Irrigated pasture soil nitrogen is a part of dynamic, living, and complex biogeochemical cycle.
Soil sampling and nitrogen management strategies will vary depending on the soil moisture and temperature regimes of the pasture.
Total nitrogen in the soil is not the same as plant available soil nitrogen (PAN). Physical and chemical characteristics of soil can alter the plant availability of soil nitrogen.
Matching multiple nitrogen applications with crop needs through out the growing season can lead to increased agricultural efficiency and reduced leaching and run-off of nitrate-nitrogen.
Here are some resources for understanding nitrogen in irrigated pasture.
Nitrogen Assessment Link
Soil Solution Page