Aug 2, 2009 - Eroded check (no amendment) and topsoil check (no desurfacing) treatments were left for comparison. ...... ments. Pages 153-158 in Ptoc' 13th.
Soil amendments and water-stable aggregation of a desurfaced Dark Brown Chernozem Haiguo Sun1, Francis J. Larney2, and Murray S. Bullock2
l
Soil and Fertitizer lnstitute, Hebei Academy of Agricutturat and Forestry Sciences, Shijiazhuang, Hebei 05.0051,
P.R. China.2Land Resource Sciences Seciion, Research Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada T1J 481. Lethbridge Besearch Centre Contribution no. 3879401, received 16 March 1994' accepted 10 March 1995. Sun, H., Lamey, F. J. and Bullock, M. S. 1995. Soil amendments and water-stable aggregation of a desurfaced Dark Brown Chernozem. ian. J. Soil Sci. 75: 3lg-325. Aggregate stability, which influences soil resistance to wind and water erosion, can be improved by the application of organic u-"nd-*tr. In spring 1992, a desurfaced Dark Brown Chernozem in southern Alberta was amended with six animal manures, four crop residuis ant two rates of phosphate fertilizer, to determine their efficacy in restoring soil productivity. Eroded check (no amendment) and topsoil check (no desurfacing) treatments were left for comparison. One year later, wet aggregate stability at five levels of aggregate pre-wetting was determined. Aggregate stabilities of crop residueu-"nd"d soils were irgnincatrtty higher (P < 0.01) than thoie oi soils treated with animal manures or fertilizer/checks at all wetness levels. Signifrcant (P < 0.01) quadratic response and plateau relationships between aggregate subilty and soil water content showed that there was a threshold moisture content for maximum stability. With the onset of rainfall, aggregates on the crop residue-amended treatments would reach maximum stability sooner than those on the fertilizer/check treafinents, thereby decreasing the potential for water erosion. Stability of air-dry aggregates showed weak positive relationships with organic and inorganic C. Amendment of eroded soils with crop ."iido"r is ti-tely more effective in limiting erosion than amendment with animal manures
or chemical fertilizers, at least in the first year after incorporation.
Key words: Soil erosion, aggregate stability, animal manure, crop residue M. S. 1995. Effets d'amendements organiques sur la stabilit6 i l'eau des agr6gats dans un chernozem brun fonc6 d6cap6. Can. J. Soil Sci. 75:319-325. La stabilit6 des agr6gats, qui influe sur la_rdsistance du sol i 1'6rosion 6olienne et hydrique, perit Ctre am6lior6e par I'apport d'amendements organiques. Au printemps 1992, nous avons incorpor6 de dans un chernozem brun fonc6 d6cap6 (d6banass6 dila couche arable) du sud de l'Alberta, six types de fumier, quatre sortes Coqne productivit6. sol sa au d rendre leur efficacit6 de mesurer doses, afin deux phosphat6 d engrais r6sidus de culture et un ann6e plus base de comparaison, on utilisait un timoin 6rodd (sans amendement) et un t6moin intact, c'est-d-dire non d6cap6. Une parcelles les dans des agr6gats La stabilit6 mesur6e. 6tait pr6humectation de niveaux cinq tard, la stabiiit6 h I'eau des agr6gats i trait6es aux r6sidus de culturJ 6iait signifiiativement plus forte (P < 0,01), ir tous les niveaux d'humectation, que dans le traite(P < 0'001) de r6ponse ment au fumier, dans les traitements, aiec engrais ou dins les traitements t6moins. Des rapports significatifs quadratique et de plafonnement 6taient observds entre la stabilit€ des agr6gats et la teneur en eau du sol, ce qui r6vdle I'existence d'un seuil hydriqui pour la stabilit6 maximale. Aprds un 6pisode de pluie, ies agr6gats dans les parcelles amend6es aux r6sidus de culture atteignaient ieur stabilit6 maximale plus t6t que les traitements avec engrais ou que les_traitements t6moins, abaissant du la m6me coup les possibilit6s d'6rosion hydrique. La stabitit6 des agr6gats s6ch6s h I'air affrchait des rapports positifs faibles avec teneur en - orginique et en C min6ral. L'amendement des sols 6.od6* uu"c des restes de culture parait plus efficace pour freiner 1'6rosion que famendement au fumier d'(levage ou aux engrais chimiques, tout au moins dans I'ann6e suivant I'incolporation' Sun, H., Larney, F. J. et Bullock,
MOIS cl6s: Erosion du sol, stabilit6 des agr6gats, fumier d'6levage, restes de culture
41.5 km for manure aimed at restoring productivity of erod-
Agrir:ultural landscapes throughout the Canadian prilnes show' evidence of erosion by water and wind (eroded knolls, "blorvout' areas). The potential for further soil degradation on ttrese areas is high, partly because erosion leads to the loss ,cf soil organic matter which helps maintain aggregate stability (Tisdall and Oades 1982; Oades 1984; Boyle et al. 1989). Degree of aggregation affects interrill erosion (Foster et al. 1985) and soil detachment (Francis and Cruse 1983),
ed wheat cropland (< 20 cm of topsoil removed).
