Upload
g-s
View
224
Download
0
Embed Size (px)
Citation preview
DIVISION S-7—FOREST AND RANGE SOILS
Nutrient Flux in Litter and Surface Soil after Nitrogen and Phosphorus Fertilization1
J. M. KELLY AND G. S. HENDERSON2
ABSTRACTThe effect of urea and concentrated superphosphate additions on
the movement of N, P, K, and Ca from the litter and top 10 cm of themineral soil via the soil solution was evaluated in an upland oak forestusing tension lysimeters. The range in total flux values for eachelement over the study period were: N 24.8 to 1145.3; P 2.0 to 633.3;Ca 70.6 to 553.1; and K 49.5 to 94.0 kg/ha in response to variouscombinations of N and P fertilizer addition at levels of 0, 550, and1100 kg/ha N and 0,275, and 550 kg/ha P. Nitrogen fertilizer additionsignificantly increased the flux of N and K while reducing the flux of Pand Ca. Phosphorus fertilizer addition significantly increased N, PCa, and K fluxes. Solubilization of organic matter and the formationof insoluble calcium ammonium phosphate were important processesregulating the flux of N, P, Ca and K.
Additional Index Words: urea, superphosphate, forest fertilization,decomposition, nutrient loss, oak forest.Kelly, J. M. and G. S. Henderson. 1978. Nutrient flux in litter and surfacesoil after nitrogen and phosphorus fertilization. Soil Sci. Soc. Am. J.42:963-966.
Table 1—Selected chemical and physical properties of the0 and Al horizons of the Fullerton soil.
'T'HE ABILITY of forests to maintain large amounts ofJ. nutrients in circulation appears to explain the relatively
high productivity of forests on soils of low nutrient status.However, the intensification of forest management patternswhich alter element balances may bring about increasedleaching of both naturally occurring and added nutrients.Addition of chemical fertilizers, especially N, increases thedecomposition rate of organic detritus (Parker, 1962;Brown and Dickey, 1970; Black and Reitz, 1972). If thisgeneralization holds true for deciduous forest litter, then theaddition of chemical fertilizers could stimulate decomposi-tion and mineralization thereby releasing over a relativelyshort period of time those nutrients that would normally bereleased over a more extended period. This release ofnutrients from the litter could occur under less thanoptimum conditions for plant uptake leading to a loss fromthe feeder root zone via the soil solution. The objective ofthis study was to quantify the effect of N and P additions onnutrient flux in the litter layer and top 10 cm of the mineralsoil of a deciduous forest as reflected by the nutrient statusof the soil solution.
MATERIALS AND METHODSStudy plots were established on Walker Branch Watershed,
located on the U.S. Department of Energy's Oak Ridge Res-ervation in eastern Tennessee. The climate of the region is of the
'Research supported by the U.S. Department of Energy under contractwith the Union Carbide Corporation. Publication no. 1239, EnviromentalSciences Division, Oak Ridge National Laboratory, Oak Ridge, TN37830. Received 23 Oct. 1977. Approved 25 July 1978.2 Biologist, Div. of Environ. Planning, TVA, Muscle Shoals, AL35660, and Assoc. Prof., School of Forestry, Univ. of Missouri,Columbia, respectively. Research conducted while both authors wereassociated with Environ. Sci. Div., Oak Ridge National Laboratory.
Hori-zon
0Al
PercentBase Total Total Total Total Total organic Hydr.
CEC sat. Ca Mg K N P matter cond.
