Published online 27 October 2006
Published in J Environ Qual 35:2170-2177 (2006)
DOI: 10.2134/jeq2005.0287
© 2006 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
TECHNICAL REPORTS
Plant and Environment Interactions
Estimates of Residual Dairy Manure Nitrogen Availability Using Various Techniques
Paul R. Cusick,
Keith A. Kelling*,
J. Mark Powell and
Gabriela R. Muñoz
Dep. of Soil Science, Univ. of Wisconsin-Madison, 1525 Observatory Dr., Madison, WI 53706-1299
* Corresponding author (kkelling{at}wisc.edu)
Received for publication July 29, 2005.
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ABSTRACT
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It is common practice to repeatedly apply dairy manure to the same fields. To accurately assess the total plant availability of manure nutrients, it is necessary to account for the nutrients remaining in soil from previous manure applications. A field experiment studying manure nitrogen (N) uptake by corn (Zea mays L.) was conducted from 1998 to 2003 on a Plano silt loam (fine-silty, mixed, mesic, Typic Argiudolls). Plots received two rates of semisolid manure either every year, every 2 yr, or every 3 yr to estimate first-, second-, and third-year dairy manure N residuals. Residual manure N availability was estimated from single and multiple manure applications using (i) the fertilizer N equivalence method, (ii) the apparent recovery (difference) method, (iii) relative effectiveness method, and (iv) recovery of 15N-labeled manure. Second-year availabilities after a single manure application using the fertilizer equivalence, difference, and relative effectiveness methods were estimated to be 12, 8, and 4% of total manure N applications, respectively. Estimates of third-year availability by these methods were 3, 1, and 5%, respectively. Measurement of 15N recovered from labeled manure was 6 and 2% in the second and third year, respectively. Fertilizer equivalence, difference, and relative effectiveness methods showed great year to year variability, reducing the confidence in the residual manure N availability estimates by these methods, but using 15N-labeled manures reduced variability substantially. Based on this and other studies, we suggest that second- and third-year residual N availability from a single application of semisolid dairy manure would be 9 to 12%, and 3 to 5% of the original manure N application, respectively.
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INTRODUCTION
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A BETTER KNOWLEDGE OF CROP benefits from previous manure applications is needed to improve use of manure as a nutrient source and to avoid excess nutrient loss to the environment. Because manure is commonly applied to the same fields year after year it is important to understand the cumulative effects of these multiple applications. Producers and advisors need to understand and account for residual nutrients, and regulators are expecting these credits to be included in nutrient management plans.
The residual effects of dairy manure N in subsequent years on annual crop yields have been examined using various manures and methods (Kelling and Wolkowski, 1993; Paul and Beauchamp, 1993; Klausner et al., 1994; Pratt et al., 1973). Paul and Beauchamp (1993) used the apparent recovery method and found residual dairy slurry N availability to be approximately 9 and 2% for the second and third years after application, respectively. In their study a single manure application was applied and the comparison was made between crop N uptake in manure-amended vs. control plots for 2 yr following the application. Other studies have used multiple manure applications to determine residual N availability (Jokela, 1992; Kelling and Wolkowski, 1993; Klausner et al., 1994). For example, Kelling and Wolkowski (1993) observed dairy manure total N availabilities of 32, 36, and 42% over 3 successive years and thereby estimated second- and third- year residual N availability of 4 and 2%, respectively. The residual availability in the third successive year includes a second- and third-year residual benefit; therefore the residual benefit of 6% minus a second-year residual availability (4%) leaves a third-year residual availability of 2%. Klausner et al. (1994) used the Mitscherlich model with the fertilizer equivalence method and estimated second-, third-, fourth-, and fifth-year residual availabilities of total dairy manure N to be 9, 3, 3, and 2%, respectively.
A concept first developed by Pratt et al. (1973) is that of the decay series, or a series of decimal fractions that represent the proportion of total manure N available during successive years after manure application. For example, the decay series (decimals converted to percentages) for available N in dried dairy manure was estimated to be 45, 15, 10, and 5% (Pratt et al., 1973). The first number represents 45% of the total manure N being available the first year of application. Subsequent numbers are the percent of total manure N applied available in the second, third, and fourth years, respectively.
