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responses but often interacts with weather conditions shall County, IA ... the previous 8 yr. Annual and long-term weather data were collected from an automated weather station located 1 km ...... Jackson, L.L., D.R. Keeney, and E.M. Gilbert. 2000. ... 3:66–71. Wiese, A.F., J.M. Sweeten, B.W. Bean, C.D. Salisbury, and E.W..

MANURE MANAGEMENT Corn Response to Composting and Time of Application of Solid Swine Manure Terrance D. Loecke, Matt Liebman,* Cynthia A. Cambardella, and Tom L. Richard ABSTRACT

social impacts of doing so have some producers and scientists searching for alternative forms of management in which manure is handled as a solid (Honeyman, 1996). One option involves swine production in deep-bedded hoop structures. In Iowa, nearly one million head of swine are finished per year in these hoop structures (Leopold Cent. for Sustainable Agric., 2001). Swine hoop structures are typically bedded with corn stalks or cereal straw, which absorb urine and feces throughout the fourto six-month production cycle. During this time, some in situ composting occurs although the extent of this unmanaged decomposition varies widely. Swine manure from hoop structures can be spread on fields immediately after animals are removed from the buildings, or it can be piled for additional composting (Tiquia et al., 2000). Composted manure has a number of potential advantages over fresh manure, including reductions in viable weed seed content (Wiese et al., 1998; Eghball and Lesoing, 2000), improvements in handling characteristics (by reducing manure volume and associated transportation costs), and a reduction in particle size leading to increased uniformity of field application (Rynk, 1992). Compost-amended soils can increase crop growth beyond levels explainable by nutrient effects (Valdrighi et al., 1996), provide protection from plant pathogens (Hoitink and Kuter, 1986), and suppress weed seedling emergence (Menalled et al., 2002). Phytotoxic substances contained in fresh solid swine manure, such as high concentrations of NH4⫹–N, decrease with time of composting (Tiquia and Tam, 1998) and time following soil application. Disadvantages of composting are potentially large losses of C and N and labor and capital costs associated with extra manure handling and space requirements for the compost piles. Losses of N measured during composting of animal manure have ranged from 20 to 70% (Martins and Dewes, 1992; Rao Bhamidimarri and Pandey, 1996; Eghball et al., 1997; Tiquia et al., 2002). Garrison et al. (2001) estimated that 41% of total N contained in fresh swine hoop manure was lost during two months of intensively managed composting. Synchrony of plant-available soil nutrients and crop nutrient demand is essential for optimum crop performance and environmental protection (Magdoff, 1995). If plant-available N (NO3⫺ and NH4⫹) is not supplied in synchrony with crop demand, then substantial N losses can occur before or after periods of crop demand. The quantity of plant-available N is dynamic and reflects the balance between N mineralization, N immobilization, and removal of inorganic or organic N from the soil rooting zone (e.g., via leaching, volatilization, denitrification, soil erosion, and plant uptake). Soil physical conditions,

Swine production in hoop structures is a relatively new husbandry system in which a mixture of manure and bedding accumulates. This manure/bedding pack can be applied to crop fields directly from a hoop structure or piled for composting. During 2000 and 2001, field experiments were conducted near Boone, IA, to determine the effects of form of solid swine manure (fresh or composted) and time of manure application (fall or spring) on corn (Zea mays L.) nutrient status and yield. Fresh and composted manure were applied at 340 kg total N ha⫺1. Urea N fertilizer treatments of 0, 60, 120, and 180 kg N ha⫺1 were used to determine N fertilizer equivalency values for the manure. In 2000, but not in 2001, fresh manure decreased corn emergence by 9.5% compared with the unamended, nonfertilized control treatment. No corn yield differences due to the form or the time of manure application were detected in 2000, but all treatments receiving manure produced more corn grain than the unamended control. In 2001, fall application of manure increased corn grain yield more than spring application, and composted manure increased yield more than fresh manure, with spring-applied fresh manure providing no yield response beyond the unamended control. Mean N supply efficiency, defined as the N fertilizer equivalency value as a percentage of the total N applied, was greatest for fall-applied composted manure (34.7%), intermediate for fall-applied fresh manure (24.3%) and spring-applied composted manure (25.0%), and least for spring-applied fresh manure (10.9%).