300 18 9 280 86.0 40 864 648 4,320 1,739 324 5.5 64.9
humid mesothermal type, with moderate summer (24°C) andwinter (5°C) temperatures (Holland, 1953). Total precipitationduring the 13 months of the study was 152.3 cm. The regolith isresiduum derived from dolomite which is commonly cherty. Thesoil is a Fullerton cherty silt loam (Typic Paleudults, clayey,kaolinitic, thermic), 5 to 12% slope. This soil has a dark grayish-brown (10YR 4/2) cherty silt loam Al horizon ranging inthickness from 2.5 to 10.0 cm. The Al horizon has a moderatefine granular structure (bulk density 1.08 g/cm3) and mediumacidity (pH 5.8) (Peters et al., 1970). Additional information onthe Fullerton soil is presented in Table 1. The forest stand inwhich the study plots were located was dominated by chestnut oak(Quercus prinus L.), white oak (Quercus alba L.), black gum(Nyssa sylvatica marsh) and red maple (Acer rubrum L.) con-tributing 24, 17, 16, and 13% respectively of the total stems >2.5 cm. Dogwood (Cornus florida L.) was the principal un-derstory species.
The study utilized a randomized complete block design withtwo replicate blocks. Each block contained nine 4- by 5-mtreatment plots. A complete factorial of three levels of N as urea(45% N) and P as concentrated superphosphate (19% P, 37% Ca)constituted the treatments. Fertilizer was broadcast by hand inmid-March at rates of 0, 550, and 1,100 kg/ha N and 0, 275, and550 kg/ha P.
One tension lysimeter of the type described by Cole (1958) wasinstalled 10 cm beneath the surface of the mineral soil in eachtreatment plot to collect leachate. Vacuum for the lysimeter plateswas supplied by an automated system which maintained a constanttension of 0.1 bar at the plate surface. Measurements ofprecipitation were made with a recording rain gage located at thesame elevation in a clearing 150 m south of the study plots.
Samples of the soil solution were collected at 7-day intervalsduring periods of adequate moisture and a volume determinationmade to the nearest milliliter. A 25-ml aliquot was taken forKjeldahl-nitrogen determination using the procedure described byBremner (1965). The remainder of the sample was filteredthrough Whatman no. 1 filter paper and 1 ml of IN HC1 and 0.1 gof HgCl2 added to each sample as a preservative. A 20-mlaliquot was taken prior to the addition of HgCl2 since mercuryions interfered with the P determination method. Phosphorusdeterminations were made by the sulfuromolybdate method on aTechnicon Auto-analyzer (Lundgren, 1960). A Perkin-ElmerModel 403 Atomic Absorption Spectrophotometer was used tomake the Ca and K determinations (Kahn, 1971).
Statistical analyses were accomplished using the StatisticalAnalysis System developed at North Carolina State Univ. (Service1972). In addition to analysis of the results with the completefactorial model, analyses were conducted for each N and P levelto further uncover possible effects of interactions between N and Padditions. Tukey's "W" procedure (Steel and Torrie, 1960) wasused for comparison of treatment means. The 0.05 level of
963
964 SOIL. SCI. SOC. AM. }., VOL. 42, 1978
probability was used as the criterion for accepting or rejecting nullhypotheses in all statistical analyses.
RESULTS AND DISCUSSIONQuantity of Leachate
The representativeness of soil solution samples collectedwith tension type lysimeters has been debated in theliterature (Cole, 1958; Wagner, 1962; Cochranetal., 1970;Hansen and Harris, 1975; Marion and Leaf, 1977). Theprincipal question associated with the sideless tension platelysimeter is the volume of overlying soil from which theleachate is drawn. This problem, as discussed by Marionand Leaf (1977), becomes more acute as the sampling pointmoves downward in the soil profile owing to increasingvariability of physical properties affecting moisture flow.However, plates located within 10 to 15 cm of the soilsurface seem to draw leachate from an area more or lessequivalent to the column of soil overlying the plate and assuch provide reasonably reliable samples.
Total leachate collected during the study period rangedfrom 82.0 to 136.5 cm or 53.8 to 89.6% of precipitationinput (Table 2). A mean separation analysis indicated that,except for the 550/550 treatment, all other values were notsignificantly different. An examination of the soil columnoverlying one of the 550/550 plates revealed the presenceof a large piece of chert. This may partially account for thereduction in leachate collected. The percent of incomingmoisture values from this study, with an overall mean of79%, compares quite favorably with the 82% collected by
Table 2—Leachate and weight of elements collectedat a depth of 10 cm.
