Corn Stalk Nitrate Concentration Profile

knowledge of crop N need may be used by producers to guide future fertilizer-N management thereby improving The end-of-season stalk nitrate test provides a method of assessing profitability and reducing environmental degradation. the N available to the corn (Zea mays L.) crop during the latter part of the season. This study was conducted to determine how stalk nitrate To be a useful crop management tool, methods for test results and interpretations are affected by sample composition. collecting and analyzing samples must be straightforStalks were collected from three field sites and separated into phytomward and reasonably flexible so producers and consulers (node plus internode above), which were subdivided into three tants can adapt to field conditions as they gather samor five segments after length was measured. Nitrate-N concentration ples. It is unrealistic to assume that samples will always of phytomers decreased linearly from the soil to the ear. Within a be exactly 20-cm long and can always be collected bephytomer, segments also decreased acropetally (from base to apex). tween 15 and 35 cm above the ground under field situaNode tissue NO3–N concentration did not differ from that of the tions. For example, if samples are collected after cominternode segment immediately above the node. Weighted means bine harvest, the specified stalk segment (Binford et al., were used to compute NO3–N concentration of stalk samples collected 1990) may be destroyed or severely damaged and there5 cm higher (from 20 to 40 cm above the soil) or lower (from 10 to 30 cm above the soil) on the stalk than in the original method (from fore inappropriate for use in assessing late-season N 15 to 35 cm above the soil). Although the three samples (10–30, 15–35, nutrition of the crop. The objective of this study was to and 20–40 cm) differed in NO3–N concentration, the difference was determine the distribution of nitrate by phytomer (node only about 15% compared with the 25% difference in sampling posiand the internode above) within stalks of corn and how tion ( 5 cm of 20-cm sample length). The phytomer nearest the soil stalk nitrate test results and interpretations would be had 35 to 40% greater NO3–N concentrations than the section of stalk affected if samples were collected from a portion of the 15 to 35 cm above the soil. Critical values delineating yield-limiting, stalk different from that specified in the original method adequate, and excessive N availability should be modified if stalk (Binford et al., 1990). sections other than the standard 15 to 35 cm section are used. However, the qualitative nature of the stalk nitrate test and the range of NO3–N MATERIALS AND METHODS concentrations observed with reasonable corn cultural practices (1000 ) make this test quite robust and precise definition of sample At physiological maturity, stalks were collected from 20 composition and critical values less necessary. corn plants grown in a rainfed, general production field at the Agronomy Havelock Farm, Lincoln, NE, to conduct initial analyses (designated the 20-stalk experiment in the remainder of the paper). NC hybrid 4880 was planted in late April at T end-of-season corn stalk nitrate test (hereafter about 49 000 plants ha . Nitrogen was applied pre-plant at referred to as the stalk nitrate test) was proposed and 140 kg ha 1 as anhydrous ammonia. Weeds were controlled advocated by Binford et al. (1990) as a method of deterby a combination of pre-emergence herbicides and cultivation. mining if excessive or insufficient N was available to the Crop yield was 6.35 Mg ha . Stalks were randomly assigned corn crop during the latter part of the season. In the test, to 1 of 10 replications. Leaves were removed and stalks air20-cm segments of corn stalks (between 15 and 35 cm dried before processing. During processing, stalks were cut above the soil) are collected from several plants ( 10), immediately below each node. Each phytomer was further dried, ground, and analyzed for nitrate-N. Nitrate-N condivided into six pieces: the node and five equal-length pieces centrations 700 mg kg 1 plant tissue indicate that availof each internode. Comparable components (i.e., node from able N limited grain yield; whereas, nitrate-N concentrathe first phytomer above the soil or the third internode segment of the second phytomer down from the ear) from the tions 2000 mg kg 1 indicate excessive amounts of N two stalks in each replication were combined and ground with were available to the crop (Binford et al., 1992). Other rea Wiley mill (Thomas-Wiley Co., Philadelphia, PA) to pass searchers have evaluated the proposed test and concur that a 2-mm screen. Nitrate was extracted and analyzed with a when stalk nitrate concentrations are great ( 2000 mg nitrate electrode (Wilhelm et al., 2000). kg 1), excessive levels of N were available to the crop Corn stalks were collected from two experiments including (Varvel et al., 1997). These studies suggest that the stalk continuous corn and corn–soybean [Glycine max (L.) Merr.] nitrate test can be used as a postmortem to determine cropping systems and N rates as treatments. The first experiif yield-limiting or excessive N were present. Historical ment was irrigated (designated the irrigated experiment in the remainder of this paper) and established near Shelton, NE, on a Hord silt loam (fine-silty, mixed, mesic, Pachic HaplusUSDA-ARS, 120 Keim Hall, Univ. of Nebraska, Lincoln, NE 68583toll). The experiment was part of the research component of 0934. This paper is a joint contribution of the USDA’s Agricultural Research Service and the Agricultural Research Division of the Univ. of Nebraska. Published as Journal Series no. 14914. Received 21 Mar. 1 Mention of products and equipment are for information only and 2005. *Corresponding author ([email protected]). do not imply endorsement of products by the authors, USDA-ARS, or University of Nebraska, Agricultural Research Division. Published in Agron. J. 97:1502–1507 (2005).