Rasel Parvej, LSU AgCenter soil fertility specialist, is in the first year of a study on soybean yield response to phosphorus and potassium levels at different soil depths.
“Currently, routine soil tests are based on samples collected from the top 6 inches of soil depth,” he said.
His study will compare phosphorus and potassium levels at depths of 0 to 6 inches of soil in addition to 6 to 12 inches and 12 to 18 inches.
He said soybean roots extend beyond 6 inches, and nutrient levels in soils deeper than 6 inches affect soybean growth and development. He said it’s possible that deep soil could have adequate nutrient levels available for plant uptake, but the first 6 inches of soil could be deficient, and that often results in false positive errors for fertilizer recommendations. The result could be fertilization that fails to increase crop yield even on soils that test low in nutrient levels based on the upper 6 inches of soil.
Different levels of potassium and phosphorus will be applied in the study. Potassium levels of 0, 40, 80, 120 and 160 pounds per acre will be tested, while phosphorous levels of 0, 30, 60, 90 and 120 pounds will be used.
Parvej is using a high-tech crop sensor to collect data from the plants in the field, and he is taking leaf samples from the plants across the reproductive stages.
Using the sensing system and leaf sampling, he will determine if the crop is under nutritional stress. He hopes the data can help predict yields.
Parvej said soybeans take up the most nutrients during the reproductive stages. He said it’s possible that a soybean field could appear to be normal while suffering from nutritional deficiency.
“You wouldn’t see any symptoms, and it’s called ‘hidden hunger,’” he said.
Potassium deficiencies detected with leaf sample analyses can be overcome by applying potassium during the reproductive stage and recover crop yield loss, he said.
Yields responses among plants that receive varying potassium and phosphorus amounts will be compared, he said, and that could lead to calibrating fertilizer rates with soil test results from various soil depths.
The first year of the three-year study is being conducted in 2020 at 18 sites, including five LSU AgCenter research stations (Dean Lee, Macon Ridge, Red River, Northeast and Sweet Potato) and five farms in Avoyelles, Tensas and Franklin parishes.
This story is featured in the Louisiana Soybean and Grain Research and Promotion Board 2020 Report.
Rasel Parvej uses a sensor to help determine plant growth in a soybean field in Avoyelles Parish. Photo by Bruce Schultz
Rasel Parvej collects leaf samples in a soybean field in Avoyelles Parish. The leaves will be analyzed for nutrient content. Photo by Bruce Schultz
The LSU AgCenter and the LSU College of Agriculture