Treatment
0/00/2750/550550/0550/275550/5501,100/01,100/2751,100/550
Totalleachatecollected
cm131.5117.2136.3111.2136.582.0
113.1136.1131.4
Incomingmoisturet
Total content
N P Ca K
% ————————— kg/ha —————————79.976.989.473.089.653.874.289.386.3
24.817.919.8
437.0665.0479.0739.5
1,145.3730.9
2.040.1
633.30.8
162.4263.5
1.9178.5166.8
70.6145.9553.1105.6130.3113.8140.4133.3188.7
57.168.262.459.771.449.573.494.073.8
T Total precipitation input 152.3 cm.
Marion and Leaf (1977) at a similar depth. While sidelesstension lysimeters maintained at a fixed suction can distortsoil moisture movement (Cochran et al. 1970) and lead tobiased estimates of nutrient flux; it is felt that the leachatevalues observed in this study are equivalent to thosereported by others.
Nitrogen FluxThe data presented in Table 3 summarizes on a monthly
basis the amount of N moving to a depth of 10 cm inresponse to fertilizer additions. The analysis of varianceand subsequent mean separation analysis revealed that theaddition of fertilizer N did result in increased levels of Nleached to the 10 cm depth. From a statistical point of viewN leaching was equivalent following the addition of either550 or 1,100 kg/ha of N. However, a comparison of total Nleached from the 550/0 treatment (437 kg/ha) was ap-proximately 79% of the N added, while that leached fromthe 1,100/0 treatment (740 kg/ha) was 67% of the addition.Isenee and Walsh (1971) found a similar response in that agreater portion of the added N was removed at theintermediate fertilizer level (224 kg/ha) than at the higherrate of addition (672 kg/ha). They attributed this responseto differences in the level of nitrification and pH.
Although a comparison of the total N values (Table 2)from the 0/275 and 0/550 treatments to the control (0/0)would indicate a slight depression in N flux in response to Paddition, on a study wide basis there was a small increasein N flux in response to P additions. The N-P interactionterm was not statistically significant.
The trend in N movement can be seen from the data inTable 3. Most of the N moved during the 5 monthsfollowing fertilization with a return to normal valuesapproximately 8 months after fertilization.
Phosphorus FluxThe addition of both N and P fertilizer produced
significant changes in the amount of P moving to the 10-cmdepth. The addition of P increased treatment mean valuesfrom 0.04 kg/ha at the zero P level to 3.6 and 10.1 kg/ha atthe 275 and 550 P levels, respectively. Conversely, theaddition of N fertilizer produced a reduction in the amountof P moving to the 10 cm depth with treatment mean valuesof 6.4 kg/ha of P at the zero level of N addition and 4.0 and
Table 3—Total-nitrogen flux as a function of fertilizer treatment and time.Fertilizer treatment N/P
Date 0/0 0/275 0/550 550/0 1,100/0 550/275 550/550 1,100/275 1,100/550
MarchAprilMayJuneJulyAug.Sept.Oct.Nov.Dec.Jan.Feb.March
0.71.12.00.28.94.11.20.40.31.91.51.50.5
1.21.72.90.22.41.50.70.20.32.03.01.20.4
2.13.23.40.21.01.60.70.30.32.02.51.80.4
142.674.4
116.915.556.213.27.93.60.32.02.41.30.5
- kg/ha ———304.2136.6178.6
15.064.620.57.94.20.52.62.02.00.4
181.8109.6215.2
20.5106.4
14.95.43.40.52.02.71.70.4
178.8111.5106.0
8.453.49.91.53.50.31.32.61.20.5
680.8141.6166.941.871.513.715.64.70.32.52.92.30.4
345.5122.1121.1
14.490.219.17.94.20.42.12.92.00.5
KELLY & HENDERSON: NUTRIENT FLUX IN LITTER AND SURFACE SOIL AFTER N AND p FERTILIZATION 965
Table 4—Phosphorus flux as a function of fertilizer treatment and time.
