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TECHNICAL REPORTS

Waste Management

Estimating Plant-Available Nitrogen Release from Manures, Composts, and Specialty Products

^a Dep. of Crop and Soil Science, Oregon State Univ., Corvallis, OR 97331
^b Dep. Crop and Soil Sciences, Washington State Univ., 7612 Pioneer Way E., Puyallup, WA 98371
^c Dep. Horticulture, Oregon State Univ. North Willamette Research and Extension Center, Aurora, OR 97002

^* Corresponding author (Dan.Sullivan{at}oregonstate.edu)

Received for publication February 14, 2006.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Recent adoption of national rules for organic crop production have stimulated greater interest in meeting crop N needs using manures, composts, and other organic materials. This study was designed to provide data to support Extension recommendations for organic amendments. Specifically, our objectives were to (i) measure decomposition and N released from fresh and composted amendments and (ii) evaluate the performance of the model DECOMPOSITION, a relatively simple N mineralization/immobilization model, as a predictor of N availability. Amendment samples were aerobically incubated in moist soil in the laboratory at 22°C for 70 d to determine decomposition and plant-available nitrogen (PAN) (n = 44), and they were applied preplant to a sweet corn crop to determine PAN via fertilizer N equivalency (n = 37). Well-composted materials (n = 14) had a single decomposition rate, averaging 0.003 d^–1. For uncomposted materials, decomposition was rapid (>0.01 d^–1) for the first 10 to 30 d. The laboratory incubation and the full-season PAN determination in the field gave similar estimates of PAN across amendments. The linear regression equation for lab PAN vs. field PAN had a slope not different from one and a y-intercept not different than zero. Much of the PAN released from amendments was recovered in the first 30 d. Field and laboratory measurements of PAN were strongly related to PAN estimated by DECOMPOSITION (r² > 0.7). Modeled PAN values were typically higher than observed PAN, particularly for amendments exhibiting high initial NH₄–N concentrations or rapid decomposition. Based on our findings, we recommend that guidance publications for manure and compost utilization include short-term (28-d) decomposition and PAN estimates that can be useful to both modelers and growers.

Abbreviations: PAN, plant-available nitrogen • FNE, fertilizer nitrogen equivalency

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
RECENT ADOPTION OF NATIONAL RULES for organic production (USDA, 2002) have stimulated greater interest in organic farming and meeting crop N needs using manures, composts, and other organic materials. Current Pacific Northwest Extension recommendations for N-based amendment application, based on limited data, estimate that first-season N availability (% of total N) is 0 to 20% for separated dairy solids, 20 to 40% for dry-stack dairy manure (Bary et al., 2000), and 10 to 30% for uncomposted yard trimmings (Cogger et al., 2002). Broiler litter is one of the major N sources used in organic production in the Pacific Northwest, but current Extension guidance (Bary et al., 2000) relies on professional judgment in extrapolating research results from other regions. Estimates of PAN for other N sources used most often in organic agriculture such as fish, feather, and seed meals often are not readily available, except from the supplier. National guidance for manure use in organic crop production (Kuepper, 2003) provides only typical total N analyses for manures with no estimate of PAN.

Correlations between C and N analyses of specific organic materials and the amount and timing of available N release have been reported for crop residues (Vigil and Kissel, 1991; VanLauwe et al., 1997; Trinsoutrot et al., 2000), animal manures (Castellanos and Pratt, 1981; Chae and Tabatabai, 1986), components of dairy manure (Van Kessel et al., 2000), and municipal biosolids (Gilmour et al., 2003). As C/N decreases, the percentage of lignin in a residue typically decreases, and the amount of residue that is rapidly decomposed in soil during the first 30 d in soil increases (Ajwa and Tabatabai, 1994; Van Kessel et al., 2000). While C/N is a good indicator of PAN released for fresh crop residues or manures, it not as useful as a general indicator for a set of organic materials that may include fresh organic matter such as crop residues, partially decomposed organic matter such as stored manure, and composts. Composting or storage of organic materials with low C/N typically reduces the decomposability of residue, but it often does not appreciably change C/N, because both C and N losses usually accompany decomposition (Hansen et al., 1993). Knowledge of amendment decomposition kinetics is especially helpful for organic materials with low C/N. For example, for biosolids with C/N of 5 to 10, Gilmour et al. (1985) and Gilmour et al. (2003) reported a linear relationship with a slope not significantly different than one between net amendment N mineralized (% of organic N) and decomposition in soil.

Computer simulation models have shown potential for predicting N mineralization under a wide range of conditions. With proper calibration and verification, many models have the potential to be used for data interpretation, education, and decision support in soil N management (Schaffer et al., 2001). One general criticism of models, however, is the need for further verification (Wagner et al., 1998), particularly using data independent of those used to develop and parameterize the model (McGechan and Wu, 2001).

The model DECOMPOSITION is a mechanistic computer simulation model first described by Gilmour and Clark (1988) and subsequently described in detail by Gilmour (1998). The model uses first-order kinetics to estimate PAN. Most other models that describe N mineralization processes also utilize first-order kinetics, modified for environmental variables (McGechan and Wu, 2001). DECOMPOSITION is a relatively simple model by today's standards. It simulates only the mineralization/immobilization of N following organic amendment application. The model has proved to be reasonably accurate in predicting PAN from municipal biosolids. In an evaluation of the model DECOMPOSITION using 30 different biosolids with field sites in Arkansas, Michigan, Virginia, and Washington, Gilmour et al. (2003) found good agreement between observed PAN vs. simulated PAN during one growing season using actual decomposition kinetics, weather, and amendment analytical data (r² = 0.72). With three biosolids and one site, Gilmour and Skinner (1999) also found good agreement between observed PAN versus modeled PAN using DECOMPOSITION (r² = 0.67). Findings from the model have been used to develop national guidance for biosolids application based on average air temperature and irrigation (Gilmour et al., 2000).

