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a Dep. of Soil and Atmospheric Sciences, Univ. of Missouri–Columbia, 302 Anheuser-Busch Natural Resources Building, Columbia, MO 65211
b USDA-ARS, 246 Agricultural Engineering Building, Columbia, MO 65211
* Corresponding author (hb91d{at}mizzou.edu).
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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b), organic matter (OM), soil–water retention, and saturated hydraulic conductivity (Ksat) on a Mexico silt loam (fine, smectitic, mesic, Aeric Vertic Epiaqualf). Possible relationships between runoff and effective Ksat (Keff) were also studied. Soil properties were determined on intact cores of 76-mm diam. collected from trafficked and nontrafficked positions for the 0- to 100-mm and 100- to 200-mm depths from the Midwest Research Claypan Farm erosion plots near Kingdom City, MO. Results show that the CCF had lower b, OM, Ksat, and higher surface runoff than other treatments (P < 0.01). Tillage effects on soil properties among NT, CP, and MP were small and crop dependent. Corn had lower Ksat (7.3 mm h–1) than soybean (11.7 mm h–1; P < 0.01). Conversely, corn had slightly higher b (1.53 Mg m–3) than soybean (1.48 Mg m–3; P < 0.01). The b increased from 1.47 to 1.52 Mg m–3 and OM decreased from 15.5 to 14.0 g kg–1 with depth (P < 0.01). Wheel traffic reduced Ksat by three times and increased b by 6% (P < 0.01). Bulk density was a significant predictor of log Ksat (P < 0.01) but not for soils under CCF management. The Keff was not related to runoff with the exception of the CCF treatment, which had slightly more runoff and lower Keff (P < 0.05). Overall, tillage treatments had no significant effects on soil properties; however, cropping and WT had small significant effects on b and Ksat.
Abbreviations: CCF, continuous cultivated fallow • CP, chisel plow • Keff, effective saturated hydraulic conductivity • Ksat, saturated hydraulic conductivity • MP, moldboard plow • NT, no-tillage • OM, organic matter • USLE, Universal Soil Loss Equation • b, bulk density
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Researchers have found that long-term tillage effects on soil properties such as b, soil–water retention, and Ksat often vary by soil (Gantzer and Blake, 1978; Culley et al., 1987; Gregorich et al., 1993). For example, moldboard plowing when compared with chisel plow and no-tillage can lower b (Hussain et al., 1998; Katsvairo et al., 2002), leave b unchanged (Karlen et al., 1994; Logsdon et al., 1999) or increase b (Lal et al., 1994). No-tillage usually has been found to increase b compared with moldboard and chisel plow (Kitur et al., 1993; Lal, 1999). Bulk density usually is lowest immediately after tillage and increases with time as a result of rainfall-induced consolidation and surface sealing (Leij et al., 2002). The effects of tillage and management on soil–water retention are also often mixed. Allmaras et al. (1977) found no effect on soil–water retention at greater than –8 kPa, but no-till systems retained more water than CP systems at lower potentials for a Walla Walla silt loam (Typic Haploxeroll). Tollner et al. (1984) reported that MP resulted in greater soil–water retention than no-tillage at greater than –80 kPa but not at other potentials. Conversely, Lal (1999) found that tillage practices had no significant effect on soil-water retention at all potentials on a Wooster silt loam (Typic Fragiudalf). Tillage effects on Ksat are even more variable. The Ksat may be higher, equal, or lower for CP, or MP compared with NT (Gantzer and Blake, 1978; Gregorich et al., 1993; Karlen et al., 1994; Lal, 1999).
These findings suggest the need to improve the understanding of tillage and cropping effects on soil. Reports on long-term tillage effects on soil properties have been reported for a number of soils (Lindstrom et al., 1981; Blevins et al., 1983; Karlen et al., 1994; Lal, 1999; Rhoton, 2000). However, studies of tillage effects on properties for midwestern claypan soils are few. Claypan soils mainly comprise Major Land Resource Area 113 in Missouri and Illinois covering about 4 million ha (Ghidey and Alberts, 1998). They are highly erodible and their long-term productivity is easily degraded by erosion (Gantzer et al., 1990). These soils have an argillic horizon (clay contents > 400 g kg–1) at 130 to 450 mm deep that has very low Ksat (<2 µm h–1) that often causes large amounts of surface runoff during spring (Blanco-Canqui et al., 2002).
