Back with another Paper 1 (viti) question. This time regarding vine nutrition.
What are the major and micro nutrients a vine requires to thrive? What are their various functions and how does a vine respond when individual nutrients are available in scant amounts? In excess? How are nutritional deficiencies diagnosed? What are the best ways to correct for them? If there are chemical/fertilizer treatments, it is good to know standard application rates and doses.
It is also important to be able to define a nutrient, and to understand the mechanisms by which they are ingested by the vine.
This is a topic that has come up a lot in past exams. Here are some example questions:
2016: What steps can a viticulturalist take to provide and maintain proper vine nutrition?
2015: What nutrients are important to the grapevine for the production of quality grapes and why?
2010: How can vine nutrition be improved through soil management?
2006: Examine the elements of vine nutrition essential for the production of high quality wine.
1999: Mineral deficiencies in the vineyard can lead to numerous problems. Discuss the major elements necessary for healthy vine growth and explain how any deficiencies should be corrected.
I included your 2010 question in "soil management", but clearly it is linked to nutrition as well. I did a very long soil management essay (that I can share when we address that topic) so for the 2010 question I only did a skeleton outline. I will throw it out here as another foundation block:
How can vine nutrition be improved through soil management?
Paper 1, 2010 Exam
Define soil management
List tools (each is a body paragraph):
Hi Kelli White
Here are some bullet points that may be helpful. I have a definition and address a couple of nutrients and conditions.
Definition: a vine nutrient is one of the 16 essential nutrients required for vine growth and development.
Discussion of pH
pH isn't a nutrient (you're welcome!) but it does impact nutrient availability in the soil
Too low, defined as below 6.4
Too high, defined as above 8
Sabrina, any examples on how viticulturists may deal with Mg or N deficiencies/excess? Any specific examples on how viticulturists have dealt with low or high pH? I am aware of what can be added to adjust pH or deficiencies. Looking to get real life situations. For example, I know of a producer in Sta Barbara that welcomes serpentinite soil (high Mg, low Ca) in one of their vineyards It reduces vigor in their Sauvignon Blanc and slows down ripening.
I had the opportunity to speak with the owner of Grech vineyard in St. Helena this morning while we picked leaves out of bins. He said that when they first started selling grapes to Raymond, over a decade ago, they ran an analysis (petiole, I believe) and found the soil was low in boron. They didn't adjust the soil that year, as they had been getting about 20 tons of CS from the vineyard annually and didn't think it was a pressing issue. That year they only produced 7 tons. They added boron to the soil and production went back up the next year.
Sorry for any spelling and grammatical errors. I am on my phone during lunch break because I wanted to remember this example.
This is a question where, as someone with a production background, I could include details that are probably unnecessary. I've focused on practical details here that may not be appropriate for every question on vine nutrition, but I was hoping that some may find it helpful.
Sabrina covered the function of nitrogen.
Deficiency: Chlorosis (yellowing of the canopy) of all leaves andlow vigor (shorter and fewer shoots) even when water is abundant.
Excess: High vigor (tall shoots, lots of laterals) and dark green canopies. Fruit quality mostly considered to be lower.
Both excess and deficiency are common. Excess is considered the bigger issue for growers who prioritize wine quality.
Potassium is abundant in grapes and every year at harvest large amounts leave the vineyard system. Thus, large amounts must be added back.
Function: Potassium maintains cell structure by increasing cells’ osmotic pressure. It's involved with stomatal function and helps the vine regulate water use. It is involved with ripening dynamics including sugar transport into the grapes as well as deacidification after veraison. K+ exchanges with H+ in the berries, and H+ is transported out of the berry, lowering the pH of the fruit.
Deficiency: Results in higher acidity in the fruit and can cause low yields and uneven ripening. Causes leaf yellowing or reddening (for white and red, respectively) and the leaves may look burned or “cupped”.
Excess: Results in lower acidity in the fruit. Can induce other nutritional deficiencies.
Function: Phosphorous is important for energy storage and transport (through ATP) and photosynthesis. It’s an important component of DNA and RNA.
Deficiency: Reduces yields by decreasing fruit set and # of clusters per vine. It causes a spotted discoloration near the leaf margin that looks similar to redblotch in red grapes (it looks sort of tie-dyed). Deficiency is relatively rare (older text say this is never observed) but observed on very acidic or very basic soils. Under these conditions, phosphorous forms insoluble complexes which are trapped in the soil and the vine can’t take it up. I've seen deficiency on volcanic soils on Howell Mountain in Napa Valley. Phosphorous is a huge pain on organic vineyards as it isn't very water soluble, so once the vineyard is established, you must fertilize each vine individually (dig a hole at the base of every vine and add bonemeal).
Excess: Not really a problem except that it may induce other nutritional deficiencies.
I won't go through all of the nutrients but other relevant ones are calcium, magnesium, sulfur, iron, boron, zinc, copper, molybdenum, and manganese. In addition to N and K, I think Mg and Fe deficiencies are most widespread, though this really depends on the site.
Assessing nutrient status
In addition to visual symptoms, viticulturists can assess nutrient levels by taking petiole samples at bloom and veraison. Some of the nutrients are able to move around easily in the vine (for example, N, P, K, Mg) and in the case of deficiency, they will transport to younger leaves. This causes symptoms to show up in older leaves first. Others (Fe, Cu, Zn, B, Mo, Ca) are immobile and deficiencies will show up in young leaves. This observation is helpful in diagnosing problems.
Mechanics of fertilization
It's common to analyze the soil and amend it prior to planting.
In terms of application, where irrigation is used, NPK is often added through fertigation (dripping nutrients through the irrigation line) or broadcasting (where fertilizer is spread on the soil surface and tilled in). Various mineral fertilizers or something more complex like fish emulsion can be used. Boron, zinc, and molybdenum are generally applied through foliar sprays (spraying nutrients directly on the canopy). You can also add nutrients through compost or cover crops, which results in a SLOW release (over a few years).
Excesses can be more difficult to manage but cover cropping can help with this (particularly with nitrogen) by increasing competition. Soil has a limited holding capacity for nutrients and so excesses in one often leads to deficiencies in another.
The question of typical rates of addition is tricky since it depends on yields and the specific type of fertilizer that is used but here are a few suggested rates:
10-25 lbs N / acre / year (this is to compensate for the N leaving the vineyard annually and is a lower limit)
15-20 lbs P / acre if deficient
100-150 lbs K / acre if deficient (once the soil is deficient, large quantities are necessary)
5-10 lbs MgSO4 / acre as a foliar spray if deficient
1 lb B / acre as a foliar spray if deficient (note that Boron has a vey narrow range and high rates are toxic to vines)
3 lbs FeSO4 / acre as a foliar spray if deficient
I feel like this may be a level of detail that is unnecessary. I'd maybe remember the # for nitrogen and then know that the numbers are relatively high for N and K and low for B, Fe, and Mg.
I'd imagine that it may be important to discuss is the different management strategies between vineyards growing grapes for quantity versus quality (the former would use more N and K). It's also common to give young vines more N to get them well-established. Different rootstocks are sometimes used to modulate nutrient uptake on soils that are deficient/rich.
The pH of agricultural soils decreases naturally over time due to several practices including tillage, fertilization with ammonium nitrate, and removal of cations from the vineyard through pruning and harvest. Low pH induces other nutrient deficiencies as well as aluminum toxicity and can be corrected through liming (the addition of calcium hydroxide, calcium oxide, or dolomite).
Jennifer Angelosante Thank you, this is brilliant.