Why measuring sap flow leads to understanding nutrient uptake?
All vine organs are connected via the sap. Thanks to the flow of sap, nutrients are distributed to plant organs. For the last 10 years sap flow technogies have given new insights into how much water flows from vine root to leaves’ air interface. This new knowledge presents an opportunity to analyze precisely how nutrient uptake affects the performances of different organs and ultimately fruit and wine composition.
How to refine diagnosis of nutrient deficit in practice?
Whether you assess vine leaf area or fruit composition, it is not uncommon to confuse symptoms of water deficit with symptoms of nutrient deficit. By analyzing side by side water and nutrient uptake, you can distinguish between the two sources of deficit. With the plant- based approach, vineyard performance diagnosis can be directly improved. To help you get the most of your vineyard information, Fruition Sciences has compiled a number of studies on nutrients. Today we’ll discuss how potassium affects fruit enological composition.
Effects on vine health and wine quality
A large number of studies document potassium concentration’s impact on wine pH and quality.
Walker’s 2012 paper identifies the relationship between higher pH in wines and undesirable characteristics such as juice soluble solids and poor wine color. Michela Centinari wrote an excellent article covering key issues surrounding potassium levels. Centinari argued that excessive potassium concentration in the berries negatively affects wine quality. The author advocates for using regular leaf petiole testing in addition to soil testing to determine whether interventions are needed. Several practices aiming at regulating potassium concentration were also discussed. Keller’s book addresses vine developmental issues as well as quality issues arising from potassium deficiency.
Effects on berry composition
Mpelasoka’s paper points out issues with high potassium in berries, including need for expensive measures to adjust wine pH levels in Australian wineries. Targeting the right berry potassium concentration prior to harvest can therefore lead to savings and reducing wastes for the winery. Focusing on warm and irrigated vineyards, Kodur’s paper discusses the relation between high potassium concentration observed in the berry and high resulting pH levels, as well as the use of low K cumulating rootstocks to regulate potassium levels.
Zorb’s paper stresses the importance of potassium in yield formation and resistance to diseases and analyzes factors affecting potassium levels. The author identifies several opportunities to optimize fertilizer application techniques. Moss’s 2016 paper discusses several consequences of high juice and wine potassium concentration and methods to limit potassium levels such as liming the soil, using rootstocks and avoiding shading the canopy.
How to measure and regulate potassium levels?
Tony Wolf’s wine grape production guide and recent Viticulture Notes issue provide guidance on collecting and analyzing results from petiole analysis as well as some consideration on fertilization. At the 19th Giesco symposium, Dubernet and colleagues discussed time variations in potassium levels in petioles leading to variations of potassium and pH in musts.
Monitoring potassium levels in the petiole is clearly an useful step to monitor wine quality.
Factors affecting potassium levels
Walker’s 1998 paper suggests that vine grafting leads to higher K+ concentration and higher malic acid concentration compared to own rooted vines. Other authors have shown certain types of rootstocks can lower potassium uptake. Wolpert found that those with Vitis berlandieri genetic backgrounds show lower levels at bloom.
Beasley’s study looks at how soil characteristics are related to potassium levels. One interesting finding across samples is that even if soil potassium levels are low, petiole analysis may show high potassium levels. This highlights the limitation of using only soil testing to assess plant potassium concentration.
Rojas-Lara’s paper and Dokoozlian’s paper studied effects of shading on berry development. The authors found a correlation between shading and increased potassium concentration. Coniberti, who studied impacts of canopy management, found that partial defoliation can lower potassium concentration for vines in Uruguay without compromising other wine quality variables.
The water and the crop load
Hepner found decreasing crop load and increasing irrigation amount and frequency could lead to increased potassium concentration. More recently Coniberti, who studied impacts of canopy management, found that partial defoliation can lower potassium concentration for vines in Uruguay while not compromising other wine quality variables.
How Fruition Sciences adds value
These studies show that a plant-based approach is the most reliable way to understand what your vineyard needs. It also highlights the short and long term effects that canopy and crop load manipulation, irrigation and fertilization can have on fruit composition. Fruition Analytics analyzes plant-based indices to support your diagnosis. By sharing those references, Fruition sciences wants to help you understand more precisely the effect of potassium uptake on fruit maturation profiles and ultimately wine composition.