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Agronomy Journal 92:948-956 (2000)
© 2000 American Society of Agronomy

SOIL MANAGEMENT

Early Impact of Topsoil Removal and Soil Amendments on Crop Productivity

Francis J. Larneya, Barry M. Olsonb, H.Henry Janzena and C.Wayne Lindwallc

a Agriculture and Agri-Food Canada, Research Centre, P.O. Box 3000, Lethbridge, AB, Canada T1J 4B1
b Irrigation Branch, Alberta Agriculture, Food and Rural Development, Bag 3014, Lethbridge, AB, Canada T1J 4C7
c Agriculture and Agri-Food Canada, Semiarid Prairie Agricultural Research Centre, P.O. Box 1030, Swift Current, SK, Canada S9H 3X2

larney{at}em.agr.ca


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
Wind erosion remains a common form of soil degradation on the semiarid northern Great Plains. This study was conducted to ascertain the effects of erosion on soil productivity and methods for its amelioration. Incremental depths (0, 5, 10, 15, and 20 cm) of surface soil or cuts were mechanically removed to simulate erosion at four sites (three dryland, one irrigated) in southern Alberta in 1990–1991. Three amendment treatments (N + P fertilizer, 5 cm of topsoil, or 75 Mg ha-1 of feedlot manure) and a check were superimposed on each of the cuts. In the first three years (1990–1992), there were highly significant relationships between cut and spring wheat (Triticum aestivum L.) yield parameters (midseason biomass, grain and straw yield, head density, tillering capacity, and grain elemental concentrations). Removal of 20 cm of topsoil reduced grain yield by 53% (an average of 11 site-years). Manure proved the best amendment for restoring productivity (e.g., an 11-site-year average increase of 158% in grain yield on the 20-cm cut), with N + P fertilizer being the least effective (40% grain yield increase on the 20-cm cut). Manure's ability to supply crop P, Mg, Mn, and Zn may partially explain its positive effect. Topsoil addition was intermediate in its restorative powers (89% yield increase after 20 cm topsoil removal). The study reinforces the need to prevent erosion and indicates that application of livestock manure is an option for restoring soil productivity in the short term.

Abbreviations: GSP, growing-season precipitation


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
ALTHOUGH CONSERVATION TILLAGE has been widely adopted on the Canadian prairies, wind erosion remains a serious soil degradation problem, especially on irrigated land. Its impact on soil quality leads to a reduction in soil productivity, and hence in crop yield (Larney et al., 1998; Lowery and Larson, 1995). However, these effects are difficult to quantify. Topsoil depth is of major importance in determining soil quality and productivity (Thompson et al., 1991). Characterizing topsoil depth–soil productivity relationships is a vital step in assessing the true on-farm costs and benefits of conservation tillage and erosion control programs.

Several approaches may be used to estimate erosion effects on soil productivity. Crop yields on eroded knolls have been compared with those on noneroded downslope positions (Battiston et al., 1985; Langdale et al., 1985). However, the yield differences are often due to confounding factors such as sediment deposition and soil moisture differences, as well as the effects of erosion (Daniels et al., 1985; Whitman et al., 1985). Also, crop responses to differences in existing topsoil depth have been extrapolated to show the yield response to topsoil loss (McDaniel and Hajek, 1985). This approach implies that each incremental depth of topsoil has equal productivity. Another approach involves computer simulation models, such as Environmental Policy Integrated Climate (EPIC) (Williams et al., 1984), N Tillage Residue Management (NTRM) (Shaffer et al., 1995), and the Productivity Index (PI) (Pierce et al., 1983), which are capable of handling complex interactions between soil properties, weather conditions, and management practices.

We chose a topsoil removal or desurfacing approach whereby incremental depths of topsoil, or cuts, are mechanically removed and subsequent effects on soil productivity are monitored (Eck, 1987; Gollany et al., 1992; Ives and Shaykewich, 1987; Larney et al., 1995b; Tanaka and Aase, 1989). Levels of amendments necessary to restore original productivity may also be studied with this approach (Dormaar et al., 1997; Larney and Janzen, 1997). Desurfacing removes all size classes of soil aggregates and does not simulate the preferential sorting of natural erosion. Despite this shortcoming, the confounding aspects of landscape position and inherent topsoil depth variability can be overcome with this approach.