Burwell and Kramer (1983), Wendt and Burwell (1985), and Ghidey and Alberts (1998) reported on long-term tillage effects (
10 yr) on runoff and soil loss for claypan soils. However, information on tillage-crop effects on soil properties has not been reported. Research suggests that tillage-crop effects on b, soil–water retention, and Ksat are often soil specific (Culley et al., 1987; Lal et al., 1994; Ankeny et al., 1995). Moreover, it is important to document any relationships between soil properties such as Ksat and runoff for these soils. Work relating measured Ksat to runoff for different tillage treatments is limited (Risse et al., 1995; Blanco-Canqui et al., 2002). Furthermore, the interrelationships among b, OM, soil–water retention, and Ksat induced by long-term tillage-crop management systems are important and can help development of hydrologic models (Edwards, 1982). Tillage changes in one soil property may cause associated changes in other soil properties (Culley et al., 1987).
Studies on WT effects on soil properties in long-term tillage systems for claypan soils are also limited (Lindstrom et al., 1981; Lal, 1999). Traffic compacts soil, and often reduces Ksat and increases b (Culley et al., 1987). In some cases, traffic may have little effect (Lindstrom et al., 1981). The size of traffic-induced changes in soil properties is often site specific depending on texture, duration of tillage and crop management, equipment, and climate (Lindstrom et al., 1981). A better understanding of long-term tillage-crop systems on soil properties on claypan soils is needed to ensure the best management for these soils.
The objectives of our study are to (i) determine the impact of long-term tillage treatments of NT, CP, and MP under corn and soybean management including a control treatment of CCF on b, OM, soil-water retention, and Ksat after 13 yr, (ii) evaluate the effects of WT, and (iii) determine the possible utility of using Ksat determined on intact cores for estimating differences in runoff among the treatments.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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In 1981, plots studied in this paper were evaluated for uniformity of soil depth, texture, OM, erosion and runoff. No significant differences in these properties were found (Wendt et al., 1986). In 1982, a replicated study was initiated to examine the effects of NT, CP, and MP planted to corn and soybean, and a CCF (a check treatment) on runoff and erosion. The study initially had four replicates in a completely randomized block design with treatments remaining in the same locations over time. The results of the study are reported by Ghidey and Alberts (1998). In 1992, two blocks of the 1982 experiment were removed for other uses, resulting in a continuing experiment with seven treatments and two replicates for a total of 14 plots. The CP plots were chiseled twice before planting using a tractor weighing 3.6 Mg. Primary and secondary tillage depths were approximately 150 and 80 mm, respectively. The MP plots were plowed with a 2-bottom plow pulled with a tractor weighing 2.6 Mg a day before planting. Anhydrous ammonia was knifed in to all corn plots before planting. Each plot was planted with a four-row planter. Row spacing was 0.76 m, with rows remaining in the same location over time. A rear-mounted cultivator on the 2.6-Mg tractor was used for weed control in CP and MP plots. Wheel traffic for tractor and implements occurred between the first and second rows and between the third and fourth rows. After grain harvest, cornstalks were chopped and residues left on the soil surface. The CCF treatment was spring moldboard plowed, disked, and cultivated after major rainfall events to break soil crusts and to kill weeds. Collection of runoff and eroded sediment was terminated in April 1995, and the soil was left undisturbed for 60 d before sampling.
Intact 76 by 76 mm diam. soil cores were taken from all plots in June 1995. Three replicate cores were collected vertically from 0 to 100 and 100 to 200 mm from trafficked and nontrafficked interrow positions for a total of 168 cores. Cores were taken in an upslope plot position. A double-cylinder, hammer-driven core sampler was used to collect cores manually to ensure sampling with minimal disturbance (Blake and Hartge, 1986). Cores were sealed in 2-mil plastic bags, transported to the laboratory, and stored at 4°C for 
3 d before taking measurements. Samples were slowly wet from the bottom with de-aired tap water using a Mariotte bottle having a supply of approximately 3 mm h–1 increase in head. The EC of the water was 0.68 dS m–1, and the sodium adsorption ratio (SAR) of the water was 2.34. The Ksat was determined by either the constant- or falling-head methods where appropriate (Klute and Dirksen, 1986). An 8:1 water/bentonite slurry was used to seal macropores (1 mm diam.) and the interfacial voids between the soil sample and the core cylinder wall to minimize bypass flow. The reason for this was to eliminate the free flow of water through these voids. Elimination of bypass flow in small cores during Ksat determinations is a recommended methodology (Klute, 1965; Blanco-Canqui et al., 2002).
