Nutrient Cycling in Agroecosystems 62: 185–194, 2002. 185 2002 Kluwer Academic Publishers. Printed in the Netherlands.

Effect of poultry litter and composts on soil nitrogen and phosphorusavailability and corn production

1, 2 3* ´Leslie Cooperband , German Bollero and Frank Coale1Department of Soil Science, University of Wisconsin, 1525 Observatory Drive, Madison, WI 53706, USA;2Crop Sciences Department, University of Illinois, 1102 South Goodwin Ave., Urbana, IL 61801, USA;3Department of Natural Resource Sciences and Landscape Architecture, University of Maryland, College

*Park, MD 20742, USA; Author for correspondence (e-mail: lrcooperband@ facstaff.wisc.edu)

Received 24 October 2000; accepted in revised form 25 May 2001

Key words: Biological stabilization of P, Compost, Corn, Nitrate, Phosphorus, Poultry litter

Abstract

Environmental problems associated with raw manure application might be mitigated by chemically or biologicallyimmobilizing and stabilizing soluble phosphorus (P) forms. Composting poultry litter has been suggested as ameans to stabilize soluble P biologically. The objectives of this study were to assess the nutrient (N, P) value ofdifferent-age poultry litter (PL) composts relative to raw poultry litter and commercial fertilizer and determineeffects of poultry litter and composts on corn (Zea mays) grain yield and nutrient uptake. The research wasconducted for two years on Maryland’s Eastern Shore. Six soil fertility treatments were applied annually to aMatapeake silt loam soil (Typic Hapludult): (1) a check without fertilizer, (2) NH NO fertilizer control (168 kg4 3

21 21 21N ha ), (3) raw poultry litter (8.9 Mg ha ), (4) 15-month old poultry litter compost (68.7 Mg ha ), (5)21 214-month old poultry litter compost (59 Mg ha ) and (6) 1-month old poultry litter compost (64 Mg ha ). We

monitored changes in available soil NO -N and P over the growing season and post harvest. We measured total3

aboveground biomass at tasseling and harvest and corn yield. We determined corn N and P uptake at tasseling.Patterns of available soil NO -N were similar between raw PL- and NH NO fertilizer-amended soils. Little3 4 3

NO -N was released from any of the PL composts in the first year of study. The mature 15-month old compost3

mineralized significant NO -N only after the second year of application. In contrast, available soil P was highest in3

plots amended with 15-month old compost, followed by raw PL-amended plots. Immature composts immobilizedsoil P in the first year of study. Corn biomass and yields were 30% higher in fertilizer and raw PL amended plotscompared to yields in compost-amended treatments. Yields in compost-amended plots were greater than those inthe no-amendment control plots. Corn N and P uptake mirrored patterns of available soil NO -N and P. Corn P3

uptake was highest in plots amended with 15-month old compost and raw PL, even though other compostscontained 1.5–2 times more total P than raw PL. There was a linear relationship between amount of P added andavailable soil P, regardless of source. The similar P availabilities from either raw or composted PL, coupled withlimited crop P uptake at high soil P concentrations, suggest that raw and composted PL should be applied to soilsbased on crop P requirements to avoid build-up of available soil P.

Introduction tively high concentrations of total and soluble P (mostbroiler litters contain 2–3% total P of which 60–80%

Nutrient management recommendations for land ap- is in soluble form) and low N:P ratios, build-up of soilplication of poultry wastes in the U.S. mid-Atlantic P in manure-amended soils is now recognized as aregion are based on crop N supply; and, as such, do significant contributor to non-point pollution (Robin-not account for the quantity of P applied. Because son and Sharpley 1995). Environmental problemsfresh poultry litter (manure1 bedding) contains rela- associated with raw manure application might be

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mitigated by chemically or biologically immobilizing four replications. Soil fertility treatments were: (1) aand stabilizing soluble P forms. check without fertilizer, (2) NH NO fertilizer con-4 3

Composting poultry litter may be a means to stabi- trol, (3) raw poultry litter, (4) 15-month old poultrylize soluble P biologically, thereby decreasing its litter compost, (5) 4-month old poultry litter compostsusceptibility to runoff loss from agricultural fields and (6) 1-month old poultry litter compost. Plot