Fertilizer treatment N/P
Date 0/0 0/275 0/550 550/0 1,100/0 550/275 550/550 1,100/275 1,100/550
MarchAprilMayJuneJulyAug.Sept.Oct.Nov.Dec.Jan.Feb.March
0.260.240.05
<0.010.020.020.02
<0.01<0.01
0.930.360.040.01
10.37.9
13.70.61.41.10.50.20.21.61.70.70.3
310.1189.683.9
3.08.97.42.41.20.6
10.210.14.11.9
0.170.280.13
<0.010.010.010.03
<0.010.040.030.040.020.01
— kg/ha ——0.420.620.59
<0.010.030.010.02
<0.010.060.030.030.040.01
61.243.838.2
1.34.63.00.70.60.52.83.11.80.5
95.490.244.3
2.18.36.50.51.10.25.15.92.51.2
85.344.531.5
2.22.82.41.80.70.32.72.11.80.4
49.344.337.5
1.36.96.72.51.80.24.66.44.01.4
3.3 kg/ha at the 550 and 1,100 kg/ha levels of N addition,respectively.
Phosphorus flux in response to both N and P additionwas significantly different from the response observed foreither N or P fertilizer alone. The total flux values (Table 2)reflect this response with generally lower P values fortreatments where N and P were applied together. A meanseparation analysis revealed that on a statistical basis 550kg/ha of N addition was as efficient in retarding themovement of P as 1,100 kg/ha of N addition. The trend inP movement through time (Table 4) was very similar to thatof N with the greatest movement during the first 3 monthsfollowing fertilization. However, unlike N, P levels had notreturned to control levels by the end of the study (Table 4)except for the N only plots.
Calcium FluxThe flux of Ca was similar to that of P. The addition of N
significantly reduced the amount of Ca moving to the 10cm depth while P addition produced a significant increase.Treatment means for the three N levels were 7.3, 3.3, and4.4 kg/ha for the 0, 550, and 1,100 kg/ha N additions,respectively; and 3.0, 3.9, and 8.1 kg/ha for the 0, 275,and 550 kg/ha P additions, respectively. The N-P in-teraction response for Ca was similar to that of P with lowerlevels of Ca moving in the presence of combined N-Pfertilization. The total Ca weight values (Table 2) againreflect this response with comparatively lower levels of Caflux when P was applied in conjunction with N fertilizer.
Potassium FluxNitrogen treatment produced a significant increase in the
amount of K movement to the 10-cm depth as did Ptreatment also. The N-P interaction was not significant.The total flux values (Table 2) indicate a greater movementof K in the presence of 275 kg/ha P than with 550 kg/ha.As with the elements previously discussed most of the Kflux occurred during the period immediately after fer-tilization. In contrast to the other elements evaluated, Kreaching the 10-cm depth dropped to or slightly belowcontrol levels by the 3rd month after treatment.
Controlling FactorsA number of factors contributed to the individual and
collective responses observed in this study. Ogner (1972),Ogner and Schnitzer (1970), and Bengston (1970) havepreviously noted that heavy rates of urea fertilization can,as a result of increases in pH associated with ureahydrolysis and exchange of organically sorbed cations withammonium, increase the solubility of humic material inwater. Thus water percolating through the litter is capableof transporting substantial amounts of dissolved organicmaterial, and associated elements into the mineral soil(Bengston, 1970; Ogner, 1972). A significant increase insoil solution turbidity was observed (Kelly, 1973) in plotstreated with N. This change was taken as a positiveindication of increased solubilization of organic matter.The solubilization of organic matter could account for alarge portion of the nutrient flux observed on plots treatedwith N. Plots treated with P only did not exhibit anyincrease in the solubilization of organic matter (Kelly1973).
Closely associated with organic matter dissolution arepH changes following urea hydrolysis. These changes insoil solution in response to N addition (Kelly, 1973) arealso important since pH is important in determining theavailability as well as susceptibility of certain ions toleaching, immobilization, and volatilization (Overrein andMoe 1967; Meyer et al., 1961; Wahhab et al., 1960).