ver one billion metric tons of N are excreted in swine (Sus scrofa L.) manure in the United States annually (NRCS, 2000). Swine manure applied to crop fields can be an important source of plant nutrients and organic matter, which can improve soil quality (Khaleel et al., 1981). Nevertheless, current practices for management and utilization of swine manure can potentially contribute to degradation of water and air quality (Sharpley et al., 1998; Zebarth et al., 1999). Better management options are needed. Most swine manure in the USA is handled and stored as a liquid (NRCS, 2000), but the environmental and T.D. Loecke, Dep. of Crop and Soil Sci., Michigan State Univ., 539 Plant and Soil Sciences Bldg., East Lansing, MI 48824-1325; M. Liebman, Dep. of Agron., 3405 Agronomy Hall, Iowa State Univ., Ames, IA 50011-1010; C.A. Cambardella, USDA-ARS, 310 Natl. Soil Tilth Lab., Ames, IA 50011-3120; and T.L. Richard, Dep. of Agric. and Biosyst. Eng., 3222 Natl. Swine Res. and Inf. Cent., Iowa State Univ., Ames, IA 50011-3080. Partial funding for this work was provided by the Leopold Center for Sustainable Agriculture (Project 2000-42), the Iowa Department of Natural Resources (Project 00-G550-01CG), and Chamness Technology (Project 1221). We thank J. Ohmacht, D. Sundberg, and R. Vandepol for technical assistance in the field and laboratory. Received 5 Dec. 2002. *Corresponding author ([email protected] Published in Agron. J. 96:214–223 (2004).  American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA




including temperature, water status, and aeration, and the C/N ratio and C constituents (especially lignin quantities) of organic materials are the primary factors affecting mineralization rates (Jenny, 1980; Swift et al., 1979). In previous investigations, corn yield responses to composted and fresh manure have been similar when these amendments were applied at the same time (Reider et al., 2000; Eghball and Power, 1999; Brinton, 1985; Ma et al., 1999; Xie and MacKenzie, 1986). However, N use efficiencies observed in these studies indicate that plant-available N from manure-derived compost is typically equal to or less than that from fresh manure. Timing of amendment application can influence crop responses but often interacts with weather conditions (Warman, 1995; Talarczyk et al., 1996; Sanchez et al., 1997). Currently, no guidelines are available for when and in what form (composted or fresh) swine hoop manure should be field-applied to best utilize it as a nutrient resource and to minimize potential negative environmental impacts. The objective of this study was to determine first-year corn response to season of application (fall vs. spring) and form of swine hoop manure (composted or fresh).

Table 1. Characteristics of the surface 20 cm of soil in experiment fields before treatment applications.


Plant, Soil, and Amendment Sampling and Analysis

Field Site and Experimental Design

A 4-L composite sample of each amendment (fresh or composted manure) was collected immediately before materials were applied to plots, generating one sample per plot and four replicates per treatment. Samples were stored at ⫺20⬚C in plastic freezer bags, then thawed, homogenized, separated for various analyses (total P, K, NH4⫹–N, NO3⫺–N, moisture, ash content, pH, and electrical conductivity), and then refrozen until individual parameters were analyzed. Amendment total C and N were determined after acidification with 0.5 M HCl (1:2 sample/solution ratio), air drying, grinding, and dry combustion in a Carlo-Erba NA1500 NCS elemental analyzer (Haake Buchler Instruments, Paterson, NJ) as described by Cambardella et al. (2003). Total P and K were determined on dried ground samples by USEPA method 3051 at a commercial laboratory (Midwest Laboratory, Omaha, NE) following a protocol given by Dancer et al. (1998). Ammonium N and nitrate N were determined using 2 M KCl extracts (1:80 amendment/ solution ratio) and Lachat flow analysis (Lachat Instruments, Milwaukee, WI) (Keeney and Nelson, 1982). Amendment moisture content was determined by drying at 70⬚C for 48 h, ash content was determined by ignition at 550⬚C, and pH and electrical conductivity were determined using a 1:5 amendment/water slurry. To monitor plant and soil N status throughout the growing season, late-spring soil NO3⫺–N concentration, ear leaf N and chlorophyll contents, and fall stalk NO3⫺–N concentration were measured. All plant and soil parameters were measured from the center three rows of each plot. Soil NO3⫺–N samples, consisting of a composite of ten 2-cm-diam. soil cores from the surface 30 cm, were collected from each plot on 3 June 2000 and 4 June 2001 and were processed according to procedures described by Blackmer et al. (1989). Thirty leaf chlorophyll meter readings were taken in each plot using a Minolta SPAD-502 chlorophyll meter (Minolta, Ramsey, NJ) as others have done (Piekielek and Fox, 1992). Readings were taken 1.5 cm from the leaf edge of the center (lengthwise) of the topmost fully expanded leaf or the same location on the ear leaf, when developed.