Use of 15N-labeled dairy manure to determine residual N availability has been limited, although it has been suggested that labeled manure N is useful for long-term studies (Powell et al., 2004). Muñoz (2001) determined availability of residual N from dairy manure by corn using 15N, relative effectiveness, and fertilizer equivalence to be 5, 2, and 7% for the second year (2 observation years), respectively and 2, –37, and –2% for the third year (1 observation year), respectively. These residual estimates using the various approaches were quite variable with the 15N method providing the least variation and likely most precise estimates. The 15N estimates were small for both residual years, but these estimates should be considered as indicators of minimum availability (Hauck and Bremner, 1976; Jenkinson et al., 1985) because labeled N may become diluted with unlabeled soil N thereby proportionally reducing 15N uptake by corn. Pools of labeled N can exchange with pools of unlabeled N in the soil. This exchange and release of unlabeled N, although utilized by the plant, creates an "artificially" low 15N recovery.
The University of Wisconsin currently suggests residual N availability from dairy manure to be 10 and 5% of total N applied for the second and third year, respectively (Kelling et al., 1998). These estimates were based on unlabeled N methods. The objective of this study was to compare estimates of residual N from single and multiple applications of dairy manure obtained with indirect methods (apparent recovery method, relative effectiveness method, and fertilizer equivalence) and the direct 15N method.
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MATERIALS AND METHODS
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Field Experiment
The field experiment was located at the West Madison Agricultural Research Station (43°05' N, 89°31' W), Madison, WI on a Plano silt loam established as a strip block with four replicates (Fig. 1). The main strips were manure rates and the subplots were application intervals. The field experiment was initiated in 1998 and continued through 2003. The field was in alfalfa (Medicago sativa L.) from 1994 to 1996, and in corn in 1997. No manure had been applied for at least 4 yr before the start of the trial. The fertilizer treatments were included in a separate strip in each block with the same rate as subplots Individual subplots were 6.1 by 10.7 m in size. Corn was planted in 76-cm spaced rows during all years of the study. For more details related to experimental layout and management, see Muñoz et al. (2004).
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Fig. 1. Diagram showing an example of the Randomized Complete Strip Block design of field plots. Not shown to scale.
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Treatments included five fertilizer treatments (45, 90, 134, 179, and 224 kg N ha–1, applied as NH4NO3) applied every year, two rates of semisolid dairy manure (estimated to provide approximately 90 and 179 kg of available N ha–1 in the first year based on 40% total manure N availability), three manure application intervals (every 1, 2, or 3 yr), and a control that received neither fertilizer nor manure. Manure (characteristics for each year can be found in Table 1) rates will be referred to as low and high for the 90 and 179 kg available N ha–1, respectively. In 1998 and 1999, manure was applied with a small spreader. The amount applied was calculated by placing a small tarpaulin over the area where the 15N was to be applied. After spreading, the tarpaulins were removed and weighed for each plot and a subsample of the manure was frozen until analyzed. In years 2000 to 2003, manure was weighed and spread onto plots using pitchforks. To reduce N volatilization from the manure, the field was disked twice (12 to 14 cm deep) within 20 h after manure application. In plots receiving the low manure rate, micro plots (1.5 by 2.3 m) using manure labeled with 15N following the design by Jokela and Randall (1987) were incorporated within the larger unlabeled manure plots such that they were exposed to the same field conditions as the larger plots. Inorganic fertilizer was broadcast on the same day manure was applied (about 5 d before planting).
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Table 1. Rates and chemical analysis of 15N-enriched and unlabeled semisolid dairy manure applied to experimental plots at West Madison Agricultural Research Station 1998–2003.
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Manure was labeled by feeding dairy cattle (Bos taurus) 15N-labeled alfalfa and corn as described by Powell and Wu (1999) and Powell et al. (2004). Labeled feces and urine were collected separately and mixed with straw (non15N-enriched) in the combination of 11.7 kg feces, 8.1 kg urine, and 2.3 kg straw per microplot. Average atom percent 15N in feces and urine was 1.24 for years 1998 through 2003 (range 0.86 to 1.44 atom percent 15N).
To ensure an adequate supply of phosphorus and potassium and to optimize plant growth (Motavalli et al., 1993), a starter fertilizer was band-applied, 5 cm to the side and 5 cm below the seed at planting, at a rate of 224 kg ha–1 of 9–23–30 in 1998 and 1999, and 168 kg ha–1 in 2000, 2001, 2002, and 2003. About 40 d after planting, plants were thinned to a uniform target population of 74000 plants ha–1, but soil crusting in 2000 resulted in lower (60000 plants ha–1) than optimal stands. The field received herbicides at (or shortly following) planting each year, and was cultivated at least once each season.
