Nitrogen Mineralization and Ammonia Volatilization from Fractionated Poultry LitterM. L. Cabrera,* S. C. Tyson, T. R. Kelley, O. C. Pancorbo, W. C. Merka, and S. A. Thompson

ABSTRACTPassing poultry litter through a 0.83-nun sieve generates a fine

fraction higher in N concentration and cheaper to transport per unitof N than the whole litter. One objective of this work was to determineif the organic N in the fine fraction undergoes faster mineralizationthan that in the whole litter. Whole litter or fine fraction from threepoultry houses was either mixed with samples of Dothan loamy sand(fine-loamy, siliceous, thermic Plinthic Kandiudult) or applied on thesoil surface at a rate of 100 kg N ha~'. The treatments were incubatedat water field capacity and 25 °C, with samples extracted at 3, 7, and14 d. Differences in N mineralization were relatively small betweenmaterials; by Day 14, the organic N had undergone a slightly highermineralization in the fine fraction (51.5%) than in the whole Utter(44.5%). A second objective was to compare the potentials for net Nmineralization, NH3 volatilization, and respiration of whole poultrylitter and fine fraction stored for 7 d at 25 °C and at two water contents(unamended [0.12-0.26 kg H2O kg'1] and 0.5 kg H2O kg-'). On anequal-mass basis, net N mineralization and NH3 volatilization werelarger in the fine fraction than in the whole litter, whereas respirationwas similar in both materials. All processes increased with an increasein water content. These results suggest that the fine fraction shouldbe managed similarly to the whole litter when applied to soil and thatit may lose more NH3 than does the whole litter during storage,particularly at relatively high water contents.

POULTRY LITTER is a mixture of excreta, beddingmaterial, feathers, and waste feed, which is removed

from poultry houses and applied to land as fertilizer.Land application at appropriate rates not only providesnutrients to crops but also eliminates a waste disposalproblem. Land application at excessive rates, however,may lead to contamination of surface and groundwaterswith NO3~ (Liebhardt et al., 1979; Ritter and Chirnside,1987). Excessive applications usually occur in areaswhere there is limited availability of land in relation to the

M.L. Cabrera, Dep. of Crop and Soil Sciences/Inst. of Ecology; S.C.Tyson, Dep. of Crop and Soil Sciences; T.R. Kelley, Institute of Ecology;W.C. Merka, Extension Poultry Science; S.A. Thompson, Agriculturaland Biological Engineering Dep., Univ. of Georgia, Athens, GA 30602;O.C. Pancorbo, Massachusetts Dep. of Environmental Protection, Law-rence, MA 01843. Received 17 Feb. 1993. *Corresponding author.

Published in Soil Sci. Soc. Am. J. 58:367-372 (1994).

amount of poultry litter production. To avoid excessiveapplication, poultry litter could be transported to otherareas, but transportation costs per unit of nutrient arehigh because of low concentrations of N, P, and K(Bosch and Napit, 1992). Increasing the concentrationof nutrients can reduce transportation costs per unit ofnutrient, thereby increasing the distance of profitabletransport.

The concentration of N can be increased by fractionat-ing poultry litter. Ndegwa et al. (1991) passed poultrylitter through 0.83- and 3.3-mm sieves to generate fine,middle, and coarse fractions. They found the fine fractionhad a N concentration 19 to 27% higher than that of thewhole litter, with the dry matter in the fine fractioncomprising 24 to 41 % of that in the unfractionated litter.The increase hi N concentration was obtained withoutan increase hi P and K concentrations, which is importantbecause the rates of whole litter required to supply theN needed by many crops commonly supply excessiveamounts of P and K (Bosch and Napit, 1992). In theirwork, Ndegwa et al. (1991) also found that the middleand coarse fractions had N concentrations 10 to 25%lower than that of the whole litter and comprised 40 to47 and 16 to 26%, respectively, of the dry matter hiwhole litter. They proposed that the fine fraction mightbe used as a fertilizer, whereas the middle fraction mightbe a suitable bedding material in poultry houses. Thecoarse fraction could be used as mulch or as fuel inwood heating systems.

