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PRODUCTION PAPER

Using the Presidedress Soil Nitrate Test and Organic Nitrogen Crediting to Improve Corn Nitrogen Recommendations

Dep. of Soil Science, 1525 Observatory Dr., Univ. of Wisconsin, Madison, WI 53706-1299

* Corresponding author (andraski{at}facstaff.wisc.edu)

Received for publication January 21, 2002.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
The PSNT and N crediting for organic N inputs can improve the accuracy of corn (Zea mays L.) N recommendations, but are often not used due to producer concerns about their reliability. This study compared the use of these techniques for identifying optimum N rates and quantifying economic returns in 101 N response field experiments with corn conducted during 1989–1999. The accuracy of PSNT recommendations was highest for sites with average or above average May–June air temperatures and high soil yield potential. The frequency of excess N recommendations from the PSNT increased from 16 to 59% when May–June temperatures were >0.56°C below average likely due to slower organic N mineralization. Use of N recommendations based on the PSNT or book value N credits (BVNC) lowered N rates by 90 to 102 kg ha^-1 in systems with recent manure or legume N inputs and increased average economic returns for all cropping systems by $19 ha^-1 compared with unadjusted N recommendations (i.e., economic gain). Economic gains using PSNT- or BVNC-based recommendations were generally highest in the first year following organic N inputs with an average gain of $34 ha^-1 for both methods. Conversely, economic gains were higher using the PSNT ($40 ha^-1) than the BVNC ($2 ha^-1) 1 to 3 yr after the organic N additions on high yield potential soils where May–June air temperatures were average or above. Results from this work confirm that adjusting N application rates for corn using the PSNT or BVNC is more profitable than not making these adjustments.

Abbreviations: BVNC, book-value nitrogen credits • EONR, economic optimum nitrogen rate • PSNT, presidedress soil nitrate test

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
HIGH NITRATE concentrations in water supplies pose environmental and health risks. Increased ground water nitrate concentrations have resulted from excessive nitrogen (N) applications to cropland (Andraski et al., 2000; Brye et al., 2001). A recent CAST task force (1999) reported that N is the most limiting nutrient in reducing oxygen levels (hypoxic zone) in the Gulf of Mexico. Export of N, primarily from agricultural practices in the Mississippi River Basin, to the Gulf of Mexico has increased two- to sevenfold over the last century (CAST, 1999).

Reducing agricultural N flux to water supplies can be achieved through improved management practices. Fine-tuning N application rates based on the estimated amounts of plant-available N in soil from nitrate remaining from the previous growing season or from in-season mineralized N from manure and legumes, may reduce required N additions. Significant progress in the development of diagnostic N tests for corn has been made in the past 10 to 20 yr (Schröder et al., 2000), but such tests will be implemented on a wide scale only if producers can be assured that they will reap significant economic returns. Less than 2% of Wisconsin farmers surveyed are accurately crediting N from manure applied to corn (Shepard, 2000).

The presidedress soil nitrate test (PSNT) for corn developed by Magdoff et al. (1984) has proven to most accurately identify plant-available N contributions from manure and legumes. The strength of the PSNT is in identifying N-sufficient sites, and the test usually errs on the side of predicting N response where no response occurs (Fox et al., 1989; Meisinger et al., 1992; Roth et al., 1992; Bundy and Andraski, 1993; Klausner et al., 1993; Heckman et al., 1995; Sims et al., 1995; Bundy et al., 1999). Little information is available identifying site-specific factors that contribute to differences in optimum N rate recommendations where soil nitrate concentrations are below the PSNT sufficiency range. For example, Bundy and Andraski (1995) reported that the PSNT predicted optimum N rates for corn more accurately on high than on medium yield-potential soils, but the sensitivity of the characteristics that influence yield has not been determined. Medium yield-potential soils are characterized by a shallow root zone, coarse-textured subsoil, and/or poor drainage; thus, the lower accuracy in predicting required N is compounded by the greater potential of these soils to contaminate groundwater.

Those implementing the PSNT in Wisconsin since 1994 have reported that the greatest failure to accurately predict required N needs occurred in corn production where manure was recently applied or following alfalfa (Medicago sativa L.). The PSNT values were often below the critical N-sufficiency concentration (21 mg NO₃–N kg^-1) where manure or alfalfa N did not limit yield. Magdoff (1991) identified several weather-related situations and soil physical characteristics where PSNT-based N fertilizer recommendations may not be satisfactory: (i) high precipitation amounts before sampling on permeable soils resulting in nitrate leaching out of the top 0.3 m but remaining in the root zone; (ii) high precipitation amounts after sampling on very permeable soils where large quantities of nitrate are leached below the root zone; and (iii) cool and wet weather before sampling resulting in low rates of N mineralization followed by warmer temperatures resulting in high N mineralization rates.

