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SOIL FERTILITY & PLANT NUTRITION

Evaluation of the Illinois Soil Nitrogen Test for Predicting Corn Nitrogen Needs

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

^* Corresponding author (lgbundy{at}wisc.edu).

	ABSTRACT

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

 
Development of a diagnostic test to estimate soil N supplying capability is a continuing research need. The Illinois Soil Nitrogen Test (ISNT) has been proposed as a method for adjusting corn (Zea mays L.) N recommendations to account for soil organic N contributions by measuring hydrolyzable amino sugar-N and NH₄–N. The ISNT was evaluated as a tool for predicting corn N response in Wisconsin by comparing ISNT values and corn N response data from 80 experiments conducted between 1984 and 2004 with a range of crop rotations, management histories, and soils. Relationships between various hydrolyzable soil N fractions (including amino sugar-N) and corn N response data were also evaluated using a subset (13 sites) of the 80 N response experiments. The subset was selected to obtain a wide range of anticipated soil N availability. Results showed that ISNT values were not related to observed economic optimum N rates in the corn N response experiments and that the ISNT had no ability to separate N-responsive from unresponsive sites. Illinois Soil Nitrogen Test values were well correlated (R² = 0.88) with the soil organic matter content of the experimental sites, suggesting that the ISNT is measuring a constant fraction of the soil organic N rather than the readily mineralizable N component. Soil organic N fractions measured in 13 experiments were not related to corn N response although these experiments included cropping systems ranging from first-year corn following alfalfa (Medicago sativa L.) to continuous corn. Results from this work indicate that the ISNT and the soil organic N fractions studied are not reliable predictors of corn N response.

Abbreviations: EONR, economic optimum nitrogen rate • ISNT, Illinois Soil Nitrogen Test • PSNT, presidedress soil nitrogen test • SOM, soil organic matter

	INTRODUCTION

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

 
Nitrogen recommendations for corn (Zea mays L.) production that avoid yield losses due to underfertilization and also avoid the economic and environmental problems associated with overapplication have been the goal of researchers for decades. Development of improved N recommendations has been hampered by the lack of a reliable method of predicting soil N supplying capability, although many attempts to develop such a method have been made (Bundy and Meisinger, 1994). The accurate assessment of available N production through mineralization of soil organic matter (SOM) is critical for improving corn N recommendations because this component can vary across soils, cropping systems, and years.

The Illinois Soil Nitrogen Test (ISNT) has been proposed as a diagnostic tool to predict soil organic N contributions to the plant-available N supply (Khan et al., 2001), and thus could address the long-standing need for a diagnostic test for assessing the soil organic N mineralization component of the available N budget. The ISNT is based on diffusion methods developed by Mulvaney and Khan (2001) to determine N fractions in acid hydrolysates of soils. These procedures generally parallel the steam distillation procedures described by Bremner (1965), but the diffusion methods include a modification to avoid the low recoveries of amino sugar-N that occurred in the steam distillation procedures. In developing the ISNT procedure, Mulvaney et al. (2001) found that field sites that were responsive and unresponsive to N fertilization could be distinguished based on the soil amino sugar-N fraction determined by diffusion analysis of soil hydrolysates. In addition, soil concentrations of amino sugar-N were closely related to check plot corn yields and fertilizer N response in field experiments. Subsequently, Khan et al. (2001) reported a very high correlation between ISNT values and the hydrolyzable amino sugar-N fraction in soils. The ISNT method proposed by Khan et al. (2001) is a simplification of the traditional soil organic N fractionation procedure used to determine soil amino sugar-N content in that the acid hydrolysis step is eliminated and the procedure relies on direct measurement of NH₃–N liberated when soil samples are heated with 2 M NaOH for 5 h at 48 to 50°C. According to Khan et al. (2001), this method measures (NH₄ + amino sugar)-N released during the digestion, gives quantitative recovery of NH₄–N and glucosamine-N added to soil, and is highly correlated with the amino sugar-N fraction in soil hydrolysates.