The high-energy soil water retention (0 to –16 kPa) was determined on intact cores using Büchner funnels by applying the desired pressure, measuring outflow, drying the cores at 35°C for 4 d, and recording the oven-dry weight (Gardener, 1986). Because drying soil at 105°C irreversibly alters soil, samples used for high-energy measurements were dried only at 35°C. A 10 g sample of 35°C-dry sample was dried at 105°C to compute its true oven-dry weight for calculation of bulk density of the entire core (Blake and Hartge, 1986). The low-energy soil water retention (–30 to –1500 kPa) was determined using a pressure plate apparatus (Gardner, 1986). Intact soil slices, 10 mm thick, were saturated in 20 by 78 mm rings placed on a ceramic plate for water retention determinations at –30,–100, and –200 kPa. For water retention determinations less than –500 kPa, soil samples were sieved through a 2-mm sieve and packed to a 10-mm depth in rings (Gardner, 1986). Organic matter was determined by dry combustion using a Leco CR-12 C analyzer (Nelson and Sommers, 1982). Samples for OM were sieved through a 2-mm sieve. Low OM samples were determined on 500-mg samples while high OM samples were determined on 250-mg for samples, and then combusted at 900°C. Organic matter was calculated by dividing the organic C using a conversion constant of 0.58.
The runoff–Ksat relationship was studied using a Keff of the cores. The Keff was calculated as
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Rainfall and runoff data from 1991 to 1995 collected on a storm-basis were used to investigate any relationship between runoff and Keff. Runoff from the 3.2 by 27.6 m plots was collected in a series of two tanks. When the first tank was filled, runoff then flowed through a nine-slot divisor and 1/9th of runoff was then collected in the second tank (Ghidey and Alberts, 1998). The combined tank-series can collect a maximum of 180 mm of runoff. After a runoff event, the sediment-runoff mixture volume was measured and then stirred thoroughly into suspension to obtain three triplicate 1-L samples for sediment concentration determination gravimetrically (Brakensiek et al., 1979). Only runoff data collected from harvest until spring tillage was used in the analysis to ensure that the soil conditions were similar to those of the soil cores collected for Keff determination. This corresponds with the USLE crop stage Period P4 "Residue or Stubble," (Wischmeier and Smith, 1978). In 1995, runoff measurements ceased in April. Snowmelt runoff and rainfall runoff that occurred on frozen soil were excluded from the study. Snowmelt runoff was excluded according to the USLE guidelines to evaluate the runoff-Ksat relationship by rainfall-event size. Cumulative runoff for all storms during Period P4 was calculated and used to study any relationship with Keff. In addition, a select group of medium rainstorms (those between 13 and 54 mm) during Period P4 was created from the data that would be expected to reflect the greatest treatment effect related to soil Keff. Small rainstorms (<15 mm) produce little or no runoff. For large rainfall events (>50 mm), rainfall greatly exceeds infiltration capacity diminishing any differences among treatments to a small fraction of observed runoff, making differences small. Runoff associated with these medium rainstorms was summed over the four seasonal periods (1991-1995) and used in analyzing any relationship between cumulative runoff and Keff.
