Continued Assessment of Fall Soil Nitrate Test for Wheat Production MGPUB Grant # First Year Report Dr. Bob Kratochvil

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1 Continued Assessment of Fall Soil Nitrate Test for Wheat Production MGPUB Grant # First Year Report Dr. Bob Kratochvil Summary The need for fall fertilizer nitrogen for wheat can be determined by soil test that measures the amount of residual soil nitrate present in the surface 6-inches of soil. This test is called the Fall Soil Nitrate Test (FSNT). Up to 30 lb fall fertilizer N acre -1 is recommended for wheat when a concentration of 10 ppm nitrate is determined by a laboratory measurement using a Lachat QuickChem Flow Injection Platform. Forrestal and Kratochvil have recommended that residual soil nitrate can be measured using a NitraChek Quicktest kit that is currently used to conduct the PSNT (Pre Sidedress Nitrate Test) for determining need for sidedress nitrogen for corn. Currently, up to 30 lb fall fertilizer N acre -1 is recommended when a concentration of 12 ppm nitrate is measured with this kit. A total of 163 Lachat measurements for determining the need for fall fertilizer nitrogen were made. There were 326 comparisons to these Lachat measurements (two comparisons for each Lachat measurement) made by UM Extension nutrient management consultants utilizing their NitraChek Quicktest kits. Per these comparisons, the same recommendation for use of fall fertilizer nitrogen would have occurred 97% of the time. This supports the use of the NitraChek Quicktest kit for conducting the FSNT. At four of five locations, the two nutrient management consultants who analyzed the same set of samples got similar results that resulted in the same recommendation for fall fertilizer use. At one of the locations, the two nutrient management consultants made recommendations that were different for 7 of the 32 samples they analyzed. This indicates that 1) if a NitraChek Quicktest kit is to be employed, it must calibrated and checked for accuracy before doing any tests and 2) the nutrient management consultants who conduct the tests must be adequately trained so that they can provide reliable results. Per the results obtained in this first year study, the current use of either 10 ppm nitrate concentration (Lachat test) or 12 ppm nitrate concentration (NitraChek Quicktest) for recommending no fall fertilizer nitrogen is reliable. Across the five locations where wheat was grown, average wheat yield advantage with the use of 30 lb fall N acre -1 was 2.5 bu acre -1. Of those five locations, three had a statistically significant response to the use of fall N however, at only one of those three locations was the amount of yield enough to be profitable (5.4 bu acre -1 yield advantage that resulted in $5.81 acre -1 profit). Over the other four locations (all of which had residual soil nitrate concentrations that recommended fall fertilizer N be used), a net loss of nearly $13 acre -1 occurred. Introduction and Project Justification Maryland Department of Agriculture has initiated a regulation for use of fall nitrogen for small grains that is dependent upon a fall soil nitrate test (FSNT). If the residual soil nitrate concentration for a field where wheat will be planted is 10 ppm or less (6-inch sample), 30 lb N/acre will be allowed. If the nitrate concentration exceeds 10 ppm, no fertilizer fall N is allowed. For a field to be planted to barley, the residual soil nitrate concentration must be 15 ppm or less for use of 30 lb fall N.

2 This project will add to the growing number of field comparisons that have tested the fall soil nitrate test for determination of the need for fall fertilizer nitrogen. Additionally, more side by side wheat performance data will result that will allow further evaluation of the ability of this tool to assist farmers with the wheat fall nitrogen management decision. Procedures The locations used for this project are the same as those used for MGPUB # , Response of Corn Hybrid Type to N Rates and Subsequent Effect on Wheat. Those locations provided a wide range of residual soil nitrate concentrations per the corn N rate treatments that were used as well as sites that are representative of Maryland s physio-geographic regions. Following harvest of the two near-isoline corn hybrids, soil samples to a depth of six inches were collected from the plots representing four of the six corn N rate treatments. Each of these plots was divided so that ½ would receive no fall fertilizer N and the other ½ would get 30 lb N acre -1. Spring fertilizer N for the wheat was applied at all locations in two applications (~March 1 and at jointing). Locations: Lower Eastern Shore R&E Center Salisbury (irrigated site) No wheat evaluation at this location due to poor stand. Lower Eastern Shore R&E Center Poplar Hill Wye R&E Center Agronomy Farm Central Maryland R&E Center Upper Marlboro No soil samples for this location; these soil samples are part of the labeled nitrogen study (MGPUB # ) that has been given an extension until December 31, Central Maryland R&E Center Beltsville Western Maryland R&E Center Keedysville Experimental design: A split plot arrangement of treatments within a randomized complete block design with a minimum of 4 replications per site. Whole plots were the corn N rate treatments used in the Corn Hybrid Type study. Split plots were the two fall fertilizer N treatments. Soil analyses: All soil samples were air dried immediately following their collection. Each sample was divided so that it could be subjected to two types of analysis. The first analysis was conducted by a laboratory technician at the University of Maryland s Department of Environmental Science and Technology laboratory utilizing the Lachat QuikChem Flow Injection Platform analyzer. The Lachat is currently the standard piece of equipment used for measuring soil nitrate concentration in many soil testing laboratories. The second analysis was conducted by nutrient management consultants located at 10 University of Maryland Extension offices utilizing the NitraChek Quicktest kit that is also used to measure Pre Sidedress Nitrate concentrations for determining sidedress nitrogen need for corn. The NitraChek Quicktest has been recommended for use with the FSNT per results obtained by Drs. Forrestal and Kratochvil. Soil samples for each location in this study were analyzed by two nutrient management consultants who used their NitraChek Quicktest kit.