Mulvaney et al. (2006) conducted a further evaluation of the ISNT for predicting the need for N fertilization in corn production at 102 on-farm locations in Illinois. These studies included 69 sites where corn yields were increased by N fertilization, and the ISNT correctly predicted N response at 50 of these sites based on a critical test level of 230 mg N kg^–1. They speculated that the 27% test failure rate was due to various factors that decreased N availability or crop N uptake including: moisture stress during the growing season; use of a winter rye (Secale cereal L.) cover crop; weed competition; corn plant populations; inadequate soil pH, P, or K levels; reduced soil N availability in soybean [Glycine max (L.) Merr.]–corn crop sequences; or the soil sampling depth used to collect the ISNT samples.

The performance and use of the ISNT have received considerable research attention in several recent studies. Klapwyk and Ketterings (2006) reported that the ISNT alone was not effective in explaining differences in corn silage yield response to added N; however, when the ISNT values were combined with SOM measurements, the resulting model was able to separate N-responsive from unresponsive sites. Data reported by Klapwyk and Ketterings (2006) showed that a strong relationship (r = 0.94) existed between ISNT values and SOM. In further work, Klapwyk et al. (2006) showed that ISNT values were related to calculated residual N credits from manure and composts, but no relationship of ISNT to crop N response was provided in that study. Based on 43 N rate trials in Iowa, Barker et al. (2006) found that there was no relationship between the ISNT and corn yield response to N or the economic optimum N rate (EONR), and that the ISNT was not able to distinguish between N-responsive and unresponsive sites. They also found a close relationship between ISNT values and soil N, suggesting that the ISNT is measuring a constant fraction of the soil organic N rather than a readily mineralizable N fraction. Similarly, based on research with soils from nine farming systems trials throughout the United States, Marriott and Wander (2006) reported that the ISNT was not a good indicator of soil labile N (readily mineralizable soil N) and that the test was highly correlated with soil organic N and soil total N. Based on 96 experiments in six states in the North Central Region, Laboski et al. (2006) concluded that the ISNT was not useful for predicting optimum N rates in corn production.

The research reported here used results from corn N response experiments conducted in Wisconsin during 1984 to 2004 to evaluate the ISNT for its ability to assess soil N supplying capability and to predict corn response to N fertilization across a number of years, crop rotations, management histories, and soils. In addition, a subset of these experiments was selected to determine whether hydrolyzable soil N fractions such as amino sugar-N were reliable predictors of corn N response.

	MATERIALS AND METHODS

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

 
Experimental Samples
Experiments used to evaluate the ISNT for its ability to predict the EONR for corn consisted of N response studies conducted in Wisconsin from 1984 to 2004. In total, information from 80 experiments conducted on a range of soils and cropping systems was included in the evaluation (Table 1 ). Soil classification information for the soils in Table 1 is as follows: Plano and Tama soils are fine-silty, mixed, superactive, mesic Typic Argiudolls; Ringwood is a fine-loamy, mixed, superactive, mesic Typic Argiudolls; Fayette and Rozetta soils are fine-silty, mixed, superactive, mesic Typic Hapludalfs; Withee is a fine-loamy, mixed, superactive, frigid Aquic Glossudalf; and Plainfield is a mixed, mesic Typic Udipsamment. At all sites, soil test levels for available P (Bray P-1) and exchangeable K were in the unresponsive range or recommended rates of P and K were applied before planting (Kelling et al., 1998). Soil pH values were at or above 5.8, which is the recommended lime application threshold value for corn production (Kelling et al., 1998). Cropping systems in this data set ranged from corn following alfalfa (Medicago sativa L.) to long-term continuous corn and included sites with and without a history of manure application. These systems would be expected to have major differences in soil N availability, and observed corn response to N fertilization in the experiments confirmed these expectations. Where cover crops were grown during the previous growing season, herbicides were used to kill the cover crop in mid-October except for Sites 69 to 71, where cover crops were killed either by freezing over winter or by spring moldboard plowing.