Corn aboveground tissue (henceforth referred to as "whole plant") was harvested at approximately physiological maturity by cutting 10 adjacent plants 5 cm above the ground from one row in 1998 and 1999, five random plants from each of three rows (15 total) in 2000, and 1.52 adjacent m in each of 3 rows in 2001 to 2003. The harvesting procedure was changed to obtain a more representative sample and reduce variability between replications of the same treatment; however, coefficients of variability using whole plant N uptake values were 19.05, 19.29, and 21.76 for 1998 to 1999, 2000, and 2001 to 2003, respectively. Three whole plants were cut from the middle row of each 15N microplot. Whole plants from both the main plots and 15N plots were chopped in a stationary small-plot silage chopper and a subsample (
800 g wet weight) was taken for moisture content and N analysis. After sampling, to mimic a corn silage rotation the remaining plants were removed from the field each year, and the site was chisel-plowed each fall.
Chemical Analysis
Whole plant subsamples were oven-dried (55°C, 5 to 10 d) to constant moisture to determine tissue dry matter, ground in a stainless steel Wiley mill to pass a 2-mm screen, and stored in plastic bags until analyzed for total Kjeldahl nitrogen (TKN). Samples from the 15N microplots were reground in an Udy mill to pass a 1-mm screen, and analyzed for 15N and total N. Because samples from 15N microplots were very small (3 plants), the more representative main plot data were used for whole plant yield calculations. Subsamples were digested using semimicro Kjeldahl digestion described in Liegel et al. (1980), diluted, filtered, and analyzed in an automated colorimeter using Total-N QuickChem Method 13–107–06–02D (Lachat Instruments, 1996, Milwaukee, WI). Whole plant 15N isotopic ratios were analyzed using a Carlo Erba (Milan, Italy) elemental analyzer coupled with a mass spectrometer Europa 20/20 tracermass at the University of California-Davis Stable Isotope Facility.
Calculations
The availability of residual N from applied dairy manure was determined by several methods. The apparent recovery method compares corn N uptake in manure treatments and control plots (Motavalli et al., 1989). It is assumed that soil provides the same amount of N to all plots and any additional whole plant N uptake above the control is result of the treatment. It is calculated using Eq. [1].
 | [1] |
The ability of manure to provide N to crops is generally compared to that of fertilizer N. Values calculated using Eq. [1] are not proper comparisons to fertilizer because plant use of fertilizer N is not 100% efficient. Equation [2] calculates the relative effectiveness of manure N as the proportion of apparent manure N uptake by a crop in relation to crop N uptake in plots that received a generally comparable amount of fertilizer N. The fertilizer treatments chosen were 90 kg N ha–1 for the low manure rate and 179 kg N ha–1 for the high manure rate, under the assumption that approximately 40% of newly applied manure N would be available during the first growing season.
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The fertilizer equivalence method compares crop yield or N uptake in manured plots to those obtained in plots that received fertilizer N. The derived value divides the equivalent fertilizer N rate by the total manure N rate applied expressed as a percentage as shown in Eq. [3] (Motavalli et al., 1989).
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Manure's fertilizer N equivalence is the amount of fertilizer N needed to obtain the same yield or N uptake in manured plots. The percentage is the apparent availability of the manure N in terms of fertilizer, and should be considered the fertilizer replacement value of manure. Because the fertilizer equivalence method compares manure N uptake to fertilizer N uptake as the relative effectiveness method does, results between the two methods should be comparable.
The stable isotope 15N is used in N cycling studies to identify metabolic pathways of N within plant and soil microbial populations, to measure rates of soil N processes (e.g., mineralization and immobilization), and to quantify individual components of an N balance (Trehan and Wild, 1993). The use of 15N-labeled manure is similar to the difference method as it measures N recovery in the aboveground corn tissue at physiological maturity, but utilizes 15N rather than unlabeled N (Hauck and Bremner, 1976). Labeled N uptake by a crop is calculated using Eq. [4].
 | [4] |
where P is the amount of N taken up in treated crop (manure-amended plots), f is the amount of applied manure N, a is the atom %15N in the applied manure, b is the atom %15N in the unlabeled manure, c is the atom %15N taken up in treated plots (in plots amended with 15N-labeled manure), and d is the atom %15N in control plots (in plots amended with nonlabeled manure).
Statistical Analysis
Statistical analyses were performed using the SAS statistical package (SAS Institute, 1990). Analysis of variance was determined using the SAS general linear models (GLM) procedure. Crop parameters were analyzed as a randomized complete block design with treatments as fixed effects. Orthogonal contrasts were performed when fixed effects were significant at 
= 0.10 to compare one treatment or group of treatments against other treatments to test for significant differences. Nonlinear regressions for fertilizer N responses in 1999 and 2003 were performed using a quadratic function and in 2003 using the asymptotic NLIN procedure with the Marquardt iterative method (SAS Institute, 1990). Models were chose based on R2 values; however, where values were approximately similar, the simpler model was used. A probability level p 
0.10 was considered significant.