The study described here was initiated in 1990 and is one of a series of topsoil removal–amendment–soil productivity studies in southern Alberta. Larney et al. (1995a) have reported on erosion, but not amendment, effects on crop yield for the initial year only. An earlier erosion study (initiated in 1967 at the Lethbridge Research Centre) has three levels of topsoil removal and five amendment treatments (Dormaar et al., 1986, 1988, 1997; Freeze et al., 1993). Also in 1990, a study was initiated to examine three levels of topsoil removal (0-, 10-, and 20-cm cuts) and various combinations of N and P fertilizer rates (Larney et al., 1995b; Smith et al., 2000) at four sites. In 1992, the fertilizer treatments were replaced by manure application rate treatments (Larney and Janzen, 1997). A further study, established in 1992, has one level of topsoil removal (15-cm cut) and 14 amendment treatments, including various livestock manures, plant residues, and inorganic fertilizers (Larney and Janzen, 1996; Sun et al., 1995).

The objectives of this study were to (i) assess the early impact (1–3 yr) of topsoil removal on soil productivity in southern Alberta; and (ii) quantify the effectiveness of various amendments in restoring productivity to eroded surfaces in the initial 3-yr period.


   Materials and methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results and discussion
 Conclusions
 REFERENCES
 
Three sites were selected for desurfacing in spring 1990 on the basis of uniformity of Ap horizon depth and topography. Two (one dryland and one irrigated) were located at the Agriculture and Agri-Food Canada Research Centre at Lethbridge, AB (49°43' N, 112°48' W), and one was located on dryland near Taber, about 50 km east of Lethbridge. A fourth site (dryland) was desurfaced in spring 1991 at Hill Spring about 120 km west of Lethbridge. The Lethbridge soils were Dark Brown Chernozemic sandy clay loams (Typic Haploborolls), the Taber soil was a Brown Chernozemic clay loam (Aridic Haploboroll), and the Hill Spring soil was a Black Chernozemic clay loam (Udic Haploboroll). All soils were developed on glacio-lacustrine parent material and are described in more detail by Larney et al. (1995a, 1995b).

Five main treatments or cuts (12- by 10-m plots) were established at each site by removing 0, 5, 10, 15, or 20 cm of topsoil using an excavator with a grading bucket. In the initial year only (1990 at Lethbridge Dryland, Lethbridge Irrigated, and Taber; 1991 at Hill Spring), four subtreatments (3- by 10-m subplots) were superimposed (split-plot) on each of the main treatments (cuts): check, an optimum rate of N and P fertilizer (75 kg ha-1 N, 22 kg ha-1 P), or 75 Mg ha-1 (wet weight) of feedlot manure, or reapplication of 5 cm of topsoil. Fertilizer N and P rates were doubled at the Lethbridge Irrigated site. The 5 cm of topsoil applied to all cuts was saved from the 0- to 5-cm layer during the desurfacing operation. The feedlot manure had a water content of 0.35 kg kg-1 and contained 190 g kg-1 total C and 22 g kg-1 total N. In subsequent years, no further amendments were applied in order to monitor the residual effects of one-time treatments. All plots received broadcast applications of 40 kg ha-1 of N and 9 kg ha-1 of P after the initial year (rates were doubled at the Lethbridge Irrigated site). Plots were replicated four times in a randomized complete block design (5 cuts x 4 amendments x 4 replicates = 80 plots).

