Tissue Test for Excess Nitrogen during Corn Production

Abstract

Seeming conflict between the need to use N fertilizers and the need to protect groundwater quality requires better tools for distinguishing between fertilizer applications that are essential and those that are excessive. Studies were conducted to evaluate NO‐3 concentration in corn (Zea mays L.) stalks at physiological maturity as the basis for a tissue test to characterize degree of N excess during corn production. Samples of the lower portion of corn stalks were collected from plots in N‐rate experiments at 18 site‐years in Iowa. Observed relationships between grain yields and stalk NO‐3 concentrations indicated sharp breaks between NO‐3 concentrations that were not adequate and those that were adequate for obtaining maximum or near‐maximum yields. When yields were near maximum, stalk NO‐3 concentrations increased linearly with amounts of N fertilizer applied. Stalk samples collected at various times after black layering showed that NO‐3 concentrations remained constant for at least 2 wk. These observations suggest that stalk NO‐3 concentration offers great potential as the basis for a tissue test to characterize degree of N excess during corn production.

Corn stalk nitrate concentration profile: Implications for the end-of-season stalk nitrate test

“…As a result, nitrate profiles reported here (Table 2) appear to have a discontinuity that may not exist if data from all phytomers were available. Following the sampling procedures defined by Binford et al (1990) for the stalk nitrate test, the second phytomer above the soil (S+2) would most likely be sampled.…”

“…Data from this initial study with an adequate to excessive N rate (N application, yield stalk nitrate-N, 3254 mg ) suggests critical values may need to be increased by about 35% (comparison of S+2 to S+l in Table 2). New critical values would be about 950 and 2700 mg for yieldlimiting and excessive levels of N [compared to 700 and 2000 mg respectively, as reported by Binford et al (1990)]. Further research, with an array of N rates from yield limiting through excessive, will be required to accurately establish new values.…”

“…If samples are collected closer to the soil than described in the original procedure (< 15 cm above the soil), the resulting analyses will likely produce greater nitrate-N concentrations. As a result, the critical values suggested by Binford et al (1990Binford et al ( , 1992) may have to be adjusted upward. Data from this initial study with an adequate to excessive N rate (N application, yield stalk nitrate-N, 3254 mg ) suggests critical values may need to be increased by about 35% (comparison of S+2 to S+l in Table 2).…”

“…The end-of-season corn (Zea mays L.) stalk nitrate-N test (hereafter referred to as stalk nitrate test) was proposed by Binford et al (1990) as a method of determining if excessive or insufficient N was available to the corn crop during the latter part of the season. In the test, 20-cm sections of corn stalks (between 15 and 35 cm above the soil) are collected from several plants, dried, ground, and analysed for nitrate-N. Nitrate-N concentrations less than dry stalk tissue indicated that available N limited grain yield whereas concentrations greater than indicated excessive N was available to the crop (Binford et al, 1992).…”

“…It is unrealistic to assume that samples will always be exactly 20 cm long and can always be collected between 15 and 35 cm above the ground under field situations. The objective of this study was to determine how stalk nitrate test results and interpretations would be affected if samples were collected from a portion of the stalk different from that specified by Binford et al (1990).…”