Final Report for LNE96-073

At-Harvest Stalk Nitrate Testing for Sweet Corn

Project Type: Research and Education
Funds awarded in 1996: $4,710.00
Projected End Date: 12/31/1998
Matching Non-Federal Funds: $14,321.00
Region: Northeast
State: New Jersey
Project Leader:
Joseph R. Heckman
Rutgers University, Dept of Plant Science
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Project Information

Summary:

Growers evaluating new practices, such as the Presidedress Soil Nitrate Test (PSNT), are interested in relating observations about crop performance at time of harvest to their N fertility program. To learn more from field observations, growers needed a simple diagnostic test to evaluate crop N status at time of harvest. The at-harvest stalk nitrogen test (ASNT) was developed for this purpose. It indicates whether an inadequate, optimal, or excessive amount of N fertilizer was applied. Stalk N concentrations less than 11.2% are considered N deficient and under fertilized. The N status is optimal when concentrations of n are between 1.2 and 2.2. Concentrations above 2.2% N are above optimal and indicate that sweet corn was over fertilized with N. An examination of the relationship between the PSNT and the ASNT found that these soil and plant tests are complementary. When soil nitrate concentrations were optimal, as measured by the PSNT early in the season, stalk nitrate concentrations were also in the optimal range at harvest. Thus, there is a low risk of sweet corn becoming N deficient when following a no-sidedress N recommendation if indicated by the PSNT. The ASNT can be used to inspire grower confidence in the PSNT.

The ASNT is also useful to sweet corn growers not using the PSNT. A survey of 37 sweet corn fields in New Jersey revealed that about half of the commercial grower fields examined with the ASNT had optimal concentrations of N. In 30% of the fields the ASNT results suggested that the grower applied too little N fertilizer and in 20% of the fields too much N fertilizer was applied. Growers will be able to use these results to adjust their N fertility practice as needed. This is expected to benefit growers with better crop yields or reduced cost of production.

Project Objectives:

1. To determine the below-optimal, optimal, and above-optimal concentrations of nitrate in the basal portion of sweet corn stalks sampled at harvest.

2. To evaluate the at-harvest stalk nitrate test as an indicator of sweet corn crop N status.

3. To use the at-harvest stalk nitrate test to help sweet corn growers evaluate sustainable N fertility management practices such as the presidedress soil nitrate test (PSNT).

Cooperators

Click linked name(s) to expand
  • J.R. Heckman

Research

Research results and discussion:
Findings and Accomplishments

Over 60 field experiments were conducted to examine the relationship between sweet corn yield and the nitrogen status of corn stalk tissue sampled at the time of harvest. Immediately following sweet corn harvest, stalk samples were collected by cutting 8-inch segments of corn stalk from 10 randomly selected plants. The tissue samples were dried and analyzed for both NO3-N and total Kjeldahl-N (% N).

The relationship between stalk N status and sweet corn yield are presented in Figures 1 and 2. The optimal stalk NO3-N concentration range appears to be between 13,000 and 15,000 ppm. When the stalk NO3-N concentration was less than 8,000 ppm, sweet corn yield was generally less than 90% of maximum yield. When the stalk NO3-N concentration was above 13,000 ppm, yield was generally greater than 90% of maximum yield.

The optimal % N concentration range in sweet corn stalk tissue appears to be between 1.2 and 2.2% N (Figure 2). Corn plants with stalk N concentrations less than 1.2% generally produced less than 95% of maximum yield. Stalk N concentrations greater than 1.2% were generally associated with yields better than 90% of maximum.

The same experiments used to study stalk N status also measured the soil NO3-N concentration (PSNT) when the plants were 8 to 12 inches tall. A critical PSNT value of 25 ppm NO3-N has been established in previously conducted research (Heckman et al, 1995). PSNT soil test values less than 25 ppm indicate that soil N supply during the growth of the sweet corn is probably not adequate and that sidedress N fertilizer should be applied. PSNT values of 25 ppm or greater indicate that the soil N supply is adequate.

The relationship between the presidedress soil nitrate test and the at-harvest stalk N test were also examined (Figures 3 and 4) and found to be complementary. Although the PSNT samples were taken early in the season when the plants are 6 to 12 inches tall, and the at-harvest stalk N test on the day of harvest, the different tests have agreeable results. When the soil NO3-N concentration was above 25 ppm as measured by the PSNT, the stalk NO3-N and % N values were in or above the optimal range. Thus, when the PSNT predicts that that sidedress N is not needed, the sweet corn crop clearly has enough N supply from soil to complete the growing season. In other words, following a no-sidedress N recommendation, when indicated by the PSNT, has a low risk of later causing the crop to become N deficient.

