Managing Global Resources for a Secure Future

2017 Annual Meeting | Oct. 22-25 | Tampa, FL

28-6 In-Field Variability of Illinois Soil Nitrogen Test and Loss-on-Ignition for Nitrogen Management.

See more from this Division: ASA Section: Agronomic Production Systems
See more from this Session: General Nutrient Management Oral

Monday, October 23, 2017: 9:15 AM
Marriott Tampa Waterside, Florida Salon I-III

Angel Maresma and Quirine M. Ketterings, Animal Science, Cornell University, Ithaca, NY
Abstract:
The Illinois soil N test (ISNT) with loss-on-ignition at 500°C (LOI500) adjustment can effectively identify fields with low versus high soil N supply potential in New York. However, spatial and seasonal variability in ISNT-N and LOI500 can influence soil N supply classifications. We aimed to determine (i) the influence of sample density on the ISNT-N/ISNT-NCritical ratio and soil N supply classification, (ii) the implications of change in spatial and temporal variability on ISNT-N interpretations, (iii) the probability of obtaining an accurate interpretation as impacted by sampling intensity, and (iv) the influence of using LOI500 equivalents [derived from loss-on-ignition at 360°C (LOI360)] on ISNT-N interpretations. Two 4-ha silage corn (Zea mays L.) fields were sampled (150 samples per field, 0–20 cm depth; 64 in regular 25 by 25 or 23 by 27 m grids, the remainder in a pattern optimizing lag distance distribution) in July and November. Semivariograms were constructed to investigate spatial dependence. Soil nitrate showed the weakest spatial dependence. Increasing sampling intensity to 3.75 samples ha-1 reduced the confidence interval for ISNT-N/ISNT-NCritical while augmenting the probability (>95%) of obtaining an estimate within the true field mean (±6.4%), resulting in consistent classifications. The LOI500 and LOI360 results correlated well (r2 = 0.78) using LOI500 equivalents derived from LOI360 produced identical classifications for 92% of the samples. We conclude that effective sampling protocols for ISNT-N should include sampling at 3.75 samples ha-1 (or more if needed) for consistent ISNT-N interpretations, and LOI500 equivalents can be used to derive ISNT-Ncritical values.

See more from this Division: ASA Section: Agronomic Production Systems
See more from this Session: General Nutrient Management Oral