2(Vervoort et al. 1998). However, the P contributions dimensions were 4.6 m3 12.2 m (56 m ). Compostsfrom composted manure to either plant uptake or were obtained from New Earth Services, Inc., Hur-environmental losses are not well understood and are lock, MD and raw poultry litter was collected from athought to be similar to fresh manure (Gagnon and broiler house close to the experiment station. AllSimard 1999). Few studies have been conducted composts contained the same feedstocks (raw litter);which compare the nutrient (N, P) availability associ- the only difference was duration of aerobic windrowated with raw and composted poultry litters in crop composting. We collected composite samples fromfields and subsequent crop N and P uptake. The each compost and from raw poultry litter (PL) twoobjectives of this study were to (1) assess the fertility weeks prior to field application to determine moisture,value of different-age poultry litter composts relative nutrients and carbon contents (Table 2). Applicationto raw poultry litter and commercial fertilizer; (2) rates (Table 3) were based on each material’s ability

21evaluate the soil nitrogen and phosphorus availability to supply 168 kg N ha over the growing season.associated with raw poultry litter and composts ap- These rates were calculated assuming that 50% of theplied to grain corn and (3) determine effects of total organic N plus NH -N would be available for4

poultry litter and composts on corn grain yield and crop uptake in a single growing season. This is anutrient uptake. similar approach to that described in Sims (1987)

where potentially available N is calculated as 80% ofmineral N forms (NH -N and NO -N) plus 60% of4 3

Materials and methods organic N. Using raw PL as an example:21 21• [(29.32 kg total N Mg 25.57 kg NH -N Mg )4

21Site description and experimental design * 0.50]1 5.57 kg NH -N Mg 5 17.45 kg avail-421able N Mg amendment

21The field trial was established at the University of • 168 kg N ha needed21 21Maryland’s Wye Research and Education Center, • Therefore 168 kg ha /17.45 kg Mg 5 9.6 Mg

21located on the Delmarva Peninsula (Queenstown, ha application rate.MD, USA). The soil was a Maryland coastal plainMatapeake silt loam (fine, silty, mixed, semiactive Previous studies of N mineralization from com-mesic Typic Hapludult; U.S. Soil Taxonomy classifi- posts suggested that significantly less than 50% of thecation).We collected four composite soil samples (one total N became available (i.e. mineralized) over aper block) consisting of 20 cores each, 0–10 cm single growing season; 5–15% was the usual esti-depth, for baseline characterization prior to amending mated range (Chae and Tabatabai 1986; Gagnon et al.plots (Table 1). Baseline characterization showed 1998; Mamo et al. 1998a), although Hadas et al.slightly acidic, low organic matter and high available (1996) found 26% of total compost N mineralizedP conditions among all plots. under controlled incubation conditions. Nonetheless,

The trial included six soil fertility treatments ar- we chose 50% of total N for composts and raw PL toranged in a randomized complete block design with avoid excessively high application rates of composts

Table 1. Baseline soil characteristics in top 10 cm, prior to amending soils in April 1996. Meanvalues represent averages of four composite samples (one per block).

Property Mean value (n5 4)

Particle size analysis (hydrometer method) 36% sand, 46% silt, 18% claypH (2:1 deionized water:soil extraction) 6.0

21Estimated cation exchange capacity (sum of cations) 6 cmol kg soilc21Organic matter content (Loss on ignition) 22 mg kg21Melich-3 P 214 mg kg

NO -N (0.01 M K SO extractable) 2.11 (6 0.16 std) mg kg21; n5 243 2 4

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Table 2. Nitrogen, carbon and phosphorus contents of poultry litter and composts applied in 1996 and 1997.

Amendment N% NH -N% C% P% Ratio Moisture solids4

C:N N:P C:P %

1996*15-Month 0.79 0.02 14.8 0.90 18.7 0.9 16.4 38.6 61.4

4-Month 1.49 0.17 18.3 1.17 12.2 1.3 15.7 41.0 59.01-Month 1.17 0.29 18.3 0.68 15.6 1.7 26.9 45.9 54.1Raw PL 5.68 1.50 35.9 2.71 6.3 2.1 13.3 36.7 63.3199715-Month 0.84 0.06 8.0 1.06 9.5 0.8 7.5 49.8 50.24-Month 0.64 0.01 8.4 0.67 13.1 1.0 12.4 44.0 56.01-Month 0.56 0.03 6.8 0.44 12.1 1.3 15.6 38.7 61.3Raw PL 4.49 0.86 27.8 2.30 6.2 2.0 12.1 46.8 53.2*Indicates age of PL compost. Percent nutrients expressed on a dry-weight basis.

that might exacerbate high soil P levels (Eghball and determine gravimetric moisture content, and the re-Power 1999; Gagnon and Simard 1999). mainder was air-dried, ground and sieved (2 mm)