Field plot research was conducted at the Iowa State University Agronomy and Agricultural Engineering Research Farm near Boone, IA (42⬚1⬘ N, 93⬚45⬘ W), during 2000 and 2001 on Clarion loam (fine-loamy, mixed, superactive, mesic Typic Hapludolls) and Nicollet loam (fine-loamy, mixed, superactive, mesic Aquic Hapludolls) soils. Soil samples taken from the surface 20 cm before fall application of amendments indicated adequate P and K fertility levels in both years (Table 1). The field used for the 2000 experiment was cropped with oat (Avena sativa L.) in 1999; the field used for the 2001 experiment was cropped with soybean [Glycine max (L.) Merr.] in 2000. Neither field had received animal manure for at least the previous 8 yr. Annual and long-term weather data were collected from an automated weather station located ⬍1 km from the field sites (Fig. 1). The core of the experiment consisted of a factorial treatment design that crossed season of application (fall or spring) with form of manure (fresh or composted hoop manure). An additional set of treatments (0, 60, 120, and 180 kg N ha⫺1 urea) was applied to plots not receiving manure and was used to estimate N fertilizer equivalency of the manure. Treatments were arranged in a randomized complete block design with four replications. Plot size was 3.8 m (five rows with a 0.76-m row spacing) by 10.7 m in 2000 and 12.2 m in 2001. Manure treatments were applied by hand in the fall (22 Oct. 1999 and 24 Oct. 2000) and spring (25 Apr. 2000 and 25 Apr. 2001) at a rate of 340 kg N ha⫺1 based on moisture and total N content of samples taken 2 wk before application (Table 2). Amendments were incorporated with a disk into the surface 15 cm within 6 h of application. Application rates were chosen based on the assumption that one-third of the total applied N (i.e., 110 kg N ha⫺1) would be available during the first year after application, as was observed by Eghball and Power (1999). This expected quantity of available N is approximately equal to the N harvested in 9.0 Mg of corn grain, the long-term average yield per hectare from the experiment site.

Soil parameter cm⫺3

Bulk density, g Total organic C, Mg ha⫺1 Total organic N, Mg ha⫺1 Nitrate N, kg ha⫺1 Ammonium N, kg ha⫺1 Mehlich-1 P, kg ha⫺1 Mehlich-1 K, kg ha⫺1 pH Electrical conductivity, S m⫺1

14 Oct. 1999

28 Sept. 2000

1.3 43.5 3.8 13.0 4.0 115 381 6.6 0.0155

1.2 46.7 4.1 19.3 1.8 113 270 6.4 0.0178

All of the fresh and composted hoop manure was produced on the Iowa State University Rhodes Research Farm in Marshall County, IA, except for the fresh manure applied in the spring of 2001, which came from a commercial farm in Story County, IA. Urea N was side-dressed in plots that did not receive manure at corn growth stage V6 (Hanway, 1963) (9 June 2000 and 18 June 2001) and was incorporated within 24 h of application using an interrow cultivator. Corn (‘Pioneer 35P12’) was planted at 68 000 seeds ha⫺1 on 4 May 2000 and 74 000 seeds ha⫺1 on 9 May 2001. Weed control was achieved with a preplantincorporated application of metolachlor [2-chloro-N-(2-ethyl-6methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] at 1.5 kg a.i. ha⫺1, interrow cultivation at plant growth stage V6, and hand weeding.



Fig. 1. (a) Monthly average daily temperature and (b) total precipitation for 2000, 2001, and the 50-yr average at a weather station located ⬍1 km from the field sites.

Ten ear leaves were collected in each plot at growth stage R1 (Hanway, 1963) for nutrient analysis. Ear leaf samples were dried at 60⬚C for 4 d, ground to pass a 0.85-mm screen, and analyzed for total Kjeldahl N. Ear leaf P concentrations were determined by nitric acid plus peroxide digestion followed by inductively coupled plasma mass spectrometry (Harris Laboratory, Lincoln, NE). Grain was harvested with a combine from 9.8 and 10.7 m of the center three rows of each plot in 2000 and 2001, respectively. Reported grain yields are adjusted to a moisture content of 155 g kg⫺1. Fifteen stalk samples (20 cm in length) were collected 15 cm above the soil

surface from each plot at grain harvest, dried at 60⬚C for 4 d, ground to pass a 0.85 mm screen, and analyzed for NO3⫺–N (Binford et al., 1992).

