With a new growing season just around the corner, Hutchinsons agronomist, Will Robinson explained how soil analysis can help growers better target nutritional inputs in the months ahead.
Late winter into early spring is an ideal time for sampling vineyard soils, to help highlight potential deficiencies before growth begins, and tailor fertilisers to the requirements of new or established sites.
DEFRA’s Farming Rules for Water require all vineyard soils to be tested for pH and key nutrients (phosphorus, potassium and magnesium) no less than every five years. Nitrogen levels may be determined by assessment of the soil nitrogen supply, rather than soil sampling and analysis.
A more frequent, three-year, testing regime is generally recommended to monitor trends more closely, particularly where there are historical issues, variable soils, or growers are targeting consistently high yields.
Nutrient offtake in harvested grapes and woody prunings may not be as high as many other crops, but key nutrients, such as potassium, still need replacing to maintain long-term soil fertility and productivity.
Monitoring soils regularly also helps identify any other underlying issues affecting vine growth, yields or quality, such as pH variations, poor drainage, structural issues, or nutrient imbalances.
Iron, for example, becomes far less accessible in more alkaline soils (over pH 7), while high copper, manganese, or zinc, are also known to cause iron ‘lock-up’.
Good time to test
From February into March, there is usually good moisture for soil testing, and sufficient time for remedial work and/or tailoring of fertiliser recommendations before the growing season begins or new vines are planted.
Various tests are available, from a basic P, K, Mg, pH test, to a broad spectrum soil evaluation, covering a range of parameters, including macro and micro nutrients, pH, organic matter, cation exchange capacity, and textural properties.
Generally, test samples will be based on 15-20 representative soil cores per hectare, taken in a ‘W’ pattern across the site, focussing on the under-vine strip, as that is where the majority of the vine’s feeding roots are found. Avoid sampling when soils are very wet or waterlogged as this can comprise the accuracy of results. Equally, do not sample when soils are very dry (e.g in summer), as this will also affect sample quality and results.
Those looking for extra detail and accuracy should consider TerraMap digital mapping, which provides high-definition maps of up to 48 layers of information, including nutrients (plant available vs non-readily available), organic matter, carbon, active and buffer pH, and soil texture. Maps can also be used to generate variable rate application plans, allowing inputs to be accurately targeted exactly where required.
Act on results
Take time to interpret the results of any soil analysis and discuss the most appropriate remedial actions and fertiliser recommendations with your FACTS qualified advisor.
Lead times for fertiliser products can vary widely, so plan requirements and place orders in plenty of time.
Generally, most macronutrient requirements can be topped-up with a soil-applied fertiliser, however, with many vineyards located on sloping, free-draining soils, recognise the risks leaching may pose. Depending on how much you need to apply, consider whether a staged/split application may be more appropriate to minimise such risks.
Supplementary micronutrient requirements are typically met through foliar feeds, and where potential deficiencies are identified, it is important to act early.
In the case of iron, for example, apply foliar iron as soon as there is sufficient leaf area to hit, ideally from the 3-5 leaf stage, and avoid doing anything around flowering, as iron can block pollen receptors.
Products in chelate form (such as Metalosate® Iron) are a good option, as the water-soluble molecules mix easily, do not bond with other nutrients, and are more easily absorbed through leaves, allowing faster uptake and correction of any deficiency.
As a general rule, avoid applying any nutrients around flowering, as this can trigger vines to go into a vegetative, rather than reproductive, cycle, reducing fruit set and berry number.
If additional nitrogen is needed, ammonium nitrate is generally preferred over urea, as nitrogen is immediately available. In a really warm spring, vines can quickly go from bud burst to flowering, and if you have applied urea rather than AN, it takes a while to be broken down and taken up by plants, so might get into the vine too late. Note that in England, any urea fertiliser applied to soil in spring must incorporate a urease inhibitor to prevent ammonia losses.