The current study was designed to provide data to support Extension recommendations for organic amendments. Specifically, our objectives were to (i) measure decomposition and N released from fresh and composted amendments and (ii) evaluate the performance of the model DECOMPOSITION, a relatively simple N mineralization/immobilization model as a predictor of N availability.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Description of Amendments
Amendments used in this study are grouped into four categories: a fresh amendment vs. compost product comparison (n = 28 samples), other broiler litter (n = 5), other composts (n = 6), and specialty products (n = 5; Table 1).

Broiler litter was obtained from a production broiler facility (Mossy Rock, WA) that routinely markets a compost product to farmers and landscapers. Although marketed as compost, the amendment production process includes only periodic turning of large windrows without moisture addition. The fresh broiler litter was dry-stacked for 56 d (2002 sample) or 14 d (2003 sample). The composted broiler litter samples were dry-stacked for 84+ d in both years.

Separated dairy solids were collected from a dairy (Woodburn, OR) that employed a flush manure handling system. A mechanical separator removed the coarse, fibrous fraction of the manure as it passed from the animal confinement area to a storage lagoon. Fresh dairy solids were stored less than 7 d at the dairy. Composted dairy solids were produced in windrows that were turned weekly over a 60-d period with a self-propelled windrow turner. At each turning, moisture was added (if needed) to maintain moisture of 500 to 600 g kg^–1 in the compost windrow.

Yard trimmings and yard trimmings compost were produced at a large indoor commercial compost facility in Puyallup, WA. Yard trimmings consisted of approximately a 60:40 mixture (v/v) of woody tree and shrub trimmings mixed with grass clippings. Both yard trimmings and yard trimmings compost were ground with a hammer mill to reduce particle size on receipt at the facility. The yard trimmings then were placed in windrows, and allowed to heat for 7 d with periodic turning to kill weed seeds. The yard trimmings compost was prepared by placing yard trimmings in windrows and turning a minimum of 5 times over a 40-d period with a compost pile turner. Moisture was added at each turning, and windrows received forced aeration based on automated feedback from temperature probes placed in the windrows. After 40 d, the compost was placed in larger curing piles for at least 20 additional d. Before delivery to field experiments, large debris >11 mm (>7/16 in.) was removed from the yard trimmings compost by screening.

Fresh rabbit manure without bedding was obtained from a rabbit production facility near Corvallis, OR. The rabbit manure compost was produced in small outdoor windrows (50 m long, 1 m high and 2 m wide) in summer. Windrows were turned with a compost pile turner and moisture was added at least six times during 60 d of active composting. Some soil underlying the windrows was incorporated during composting. The finished rabbit manure compost was covered with plastic sheeting in the fall. The cover was removed just before transport to the field experiment locations the following spring.

The remaining organic materials used in the study (other broiler litter, other composts, specialty products; Table 1) came from a variety of sources and were included in selected laboratory incubations and field trials. Other broiler litters (n = 6) were obtained from broiler production facilities; information on storage and/or composting time and methodology was not available. Other composts (n = 6) included two samples of composted dairy solids from additional local facilities, one sample of solids from an anaerobic dairy manure digester, and three samples of composts prepared by a Puyallup, WA composting school. The anaerobically digested dairy solids were collected from a complete mix digester, operating at 36°C with a mean residence time of 28 d. The composts from the compost school were produced from a 40:20:15:5:10 v/v mixture of yard trimmings, separated dairy solids, cereal straw, horse manure, and laying-hen manure that was composted for approximately 180 d under passive aeration. Specialty amendments (n = 5) included two samples of pelleted organic fertilizer derived from fish byproducts, two feather meals, and one canola (Brassica spp.) meal.

Amendment Sampling, Handling, and Preparation for Analyses
Amendments were transported to the field experiment sites no more than 7 d before field application, and kept under cover. Immediately before amendment application at each field experiment, composite amendment samples for inorganic N analysis and for use in soil incubation experiments were collected, subsampled, placed into 1-L zippered polyethylene bags, then frozen within 24 h of collection. Each composite amendment sample was a subsample derived from a mixture of 20 grab samples collected from the amendment pile or bag.

Total solids in the fresh and thawed amendment samples were determined by drying at 55°C. There was no consistent difference between total solids in fresh samples or in samples thawed after freezing.

Field Studies
‘Jubilee’ sweet corn (Zea mays L.) was grown at both field sites located at the WSU Research and Extension Center at Puyallup, WA and at the OSU North Willamette Research and Extension Center near Aurora, OR. The Oregon site was located on a Willamette silt loam soil (fine-silty, mixed, superactive, mesic Pachic Ultic Argixerolls). The Washington site was located on a Puyallup fine sandy loam (coarse-loamy over sandy, mixed mesic Vitrandic Haploxerolls). The 2003 trials were conducted on acreage adjacent to the 2002 field trials (within the same field). The previous crop at the Oregon site in 2002 and 2003 was summer fallow. The previous crop at the 2002 Washington site was sweet corn followed by a winter triticale cover crop. The previous crop at the 2003 Washington site was sweet corn with no winter cover crop.