In the initial year (1990 at Lethbridge Dryland, Lethbridge Irrigated, and Taber; 1991 at Hill Spring), seedbed preparation consisted of one pass of a powered rotary cultivator to 10 cm depth, as the desurfaced plots were dry and compact. Subsequently, all sites were managed under a no-till system. All sites were seeded to spring wheat (Triticum aestivum L. cv. Biggar) at a 17.5-cm row spacing in May of each year from 1990 to 1992. Seeding rates were 84 kg ha-1 at the dryland sites and 100 kg ha-1 at the irrigated site. The Lethbridge Irrigated site received irrigation water during each growing season to ensure that root zone soil moisture was nonlimiting.

In 1991, plant and head counts were taken on one 1-m row length per subplot at all four sites. Upon conversion to a square meter basis, head count divided by plant density resulted in an estimate of the number of tillers per plant. Samples for midseason biomass (three 1-m-long rows per subplot) were taken just after heading. At harvest, six 5-m-long rows were hand-harvested from each subplot for grain and straw yield. In 1991, grain from the five cuts and two amendments (check and manure) was analyzed for total P, S, K, Mg, Cu, Mn, and Zn by nitric-perchloric acid digestion and inductively coupled plasma–atomic emission spectroscopy (Model 3560, Applied Research Laboratories, Ecublens, Switzerland).

Statistical analysis was performed on all data using the General Linear Models Procedure of SAS (SAS Inst., 1989) with cut as the main treatment and amendment as a subtreatment in a split-plot design. Least significant differences were used to compare treatment means.


   Results and discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
Conclusions
 REFERENCES
 
Weather Conditions
The long-term normal growing-season precipitation (GSP, 1 May–31 August) at Lethbridge is 212 mm. In 1990, GSP was near normal (182 mm at Lethbridge Dryland; 179 mm at Taber). The Lethbridge Irrigated site received 182 mm of precipitation and 175 mm of irrigation (357 mm total) in the 1990 growing season. In 1991, GSP was above normal (252 mm at Lethbridge Dryland, 220 mm at Taber, and 272 mm at Hill Spring). The Lethbridge Irrigated site received a total of 402 mm (252 mm precipitation, 150 mm irrigation) of water in 1991.

In 1992, GSP was 276 mm at Lethbridge Dryland, 240 mm at Taber, and 338 mm at Hill Spring. Total water addition was 378 mm (276 mm precipitation, 102 mm irrigation) at the Lethbridge Irrigated site. However, GSP was very unevenly distributed in 1992, with only 22 mm from 1 May to 11 June and 197 mm from 12 June to 31 July. This resulted in very patchy establishment on the shallow cuts at the three dryland sites because of their lower residual water contents due to higher crop productivity in the previous 2 yr. The wet midseason promoted late emergence of plants on the shallower cuts, resulting in uneven crop maturity at harvest. On 22 Aug. 1992, an unexpected snowstorm (20 cm snowfall with frost) affected grain filling on the greener shallow cuts compared with the more advanced deeper cuts. Additionally, a severe hail storm caused 100% crop damage at the Lethbridge Irrigated site on 2 Aug. 1992. Therefore, only midseason biomass data are reported for that site-year.

Midseason Biomass
Seven of the 11 site-years showed no significant cut x amendment interaction effects (Table 1) . Of these seven site-years, four showed significant decreases in biomass production as depth of cut increased. The other three site-years (all in 1992) showed either no significant effect of cut (Taber and Hill Spring), or a significant increase in biomass production as depth of cut increased (Lethbridge Dryland). This may be explained by dry conditions in the early growing season and low residual soil moisture in the shallow cuts as explained earlier. The manure treatment yielded significantly higher than the other amendment treatments in five of the seven site-years with no interaction effects (Table 1), the exceptions being the Lethbridge Irrigated site in 1991 and the Taber site in 1992.