Soil samples were collected to a depth of 0 to 30 cm for the ISNT measurements, and to a 0- to 15-cm depth for the soil hydrolysis and organic N fractionation work. All samples were collected in the spring (April or May before planting and fertilizer application) and dried in a forced-air dryer at a temperature of 40°C. Samples were ground to pass a 2-mm sieve for the ISNT and a 150-µm sieve for the soil hydrolysis study. Analyses were performed on stored, dried samples collected from the experimental sites when the field N response experiments were conducted. This is similar to the approach used by Khan et al. (2001), who developed the ISNT using stored samples from N response experiments conducted during 1990 to 1992. Total N and total C in the 150-µm ground soil samples were measured using a LECO CNS-2000 C, N, and S analyzer (LECO Corp., St. Joseph, MI). Soil organic matter content was determined by mass loss-on-ignition (Combs and Nathan, 1998). The presidedress soil nitrate test (PSNT) was performed on 0- to 30-cm soil samples collected from 69 of the 80 experimental sites (see Table 1) when corn plants were 15 to 30 cm tall (Magdoff et al., 1984; Bundy and Meisinger, 1994). Analysis of PSNT samples was completed in the same year as the field experiments were conducted.

Illinois Soil Nitrogen Test Procedure
The ISNT procedure used in this work was adapted from Khan et al. (2001) and University of Illinois, Department of Natural Resources and Environmental Sciences (2002), and consisted of alkaline digestion of the soil sample followed by colorimetric determination of the NH₃–N released. Specifically, we digested soil samples at 48 to 50°C on an electric hot plate (Rival Model GR100BN equipped with a modified temperature controller) for 5 h in 473-mL (1-pint) Mason jars. The Mason jars were equipped with a modified lid that suspends a 60-mm-diam. petri dish containing 5 mL of 0.02 M H₂SO₄ to sorb the NH₃–N released during alkaline digestion. In our work, 0.02 M H₂SO₄ was used in place of the 4% H₃BO₃ solution specified by Khan et al. (2001) to allow colorimetric analysis instead of acid titration for NH₃–N measurements following soil digestion. Ammonia-N sorbed during the digestion was determined using the salicylate–hypochlorite colorimetric procedure (Mulvaney, 1996) with analyses performed at 667 nm with a spectrophotometer. To confirm that the ISNT results were not influenced by this modification, we compared the original ISNT method (Khan et al., 2001) with the modified method used in this study on 10 soils. Results showed that the two procedures gave very similar results, with mean ISNT values of 228 mg N kg^–1 and 231 mg N kg^–1 for the original and modified methods, respectively, with an R² value of 0.99 for the relationship between the two procedures.

Soil Hydrolysis and Organic Nitrogen Fractionation Procedures
Soil hydrolysates were prepared and organic N fractions in the hydrolysates were measured according to procedures described by Mulvaney and Khan (2001). Specifically, 1-g soil samples (<150 µm) were digested under reflux with 6 M HCl at 100 to 110°C for 12 h. After cooling, filtering (Whatman no. 42), and neutralization with NaOH, aliquots of the hydrolysate were analyzed to determine the concentrations of the following soil N fractions: total hydrolyzable N; hydrolyzable NH₄–N; (amino sugar + NH₄)-N; amino acid-N; and amino sugar-N. Amino sugar-N in the soil hydrolysates was calculated by subtracting hydrolyzable NH₄–N from hydrolyzable (NH₄–N + amino sugar)-N.

Statistical Analysis
Statistical analysis of the data was performed with SAS statistical software using PROC REG, NLIN, ANOVA, and GLM for analysis of the corn yield data where linear, linear plateau, quadratic, or quadratic plateau models were used to determine yield-optimizing N rates (SAS Institute, 1992). Statistical analysis of soil ISNT results was performed using PROC REG for the determination of significant linear relationships among N rates. The EONR in individual N response experiments was determined as follows. Where the effect of N rate was significant (P < 0.10), the EONR was identified using the model (linear response plateau, quadratic response plateau, 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 in the highest t grouping for yield. If the N rate treatment effect was not significant (P > 0.10), the optimum N rate was zero.