Inappropriate use or application of any diagnostic test can lead to loss of user confidence. The objectives of this research were to: (i) identify site-specific factors (including crop management history, soil characteristics, and weather) that impact the accuracy of the PSNT in corn production, and (ii) to compare the PSNT and recommended book value N credits (BVNC) for legumes and manure on yield and economic returns in corn production systems.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
More than 100 field trials have been conducted in Wisconsin since 1989 to evaluate soil and plant N diagnostic tests as a means of predicting N needs for corn. These trials were conducted throughout the major agricultural region of the state and include a range of soil characteristics, crop management histories, and climatic conditions. Results from 73 of these trials were reported previously (Bundy and Andraski, 1993, 1995), whereas 28 of these trials are from more recent work. Crop management histories and selected soil characteristics for each of the 101 trials are shown in Table 1. Management histories (described in the footnote in Table 1) include several previous cropping and manure management variables. Wisconsin soil test recommendations assign each soil to a yield potential category for corn to help growers estimate potential yields when requesting nutrient recommendations (Kelling et al., 1998). Soil yield potential ratings, which are categorized as low (L), medium (M), high (H), and very high (VH), are based on the crop to be grown, length of the growing season, and soil characteristics such as drainage, depth, and water-holding capacity. These soil characteristics associated with these categories are also related to the ability of the soil to retain nitrate in the plant root zone.

Soil samples were collected when corn plants were 0.15 to 0.3 m tall by obtaining four to eight cores to a 0.3-m depth from the control plot (0 kg N ha^-1) in each replicate. Soil samples were dried at 33°C in a forced-draft dryer and ground to pass a 2-mm screen. Nitrate-N in the soil samples was determined by automated analysis of 2 M KCl extracts (Bundy and Meisinger, 1994). Corn grain yields were determined by harvesting all ears from the middle two rows in each plot and grain subsamples were retained for moisture determination.

An analysis of variance was performed to determine N rate treatment effects on grain yield (SAS Inst., 1992). Optimum N rate and yield at the optimum N rate were determined by regression analysis and consisted of comparing linear-response plateau (LRP) and quadratic-response plateau (QRP) models developed using PROC NLIN, and quadratic regression models using PROC REG. Economic optimum N rates (EONR) reflect a fertilizer/corn price ratio calculated from prices of $0.33 kg^-1 fertilizer N ($0.15/lb) and $39.87 Mg^-1 of corn ($2.50/bu). A standardized method was used to determine the EONR due to the variability of economic optimum N rates typically determined by the various models (Bundy and Andraski, 1995). Where the effect of N rate was significant (P < 0.10), the EONR was identified using the model (LRP, QRP, or quadratic) with the highest R² value if that value was 0.25. If the R² value was <0.25, mean separation analysis was used to identify the optimum N rate as the lowest N rate treatment in the highest t-grouping for yield. If N rate was not significant (P < 0.10), the EONR equals zero.

Nitrogen rate recommendations adjusted for book-value N credits (BVNC) for manure and legumes were determined by subtracting the book value N credit from the unadjusted base N rate recommendation (Kelling et al., 1998). The PSNT N rate recommendations were determined for each site according to current Wisconsin recommendations (Bundy and Sturgul, 1994). Base N rate recommendations were not adjusted for N credits from manure or legumes (Kelling et al., 1998).

Accuracy categories were established for PSNT N rate recommendations that resulted in correct, over-application, or under-application of N relative to the observed EONR for each site. These categories were based on the lowest N rate increment used in the N response trials typical of the limit of farmer's N rate accuracy. Recommendations were categorized as: (i) correct if the PSNT N recommendation was ±34 kg N ha^-1 of the EONR; (ii) over-applied if the PSNT N recommendation was >34 kg N ha^-1 above the EONR; and (iii) under-applied if the PSNT N recommendation was >34 kg N ha^-1 below the EONR.

Site-specific variables were categorized to determine the effect of these variables on the percentage of sites within each accuracy category (Table 2). Crop management history was divided into three categories based on the number of years since the most recent addition of manure and/or legumes. These categories represent a range of cropping and manure management histories typical of both grain-based and livestock-based farming systems. Soil yield potential was categorized as medium or high, as described earlier. Monthly average air temperature and total precipitation data obtained from the nearest weather station during the study year was divided into two categories based on comparisons with the 30-yr average (National Climatic Data Center, Asheville, NC; http://lwf.ncdc.noaa.gov/oa/ncdc.html; verified 31 July 2002). Monthly temperature was categorized as below average where the observed monthly average air temperature was >0.56°C (1°F) below the long-term average and as average or above where the observed monthly average air temperature was <0.56°C below the long-term average. Monthly precipitation was categorized as average or below where the observed monthly total precipitation was <25 mm above the long-term average and as above average where the observed monthly total precipitation was >25 mm above the long-term average.