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  		Table 1 Effect of topsoil removal (cut) and amendment on midseason biomass, 1990–1992.{dagger}*

 
The significant cut x amendment interactions at the Lethbridge Dryland (Fig. 1a) and Lethbridge Irrigated sites in 1990 (Fig. 1b) and 1991 (Fig. 1c) showed that the effect of cut on plant biomass was negated by the addition of manure. However, fertilizer rather than manure produced the highest biomass yields on the intact topsoil (0-cm cut) at the Lethbridge Dryland and Lethbridge Irrigated sites in 1990. In fact, manure application on the 0-cm cut at Lethbridge Dryland depressed biomass production (by 12% compared with the 20-cm-cut manure treatment). This agreed with McCalla (1974), who cited several studies reporting reduced yields with high manure rates.



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  		Fig. 1 Effect of cut and amendments on midseason biomass yield at (a) Lethbridge Dryland, 1990; (b) Lethbridge Irrigated, 1990; (c) Lethbridge Dryland, 1991; and (d) Lethbridge Irrigated, 1992. Bars represent the value for the cut x amendment means

 
The cut x amendment interaction also showed that there were only small differences between biomass yields on the manure, topsoil, and check treatments at the 0-cm cut, with yields diverging as the severity of erosion increased (Fig. 1a–1c). At the Lethbridge Irrigated site in 1992 (Fig. 1d), the interaction effect lay in the lack of a biomass yield difference between the check, fertilizer, and topsoil treatments until erosion was >10 cm, when the topsoil amendment performed much better. The application of water, combined with optimum rates of fertilizer, failed to restore productivity on the 15- and 20-cm cuts at the Lethbridge Irrigated site.

Grain Yield
There were significant cut x amendment interactions in 6 of the 10 site-years for grain yield (Table 2) . The trends found in midseason biomass production were repeated for grain yield at Lethbridge Dryland (Fig. 2a) and Lethbridge Irrigated (Fig. 2b) in 1990 and at Lethbridge Dryland in 1991 (Fig. 2c). At Lethbridge Irrigated in 1991 (Fig. 2d), the interaction effect showed that topsoil removal did not affect grain yield if the soils were amended with manure or topsoil. At the Taber site in 1991 (Fig. 2e), there was no difference in grain yield between the four amendment treatments on the 0-cm cut. However, on the deeper cuts, manure and topsoil additions were able to compensate for the loss of topsoil. At Hill Spring in 1991 (Fig. 2f), there was no effect of erosion on grain yield if the soils were amended with manure. The yields on the 20-cm-cut manure treatment (2.97 Mg ha-1) were almost double those on the 0-cm-cut check treatment (1.52 Mg ha-1).


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  		Table 2 Effect of topsoil removal (cut) and amendment on grain yield, 1990–1992.{dagger}

 


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  		Fig. 2 Effect of cut and amendments on grain yield at (a) Lethbridge Dryland, 1990; (b) Lethbridge Irrigated, 1990; (c) Lethbridge Dryland, 1991; (d) Lethbridge Irrigated, 1991; (e) Taber, 1991; and (f) Hill Spring, 1991. Bars represent the value for the cut x amendment means

 
Most studies on exposed soils have found that nutrient deficiencies were principally responsible for reduced yields (Batchelder and Jones, 1972; Hays et al., 1948). Nitrogen alone was ineffective in restoring productivity to leveled land in Montana (Reuss and Campbell, 1961). In Texas, N and P restored grain sorghum (Sorghum bicolor L.) yields where up to 30 cm of topsoil was removed (Eck et al., 1965). Our study showed that N and P were less effective in restoring soil productivity than either topsoil or manure additions. Other studies have also found that large quantities of commercial fertilizer did not improve yields to the level of noneroded soil (Mahli et al., 1994; Massee, 1990; Mbagwu et al., 1984; Olson, 1977).