3 Data analyses: Wheat yield analyzed for determination of differences for yield between the use and non-use of fall fertilizer nitrogen. Soil nitrate concentration the two measurements (Lachat and NitraChek kit) were compared to determine accuracy of recommendation and to determine how much variation exists between the two. Results Salisbury was 6.3 ppm. Average soil nitrate concentration for the measurements made by two nutrient management consultants using the NitraChek Quicktest was 3.1 ppm. There were no differences in residual soil nitrate concentration among the previous corn N rate treatments for either the Lachat measurements (range =5.7 to 6.7 ppm across the four corn N rates tested) or the Nitrachek measurements (range = 2.6 to 3.4 ppm). The association between the two tests (R=0.12) was not good primarily because the NitraChek test consistently measured concentrations 2 to 4 ppm less than those measured by the Lachat. However, the results were similar for both nutrient management consultants who analyzed the Salisbury samples. The low soil nitrate concentrations measured by both tests were somewhat surprising given the corn yield at Salisbury (124 bu acre -1 average over all N rates excluding the 0 N rate). This yield did not meet the expectation for this location per the good growing conditions and supplemental irrigation that occurred. And, this yield should have indicated that a greater amount of residual soil nitrate remained which was not the case. Soil type provides the explanation for these low FSNT results. This location has a loamy sand soil type that does not retain soil nitrate well so it is not surprising that the soil nitrate concentrations were low. Both the Lachat and the NitraChek Quicktest results supported a recommendation to use fall fertilizer nitrogen when planting the wheat. However, no wheat harvest occurred because of poor stand establishment that forced abandonment of the plots. Poplar Hill was 2.5 ppm. Average soil nitrate concentration for the measurements made by two nutrient management consultants using the NitraChek Quicktest was 3.9 ppm. Because the NitraChek test used by the nutrient management consultants consistently predicted the residual nitrate concentration to be 1.45 ppm greater than those attained by the Lachat test, the association between the Lachat and the NitraCheck tests was considered fair (R=0.30) at best. There were no significant differences in residual soil nitrate present among the previous corn N rate treatments for either the Lachat measurements or the Nitrachek measurements. The low amounts of residual soil nitrate were the result of favorable growing conditions that allowed the corn to consume the nitrogen that was supplied. Average corn yield across all corn N rate treatments (excluding the 0 N treatment) at Poplar Hill was over 219 bu acre -1. Both soil test types recommended that 30 lb fall fertilizer N acre -1 should be used. And, there was a 3.5 bu acre -1 yield advantage attained with its use. However, using a wheat price of $5.15 bu -1 (average 2014 Perdue price Salisbury) and $0.50 lb -1 N and $7.00 acre -1 application cost, there would have been a net loss of approximately $4 acre -1 with the use of fall N. Wye