Incorporation of crop residues on eroded areas may be a feasible alternative for producers without access to a manure supply. Dormaar et al. (1988) and Larney and Janzen (1994) showed that crop residue amendments can restore yields on desurfaced or artificially eroded soils. However, the effect of amendments from various sources and at various levels of decomposition on restoration of structural stability to eroded soils has not been adequately examined. Defining such relationships may provide a measure of the efficacy of organic amendments in retaining soil structural integrity aeainst external forces such as rainfall or irrigation.
while stable non-erodible aggegates reduce wind erosion by sheltering erodible particles (Chepil 1951). Application of cattle manure is a means of restoring productivity to eroded knolls in southern Alberta. Fteeze et al. (1993) reported a mean breakeven hauling distance of 319
320
CANADIAN JOURNAL OF SOIL SCIENCE
Therefore, the objective of this study was to determine the a range of livestock manures, crop residues and fertilizer amendments on wet aggregate stability of a severely eroded soil. We used a desurfaced or artificially eroded soil (mechanical removal of Ap horizon) to achieve a severely eroded surface. This approach has been commonly used in erosion/productivity studies (Dormaar et al. 1988; Tanaka and Aase 1989), as it creates a more uniform environment in which to compare erosion control treatments than a naturally eroded surface where differential rates of topsoil removal and deposition cause considerable variation.
effect rrf
MATERIALS AND METHODS The study was carried out at Lethbridge, Alberta, on a Dark Brown Chernozemic soil with a sandv clay loam texture (52%o sand, 20Vo sllt and. 28Vo clay) and a slope of < lTo . On I May 1992, the Ap horizon (= 15 cm depth) was removed with an excavator to simulate erosion. On 26 May 1992, amendment treatments were incorporated to l0 cm with a rototiller. Plots (10 x 6 m) were affanged in a randomized complete block design with four replications of 14 treatments. However, only three replicates were used for this aspect of the study.
The treatments included six animal manure amendments:
fresh, old or composted cattle manure, cattle manure + wood shavings, hog manure, or poultry manure. There were four crop residue amendments: alfalfa (Medicago sativa L.) hay, pea (Pisum sativum L.) hay, barley (Hordeum vulgare L.) straw + 200 ke ha-l of N, or barlev straw + 200 kg ha-l of P. There werE also two phosphate fertllizer amendments: 200 or 400 kg ha-l of p. Eroded check (topsoil removed, no amendment), and topsoil check
(no topsoil removed, no amendment) treatments
were
included for comparison.