From the standpoint of using litter (fine fraction orwhole litter) as a N fertilizer, there are two importantcharacteristics: (i) the inorganic N content, and (ii) therate of mineralization of the organic N (Bitzer and Suns,1988). Under favorable laboratory conditions, mineral-ization of N from poultry litter mixed with soil is usuallyvery rapid; most of the mineralizable N is released within2 wk after application (Castellanos and Pratt, 1981;Hadas et al., 1983; Gale and Gilmour, 1986; Westermanet al., 1988). This potential for a rapid N mineralizationrate may pose a high risk of NOs" leaching when litteris applied to pastures or crops that are not actively takingup N (i.e., early spring or late fall applications). The

368 SOIL SCI. SOC. AM. J., VOL. 58, MARCH-APRIL 1994

risk of NOf leaching could be increased with fine fraction(<0.83 mm) applications if the fine fraction released asignificantly larger proportion of the organic N thanwould the whole litter. Thus, knowing if N in the finefraction is more mineralizable than that in the whole litteris important for managing applications. Accordingly, oneobjective of this study was to compare the short-term Nmineralized from whole litter and that from the finefraction (mixed with or surface applied to soil) in a 2-wkincubation at 25 °C.

Because poultry litter is commonly stored outdoorsbefore land application, N mineralization and NH3 vola-tilization may occur during storage. Both N transforma-tions are important because of their effect on the fertilizervalue of the litter and because of the potential environ-mental impact of N leached or volatilized from stockpiledlitter. In addition to N losses, stored litter may also loseC through respiration. The ratio of N to C losses isimportant because it determines how the concentrationof N in the material changes during decomposition. Thesecond objective of this work was to compare net Nmineralization, NH3 volatilization, and respiration inwhole poultry litter and fine fraction stored at 25 °C andat two water contents (unamended [0.12-0.26 kg rfcOkg-1] and 0.5 kg H2O kg-1) for 7 d.

MATERIALS AND METHODSSample Collection

Poultry litter was collected from three broiler houses, twothat housed one flock each (Houses 1 and 2) and one thathoused several flocks (House 3). All houses had wood shavingsas bedding material. A portion of the poultry litter (largestparticle <0.6 cm in length) was passed through a cylindricalseparator with a 0.83-mm sieve to generate a fine fraction asdescribed by Ndegwa et al. (1991). The dates of separationwere 13 Feb. 1991 for House 1, 21 Feb. 1991 for House 2,and 18 Mar. 1991 for House 3. After fractionation, wholelitters and fine fractions were stored at 4 °C until use.

Soil Incubation ExperimentNet N mineralization in whole litter and in the fine fraction

was evaluated in a soil incubation study initiated on 13 May1991. The soil was collected moist from the upper 15 cm of

a site mapped as Dothan loamy sand, which is representativeof areas in Georgia where the fine fraction could be used asfertilizer. The moist sample was passed through a 4-mm,round-hole sieve and stored at room temperature until use.The soil had a pH (1 g soil/2 mL H2O) of 4.9 and contained4.11 g C kg'1, 0.47 g total N kg'1, 4.9 mg NO3~-N kg-' and0.2 mg NW-N kg'1.

Carbon and N contents of the soil and litter materials (Table1) were measured by dry combustion (Nelson and Sommers,1982). Inorganic N was extracted from 1 g (oven-dry) litterwith 40 mL of 1 M KC1, after shaking for 30 min. (Nitrite+ nitrate)-N was determined by the Griess-Dosvay technique(Keeney and Nelson, 1982), after reduction of NOf to NO2~with a Cd column. Ammonium-N was measured by the salicy-late-hypochlorite mediod (Crooke and Simpson, 1971), andwater contents of the fine fraction and whole litter were deter-mined by drying at 65 °C for 48 h. All analyses were expressedon a dry-weight basis.