We hand applied all amendments including com- prior to nutrient analyses. Dried soil (5 g) was shakenposts and raw PL in mid-April of 1996. After weigh- with 20 mL of 0.01 M K SO at low speed for 1 h.2 4

ing out the total amount needed per plot, we spread After shaking, sample extracts were centrifuged atthis amount evenly over each plot using buckets and 3000 rpm for 15–20 min, and then filtered throughrakes. In 1997, we applied amendments using a Reel 0.45 mm nylon filters and frozen prior to nutrient

Auggie Feed mixer with a scale. The total amount concentration determinations. We used a low ionicper plot was weighed into the mixer then applied strength salt solution (K SO ) to extract only the2 4

down the center of each plot as a thin windrow. It was most readily available forms of N and P. Nitrate-Nthen spread evenly over each plot using a rake. In both and ortho-P were determined colorimetrically (NO -3

years, we incorporated raw PL and composts within N using the salicylic acid method; Mulvaney (1996);24 hours into the top 10-cm of soil using a disk and and ortho-P using the molybdate-ascorbic acid meth-chisel plow. Non-amended plots were disked and od; Kuo (1996)).plowed at the same time. Potassium fertilizer wasapplied to the entire field prior to corn planting (using Corn biomass and nutrient content measurements

21a single application rate of 74 kg K ha ). NoWe measured total aboveground biomass at tasselingfertilizer P was applied to N fertilized or control plots(July 1996 and 1997). We measured biomass andsince baseline soil sampling had indicated high

21 nutrient uptake only in a subset of the six treatments:Melich-3 P concentrations (214 mg kg in 0–10 cm21 raw PL, 15-month old PL compost, N-fertilized anddepth; 155 mg kg in 10–20 cm depth). We broad-

21 no-fertilizer control plots. We randomly selected fourcast 168 kg ha of N as NH NO granular fertilizer4 3

plants per plot, two representative of ‘average’ growthat corn planting. Corn (Zea mays), Pioneer Brandand two representative of ‘extreme’ (small and large)Hybrid 3394, was planted in 76-cm rows at a planting

21 plants. We weighed each plant whole to determinedensity of 70,000 plants ha in mid-May of eachindividual plant fresh weights and then took a compo-year. The Wye Research Center farm crew managedsite sample per plot for dry weight determinations.weeds and pests using best management practices.The composite sample was dried at 60 8C, weighedand then ground to pass through a 1 mm screen

Soil measurements (Wiley Mill). Total N and P were determined onground samples by acid digestion and ICP-OES.

We monitored changes in available soil N (NO -N)3

and P over the growing season and post harvest. We Corn yieldcollected one composite soil sample per plot (20 coresper composite; 0–10 cm depth) monthly from April Corn grain was harvested in September of 1996 and1996 to October 1997. A subsample was used to 1997 using a self-propelled MF8 8xp two-row com-

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bine. We collected yield data from the two inner rows peak transpiration rate. There was less water availableof each plot. Yield was corrected to 15.5% grain in the fertilized (no organic amendment) treatment

21moisture, and calculated as kg ha . relative to compost-amended and raw PL treatments(in 1996: 13.4% w/w for fertilized plots vs. 16.8%

Statistical analyses w/w for composts and raw PL treatments; in 1997:11.3% vs. 13.7%; P, 0.05). This difference most

We evaluated changes in soil nutrients and moisture in likely reflects the vigorous crop growth and concur-the same experimental units over a two-year period. rent drawdown of soil water in fertilized plots com-As such, the effect of years was reflected in each pared to plots amended with PL composts. It issampling time. The months during this two-year unlikely that the higher moisture content in PL andperiod were enumerated starting with ‘4’ (April 1996) compost-amended plots resulted from an increase inand ending with ‘22’ (October 1997). Given this soil water holding capacity, since the non-fertilizedsampling approach, we used repeated measures analy- control also had higher soil moisture content (Figuresis on soil NO -N and P data and on soil moisture data 1).3

using the Mixed procedure of SAS (SAS 2000). Patterns of available soil NO -N in fertilized and3

Treatment effects on corn biomass, nutrient uptake PL amended plots were typical for soils receivingand yield were evaluated using the Mixed procedure soluble fertilizer (as NH NO ) and raw PL (Figure 2).4 3

in SAS (SAS 2000). For these effects, years were Raw PL and fertilizer treatment soil NO -N pulses3

considered random. Least significant differences tracked each other in early May-June for both years of(LSD) were calculated using the appropriate standard study. However, during those peaks in available NO -3

errors at an alpha level of 0.05. N, there was 1.5–2 more NO -N available from3

fertilizer compared to raw PL. Sims (1987) foundsimilar patterns and magnitudes of available N re-

