Sonja Peters
Sonja Peters, agrologist and owner of Greenbush Greenhouses and Farm and Greenbush Consulting of Lumby.
The best fruit comes from the right soil, making soil testing an essential part of growing.
On her website, the microgardener.com, Anne Gibson says, “Invest in your soil. Your plants will only be as healthy as the soil they’re grown in.”
While her advice is intended for small-scale gardeners, the same facts hold true for commercial-scale growers with orchards and vineyards. Healthy plants grow in healthy soils that meet plant needs and the plants, in turn, will deliver the best quality fruit.
Soil health is just as important in an established orchard, berry field or vineyard as it is for a new planting area because over time, climate, growing conditions, pests and other factors change the soil. It needs to be considered in all stages of fruit production from planting to harvest as soil health is part of the overall ecosystem of the plants. In fact, in a talk about growing for seeds, Connie Kuramoto of Gardens on the Go Horticultural Training and Services says optimal soil conditions grow healthy plants that produce healthy seeds.
“No matter how you slice it, healthy soil is important,” she says.
She suggests that examining the soil for biological fertility (macro and microfauna, organic matter, biological activity) is even more important than the chemical composition. The physical fertility (structure, composition, water movement, etc.) is also key to the entire soil health – and therefore plant health – outcome.
Sonja Peters, agrologist and owner of Greenbush Greenhouses and Farm and Greenbush Consulting of Lumby, refers to Gibson’s point about soil health when asked why soil testing is important.
“The soil in an orchard or vineyard is such an important aspect of crop management,” she says. “Soil health and quality are important in producing high-yielding, top-quality fruit. It’s also important for long-term plant health, especially in adverse weather conditions.”
Almost all growers have some sort of soil and/or nutrient plan, but what is that based on? If established planting areas haven’t been tested in more than three years, it’s time. Plans for new planting areas need to include soil testing as well. Samples should be taken in the spring or the fall. Not only do sample results allow the grower to add amendments to the area before peak growing begins, they also ensure money isn’t wasted on additives that may not be needed and could adversely impact the environment.
Soil tests fall into two different categories, according to Peters.
“Soil tests help determine the acidity of or alkalinity, salinity, relative quantities of available plant nutrient and organic matter content of the soil,” she explains. “Foliar or petiole testing can also help determine which nutrients are lacking.”
Soils can vary dramatically within a growing block, so multiple samples should be taken and sent to a lab for analysis. For detailed advice on taking soil samples, she recommends the BC Tree Fruit Production Guide (in the fruit tree nutrition section) or the British Columbia Wine Grape Council’s Best Practices Guide for Grapes (in the vineyard establishment and vineyard maintenance sections).
Simplistically, she explains the process as:
“Traverse the sample area in a zigzag pattern and sample one meter from the trunk of 20 to 30 trees, depending on the size of the field. The more samples that are taken, the more accurate the results will be.”
The hole should be 15 to 30 centimeters deep before taking a 2.5-centimeter slice from the bottom (about 500 grams of soil), place in a bucket and repeat for each tree.
“When done, remove any rocks or organic matter like grass, leaves or roots from the sample, mix it well and place it in the sample container.”
Each lab has its own sampling form, so label the sample containers correctly and fill out the forms including the type of crop before mailing the sample in. Results will be provided by email within a week or two including interpretation and potentially some recommendations.
“Be sure to use values that are specific to your crop,” she advises. “When comparing target values with those on the lab report, ensure that the units and method are the same. The goal is to determine if your levels for each nutrient are low, optimal or excessive.”
She recommends the Best Practices Guide for Grapes for grape target values and the Washington State University guide to fruit tree nutrition and management. Growers might also ask their fruit associations for crop-specific resources.
“Once you know which nutrients are low in the soil of your field, you can now take this information and update your nutrient program,” she says. “Organic matter, soil structure and nutrients can be added using quality compost and manure products. If you have access to compost or manure, then this is an excellent option and can be applied at the base of the trees. Be sure to keep the material away from the trunk of the tree.”
Any manure or compost applied to a field should also be tested as explained by Lindsey Slaughter, soil microbial ecology/biochemistry assistant professor with the department of Plant and Soil Science with Texas Tech University. She oversaw thesis research of graduate student Rael Otuya, who had the team undertake a two-year study exploring the interaction between composted manure application and increased soil health.
“If someone is using their own manure or locally provided manure from another farmer, they should definitely get the manure analyzed for nutrient levels including nitrogen if possible, phosphorus, potassium and other nutrients that we commonly test for in fertilizers and soils before use,” Slaughter says. “Farmers should treat manure like a fertilizer, where the carbon and benefits to soils and microbes is a bonus.”
Because the study was done in a semi-arid region, the soil was lacking in soil microbial biomass and soil carbon, both of which assist in the breakdown of organic matter, improve overall soil health and increase the vigor of plants. Although this testing was done in forage fields, the outcomes can be extended to other crop types.
“There are some general results from our study and others that hold true across North America, namely adding manure increases soil carbon and microbes,” Slaughter notes.
Peters suggests referring to management schedules in the BC Crop Production Guides to help determine what types of fertilizers to apply and when. Manure may not be the ideal solution depending upon crop and soil needs. Additionally, she says some types of nutrients may be better applied by foliar fertilization, such as boron, zinc, magnesium and sometimes calcium.
Soil health is the very foundation of quality fruit, yet sometimes it is overlooked or assumed to be the same as it had been in previous years. Regular soil tests will give growers the information they need to ensure their fruit has the best start possible.