Based on the 83 test sites in three states of two years, the critical concentration PSNT was found to be 25 ppm (Figure 3). This is less than the 30 ppm originally postulated.
At demonstration sites on commercial farms in Connecticut, 70% of the field samples used less nitrogen in 1995 and 75% in 1996. Comparable figures for New Hampshire are 60% and 70%, respectively. New Jersey reported 61% of the sites sampled in 1995 required reduced nitrogen, and project a 30% overall reduction in nitrogen use on sweet corn as a result of adoption of the PSNT.
The PSNT will be available as a routine soil test option in Connecticut, New Hampshire and New Jersey as well as other northeastern states.
* Aggressively advocate the adoption of PSNT to determine N requirements for sweet corn.
* Conduct an agronomic and economic evaluation of the recently establishment 30 ppm critical concentration (Heckman, 1993) for the PSNT in sweet corn.
* Conduct an agronomic and economic evaluation of the UV 200 preplant soil nitrate test (Fox et al., 1993) as an indicator of available soil N and as a predicator of N requirements for sweet corn.
Connecticut and New Hampshire
Each of the commercial grower cooperators were asked to apply only 20 lbs N/A as a starter fertilizer at time of sweet corn planting. The remainder of the N was sidedressed when plants were 12 to 18 inches tall.
The sidedress N rates applied by hand were 0, 40, 80, 120, or 160 lbs N/A. PSNT soil samples were taken from the 0 to 12 inch soil depth just before applying the sidedress N.
Each of the commercial grower cooperators were asked to apply only 20 lbs. N/A as a starter fertilizer at time of sweet corn planting. The remainder of the N was side-dressed when plants were 12 inches tall. At two of the six NJAES farms, 40 lbs. N/A was broadcast prior to planting.
The sidedress N rates applied by hand were 0, 40, 80, 120, or 160 lbs. N/A. PSNT soil samples were taken from the 0 to 12 inch soil depth just before applying the sidedress N.
The results for each of the PSNT experiments are illustrated in Figure 1, 2, 4, 5 which gives the PSNT value, amount of sidedress N recommended by the PSNT, and the number of marketable sweet corn ears produced.
The six commercial grower farms were located in northern New Jersey on silt loam soils and the six NJAES farms were in central New Jersey on sandy loam soils. None of the twelve farms had a recent history of manure application. The PSNT values at the six commercial grower sites were relatively low. Because these sites had PSNT values less than 25 ppm NO3-N, sidedress N fertilizer was recommended for each site. In 1995 (figure 1), the three commercial grower sites did not respond to sidedress N fertilizer. Although these three sites represent examples of where the PSNT would have incorrectly predicted a need for sidedress N fertilizer, the recommendations were not different from the growers usual practice to apply sidedress N. At two of the NJAES farms, the PSNT values are low and sidedress N was therefore recommended. At these two sites, the PSNT correctly predicted that sidedress N was needed. At the third NJAES farm, the PSNT was 25 ppm. This value is right at the PSNT critical concentration and the sweet corn crop, as predicted, did not need sidedress N.
In 1996, rainfall amounts in the spring were about two times above normal. This extremely wet weather caused loss of soil nitrate nitrogen and this is reflected in the lower PSNT values for the field sites in 1996 (Figure 2). All sites exhibited responses to sidedress N and this was predicted by the PSNT. The rates of sidedress nitrogen recommended based on the PSNT were generally appropriate for the crop yield responses that were obtained.
The non-response of the commercial grower fields to sidedress N when it was predicted in 1995 may be explained by their rather low plant populations and lower yield levels. Our target population for the NJAES research farms is 24,000 plants per acre. Because the sidedress N requirement for sweet corn likely decreases as population decreases, PSNT recommendations should be adjusted accordingly. If commercial sweet corn growers would increase their plant population they would likely also increase their net return per acre. In 1996, we attempted to establish higher plant populations at all farms but the target population was only achieved at the Donaldson farm. This farm obtained an excellent yield and the PSNT made a correct prediction for the amount of sidedress N required.
A sweet corn population trial was conducted in Connecticut with 5 populations (12, 16, 20, 24, and 28,000 plants/acre) and 4 replications. The 24,000 plants/acre treatment produced significantly higher (P>F=0.01) yield of marketable ears than all other treatments.
Two research sites were used for soil test calibration in 1995.
Treatments were replicated four times at each site. Soil nitrate concentration ranged from 27 to 104 ppm N. There were no significant yield increases from nitrogen applications at either site. Rates applied were 0, 40, 80, 120 and 160 lbs N/A.
