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Agriculture and Agri-Food Canada, P.O. Box 3000, Lethbridge, AB, Canada T1J 4B1
* Corresponding author (millerjj{at}em.agr.ca)
Received for publication May 21, 2001.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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0.05) increased soil water retention (0–5 and 10–15 cm) by 5 to 48% compared with the control at most potentials between 0 and -1500 kPa. Field soil water content (0–5 and 10–15 cm) was increased by 10 to 22% in the summers of 1997 and 1998. Manure increased ponded infiltration by more than 200% at 90 Mg ha-1 under dryland (1998) and at rates 
120 Mg ha-1 under irrigation (1997). Field-saturated hydraulic conductivity (Kfs) of surface soil (1-cm depth) was significantly increased by 76 to 128% under dryland (1998) and irrigation (1997), as were number of pores > 1120 µm in diameter (37–128% increase). In contrast, manure rate had little or no effect on unsaturated hydraulic conductivity [K(
)] values (-0.3, -0.5, -0.7, and -1.0 kPa) in 1997 and 1998. Overall, soil hydrological parameters generally had a neutral or positive response to 24 yr of annual manure addition.
Abbreviations: EC, electrical conductivity • Kfs, field-saturated hydraulic conductivity • K(), unsaturated hydraulic conductivity • PAW, plant-available water • SAR, sodium adsorption ratio
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Water content or potential is the key variable of the soil physical parameters directly related to crop productivity (Letey, 1985). Most studies have reported an increase in soil water retention (Hafez, 1974; Unger and Stewart, 1974; Salter and Williams, 1969; Mbagu, 1989; Rose, 1991; Schjønning et al., 1994; Benbi et al., 1998) or plant-available water (Salter and Williams, 1969; Rose, 1991; Mbagwu, 1989) under beef cattle manure or farmyard manure application, but variable responses have been reported for the latter parameter (Sommerfeldt and Chang, 1987). Few studies have measured seasonal changes in field soil water content under beef cattle manure. N'Dayegamiye and Angers (1990) reported significant improvements in field water content with manure addition using the neutron probe method, but did not report seasonal changes under manure. Martens and Frankenberger (1992) measured seasonal changes in gravimetric soil water under hog manure addition (25 Mg ha-1), and found that hog manure increased soil water 3% compared with the unamended soil. Improved water storage under manure has been attributed to changes in soil aggregation and structure, total porosity, and pore-size distribution caused by organic C addition, as well as the direct effect of greater water adsorption by the high specific surface area of organic C (Khaleel et al., 1981; Sweeten and Mathers, 1985; Boyle et al., 1989; Haynes and Naidu, 1998).
Organic amendments such as manure are reported to increase soil organic matter, which binds soil particles together into aggregates, and this improved soil structure favors the downward flow of water into soil (Boyle et al., 1989). There is little information on the effect of manure on infiltration rate and hydraulic conductivity of soils (Khaleel et al., 1981). In particular, we could not find any studies in the literature that measured unsaturated hydraulic conductivity under manure application. Previous researchers have reported no response (Sommerfeldt and Chang, 1987) or a positive response (Mazurak et al., 1975; Mathers et al., 1977; Ekwue, 1992) of infiltration rate to manure application. Similarly, manure rate had no effect (Sommerfeldt and Chang, 1987) or increased (Tiarks et al., 1974; Benbi et al., 1998) saturated hydraulic conductivity (Ksat). Some researchers reported no effect on Ksat after one initial wetting of soil, but found a positive effect after two to five wet and dry cycles (Hafez, 1974). The latter authors attributed the increased Ksat values of beef manure to straw fibers > 1 mm.
The pore-size distribution determines the rate of movement of air and water into and through soil (Boyle et al., 1989). The volume of large pores (macropores) increases with improved aggregation (Allison, 1973), and more macropores favor high infiltration rates, good tilth, and adequate aeration for plant growth (Boyle et al., 1989). There are few studies on the effect of manure addition on pore-size distribution. Pagliai et al. (1987) found that poultry manure increased pores 30 to 500 µm and those >500 µm. Rose (1991) found a decrease in macroporosity (volume of water for cores equilibrated at -5 kPa) and an increase in microporosity (total porosity minus macroporosity). Schjønning et al. (1994) reported that farmyard manure or slurry significantly increased the volume of pores < 0.2 and 0.2 to 30 µm at the 0- to 20-cm depth, but had no affect on pores > 30 µm.
