Diagnostic Efficiency of the Blacklayer Stalk Nitrate and Grain Nitrogen Tests for Corn

Abstract

Protecting water quality and maintaining profitable corn (Zea mays L.) production requires diagnostics that can distinguish between N deficiency, sufficiency, and excess. This study evaluates initial recommendations on blacklayer basal‐stalk NO3–N ranges and critical concentrations for diagnosing N status, and it compares the performance of this test with grain analysis. Observations (428) were collected from 13 N‐response experiments. Linear response and plateau (LRP) and binary logistic regression (BLR) were used to characterize the relationships between yield and tissue‐test values. With the LRP, stalk NO3–N and grain N concentrations separating deficient from sufficient observations were 0.42 and 13.1 g kg−1, respectively, and the success rates of the two tests were comparable (77 and 75%, respectfully). The BLR also identified critical concentrations, but the values increased with decreasing yields, a desirable decision‐rule attribute given that extreme deficiency can result in higher‐than‐expected tissue concentrations. The success rates of multiple BLR functions using yield and stalk or grain analysis as factors were again comparable (88 and 87%, respectively), but they were significantly greater than with the LRP analysis. Stalk analysis was superior to grain analysis for distinguishing sufficiency from excess. A constant stalk NO3–N concentration (1.67 g kg−1) separated sufficient from excessive cases, and fertilizer efficiency approached zero at 2.9 g kg−1. Premature sampling resulted in stalk NO3–N levels that were 40 to 600% greater than levels observed after blacklayer formation, with the greatest error occurring when N fertility was low. When not testing for N excess, the advantages of grain analysis are the ease of sampling during harvest and the reduced risk of error associated with premature sampling.

Improving Sample Collection, Sample Processing, and Laboratory Analyses for Corn Stalk Nitrate Test

“…The extract was then analyzed using the MgO-Devarda alloy steam distillation procedure described by Keeney and Nelson (1982). The permanganate-reduced Fe method to include nitrate was used to determine Kjeldahl N. Binford et al (1992a) used the same methods, with a Lachat flow-injection procedure, as did Brouder et al (2000) and Fox et al (2001). In the study of Hooker and Morris (1999), samples were extracted by shaking with 0.05 M Al 2 (SO 4 ) 3 for 20 min.…”

Testing Soils and Cornstalks to Evaluate Nitrogen Management on the Watershed Scale

“…A relatively new tissue test for measuring the sufficiency of N for corn is based on NO 3 –N concentrations in the lower portions of cornstalks at the end of the season (Binford et al, 1990, 1992b; Hooker and Morris, 1999; Brouder et al, 2000; Fox et al, 2001). Studies across a wide range of conditions show that cornstalk NO 3 –N concentrations greater than 0.75 g N kg −1 indicate that N supplies were sufficient for plant growth.…”

Late-season digital aerial imagery and stalk nitrate testing to estimate the percentage of areas with different nitrogen status within fields

“…The test provides feedback in N status that can be used for assessing whether N management (i.e., N rate, timing, form, or method of application) was optimized or not in a given year. The high accuracy of the CSNT for diagnosing the N status of corn in the near-optimal and excessive categories has been confirmed in several studies conducted across the Midwest (Balkcom et al 2003;Brouder et al 2000;Wilhelm et al 2005;Yang 2000). The DAI has a high sensitivity for diagnosing the deficient or below-optimal N status of corn Hatfield et al 2008).…”