There were three replicated research trials in 1996. One was at the University of Connecticut’s Agronomy Research farm and two were on commercial grower fields. At two of the trials, the soil nitrate-N concentrations were greater than the 25 ppm critical level; one trial tested 27 ppm; and one tested 33 ppm. This indicates that no additional N fertilizer is needed. Statistical analysis of the data confirmed that there was no significant yield increase from application of sidedress N fertilizer at either trial. At the third trial, Freund number 2, the soil nitrate-N concentration was 10 ppm and a statistically significant yield increase was measured. A sidedress N rate of 40 pounds/acre increased yields about 10,500 marketable ears/acre. Yields for N rates greater than 40 pounds were statistically the same as the 40 pound rate. These results confirm the 1995 findings and agree with the results reported by the other participants.
Thirty seven sweet corn fields totaling 130 acres were sampled in 1996 for the Presidedress Nitrate Test (PSNT). Of the fields sampled, 75% tested above the 25 ppm threshold and required no N sidedressing. A further 8% tested between 20 and 25 ppm and received 10 lb./A N as a sidedressing. The balance tested in the 9 to 14 range and received the full 60 lb./A N side-dressing. 1996 was a severe test for the PSNT in Connecticut. The growing season was very wet and growers were concerned about leaching loss. The PSNT proved very accurate. Grower evaluations of yield and quality were positive at every site.
The savings from the use of PSNT were significant. Ninety eight acres were not sidedressed for a savings of 5,880 lbs. of N or 13,067 lbs. of urea or 17,818 lbs. of ammonium nitrate. At 30¢ per pound for N, that is a savings of $1,764 or about $18/A.
Three research sites were used in New Hampshire for soil test calibrations in 1995. The sites had soil nitrate concentrations of 9, 52 and 61 ppm N. There was a yield response to nitrogen fertilizer only at the testing site with 9 ppm N. At this site, the Brookdale Farm, there was a statistically significant yield increase up to 80 lbs N/acre.
There were three trials reported in 1996. One was at the University of New Hampshire’s Kingman Research farm and two were on commercial growers’ fields. At two of the trials the soil nitrate-N concentration was greater than 25 ppm and there was no statistically significant yield increase. At one trial, the Wilson farm, the soil nitrate-N concentration was 23 ppm and there was no statistically significant yield increase. Lack of a yield response when the soil test nitrate concentration is less than 25 ppm is not uncommon in corn. In 33 Connecticut field corn trials eight of the trials tested between 20 and 25 ppm, but a yield response to N fertilizer was observed at only half of the trials.
Nine farmers in Hillsborough County used the PSNT to estimate N fertilizer needs for sweet corn in 1995. These farmers tested 51 fields and 250 acres of sweet corn. This is 39% of the total sweet corn acreage in Hillsborough County. Almost 60% of the acreage tested greater than 25 ppm and required no additional nitrogen. Almost one-third of the samples tested greater than twice the concentrations needed for maximum yield. In 1996, 12 farms participated in the PSNT sampling program. Seventy percent of the sweet corn fields sampled required no additional nitrogen. This resulted in a reduction of 15,219 pounds of nitrogen fertilizer.
In New Jersey, we are building on the successful adoption of the PSNT to field corn production by encouraging extension of its use to sweet corn. In field corn, the PSNT reduces N fertilizer usage by about 30% while maintaining crop yield. Field corn production costs are reduced by an average of $12.00 per acre where the PSNT is used and the potential for nitrate pollution of ground water is reduced. Research was conducted at 73 locations from 1991 to 1996 to calibrate the PSNT for use with sweet corn and to aggressively advocate its use. Twelve replicated PSNT experiments — six on commercial grower fields and six on New Jersey Agricultural Experiment Station (NJAES) farms — were conducted from 1995 to 1996. Based on the results of the latest research, the PSNT critical concentration has been lowered from the preliminary value of 30 ppm NO3-N to 25 ppm (Heckman et al., 1995). The establishment of the lower critical concentration means that fewer sweet corn fields will receive unnecessary applications of sidedress N fertilizer.
Rutgers Cooperative Extension personnel are directly assisting commercial growers with the adoption of the PSNT. Soil samples were collected on 16 different farms from a total of 46 acres of commercially grown sweet corn in 1995 and 1996. Nitrogen fertilizer recommendations were provided to the growers based on the results of the soil analysis for nitrate nitrogen (PSNT).