Statistical Analysis Analysis of variance (ANOVA) was conducted using the PROC GLM routine of SAS (SAS Inst., 1999) to test for main and interaction effects, with blocks, years, and treatments in the model. Single degree-of-freedom contrasts were used to test specific hypotheses and main and interaction effects. Stalk



Table 2. Composition of organic amendments. Total Time of application 1999








Form Fresh manure Composted manure Fresh manure Composted manure Fresh manure Composted manure Fresh manure Composted manure

H 2O 624 340 631 313 389 317 613 534

Ash 406 624 302 726 284 608 418 595

P g 11.5 11.7 11.0 8.8 11.3 7.4 5.2 6.7






21.7 20.6 24.7 15.4 20.5 12.9 13.0 16.6

323 181 343 144 323 199 316 206

28.6 16.9 30.0 12.8 24.8 17.2 22.3 16.3

11.3 10.7 11.5 11.2 13.0 11.6 14.2 12.7


NHⴙ4 –N




8.8 8.0 8.2 8.1 8.5 7.4 8.3 8.3

S m⫺1 0.46 0.59 0.57 0.55 0.70 0.50 0.23 0.51


3500 500 2770 730 910 360 1560 940

15 820 78 750 18 750 96 140

† Electrical conductivity (EC) and pH were determined using a 5:1 water/amendment slurry. ‡ Moisture content is expressed on a wet weight basis, and all other concentration parameters are expressed on a dry matter basis.

nitrate concentrations were square-root–transformed before statistical analysis to meet the ANOVA assumption of homogeneity of variances. Correlations between soil and plant parameters were made on an experimental unit basis using PROC CORR in SAS. PROC REG of SAS was used to fit quadratic equations to the relationship between grain yields and urea N fertilizer rates.

RESULTS AND DISCUSSION Weather Conditions The period from amendment application in October 1999 until corn planting in May 2000 was warmer and drier than the 50-yr average (Fig. 1a and 1b) whereas the 2000–2001 winter was colder and wetter than the 50-yr average (Fig. 1a and 1b). Mean monthly temperatures during the 2000 and 2001 growing seasons were typical compared with the 50-yr average (Fig. 1a). Both growing seasons had lower-than-normal total precipitation (Fig. 1b), but the precipitation patterns differed between years. The 2000 growing season began with dry soil conditions followed by timely but limited precipitation. In contrast, the 2001 growing season was drier than normal from mid-June until September but began with moist soil conditions in May following the wet winter season (Fig. 1b).

Amendment Composition and Application Carbon/N ratios of the applied amendments ranged from 10.7:1 to 14.2:1 with means of 12.5:1 and 11.6:1 for fresh and composted manures, respectively (Table 2). Materials with C/N ratios of less than 20:1 are generally thought not to immobilize soil N (Mathur et al., 1993) although short-term immobilization with partially composted hoop manure (C/N ratios of 12:1 to 15:1) has been observed (Cambardella et al., 2003). The amendments applied in the spring of 2001 had the highest C/N ratios, perhaps due to the cool and wet conditions of the fall– winter–spring period of 2000–2001, which may have slowed decomposition in the compost windrows. These weather conditions also likely increased the bedding requirement and/or altered the bedding management on the commercial farm from which the fresh manure applied in the spring of 2001 was obtained. The ratio of NH4⫹–N to NO3⫺–N has been used as an indicator of compost maturity (Mathur et al., 1993), with lower ratios indicative of greater decomposition. The

NH4⫹–N to NO3⫺–N ratios observed here suggest that the composted manure generally was more decomposed than the fresh manure; the exception being the manure applied in the spring of 2001, which had a more similar NH4⫹–N/NO3⫺–N ratio than at all other application times (Table 2). Each of the applied amendments contained a substantial quantity of total P (Table 2). Annual applications of livestock manure to fields in corn–soybean rotations at rates sufficient to meet corn N requirements have the potential to accumulate soil P (Jackson et al., 2000) due to higher P application rates than grain P removal rates. In our study, the P application rate ranged from 79 to 242 kg P ha⫺1 (Table 3), with mean P application rates of 121 and 188 kg P ha⫺1 for fresh and composted hoop manure, respectively, and 167 and 142 kg P ha⫺1 for fall- and spring-applied amendments, respectively (Table 3). During 2000–2001, corn and soybean yields in Boone County, IA, averaged 9.7 and 2.7 Mg ha⫺1 (NASS, 2002), respectively, which would have removed an estimated 28 kg P ha⫺1 yr⫺1 for corn and 16 kg P ha⫺1 yr⫺1 for soybean (Voss et al., 1999). The combined P removal rate from one cycle of a corn–soybean rotation therefore would have been 44 kg P ha⫺1. A comparison of the P applied in this study with the estimated P grain removal indicates that one application of either fresh or composted hoop manure per rotation cycle would lead to soil P accumulation. It should be noted, however, that fresh hoop manure had a higher N/P ratio (Table 3), which would slow soil P accumulation compared with composted hoop manure if P removal rates for grain were equal in the two management systems. Table 3. Loading rates of organic amendments. Application rate† Time of application Fall








Form Fresh manure Composted manure Fresh manure Composted manure Fresh manure Composted manure Fresh manure Composted manure

N kg 340 340 340 340 340 340 340 340

P ha⫺1 130 240 120 230 150 140 80 140



Mg ha⫺1 3.66 11.3 3.74 20.7 3.85 11.2 3.76 26.1 4.38 13.6 3.89 19.5 4.77 15.1 4.24 20.6

† Application rates of total N, P, and C contained within each manure. ‡ DM, dry matter.