Pre-amendment soil samples collected in March or April of each year at each field site indicated that soil pH (>6.1) and soil test concentrations of P, Ca, Mg, and K were above established sufficiency levels for sweet corn production (Marx et al., 1999). At the Oregon sites only, blanket applications of soluble boron and sulfate of potash magnesia fertilizer (K₂SO₄.2MgSO₄) were applied before seeding to supply 1 kg B ha^–1 and 30 kg S ha^–1. Soluble boron was sprayed on the soil surface with a boom sprayer. Granular sulfate of potash magnesia fertilizer was broadcast on the soil surface.

Both sites had a typical maritime Pacific Northwest climate with cool, wet winters and mild, dry summers. Mean growing season temperatures were 18°C in 2002 and 20°C in 2003 at the Oregon site, and 16°C in 2002 and 17°C in 2003 at the Washington site. Seeding dates were 25 May for the OR 2002 site, 13 June for the OR 2003 site, 21 May for the WA 2002 site and 28 May for the WA 2003 site. Degree days (0°C base temperature) from amendment application to harvest averaged 2240 across sites (Table 2). Growing season precipitation was 72 mm in 2002 and 42 mm in 2003 at the Oregon site, and 81 mm in 2002 and 37 mm in 2003 at the Washington site. Irrigation was supplied by solid-set sprinklers on a schedule designed to limit leaching losses but provide adequate moisture for crop production. Approximately 2.5 cm irrigation was supplied every 7 d during peak crop evaporative demand.

View this table: [in this window] [in a new window]   Table 2. Degree days elapsed between organic amendment incorporation and soil sampling for PAN determination in field and laboratory.

Urea treatments (no organic amendment) supplied a total of 0, 56, 112, 168, or 224 kg N ha^–1 during the growing season, split into starter and sidedress applications. Starter urea was broadcast 1 or 2 d before planting, with additional side-dress urea broadcast just before irrigation at the four- to six-leaf growth stage. The side-dress fertilizer application took place 1 to 3 d following the date of mid-season soil sample collection (Table 2). In Year 1, 28 kg ha^–1 of urea-N was applied before planting with the remainder added at the six-leaf growth stage. In Year 2, 56 kg ha^–1 of urea-N was applied before planting with the remainder at the six-leaf growth stage.

Organic amendments were weighed, and then broadcast on the soil surface. Amendment application rates (Table 1) were based on estimates of amendment PAN, targeted to supply 40 to 120 kg PAN ha^–1 during the growing season, based on current Extension guidance for the Pacific Northwest (Bary et al., 2000). To calculate application rates, we estimated PAN (% of total N) of 45% for broiler litter, 10% for dairy solids, 30% for rabbit manure, 15% for yard trimmings, 10% for composts, and 50% for specialty products and assumed typical total N analyses and total solids concentrations. Urea was not applied to plots receiving organic amendments. Actual amendment application rates were determined after application by multiplying amendment application amount by measured total solids concentration. Amendments were incorporated into soil by rototilling to a depth of 15 cm. Broiler litter and rabbit manure were incorporated within 2 h of application to limit NH₃ loss. Other materials with lower potential for NH₃ loss were incorporated within 24 h.

Soil samples were collected at three times following organic amendment application: pre-plant (after 14 to 28 d), mid-season (after 44 to 75 d), and post-harvest (after 121 to 133 d; Table 2). Each sample was a composite of 8 to 12 soil cores (0- to 30-cm depth) collected per plot with a 25-mm-i.d. push probe. Soil samples were air-dried within 1 d to stop microbial activity.

Laboratory Incubations
Decomposition of amendment organic matter was estimated via incubation with soil. The incubation was performed at 22°C in sealed 0.95-L Mason jars, with three replicates per amendment sample. Soil for incubation was collected in May from each field site approximately 30 d before the start of the laboratory incubations, and held at field moisture at 4°C. At the start of each incubation, soil was allowed to warm to room temperature for 3 d, then sufficient moisture added to bring gravimetric soil moisture to 200 to 250 g kg^–1. Thawed amendment samples equivalent to 1 g dry weight were incorporated into 50 g soil for an application rate of 20 g kg^–1 in Year 1. In Year 2, we reduced amendment incorporation rates to bring laboratory incubation amounts closer to those used in the field experiments. Incorporation rates were 5 g kg^–1 for broiler litter samples, feather meal, and pelleted fish; other amendments were incorporated at a rate of 10 g kg^–1. Each incubation included soil-only control jars to allow calculation of net CO₂ evolution associated with amendment incorporation.

We used a titration method to determine CO₂ evolution in Year 1, and a gas chromatograph method to determine CO₂ in Year 2. Measurements were made after 3, 7, 14, 21, 28, 35, 42, 49, and 70 d. In Year 1, CO₂ was collected in vials containing 20 mL 1M NaOH that were placed inside the incubation jars. Vials were replaced inside the jars after each incubation interval. For CO₂ determination in Year 1, the carbonate trapped by NaOH was precipitated with excess BaCl₂, and the remaining NaOH was back-titrated with standardized 0.1 M HCl, using phenolphthalein as the indicator (Anderson, 1982). In Year 2, air was collected from sample jars by inserting a syringe through a rubber septum in the jar lid. Carbon dioxide was determined with a He-carrier gas chromatograph (Carle Series 100 AGC, Hach, Loveland, CO). A calibration experiment verified that the chromatograph CO₂ method used in Year 2 yielded comparable data to the titration method used in Year 1. We incubated 15 amended jars (5 amendments x 3 replicates) and determined CO₂ evolved after 3, 7, and 14 d. A regression between the two methods yielded an r² of 0.98, a slope not significantly different than one, and an intercept not significantly different from zero.

