Soil Nitrate Concentrations Used to Predict Nitrogen Sufficiency in Relation to Yield in Perennial Grasslands

摘要

A method of evaluating soil N present in a perennial grassland system could help determine the need for additional N and enable more accurate N fertilization recommendations. The purpose of this study was to establish a relationship between a critical level (CL) of soil nitrate N under perennial grassland and optimum yield in a three-harvest system. A range of fertilizer treatments from 0 to 613 kg ha–1 was applied across two growing seasons to mixed stands of perennial forage grasses at two sites in Connecticut. Soil samples were taken on a weekly basis, and soil ammonium N and nitrate N were measured. Nitrate N was correlated with relative yield for three harvests within each growing season, and CLs of nitrate were generated using Cate–Nelson, linear response plateau, and quadratic response plateau models. Ranges of critical nitrate levels during the first 2 wk of each cycle were established: 2.0 to 4.5 mg kg–1 for the first harvest, 4.0 to 9.8 mg kg–1 for the second harvest, and 2.0 to 11.0 mg kg–1 for the third harvest. These values could be used to evaluate the necessity of adding N to a perennial grassland system in a three-harvest rotation and aid in a more correct fertilization of perennial grasses by offering soil-specific N evaluations.