Effects of intensive potato production on soil quality and yield at a benchmark site in New Brunswick

Soil& Tillage Research, 29 ( 1 9 9 4 ) 2 3 - 3 4

23

0 1 6 7 - 1 9 8 7 / 9 4 / $ 0 7 . 0 0 © 1994 - Elsevier Science B.V. All rights reserved

Effects of intensive potato production on soil quality and yield at a benchmark site in New Brunswick Y.Z. Cao a, D.R. Coote *'a, H.W. Rees b, C. Wanga, T.L.

Chow b

aCentre for Land and Biological Resources Research, Research Branch, Agriculture Canada, Ottawa, Ont. K1A 0C6, Canada bNew Brunswick Land Resource Unit, Centre for Land and Biological Resources Research, Research Branch, Agriculture Canada, Research Station, Fredericton, N.B. E3B 4Z7, Canada (Accepted 25 August 1993)

Abstract

The cumulative extent of soil redistribution by erosion and tillage was measured by comparing the t37Cs content of a soil under intensive potato production with that of an undisturbed forest soil. Soil redistribution rates estimated from ~37Cs contents for the cultivated site varied from a loss of as high as 19.0 kg m -2 year -~ (190 t ha - l year - t ) to a gain of as much as 4.3 kg m -2 year - j (43 t ha -~ year-~), with an average of 5.3 kg m -2 year -~ (53 t ha -~ year -~) soil loss. Measured soil ~37Cs content and calculated soil loss (and deposition ) were both found to be correlated with total potato yield ( P < 0 . 0 1 ) , and with tuber specific gravity ( P < 0.05 ), in the two years of yield measurements ( 1991 and 1992 ). These years had near normal growing season precipitation, but contrasting distri bution patterns of precipitation during the growing season. Estimated soil loss and gain were also correlated ( P < 0.01 ) with soil organic carbon and soil phosphorus contents. It is concluded that soil redistribution within the site, caused by either water erosion or tillage, or a combination of both these processes, had a marked effect on soil productivity.

Introduction Maintaining soil quality is a major concern of agricultural and environmental scientists, and of governments. It is a fundamental requirement of sustainable agriculture. Soil quality monitoring and modelling is a principal objective of the Soil Quality Evaluation Project (SQEP) that has been initiated under the National Soil Conservation Program (NSCP) of the Govern*Corresponding author. ~Contribution No. C L B R R 93-11.

SSDI 0 1 6 7- 19 8 7 ( 9 3 ) 0 0 3 6 4 - 7

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Y.Z. Cao et aL /Soil & Tillage Research 29 (1994) 23-34

merit of Canada, in cooperation with the provinces (Centre for Land and Biological Resources Research (CLBRR), 1992 ). Soil degradation in the potato-growing region of New Brunswick has been identified as one of the most serious soil quality problems in Canada (Coote et al., 1981 ). Average annual soil losses of 17 t h a - 1 year- 1 were reported by Saini and Grant (1980) for continuous potatoes. Small quantities of data have been obtained through plot measurements showing that soil erosion rates in New Brunswick are between 1.2 and 24.3 t h a - 1year- 1 (Chow et al., 1990 ). De Jong et al. (1986) used the 137Cstechnique to estimate soil displacement along hill-slope transects in potato fields near Grand Falls, New Brunswick. Average annual soil movement was estimated to range from 12 to 32 t h a - l for the eroded portions of the three transects investigated. The results correlated well with expected soil erosion rates as predicted by morphological features (A horizon thickness), and by application of the Universal Soil Loss Equation. Estimates of yield loss caused by soil erosion in this region have been as high as 30% (Fox and Coote, 1986). These estimates were obtained from interviews with farmers and agricultural extension personnel, and have not been quantified through field measurement. Research in Ontario (Kachanoski et al., 1992) and Quebec (Cao et al., 1993 ) has found soil movement on slopes that far exceeded that measured as soil erosion by water. These high rates of soil loss have been attributed primarily to the effect of tillage rolling soil downslope, which is particularly marked on shoulder slopes. Geng and Coote (1991) used the ~37Cs method to estimate the effect of past soil loss on soil quality at sites in eastern Ontario. They found that organic carbon, total N and available P were reduced by soil loss, and the effect was still evident 17 years after the erosion had been controlled by continuous grass cover. Benchmark sites established during 1989-1992 under the NSCP-SQEP have provided an opportunity to develop field-scale monitoring techniques for quantifying many soil quality parameters and related crop yields. In New Brunswick, two such benchmark sites are located in the potato-growing region near Grand Falls. The objectives of the study reported here are to determine the degree of soil redistribution that has occurred at one of the benchmark sites (20-NB) as a result of intensive cultivation, including the effects of soil erosion and tillage on soil movement, and to determine the effect of this soil redistribution on soil quality and productivity. Materials and methods

The NSCP-SQEP benchmark site program rationale and approach have been described by CLBRR ( 1992 ). The site used in this study (20-NB) is located about 8 km southeast of Grand Falls, New Brunswick. It consists of