Table 4. Treatment means, analysis of variance, and correlation to yield for plant population and late-spring soil nitrate concentration during 2000 and 2001. Plant population Time of application None Side-dressed (at V6) Side-dressed (at V6) Side-dressed (at V6) Fall Fall Spring Spring

Form None (control) Urea Urea Urea Fresh manure Composted manure Fresh manure Composted manure Standard error (SE)

Total rate kg N ha⫺1 0 60 120 180 340 340 340 340

Source of variation Treatment contrasts Forms (F) Urea fertilizer linear response Urea fertilizer quadratic response Urea fertilizer cubic response Control vs. all organic amendments Among amendments (fresh vs. composted) Time of application (A) Amendments (fall vs. spring) F⫻A Amendments (fresh vs. composted) ⫻ (fall vs. spring) Correlation to yield (r )


Soil nitrate



65 900 63 300 67 400 65 200 61 000 63 500 58 300 64 000 1 050


⫺1 NO⫺ 3 –N, ␮g g 8.3 3.3 7.8 3.2 8.5 4.6 8.9 3.5 10.7 5.8 15.8 5.3 9.1 5.2 19.6 5.8 1.1 0.5

Plants ha⫺1 72 800 72 700 73 300 72 900 72 800 72 700 72 500 73 800 910 P⬎F ns ns * ** ***

ns ns ns ns ns

ns ns ns *** ***

ns ns ns *** ns





ns ⫺0.20ns

ns ⫺0.11ns

* 0.47*

ns 0.18ns

* Significant at the P ⬍ 0.05 probability level. ** Significant at the P ⬍ 0.01 probability level. *** Significant at the P ⬍ 0.001 probability level.

Corn Emergence In 2000, corn emergence was negatively affected by fresh manure applied in both fall and spring (Table 4). We believe these plant emergence effects were likely caused by a combination of physical and chemical influences of the fresh manure. In the spring of 2000, freshmanure clods were visible on the soil surface despite tillage. Combined with dry soil surface conditions, which required a deeper-(8–10 cm)-than-normal (4–6 cm) planting depth for seed to soil moisture contact, the physical and/or chemical effects of the fresh-manure clods on the soil surface over the plant row prevented consistent emergence. Fall-applied fresh manure tended to reduce plant emergence less than spring-applied fresh manure in 2000 (Table 4). This was probably due to degradation and/or dispersion of any potential phytotoxic substances and physical degradation of the fresh manure clods that occurred during the winter following fall application of manure. Tiquia et al. (1996) found NH4⫹–N concentration (ranging from ⬍500 to 4200 ␮g g⫺1) to be the most important chemical component of solid swine manure in predicting phytotoxic effects on vegetable seedlings. Despite the stand reductions observed in the present study, plant population densities were not correlated with grain yields (Table 4). In 2001, plant emergence was not affected by manure treatments (Table 4). Moist soil conditions throughout the spring of 2001 allowed for adequate reductions of fresh-manure clod size during tillage and thus eliminated the plant emergence problems observed in 2000.

Late-Spring Soil Nitrate Concentration The NO3⫺–N concentration in the surface 30 cm of soil when corn is 20 to 30 cm tall has been used in the

midwest and northeast USA to predict corn yield response to N fertilizer (Blackmer et al., 1989; Magdoff, 1991). Although this method has been calibrated for synthetic N fertilizer sources and to a limited extent for soils amended with liquid swine manure (Hansen, 1999), it has not been calibrated for soils receiving solid livestock manure. In an evaluation of corn yield responses to variations in soil NO3⫺–N concentration, Blackmer et al. (1989) set the maximum soil NO3⫺–N concentration in the surface 30 cm at which to expect a yield response from applications of synthetic N fertilizer at 25 ␮g g⫺1 for unmanured soils in years with normal or belownormal spring precipitation, at 20 to 22 ␮g g⫺1 for unmanured soils in years with wet springs, and at 11 to 15 ␮g g⫺1 for manured soils. In both years of our study, soil NO3⫺–N concentrations were higher in plots receiving manure than in the unamended fertilizer-free control (Table 4). A significant manure form ⫻ application time interaction was detected for soil NO3⫺–N concentrations in 2000 (Table 4), with the highest soil NO3⫺–N concentrations found in plots treated with spring-applied composted manure and the lowest found in plots amended with springapplied fresh manure. The lower soil NO3⫺–N concentrations observed in 2001 compared with 2000 (Table 4) may have reflected the high soil moisture conditions before sampling (Fig. 1b), which could have caused nitrate leaching or denitrification losses.