Inorganic N accumulation was measured using incubation intervals of 14, 42, and 70 d, and the same amendment incorporation rates were used to measure CO₂ evolution. For inorganic N measurement, moist soil (650 g dry wt.) + amendment were incubated in zippered 3.8-L polyethylene bags. The larger incubation samples provided a larger amount of soil for repeated subsampling, and allowed for ventilation while maintaining consistent soil moisture. The target soil moisture content used in this experiment (200 to 250 g H₂O kg^–1) allowed thorough mixing of the amendments with soil, and it allowed the soil aggregates to remain small. The small soil aggregates were easily subsampled, and porosity was maintained throughout the soil-amendment mixture. The zippered tops of the bags were left partially open during incubation to facilitate air exchange, thereby reducing the potential for denitrification. Incubation bags were placed within 20-L plastic tubs that contained moistened foam pads to increase humidity. At 14-d intervals, soil moisture in the bags was measured and replenished if necessary. Soil subsamples (15 g) for inorganic N analysis were collected from the bags on Day 0, 3, 7, 14, 42, and 70 in Year 1 and at Day 0, 14, 42, and 70 in Year 2, extracted with 50 mL 2M KCl, and refrigerated (4°C) until analysis. Additional soil samples were collected at each sampling date for determination of actual soil moisture. Soil moisture data were used to convert inorganic N concentrations in moist soil to a dry weight basis.

Soil and Amendment Analyses
Inorganic N in all soil samples and in amendment samples was determined by automated colorimetric methods after extraction with 2M KCl at the Oregon State University Central Analytical Laboratory. Ammonium-N was extracted from both fresh and dried amendment samples using a 1:5 solids/extractant ratio. Nitrate-N was extracted from only the fresh amendment samples, because nitrate is not volatilized when samples are oven-dried. After shaking for 30 min, KCl extracts were filtered through Whatman No. 42 paper and refrigerated before analysis. Extracts were diluted to prevent interference from dissolved organic matter in colorimetric N determinations. Ammonium-N was determined using a salicylate-nitroprusside method (Gavlak et al., 1994) and nitrate-N was determined by a cadmium reduction method (Gavlak et al., 1994). For total N and C determination, organic amendments were prepared by grinding to pass a 2-mm screen. Total N and C were determined using a combustion analyzer equipped with an infrared detector (LECO Instruments Model CNS 2000, LECO Instruments, St. Joseph, MI; Sweeney, 1989).

Calculations and Statistics
Total N concentrations (N_t) in amendment samples were calculated as:

[1]

where N_t = total N in fresh amendment (g kg^–1; dry wt basis), total N_dried = total N in dried amendment (g kg^–1; dry wt basis), NH₄–N_dried = NH₄–N in dried amendment (g kg^–1; dry wt basis), and NH₄–N_fresh = NH₄–N in fresh amendment (g kg^–1; dry wt basis).

For each field trial site-year, we calculated full-season PAN supplied by amendments with a two-step calculation. First, we used linear regression to calculate the fertilizer N efficiency coefficient (eff) for the urea fertilizer treatments:

[2]

where N_rec = N recovered at harvest (kg ha^–1), calculated as the sum of N in above-ground biomass at harvest + post-harvest soil nitrate N (0- to 30-cm depth); eff = fertilizer efficiency coefficient, or the fraction of fertilizer N that was recovered at harvest; N_rate = the rate of urea-N (kg ha^–1) applied for a given site and year; and b = N recovery intercept (kg ha^–1), a regression estimate of the N recovered from the zero N fertilizer control plot.

Then Eq. [2] was rearranged and amendment PAN calculated using a fertilizer N equivalency approach:

[3]

where PAN = percentage of amendment total N recovered (kg ha^–1); N_rectrt = N recovered (kg ha^–1) for a treatment receiving application of pre-plant organic amendment; eff and b are substituted from the fertilizer efficiency regression (Eq. [2]) for the appropriate site and year; and amendment N applied = total N application rate for each amendment (kg ha^–1; Table 1).

For field pre-plant soil samples, and for mid-season soil samples, we calculated PAN as the additional N recovered from soil following organic amendment application, as:

[4]

where PAN = percentage of amendment total N recovered (kg ha^–1) from amended soil; treatment inorganic N = soil NH₄–N + NO₃–N (kg ha^–1) for soil receiving amendment application; control N = soil NH₄–N + NO₃–N (kg ha^–1) for soil alone (no amendment or fertilizer applied); and amendment N applied = amendment total N applied (kg ha^–1).

Equation [4] was also used for laboratory PAN calculation, except that it was calculated using units of mg kg^–1.

Amendment decomposition, as measured by CO₂ evolution, was calculated as:

[5]

where decomposition = percentage of amendment C evolved as CO₂–C; treatment CO₂–C = cumulative CO₂–C evolved (mg) from soil receiving amendment application; control CO₂–C = cumulative CO₂–C evolved (mg) for soil alone; and total C applied = amendment C addition (mg).

Linear regression was performed using S-Plus (S-Plus 6.1 for Windows, Insightful). Regression equations for observed vs. modeled PAN were tested at P = 0.05 to determine whether the regression intercept was different than zero, and whether the slope of the regression equation was different than one.