The ASNT is also useful to sweet corn growers not using the PSNT. A survey of 37 sweet corn fields in New Jersey revealed that about half of the commercial grower fields examined with the ASNT had optimal concentrations of N. In 30% of the fields the ASNT results suggested that the grower applied too little N fertilizer and in 20% of the fields too much N fertilizer was applied. Growers will be able to use these results to adjust their N fertility practice as needed. This is expected to benefit growers with better crop yields or reduced cost of production.

Site Information

New Jersey sweet corn acreage is approximately equally split between sandy textured coastal plain soil and finer textured or loamy soils in the piedmont. We conducted our field trials on a wide range of soils to include soil textures that are representative of where sweet corn is commonly grown. Field sites were located in Warren, Hunterdon, Somerset, Monmouth, Burlington, Middlesex, and Cumberland counties. Approximately a third of the sweet corn PSNT trials were conducted on manured land. Most sweet corn study sites were irrigated and produced useful data.

Participation Summary

Education

Educational approach:
Dissemination of Findings

News Articles, Newsletters and Fact Sheets

In newsletter:

Heckman, J.R. 1998. Technologies for Sweet Corn Nitrogen Management. The Soil Profile. Vol. 8, No. 1.

Presentations to Growers

Heckman, J.R. 1999. (Invited) Sweet Corn Nitrogen Management with the Nitrogen Stalk Test. New Jersey Annual Vegetable Meeting.

Heckman, J.R. 1998. Sweet Corn Stalk Nitrogen Tissue Status at Harvest. American Society of Agronomy Meeting. Baltimore, MD.

Heckman, J.R. 1998. Techniques for Improving the Nitrogen Management of Sweet Corn (Poster) 10th Anniversary SARE Conference,Austin, TX.

Heckman, J.R. 1998. Technologies for Sweet Corn Nitrogen Management. Pennsylvania Sweet Corn School.

Heckman, J.R. 1998. Update on the At-harvest Sweet Corn Stalk Test. New Jersey Annual Vegetable Meeting.

Heckman, J.R. 1997. End-of-season Evaluation of Nitrogen Fertility Program by Stalk Tissue Test. New Jersey Annual Vegetable Meeting. 80 participants.

Project Outcomes

Impacts of Results/Outcomes

The major contribution of the findings from this project is that sweet corn growers have a new tool by which they can evaluate and improve their crops’ N fertility management. At-harvest stalk tissue testing is of little value in the current season. The knowledge gained, however, from several years of testing should enable growers to determine if their N fertility program is on target or needs adjustment. The ultimate benefits are expected to be improved production and/or more efficient use of N fertilizers.

The at-harvest stalk N test may be used along with the PSNT. The results of the at-harvest stalk tissue test may help growers gain increased confidence in the accuracy of PSNT recommendations. The benefits of the PSNT on making more efficient use of N supplied by soil and fertilizer are already well documented. Nitrogen fertilizer recommendations based on the PSNT are generally reduced about one-third on average compared to growers’ usual practice.

Economic Analysis

The cost of performing the at-harvest stalk tissue test is minimal. The tools required include a ruler, sharp knife, paper bag, marking pen, box to mail the samples, and postage. The samples must be sent to a laboratory capable of stalk nitrate or Kjeldahl analysis. The cost per sample is typically $5.00 for nitrate analysis or $6.00 for total Kjeldahl N.

Farmer Adoption

A. Changes in Practice

Growers have become aware of the potential benefits of at-harvest stalk N testing as a result of Extension meetings. More growers will likely adopt the practice once the methods and interpretation are further developed and presented in the form of a Fact Sheet. The at-harvest N test is currently offered to NJ growers for free. Rutgers Cooperative Extension collected stalk samples from 37 commercial sweetcorn fields in 1997 and 1998. The results are being reported to the growers.

B. Operational Recommendations

Growers who are adopting this new diagnostic practice should keep careful records of their N fertility practices and the results of the at-harvest stalk N test for at least two or three seasons. If their stalk samples consistently do not test near the optimum range for N, they should be prepared to make appropriate adjustments in their N fertility program.

Areas needing additional study

Growers are more likely to adopt a practice if it can be made more simple and easy to perform. Procedures to evaluate sweet corn N status in the field should be investigated. Possibilities include extraction of sap from the stalk and analysis for nitrate in the field or the use of a leaf chlorophyll meter.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.