Results and discussion leased from raw PL and NH NO fertilizer during the4 3

growing season.Changes in soil moisture and available nutrients Nitrate released from all composts was 3–4 times

lower than that released from raw PL or fertilizerAs expected, there were seasonal fluctuations in soil during peak crop demand months (May-June). More-moisture content corresponding to rain events and over, there were no significant differences in availablevegetative demand for water (Figure 1). Overall, there soil NO -N among composts and the no-fertilizer3

was little significant effect of amendments on soil control. However, in the second year of amendmentmoisture. The exceptions occurred in early August application (May, 1997), there was a statistically1996 and mid-July 1997 when crops were at their significant NO -N pulse released from the 15-month3

old compost compared to the other two composts.These results exemplify frequently described phe-

nomena of N immobilization and low mineralizationrates for both immature and stable composts. The lowN availability from composts relative to raw litter inthe first year of study could be partly explained bydifferences in C:N ratios (Table 2). The C:N ratios ofcomposts were two to three times higher than the C:Nratio of raw PL (12–19 vs. 6). However, in the secondyear of study, the C:N ratios of composts ranged from9.5–13 compared to raw litter C:N of 6; none of theC:N ratios exceeded 20:1, considered to be the ‘thres-hold’ C:N above which N immobilization is likely tooccur (Richards 1987).

It is also possible that initial NH -N contents4

among composts and raw PL contributed to differ-ences in available soil NO -N, particularly early inFigure 1. Amendment effects on gravimetric soil moisture content 3

over two years of corn production (April 1996-October 1997). the growing season. This was likely true in the second

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Figure 2. Amendment effects on soil nitrate over two years of corn production (April 1996-October 1997). Small graph insert shows effects ofcomposts relative to no-amendment control only.

year of study where raw PL had 19% of its total N as tained 25 and 11% of total N as NH -N, respectively.4

NH -N and the composts contained only 1.5–7% of Despite their relatively high NH -N contents, the two4 4

their total N as NH -N. However, in the first year of immature composts immobilized N in the soil during4

study, raw PL contained 26% of total N as NH -N, the first growing season. As such, other factors like4

while 1-month old and 4-month old composts con- biological stability were more likely to influence

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patterns of nitrate availability than initial total and compost, suggesting that cumulative applicationmineral N contents of organic amendments. rather than P source determined available soil P. In

Mamo et al. (1998b, 1999) found prolonged N addition, Vervoort et al. (1998), comparing raw PLimmobilization from a high C:N municipal solid with composted PL effects on runoff P, found that thewaste (MSW) compost and less than 8% of the total N highest runoff P came from the raw PL1 compostmineralized from a low C:N MSW compost. They treatment and was directly related to the total amountsuggested that the amount of mineralizable N de- of P added to the soil.pended more on compost quality (stability; composi-tion of original feedstocks) than the total amount of C Corn growth, yield and nutrient uptakeapplied. Hartz and Giannini (1998) reported that only2–3% of the total N applied in yard waste compost Corn biomass produced at tasseling and just prior tomineralized over a 16-week incubation with fescue. harvest showed similar trends among treatmentsGagnon et al. (1998) determined that the contribution (Table 4). Biomass produced in plots treated withof N from the organic N pool of dairy manure either raw PL or fertilizer was similar and greater thancomposts was very small, 7–15% or zero (at lower biomass produced in compost (15-month only)application rates), especially in the first year of appli- amended plots. Compost produced significantly great-cation. These findings along with those of our study er biomass than the no-amendment, no-fertilizer con-confirm the limited N-fertilizer value of composted trol.manures compared to fresh manures, particularly in The trends in biomass translated to 30% greatersoils with a limited history of receiving organic corn yield in plots treated with raw PL or fertilizeramendments. compared to those amended with any of the composts

The fluctuations in available soil P contrasted (Table 5). Sims (1987) also found no differences instrongly with those of available NO -N (Figure 3). corn grain yield from raw PL or ammonium nitrate3