The hog manure and poultry manure contained large amounts of wheat straw. The old cattle manure was from the same source as the fresh material but had been stockoiled for 2-3 yr. The composted manure came from a diffirent
source, and had been composted for 1 yr in large windrows which were regularly aerated. The alfalfa hay, pea hay and barley straw had been harvested and baled in summer 1991. All amendments were applied at a rate of 20 Mg ha-l 1dry
weight). Samples of amendments were finely ground (< 150 pm) and total C, total N and CA.{ ratios (Table 1) determined in an automated elemental atalyzer (Carto Erba,
Milan,Italy). Spring wheat (Triticum aestivum L.) was direct seeded on 3 June I992,but was destroyed by a severe hail storm on 2 August l992.The hail-damaged crop was chopped with a flail-mower and left on the soil surface. On 20 May 1993, (1 yr after amendment application) a composite surface (= 0-2.5 cm depth) soil sample of 4-5 kg was taken from each plot (14 treatments x 3 replicates = 42 samples) with a flat shovel. After air-drying for 24 h, the samples were gently sieved and the 1- to 2-mm diameter aggregates retained for wet aggregate stability analysis by a modification of a wet-sieving method described by Kemper and Rosenau (1986). This method uses 4 g of aggregates and a single sieve with an opening of 0.26 mm.
Table 1. Total C concentrations, total N concentrations and for organic amendments Amendmenl
Total C (g kg-r)
C/1.{
ratios
ca{
Total N (g kg-t)
ratio
Fresh cattle manure
296
18.8
15.7
Old cattle manure
129
14.3
9.0
Composted cattle manure
100
9.7
10.3
Cattle manure + wood shavings
330
8.3
39.8
Hog manure
358
23.9
15.0
Poultry manure
315
39.6
8.0
Alfalfa hay
413
26.5
15.6
Pea hay
397
26.0
15.3
Barley straw
474
4.3
96.3
Wet stability analysis was conducted on air-dry aggregates (0.03-{.04 kg kg-1 moisture) and on aggregates pre-
to four different moisture contents [0.09-0.11, 0.16-0.18, 0.24-0.26 or 0.31-0.36 kg kg-l (saturation)1. As the surface few mm of soil are often close to air-dry in semiarid southem Alberla, wet stability determination of air-dry aggregate samples reflects the behaviour offield aggregates wetted
subjected to sudden wetting (e.g., at the onset of a thunderstorm). Truman et al. (1990) showed that an increase in initial water content increases the resistance of an aggregate to the forces of raindrops and flowing water, thereby lessening particle detachment and greatly influencing soil erosion rates during rarnfall. Therefore, pre-wetting simulates field scenarios where surface aggregates are wet prior to the onset of a potential erosion event. The four levels of pre-wetting were achieved by subjecting the aggregates on the sieves to a distilled water vapour sffeam for periods of 6, 1 l-13, 78-20 and 28-30 min. Each sieve was then sealed in an airtight container and the prewet aggregates were allowed to equilibrate for about 18 h. All aggregates (two sub-samples from each plot) were sieved in distilled water for 5 min using an apparatus with a stroke length of 1.3 cm and a frequency of 35 cycles min-l. The material passing through the sieve (unstable aggregates) was oven-dried at 110"C. Sand particles > O.26 mm were separated from the material remaining on the sieve (stable aggregates) with a dispersing solution containing sodium hexametaphosphate. The stable material was then ovendried. Aggregate stability was calculated as the mass of stable aggregates expressed as a percentage of the total mass (stable + unstable aggregates). Sub-samples of 1-2 mm aggregates were finely ground (< 150 pm) and analyzed for total C content using an automated elemental analyzer (Carlo Erba). Inorganic C content was determined by measuring CO, evolved upon addition of 0.5 N HCI (Tiessen et al. 1983), and organic C was calculated as the difference between inorganic and total C.
The data were analyzed using the General Linear Models (GLM) procedure (SAS Institute Inc. 1989) wirh orthogonal contrasts for the tlree groups of amendments (six animal manure treatments, four crop residue treatments and three fertllizerlcheck treatments). The two phosphate fertllizer treatments (inorganic amendments) and the eroded
SUN
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SOIL AMENDMENTS AND WATER.STABLE AGGBEGATION 321
check comprised the fertllizer/check group. The topsoil check treatment was not used in orthogonal contrasts as it was nrct an amendment treatment or a desurfaced treatment.
moisture contents. This may have been due to its higher straw content.