The soil incubation study was a factorial experiment withhouse (1, 2, and 3), fraction (fine fraction, whole litter) andmethod of application (surface, mixed) as main factors, andit included a control treatment, which did not receive anylitter application. For the surface-applied treatments, moistsoil (water content = 0.083 kg kg"1 = field capacity) equivalentto 80 g of oven-dry soil was packed to 1,3 g cm"3 in a 100-mLsquare glass bottle (14.8-cm2 cross-sectional area), and 14.8mg of total N from whole litter or fine fraction was appliedon the soil surface (100 kg N ha^on an area basis). For themixed treatments, die soil and whole litter or fine fractionwere first mixed in a polyethylene bag and then packed in a100-mL square bottle. All bottles were capped with a polyure-thane sponge containing 1 mL of H3PO4-glycerol solution (250mL of glycerol, 35 mL of concentrated H3PO4, and 715 mLof deionized water per liter), which trapped NH3. These mea-surements were required to account for NH3 volatilized whencalculating net N mineralized. Sufficient bottles were preparedto allow three replicates of each treatment to be extracted after3, 7, and 14 d of incubation. The bottles corresponding toeach replication were placed in separate high-humidity cham-bers (25.5 cm wide by 49.5 cm long by 30 cm high) throughwhich humidified air (« 98% relative humidity) was circulatedat 0.8 L min"1. The chambers were placed inside an incubatorat 25 °C.

At each extraction, the sponge in each bottle was removedand placed inside a polyethylene bag containing 30 mL of 1 MKC1. The NH3 trapped in the H3PO4 was extracted by repeatedlysqueezing the sponge and subsequendy allowing it to absorbKC1. The KC1 extract was poured into a 100-mL volumetric

Table 1. Selected properties of whole poultry litter and fine fraction from three broiler houses.

Property

House 1 House! House 3

Fine Whole Fine Whole Fine

t Values in parentheses are standard errors.t Includes NOf and NOf.§ 1 g dry litter/5 mL water.

Whole

Total C, g kg-1

Total N, g kg-1

NW-N, mgkg-1

NOf-N,mgkg-4H20, g kg-1

Total N, g kg"1

NH4+-N,mgkg-1

Noj'-N, mgkg-'ipH§H20, g kg"'

326 (l)t57.3 (0.1)

1432 (10)144(4)101 (5)

63.6 (0.2)5344 (27)2256 (16)

8.10 (0.02)173 (1)

341 (2)38.6 (0.2)

2112 (16)416 (12)175 (3)

43.9 (0.2)5680 (61)2168 (29)

8.69 (0.02)261 (2)

Soil incubation study374 (1)64.3 (0.2)

952 (5)0(0)

115 (3)Litter storage study

67.1 (0.1)3440 (25)

0(0)8.03 (0.02)

170 (1)

367 (2)52.3 (0.3)

950(7)0(0)

90(1)

54.8 (0.4)3152 (34)

0(0)8.39 (0.01)

134 (1)

327 (1)68.4 (0.1)

1336 (7)96(4)

133 (3)

73.9 (0.2)4576 (60)2174 (22)

8.40 (0.01)115 (4)

367 (2)53.6 (0.2)

1540 (13)376 (12)141 (1)

58.5 (0.2)4280 (44)2454 (53)

8.52 (0.01)152 (6)

CABRERA ET AL.: FRACTIONATED POULTRY LITTER 369

flask, and the process was repeated twice more with 30 mLof 1 M KC1 each time. The volumetric flask was brought to100 mL, and the extract was analyzed for NHl-N with thecolorimetric procedure described above. Preliminary studieswith NKUOH standards indicated that this method allowedcomplete recovery of the NH3 trapped in the sponges (Kisseland Cabrera, 1988). The soil was extracted by adding 60 mLof 1 M KC1 to each bottle, shaking the bottle for 30 min,filtering the soil through Whatman no. 41 filter paper in aBuchner funnel, and subsequently leaching the soil in the funnelthree times with 40 mL of 1 M KC1 each time. The filtratewas made up to 200 mL, centrifuged, subsampled, and analyzedfor inorganic N by colorimetry, as described above.

Net NH3 volatilized from the litter was estimated by sub-tracting the NH3-N volatilized in control treatments from theNHs-N volatilized in each litter treatment. Net N mineralizedfrom each of the materials was calculated by: (i) subtractinginorganic N in the control from the inorganic N found in thetreatments, (ii) adding the net NH3-N volatilized, and (iii)subtracting the initial inorganic N in each of the materials.To compare the susceptibility to mineralization of the differentmaterials, net N mineralized was expressed as a percentageof the organic N initially present, which was calculated bysubtracting the initial inorganic N concentration from the initialtotal N concentration in the whole litter and fine fraction (Table1). An analysis of variance considering house, fraction, methodof application, and all interactions among these factors wascarried out with the results from each extraction.