Computer Simulation Model
The model DECOMPOSITION is a mechanistic model first described by Gilmour and Clark (1988) and described in detail by Gilmour (1998). The model uses first-order kinetics to estimate the rates of C and N transfer between six pools: fresh organic amendment (rapid and slow fractions), microbial biomass (indigenous and new), and soil organic matter (decomposable and recalcitrant) using daily time steps. Initial soil organic matter is divided equally between decomposable and recalcitrant pools. Default decomposition rate constants (d^–1) are 0.035 for fresh biomass, 0.00093 for indigenous biomass, and 0.00020 for decomposable soil organic matter. The recalcitrant soil organic matter pool does not decompose. The decomposition of amendments is modeled using a sequential first-order model where the rapid fraction is entirely decomposed before decomposition of the slow fraction begins. Amendment decomposition rate constants (k_r for the rapid pool and k_s for the slow pool) are determined from 25°C laboratory incubation data using a segmented regression of the natural log of the percent C remaining. Nitrogen mineralization and immobilization in the model are driven by C decomposition, microbial efficiency, and C/N of the amendment, biomass, and soil organic matter. Microbial efficiency is assumed to be 0.4. Carbon/nitrogen ratios are assumed to be 10 for soil organic matter and 8 for microbial biomass. As the amendment decomposes, if amendment C/N is >15, then soil inorganic N is immobilized in microbial biomass. The model assumes zero N loss via NH₃ volatilization or denitrification processes. Amendment decomposition rates (measured at 25°C) are modified for temperature using a Q₁₀ approach and modified for soil moisture using a soil water factor scaled from 0 to 1 (Gilmour, 1998). Soil temperature is assumed to equal air temperature.

John Gilmour (John Gilmour, Fayetteville, Arkansas) received input data from our project consisting of a numeric amendment sample ID, amendment analyses for total N, total C, and NH₄–N (dry weight basis), and amendment application rate. Gilmour calculated fast and slow decomposition rate constants for use in the simulations (Table 3) using our data for cumulative amendment CO₂ loss over 70 d (Fig. 1). For use in the model, he multiplied our measured decomposition rate constants by 1.28, assuming a Q₁₀ of 2, to estimate the amendment decomposition rate constant at 25°C. For modeling of inorganic N release in the laboratory incubations, Gilmour received data on soil moisture during incubation, temperature, and inorganic N recovered from the soil-only control (no amendment) at each soil incubation sampling date. For the field experiments, we provided Gilmour with dates of amendment application, daily average air temperatures collected from weather stations located within 1 km of each field site, and daily precipitation and daily irrigation application amounts.

View this table: [in this window] [in a new window]   Table 3. Fitted kinetic parameters for sequential decomposition of organic amendments in the laboratory, and measured cumulative decomposition after 70 d at 22°C.

View larger version (22K): [in this window] [in a new window]   Fig. 1. Cumulative decomposition in the laboratory at 22°C for organic amendments incubated in soils from Washington (WA) and Oregon (OR) field sites in 2002 and 2003. Open symbols represent uncomposted organic amendments, whereas filled symbols represent amendments that were "composted." Fitted regression equations for cumulative decomposition of each amendment are shown in Table 3.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Decomposition of Fresh and Composted Amendments
We incubated the organic amendment sample collected from the bulk amendment pile or bagged amendment at each field site with the soil found at the site. This sampling method permitted direct comparison of amendment performance in the field and laboratory within each site-year. Amendments used at both field sites (fresh vs. composted product comparison) had similar C and N analyses within 2002 or 2003 (Table 1). Because each amendment sample was incubated with only one soil, we cannot statistically compare decomposition for amendments between the two soils. For amendment sources incubated in both soils (fresh vs. compost product comparison, n = 14), the average difference in 70-d decomposition between soils was small (2% of amendment total C).

Composting reduced cumulative decomposition (70 d in laboratory) from 62 to 29% of applied C for dairy solids, from 66 to 9% for rabbit manure, and from 24 to 11% for yard trimmings (Fig. 1; Table 3). Dry stacking of broiler litter (sold as "compost") did not consistently reduce amendment decomposition in soil. Amendments sold as broiler litter "compost" retained most of the characteristics of raw broiler litter: rapid decomposition during the first 7 d in soil, amendment C/N of 9 to 10, and NH₄–N of 5 to 9 g kg^–1 (Table 1). Most of the difference in cumulative decomposition between composts and raw materials occurred during the first 7 to 30 d of incubation in soil at 22°C. Anaerobically digested dairy solids had decomposition (39% in 70 d) that was intermediate between raw dairy solids and composted dairy solids. Other composts included in the study averaged 17% decomposition in 70 d. Specialty products (fish, feather, and canola meals) had very high cumulative decomposition (average = 76% in 70 d) as expected for raw amendments with C/N of 4 to 8. Decomposition rates observed in this study are similar to those reported by others for fresh and composted organic amendments (Ajwa and Tabatabai, 1994; Gilmour, 1998).

Values for rapid and slow decomposition rate constants also reflect differences among amendments (Table 3). Composted amendments generally had a single rate of decomposition using the rate constant fitting procedure described by Gilmour (1998). Averaged over all composts (n = 14; excluding broiler litter "compost"), the average decomposition rate was 0.003 C d^–1 (0.3% of remaining C per d). Values for rapid pool decomposition (k_r) demonstrated relative differences among materials in early decay rate (Table 3). For example, the first-order decay rate for the rapid pool (k_r) for fresh broiler litter was, on average, 2.0 times the k_r value for dairy solids. The k_r values for composted dairy solids, composted yard trimmings, and composted rabbit manure were of the same order of magnitude as the k_s values for their raw counterparts. This finding demonstrated that once the easily decomposable fraction of a raw material was broken down, the remaining material exhibited a decomposition rate similar to that of compost.