Ear Leaf Nitrogen and Phosphorus Concentrations and Chlorophyll Meter Readings Chlorophyll meter readings of corn ear leaves at growth stage R1 responded positively to urea application in both years (Table 5). A significant quadratic response to in-



Table 5. Treatment means, analysis of variance, and correlation to grain yield for SPAD chlorophyll meter readings and corn ear leaf N and P concentrations at growth stage R1, and fall stalk nitrate concentrations in 2000 and 2001. SPAD Time of application None Side-dressed (at V6) Side-dressed (at V6) Side-dressed (at V6) Fall Fall Spring Spring

Form None (control) Urea Urea Urea Fresh manure Composted manure Fresh manure Composted manure Standard error (SE)

Rate kg N ha⫺1 0 60 120 180 340 340 340 340

Source of variation Treatment contrasts Forms (F) Urea fertilizer linear response Urea fertilizer quadratic response Urea fertilizer cubic response Control vs. all organic amendments Among amendments (fresh vs. composted) Time of application (A) Amendments (fall vs. spring) F⫻A Amendments (fresh vs. composted) ⫻ (fall vs. spring) Correlation to yield (r )

2000 55.7 60.4 61.2 61.8 58.0 60.1 57.2 60.0 0.53

Ear leaf N 2001 52.6 54.6 56.2 58.0 57.5 58.3 50.7 55.1 0.81

2000 20.5 24.5 26.5 27.0 24.1 24.6 23.1 25.5 0.9

Ear leaf P

2001 25.2 25.1 26.7 27.9 26.2 26.3 23.2 25.5 0.7


g kg⫺1 2.5 2.9 3.1 3.3 3.5 3.0 3.4 3.4 0.1

Fall stalk nitrate

2001 2.0 2.2 2.1 2.2 2.2 2.2 2.1 2.2 0.1

2000 NO⫺ 3 –N, 4.5 (20) 4.5 (20) 26.0 (815) 77.7 (6123) 10.1 (135) 9.6 (119) 5.3 (31) 7.1 (58) 3.2

2001 ␮g g⫺1† 4.9 (38) 4.3 (25) 23.3 (566) 37.9 (1491) 18.3 (402) 6.5 (52) 8.0 (66) 5.0 (36) 2.4

P⬎F *** *** ns *** ***

*** ns ns ** **

*** ‡ ns *** ns

** ns ns ns ‡

*** ns ns *** ns

‡ ns ns * ns

*** *** ns ns ns

*** ** ns ns **









ns 0.70***

* 0.51*

ns 0.44*

‡ 0.55**

‡ 0.25ns

ns 0.35*

ns 0.54**

‡ 0.37*

* Significant at the P ⬍ 0.05 probability level. ** Significant at the P ⬍ 0.01 probability level. *** Significant at the P ⬍ 0.001 probability level. † Analysis of variance conducted on square-root–transformed data. Data in parentheses are means of raw data. ‡ Significant at the P ⬍ 0.1 probability level.

creasing rates of urea fertilizers ( p ⬍ 0.001) was found in 2000, suggesting that N was not limiting in the higher urea application rates (120 and 180 kg N ha⫺1) at this point in the season (Table 5). However, because chlorophyll meters are useful for indicating N deficiencies, but not for determining excessive soil N availability (Schepers et al., 1992), this issue remains unresolved. Eghball and Power (1999) found similar chlorophyll meter reading results when comparing composted and noncomposted beef feedlot manure to unamended controls throughout the growing season. In 2000 of our study, composted manure treatments (fall- and spring-applied) had higher chlorophyll readings than fresh manure (falland spring-applied), and the mean of all manure treatments was greater than the no-amendment control (Table 5). A significant interaction was detected in 2001 between form of manure and timing of application (Table 5). Spring-applied fresh-manure plots in 2001 had the lowest chlorophyll readings among the manure treatments whereas fall-applied fresh and composted manure had the highest readings and the spring-applied composted manure gave an intermediate value (Table 5). Corn ear leaf N concentration at growth stage R1 responded positively to urea application in both years (Table 5) although the intensity of the response was greater in 2000 than in 2001. The mean ear leaf N concentration of all manure treatments was higher than that of the control in 2000, but no difference between manure treatments and the control was detected in 2001 (Table 5). The season of manure application was important for the 2001 corn crop; fall-applied manure generated higher ear leaf N concentrations than did spring-applied manure (Table 5). Both the corn ear leaf N concentrations and chloro-