Statistical analysis of data was performed using analysis of variance techniques (SAS Inst., 1992). PROC GLM was used for unbalanced data to determine the effect of site-specific variables (crop management history, soil yield potential, air temperature, and precipitation) on the accuracy of N recommendation methods.

Economic returns were determined for three N rate recommendation methods at each site. These methods included the PSNT, BVNC, and base N rates as described previously. Gross economic returns were calculated for each method from the yield at the recommended N rate according to the regression function used to determine the EONR (discussed previously). Economic gains were calculated as the difference in gross economic returns between the PSNT or BVNC recommendation and the base N rate.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
Accuracy of PSNT-Based Nitrogen Rate Recommendations
Presidedress soil NO₃–N values in the top 0.3 m, N rate recommendations based on the PSNT, and observed economic optimum N rates (EONR) for each site are shown in Table 1. The PSNT values ranged from 3 to 59 mg NO₃–N kg^-1, PSNT-based N rate recommendations ranged from 0 to 180 kg N ha^-1, and EONR ranged from 0 to 215 kg N ha^-1. Only Sites 4 and 11 had EONR that were higher (215 and 189 kg N ha^-1, respectively) than the base N rate recommendation for corn on high yield potential soils (180 kg ha^-1).

Analyses of variance were performed to determine the influence of several site-specific factors (Table 2) on the percentage of sites where N rate recommendations based on the PSNT were correct, over-applied, and under-applied and are summarized in Table 3. Overall, PSNT-based N rate recommendations were correct at 58% of the sites and resulted in over-application at 36% of the sites, and under-application at 6% of the sites (Table 3). Four of the six sites in the under-applied category had medium soil yield potentials, suggesting greater risk of nitrate loss from the root zone following PSNT sampling on these soils. None of the site-specific variables listed in Table 3 were related to the percentage of sites in the under-applied category.

View larger version (27K): [in this window] [in a new window]   Fig. 1. Effect of May–June air temperature (relative to the long-term average) on the percentage of sites in three PSNT-based N recommendation accuracy categories, 1989 to 1999.

An analysis of variance was performed for sites where May–June air temperatures were: (i) below average and (ii) average or above to further identify factors affecting the accuracy of PSNT-based N rate recommendations (Table 4). The accuracy of the PSNT was not associated with site-specific factors where May and June air temperatures were below average, but soil yield potential was critical to the accuracy of the PSNT (P = 0.03) where May–June air temperatures were average or above. The PSNT resulted in 87% accuracy for high yield potential soils and 63% accuracy for medium yield potential soils (Fig. 2) . High yield potential soils had a significantly lower percentage of sites in the over-applied category (6%) compared with medium yield potential soils (29%). The effect of soil yield potential on the percentage of sites in the under-applied category was not significant.

View larger version (22K): [in this window] [in a new window]   Fig. 2. Effect of soil yield potential on the percentage of sites in three PSNT-based N recommendation accuracy categories where May–June average air temperatures were average or above (relative to the long-term average), 1989 to 1999.

View larger version (22K): [in this window] [in a new window]   Fig. 3. Relationship between May–June air temperatures (departure from the long-term average) and excess N rate applied using the PSNT-based N recommendation for medium and high yield potential soils, 1989 to 1999.

Economic Gains Using PSNT- and BVNC-Based Nitrogen Rate Recommendations
Economic gains using N rate recommendations based on BVNC and the PSNT relative to unadjusted base N rate recommendations (no N credits for manure or legumes) were determined (Table 5). Nitrogen rate recommendations based on BVNC or PSNT did not provide economic gains compared with the unadjusted base N rate recommendations for sites without manure or legume additions for more than 3 yr. The absence of economic gain using the BVNC method is expected since N credits are not recommended for manure or legume additions applied more than 3 yr before the growing season. Likewise, the PSNT confirmed the absence of organic N contributions resulting in unadjusted base N rate recommendations.