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RESULTS AND DISCUSSION
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Corn N uptake responses to fertilizer N addition over the 5-yr study period are shown in Fig. 2. During all study years except 2002, fertilizer N significantly increased corn N uptake. Lack of response in 2002 was likely due to dry conditions and the widespread presence of corn smut (Ustilago spp.). Corn N uptakes obtained from the 90 and 179 kg ha–1 N rates were used to evaluate the relative effectiveness of manure N (Eq. [2]) and manure N availability (Eq. [3]) from single and multiple manure applications; however, as shown by the significant treatment x year ANOVA interaction (Table 2) the between-year variability (Fig. 2) made it necessary to compare corn N uptake responses due to fertilizer N and manure N applications separately for each year.
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Fig. 2. Whole plant corn N uptake responses to fertilizer N applications, West Madison Agricultural Research Station, Madison, WI, 1999–2003.
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As discussed in Muñoz et al. (2004), there was little uptake differential between the control and the treatments. We contribute this observation to the initial high fertility of the Plano soil which is also noted by Andraski et al. (2000) and the impacts from the alfalfa stand that was present from 1994 to 1996 which may have been still contributing to the N pool (Voss and Shrader, 1984; Fox and Piekielek, 1988).
Recovery of Manure Nitrogen in the Second and Third Year after a Single Application
Whole plant N uptake in the second and third year following single and multiple manure applications can be found on Table 3. Based on orthogonal contrasts, second-year residual benefit from a single manure application compared to the control was statistically significant only in 2003 and examination of the data shows this is true only for the high manure rate. Third-year residual benefits were not statistically significant (p > 0.10). Second-year residual aboveground N uptake exceeded third-year uptake only in 2003.
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Table 3. Second- or third-year residual effect of manure N rate on total corn N uptake based on single-year or continuous manure applications at West Madison Agricultural Research Station, Madison, WI, 1999–2003.
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Apparent recovery of second- and third-year residual N from single manure applications (Eq. [1]) averaged 8 and 1%, respectively, over all trial years (Table 4). Average second- and third-year residual N recoveries using the relative effectiveness (Eq. [2]) method were 4 and 5%, respectively. Based on these results, the relative effectiveness calculation did not result in substantially different results by correcting for conventional fertilizer efficiency (p = 0.965). Relative effectiveness depends heavily on apparent recoveries of N from equivalent fertilizer applications. Calculations from 2000 and 2002 were affected by low apparent recoveries of equivalent fertilizer applications.
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Table 4. Second- and third-year N availability using various methods, based on single manure applications, West Madison Agricultural Research Station, Madison, WI.
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Both apparent recovery and relative effectiveness calculations gave quite variable results. The fertilizer equivalence method using whole plant N uptake averaged 12 and 3% for second- and third-year N residual availability for a single manure application, respectively (Table 4). Data from 2002 is excluded from these calculations as the response curve from this cropping year was flat and produced no statistically significant response to added N (Fig. 2). This was likely due to dry weather and a severe smut infestation in that season. The fertilizer equivalence method produced much more consistent results over the apparent recovery method as results were positive for all but third-year residuals in cropping years 2000 and 2003. Similar to our findings, Klausner et al. (1994) reported residual availabilities of 9 and 3% for dairy manure the second and third year after application, respectively, based on the fertilizer equivalence method.
The most consistent results for determining residual N availability from a single manure application were achieved using 15N. We found that 6 and 2% of the applied 15N from manure was recovered in the second and third years, respectively (Table 4). The 15N estimates had the lowest standard errors and the most consistent estimates over the several years of the trial. Our mean estimates compare favorably with those of Jensen et al. (1999), where 15N-labeled sheep manure residual uptake by perennial ryegrass (Lolium perenne L.) in years 2 and 3 after application were estimated to be 4 and 1%. Estimates for the Jensen et al. (1999) study were from 1 yr of data, whereas we estimated second- and third-year residuals from 5 and 4 yr of data, respectively.