RESULTS AND DISCUSSION The barley straw + 200 kg ha-l P treatment resulted in the higher;t stability at all levels of aggregate wetness except air-
dry (Iable 2), and was significantly different from
the
ha-l of P at all levels of aggregate wetness. One year after incorporation, barley straw had increased the stability of ther desurfaced soil by 15.5Vo at the air-dry aggregate
200
ed in significantly higher stabilities than old cattle manure' Hog manure gave significantly higher stabilities than the three types of cattle manure at the two lowest aggregate
k1g
moisfirre content, l9.lVo at 0.09-0.11 kg kg-r, 12.57o at 0.16-11.18 kg kg-1, 5.5Va at0.24-0.26 kg kg-t and 5.l7o at saturated moisture content (Table 2). In sremi-arid areas like southern Alberta, moisture content of surface aggregates is quite likely to be in the range where maxirnum increases in stability due to straw incorporation
occurred (air-dry to 0.11 kg kg-l). In addition to physical protection from raindrop impact, the higher stability of airdry aggregates on the surface of the straw-amended soil would help them withstand slaking forces during rapid wetting at the onset of a rainstorm. Their higher stability at the 0.09-0.11 kg kg-l moisture content suggests that with initial slow wetting (e.g., light rainfall) these aggregates could maintain much of their structural integrity (82.97o, Table 2) compared with the equivalent treatment without barley straw (63.27o, Table 2). Cattle manure + wood shavings and old cattle manure were the only organic treatments that did not significantly increase stability of air-dry aggregates over that ofthe eroded check treatment (Table 2). Among the animal manure treatments, there was no significant difference between fresh, old and composted cattle manure except at the two wettest pre-wetting levels, when composted manure result-
Avnimelech and Cohen (1989) concluded that amendments with C/N ratios between 15 and 40 resulted in the greatest soil structural improvement. Microbial polysaccharide production, which aids soil aggregation (Lynch 1981)' is reJtricted by a deficiency of organic C in substrates with a CA.{ ratio < 15. At CA'{ ratios of 15-40' organic carbon supply su{passes microbial demands for protein production. Too wide a C/N ratio (> 40, i.e., N supply very low), results
in low microbial activity and hence low microbial polysac-
charide production. Our results are in general agreement with these findings. Old cattle manure' composted manure and poultry manure had CA{ ratios of 8-10 (Table 1) and these treatments had an average air-dry aggregate stability of 36.I%o (Table 2). Fresh cattle manure, hog manure, alfalfa hay and pea hay had CA{ ratios of 15-16 and these treatments resulted in an average stability of 44'57o. The cattle manure + wood shavings had a C/N ratio of 40 and a resulting soil aggregate stability of 31.27o. However, the barley straw treatments, which had a C/N ratio of 96, resulted in the hiehest asqregate stabilities whether supplemented with ZOb tg ha:l-ofJ.l GBVo) or without N (barley straw + 200 kg ha-l P, 45.4Vo). This may mean that microbial polysaccharide production was not the main mechanism of soil stabi-
lization on these treatments. The crop residue treatments resulted in significantly higher stabilities than the animal manure treatments and fertilizerlcheck treatments at all five levels of aggregate moisture (Table 2). The animal manure treatments had signihcantly hisher stabilities than the ferlllizerlcheck treatments at the
Table 2. Effect of amendment on aggregate stability at fiYe water contents Aggregate water content Amendment
Air-dry
0.09-{.11 kg kg-r
0.164.18 kg kg-r
3'7.6
84.1
l.a
63.4 66.9 68.5 66.6
46.2
77.4
89.2
39.5
72.7
89.2
0.24-{.26 kg kg-l
Satulated
92.1 89.7 94.6 88.9
93;7 90.3 93.9 92.7 95.2
(vo)
Fresh cattle manure Old cattle manure Composted cattle manure Cattle manure + wood shavings Hog manure Poultry manure
32.3 36.6 -)
8'7.4
86.1 82.9
95.9 94.3
92.2
91.5
91.0
85.4
92.6 90.7
85.7
91.8
93.6
4.6
4.1
J.J
NS
NS
NS
45.7
78.1
92.2
Pea hay
48.3
'75.3
90.2
45.4
82.9 81.1
96.1
48.0 29.9 28.6 28.5
63.2
65.9 58.0
83.6 83.8
200 kg ha-1 P
400kgharP Eroded check
Topsoil check LSD (P = 0.0s) Significance of contrasts Animal vs. crop Animal vs. fertilizer/check Crop vs. fertilizer/check
