Late Season Corn Stalk Nitrate Test: Sampling and Laboratory Analyses.

The corn stalk nitrate test (CSNT) is a site-specific, diagnostic tool for nitrogen (N) management of grain corn (Zea mays L.). Although an effective tool, widespread adoption of the CSNT is limited due to somewhat impractical sampling/sample handling protocols. Four studies were conducted to evaluate the impact of various changes in sampling, handling, and analytical procedures on CSNT results. In study 1 we determined the impact of placement and length of the stalk on CSNT results. In study 2 impact of timing of sampling on the CSNT was evaluated. Study 3 focused on the impact of (a) quartering of the samples, (b) moldy samples, and (c) temperature during storage (fridge, freezer, room temperature) on the CSNT. Laboratory grinding, extraction and determination procedures were compared in study 4. The results suggest that protocols can be adjusted to include slightly shorter stalks (15–17.5 cm stalks), sampling at or after silage harvest, reduction of sample volume through quartering of the stalks, multiple day storage of samples in a fridge, 2-mm grinding as opposed to 1-mm or less, and extraction with distilled water rather than the use of more expensive chemistries. The distilled water extraction also allows for use of either a nitrate specific ion electrode (SIE) or flow injection analyses (FIA). Although a filtration step is required when using the FIA, more samples can be processed per day. We conclude adjustments in sampling protocols and sample processing can be made, possibly increasing farmer acceptance of the test and reducing the cost of laboratory analyses.