Our findings correspond with those of Bachtell et al. (1956), who found that manure was more valuable as an amendment on subsoil than on topsoil. However, they disagree with those of Carlson et al. (1961), who reported that yields on cut areas of leveled land receiving manure (up to 100 Mg ha-1) were not as high as those that received applications of N (up to 200 kg ha-1), P (up to 100 kg ha-1), and Zn. On leveled land in Colorado, Whitney et al. (1950) found that corn (Zea mays L.) yields on manure plots were considerably higher than those on fertilizer plots that received half the amount of N and P supplied by the manure. However, when N, P, and K were applied at equal rates, either in the form of manure or commercial fertilizer, the fertilizer resulted in higher yields. No attempt was made to equalize the application of N and P in the manure and fertilizer treatment in our study. Dormaar et al. (1988) found that 30 Mg ha-1 of manure and 150 kg ha-1 of N + 150 kg ha-1 of P2O5 had similar restorative powers on land-leveled soil in the year following application. However, during years of drought stress, the manure treatment resulted in greater yields.

Straw Yield
Straw yield (Table 3) essentially followed the same trends as grain yield. However, straw yield at the Lethbridge Dryland site in 1992 provided a better reflection of treatment effects than grain yield, which was suppressed by early frost. The significant cut x amendment interaction meant that the manure effect was much greater on the 15- and 20-cm cuts than on the 0-, 5-, and 10-cm cuts (data not shown). For example, on the 10-cm cut, the manure treatment straw yield (1.84 Mg ha-1) was close to the average straw yield of the check, fertilizer, and topsoil treatments (2.02 Mg ha-1), while on the 20-cm cut, it was over twice as high (4.3 vs. 1.78 Mg ha-1).


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  		Table 3 Effect of topsoil removal (cut) and amendment on straw yield, 1990–1992.{dagger}

 
Head Density and Tillering Capacity
In 1991, the effects of topsoil removal and amendment were examined for head density and tillering capacity, which are important components of crop yield. There was a significant negative impact of erosion on head density at all sites except Hill Spring (Table 4) . There was a 72 to 74% increase in head density on the 0-cm-cut check treatment compared with the 20-cm-cut check treatment at the Lethbridge Dryland and Taber sites and a 44% increase at the Lethbridge Irrigated site. The manure amendment treatment resulted in a significantly higher head density than the topsoil treatment at Lethbridge Dryland, Taber, and Hill Spring (Table 4). Head density and tillering capacity on the fertilizer treatment at Hill Spring was higher than that on the topsoil treatment, which agreed with the trends found for biomass, grain, and straw yields at this site.


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  		Table 4 Effect of topsoil removal (cut) and amendment on head and tiller density, 1991.{dagger}***

 
At Lethbridge Irrigated, the 0- and 5-cm cuts had significantly more tillers per plant than the deeper cuts, while there was no effect of erosion at Hill Spring (Table 4). Again, the manure treatment increased tillering capacity at both Lethbridge Irrigated and Hill Spring. There were significant cut x amendment interactions at both Lethbridge Dryland and Taber (data not shown). At both sites, addition of manure negated an erosion effect on tillering capacity; e.g., at Lethbridge Dryland, the 20-cm-cut check treatment had 1.4 tillers plant-1, while the 20-cm-cut manure treatment had 3.5 tillers plant-1. Also, the topsoil treatment resulted in more tillers than the manure treatment on the 0-cm cut, but not on the other cuts.

Grain Elemental Analysis
Although soil nutrient data are not presented, grain elemental analysis gave some indication of treatment effects on soil nutrient bioavailability or deficiency. Data are presented graphically for sites and elements that showed significant treatment effects. There were no significant cut, amendment or interaction effects for grain Mg concentration at Lethbridge Dryland and Hill Spring, grain S concentration at Lethbridge Irrigated and Taber, or grain K concentration at Hill Spring.

There were significant effects on grain P concentration at all four sites (Fig. 3a–3d) . As depth of cut increased, grain P concentration decreased. This agrees with the findings of Tanaka (1995) in Montana. Also, grain from manure plots had significantly higher P concentrations than check plots. This suggests that P loss by topsoil removal was offset by P applied in manure.



