Water Use and Nitrogen Leaching with Perennial Grass
Urbana – As University of Illinois researchers investigate biomass crops, many questions arise about production practices, growing conditions, nutrients needed, and soil conditions to name a few. Greg McIsaac, an associate professor for the Department of Natural Resources and Environmental Sciences, was interested in learning more about how growing perennial grasses affects soil moisture and inorganic nitrogen movement through the soil profile, which is sometimes referred to as leaching.
In 2005, McIsaac, along with Mark David and Corey Mitchell, began an evaluation of water use by and nitrogen leaching from biomass crops compared to a conventional corn and soybean rotation. In tile-drained areas, inorganic nitrogen loss is high (25 lb N/ac or 27.5 kg N/ha) with corn and soybean crops. The research was funded through a C-FAR grant.
The research was conducted throughout the year because of the annual hydrologic cycle, which includes precipitation, soil moisture and stream flow.
In order to assess soil moisture, the team installed 94 tubes, with four tubes per plot leading to 16-24 replicate tubes per crop. The tubes are 90 cm long. Researchers used a Diviner2000 Portable Water Monitoring Device, which utilizes Frequency Domain Reflectometry (FDR) to measure soil water content every 10 centimeters in the 90 centimeter tube. These measurements were taken every three to four days during the growing season.
Although the data are still being analyzed, initial findings indicate that soil moisture early in the growing season is reduced in biomass crops compared to corn and soybeans. And, at the end of the growing season soil moisture is significantly lower with Miscanthus than other crops. The next question is, “to what extent could widespread adoption of switchgrass or Miscanthus have the potential to reduce flood flows during the spring?” posed McIsaac. He said the research also indicates that Miscanthus has some potential to extend and intensify low stream flow periods of later summer and early fall.
“During August switchgrass is putting energy into producing seed. Miscanthus is still growing biomass, which uses more water,” said McIsaac. “By the end of the season there is a big difference (in soil moisture).”
Assessing Nitrogen Leaching
Assessing nitrogen leaching through water was a little more difficult than testing soil moisture.
“We basically created a cup without a bottom,” said McIsaac as he explained the Ion Exchange Resin (IER) Lysimeters. The IER Lysimeters are made with a PVC coupling and Ion Exchange Resin sandwiched between layers of sand.
The lysimeters are placed 50 centimeters deep in the soil and then 15 centimeters to one side of the hole that was dug to install the lysimeter. This ensures that the water percolating through the lysimeter has drained from the undisturbed soil profile above it.
The first lysimeters were installed in May 2005. They are sampled and replaced annually in April. Currenty 36 lysimeters are installed.
Preliminary analysis shows that the perennial grasses, switchgrass and Miscanthus, greatly reduce inorganic nitrogen leaching compared to corn and soybeans.
McIsaac said that this research is confirming other research that grasses help retain nitrogen in the soil. However, he cautions that it can fluctuate, depending upon the amount of rainfall during the year. Given the large amount of rainfall during the spring 2008 growing season, it is likely that the amount of nitrogen leaching from all crops is higher than in previous years.
McIsaac’s research has been conducted on the South Farms at the University, which is tile-drained. He said the next step would be to “assess the size of impacts in different landscape settings and climate scenarios.”
“There are a lot of considerations about the consequences of planting large areas of perennial grasses—carbon sequestration, wildlife, water quality and the return to the landowner,” said McIsaac. “We want to find the crop characteristics that accomplish the landowners’ goals for each landscape.”
Writer Natalie Bosecker (217) 244-9273
Source Greg McIsaac (217) 333-9411