The long-term (since 1973) manure (beef cattle) plots at the Lethbridge Research Centre provide an excellent opportunity to study the effect of long-term manure addition on soil hydrological properties. Limited information has been reported on the effect of manure on soil hydrological properties after 12 yr of annual applications (Sommerfeldt and Chang, 1987), but a more comprehensive study of the response (including seasonal changes) of various hydrological properties to longer (>20 yr) manure addition has not been reported.
The objective of this study was to determine the effect of long-term (24 yr) application of beef cattle manure on selected soil hydrological properties.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Selected hydrological properties were measured on 20 plots (4 manure rates, 5 replicates) under dryland and irrigated conditions. The soil properties measured were water retention, plant-available water, seasonal changes in field soil water content, infiltration rate, "field-saturated" hydraulic conductivity (Kfs), unsaturated hydraulic conductivity [K()], percentage of total water flux through specific pore sizes, and pore-size distribution.
Chemical Analyses
In the spring of 1997, soil samples (0- to 10- and 10- to 20-cm depths) were taken with a core auger (4-cm diameter) on each plot. The soil samples were then air-dried and a subsample was ground to <0.5 mm for organic C analysis. Total carbon was determined with the Dumas automated combustion technique (McGill and Fiqueiredo, 1993) using a CNS analyzer (Carlo Erba, Milan, Italy). Inorganic carbon was measured by the method described by Amundson et al. (1988), and organic carbon was calculated as the difference between total and inorganic C. Soil samples were taken in the fall of 1998 (0- to 15-cm depth) and electrical conductivity (EC) and sodium adsorption ratio (SAR) were determined using a saturation-paste method (Janzen, 1993). The EC was measured with a conductivity meter, and SAR was determined by measuring Ca and Mg using atomic absorption spectroscopy and Na by atomic flame emission spectroscopy (Janzen, 1993).
Physical Analyses
Undisturbed soil cores (3-cm length x 5.5-cm inside diameter, vertical orientation) were taken from the 0- to 5- and 10- to 15-cm depths every two weeks from spring to fall (1997 and 1998), and approximately every month during the winter. Bulk density was determined from the oven-dry weight and the volume of soil in the core. Volumetric soil water content was determined from gravimetric water contents and bulk density values (Topp, 1993).
Soil water retention was determined using a modified tension table method and pressure plate method (Topp et al., 1993). Duplicate undisturbed soil cores (5.5-cm diam., 3-cm height) were taken at the 0- to 5- and 10- to 15-cm depths (vertical orientation) in the fall of 1997. Soil water retention was measured on the cores using a modified tension table method (-0.2, -0.5, -1.5, -4.5, and -7.5 kPa) and pressure plate method (-10, -30, -50, -75, -100, -500, and -1500 kPa). The tension table consisted of a stainless steel tank (40-cm length x 30-cm width x 10.5-cm height) with glass beads (<53-µm diam., 5-cm-thick layer), and a water manometer to control and measure water potential. Plant-available water (PAW) was determined as the difference in volumetric soil water content between -20 (field capacity) and -1500 kPa (permanent wilting point) water potential. Water content at -20 kPa was estimated as the mean value of water content at -10 and -30 kPa. Oosterveld and Chang (1980) reported that field capacity of a Lethbridge clay loam soil should be at -22 kPa.
