Resource Gradient Experiment

The Resource Gradient Experiment is a long-term study to investigate nitrogen and water constraints on crop yield. Annual crops of the Main Cropping System Experiment (MCSE) No-till treatment (T2) are nitrogen-fertilized at 9 different rates and either rainfed or irrigated. Since 2006, the crop rotation has followed that of the MCSE. Since 2007, fertilizer rates have differed by crop; the range for corn is 0 to 291 kg N/ha and for wheat is 0 to 180 kg N/ha. Soybeans are normally not fertilized but were in 2012 (only) at 0 to 146 kg N/ha. Sufficient irrigation is applied to meet plant water needs, as predicted by weather and a crop growth model that estimates evapotranspiration. Water is applied 0-3 times per week during the growing season by a linear move irrigation system.

The experiment moved to its current location at the LTER Main Site in 2005. Treatment plots are 4.6 x 27.4 m and are replicated in 2 sets of 4 randomized blocks—one set rainfed and one set irrigated. Lysimeters (soil water samplers) are installed in various plots

Note that the name, location and management of this experiment has changed throughout its history. The experiment began in 1999 as an unreplicated demonstration study and moved to a different location at the LTER Main Site during 2000-2005 where treatments were replicated. Corn was the only crop grown during this period.