Litter Storage ExperimentPotential net N mineralization, NH3 volatilization, and respi-

ration during storage were evaluated immediately after thewhole litter from each house was sieved to separate the finefraction. The storage study was a factorial experiment withfraction (fine fraction, whole litter) and water content (un-amended or 0.5 kg kg"1) as main factors. The unamendedwater content of the materials ranged from 0.115 to 0.261 kgkg"1 (Table 1). A uniform water content of 0.5 kg kg"1 wasalso used because this is often the water content of poultrylitter recently removed from poultry houses (Bosch and Napit,1992) and of poultry litter stored outside.

An amount of whole litter or fine fraction equivalent to 1 g(oven dry) was weighed into a 50-mL centrifuge tube, whichwas placed inside a 0.95-L jar containing one vial with 5 mLof 2% H3BO3 (to trap NH3) and another vial with 15 mL of1.5 M NaOH (to trap CO2). The water content of samples tobe incubated at 0.5 kg H2O kg"1 was increased by addingdeionized water with a syringe after the material was weighedinto the tube. Empty tubes were placed inside 0.95-L jars(with corresponding traps) as controls. After five replicatesof each treatment were prepared, the jars were hermeticallysealed and placed in an incubator at 25 °C. At 3.5 d, the jarswere aerated and returned to the incubator to complete 7 d ofincubation. The NH3 trapped in H3BO3 was determined bytitrating with 0.005 M H2SO4, and the CO2 trapped in NaOHwas measured by precipitating the carbonate formed with BaCl2and subsequently titrating the unreacted NaOH with 1.6 MHC1 (Anderson, 1982). Net NH3 volatilized and CO2 evolvedfrom each of the materials were calculated by subtractingvalues measured in control treatments. The inorganic N in thelitter at the end of the incubation was determined as describedabove. Net N mineralized was estimated by: (i) adding inor-ganic N at the end of the 7-d storage to the net NH3 volatilized,and (ii) subtracting initial inorganic N in each of the materials.These calculations may underestimate net N mineralized be-cause they do not account for denitrification losses. However, apreliminary study in our laboratory indicated that denitrification

losses from poultry litter were negligible at water contentsbelow 1.2 kg H2O kg"1 dry litter.

The change in the N concentration of the litter caused byC and N losses during decomposition was estimated as FinalN concentration (g N kg"1) — Initial N concentration (g Nkg"1), where final N concentration was ([Initial N cone (g Nkg-1) - NH3-N lost (g N kg-')]/[Initial weight (g kg"1) -Weight loss (g kg"1)]) X 1000. Initial weight was 1000 g kg"1

and weight loss was estimated as (NH3-N lost [g N kg"1] +CO2-C lost [g C kg"1]). An analysis of variance was carriedout for each variable measured, considering fraction, watercontent, and their interaction (SAS Institute, 1985).

RESULTS AND DISCUSSION

The fine fractions generated in this study had N concen-trations that were 22 to 48% higher than those of thewhole litter (Table 1). These results confirm those ofNdegwa et al. (1991) and point to the potential use ofthe fine fraction as a N fertilizer. The distance thispotential fertilizer could be transported will depend,among other factors, on N concentration and processingcosts (Bosch and Napit, 1992). Research is underwayto investigate efficient methods to achieve a low-costfractionation of the litter (S.A. Thompson, personal com-munication 1993).

Soil Incubation ExperimentMineralization of the organic N in the whole litter

and fine fraction was rapid hi both mixed and surfaceapplications, with values ranging from 36.4 to 51.7%in 3 d (Table 2). At 3 d, there was a significant housex fraction interaction (P < 0.01) because the fine fractionhad a significantly larger percentage of organic N miner-alized than did die whole litter from House 1 but notfrom the other two houses (Table 2). The differenceobserved in House 1 was probably related to the largedifference hi total N content between fine fraction andwhole litter (Table 1). At 3 d, there was also a significanthouse x method interaction (P < 0.05) because thepercentage of organic N mineralized in surface applica-tions was similar to that in mixed applications for House1, less than that hi mixed applications for House 2, andgreater than that in mixed applications for House 3 (Table2). Reasons for these differences are not clear.