26;7 6.8
68.9 6.2
92.2
94-8 94.0 97.7 94.4
Alfalfa hay Barley straw + 200 kg ha I P Barley straw + 200 kg he I N
94.0 92.4
9r.2
96.6 95.6
94.5
322
CANADIAN JOURNAL OF SOIL SCIENCE
two lowest levels of aggregate moisture only. Martin (1942) found that fresh organic material, that is readily available to microorganisms, may be the most effective amendment for increasing soil aggregation. In our study, the amendments which had undergone the least microbial decomposition, the crop residues, had the greatest effect on water-stable aggregation. In comparison, the animal manures may be considered "composted" or slowly decomposable, and hence resulted in smaller increases in aggregation. Martin and Waksman (19a0) found increases in aggregation of the order alfalfa > manure > peat, as alfalfa contained the greatest amount of readily available organic material and therefore allowed more abundant growth of microorganisms. Tisdall et al. (1978) found thit easily decompoJable materials such as wheat straw, sheep manure, lucerne hay, glucose and starch increased aggregate stability, while slowly decomposable materials such as rotted wheat straw, rotted sawdust, old compost and peat moss had little effect on stability over 16 wk incubations. All amendment treatments increased soil orsanic C in the surface 2.5 cm compared with the eroded chEck ffeatment (Table 3). The increase was significant on the hog manure, alfalfa hay, fresh cattle manure, barley straw + 200 kg ha-1 of P and manure + wood shavings treatments. These amendments increased organic C to levels not significantly different from that of the topsoil check treatment. However, an important consideration is that organic C and hence aggregation may not be "permanently" improved by one application of organic material but must be maintained by continu-
ous or periodic additions of organic materials (Kladivko 1994).T\e lag time, amplitude and duration of the improvement in aggregation depends largely on the decomposition rate of the materials (Boyle et al. 1989). There were significant positive relationships between aggregate stability and organic C for air-dry aggregates (R = 0.24, P < 0.05), aggregates ar 0.09-0.11 kg kg-1 moisture content (R = 0.44, P < 0.01) and saturated aggregates Table 3. Soil organic C concentrations, May 1993 (1 yr after application
of amendments), 0-2.5 cm depth Amendment
Organic C tg kg-l)
p = 0.05). However, the low correlation coefficients imply that changes in structural stability may be observed without detectable changes in organic C, which (R = 0.31 ,
agrees with the findings of Angers et al. (1993), Carter et al.
(1994) and Hamblin and Greenland (1977). Stronger relationships between aggregate stability and organic matter
may occur if specific fractions of organic matter are correlated with stability. These fractions include fungal biomass (Angers et al. 1993; Gupta and Germida 1988), labile soil organic matter (Baldock et al. 1987), heavy-fraction carbohydrates (Roberson et al. I99l), hot-water-soluble carbohy-
drates (Haynes and Swift 1990), and the aliphatic of organic matter (Dinel et al.
hydrophobic component 1992).
Since inorganic C may act as a stabilizing agent (Allison 1968; Muneer and Oades 1989) aggregate stability/organic amendment relationships may be confounded on eroded areas by inorganic C in exposed CaCOr-rich soil. The erod-
ed check (topsoil removal, no amendment) treatment showed evidence of inorganic C as a binding agent for airdry aggregates. There was no significant difference in air-
dry aggregate stabilities of the eroded check(28.5Vo) and the
topsoil check (26.77o), (Table 2), even though the topsoil check treatment had a significantly higher organic C concgntration than the eroded check (18.5 vs. 11 g kg-l, Table 3). The eroded check treatment had an inorganic C content of 9.3 compared with 1.8 g kg-l on the topsoil check treatment, which may have offset the lower organic C content and acted as a cementing agent. In contrast, the eroded check treatment had a significantly lower stability (58%) than the ropsoil check (68.9Vo) at the 0.09-0.11 kg kg-l aggregate moisture content (Table 2). Lkely , in the pre-wet aggregates, flocculation of CaCO, (Chepil 1954) rendered it a less effective binding agent than organic C.