Plant-Available Nitrogen
We estimated fertilizer nitrogen equivalency (FNE) in the field trials using crop N uptake + post-harvest soil inorganic N as the measured response variable (Eq. [3]; Table 4). We chose crop N uptake + post-harvest soil inorganic N as the best indicator of FNE because it accounts for N mineralized late in the growing season, and it yielded a linear N response curve across all rates of applied fertilizer N. The FNE regression equations used to estimate PAN had reasonable fertilizer N recovery efficiency, averaging 68% across the four field site-years (Table 4). We also determined FNE based on other crop response variables: crop N uptake, fresh weight ear yield, and chlorophyll meter readings of leaves (Gale, 2005). All methods used for estimating FNE yielded similar values for the organic amendment treatments. Coefficients of determination (r²) between FNE determined using crop N uptake + post-harvest soil inorganic N (Eq. [3]) and other variables were: 0.80 for chlorophyll readings, 0.96 for crop N uptake, and 0.90 for fresh weight ear yield (Gale, 2005).

View this table: [in this window] [in a new window]   Table 4. Linear regression equations describing effect of urea-N fertilizer rate on full-season nitrogen recovery (above-ground biomass N at harvest + post-harvest soil nitrate N) in field trials.

View larger version (15K): [in this window] [in a new window]   Fig. 2. Plant-available nitrogen (PAN) observed for the full season in the field vs. PAN observed at 70 d in laboratory incubations at 22°C.

View larger version (18K): [in this window] [in a new window]   Fig. 3. Relationship between full-season PAN in field trials and organic amendment C/N.

View larger version (26K): [in this window] [in a new window]   Fig. 4. Observed and modeled PAN for laboratory incubations of amendments included in the fresh vs. "composted" product comparison. Data points represent averages across soils and years (n = 2 for rabbit manure; n = 4 for others). Error bar is standard error of the mean computed across soils and years. Point estimates of PAN were estimated by the DECOMPOSITION model for 14, 42, and 70 d of incubation at 22°C.

Model Verification: Laboratory and Field
Across all amendments, observed PAN was strongly correlated with PAN estimated by the DECOMPOSITION model, as demonstrated by regressions at 70-d in the laboratory (r² = 0.74) and for the full season in the field (r² = 0.78; Fig. 5). Although strongly correlated, modeled PAN was often greater than observed PAN. For the 70-d laboratory incubation, the slope of the regression line was not different than one, but the intercept was significantly greater than zero at P = 0.05. For the full season in the field, the regression line was not different than the 1:1 line in slope or intercept. Across all amendments, the average model overprediction of PAN determined by subtraction (modeled PAN minus observed PAN for each amendment) was 3% PAN at 14 d, 7% at 42 d, and 10% at 70 d in the laboratory (Table 5). In the field, the model overpredicted by an average of 3% PAN at preplant, 10% at mid-season, and 8% for the full season (Table 5).

View larger version (18K): [in this window] [in a new window]   Fig. 5. Observed and modeled PAN for laboratory incubation at 22°C and for full-season field trials. Dotted line is 1:1 line.

The model was more accurate in predicting PAN from composts having a single decomposition rate constant than for uncomposted materials that had rapid and slow decomposition rate constants in the laboratory (Fig. 4) and in the field (Fig. 5). The composts had very low decomposition rates compared to fresh materials (Table 3). Compost PAN increased slowly with time in the laboratory (Fig. 4) and in the field (Table 5). Often the 70-d PAN for composted materials was close to that measured at the start of the incubation. Thus, the modeling of PAN for composts did not provide a strong test of model capacity to simulate N mineralization and/or immobilization processes.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Recommendations for Estimating PAN for Organic Amendments
Three categories of amendment PAN were observed in our study. Well-composted amendments with slow decomposition rates in soil supplied little PAN; their major value lies in supplying organic matter for improving soil tilth. Plant-available N varied widely for rapidly decomposing materials with C/N less than 15, with PAN increasing as C/N decreased. We recommend early season soil nitrate N monitoring when using these materials to supply N for crop production. Many of the amendments in this group contain substantial amounts of NH₄–N at application, which can be rapidly lost as ammonia gas if the amendment is not immediately incorporated by tillage. One amendment used in the study, separated dairy solids, immobilized available N for 30 to 60 d following soil incorporation in our studies. To avoid N deficiency, this amendment should be applied far enough ahead of seeding so that rapid decomposition in soil is completed before planting the crop.

This study demonstrated that field and laboratory measurements of PAN were strongly correlated with PAN modeled by DECOMPOSITION, a model that includes only the mineralization/immobilization portion of the nitrogen cycle. The model tended to overpredict PAN, particularly for amendments with high initial NH₄–N concentrations, and for amendments with rapid decomposition rates in soil. The simplest explanation for this discrepancy is that in our trials, some PAN was lost as NH₃. However, this explanation is not supported by the 1:1 relationship observed between field PAN (some potential for NH₃ loss) and laboratory PAN (very low potential for NH₃ loss). The strong correlations between measured and modeled PAN in the field trials suggested that the algorithms used by DECOMPOSITION to predict N mineralization from amendments are sufficiently detailed to use for planning purposes, when excellent N management practices are used. In situations where substantial PAN losses are expected, the mineralization/immobilization algorithms used in DECOMPOSITION must be integrated into a more complete model. Our study included only one amendment that demonstrated N immobilization (fresh dairy solids). Therefore, we did not obtain sufficient data to verify outputs from the N immobilization algorithms in DECOMPOSITION. The DECOMPOSITION model approach was most valuable for organic materials with C/N of 10 to 15. These materials had the widest range in N availability, depending on whether the organic fraction of the amendment was readily decomposable (e.g., fresh manure) or stable (compost).