A split-split plot design was used for analysis, with tillage as the main effect, WT as the first split, and depth as the second split. Six, single-degree of freedom contrasts, were used to test differences among tillage and crop treatments. The contrasts were: (i) NT vs. the average of MP and CP [NT vs. (MP + CP)], (ii) MP vs. CP, (iii) Corn vs. Soybean, (iv) an interaction of tillage with crop [NT vs. (MP + CP) x Crop], (v) an interaction of MP vs. CP with crop [(MP vs. CP) x Crop], and (vi) CCF vs. (NT + MP + CP). Computations were done using SAS statistical software (SAS Institute, 1999). Stepwise regression was conducted to evaluate relationships of log Ksat with b, OM, and macroporosity (pores that drain at greater than –2 kPa of soil–water potential). Mean data were depicted using box-whisker plots.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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b values for all treatments, traffic positions, and depths and the summary of the analysis of variance (ANOVA) are presented in Table 1. The b values averaged across depths for trafficked and nontrafficked zones are given in Fig. 1
. Tillage effects on b among NT, CP, and MP were not significant. The small effects depended on the crop as shown by the interaction [NT vs. (MP + CP)] x Crop (P < 0.01; Table 1). The interaction shows that NT in soybean had a slightly lower b (1.47 Mg m–3) than the average of MP and CP tillage (1.49 Mg m–3), whereas NT in corn had greater b (1.55 Mg m–3) than the average of MP and CP (1.52 Mg m–3; Table 2). The relative higher b found in NT corn in this study agrees with an 8-yr tillage study that showed higher b in NT (1.39 Mg m–3) than in MP (1.31 Mg m–3) on a Grantsburg silt loam (Typic Fragiudalf; Hussain et al., 1998). The tillage by crop interaction for b [(MP vs. CP) x Crop] was significant (Table 1). The interaction reflects the fact that b of MP in corn (1.53 Mg m–3) was slightly higher than the b of CP (1.50 Mg m–3), whereas MP in soybean (1.48 Mg m–3) was slightly lower than CP (1.49 Mg m–3). The MP in corn was slightly more compact than CP, but this was not the case for soils under soybean.
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b (P < 0.01; Table 1). Corn resulted in slightly higher b (1.53 Mg m–3) than soybean (1.48 Mg m–3). We speculate that this may be a result of the differential soil water content at the time of planting that influences soil compaction. Less surface residue occurred with soybeans compared with corn (Gantzer et al., 1987) allowing soil to dry more thoroughly before planting, thus reducing the potential for compaction. The largest tillage effect occurred from the CCF treatment. The CCF averaged across traffic and depth had the lowest b (1.44 Mg m–3), which was highly significant (P < 0.01) as shown in Table 1. This is attributed to the continuous loosening by tillage.
Wheel traffic had a significant effect on b (P < 0.01; Table 1). Figure 1 shows that soils under the wheel trafficked interrow had higher b (1.54 Mg m–3) than nontrafficked interrows (1.45 Mg m–3). This agrees with results from Vervoort et al. (2001) who found higher b (1.49 Mg m–3) in trafficked vs. nontrafficked zones (1.43 Mg m–3) on a Grenada silt loam (Oxyaquic Fraglossudalfs). Another study on a Capac loam (Aeric Ochraqualfs) reported that WT increased b by 29% in tilled soils (Pierce et al., 1994). The higher b in trafficked positions implies soil consolidation and reduction of macropores resulting in decreased soil porosity; however, it is not likely to reduce plant root growth as it is below the growth limiting value of b (1.55 Mg m–3; Radcliffe et al., 1988).
The depth effect on b was significant (P < 0.01; Table 2). The b at the 0- to 100-mm depth was lower (1.47 Mg m–3) than at the 100- to 200-mm depth (1.52 Mg m–3) for all treatments. Lower b at the upper depth is commonly due to the greater amounts of organic material near the surface, lower overburden pressure, and greater disturbance. The increase of b with depth is consistent with a study on a Maury silt loam soil (Typic Paleudalfs) by Ismail et al. (1994) who showed that b under NT and MP in corn decreased with depth after 20-yr of tillage.
Our results show that tillage effects on b were small; however, crop had a significant effect where corn increased b compared with soybean. Differences in b among NT, CP, and MP were not significant and would not limit crop production.
Organic Matter
Geometric means of OM values and the ANOVA summary are shown in Table 2. Values for all treatment-depths averaged across traffic are presented in Fig. 2
. Normality tests showed that OM data were nonnormally distributed (P < 0.01). Since a logarithmic transformation improved the normality, statistics were conducted on log-transformed OM data. The tillage by crop contrast of NT vs. the average of CP and MP and the interaction [NT vs. (MP + CP)] x Crop was significant (P < 0.04; Table 2). The interaction of tillage treatments with crop is illustrated by the fact that NT in corn (19.3 g kg–1) had higher OM than the average of the MP and CP treatments (14.8 g kg–1), but not in soils under soybean. The greater amount of corn residues in NT increased OM content in contrast with soils in soybean. The higher OM in NT corn agrees with studies conducted for other silt loam soils. Blevins et al. (1983) reported that after 10-yr of continuous tillage, NT in corn had higher OM content (47 g kg–1) than MP (24 g kg–1) on a Maury silt loam (Typic Paleudalfs). After 4-yr tillage, Rhoton (2000) also showed that NT soils in corn had higher OM (32 g kg–1) than MP soils (19.1 g kg–1) at the 0- to 25-mm depth on a Grenada silt loam (Glossic Fragiudalfs). The higher OM content in NT corn (19.3 g kg–1) is a result of corn residue near the soil surface. In contrast, inverted crop residues in MP treatments are mixed throughout the depth of tillage.