Tension infiltrometer and single-ring infiltrometer rates were determined during the field seasons of 1997 and 1998. A tension infiltrometer (Model no. SW-080B, 20-cm-diam. base plate; Soil Measurement Systems, Tucson, AZ) was calibrated in the spring of 1997 as outlined in the user manual and as described by Ankeny (1992). The calibration water potentials at the soil surface () were -1.0, -0.7, -0.5, -0.3, and 0.03 kPa (-97, -67, -47, -27, and 3 mm, respectively). Before tension infiltration measurements commenced, the surface crust, large soil clods, and large pieces of manure were removed from the soil surface to achieve a level surface for the tension infiltrometer (Ankeny, 1992). Measurements were made at a depth of approximately 1 cm as previously described by Miller et al. (1998). Steady-state flow rates, Qs (cm3 s-1), were determined for the wetting sequence from -1.0 to 0.03 kPa because of large lag times associated with the drainage sequence. Unsaturated hydraulic conductivity values at < 0 were estimated using the method of Reynolds and Elrick (1991). The "field-saturated" hydraulic conductivity (Kfs) was estimated at a slight positive potential (0.03 kPa) using the method (single-head analysis) of Reynolds and Zebchuk (1996). A Fortran program (W.D. Reynolds, personal communication, 2001) was used to estimate Kfs and K(). Input parameters for the program included Qs, disk radius (10.5 cm), depth of ring insertion (0 cm), shape factor (0.237 [dimensionless]), saturated hydraulic conductivity of contact sand material (0.16 cm s-1), and a soil texture-structure parameter, 
* (0.12 cm-1).
Pore-size classes for successive water potentials (using capillary rise equation), the number of pores for each pore-size range, and the percentage of total water flux through each pore-size class were estimated using the methods and equations of Watson and Luxmoore (1986). The maximum number (N) of effective pores per unit area (m2) was estimated by:
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where µ is the viscosity of water (0.01002 g cm-1 s-1), Km is the difference in hydraulic conductivity (cm s-1) between two successive water potentials, 
is the density of water (1.0 g cm-3), g is the acceleration due to gravity (980.7 cm s-2), r is the minimum pore-size radius (cm) derived from the capillary rise equation, and 10000 is a factor to convert number of pores per cm2 to number per m2. The percentage of total water flux through each pore-size class was determined as the difference in unsaturated hydraulic conductivity values at two successive water potentials divided by Kfs.
Infiltration rates were determined using the single-ring (20-cm diameter) infiltrometer method (Bouwer, 1986). The water reservoir of the tension infiltrometer served as the constant-head (approximately 10 mm) Mariotte device. Ponded infiltration was determined immediately after the tension infiltrometer measurement at 0.03 kPa, so soil water conditions were probably relatively constant and close to saturation. The temperature of the water during tension infiltrometer and single-ring infiltrometer measurements was recorded, and steady-state infiltration rates were corrected for viscosity to 20°C.
Statistical Analysis
All statistical analyses were performed using Statistical Analysis Software (SAS Institute, 1989). Population data were tested for normality and homogeneity of variances (Bartlett test) prior to performing the analysis of variance using the General Linear Model procedure (Proc GLM). If the variances were not homogenous for either the untransformed or log-transformed data, the variances were then weighted (WEIGHT statement) and used in the GLM. In most cases, a log transformation was sufficient. Arithmetic means and standard errors are reported in this paper. A protected least-significant difference (LSD) test (P 0.05) was used to determine the significance of main treatment effects for arithmetic means, logarithmic means, or arithmetic means with weighted variances. If there were other factors in the experiment (e.g., depth, year) besides manure rate, the data were analyzed separately for each level of factor involved. Some parameters (field soil water) were analyzed by season: spring (April–May), summer (June–August), fall (September–October), and winter (November–March). Correlation coefficients (r) were considered significant at P 0.05 (n = 4).
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Manure addition had no significant effect on plant-available water (PAW) at either the 0- to 5- or 10- to 15-cm depths under dryland (data not shown). The PAW was significantly reduced at rates 120 Mg ha-1 for the 0- to 5-cm depth under irrigation, and for all manure treatments at the 10- to 15-cm depth. Sommerfeldt and Chang (1987) reported a significant decrease in PAW for the 0- to 15-cm depth under dryland and irrigation after 12 yr of manure application. In comparison, other researchers have generally reported an increase in PAW with manure addition (Salter and Williams, 1969; Mbagwu, 1989; Rose, 1991). If manure increases water retention at both field capacity and wilting point, PAW is not greatly affected (Haynes and Naidu, 1998).
