility between the sprays, so consulting with your agronomist or supplier is critical to avoid damaging foliage or reducing the effectiveness of these sprays.
- Cost/benefit: It may not make sense to remedy a minor deficiency of certain elements in some seasons.
- Weather constraints: In wet conditions, foliar sprays and fertigation may not be feasible or effective given rain washes the spray off before it's absorbed and nutrient uptake is reduced in waterlogged soils. Conversely, if there's no rain forecast soon after spreading urea, the fertiliser is exposed to loss by volatilisation.
When will I see a result?
How long it takes for results to become visible varies depending on the nutrient, the severity of the deficiency and the application method. A useful way to think about nutrition decisions is that some are aimed at improving vine performance this season while others are an investment in next season.