The interrelation between macronutrients and micronutrients is extremely complex, which means that managing the soil and reaching the exact balance is almost a form of art. However, the knowledge handed over from one generation to another, now has the scientific and technological progress of precision viticulture on its side to make the task easier.
Any fertilization schemes must be supported by an efficient diagnostic system, that allows monitoring nutrient levels in advance to correct deficiencies or excesses in the vineyard. A vibrant, balanced, and healthy soil is critical to achieving the right vegetative and reproductive balance, that leads to an optimal wine and the expected yields. Balance is, after all, the holy grail of any oenologist.
Roots and leaves, a delicate balance for vineyard nutrients
They say, that roots are the brain of a grapevine, but at the end of the day, they belong to a single being together with the leaves, used by the plants metabolize nutrients and channel them to the grapes, that will become wine. While the vine obtains nutrients from the soil through its roots, the leaves are the canary in the mine, that betray any unbalance in the quest for the best wines.
Fertilization and nutrition of the vine are focused on keeping that delicate balance between minerals, especially nitrogen, potassium, and phosphorus, but also calcium, magnesium, sulfur, iron, boron, copper, manganese, and zinc. To achieve it, a fertilizing plan must be carried out before planting the vines and throughout their lives, with a calendar that establishes the exact amounts, how to apply them, and the specifications of the fertilizers.
The lack of any of these elements on the soil manifests itself through specific symptoms. We could say, that the right vigor for the plant depending on: nitrogen (N) levels, phosphorus (P) is key to the resistance of the vine and potassium (K), will define the quality of the grapes.
Symptoms of nitrogen (N), potassium (K) and phosphorus (P) deficiencies in the vineyard
Nitrogen levels should be kept at reasonable levels. Nitrogen deficiencies will hamper the growth of the plant and the accumulation of stock carbohydrates, which will affect yields in the following production cycle. An excess will reduce those carbohydrates, leading to excessive vegetative growth that could limit the ripening of the fruit and the fungal outbreaks associated with rotting. Nitrogen deficiencies will show as uniformly colored leaves with pale green or even yellow hues, although symptoms will not become visible until the deficiencies become acute. Nitrogen excess, on the other hand, is much easily assessed. The foliage will be abundant, with dark green leaves, overdeveloped stems, and flat and elongated fanleaves. Leaves will also show white spots attributable to the accumulation of salt. Finally, the excessive shade will hamper flowering.
Secondly, potassium (K) is crucial for the development of vegetal cells. In addition to the activation of the plant growth, it helps the foliage carrying out the photosynthesis and contributes to the accumulation of sugars in the grapes. It has a quantitative effect, but also a qualitative one. K allows an efficient distribution of moisture, which carries nutrients to the whole plant. Low K levels can be detected through the discoloration of leaf tips, especially the youngest ones, that also start curling towards the start of the veraison and show a yellowish appearance (in white varieties) or reddish tones (red varieties). In extreme situations, leaves dry and fall prematurely, which hinders the ripening of grapes and the correct withering of the vine shoots, leading to potential problems in the next bud break.
Thirdly, phosphorus (P) is similarly essential for the growth of the vine, but not so much in terms of vigor as in the prevention of coulure (poor grape cluster development) and cryptogamic diseases. P is beneficial for root development, especially in the first years of the stock, and it helps to produce more fertile shoots. Phosphorus requirements are lower than N and K, so deficiency symptoms, such as reddish leaves, are a rarer sight.
High tech applied to nutrient control
To achieve the best starting point in the production of high-quality wines at the winery, a complex process must be followed from bud break to harvest, which means collecting as much data as possible from different sources. There is a large body of research on the techniques to make the right nutrient estimates. These combine factors such as production and weather with other parameters collected through what could be called visual and non-visual systems.
A non-visual system would be a lab analysis of soil composition, together with water and sap analytics, among others. Visual analysis focuses on the appearance of the vine and its leaves, which can be done through satellite imaging or drone flights. Nowadays, new tools such as artificial intelligence and machine learning software, which can even be used from a smartphone, can help to achieve an optimal management of nutrient needs. Thus, a visual analysis aided by AI can detect nutrient deficiencies in the early stages, even sparing from some visits to the lab.