	RESULTS AND DISCUSSION

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

 
Illinois Soil Nitrogen Test
The relationship between ISNT values and EONR in the 80 experiments used in this evaluation is illustrated in Fig. 1 . These results indicate that that there is a poor relationship (R² = 0.001, P = 0.75) between the ISNT and EONR. In addition, the ISNT critical value of 225 mg kg^–1 N identified by Khan et al. (2001) does not separate N-responsive from unresponsive sites in this data set. Results from Iowa (Sawyer et al., 2003; Barker et al., 2006) and Michigan (Laboski, 2004) also showed no useful predictive relationship between ISNT values and observed crop N response.

View larger version (10K): [in this window] [in a new window]   Fig. 1. Relationship between Illinois Soil Nitrogen Test (ISNT) values (0–30 cm) and economic optimum N rates (EONR) for corn grain production in 80 N response experiments, 1984 to 2004. Vertical dashed line indicates the critical ISNT value reported by Khan et al. (2001).

To study the influence of corn yield level at the EONR on the ISNT vs. EONR relationship, the 80-site database was divided into the 40 sites with the lowest yields and the 40 sites with the highest yields. Grain yields in the low category ranged from 5.5 to 11.9 Mg ha^–1 (mean = 9.3 Mg ha^–1), and in the high-yield group, yields ranged from 12.0 to 14.7 Mg ha^–1 (mean = 13.3 Mg ha^–1). Results in Table 2 show that the ISNT was not effective in predicting EONR in either of the yield categories.

Overwinter cover crops were used at 17 of the 80 experimental sites, and the potential influence of this practice on performance of the ISNT was examined by separating the database into sites with and without cover crops. As illustrated in Table 2, the ISNT was an ineffective predictor of EONR either with or without cover crops. Mulvaney et al. (2006) speculated that the presence of an overwinter rye cover crop contributed to poor ISNT performance in their study. Results from our work suggest that the ISNT is a weak but somewhat better predictor of EONR where cover crops are present (R² = 0.26) than where they are absent (R² = 0.008). We also investigated the effects of site histories of organic inputs on the ability of the ISNT to predict EONR by segregating those sites with previous-year cover crops or a history of alfalfa production or manure application from the remaining sites. As shown in Table 2, the ISNT was not a reliable predictor of EONR in either of these groups, but a significant correlation and a higher R² value were obtained for the sites with organic inputs.

Nitrogen responsiveness at the 80 sites varied, potentially due to soil NO₃ level or factors influencing in-season N mineralization (Fig. 1). To determine if site N responsiveness influenced the effectiveness of the ISNT in predicting EONR, the data in Fig. 1 were separated into groups with observed EONR values greater than or less than 100 kg N ha^–1. Thus, sites with limited N responsiveness are included in the <100 kg N ha^–1 group, while the more responsive sites are in the >100 kg N ha^–1 category. The ISNT was ineffective in predicting EONR in either category of N responsiveness (Table 2).

The database used to evaluate the ISNT included experiments conducted during 1984 to 2004, and soil samples used for the ISNT analysis were in storage for varying time periods. To evaluate the influence of soil sample age or storage time on the performance of the ISNT, experimental sites were separated into four time periods, and the ISNT vs. EONR relationship was calculated separately for each period (Table 2). In general, no consistent effect of sample storage time on the ISNT vs. EONR relationship is apparent. While a significant relationship between ISNT and EONR was found for the 1993 to 1996 period, the predictive value of the relationship is weak (R² = 0.36). The other time periods showed no relationship between ISNT and EONR. Results from the two most recent time periods are interesting since samples in the 2000 to 2004 group were analyzed using the ISNT with limited or no storage time, while those in the 1997 to 1999 group were stored for varying periods up to 7 yr before analysis. With samples from both of these groups, the ISNT was ineffective in predicting EONR.