Over the two years of study, the 15-month old com- fertilizer treated fields. All amended plots (includingpost applications resulted in the highest available soil compost-amended) produced higher yields than theP concentrations; approximately three times more P no-amendment, no-fertilizer control. In contrast,than all other treatments. The 1-month and 4-month Mamo et al. (1998b) found neutral to negative effectsold composts did not result in elevated soil P levels in of compost additions on corn grain yield in the first1996, despite large amounts of total P added (Table year of study. However, in subsequent years, grain3). This suggests some P immobilization when these yield was greater for all compost-amended plotsrelatively immature composts were added to the soil compared to a no-fertilizer control treatment. Biomass(Gagnon and Simard 1999). In the fall of 1996 and yield differences between composted and raw(November), there was a pulse of available P released manures were anticipated based on low N availabilityfrom both the 4-month old compost and the fertilizer from composts during the growing season. However,plots. Following the second year of amendment appli- other studies have achieved comparable yields be-cation, there was a near doubling of available soil P tween raw and composted manure amended soils,from all composts and the raw PL. particularly when supplemented with commercial fer-

These findings corroborate studies showing poultry tilizer (Warman 1995; Eghball and Power 1999).litter’s ability to elevate soil P compared with other Total corn N uptake patterns mirrored treatmentorganic by-products (Hue and Sobieszczyk 1999). effects on corn biomass and yield (Table 6). ThereGagnon and Simard (1999) compared the effects of was no significant difference in N uptake between rawseveral manure- and industrial-derived compost PL and fertilizer-treated plots, despite higher soilamendments on available soil P (Melich-3 P). They NO -N concentrations in fertilizer-treated plots com-3

found that Melich-3 P varied from 11% of total P pared to raw PL-treated plots. Corn plants in theseadded (industrial compost) to 38% in PL compost and two treatments took up approximately two times morewas linearly related to the amount of total P added N than plants in plots amended with ‘immature’ (1-from the composts. We also demonstrated a linear month and 4-month old composts) and 1.5 times morerelationship between P added and available soil P N than plants in ‘mature’ (15-month old) compostdespite P source (Figure 4). Eghball and Power plots. There was slightly more corn N uptake (and(1999) also found a strong linear correlation between statistically significant) in plots receiving 15-monthsoil test P and the total P applied from manure or old compost compared to N uptake in the other two

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Figure 3. Amendment effects on available soil P over two years of corn production ((April 1996-October 1997).

compost-amended plots. Tissue N concentration was were borderline sufficient for corn (approximatelyhighest in fertilized and raw PL treatments (Table 6). 2%).Although N uptake was lowest in immature compost Gagnon et al. (1998) determined that plant Ntreatments, tissue N concentrations were slightly uptake was positively correlated (curvilinear relation-higher than those in mature compost and no fertilizer ship) with available soil N measured 30 days aftertreatments. This likely reflects a reverse ‘dilution amendment application. In comparing available soileffect’; lower biomass resulting in higher tissue nu- NO -N pulses with corn N uptake in this study,3

trient concentrations. In all treatments except com- available soil NO -N 30–60 days after amendment3

mercial N fertilizer, N concentrations at tasseling application was significantly correlated with corn N

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1Table 3. Application rates and total amounts of N, P and C for each amendment .

Amendment type Application rate Total N added Total P added Total C added21 21 21 21Mg ha kg N ha kg P ha kg C ha

1996* a15-Month 71.7 351.2 401.0 6559

4-Month 34.7 326.4 254.9 39891-Month 36.5 277.5 161.2 4330Raw PL 8.1 280.6 173.9 1774199715-Month 65.6 367.5 464.6 35054-Month 83.3 341.6 360.5 44661-Month 92.3 323.0 250.1 3904Raw PL 9.6 282.2 144.4 1749aIndicates age of PL compost.1Application rates and nutrients applied expressed on ‘as-is’ field moist basis.

reflective of patterns seen in soil P (Table 7). Likeavailable soil N, soil P was correlated with plant Puptake; the relationship was statistically significantbut not very linear (r5 0.46; p, 0.0001). There wasapproximately 20% less P taken up in corn grown infertilizer plots (NH NO fertilized, no soluble P4 3

added) compared to P taken up from plots receivingeither raw PL or 15-month old compost. Corn Puptake in plots receiving either of the immaturecomposts or no amendments (control) was signifi-cantly less than P uptake in plots receiving either theraw PL or the mature compost. Overall, tissue Pconcentrations among treatments fell within suf-ficiency range for corn (0.2–0.4%; Table 7;Davidescu and Davidescu (1982)).Figure 4. Relationship between total P added from either raw

When corn P uptake was plotted against total Ppoultry litter (PL) or PL composts and yearly average available soilP (1996 and 1997). Available soil P averages in fertilized orno-fertilized control plots are included, even though no P was Table 5. Corn yield averaged over 1996 and 1997.added in those treatments.

