Predicting Cover Crop Nitrogen Content with a Handheld Normalized Difference Vegetation Index Meter

Core Ideas: Cover crop biomass N content (CC-N) can be estimated in the field with a handheld NDVI meter. Separate calibration equations exist for different cover crop types in fall and spring. Rapidly estimating CC-N could facilitate management of N-related services provided by cover crops. Cover crop (CC) biomass nitrogen content (CC-N; kg ha⁻¹) is related to a number of ecosystem services but is rarely measured by farmers and agronomists because of the expense of sampling and analysis. We hypothesized that normalized difference vegetation index (NDVI) measured by a handheld meter could predict CC-N. Using a dataset of 598 observations, we predicted fall biomass N with two separate calibrations for (i) clover-type legumes and (ii) CCs consisting of brassicas (Brassica spp.), cereal grasses, vining legumes, and grass–legume–brassica mixtures. Spring biomass N was predicted with three separate calibrations for (i) cereal grain CCs, (ii) brassicas, and (iii) CCs consisting of pure legumes and grass–legume–brassica mixtures. Quality of the calibrations ranged from r² = 0.72 to r² = 0.87. Rapidly and inexpensively estimating CC-N with an NDVI meter could enhance the ability of farmers and agronomists to routinely monitor and manage the N-related ecosystem services provided by CCs.