Morris County Agricultural Agent, Pete Nitzshe, worked with growers using the test on loamy soils and compared PSNT recommendations to the growers usual practice. In ten different fields where the PSNT was used, the average potential saving was 48 lbs. N/acre or the equivalent of $14.31 per acre.
Middlesex County Agricultural Agent, William Hlubik, worked with growers using the test on sandy soils and compared PSNT recommendations to the growers’ usual practice. In six different fields where the PSNT was used, more sidedress N was generally recommended than the growers’ usual practice. In one field, the PSNT recommendations decreased the sidedress N rate, and in another field there was no change from the growers’ usual practice. On average, the PSNT recommended 38 lbs. N/acre more than the growers’ usual practice. In at least two fields where the PSNT recommended more sidedress N than the growers’ usual practice, marketable sweet corn yield was increased 35%.
Soil samples collected from loamy soils in Morris County generally had higher PSNT values than samples collected from sandy soils in Middlesex County. The PSNT appears to be most useful for sweet corn produced on finer textured soils where significant concentrations of NO3-N are more likely to be found.
Published Scientific Articles
Heckman, J.R., R. Govindasamy, D.J. Prostak, E.A. Chamberlain, W.T. Hlublik, R.C. Mickel, and E.P. Prostko. 1996. Corn Response to Sidedress Nitrogen in Relation to Soil Nitrate Concentration. Communications in Soil Science Plant Analysis. 27: 575-583.
Weliwata, A., R. Govindasamy, and J.R. Heckman. 1996. Economically Optimum Nitrogen Fertilizer Rates for Corn in New Jersey. New Jersey Agricultural Experiment Station. P-02137-1-96. 22pp.
Heckman, J.R., W.T. Hlubik, D.J. Prostak and J.W. Paterson. 1995. Presidedress Soil Nitrate Test for Sweet Corn. HortScience, 30: 1033-1036.
Heckman, J.R., W.T. Hlubik. 1995. Sweet Corn Nitrogen Recommendations Based on the Presidedress Soil Nitrate Test. Agronomy Abstracts, p. 253.
Heckman, J.R. 1996. Presidedress Soil Nitrate Testing. NE67: Coordinating Committee for Soil Testing. Training Session for Certified Crop Advisors. Cornell University.
Heckman, J.R., W.J. Hlubik, D.J. Prostak. 1995. Sweet Corn Nitrogen Recommendations Based on the Presidedress Soil Nitrate Test. American Society of Agronomy Annual Meeting, October 29 – November 3, St. Louis, Missouri.
Heckman, J.R. 1995. In-Season Nitrogen Availability Testing to Predict Need for Sidedress Nitrogen. NE67: Coordinating Committee for Soil Testing. Training Session for Certified Crop Advisors. University of Maine.
Heckman, J.R. 1995. Extension of the Presidedress Soil Nitrate Test for New Jersey Field and Sweet Corn. Presented to the Northeast Region Sustainable Agriculture Research and Education Symposium. Newark, New Jersey.
Presentations to Growers
Heckman, J.R. 1995. Sidedress Nitrogen Rates for Sweet Corn Based on Soil Test. New Jersey Annual Vegetable Growers Meeting. Atlantic City, New Jersey.
Heckman, J.R. 1995. Field Demonstration of the Presidedress Soil Nitrate Test on Sweet Corn. North Jersey Vegetable Growers Twilight Field Meeting.
Ashley, R.A. January 26, 1995. Matching Fertilizer Applications to Crop Needs. Connecticut Small Fruit and Vegetable Growers Annual Meeting. Attendance: 80.
Morris, T.F. January 26, 1995. A Nitrogen Soil Test for Sweet Corn. Connecticut Small Fruit and Vegetable Growers Annual Meeting. Attendance: 80.
Hamilton, G.W. March 8, 1995. Benefits and Use of the PSNT for Sweet Corn. New Hampshire State Vegetable Meeting. Concord, NH. Attendance: 110.
Hamilton, G.W. April 20, 1995. A Win-Win Situation – The Benefits and Uses of the PSNT for Crop Production and the Environment. Hudson-Litchfield Rotary, Hudson, NH. Attendance: 25.
Hamilton, J.R. June 13, 1995. Use of the PSNT for Sweet Corn Production. New Hampshire Vegetable and Small Fruit Twilight Meeting. Brookdale Farm, Hollis, NH. Attendance: 250.