Finally, the relationship between PSNT and ISNT results was studied using the 69 sites where both of these tests were performed. Both tests were developed to assess N availability to corn, and the PSNT is widely recognized as a method for separating responsive from unresponsive sites (see Bundy and Meisinger, 1994, for review). For example, Klapwyk and Ketterings (2006) found that the PSNT was an effective predictor of corn N response while the ISNT alone was not. Although the PSNT measures soil NO₃ as an indicator of N availability to corn, and the ISNT does not include NO₃–N, both tests should assess N availability and thus should be related. As shown in Table 2, no useful relationship exists between PSNT values and ISNT results in this database.

In contrast, a strong correlation (R² = 0.88) was found between SOM concentration and ISNT values (Fig. 2 ). Sawyer et al. (2003) reported a similar strong relationship between ISNT and SOM content in Iowa experiments, and Barker et al. (2006) found a strong relationship between ISNT values and total soil N. These findings suggest that the ISNT is measuring a constant fraction of soil organic N rather than the readily mineralizable portion of soil N. To assess soil N supplying capability on a site-specific basis, a diagnostic tool must selectively estimate the size of the readily mineralizable soil N pool. Results from this study suggest that the ISNT does not have this ability and therefore is not providing a useful prediction of soil N supplying capability. This observation is also supported by the poor relationship found between ISNT and EONR in corn N response experiments (Fig. 1).

View larger version (9K): [in this window] [in a new window]   Fig. 2. Relationship between soil organic matter content and Illinois Soil Nitrogen Test (ISNT) values (0–30 cm) in 80 N response experiments, 1984 to 2004.

The concentrations of the five hydrolyzable soil organic N fractions measured in the 13 soils are shown in Table 3 . Soil organic matter, total C, total N, and corn yields in control plots and at maximum levels are summarized for the same sites in Table 4 . Mean concentrations for the hydrolyzable N fractions were variable (coefficients of variation) and standard deviations were generally greater than those reported by Mulvaney et al. (2001).

View larger version (10K): [in this window] [in a new window]   Fig. 3. Relationship between Illinois Soil Nitrogen Test (ISNT) values (0–15 cm) and soil amino sugar-N values in 13 N response experiments, 1998 to 2004.

View larger version (10K): [in this window] [in a new window]   Fig. 4. Relationship between Illinois Soil Nitrogen Test (ISNT) values (0–15 cm) and soil total N in 13 N response experiments, 1998 to 2004.

View larger version (9K): [in this window] [in a new window]   Fig. 5. Relationship between Illinois Soil Nitrogen Test (ISNT) values (0–15 cm) and soil total C in 13 N response experiments, 1998 to 2004.

	CONCLUSIONS

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

Relationships found between soil hydrolyzable N fractions and corn N response indicate that amino sugar-N or any of the other hydrolyzable N fractions measured in this work are not reliable predictors of corn N response. The strong correlations between ISNT values and amino sugar-N, (amino sugar + NH₄)-N, and NH₄–N in soil hydrolysates indicate that the ISNT is measuring both amino sugar-N and NH₄–N.

The finding that ISNT values were highly correlated with soil total N and total C supports the conclusion that the ISNT is measuring a constant fraction of soil organic N instead of measuring the readily available N pool, as would be required for this procedure to predict soil N supplying capability and corn N response. Our results indicate that the ISNT and the hydrolyzable soil N fractions studied, including amino sugar-N, are not useful tools for assessing corn N needs in Wisconsin cropping systems.

	NOTES

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

 
Research supported by the Wisconsin Fertilizer Research Fund, the Univ. of Wisconsin Nonpoint Pollution and Demonstration Project, the College of Agricultural and Life Sciences, Univ. of Wisconsin, Madison (Project no. 3879); and the Leo M. Walsh/Wisconsin Fertilizer and Chemical Association Distinguished Graduate Fellowship in Soil Fertility, Univ. of Wisconsin, Madison.

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Received for publication June 1, 2006.