Increases
in
aggregate stability due
to pre-wetting
(Table 2) have long been recognized (Yoder 1936). Air-dry aggregates may explode when immersed in water due to the pressures of entrapped air in capillaries and differential swelling forces (Tisdall and Oades 1982; Grant and Dexter 1990). With vapour pre-wetting before laboratory determination of aggregate stability, water inside aggregates is held by molecular attractions and diffuse layer osmotic forces, imparting extra stability when immersed in water, as the pressure inside a capillary wedge of water between soil particles is lower than air pressure (Kemper and Rosenau 1984;
Fresh cattle manure
17.8
Old cattle manure
13.0
Composted cattle manure
t2.5
Cattle manure + wood shavings
16.6
Bullock et al. 1988).
Hog manure
18.7
Poultry manure
12.4
Alfalfa hay
17.8
Using non-linear segmented regression models (SAS Institute, Inc. 1989), our results suggest that exffa stability with pre-wetting is only imparted to a threshold moisture
Pea hay
t4.6
Barley straw + 200 kg ha-r P
16.7
Barley straw + 200 kg ha-l N
l^
a
20O kg ha-r P
12.2
400 kg ha-r P
12.5
Eroded check
11.0
Topsoil check
18.5
LSD (P < 0.05)
2.9
content which is influenced by amendment (Fig. 1). Maximum aggregate stability (AS-o) is reached at the threshold moisture content below which the moisture-stability relationship is quadratic and above which it is linear and constant (a plateau). Beyond the threshold aggregate moisture, binding and slaking forces apparently counterbalanced and maximum aggregate stability of all treatments reached similar values of > 9O7o (Fig. 1). For a valid statistical comparison of amendment effects on the relationship between aggregate moisture and
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SOIL AMENDMENTS AND WATER-STABLE AGGBEGATION 323
bR Ca
q) qJ
60 s)
r-
OO OO
\
q)
.a
q
\
40
q)
bR
4 q) qJ OO
q)
t*
OO OO
\\) s r; \ q)
bR
4 q)
s OO \) L
60
\s)
Fig. 1. Comparison of
(;
stable aggregation for the three groups of amendments (a) croP residue and felTlizer/check treatments, (b) crop residue and animal manure treatments and (c) animal manure and fertilizer/check treat-
OO
quadratic
response and plateau relationships for aggregate moisture content vs. water-
.a S
L q) cl
Thirty aggregate stability data points per treatment (five aggregate moisfure contents by two subsamples by three replications) are used in the ments.
o.rc 0.8 0.20 0.25 Aggregate Moisture, kg kg-'
0.30
o.35
0.44
reeressions.
324
CANADIAN JOURNAL OF SOIL SCIENCE
Table 4. Threshold moisture content for maximum aggregate stability for each amendment Amendment
kg kg-'
Fresh cattle manure
0.266 0.208 0.240 0.194 0.218
Old cattle manure Composted cattle manure Cattle manure + wood shavings Hog manure Poultry manure
0.194
Pea hay
0.2t9
Barley straw + 200 kg ha-r P Barley straw + 200 kg ha-l N
0.1 66 0.181
200 kg ha-] P 400 kg ha-r I Eroded check
0.231 0.220 0.266
LSD (P < 0.0s)
0.052
Significance of contrasts Animal vs. crop Animal vs. fertilizer/check Crop vs. fertilizer/check
related
0.20'7
Alfalfa hay
NS
stability, threshold moisture content values were calculated
for each of the 42 plots (14 treatments x 3 replicates)
reach maximum stability faster, hence reducing water erosion potential. Short-term changes in soil aggregation were not strongly related to organic C, indicating that organic C alone may not be a sufficiently specific measure to fully explain the relationship between organic matter and aggregate stability in this study. Stability of pre-wet aggregates was negatively
and
subjected to analysis ofvariance (Table 4). The crop residue group had significantly lower threshold moisture contents (190 kg kg-r) than the animal manure group (222 kg kg-1)
and the fertllizer/check group (239 kg kg-1). Threshold aggregate moisture for AS-,, varied from 0.166 kg kg-l for the barley straw + 200 kg iiill of p to 0.266 kg kg:t ior the eroded check treatment (Table 4). These laboratory findings have implications for amendment effects on aggregate moisture/stability relationships in the field. With the onset of rainfall, aggregates on the crop residue-amended treatments would reach maximum stability sooner than those of the animal manure group and the fer-
tilizerlcheck group, thereby decreasing the potential for water erosion.