Heckman, J.R. 1995. Sweet Corn Nitrogen Fertility Management. Central Jersey Vegetable Growers Meeting.
Heckman, J.R. 1995. Managing Sweet Corn Nitrogen Using the Presidedress Soil Nitrate Soil Test. Burlington County Sweet Corn Growers Meeting.
Morris, T.F. September 8, 1995. Use of PSNT for Sweet Corn. Vegetable Growers Twilight Meeting, University of Connecticut Field Research Facility . Attendance: 15.
Ashley, R.A. October 31, 1995. PSNT in Connecticut, New England Extension Vegetable Team In-service Training. Portsmouth, NH. Attendance: 14.
Hamilton, G.W. October 31, 1995. PSNT use by Vegetable Growers in Hillsborough County. New England Extension Vegetable Team In service Training. Portsmouth, NH. Attendance: 14.
Morris, T.F. 1995. Nitrate testing for Sweet Corn. 1995 New England Vegetable and Berry Growers Conference. Sturbridge, Massachusetts.
Heckman, J.R. 1995. Problem Solving with Soils and the PSNT. Integrated Crop Management Workshop.
Heckman, J.R. 1996. Presidedress Soil Nitrate Testing in a Wet Season. Integrated Pest Management Program. Northwest Jersey Twilight Meeting.
Heckman, J.R. 1996. Double Cropping Fall Cabbage and the Presidedress Soil Nitrogen Test. Northwest Jersey Horticultural Research Twilight Meeting.
Heckman, J.R. 1996. Using the Presidedress Soil Nitrate Test for Sweet Corn Fertility Management. New Jersey Annual Vegetable Meeting.
Heckman, J.R. 1996. Use of the Presidedress Soil Nitrate Test in Sweet Corn. Burlington County Sweet Corn Growers Meeting.
Hamilton, G.W. 1995. Information sheet on use and directions for PSNT for sweet corn.
Heckman, J.R., E.A. Chamberlain, W.T. Hlubik, E. Prostko, R.C. Mickel, and D.J. Prostak. 1995. Using the Presidedress Soil Nitrate Test to Cut Costs for Nitrogen Fertilizer. New Jersey Grain and Forage Journal, 2:28-54.
Morris, T.F. 1995. Finally! A Nitrogen Test for Sweet Corn. Grower 95(3):3.
Hamilton, G.W. 1995. Evaluation of the Presidedress Soil Test for Sweet Corn. Grower 95(4):2.
Heckman, J.R. 1995. Presidedress Soil Nitrate Test (PSNT) Research Update. The Soil Profile. Volume 5, No. 2.
Heckman, J.R., and W.T. Hlubik. 1995. Know Your Nitrogen: PSNT Can Help Sweet Corn Growers Determine the Need for Sidedress Nitrogen Application. American Vegetable Grower, June, p. 22.
Morris, T.F. 1995. Past, Present and Future of Nitrogen Management. Grower 95(11):1-2.
Morris, T.F. 1996. Past, Present and Future of Nitrogen Management – Part 2. Grower 96(4):3-5.
Heckman. J.R. 1996. Sweet Corn Yield in relation to Plant Population. Plant and Pest Advisory. Vegetable Crops Edition. April.
Heckman, J.R. 1996. Starter, Broadcast, and Sidedress N Fertilizer Decisions. Plant and Pest Advisory. Field Crops Edition. April.
Heckman, J.R. P. Nitzsche, and W.J. Hlubik. 1996. Sidedress Nitrogen Fertilizer Decisions for Sweet Corn. Plant and Pest Advisory. Vegetable Crops Edition. May.
Hamilton, G.W. 1996. Farmers’ Using PSNT to Modify Sweet Corn Production Practices. Grower 96(11/12):7.
Ashley, R.A. 1996. Connecticut Sweet Corn Growers Like PSNT. Grower 96(11/12):12.
Extension Fact Sheets
Morris, T.F., 1995. Soil testing to manage nitrogen for sweet corn. CT Cooperative Extension fact sheet 95-11.
Morris, T.F., 1995. Soil testing to improve nitrogen management for corn. CT Cooperative Extension fact sheet 95-1.
Heckman, J.R., D. Prostak, and W.T. Hlubik 1995. Presidedress Soil Nitrate Test (PSNT) Recommendations for Sweet Corn. FS 760. 2pp.
Heckman, J.R., D. Prostak, and W.T. Hlubik. 1995. Presidedress Soil Nitrate Test (PSNT) Equipment and Laboratories. FS 799. 1pp.