This study demonstrated that traditional laboratory analyses of amendments (C/N and total N) and short-term laboratory incubations that determine decomposition and net available N released from amendments have value in providing improved estimates of field PAN for the first growing season. We suggest a minimum data set be used to characterize typical amendment characteristics in guidance publications for organic farmers and others that use manure to supply N, including: amendment total N, C/N, total solids, NH₄–N and NO₃–N, decomposition of the amendment determined after 7, 14, and 28-d incubation, and PAN released from the amendment after 28-d incubation at room temperature (approximately 22°C). Guidance should also include the number of independent amendment samples used to determine typical values. Having three decomposition data points (7, 14, and 28 d) is sufficient to demonstrate whether an amendment has been composted (relatively constant decomposition rate over time) or not composted (rapid decomposition in the first 7 d, followed by slower decomposition). In both our field and laboratory studies, a large fraction of amendment PAN was recovered in the first 28 d after application. Decomposition over 28 d is also suitable for determining whether a single decomposition rate constant, or two rate constants (rapid and slow decomposition) are appropriate representation of decomposition kinetics for use in computer simulation models.

	ACKNOWLEDGMENTS

 
This project was supported by Initiative for Future Agriculture and Food Systems Grant no. 2001-52101-11349 from the USDA Cooperative State Research, Education and Extension Service. We thank John Gilmour for running the DECOMPOSITION computer simulation model using our inputs. Soil and organic amendment analyses were performed by the Oregon State University Central Analytical Laboratory under the supervision of Will Austin. Joan Sandeno graciously provided assistance with laboratory research and editing of the manuscript.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Ajwa, H.A., and M.A. Tabatabai. 1994. Decomposition of different organic materials in soils. Biol. Fertil. Soils 18:175–182.
• Anderson, J.P.E. 1982. Soil respiration (Method 41–3.2). p. 841–845. In Methods of soil analysis. Chemical and microbiological properties. Agronomy Monograph 9 (Part 2). ASA, CSSA, and SSSA, Madison, WI.
• Bary, A.I., C.G. Cogger, and E.A. Myhre. 2004. Yard trimmings as a source of nitrogen for crop production. Compost Sci. Util. 12(1):11–17.
• Bary, A.I., C.G. Cogger, and D.M. Sullivan. 2000. Fertilizing with manure. Pacific Northwest Extension Publication 533. Washington State University Cooperative Extension, Pullman, WA.
• Castellanos, J.Z., and P.F. Pratt. 1981. Mineralization of manure nitrogen–correlation with laboratory indexes. Soil Sci. Soc. Am. J. 45:354–357.[Abstract/Free Full Text]
• Chae, Y.M., and M.A. Tabatabai. 1986. Mineralization of nitrogen in soils amended with organic wastes. J. Environ. Qual. 15:193–198.
• Cogger, C., A. Bary, and D.M. Sullivan. 2002. Fertilizing with yard trimmings. Publ. EB1926-E. Washington State Univ. Cooperative Extension. Pullman, WA. Available at http://cru.cahe.wsu.edu/CEPublications/eb1926e/eb1926e.pdf (verified 26 July 2006).
• Gale, E.S. 2005. Estimating plant-available nitrogen release from manures, composts, and crop residues. M.S. thesis. Oregon State University, Corvallis, Oregon.
• Gavlak, R.G., D.A. Horneck, and R.O. Miller. 1994. Plant, soil, and water reference methods for the western region. Western Regional Extension Publ. 125, Univ. Alaska-Fairbanks.
• Gilmour, J.T. 1998. Carbon and nitrogen mineralization during co-utilization of biosolids and composts. p. 89–112. In S. Brown, J.S. Angle, and L. Jacobs (ed.) Beneficial co-utilization of agricultural, municipal and industrial by-products. Kluwer Academic Publ., Dordrecht, the Netherlands.
• Gilmour, J.T., and M.D. Clark. 1988. Nitrogen release from wastewater sludge: A site-specific approach. J. Water Pollut. Control Fed. 60:494–498.
• Gilmour, J.T., M.D. Clark, and G.C. Sigua. 1985. Estimating net N mineralization from carbon dioxide evolution. Soil Sci. Soc. Am. J. 49:1398–1402.[Abstract/Free Full Text]
• Gilmour, J.T., C.G. Cogger, L.W. Jacobs, G.K. Evanylo, and D.M. Sullivan. 2003. Decomposition and plant-available nitrogen in biosolids: Laboratory studies, field studies, and computer simulation. J. Environ. Qual. 32:1498–1507.[Abstract/Free Full Text]
• Gilmour, J.T., C.G. Cogger, L.W. Jacobs, S.A. Wilson, G.K. Evanylo, and D.M. Sullivan. 2000. Nitrogen management protocols for biosolids beneficial reuse. Final report. Water Environment Federation Project 97-REM-3. WEF stock no. D00307. Water Environment Federation, Alexandria, VA.