Earlier discussion indicated that solubilization of organicmatter was an important process contributing to total Nflux. The total amount of N moving to the 10-cm depth inthe 1,100/275 treatment (1,145.3 kg/ha) indicates that atleast 45 kg/ha of N was mobilized from litter and soil Npools. This estimate does not include volatilization or plantuptake and therefore should be regarded as a lower limit ofaddition due to solubilization.
The formation of insoluble calcium ammonium phos-phate compounds may partially explain the lower levels ofN moving to the 10 cm depth in the 550/550 and 1,100/550treatments compared to the 550/275 and 1,100/275 treat-ments (Table 2). Mees and Tomlinson (1964) and Hauckand Stephenson (1965) have noted that N volatilization losswas reduced when urea was applied in conjunction withmonocalcium phosphate. They attributed this reduction to alower pH of hydrolysis. Thus when urea was applied inconjunction with concentrated superphosphate, volatiliza-tion loss was reduced, and leaching was reduced due toadditional Ca being available for incorporation into in-
966 SOIL. sci. soc. AM. J., VOL. 42, 1978
soluble calcium ammonium phosphate. The formation of nutrient movement occurred within 3 months after fertilizerthis compound must have occurred in the mineral soil since application; although, the influence of certain fertilizerthere was no evidence of N accumulation in the litter treatments on nutrient flux could be seen up to 1 year after(Kelly, 1973). While the literature and theoretical cal- fertilization,culations indicated that this phenomenon could occur, it isonly a hypothesis in this case and has not been sub-stantiated by chemical analysis.
Phosphorus losses are in general agreement with the Nfixation hypothesis. Equivalent amounts of P movementwere found in the 1,100/275 and 1,100/550 treatmentsindicating greater fixation at the higher P level (Table 2).Chemical fixation appears to be the most plausible ex-planation since increasing P level reduced microbial pop-ulation level (Kelly, 1973).
The P flux data suggest that the litter and soil were ableto immobilize P up to a certain level either throughmicrobial fixation or chemical precipitation, but when thatlevel was exceeded the immobilization process became lessefficient (Table 2). Most of the P appearing in the leachatewas probably of fertilizer origin since the addition of Pretarded microfloral activity and thus reduced the level ofmicrobial fixation as well as the mineralization of naturallyoccurring P. Additional P contributions were also obtainedfrom the solubilization of organic matter.
Little of the Ca released in the breakdown of theconcentrated superphosphate was fixed in the litter (Kelly,1973). Some form of immobilization occurred in the plotsreceiving the 0/275 treatments since movement due to the0/550 treatment was slightly less than four times the flux at0/275. This response could possibly be explained by a verylow level of microbial immobilization in the 550-kg/ha P.treated plots due to the inhibitory effects of P, or theamount of Ca added exceeded the chemical fixation limitsof the litter. The increase in Ca leached from the litter andtop 10 cm of the mineral soil after N fertilization couldhave been due to an increase in nitrate level as a result ofurea hydrolysis, or the replacement of Ca with ammonium.Likens et al. (1970) noted that the soil solution con-centration and subsequent loss of Ca increased as the nitratelevel increased. This response could also have been afunction of increased decomposition due to the added N(Kelly 1973).
The increased levels of K flux in response to fertilizertreatment may have been due to increased solubilizationand decomposition of organic matter, or displacement onthe exchange complex by ammonium. The increase in Kflux due to P treatment could be attributed to reducedmicrobial fixation (Kelly, 1973) or more likely to somechemical phenomena such as replcement of K with Ca onthe exchange complex.
SUMMARYThe results of this study indicate that the alteration of
element balances as a result of N and P addition resulted ina significant short-term increase in nutrient fluxes. It shouldbe emphasized, however, that the levels of fertilizerapplication used in this study are well above the upper limitof economically feasible fertilzer application, with normalcommerical applications being two to four times less thanthe rates used in this study. As postulated, most of the