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  		Fig. 3 Effect of cut and amendments on grain P concentration at (a) Lethbridge Dryland, (b) Lethbridge Irrigated, (c) Taber, and (d) Hill Spring; and on grain K concentration at (e) Lethbridge Dryland, (f) Lethbridge Irrigated, and (g) Taber in 1991. C, Cut; A, Amendment; C x A, Cut x Amendment interaction. *, **, *** Significant at the 0.05, 0.01, and 0.001 levels, respectively; ns = nonsignificant

 
There were significant treatment effects on grain K concentration at all sites except Hill Spring (Fig. 3e–3g). At Lethbridge Dryland, grain K concentrations decreased with depth of cut in both the check and manure plots (Fig. 3e). At Lethbridge Irrigated, a cut x amendment interaction meant that manure plots had higher grain K concentrations at the 0-, 5-, and 20-cm cuts only (Fig. 3f). At Taber, manure plots had higher grain K concentrations than check plots (Fig. 3g), again pointing to the potential for manure to supply crop K when topsoil was removed.

There was evidence that artificial erosion to 15 to 20 cm with manure amendment decreased grain S concentration at Lethbridge Dryland (Fig. 4a) and Hill Spring (Fig. 4b). This may be related to a dilution effect, whereby S was diluted in the greater amounts of biomass produced on the manure plots and concentrated on the smaller amounts of biomass produced on the check plots. Grain Mg concentration at Lethbridge Irrigated and Taber was significantly lower on check plots than on manure plots (Fig. 4c–4d), pointing to the Mg-supplying power of manure as a reason for yield restoration.



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  		Fig. 4 Effect of cut and amendments on grain S concentration at (a) Lethbridge Dryland and (b) Hill Spring; and on grain Mg concentration at (c) Lethbridge Irrigated and (d) Taber in 1991. C, Cut; A, Amendment; C x A, Cut x Amendment interaction. *, *** Significant at the 0.05 and 0.001 levels, respectively; ns = nonsignificant

 
Mbagwu (1985) reported that corn nutrient uptake data indicated that N, P, K, and Mg might be limiting in subsoil in an artificial erosion study in Nigeria. Aina and Egolum (1980) reported that manure addition to subsoil resulted in increased P and K uptake by corn. However, Siebert and Scott (1990) found that neither topsoil removal nor fertilizer application influenced K levels in aboveground biomass of peanut (Arachis hypogaea L.) in Indonesia. In southern Alberta, Dormaar et al. (1997) reported no significant differences in grain P, K, or Mg concentrations among erosion treatments or fertility amendments.

There were significant treatment effects on grain Cu (Fig. 5a–5d) and Mn (Fig. 5e–5h) concentrations at all four sites, and on Zn concentrations at all sites except Taber (Fig. 6a–6c) . The check treatment had higher grain Cu concentrations than manure at all four sites, except for a significant cut x amendment interaction at Hill Spring, which showed that this was not the case on the 0-cm cut. This points to nonlimiting Cu in the check plots, as biomass production was suppressed more than Cu uptake, which concentrated Cu in the grain. Depth of cut had a nonsignificant effect on grain Cu concentration at all four sites (Fig. 5a–5d), also indicating that Cu availability was not affected by topsoil removal.



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  		Fig. 5 Effect of cut and amendments on grain Cu concentration at (a) Lethbridge Dryland, (b) Lethbridge Irrigated, (c) Taber, and (d) Hill Spring; and on grain Mn concentration at (e) Lethbridge Dryland, (f) Lethbridge Irrigated, (g) Taber, and (h) Hill Spring in 1991. C, Cut; A, Amendment; C x A, Cut x Amendment interaction. *, **, *** Significant at the 0.05, 0.01, and 0.001 levels, respectively; ns = nonsignificant

 


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  		Fig. 6 Effect of cut and amendments on grain Zn concentration at (a) Lethbridge Dryland, (b) Lethbridge Irrigated, and (c) Hill Spring in 1991. C, Cut; A, Amendment; C x A, Cut x Amendment interaction. *, *** Significant at the 0.05 and 0.001 levels, respectively; ns = nonsignificant