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Wheel traffic had no effect on OM (Table 2). As expected, WT would not significantly affect OM (Pierce et al., 1994; Lal, 1999). The OM distribution was significantly influenced by depth (P < 0.01; Table 2). The OM averaged across tillage-crop and traffic at the 0- to 100-mm depth (15.5 g kg–1) was significantly higher than at the 100- to 200-mm depth (14.0 g kg–1). This is caused by the greater concentration of OM near the soil surface (Pierce et al., 1994; Rhoton, 2000).
Soil–Water Retention
Soil–water retention data averaged across crop, WT, and depth for all treatments are given in Fig. 3A
, and soil–water retention data for trafficked and nontrafficked zones in CCF are presented in Fig. 3B. Analysis of variance results for –4 kPa are given in Table 3. Because differences were greater at high-energy potentials, only data greater than –100 kPa are plotted in Fig. 3. Tillage and cropping effects on soil–water retention among NT, CP, and MP were not significant. In contrast, tillage effects on CCF were significant (P < 0.05). Comparison of regression lines in Fig. 3A between CCF and the average of NT, CP, and MP treatments using analysis of covariance showed that the slopes of the lines were not significantly different (P > 0.07) and the elevations of the regression lines differed (P < 0.05; Snedecor and Cochran, 1989). Results indicated that CCF retained more water than the average of NT, CP, and MP at high-energy soil–water potentials (P < 0.01). The water content for CCF was approximately 4% higher at –1 kPa and approximately 2% higher at –100 kPa as compared with the average for NT, CP, and MP (Fig. 3A). Continuous cultivation increases fine pores, lowers OM content, and destroys macropores (Jordan et al., 1997; Hussain et al., 1998).
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Depth had a significant effect on soil–water retention only at –4 (P < 0.01) and –1.5 MPa (P < 0.05) of soil–water potential. Mean water content averaged across tillage-crop and traffic was 0.36 mm mm–3 at the 0- to 100-mm depth and 0.39 mm mm–3 at the 100- to 200-mm depth for the –4 kPa, while the averaged values for the –1.5 MPa were 0.12 mm mm–3 at the 0- to 100-mm depth and 0.14 mm mm–3 at the 100- to 200-mm depth. The greater soil–water retention at the lower depth may be due to higher proportion of micropores and more compaction compared with the upper depths (Radcliffe et al., 1988). Overall, the effects of tillage-crop, WT, and depth on soil–water retention were small, and differences were not significant in most cases except for CCF that retained the highest amount of water of all treatments for high energy soil–water potential.
Saturated Hydraulic Conductivity
Geometric means of Ksat and the related ANOVA summary are presented in Table 3. The geometric mean Ksat values averaged across depth for trafficked and nontrafficked positions are presented as a box-whisker plot in Fig. 4
. Data were found to be significantly nonnormal (P < 0.01). Therefore, statistical analysis was performed on log-transformed values. No differences were found for the single-df contrast of NT vs. (CP and MP) averaged across traffic, depth, and crop (P = 0.57).
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The type of crop grown had a significant effect on Ksat (P < 0.01; Table 3). The Ksat under soybean management (11.7 mm h–1) was 1.6 times higher than under corn management (7.3 mm h–1). The Ksat differences may be partially explained by the lower b in soybean and higher b in corn. The Ksat was negatively correlated with b (r = –0.54, P < 0.05). Mankin et al. (1996), while investigating the cropping effects on soil properties in the major corn and soybean production regions in the USA, found higher Ksat in soybean than in corn particularly in clay soils. While crop residue from soybean is only about 50% of that from corn, soybean residues have a greater proportion of soluble compounds, lower cellulose, and are more easily decomposed into humidified organic compounds interacting with soil particles and probably improving soil aggregation and water infiltration (Broder and Wagner, 1988).