4 was 2.4 ppm. Average soil nitrate concentration for the measurements made by two nutrient management consultants using the NitraChek Quicktest was 5.7 ppm. Due to the consistent 3.3 ppm greater (range = -2 to +8 ppm) soil nitrate concentration measured with the NitraChek test, the association between the two was considered relatively poor (R=0.18). There was a significant difference in residual soil nitrate present among the previous corn N rate treatments for the Lachat measurements but they were not important because the difference between the 0 N rate (2 ppm) and the 275 lb N rate (2.95 ppm) was meaningless agronomically. There were no differences in soil nitrate concentration among the corn N rate treatments for the NitraChek Quicktest measurements. These low residual soil nitrate concentrations found by both tests were the result of favorable growing conditions that allowed the corn to consume the nitrogen that was supplied. Average corn yield during 2013 across all corn N rate treatments (excluding the 0 N treatment) at Wye was 170 bu acre -1. Both soil test types indicated that 30 lb fall fertilizer N acre -1 was allowed. The use of this fall N resulted in a significant 5.4 bu acre -1 yield advantage. Using a wheat price of $5.15 bu -1 (average 2014 Perdue price Salisbury) and $0.50 lb -1 N and $7.00 acre -1 application cost, there would have been a net gain of approximately $5.81 acre -1 with the use of fall N. It is important to note that there were differences in the results obtained by the two nutrient management consultants using the NitraChek test kits. All 32 samples analyzed by consultant one were within +/- 2 ppm of those obtained using the Lachat and did not result in any incorrect recommendations for use of fall N. However, for consultant two, the average variation compared to the Lachat measurements was +5.7 ppm. And, this consultant had 7-32 instances when a recommendation to not use fall N (soil nitrate concentration was >12 ppm allowed when using the NitraChek kit) would have been made. These results indicate that there may be variability among the NitraChek kits and among the skills of the nutrient management consultants who use them and that this needs to be considered when the NitraChek test kit is used. Beltsville was 5.8 ppm. Average soil nitrate concentration for the measurements made by the two nutrient management consultants using the NitraChek kits was 4.4 ppm. The average variability for the NitraChek compared to the Lachat was ppm. The association between conducting the FSNT with the Lachat compared to having it done by a nutrient management consultant with the NitraChek kit was good (R=0.75). There were significant differences in residual soil nitrate present among the previous corn N rate treatments for the Lachat measurements but they were considered not important because the difference between the 0 corn N rate (4.2ppm) and the 275 lb corn N rate (7.7ppm) would not have caused a different fall N use recommendation. There also were significant differences in soil nitrate concentration measured by the nutrient management consultants using the NitraChek kits. The 0 corn N rate concentration with the kits was 3.2 ppm and the 275 lb corn N rate concentration was 7.1 ppm. Both soil test measurements indicated that 30 lb fall fertilizer N acre -1 was allowed. However, the use of this fall N resulted in no yield advantage. Since no yield advantage was attained, there was a net loss of $22.00 acre -1 (cost of fertilizer and application) with the use of fall N. Of the 40 soil samples analyzed with the Lachat, there were three instances when the soil nitrate concentration was >10 ppm and the recommendation would have been to not use

5 any fall nitrogen. For two of those instances, the results obtained with the nutrient management consultant s analyses would have resulted in the same recommendation as the Lachat, to not use any fall N. And, for one of those instances, a recommendation to use fall N would have occurred with the NitraChek test but a no nitrogen recommendation would have occurred with the Lachat test. The two nutrient management consultants obtained very similar results with their NitraChek kits. There would have been only one instance out of the 40 samples they each analyzed where there would have been a different recommendation for use of fall nitrogen made. Upper Marlboro There was a 3.6 bu acre -1 wheat yield advantage for the use of 30 lb acre -1 fall nitrogen. The soil sample data for this location has not yet been analyzed so it is not known if the soil nitrate concentrations supported the use of fall fertilizer N. However, the amount of yield attained with use of fall N would have resulted in a net loss of $3.46 acre -1. Keedysville There was a significant difference in amount of residual soil nitrate that was dependent upon the previous corn N rate. For the three lowest corn N rate treatments tested (0, 100, and 150 lb N acre -1 ), the average residual soil nitrate concentrations were 5.4 ppm and 5.9 ppm for the Lachat and NitraChek measurements, respectively. These amounts of soil nitrate suggested that 30 lb fall N was needed when planting wheat. For the 275 lb N acre -1 treatment, the soil nitrate concentrations were 27.9 ppm and 20.0 ppm for the Lachat and NitraChek measurements, respectively. These amounts of residual soil nitrate indicated that no fall N was needed for the wheat. The use of fall N at wheat planting resulted in no yield advantage for any of the previous corn N rate treatments. For the 0, 100, and 150 lb N acre -1 rates, this outcome was opposite to what the FSNT recommendation suggested. For the 275 lb N acre -1 rate, no wheat yield benefit with use of fall N followed the FSNT recommendation. Since no wheat yield advantage was attained at the three lowest corn N rates tested, use of fall N for those treatments would have resulted in a net loss of $22.00 acre -1 (cost of fertilizer and application). There was an excellent relationship between the measurements made with the Lachat and those made by the two nutrient management consultants using the NitraChek kits (R = 0.99).