• Gilmour, J.T., M.A. Koehler, M.L. Cabrera, L. Szajdak, and P.A. Moore, Jr. 2004. Alum treatment of poultry litter decomposition and nitrogen dynamics. J. Environ. Qual. 33:402–405.[Abstract/Free Full Text]
• Gilmour, J.T., and V. Skinner. 1999. Predicting plant-available nitrogen in land-applied biosolids. J. Environ. Qual. 28:1122–1126.[Abstract/Free Full Text]
• Haney, R.L., F.M. Hons, M.A. Sanderson, and A.J. Franzluebbers. 2001. A rapid procedure for estimating nitrogen mineralization in manured soil. Biol. Fertil. Soils 33:100–104.
• Hansen, R.C., H.M. Keener, C. Marugg, W.A. Dick, and H.A.J. Hointink. 1993. Composting of poultry manure. p. 131–153. In H.A.J. Hoitink and H.M. Keener (ed.) Science and engineering of composting: Design, microbiological and utilization aspects. Renaissance Publications. Worthington, OH.
• Hartz, T.K., J.P. Mitchell, and C. Giannini. 2000. Nitrogen and carbon mineralization dynamics of manures and composts. HortScience 35:209–212.[Abstract/Free Full Text]
• Kirchmann, H. 1990. Nitrogen interactions and crop uptake from fresh and composted ¹⁵N-labelled poultry manure. J. Soil Sci. 41:379–385.
• Kuepper, G. 2003. Manures for organic crop production. Appropriate Technology Transfer for Rural Areas (ATTRA). Fayetteville, AR. Available at http://www.attra.org/attra-pub/PDF/manures.pdf (verified 26 July 2006).
• Marx, E.S., J. Hart, and R.G. Stevens. 1999. Soil test interpretation guide. EC 1478. Oregon State University Extension, Corvallis, OR.
• McGechan, M.B., and L. Wu. 2001. A review of carbon and nitrogen processes in European soil nitrogen dynamics models. p. 103–171. In M.J. Schaffer, L. Ma, and S. Hansen (ed.) Modeling carbon and nitrogen dynamics for soil management. Lewis Publishers, Boca Raton, FL.
• Preusch, P.L., P.R. Adler, L.J. Sikora, and T.J. Tworkoski. 2002. Nitrogen and phosphorus availability in composted and uncomposted poultry litter. J. Environ. Qual. 31:2051–2057.[Abstract/Free Full Text]
• Schaffer, M.J., L. Ma, and S. Hansen. 2001. Preface. In M.J. Schaffer, L. Ma, and S. Hansen (ed.) Modeling carbon and nitrogen dynamics for soil management. Lewis Publishers, Boca Raton, FL.
• Serna, M.D., and F. Pomares. 1991. Comparison of biological and chemical methods to predict nitrogen mineralization in animal wastes. Biol. Fertil. Soils 12:89–94.[CrossRef]
• Shi, W., and J.M. Norton. 2000. Microbial control of nitrate concentrations in an agricultural soil treated with dairy waste compost or ammonium fertilizer. Soil Biol. Biochem. 32:1453–1457.[CrossRef]
• Sullivan, D.M., S.C. Fransen, A.I. Bary, and C.G. Cogger. 1998. Fertilizer nitrogen replacement value of food residuals composted with yard trimmings, paper, or wood wastes. Compost Sci. Util. 6(1):6–18.[Medline]
• Sullivan, D.M., T.J. Nartea, A.I. Bary, C.G. Cogger, and E.A. Myhre. 2004. Nitrogen availability and decomposition of urban yard trimmings in soil. Soil Sci. 169:697–707.[CrossRef]
• Sweeney, R.A. 1989. Generic combustion method for determination of crude protein in feeds: Collaborative study. J. Assoc. Off. Anal. Chem. 72:770–774.[Medline]
• Trinsoutrot, I., R. Recous, B. Bentz, M. Lineres, D. Cheneby, and B. Nicolardot. 2000. Biochemical quality of crop residues and carbon and nitrogen mineralization kinetics under nonlimiting nitrogen conditions. Soil Sci. Soc. Am. J. 64:918–926.[Abstract/Free Full Text]
• Tyson, S.C., and M.L. Cabrera. 1993. Nitrogen mineralization in soils amended with composted and uncomposted poultry litter. Commun. Soil Sci. Plant Anal. 24:2361–2374.
• USDA. 2002. The National Organic Program Standards [Online]. USDA, Washington, DC. Available at http://www.ams.usda.gov/nop/NOP/standards.html (accessed 2 Sept. 2004; verified 26 July 2006).
• Van Kessel, J.S., and J.B. Reeves, III. 2002. Nitrogen mineralization potential of dairy manures and its relationship to composition. Biol. Fertil. Soils 36:118–123.
• Van Kessel, J.S., J.B. Reeves, III, and J.J. Meisinger. 2000. Nitrogen and carbon mineralization of potential manure components. J. Environ. Qual. 29:1669–1677.[Abstract/Free Full Text]
• VanLauwe, B., J. Diels, N. Sanginga, and R. Merckx. 1997. Residue quality and decomposition: An unsteady relationship? p. 157–166. In G. Cadisch and K.E. Giller (ed.) Driven by nature: Plant litter quality and decomposition. CAB International, Wallingford, UK.
• Vigil, M.F., and D.E. Kissel. 1991. Equations for estimating the amount of nitrogen mineralized from crop residues. Soil Sci. Soc. Am. J. 55:757–761.[Abstract/Free Full Text]
• Wagner, M.G., M.L. Cabrera, and N.N. Ranells. 1998. Nitrogen and carbon cycling in relation to cover crop residue quality. Soil Water Conserv. 53:214–218.

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