CONCLUSIONS
On a desurfaced Dark Brown Chernozemic soil, crop residue amendments were more effective than animal manures or fertilizer in increasing water-stable aggregation one year after incorporation. Incorporation of crop residues into an eroded surface increased stability of air-dry aggregates from 28.57o (eroded check) to 46.97o (average of four crop residue treatments) and stability of 0.09-{.11 kg kg-l
moisture content aggregates from 58 to j9.4Vo. Incorporation of animal manures increased air-dry aggre-
gate stability from28.57o (eroded check) to 37 .2Vo (average
of six animal manures) and stability of 0.09-{.11 kg kg-l aggregates from 58 to 69.2Vo.
Significant (P < 0.001) quadratic response and plateau relationships between aggregate stability and aggregate soil water content showed there was a threshold moisture content for maximum aggregate stability. The threshold moisture content was lowest for crop-residue amended treatments, indicating that with the onset of rainfall they would
to inorganic C, possibly due to flocculation of
CaCOr, weakening its role as a binding agent. Eroded soils amended with crop residues are more likely to resist further wind and water erosion than soils amended with animal mamues or chemical fertilizers, at least in the first year after amendment. However, the effects of organic residues on aggregate formation are intimately linked with the decomposition rate of the residues. Materials that decompose quickiy (e.g., crop residues) may produce a rapid increase in aggregation, but then a rapid decline to former conditions, whereas residues that decompose more slowly may produce a smaller but longer-lasting improvement in aggregation. Crop residue incorporation is an effective and possibly better alternative to animal manures for stabilizing eroded soils in areas where hauling distances make application of animal manure uneconomical. However, the magnitude and longevity of crop residue effects on eroded soils compared to those of animal manures requires further study.
ACKNOWLEDGMENTS
This study was supported by the Alberta Agricultural Research Institute's Farming for the Future Research Program (Project no. 920118). H. Sun thanks the Canadian International Development Agency (CIDA) for a visiting fellowship to the Lethbridge Research Centre as part of the China-Hebei Dryland Project. Allison, F. E. 1968. Soil aggregation some facts and some fallacies as seen by a microbiologist. Soil- Sci. 106: 136-143. Angers, D. A., Samson, N. and L6gbre, A. 1993. Early changes in water-stable aggregation induced by rotation and tillage in a soil under barley production. Can. J. Soil Sci. 73: 51-59. Avnimelech, Y. and Cohen, A. 1989. Use of organic manures for amendment of compacted clay soils. IL Effect of carbon to ryfuogen ratio. Commun. Soil Sci. Plant Anal. 20 1635-1644, Baldock, J. A., Kay, B. D. and Schnitzer, M. 1987. Influence of cropping practices on the monosaccharide content ofthe hydrolesates of a soil and its aggregate fractions. Can. J. Soil Sci. 67: 489499. Boyle, M., Frankenberger, W. T. and Stolzy, L. H. 1989. The influence of organic matter on soil aggregation and water infiltration. J. Prod. Agic.2:29U299. Bullock, M. S., Kemper, W. D. and Nelson, S. D. 1988. Soil cohesion as affected by freezing, water content, time and tillage. Soil Sci. Soc. Am. J.52:770-776. Carter, M. R., Angers, D. A. and Kunelius, H. T. 1994. Soil strucfural form and stability, and organic matter under cool-season perennial grasses. Soil Sci. Soc. Am. J.58: 1194-1199. Chepil, W. S. 1951. Properties which influence wind erosion. IV. State of dry aggregate structure. Soil Sci. 72: 387401.
Chepil, W. S. 1954. Factors that influence clod structure and erodibility of soil by wind: III. Calcium carbonate and decomposed organic matter. Soil Sci. 77: 473480. Dinel, H., L6vesque, P. E. M., Jambu, P. and Righi, D. 1992.
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SOIL AMENDMENTS AND WATER-STABLE AGGBEGATION 325
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