phyll meter readings at growth stage R1 correlated well with final corn grain yield (Table 5). Eghball and Power (1999) also found a strong correlation (r ⬎ 0.71) between chlorophyll meter readings and grain yield, except in a season of low precipitation. In our study, ear leaf N concentration and chlorophyll readings at R1 were also well correlated with each other (2000: r ⫽ 0.54, P ⬍ 0.01; 2001: r ⫽ 0.64, P ⬍ 0.0001). Corn ear leaf P concentrations increased linearly with increasing rates of urea application in both years (Table 5). This may indicate that plants in the higher urea treatments foraged for soil P more efficiently and/or that the hydrolysis of urea lowered soil pH, thus making more soil P available to plants (Miller and Ohlrogge, 1958; Olson and Dreier, 1956). Differences in ear leaf P between years may have been due to differences in early-season soil moisture although many fertility and environmental factors can interact to influence ear leaf P concentrations (Voss et al., 1970). In 2001, there were minimal differences between treatments with regard to ear leaf P concentration (Table 5).

Corn Grain Yield Corn grain yields increased in both years in response to increasing rates of urea application (Fig. 2; Table 6). The highest yields in response to urea application were similar in both years, but the yield of the control treatment was lower in 2000 than in 2001. This pattern was similar to that observed for the ear leaf N concentration at plant growth stage R1 and may reflect the influence of the previous year’s crop on the quantity and quality of organic matter added to the soil and its N mineralization rate (Green and Blackmer, 1995). At 0 kg N ha⫺1,



Fig. 2. Grain yield from urea N rates side-dressed at plant growth stage V6 and fresh manure and compost treatments from 2000 and 2001. Error bars represent plus/minus one standard error. Grain yields were adjusted to a moisture content of 155 g kg⫺1. Treatment contrasts are presented in Table 6.

the 2000 corn crop, which followed oat, had a lower yield than the 2001 corn crop, which followed soybean (6.7 vs. 8.1 Mg ha⫺1). The mean grain yield from manure treatments was greater than the control in both years (Table 6; Fig. 2). In 2000, no grain yield differences were detected due to the time of application or the form of manure (composted or fresh manure) (Table 6). In contrast, in 2001, grain yields from composted manure treatments were Table 6. Analysis of variance of corn grain yields in 2000 and 2001. Source of variation Treatment contrasts Forms (F) Urea fertilizer linear response Urea fertilizer quadratic response Urea fertilizer cubic response Control vs. all organic amendments Among amendments (fresh vs. composted) Time of Application (A) Amendments (fall vs. spring) F⫻A Amendments (fresh vs. composted) ⫻ (fall vs. spring) ** Significant at the P ⬍ 0.01 probability level. *** Significant at the P ⬍ 0.001 probability level.

P⬎F 2000


*** ns ns *** ns

*** ns ns ** ***





greater than those from fresh-manure treatments (10.3 vs. 8.8 Mg ha⫺1). Additionally, fall-applied manure produced higher yields than did spring-applied manure (10.1 vs. 8.9 Mg ha⫺1) (Table 6). The poor yield response to spring-applied fresh manure was more pronounced in 2001 when early-season soil conditions were moist and cool relative to 2000. In Wisconsin, similar results were found in wet-cool springs if fresh solid dairy manure was applied immediately before corn planting (Talarczyk et al., 1996). Talarczyk et al. (1996) attributed this result to a pattern of manure N mineralization that was slower than normal. Fall application of solid manure in their study and in our study resulted in more consistent yield benefits than did spring applications. This may be due to more timely net N mineralization relative to plant N demand with fall application vs. spring application.

Nitrogen Fertilizer Equivalency and Nitrogen Supply Efficiency A quadratic equation was fit to the yield data of urea N treatments for each year (Fig. 2). Although only the


Table 7. Calculated N fertilizer equivalency values and N supply efficiencies of amendments, based on corn yield response to urea fertilizer side-dressed at corn growth stage V6, in 2000 and 2001. Time of application Fall Fall Spring Spring

N fertilizer equivalency value Form Fresh manure Composted manure Fresh manure Composted manure

N supply efficiency†

2000 2001 Mean 2000 2001 Mean 103 96 79 97

kg N ha⫺1 60 82 137 117 ⫺6 37 71 84

% 30.7 17.9 28.6 40.8 23.5 ⫺1.8 28.9 21.1

24.3 34.7 10.9 25.0

† N supply efficiency defined as the N fertilizer equivalency value expressed as a percentage of the total N applied (340 kg N ha⫺1).