	REFERENCES

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

 

• Andraski, T.W., and L.G. Bundy. 2002. Using the presidedress soil nitrate test and organic nitrogen crediting to improve corn nitrogen recommendations. Agron. J. 94:1411–1418.[Abstract/Free Full Text]
• Barker, D.W., J.E. Sawyer, M.M. Al-Kaisi, and J.P. Lundvall. 2006. Assessment of the amino sugar-nitrogen test on Iowa soils: II. Field correlation and calibration. Agron. J. 98:1352–1358.[Abstract/Free Full Text]
• Bremner, J.M. 1965. Total nitrogen. p. 1149–1178. In C.A. Black et al. (ed.) Methods of soil analysis. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
• 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. Microbiological and biochemical properties. SSSA Book Ser. 5. SSSA, Madison, WI.
• Combs, S.M., and M.V. Nathan. 1998. Soil organic matter. p. 53–58. In Recommended soil test procedures for the North Central Region. North Central Regional Res. Publ. 221 (revised). Missouri Agric. Exp. Stn., Columbia.
• 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.
• Khan, S.A., R.L. Mulvaney, and R.G. Hoeft. 2001. A simple soil test for detecting sites that are nonresponsive to nitrogen fertilization. Soil Sci. Soc. Am. J. 65:1751–1760.[Abstract/Free Full Text]
• Klapwyk, J.H., and Q.M. Ketterings. 2006. Soil tests for predicting corn response to nitrogen fertilizer in New York. Agron. J. 98:675–681.[Abstract/Free Full Text]
• Klapwyk, J.H., Q.M. Ketterings, G.S. Godwin, and D. Wang. 2006. Response of the Illinois Soil Nitrogen Test to liquid and composted dairy manure applications in a corn agroecosystem. Can. J. Soil. Sci. 86:655–663.
• Laboski, C.A.M. 2004. Michigan prospects for using the Illinois N soil test. Proc. Wis. Fert., Aglime and Pest Manage. Conf. 44:77–83.
• Laboski, C.A.M., J.E. Sawyer, D.T. Walters, L.G. Bundy, R.G. Hoeft, G.W. Randall, and T.W. Andraski. 2006. Evaluation of the Illinois soil nitrogen test in the North Central Region. p. 86–93. In Proc. North Central Ext. Ind. Soil Fertil. Conf., Des Moines, IA. Vol. 22. Potash and Phosphate Inst., Brookings, SD.
• 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]
• Marriott, E.E., and M.M. Wander. 2006. Total and labile soil organic matter in organic and conventional farming systems. Soil Sci. Soc. Am. J. 70:950–959.[Abstract/Free Full Text]
• Mulvaney, R.L. 1996. Nitrogen—Inorganic forms. p. 1123–1184. In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical methods. SSSA Book Ser. 5. SSSA, Madison, WI.
• Mulvaney, R.L., and S.A. Khan. 2001. Diffusion methods to determine different forms of nitrogen in soil hydrolysates. Soil Sci. Soc. Am. J. 65:1284–1292.[Abstract/Free Full Text]
• Mulvaney, R.L., S.A. Khan, and T.R. Ellsworth. 2006. Need for a soil-based approach in managing nitrogen fertilizers for profitable corn production. Soil Sci. Soc. Am. J. 70:172–182.[CrossRef][Web of Science]
• Mulvaney, R.L., S.A. Khan, R.G. Hoeft, and H.M. Brown. 2001. A soil organic nitrogen fraction that reduces the need for nitrogen fertilization. Soil Sci. Soc. Am. J. 65:1164–1172.[Abstract/Free Full Text]
• SAS Institute. 1992. SAS/STAT user's guide. Release 6.03, 4th ed. SAS Inst., Cary, NC.
• Sawyer, J.E., D.W. Barker, J.P. Lundvall, and M. Al-Kaisi. 2003. Evaluation of the amino sugar-N based soil test in Iowa corn production. p. 125–136. In Proc. North Central Extension–Industry Soil Fert. Conf., Des Moines, IA. 19–20 Nov. 2003. Potash and Phosphate Inst., Brookings, SD.
• University of Illinois, Department of Natural Resources and Environmental Sciences. 2002. The Illinois soil nitrogen test for amino sugar-N: Estimation of potentially mineralizable soil N and ¹⁵N. Tech. Note 02–01 (rev. ed.). NRES, Univ. of Illinois, Urbana.

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