Morris, T.F. and G.W. Hamilton. New England Vegetable Extension In-service Training. Nov. 18-19, 1996. Portsmouth, NH.
Impacts of Results/Outcomes
Our research confirms that the PSNT critical concentration is less than 30 ppm or about 25 ppm (Figure 3). One of the PSNT experiments had a PSNT of 25 ppm and there was no response to sidedress N (Figure 1, Adelphia farm). Using the PSNT at this site would have saved about 125 lbs. N/A or an equivalent of $37.50 per acre. Using the PSNT recommendations for sweet corn (as published in Table 1 of Rutgers Cooperative Extension Fact Sheet 760) for each of the twelve PSNT experiments would have resulted in an average sidedress N recommendation of 95 lbs. N/A. This is about 30 to 65 lbs. less than the standard recommendation of applying 125-160 lbs. N/A without the PSNT. Results suggest that using the PSNT to make sidedress N recommendations for sweet corn may reduce N fertilizer usage by about 30%. This savings is similar to that which has been found for using the PSNT on field corn.
The sidedress N requirement for sweet corn should decrease as the plant population decreases below an optimum population of about 24,000 plant/A. PSNT recommendations should be adjusted downward accordingly.
A recently published study (Nitrogen and Sulfur Fertilization Influences Aromatic Flavor Components in Shrunken 2 Sweet Corn Kernels, J. Amer. Soc. Hort. Sci. 120 (5): 771. 1995) suggests that certain sweet corn hybrids have a higher N fertilizer requirement for flavor development. PSNT recommendations may need to be adjusted for various sweet corn hybrids.
All three participants observed significant reductions in nitrogen use on PSNT sampled sweet corn fields. Reductions ranged from 0 to 160 lb/A in research calibration plots. On commercial farms, 75% of Connecticut fields and 70% of New Hampshire fields required no nitrogen sidedressing. This would result in savings of $18-20 per acre. New Jersey reports anticipated reduction in nitrogen fertilizer of 30% valued at about $14-15 per acre.
Changes in Practice
In 1995 and 1996, at least 12 commercial sweet corn growers in New Jersey used the PSNT on part of their crop acreage. The PSNT was used on a total of 46 acres of sweet corn. We compared the PSNT recommendation to the growers usual practice. The results showed that in 61% of the fields, the PSNT recommendations lowered the N fertilizer use from the farmers’ usual practice; in 6% of the fields there was no change from the usual practice, and in 33% of the fields the PSNT recommended more N than the farmers had intended to apply. Overall use of the PSNT on these 46 acres reduced N fertilizer recommendations by an average of 31 lbs. N/A. This amounts to a potential net savings of $9.30 per acre.
The PSNT is probably most useful to growers that produce sweet corn on manured land or have fine textured soils with relatively high organic matter content. In these situations, the PSNT will likely measure significant levels of NO3-N and reduce sidedress N application rates accordingly.
The PSNT also can be used where modest amounts of preplant nitrogen fertilizer have been applied. Growers in Connecticut and New Hampshire have successfully used the test by applying 60 to 100 pounds of preplant nitrogen and then sidedressing the amount of nitrogen recommended by use of the PSNT. Frequently the test recommendation is for little or no fertilizer nitrogen.
“After using the PSNT for a few years, I am much more confident about the amount of nitrogen fertilizer my corn crop needs.”
“Trying the PSNT is causing me to reevaluate my N fertility program for sweet corn.”
“It helped me to realize that some of my fields were underfertilized. Applying more sidedress N when recommended by the PSNT increased sweet corn yield about 35%.”
Number of growers/producers in attendance at:
Field Days: 390
Other Events – New England Vegetable Extension In-service Training: 28
Areas needing additional study
Recent studies with field corn have shown that the nitrogen status of the crop can be assessed by measuring the NO3-N concentrations in the lower portion of cornstalks at the end of the growing season. This tissue test is designed to determine if the amount of N fertilizer that was applied to the crop was too low, optimal, or excessive. If this tissue test was calibrated for sweet corn, growers would have a new method to evaluate the consequences of their N fertility management practices and to learn from experience. This “end-of-season cornstalk test” may be useful to evaluate sweet corn fields where the PSNT has been used and it may help to increase grower confidence in the PSNT. This is currently under investigation as a SARE/ACE project (number 96 LNE96-73) entitled: “At-harvest Stalk Nitrate Testing for Sweet Corn.”