Method of application was the only significant effectat 7 d of incubation (P < 0.01). Mixed treatments hada significantly lower proportion of organic N mineralized(44.5%) than did surface treatments (56.9%), possiblybecause of higher denitrification or higher N immobiliza-tion hi the mixed treatments. Between Days 3 and 7there was a significant increase hi nitrification hi themixed treatments (data not shown), which may havesupplied substrate for denitrification. In addition, con-sumption of O2 by nitrifiers and heterotrophs may haveprovided anaerobic microsites adequate for denitrifica-tion (Tiedje, 1988). The lower net N mineralizationobserved hi mixed treatments could also have been dueto a larger N immobilization caused by an ultimate contactbetween soil and litter. Another possible explanation islower availability of O2 hi mixed treatments than hisurface-applied treatments.

370 SOIL SCI. SOC. AM. J., VOL. 58, MARCH-APRIL 1994

Table 2. Effects of fraction (whole litter or fine fraction) and application method (mixed or surface) on organic N (%) mineralized frompoultry litter (from three houses) incubated with soil at 25 °C for 14 d.

House TimePoultry litter Application

Fine Whole Mixed Surface LSDo.o!d

1 323Means1 723Means1 1423MeansSource

House (H)Fraction (F)Method (M)H x FH x MF x MH x F x M

44.7t39.950.345.050.153.152.651.947.455.751.451.5

\

Day 3****NS***

NSNS

30.740.347.239.438.856.053.749.535.147.550.944.5

% organic N rain36.8f43.845.742.140.947.844.944.538.248.251.542.6

eralized ——

Day?NSNS**NSNSNSNS

38.636.451.742.247.861.361.456.944.455.150.149.9

Day 14**

NSNSNSNSNS

6.0§

3.41

12.7

7.4

10.4

6.0

*, ** Significant at 0.05 and 0.01 probability levels, respectively.t Means across application methods.$ Means across fractions.§ LSD value for comparison of means within application x house or within fraction x house.1 LSD value for comparing means of application method or means of fractions.

House and fraction affected mineralization at 14 d ofincubation (P< 0.05). The average proportion of organicN mineralized for House 1 (41.3%) was significantlylower than those for Houses 2 (51.6%) and 3 (51.2%),probably because of the lower total N concentration inmaterials from House 1 (Table 1). Also, the averageproportion of organic N mineralized was slightly higherin the fine fraction (51.5%) than in the whole litter(44.5%, Table 2). This effect may have been due toimmobilization of N in the whole litter because, althoughthe average percentage of organic N mineralized fromthe fine fraction did not change much between 7 and14 d, the percentage of organic N mineralized from thewhole litter tended to decrease in that period (Table 2).The presence of relatively large pieces of wood shavings(0.3-0.6 cm) in the whole litter could have led to immobi-lization of some of the mineralized N. Immobilizationof mineralized N may also have been responsible forthe disappearance of the effect of method of applicationbetween Days 7 and 14.

The proportions of organic N mineralized in 14 d(35.1-55.7%) are not very different from values obtainedby other researchers using longer incubation times. Sims(1986) reported that 25 to 40% of the organic N inbroiler litter was mineralized in 150 d at 25 °C, whereasCastellanos and Pratt (1981) found that «45% of theorganic N in chicken manure was mineralized during a70-d incubation at 23 °C. In a study with 20 poultrymanure samples, Bitzer and Sims (1988) found that, onaverage, 67% of the organic N was mineralized in 140 dat 23 °C. Our results support the observation that, underlaboratory conditions, most of the mineralizable N inpoultry litter is usually released within the first 2 wk of

incubation (Hadas et al., 1983; Gale and Gilmour, 1986;Westerman et al., 1988).

In summary, the proportion of organic N mineralizedwas in some cases slightly higher in the fine fractionthan in the whole litter for both mixed and surfaceapplications. These differences, however, do not seemlarge enough to warrant different management strategiesfor these materials.

Litter Storage ExperimentPotentials for net N mineralization, NHa volatilization,

and respiration were evaluated immediately after thewhole litter was sieved. Because of that, total N, inor-ganic N, and water contents were higher in these samplesthan in those used for the soil incubation study (Table 1).

In general, net N mineralized was higher in the finefraction than in the whole litter, and the difference waslarger at a constant water content (Table 3). If the miner-alization values are expressed as a percentage of organicN, the figures obtained (0-12%) will be much lowerthan those observed when these materials were incubatedwith soil for 7 d (39-56%, Table 2). The presence ofsoil may provide a better environment for N mineraliza-tion partly by buffering the system and maintaining abetter pH for biological activity.