21Treatment Yield (kg ha )

15-Month old compost 5578 buptake (r5 0.55; p, 0.0001). While Warman (1995) 4-Month old compost 5053 bcsaw a positive linear relationship between plant N 1-Month old compost 5367 b

Raw PL 7183 auptake and N added in dairy manure compost at rates21 Fertilizer 7591 aup to 180 t ha , we did not see significant N uptake

No-amendment control 4063 cfrom PL compost until the second year of study.

LSD for yield (p, 0.01)5 1035.Treatment effects on total corn P uptake also were

Table 6. Plant nitrogen (total N) uptake (and tissue N concentration21Table 4. Corn above-ground biomass (kg ha ) at tasseling and just %) at tasseling.

prior to harvest. 21Treatment N uptake (kg ha )Treatment Biomass at tasseling Biomass at harvest

15-Month old compost 79 b (1.48%)15-Month old compost 37,114 b 206,738 b 4-Month old compost 59 bc (1.50%)Raw PL 47,866 a 244,391 a 1-Month old compost 56 bc (1.63%)Fertilizer (N) 44,926 a 253,715 a Raw PL 120 a (1.74%)No amendment control 24,794 c 160,356 c Fertilizer 120 a (1.93%)

No-amendment control 52 c (1.46%)LSD (p, 0.05) at tasseling5 7630, LSD (p, 0.05) at harvest535,420. LSD (p, 0.01)5 23.1.

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Table 7. Plant phosphorus (total P) uptake (and tissue P con- limited crop P uptake at high soil P concentrations,centration %) at tasseling. suggest that raw and composted PL should be applied

21Treatment P uptake (kg ha ) to soils based on crop P requirements to avoid buildup of available soil P.15-Month old compost 23 a (0.43%)

4-Month old compost 15 bc (0.33%)1-Month old compost 14 bc (0.36%)Raw PL 21 a (0.32%) ConclusionsFertilizer 17 b (0.27%)No-amendment control 14 bc (0.40%)

Available soil NO -N was comparable between raw3LSD (p, 0.01)5 5.0PL- and NH NO fertilizer-amended soils. However,4 3

little NO -N was released from any of the PL com-3added (from composts or raw PL) the relationship was posts in the first year of study. The mature 15-monthnot linear (Figure 5). Even though total P added from old compost mineralized significant NO -N only after3immature composts was 1.5–2 times more than that the second year of application. In contrast, availableadded from raw PL, there was approximately 33% soil P was highest in plots amended with 15-monthmore P taken up from raw PL. This confirms specula- old compost, followed by raw PL-amended plots.tions that the immature composts immobilized avail- Immature composts immobilized soil P in the firstable soil P. year of study.

In addition, there was no difference in plant P Corn biomass and yields were highest in fertilizeruptake between raw PL and mature compost despite a and raw PL-amended plots. Yields in compost-3.5-fold difference in the total P added. When we amended plots were only greater than those in thecalculated the percent of total P added that was taken no-amendment control plots. Corn N and P uptakeup by corn, it was 4.5 – 7% for PL composts and 15% mirrored patterns of available soil N and P. Corn Pfor Raw PL. This suggests that the baseline status of uptake was highest in plots amended with 15-monthsoil P was sufficient for corn growth and that adding old compost and raw PL, even though other compostsmore P to the soil would not lead to greater corn P contained 1.5–2 times more total P. In general, avail-uptake. able soil P was linearly related to the amount of P

Few studies have evaluated crop P uptake from added, regardless of P source. If farmers continue tocomposted versus raw manure composts. Lucero et al. apply raw PL or PL composts to soils based on their(1998) found a curvilinear relationship between pas- ability to supply crop N, they will exacerbate en-ture P uptake and soil test P from soils amended with vironmental problems associated with high availableraw PL only. Their study and our findings confirm P levels.that corn and other grasses do not take up excess soilP as luxury consumption. The similar P availabilitiesfrom either raw or composted PL, coupled with Acknowledgements

This research was supported by funds from the Uni-versity of Maryland, College of Agriculture and Natu-ral Resources and from the W.K. Kellogg ‘FutureHarvest’ Initiative. We thank Theresa Almario, Uni-versity of Maryland, Wye Research and EducationCenter, for her assistance with field sample collection,sample processing and analyses. We also thank theWye Research and Education Center’s farm crew forhelp in amendment application, tillage, planting,weed/pest management and harvesting.

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