The Ksat for CCF was five times lower (1.9 mm h–1; P < 0.01) than the average of the other treatments (9.5 mm h–1). This lower Ksat reflects the impact of frequent cultivation on reducing the OM, and thus deteriorating soil aggregation and destroying macropores (Radcliffe et al., 1988; Jordan et al., 1997). Because of the lower Ksat, less infiltration and higher runoff are expected from CCF management compared with NT, CP, and MP tillage.
Wheel traffic reduced Ksat in all tillage treatments (P < 0.01). Figure 4 shows that Ksat in nontrafficked zones averaged across tillage, crop, and depth was 3.1 times higher (14.3 mm h–1) than Ksat in trafficked zones (4.4 mm h–1). The higher Ksat values in nontrafficked positions are in accord with Culley et al. (1987) who found that nontrafficked Ksat was nine times higher than trafficked Ksat on a Webster silty clay loam. The reduction of Ksat from equipment traffic is caused primarily by soil surface consolidation associated with increased bulk density and reduced soil porosity. Lindstrom et al. (1981) on a Nicollet clay loam (Aquic Hapludolls) found that WT reduces the random roughness of the soil surface and compacts the plow layer resulting in decreased water infiltration rates.
In general, the Ksat did not vary significantly with depth (Table 3). The Ksat averaged across tillage, crop, and traffic was 9.4 mm h–1 in the 0- to 100-mm depth, and 9.2 mm h–1 in the 100- to 200-mm depth. Our results agree with Lal (1999) who found no Ksat differences with depth under NT, CP, and MP management after 5-yr tillage in Ohio. Unlike b, the Ksat distribution with depth did not change significantly.
Effects of 13-yr continuous tillage management on Ksat were for the most part small, but cropping system had a significant effect on Ksat. The nonsignificant changes in Ksat found in this study suggest that long-term NT, CP, and MP management in claypan soils would not be expected to affect crop production. The main finding was that the CCF treatment reduced Ksat by five times (P < 0.01).
Interrelationships of Soil Properties
Investigation of relationships of log Ksat with b, OM, and macroporosity among NT, CP, and MP treatments using regression showed that b was the only significant variable related with log Ksat. The relationship found was:
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The intercept and the slope for the NT, CP, and MP treatments were significant at P < 0.01. The negative slope implies that the conductivity would decrease with increasing b. The ability for b to predict log Ksat in NT, CP, and MP treatments is corroborated by work of Edwards (1982). However, it was found that the regression of b on log Ksat for the CCF treatment was not significant (P > 0.10). Despite the fact that this treatment had lower bulk densities, the conductivities were often the lowest. The fact that b was not significantly related to conductivity for the CCF is at odds with knowledge that low b is often related to increased Ksat. We attribute this behavior to structural instability of soil aggregates in the CCF treatment due to intensive cultivation, which decreased OM, and weakened soil aggregates. On wetting, aggregates slump, causing decreased pore continuity, thus lowering Ksat. Overall, macroporosity was highly correlated with b (r = –0.83) and moderately correlated with conductivity for all treatments (r = 0.44). An interesting finding is that b and Ksat in the CCF treatment were the lowest of all tillage-crop treatments. In contrast, NT, CP, and MP management had no significant differences in b and Ksat.
Runoff–Keff Relationship
The graphs of cumulative runoff versus log Keff for the tillage-crop treatments in January through April 1995 and during the Period P4 in 1991 through 1995 are depicted in Fig. 5
. The runoff–Keff linear regression using cumulative runoff data from January to April of 1995 where soil conditions would be nearly the same as those during our soil sampling date (14 June 1995) showed no relationship between runoff and Keff (r2 = 0.01). In addition to the above analysis, an investigation of a longer-term runoff–Keff regression was conducted using cumulative runoff data from 1991 through 1995. The linear regression indicated that Keff was not related to runoff from NT, CP, and MP under corn and soybean for all runoff events and rainfall storm sizes between 1991 through 1995 (r2 = 0.10). For medium rainstorms (between 13 and 54 mm), the linear regression r2 increased but was not significant (r2 = 0.15; Fig. 5).
