N source and water quality affect foliar and root N uptake

Photo by Boaxin Chang

Editor’s note: The following research project is in progress and was featured in the Cutting Edge section of GCM. This research project was funded by a grant to GCSAA from the Environmental Institute for Golf.

Knowledge of potential interactions of water chemistry on foliar or root uptake efficiency of various inorganic nitrogen (N) sources is important for optimizing plant health and for minimizing environmental losses of N.

Sod plugs (4 inches in diameter) were obtained from established Champion bermudagrass putting green and Tifway fairway research plots at the Texas A&M Turfgrass Research Field Laboratory, established into medium-coarse USGA-recommended sand in PVC columns, and then transferred to the greenhouse for a 10-week establishment/acclimation period.

During this period, pots in the foliar application study (Champion) were watered twice weekly using reverse osmosis, sodic potable or saline (2.5 dS/m) irrigation. For the root uptake study (Tifway), 5 and 10 dS/m salinity irrigation levels were maintained during establishment. All plants were fertilized with ammonium sulfate, urea or potassium nitrate, corresponding to the N treatment being evaluated. Evapotranspiration rates and lightbox images were also obtained to determine percent green cover differences between treatments. Upper-root-zone (0 to 1 inch) electrical conductivity was also monitored.

After 10 weeks of establishment and acclimation to the respective ¹⁴N-based N sources, ¹⁵N-labeled N fertilizer solutions (ammonium sulfate, urea or potassium nitrate) were foliar-applied to Champion bermudagrass treatments using a mist atomizer. For the root uptake study, ¹⁵N-labeled N solutions were supplied to the Tifway bermudagrass pots in the upper 1 inch of soil.

After the allotted uptake periods, samples of shoot, root and soil fractions will be prepared to determine total N and % ¹⁵N via mass spectrometry analysis. Both water quality and fertilizer source effects on N uptake efficiency will be analyzed.

— Benjamin Wherley, Ph.D., Boaxin Chang, and Jacqueline Aitkenhead-Peterson, Ph.D., Texas A&M University, College Station, Texas

Teresa Carson is GCM’s science editor.