A panel of viticulture experts featured at the Grape and Wine Show, held at the International Agri-Center in Tulare, Calif. on November 3, offered a variety of perspectives on vineyard nutrition. They all agreed, however, that the key to successful nutrition is consistent sampling and testing.
“You have to know what is happening in the vineyard to really make decisions in terms of purchasing fertilizers and applying fertilizers,” said Steve Vasquez, technical viticulturalist with Sun-Maid Growers, who moderated the session.
“Tissue sampling is the check that I use in season,” said Paul Crout, senior product manager and agronomist for Helena Agri-Enterprises. “I sample everything (soil, water and tissue) when I’m building a fertility program. I use tissues to check my work during the season.
“The key for me is keeping constant, using the same lab and using the same technology year over year, over year,” he continued. “You can use whatever you use, just use it consistently.”
Crout, who has sampled blades and petioles as well as used the same lab and same techniques for 18 years, looks for consistency before creating correlations between the tissues and numbers in the field. He also takes a lot of samples to get as much coverage as possible.
Jerel Kratt, CEO of Regenerative Crop Consulting, Inc., has been experimenting with sap testing for several years.
“Sap testing is extracting the actual sap within the leaf, and some labs will include the petiole,” explained Kratt. “That’s going to give you a different number and a different result than standard tissue testing.”
Kratt started by using a lab in Oregon that sent him “10-page reports with all these graphs, and my head was spinning.” He later used a lab in the Netherlands that many consider to be the originator of modern sap analysis, a technique originally developed in 1920 before new technologies and equipment were available. He described the shipping costs as “incredibly expensive,” and said that customs delays caused the nitrogen in the leaves to break down, making the test results meaningless. More recently, he started working with a lab in Michigan that maintains a database of critical values, which shows what the numbers should be and creates usable results.
Although his testing method is different, he agreed with Crout about the importance of using consistent testing methods and getting multiple samples for data that can be used in spreadsheets.
Larry Bettiga, viticulture farm advisor with UCCE in Monterey County, also agreed that the key is consistency. “Traditionally, we’ve done petioles in California. That works pretty well for most nutrients. Maybe the exception would be nitrogen, and that’s because we see a lot of variation.”
Bettiga also stressed the need to take a lot of samples, especially if you have a lot of variables. “It’s really consistency and where you take samples,” he said. “You have to make sure your samples reflect your management zones. Especially for nitrogen, it goes up and it goes down, so you need to be there the same time every year.”
“There’s different ways to look at the data,” said Tian Tian, Ph.D., viticulture farm advisor with UCCE in Kern County. “In this case, historical data is our friend. If you have similar timing and you stick with similar rows to decrease the variability caused by sampling error, and you have record for yield, how you fertilize, how you irrigate, all those will be a powerful tool and provide valuable information to guide fertilization.”
Rootstock Choice Matters
Tian described using rootstocks as “choosing a life companion for your friends.” She advised sampling them separately because there is a difference in the amounts of micronutrients such as magnesium and calcium.
“We plant rootstocks for pest situations, so that still is the first reason you should be planting a certain rootstock,” said Bettiga, who has conducted many rootstock trials. “A lot of what we do should be based on how those vines perform and what your production goals are, and if they meet it.
“Sap analysis was the one tool that actually spelled out the differences in rootstocks more than any other tool I’ve seen, other than your visual eye,” said Kratt. “Salt is probably the number-one thing I was seeing show up differently in rootstock than the standard leaf testing would be.”
He also advised, “Absolutely without a doubt, always separate your rootstock blocks for sampling because I think it will tell you a lot more about what’s going on. Iron and magnesium are probably the two most common nutrients impacted by rootstock.”
“As a grower, a lot of times I’m at the mercy of the nursery and what’s available,” said Crout, “so a lot of time we don’t have the luxury of making those proper rootstock-scion selections.”
Crout has one vineyard with 14 different varieties and 20 different rootstock combinations, and another vineyard with 10 different varieties with one rootstock. As a result, he has had multiple rootstocks in his irrigation block and management zone.
“I’m handcuffed from a practical perspective to manage this in a realistic way that makes sense,” he said.
Making Appropriate Applications
Crout said he includes dry applications in the fall and winter for his calcium- and magnesium-dominated soils. He uses compost, organic matter, calcium (gypsum or lime) and potassium.
“Typically, I vary the rate by block,” he said. “There’s some variable rate technology out there that allows us to vary the amount based on soil mapping.”
Kratt discussed the practices his company is currently developing, such as using sheep, cover crops, compost, biological inoculants and biostimuluants. He noted the increasing costs of current grape-growing methods.
“There’s no better time to look at other alternative methods to improve vine health and quality of your vine and your yield,” he said. “As far as best management practices, we really want to try to reduce these heavy, large slugs of nitrogen to the soil. I have definitely seen through the testing I’ve done a large suppression of microbial activity with a large application of synthetic fertilizer.”
“I think it depends on whether you are dealing with a new planting or established planting,” said Bettiga. “There’s been some recent work on the Central Coast looking at the additions of either compost or biochar. If you can actually incorporate those in the row as you’re whipping and tilling those fields, especially in those less fertile soils, there’s some very dramatic improvements in vine growth and yield that more than compensate the cost of those materials.”
“When you’re putting your fertilizer program together, you really need to have a plan,” said Vasquez in his closing remarks. “Know what your goal is for that vineyard or block. Really understand what you’re trying to achieve there and some of the issues that may be brought by having that vineyard or block, such as irrigation. If you’ve got four rootstocks and one scion, you may have some challenges there.
“Understand your lab results,” he continued. “If you don’t understand what those results are telling you, find an expert and have them help you interpret those results. And it’s important to use the same lab and the same techniques to make sure that you’re getting a good analysis, and you’re making a good decision based on those lab results.”