The amount of NHs volatilized in 7 d showed a signifi-cant fraction x water content interaction in all threehouses (P < 0.01). In general, the fine fraction showedhigher NH3 volatilized than did the whole litter, butthe difference was larger at 0.5 kg H2O kg"1 than atunamended water contents (Table 3). The results forunamended water contents are confounded by the fact

CABRERA ET AL.: FRACTIONATED POULTRY LITTER 371

Table 3. Net N mineralized, NH3 and CO2 losses, and increase in N concentration in whole poultry litter and fine fraction from threehouses during incubation without soil at 25 °C for 7 d.

House 1 House 2 House 3

Water content Fine Whole Fine Whole Fine Whole

Net N mineralized, mg kg"1 wk~'Unamendedt0.5 kg kg-1

LSD (0.05)

Unamended0.5 kg kg-'LSD (0.05)

Unamended0.5 kg kg-1

LSD (0.05)

Unamended0.5 kg kg-'LSD (0.05)

24105620

6004310

31100

1.52.6

750-150

970

7802480

210

4387

4

1.21.6

0.3

25207980

590NH3 lost, mg N kg-570

4630270

CO2 lost, mg C g-'41116

4Increase in N concentration,

2.33.9

0.3

-3602810

•wk-1

1002400

wk-1

21108

g N kg-1 wk-1

1.14.1

9005420

10705420

28103

1.12.9

4603020

920

6503630

215

2792

6

1.02.2

0.4t Refer to Table 1 for unamended water contents.

that water content varied among materials. In House 1,the whole litter had a much higher water content thandid the fine litter (Table 1) and NH3 volatilization wasnearly equal (Table 3). Where water contents were simi-lar for both materials (Houses 2 and 3), the fine fractionlost more NH3 than did the whole litter. Another factorconfounding results is the different pH of the materials;a higher pH tends to enhance NH3 loss.

Differences in NH3 volatilized between whole litterand fine fraction were more consistent at a constant watercontent of 0.5 kg kg"1. These differences cannot beexplained by initial inorganic N levels because thoselevels were similar in both materials (Table 1). Morelikely, the high rate of NH3 volatilization from the finefraction was due to a high rate of N mineralization (Table3). A high rate of mineralization not only generatesammoniacal N but also increases the pH (Giddens andRao, 1975), causing a larger proportion of the ammonia-cal N to be present as NH3 (Koelliker and Kissel, 1988).The increase in pH that occurs during mineralization ofN from poultry litter is believed to be due in part tothe decomposition of uric acid and urea. Uric acid isconverted to urea by aerobic bacteria (Schefferle, 1965),and urea is hydrolyzed to NH| by the enzyme ureasein a reaction that consumes H+ and raises the pH (Kisseletal., 1988).

Losses of C through respiration tended to be higherin the fine fraction than in the whole litter, but thedifferences do not appear to have practical significance.Increasing the water content to 0.5 kg kg""1 increasedthe emission of CO2 two- to fivefold, depending on theunamended water content of the material (Table 3).

The ratio between CO2-C and NH3-N losses wassuch that it caused small increases (1.5-7.5%) in the Nconcentration of both litter materials (Table 3). In gen-eral, the increase was larger for the fine fraction thanfor the whole litter. Although it may appear advantageousto allow decomposition to increase the N concentrationin these materials, the N lost as NH3 is inorganic N

which, if not lost, would be readily available to plants.An increase hi the N concentration of the litter with asimultaneous loss of inorganic N may imply that a largerproportion of the remaining N is organic, part of whichis difficult to mineralize (Bitzer and Sims, 1988). Thus,allowing the litter to lose NH3 and CC>2 does not appearto be a sound management practice, even though suchlosses may lead to a slight increase in the concentrationof N.

In summary, our results indicate that, on an equal-massbasis, net N mineralization and NH3 volatilization duringstorage may be higher hi the fine fraction than in thewhole litter and that NH3 losses may be significantlyincreased by an increase hi water content. These findingssuggest that both fractions should be maintained dryduring storage to reduce N losses.

ACKNOWLEDGMENTSThis work was supported by a grant from the USDA Low

Input Sustainable Agriculture Program.

372 SOIL SCI. SOC. AM. J., VOL. 58, MARCH-APRIL 1994