 
The findings for Mn contrasted with those for Cu, especially at the Taber (Fig. 5g) and Hill Spring (Fig. 5h) sites, where grain from manure plots had significantly higher concentrations of Mn than that from check plots. The 20-cm-cut manure treatment at Lethbridge Irrigated (Fig. 5f) also had a higher grain Mn concentration than the check plot, demonstrating a possible Mn deficiency that was alleviated by manure addition. The Mn deficiency on the check plots is corroborated by the decreased grain Mn concentration with increasing depth of cut at Hill Spring (Fig. 5h). There was also a significant decrease in grain Mn concentration with depth of cut at Lethbridge Dryland (Fig. 5e), but this was independent of amendment treatment. Sharma and Yadav (1986) reported that manure additions greatly reduced leaching of Mn from surface layers. This mechanism may partly explain our findings, in that Mn leaching may have occurred on the check treatments.

Erosion significantly reduced grain Zn concentration on the check and manure plots at Lethbridge Dryland (Fig. 6a) and on the check plots only at Lethbridge Irrigated (Fig. 6b). Lindstrom et al. (1986) found low Zn availability in a calcareous clay loam soil after 30 and 45 cm of topsoil removal. A significant cut x amendment interaction at Lethbridge Irrigated showed that manure addition mitigated grain Zn concentration at cut depths >10 cm. However, the much higher grain Zn concentrations on the check treatment indicated that Zn deficiency did not occur at Hill Spring (Fig. 6c). Carter et al. (1985) found that Zn application did not restore yield to seven crops on an artificially eroded irrigated soil in southern Idaho. However, Robbins et al. (1997) found that dairy manure application at 44 Mg ha-1 dry weight (similar to our rate of 50 Mg ha-1 dry weight) and its accompanying Zn increased bean (Phaseolus vulgaris L.) yields on subsoil (30 cm of topsoil removal) to values similar to those on intact topsoil. Carlson et al. (1961) found Zn deficiency in subsoil exposed by land-leveling in North Dakota, while Grunes et al. (1961) reported that manure application alleviated the deficiency.

Early Impact of Topsoil Removal and Amendments
Average grain yield of the 11 site-years (three in 1990, four in 1991, and four in 1992) for the five check treatments gave an indication of the early impact (3 yr) of topsoil removal on crop yield (Fig. 7a) . Grain yield for the Lethbridge Irrigated site in 1992 (100% hail damage before harvest) was estimated from biomass yield using a regression equation from the previous year. The yield–depth-of-cut relationship is described by a polynomial rather than a linear equation. Christensen and McElyea (1988) pointed out that a linear relationship is a naive representation of a yield–topsoil depth relationship, as its constant slope assumes that loss of each incremental depth of topsoil exerts a constant incremental decrease in soil productivity.



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  		Fig. 7 Effect of cut on (a) grain yield on check treatment and (b) grain yield change due to amendments, 1990–1992 (average of 11 site-years)

 
The equation in Fig. 7a is different from those presented by Larney et al. (1995a) for the effect of erosion on first-year grain yields at each site. It has a negative c coefficient, showing that it was removal of the deeper increments of topsoil that most affected the average yield of the initial 3 yr, unlike the first year, when loss of topsoil close to the surface resulted in the largest yield declines. The trend in Fig. 7a may be related to the lack of a cut effect on grain yield as the study progressed (e.g., the 1992 sites, Table 2). It may also be due to a faster recovery of productivity on the 5- and 10-cm cuts than on the 15- and 20-cm cuts in the initial years, due to their increased productivity and hence higher amounts of root and residue mass returned to the soil. Eck (1987) reported an increase in productivity of exposed subsoils over time. On average (11 site-years), grain yields in our study were reduced by 8% with removal of 5 cm of topsoil, by 28% with 10-cm removal, by 39% with 15-cm removal, and by 53% with 20-cm removal, compared with the 0-cm-cut check plots.

