By STEVE BROWN
PUYALLUP, Wash. -- Farmers growing a variety of vegetable crops can see a bottom-line benefit with more precise soil testing.
Doug Collins, a soil scientist and educator at Washington State University Extension in Puyallup, has produced a fact sheet to help growers decide where and when to sample and how to turn the results into profit.
"Some make (sampling) an annual event and make decisions based on that," Collins said. "Some never sample their soil. Even annually, they are typically combining several management zones when they do that.
"I'm arguing to get better data about a smaller area, growers make reasoned decisions about where to sample."
A management zone could be as small as a single bed, he said. The zones he has worked with ranged from 1 acre down to 0.034 acre.
In his publication -- "Soil Testing: A Guide for Farms with Diverse Vegetable Crops" -- Collins describes how to take into account topography, soil types and the farmer's observations of drainage and plant performance.
On less-diverse farms, especially in the Midwest, a farm will have fewer zones that require soil testing. On small farms growing 30 or more different vegetable crops, "The challenge is, do you take 30 different samples?"
Diagrams in the guide suggest how to sample representative areas. Those results can then be applied to other areas of the farm.
Adam McCurdy, who grows about 60 different vegetable varieties at Oxbow Farm near Carnation, Wash., worked with Collins starting in March. He had been testing his soil annually for the past five years at Oxbow. He has now added a second testing each year.
"I hope to minimize overfertilizing," he said. "I look to increase yields and save resources of labor, minds and minerals."
What he's learning about his soil can also help him choose which crops to grow.
"You can nail a rotation," he said.
Soil test results can indicate nutrient deficiencies or excesses, nutrient-holding capacity, organic matter content and soil alkalinity or acidity, Collins said. Soil analysis can guide farmers in making soil amendment and soil management decisions.
The guide helps a farmer discover the variability in a single farm and from farm to farm, he said. The amount of fertilizer needed for the same crop can vary at different farms.
Collins is leading a team developing soil-fertility tests for use by organic farmers. He emphasized the importance of assessing particular sites for soil fertility.
"What we've found is that you really have to know what is going on with a particular piece of ground," he said. "You can't offer generalized advice about fertility management. That's why we're developing these tests."
https://pubs.wsu.edu/ (enter "Soil Testing")