Can Frequent Measurement of Normalized Difference Vegetative Index and Soil Nitrate Guide Nitrogen Fertilization of Kentucky Bluegrass Sod?

Objective approaches to guide N fertilization of turfgrass sod crops are lacking. This study was conducted to determine the relationships among normalized difference vegetative index (NDVI), frequently-measured soil NO3-N concentrations, and peak-shear force of predominately Kentucky bluegrass (Poa pratensis L.) sod, and to evaluate if those relationships could help guide N fertilization. Ramp calibration strips (RCS) with varying N rates were established within production sod fields in Rhode Island across three consecutive years. At 2-wk intervals during each growing season, soil NO3-N concentrations and NDVI readings were recorded and correlated. Biweekly relative NDVI readings plateaued when soil NO3-N concentrations ranged between 5 and 12 mg kg(-1). Mean relative NDVI plateaued at 196 kg N ha(-1) yr(-1). Relative sod peak-shear force was negatively correlated to soil NO3-N concentrations and the total amount of N applied per year. Relative peak-shear force was maximized when mean relative NDVI readings ranged from 0.969 to 0.982, but declined as mean relative NDVI increased towards 1.0. The results suggest that frequently measured NDVI and soil NO3-N concentrations show promise as guides for N fertilization of predominately Kentucky bluegrass sod. Further research will be required to validate these approaches on larger-scale sod fields.