Seasonal Soil Water
There was a clear trend of manure addition increasing soil water content for all seasons at both depths (0–5 and 10–15 cm) under dryland and irrigation; however, significant differences were dependent on depth or season (Fig. 2)
. Manure under dryland at the 0- to 5-cm depth significantly increased soil water content by 27% in the spring at the 90 Mg ha-1 rate, and at all rates by 10 to 20% in the summer (Fig. 2). Soil water at the 10- to 15-cm depth under dryland was significantly increased by 11 to 21% for all manured treatments in the summer, and was increased by 38 to 53% at rates 60 Mg ha-1 in the fall. Manure addition under irrigation at the 0- to 5-cm depth significantly increased soil water by 16 to 22% at rates 120 Mg ha-1 in only the summer, but it was significantly increased by 10 to 29% for all manured treatments at the 10- to 15-cm depth in all seasons except winter (Fig. 2). Soil water content in the spring at the 0- to 5-cm depth under dryland was significantly and positively correlated with clay content (r = 0.98).
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Ponded Infiltration
Ponded infiltration rates ranged from 15.4 to 25.2 µm s-1 under dryland in 1997, and there were no significant differences among treatments (Table 1). Infiltration rates were between 28.3 and 95.9 µm s-1 under dryland in 1998; and the infiltration rate at 90 Mg ha-1 was significantly higher than the control by 232%. Infiltration rates ranged from 32.0 to 126 µm s-1 under irrigation in 1997, and values at 120 and 180 Mg ha-1 were significantly higher than the control by 205 and 294%, respectively. Infiltration rates were between 36.0 and 62.7 µm s-1 under irrigation in 1998, and there were no significant differences among treatments. There was a significant positive correlation of ponded infiltration with organic C content in 1997 (r = 0.99).
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Field-Saturated and Unsaturated Hydraulic Conductivity
Manure rate significantly affected Kfs under dryland in 1998 and under irrigation in 1997 (Table 2). The Kfs was increased by 76% for the 90 Mg ha-1 rate compared with the control under dryland in 1998, and it was increased by 123% at the 120 and 180 Mg ha-1 rates relative to the control under irrigation in 1997. Manure rate generally had no significant effect on K() values between -1.0 and -0.3 kPa (Table 2). The exceptions were at -0.3 kPa under irrigation in both years, where manure rates 120 Mg ha-1 increased conductivity by 137% compared with the control.
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) flux in the soils of all plots in 1997 and 1998 occurred through pores > 1120 µm in diameter, followed by pores 640 to 1120 µm (3–34%), pores 440 to 640 µm (0.7–6%), and pores 300 to 440 µm (0.4–3%) (data not shown). Since the water flow rate in soil pores (cylindrical) is proportional to the fourth power of the radius, macropore spaces will account for most of the unsaturated water movement (Brady, 1974). There was no significant treatment effect on percent water flux under dryland in both years, and under irrigation in 1997. Under irrigation in 1998, percent flux through pores 640 to 1120 µm was increased by 230% at all manure rates compared with the control. In contrast, percent flux through pores > 1120 µm under irrigation in 1998 was decreased by 17% at the 120 and 180 Mg ha-1 rates compared with the control. There were generally no significant correlations of Kfs or K() with sand, clay, or organic carbon content (data not shown). The only exceptions were a significant negative correlation of K() at -1.0 kPa with organic carbon content (r = -0.95) under dryland in 1998, and a negative correlation of K() at -0.3 kPa with sand content (r = -1.00) under irrigation in 1998.