The average grain yield (over 11 site-years) changes (compared with the check treatments at each cut) due to the addition of fertilizer, manure, and topsoil demonstrate the early impact of these one-time applications on crop productivity. The performance of the amendments was of the order manure > topsoil > fertilizer (Fig. 7b). For example, on the 10-cm cut, grain yield increased 73% with manure, 38% with topsoil, and 28% with fertilizer, while on the 20-cm cut, increases were 158% with manure, 89% with topsoil, and 40% with fertilizer.

Larney et al. (1995b) found that low yield responses to fertilizer P were due to high levels of calcium carbonate in the artificially eroded surfaces. This may have caused precipitation of insoluble Ca–P (Lewis and Racz, 1969), making P unavailable for crop uptake. In contrast, Abbott and Tucker (1973) found that manure assured adequate availability of P in calcareous soils, while Hannapel et al. (1964) found that organic amendments increased P movement in calcareous soils.

The manure and topsoil amendment relationships with cut were significantly linear (Fig. 7b), showing that the yield benefit increased as the depth of cut increased. In contrast, there was no significant effect with fertilizer, indicating that yield increases were similar irrespective of the depth of topsoil removal. Mielke and Schepers (1986) reported that yield increases of corn and oats (Avena sativa L.) over a 4-yr period averaged 19% for 10 cm of topsoil addition and 26% for 20 cm of addition to a naturally eroded ridge top in Nebraska. These increases were lower than those achieved with only 5 cm of topsoil addition in our study. Averaging the 11 site-years, 5 cm of topsoil addition resulted in yield increases of 38% on the 10-cm cut, 59% on the 15-cm cut, and 89% on the 20-cm cut. Verity and Anderson (1990) increased spring wheat yields by 45 to 58% by adding 5 cm of topsoil to an eroded knoll in Saskatchewan. These increases fall within the range of those achieved by adding 5 cm of topsoil to the 10- and 15-cm cuts in our study. Verity and Anderson (1990) also showed that topsoil additions of 10 or 15 cm resulted in only slight yield increases compared with addition of 5 cm of topsoil.

By comparing grain yields on the 0-cm-cut check with those on the 0-cm-cut topsoil and those of the 5-cm-cut check, the effect of 5 cm of topsoil removal and 5 cm of deposition on soil productivity can be estimated. The 0-cm-cut check simulates a noneroded area, the 0-cm-cut topsoil a depositional area, and the 5-cm-cut check an eroded area. Taking the average grain yield for the 11 site-years showed that a yield increase of 7% on the depositional areas (with respect to the noneroded area) essentially offset a yield decrease of 8% on the eroded areas.


   Conclusions
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
REFERENCES
 
Results from 11 site-years in the first year after desurfacing were consistent across three soil types and with both dryland and irrigated management, allowing conclusive information to be drawn from our study. Topsoil removal reduced yield components such as head density and tillering capacity, and this drastically reduced final yield. Our results showed that different soil moisture regimes (dryland vs. irrigated) gave similar results with respect to erosion effects on soil productivity and methods for its amendment. Removing moisture stress as a yield- and fertilizer response-limiting factor through irrigation did not offset the loss of topsoil, even with adequate N and P fertilizer inputs.

Manure proved very effective in restoring productivity in the early phase of this study. This was attributed to its ability to supply crop P as well as other macro- and micronutrients (Mg, Mn, and Zn). Since the longevity of this effect is unknown, no further manure will be applied so as to assess its residual restorative abilities. Our findings show that effort must be maintained to reduce water and wind erosion on the northern Great Plains. On eroded soils, an organic amendment like manure was the most successful in restoring productivity.SAS Institute 1989


   ACKNOWLEDGMENTS
 
We thank Tony Curtis, Marlene McCann, and Lorna Selinger for technical assistance; the Saskatchewan Soil Testing Laboratory, University of Saskatchewan, Saskatoon, SK, for grain elemental analysis; and landowners Blair Jespersen and Rod Fitzpatrick for their cooperation. This research was supported by the Canada-Alberta Soil Conservation Initiative (CASCI).


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
LRC contribution no. 3879955.

Received for publication August 30, 1999.
   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 




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