The highest economic gains occurred for sites with manure and/or legume additions in the study year and ranged from $23 to $43 ha^-1. Economic gains were not significantly different between the BVNC and PSNT methods for sites with high yield potential soils where manure and/or legume additions occurred in the study year. Significantly (P = 0.08) higher gains occurred for the BVNC method ($43 ha^-1) than for the PSNT ($35 ha^-1) for sites with medium yield potential soils where May–June air temperatures were average to above average.

These results indicate that recommended book value N credits are equally, or more effective than the PSNT in adjusting N rates for the manure and legume N contributions in the application year or 1 to 3 yr before the study on medium yield potential soils. Knowing the manure application rate or legume stand density is critical when using book value N credits. The relative advantage of the PSNT would probably be greater where less precise information is available for calculating manure and legume book value N credits. The greatest potential for economic gain using the PSNT compared with BVNC occurred 1 to 3 yr following legumes and/or manure additions on high yield potential soils at average or above early season temperatures (P = 0.06). The higher economic gain using the PSNT compared with BVNC in corn systems where organic N additions were made 1 to 3 yr before the study year demonstrates the PSNT has the capability of measuring mineralized N from these sources beyond the year of application more accurately than the BVNC method. Assigning second- and third-year book value N credits for manure and legume additions following the year of application does not accurately account for the amount of fertilizer N applied and crop N uptake in the previous growing season, or subsequent potential N losses via leaching or denitrification.

Producers are often persuaded not to adjust N rates to account for manure and legume N because of perceived risks that economic returns will be lowered due to inadequate crop N supplies. Results from this study show that ignoring appropriate manure and legume N credits actually have the opposite effect on profitability. Adjusting N rates using BVNC or the PSNT, respectively increased overall economic gains by $33 and $34 ha^-1 in the first year after legume crops or manure applications, and by $7 and $11 ha^-1 where manure and/or legume additions occurred 1 to 3 yr before the study year.

	SUMMARY

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
Our results show that the accuracy of PSNT-based N rate recommendations for corn is lower where average air temperatures 6 to 8 wk preceding PSNT sampling are below average (37% accuracy) than where temperatures are average or above (76% accuracy). Likewise, the percentage of sites where PSNT-based N rate recommendations were greater than the economic optimum N rate decreased from 59 to 16%. Greater accuracy occurred for sites with high yield potential soils (87%) than for sites with medium yield potential soils (63%). The lower accuracy on medium yield potential soils appears to be related to greater variability in corn response to N.

The N rate recommendation method resulting in the highest economic gain depended on early season air temperature, soil yield potential, and the number of years since manure and/or legume additions. In general, the PSNT method resulted in higher economic gains than BVNC where May–June air temperatures were average or above, soil yield potential was in the high category, and manure and/or legume N additions occurred 1 to 3 yr before the study year. The BVNC method resulted in higher economic gains than the PSNT where the soil yield potential was in the medium category and manure and/or legume additions occurred in the study year. The accuracy of BVNC-based N recommendations depends on the use of precise quantitative information about the manure and legume N sources to calculate the N credit value.

Nitrogen rate recommendations based on the PSNT and BVNC yielded higher economic returns than base N rate recommendations unadjusted for recent N contributions from manure and/or legumes. These results confirm that adjusting N rate recommendations using BVNC or the PSNT is more profitable than not making these adjustments. In addition, using recommendations based on BVNC or the PSNT lowered N application rates by an average of 90 to 102 kg ha^-1 in systems where manure was applied or legumes were grown within the previous 3 yr, thereby reducing potential N losses to the environment. Results from this study demonstrate that the use of site-specific factors such as early season air temperature, soil yield potential, and history of organic N applications will help determine the N recommendation method with the highest profit potential through accurate identification of optimum N rates while greatly reducing the risk of losing excess N to water resources.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 
Research supported by the USDA-CSREES Water Quality Research Program (Agreements 91-34214-6009 and 92-34214-8168); the Wisconsin Dep. of Agric., Trade, and Consumer Protection–Sustainable Agriculture Program; the Wisconsin Fertilizer Research Fund, the Univ. of Wisconsin Nonpoint Pollution and Demonstration Project, the Tennessee Valley Authority; the Univ. of Wisconsin System Water Resources Institute–Groundwater Research Council; and the College of Agric. and Life Sci., Univ. of Wisconsin–Madison (Project no. 3879).