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The limited relationship between runoff vs. Keff in NT, CP, and MP agrees with Edwards (1982) who reported that Ksat is not as sensitive a variable as precipitation, and antecedent soil moisture for predicting runoff. The reasons for the limited relationship in this study may be attributed to (i) temporal variability of Keff in tillage systems, and (ii) low claypan conductivity. The dynamic temporal variability of tilled soils may create difficulties in establishing a surface runoff vs. Keff relationship. The Keff may be more related to runoff immediately after tillage when differences in surface physical properties between tilled and no-till soils are great. Tillage loosens the soil and creates unstable structure increasing the Keff and reducing runoff after tillage relative to no-tillage that remains consolidated over time. However, tillage effects on soil surface conditions dissipate rapidly with time as external forces (traffic, overburden pressure, rainfall-induced consolidation, and surface sealing) take place. Tilled soils may thus be physically similar to no-till, as the residual effects of tillage diminish within 21 to 28 d. Or et al. (2000) and Leij et al. (2002) affirmed that soil immediately after tillage is highly unstable and undergoes dynamic changes in the interaggregate porosity significantly altering the hydraulic properties. The Ksat after plowing can be one or two orders of magnitude higher compared with Ksat measured before tillage. Such Ksat changes diminish with time as the natural structural pore system gradually evolves. Our soil samples were collected almost a year after primary tillage, and thus differences in initial soil conditions among NT, CP, and MP would have diminished.
An understanding of the Keff variations by crop-stage period, and seasonal variations induced by management would be desirable. An important factor reducing differences in runoff among treatments is related to the claypan soil that has a nearly impermeable claypan at approximately 230 mm (Ksat 0.003 mm h–1). The low claypan Ksat limits downward water movement and redirects the flow laterally into interflow (Blanco-Canqui et al., 2002). Indeed, runoff rates are equal to precipitation when these soils are saturated particularly in spring (Saxton and Whitaker, 1970). Thus, claypan Ksat is the main control that inhibits vertical water flow. This would be expected to have a significant influence on the surface runoff vs. Keff relationship. Assessment of soil parameters that are sensitive to tillage and crop management changes in soil structure such as least limiting water range may help to evaluate tillage management impact effects on hydraulic properties (Da Silva et al., 1994).
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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b, OM, soil–water retention, and Ksat occurred from the NT, CP, and MP treatment under corn and soybean management. Results suggest that the tillage systems are of little importance to soil properties in claypan soils, and thus would not greatly affect crop production. However, the CCF treatment had a major effect on soil properties decreasing Ksat, b, and OM in contrast to NT, CP, and MP. This confirms the idea that excessive tillage has a deleterious effect on soil properties.
The kind of crop (corn vs. soybean) had a greater effect on soil properties compared to tillage. Soils in corn had decreased Ksat, and increased b and OM as compared with soils in soybean. Increased compactness of soils in corn may significantly reduce saturated water flow while increasing OM in claypan soils. Tractor WT caused soil consolidation and reduced saturated water flow. No consistent relationship between runoff and effective Ksat for NT, CP, and MP treatments was identified. Thus, Ksat determined on small intact cores was not a significant predictor of runoff. However, runoff from excessively tilled plots (CCF) was related to effective Ksat where runoff increased. The b was a significant predictor of log Ksat for NT, CP, and MP but not in CCF because of excessive soil disturbance that lowered Ksat, b, and OM. While conservation tillage is beneficial for soil and water conservation and for reduced tillage costs, changes in topsoil physical properties due to conservation tillage management are small.
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication April 29, 2003.
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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K. Oorts, P. Garnier, A. Findeling, B. Mary, G. Richard, and B. Nicolardot Modeling Soil Carbon and Nitrogen Dynamics in No-till and Conventional Tillage Using PASTIS Model Soil Sci. Soc. Am. J., March 12, 2007; 71(2): 336 - 346. [Abstract] [Full Text] [PDF]
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D. Ginting and B. Eghball Nitrous Oxide Emission from No-Till Irrigated Corn: Temporal Fluctuation and Wheel Traffic Effects Soil Sci. Soc. Am. J., May 6, 2005; 69(3): 915 - 924. [Abstract] [Full Text] [PDF]
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