The finding that manure treatment had little or no significant effect on K() values raises the question of whether the potential negative effect of salinity and sodicity counteracted the positive effect of organic matter. The manure applied had an EC value of 23.0 dS m-1 and a SAR value of 21.8 (Chang et al., 1991). Mean EC values of soil (0–15 cm) for the control and manured treatments under dryland ranged from 0.8 to 4.8 dS m-1 and SAR values from 1.5 to 4.7. Mean EC values of the soil under irrigation ranged from 1.1 to 3.8 dS m-1, and the SAR values from 0.9 to 4.5. Using the criteria of Ayers and Westcot (1987) for potential infiltration and hydraulic conductivity problems based on the EC and SAR of saturation extracts, none of the mean EC–SAR combinations of soil in our control or manured treatments should restrict water flow. In addition, we generally found no significant correlations between soil hydraulic properties and soil EC or SAR. The only exception was under dryland in 1998, where there was a negative correlation of K() at -1.0 kPa with SAR (r = -0.95).
Other possible factors that may have contributed to a lack of a response of K() to manure addition may have been the hydrophobic nature of manure, the good structure and finer texture of the original soil, or the lack of straw bedding. Some researchers have suggested that with high organic waste additions, the soil may become hydrophobic or water repellent and restrict infiltration (Haynes and Naidu, 1998; Olsen et al., 1970). Water-repellent organic substances produced by fungi during decomposition of manure are thought to be responsible, and a water-repellent layer of partially decomposed manure and abundant white fungal mycelia is often evident (Weil and Kroontje, 1979). However, we observed no visual evidence of this layer in our soil.
Sommerfeldt and Chang (1985) also attributed inconsistent treatment effects at this site after 5 yr of manure addition to the soil's good physical condition. The degree of improvement in soil physical condition seems to be greatest in less productive soils (Fogg, 1978). In addition, the clay loam texture of the soil may have contributed to the lack of significant differences, since improvement of soil physical condition seems to be greater for coarser-textured soils (Mbagu, 1989; Khaleel et al., 1981). Little or no straw bedding in the manure applied may partially explain the lack of a positive response of K() to manure rate. Hafez (1974) reported a greater saturated hydraulic conductivity in a sandy loam soil with 5% straw fibers separated from beef cattle manure compared with when 5% beef cattle manure was added, and attributed increased water flow to the straw fibers (>1-mm diam.) in the manure.
Pore-Size Distribution
Number of soil pores in all plots, from largest to smallest pore size, ranged from 36 to 155 m2 (>1120-µm diam.), 30 to 231 m2 (640–1120 µm), 34 to 427 m2 (440–640 µm), and 67 to 451 m2 (300–440 µm) (Table 3). Manure rate had no significant effect on number of pores for the four pore-size classes under dryland in 1997, but in 1998 the number of pores > 1120 µm was significantly higher for the 90 Mg ha-1 treatment than the control by 82%. Number of pores > 1120 µm under irrigation in 1997 was significantly greater at 120 and 180 Mg ha-1 compared with the control by 119 and 128%, respectively. Number of pores 640 to 1120 µm under irrigation in 1998 was significantly greater at 120 and 180 Mg ha-1 by 463 and 359%, respectively.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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61% of the total water flow. Greater preferential flow in macropores under saturated conditions has important implications in terms of a greater potential for leaching (assuming macropore continuity) and possible influence on ground water quality. High intensity rainstorms that cause surface ponding and saturated conditions in surface soils under long-term manure application may result in less runoff and more infiltration and percolation through these large macropores. We found that surface ponding on clay loam soils (nonmanured) in this area did not occur at rainfall intensity durations of 22 mm h-1 in 60 min, but did occur at 44 mm h-1 in 30 min and 88 mm h-1 in 15 min (Miller and Larney, 1997). These rainstorms are equivalent to annual extreme values for return periods of 2 to 5, 5, and 10 yr, respectively. Consequently, surface ponding and saturated conditions would be expected to be relatively rare occurrences, particularly in manured soils that increase ponded infiltration and saturated water flow. In contrast, manure had little or no effect on percolation of water through surface soils under unsaturated conditions, and most water flow in soils occurs when the pores are not completely saturated with water. Overall, soil hydrological parameters generally had a neutral or positive response to 24 yr of annual manure addition, and long-term application of beef cattle manure should not cause any detrimental effects to water retention and storage, water flow, or pore-size distribution. |
ACKNOWLEDGMENTS |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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