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY REFERENCES

 

• Andraski, T.W., L.G. Bundy, and K.R. Brye. 2000. Crop management and corn nitrogen rate effects on nitrate leaching. J. Environ. Qual. 29:1095–1103.[Abstract/Free Full Text]
• Brye, K.R., J.M. Norman, L.G. Bundy, and S.T. Gower. 2001. Nitrogen and carbon leaching in agroecosystems and their role in denitrification potential. J. Environ. Qual. 30:58–70.[Abstract/Free Full Text]
• Bundy, L.G., and T.W. Andraski. 1993. Soil and plant nitrogen availability tests for corn following alfalfa. J. Prod. Agric. 6:200–206.
• Bundy, L.G., and T.W. Andraski. 1995. Soil yield potential effects on performance of soil nitrate tests. J. Prod. Agric. 8:561–568.
• Bundy, L.G., and J.J. Meisinger. 1994. Nitrogen availability indices. p. 951–984. In R.W. Weaver et al. (ed.) Methods of soil analysis. Part 2. 3rd ed. ASA and SSSA, Madison, WI.
• Bundy, L.G., and S. Sturgul. 1994. Soil nitrate tests for Wisconsin cropping systems. UWEX Publ. A3624. Univ. of Wisconsin-Extension, Madison, WI.
• Bundy, L.G., D.T. Walters, and A.E. Olness. 1999. Evaluation of soil nitrate tests for predicting corn nitrogen response in the North Central region. North Central Reg. Res. Publ. 342. Univ. of Wisconsin Agric. Exp. Stn., Madison, WI.
• Council for Agricultural Science and Technology. 1999. Gulf of Mexico hypoxia: Land and sea interactions. Task force rep. no. 134. CAST, Ames, IA.
• Fox, R.H., G.W. Roth, K.V. Iversen, and W.P. Piekielek. 1989. Soil and tissue nitrate tests compared for predicting soil nitrogen availability to corn. Agron. J. 81:971–974.[Abstract/Free Full Text]
• Heckman, J.R., W.T. Hlubik, D.J. Prostak, and J.W. Paterson. 1995. Pre-sidedress soil nitrate test for sweet corn. HortScience 30:1033–1036.[Abstract/Free Full Text]
• Kelling, K.A., L.G. Bundy, S.M. Combs, and J.B. Peters. 1998. Soil test recommendations for field, vegetable, and fruit crops. UWEX Publ. A2809. Univ. of Wisconsin-Extension, Madison, WI.
• Klausner, S.D., W.S. Reid, and D.R. Bouldin. 1993. Relationship between late spring soil nitrate concentrations and corn yields in New York. J. Prod. Agric. 6:350–354.
• Magdoff, F.R. 1991. Understanding the Magdoff pre-sidedress nitrate test for corn. J. Prod. Agric. 4:297–305.
• Magdoff, F.R., D. Ross, and J. Amadon. 1984. A soil test for nitrogen availability to corn. Soil Sci. Soc. Am. J. 48:1301–1304.[Abstract/Free Full Text]
• Meisinger, J.J., V.A. Bandel, J.S. Angle, B.E. O'Keefe, and C.M. Reynolds. 1992. Presidedress soil nitrate test evaluation in Maryland. Soil Sci. Soc. Am. J. 56:1527–1532.[Abstract/Free Full Text]
• Roth, G.W., D.B. Beegle, and P.J. Bohn. 1992. Field evaluation of a presidedress soil nitrate test and quicktest for corn in Pennsylvania. J. Prod. Agric. 5:476–481.
• Sarrantonio, M., and T.W. Scott. 1988. Tillage effects on availability of nitrogen to corn following a winter green manure crop. Soil Sci. Soc. Am. J. 52:1661–1668.[Abstract/Free Full Text]
• SAS Institute. 1992. SAS/STAT user's guide. Release 6.03/4th ed. SAS Inst., Cary, NC.
• Schröder, J.J., J.J. Neeteson, O. Oenema, and P.C. Struik. 2000. Does the crop or the soil indicate how to save nitrogen in maize production? Reviewing the state of the art. Field Crops Res. 66:151–164.
• Shepard, R. 2000. Nitrogen and phosphorus management on Wisconsin farms: Lessons learned for agricultural water quality programs. J. Soil Water Conserv. 55:63–68.
• Sims, J.T., B.L. Vasilas, K.L. Gartley, B. Milliken, and V. Green. 1995. Evaluation of soil and plant nitrogen tests for maize on manured soils of the Atlantic coastal plain. Agron. J. 87:213–222.[Abstract/Free Full Text]

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (16) Citing Articles via Google Scholar Google Scholar Articles by Andraski, T. W. Articles by Bundy, L. G. Search for Related Content PubMed Articles by Andraski, T. W. Articles by Bundy, L. G. Agricola Articles by Andraski, T. W. Articles by Bundy, L. G. Related Collections Best Management Practices Nitrogen Nutrient Management Production Agriculture Soil Fertility and Productivity