linear trend was statistically significant (Table 6), the quadratic function produced a better fit to the data and thus allowed for a more realistic extrapolation between the yield data of urea N fertilizer and manure treatments (see Blevins et al., 1990). Based on each quadratic urea response curve, N fertilizer equivalency values were calculated for each manure treatment mean (Table 7). Nitrogen supply efficiencies for the different manure treatments were calculated by dividing N fertilizer equivalency values by the total amount of N applied in each manure (Table 7). On average, fall application of manure gave higher N fertilizer equivalency values and higher N supply efficiencies than did spring application, and composted manure provided more consistent N benefits than did fresh manure. At the application rate used in this experiment, spring-applied fresh manure produced inconsistent N benefits. It is not surprising that fall application of manure tended to be more effective in supplying N to corn, given the longer time and greater number of accumulated heat units associated with fall, rather than subsequent spring, application. Nevertheless, monitoring of soil N losses and net N mineralization in response to the timing of manure application would help to clarify whether the observed N fertilizer equivalencies and N supply efficiencies were due to patterns of N transformation and release or other non-N-related factors. More research is needed to address this question.

Fall Stalk Nitrate Concentration Nitrate concentration in the lower portion of a corn stalk (the section between 15 and 35 cm above the soil surface) at plant maturity has been used as an indicator of late-season soil NO3⫺–N concentrations and/or environmental stress (Binford et al., 1992). A stalk NO3⫺–N concentration of ⬎2000 ␮g g⫺1 indicates excessive soil NO3⫺ or stress whereas concentrations ⬍200 ␮g g⫺1 indicate insufficient inorganic soil N for maximum economic grain yield (Binford et al., 1992). In our study, urea application resulted in positive stalk NO3⫺ responses in both years (Table 5). The significant quadratic responses that were observed typically occur as plant-available soil N becomes greater than the plant’s ability to assimilate NO3⫺ into amino acids (Binford et al., 1992). In both years, all manure treatments resulted in stalk NO3⫺–N concentrations ⬍500 ␮g g⫺1, and the mean stalk NO3⫺–N concentration of manure treatments was not different from the control treatment


(Table 5). In 2001, fresh-manure applications resulted in higher stalk NO3⫺–N concentrations than compostedmanure applications, and fall applications gave higher stalk NO3⫺–N concentrations than did spring-applied manure. The relationship of stalk NO3⫺–N concentration to grain yield in 2000 followed closely the relationship described by Binford et al. (1992), but this pattern was not as distinct in 2001 (figure not shown). It is unclear if this was due to limited available soil N or increased NO3⫺ assimilation efficiencies. For example, in 2001, despite having similar yields, the fall-applied compostedmanure treatment resulted in lower stalk NO3⫺–N concentrations than did the 120 and 180 kg N ha⫺1 urea N treatments. This suggests that factors other than N effects may have contributed to the grain yield response to manure.

SUMMARY At the rates used in this study, spring application of fresh hoop manure resulted in problems with corn emergence, lower N use efficiencies, and inconsistent yields. Although treatment effects were not always significant, measurements of soil NO3⫺–N concentrations at plant growth stage V6 and apparent ear leaf chlorophyll and N concentrations at growth stage R1 indicated that springapplied fresh manure supplied less N to the plants before and during flowering than did the other manure treatments. Thus, N deficits may have contributed to lower yields in the spring-applied fresh-manure treatment compared with the other manure treatments. Increasing spring-applied fresh hoop manure application rates to meet crop N demands may be detrimental to plant emergence and may increase soil N immobilization. In 2001, stalk NO3⫺–N concentrations in the manure treatments were low (⬍500 ␮g g⫺1) compared with the stalk NO3⫺–N concentrations of urea N treatments despite similar grain yields (Tables 5 and 6; Fig. 2). A similar pattern was observed in the soil NO3⫺–N concentrations in the late spring of 2001 relative to grain yield where manure treatments resulted in soil NO3⫺–N concentrations below levels predicted to provide for optimal yield despite similar yields to urea N treatments. This finding supports the concept that soils freshly amended with biologically active organic materials have different N dynamics than those amended with mineral N fertilizers (Magdoff, 1991; Cambardella et al., 2003). A more detailed examination of the seasonal N mineralization and crop N uptake patterns in response to fresh or composted hoop manure is needed to determine when and if supplemental N fertilizers may increase N use efficiencies. Although we observed similar mean N supply efficiencies for fall-applied fresh manure (24.3%) and spring-applied compost (25.0%) (Table 7), the potential for large N losses during composting of fresh hoop manure (Garrison et al., 2001) suggests that fall-applied fresh manure may be more desirable than spring-applied compost for whole-farm N conservation. However, nitrate leaching potential could be relatively high with fall-applied fresh manure, which might result in negative impacts on water quality. The multiple pathways through



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