Residual Nitrogen Based on Multiple Manure Applications
Increases in crop response to multiple manure applications as compared to single applications is an additional way in which residual manure N effects may be evaluated. In all cases apparent N recovery from the low manure rate exceeded recovery from the high manure rate (Table 5), similar to what has been reported previously by others (Hensler et al., 1970; Motavalli et al., 1989; Ma et al., 1999; Muñoz et al., 2004). Apparent N recovery estimates from consecutive manure applications exceeded recovery values from single applications in only 3 of 5 yr (2000, 2001, and 2003) (based on the mean of both high and low manure rates). Because of this, it was not always possible to predict residual availabilities for a second or third year using multiple manure applications, but averaged over the whole study period we were able to calculate an annual residual benefit. Over the 5 yr, multiple manure apparent recovery estimations were 21 vs. 15% for single manure apparent recoveries (averaged for high and low manure rates), yielding an estimate of 6% residual N availability with the apparent recovery method.
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Table 5. Comparison of recovery and apparent availability nitrogen availability using various methods, based on single and multiple manure applications, for all applicable years, West Madison Agricultural Research Station, Madison, WI.
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Whole plant N uptake from plots that received successive annual manure applications (Table 2) showed a benefit over successive annual fertilizer applications of comparable available rates (low manure rate vs. 90 kg N ha–1 and high manure rate vs. 179 kg N ha–1); this was true for the low manure rate in 2000 and 2001 and for the high rate in 2002 and 2003. The high manure rate had a statistically higher whole plant N uptake over the low manure rate in years 2001 to 2003.
In all cases, apparent availability estimates using the fertilizer equivalence method from the low manure rate exceeded that for the high manure rate for all years. Using this method, availability estimates from multiple manure applications exceeded the estimates from single manure applications in only 2 out of 5 yr; average fertilizer equivalence estimations were 44% for multiple manure applications vs. an average of 37% for single manure applications, yielding an estimate of 7% residual N availability with the fertilizer equivalence.
The results from these indirect methods using multiple manure applications did not show consistent residual N availability estimations, in contrast to what has been observed by others (Jokela, 1992; Kelling and Wolkowski, 1993). Neither the fertilizer equivalence nor the apparent recovery method produced a consistent increase in estimated availability for successive manure applications, raising the question as to the dependability of either method for relatively limited data sets. Kelling and Wolkowski (1993) reported similar problems where one location of the three tested showed no residual responses.
The average recovery of 15N from multiple manure applications was 26 vs. 19% for single manure applications (Table 5). The residual availability was estimated to be 6 and 2% for second- and third-year residuals using single manure applications (Table 4) and the sum of the single manure application residuals for the second and third year (8%) was similar to the average difference between multiple manure and single manure applications (7%) as shown in Table 5. If we assumed that residual benefits from manure do not occur to a significant extent after 3 yr, it appears that estimates of residual manure 15N availability using single or multiple applications manure are nearly identical.
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CONCLUSION
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With the exception of the 15N method, estimates of second- and third-year manure N availabilities using single manure applications produced better results than using multiple manure applications. Multiple manure applications did not always show a residual benefit compared to single manure applications and we were not able to consistently estimate residual year benefits as has been done in other studies (Jokela, 1992; Kelling and Wolkowski, 1993). In reference to the indirect methods, if a larger difference between the control and treatments was found, the estimates of availability would be more precise. With the relatively flat response curves, small changes in uptake resulted in large changes in availability estimates (Muñoz et al., 2004). Similar to our findings of 12 and 3%, Klausner et al. (1994) reported residual availabilities of 9 and 3% for semisolid dairy manure the second and third year after application, respectively, based on the fertilizer equivalence method.
The 15N method had the most consistent results. Estimates using 15N were lower than those obtained using the fertilizer equivalence method and should be considered a minimum residual manure N availability as some exchange and therefore dilution with unlabeled soil N is likely. These low results may be a result of the dilution of the labeled manure as 15N-labeled manure being tied up in the large C pool of the soil mobilizing and immobilizing N or being left in corn residues. Powell et al. (2005) found that 47% of applied 15N-labeled manure was still accountable in the soil profile 2 yr after application. This emphasizes what the potential residency and mobilization time is for applied manure N. Based on this and other studies (Kelling and Wolkowski, 1993; Klausner et al., 1994; Paul and Beauchamp, 1993), we suggest that second- and third-year residual N availability from a single application of semisolid dairy manure would be 9 to 12% and 3 to 5% of the original manure N application, respectively. These results confirm the residual manure N availability estimates used in the Wisconsin soil test recommendations (Kelling et al., 1998).
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ACKNOWLEDGMENTS
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The authors would like to thank Phil Speth and Peter Wakeman for their help on the field portion of this study. Support for this project was provided by the UW Consortium for Agriculture and Natural Resources, the UW-Madison College of Agricultural and Life Sciences. USDA-ARS is also gratefully acknowledged.
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REFERENCES
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TOP
ABSTRACT
INTRODUCTION