25

E Z Cao et aL / Soil & Tillage Research 29 (1994) 23-34

an area of approximately 130 m X 350 m. The soils have developed on coarseloamy till deposits and are classified as Orthic Humo-Ferric Podzols, Orthic Sombric Bunisols and Orthic Humic Regosols. Topographic conditions (Fig. 1 ), which were m a p p e d by a computer-based graphics package, SURFER (Golden Software, 1990), are complex. In general, slopes are about 2-15%. Between 1960 and 1974, the site was in a rotation of 2 years potatoes followed by 1 year small grains and 2-3 years hay. The site has been intensively cultivated for potato production since 1974, with potatoes grown in all but 4 years from 1975-1990. During these 4 years when potatoes were not grown, the site was in cereal grain. Between 1960 and 1990, the site was used to grow potatoes for a total of 16 years. Potatoes are grown with the rows parallel to the longest dimension of the field, which is primarily up-and-down slope. Since the method of estimation of soil redistribution used in this study was based on soil 137Cscontent, land use information was not obtained for the period prior to 1960. This was the date at which the peak of atmospheric deposition of 137Csfrom nuclear weapons testing was reached (De Jong et al., 1982 ). The site was sampled in 1989 using a grid sampling scheme (Fig. 1; the blank area was excluded from the study as it is not cultivated land). Soil samples were taken from the Ap horizon, air-dried and passed through a 2 m m sieve. Laboratory analyses for organic carbon, exchangeable Ca, K, and Mg, available P (bicarbonate m e t h o d ) , and pH (in water and CaC12) were conducted using standard methods reported by Sheldrick (1984). In the fall of 1990, the grid points were resampled for 137Cs analyses. A representative sample of Ap horizon material sufficient to provide a m i n i m u m of 1 kg after air drying and sieving through a 2 m m screen was collected. An exposed vertical wall of the excavation at each grid point was used to measure Ap thickness to the nearest 0.5 cm, using color and structure to differentiate soil layers. Bulk density samples were taken at the same time. A modified core sampler was used to extract undisturbed samples 5.08 cm in diameter and 5.08 cm in length. Where uniform in consistence and structure, one core sample was taken to characterize the bulk density of the Ap. Where soil morphology indicated E"

* Soil sample points

r~

DiStance (m)

e

e 0

Fig. 1. Reliefand soil sample points at Site 20-NB in New Brunswick.

-41

x5~ ~°~ e,~c,e~ ~

26

l
29 (1994) 23-34

variation within the Ap horizon (i.e. Apl, AP2, or APb) two or more cores were taken (one for each Ap horizon layer) and results weighted based on layer thickness. These samples were oven dried and weighed to obtain an estimate of the bulk density of the Ap horizon. Samples of Ap horizon were passed through a 2 m m sieve, and a 1 kg subsample was analyzed for 137Cs content using a germanium crystal gammaradiation counter (De Jong et al., 1982 ). The 137Cs content was corrected for coarse fragments removed during sieving by multiplying the 137Cs content of the sieved subsample by the percentage of soil passing through the sieve. The quantity of ~37Cs per unit area was then computed from the corrected 137Cs content of the sample (Bq kg -~ ) and the bulk density of the Ap horizons. The baseline ~37Cscontent, representative of the quantity of 137Cs expected in an uneroded soil, was estimated to be 3000 Bq m -2 from the results of analyses conducted in 1985 by De Jong et al. (1986), adjusted for natural 13VCs decay. At each grid point with less than 3000 Bq m -2 137Cs content, the loss of soil was estimated from the present content of ~37Cs and that of an uneroded soil using the following relationships (Kachanoski et al., 1992; Cao et al., 1993) E , = B D Dp[1 - ( C , / C o ) '/" ]

(1)

where E, is the net average soil erosion (kg m -2 year-1 ) in n years, BD is the bulk density (kg m - 3 ) of the layer in which ~37Cs is present, Dp is the cultivation layer (Ap) thickness (m) in which ~37Csis present, Co is fallout input of 137Cs (Bq m -z) after decay, estimated from local uncultivated land, C, is '37Cs activity (Bq m -2) at sampling sites in year n, and n is the number of years over which the soil loss occurred, assumed to be 30 ( 1960-1990). This equation adjusts for the dilution of plow-layer ~37Cs over time by incorporation of subsoil, low in ~37Cs, from below. It is not valid if (Cn/ Co) > 1.0. Therefore, at each grid point with more than 3000 Bq m -2 137Cs content, the gain of soil was estimated as follows (De Jong et al., 198 3 ) En = - B D ( D e -Dr,)

(2)

where De is the effective depth (m) in which '37Cs was present. The computed soil loss and gain for the site was mapped by a computerbased graphics package, SURFER (Golden Software, 1990). In September 1991 and 1992, potato yield samples were collected by lifting and removing tubers from plants in five 1.22 m lengths of row at each grid point. The tubers were graded and weighed, and yields calculated in kilograms per square meter. Samples were taken for specific gravity, as an indicator of tuber quality. Precipitation data for the region were obtained from the Atmospheric Environment Service weather station located at Grand Falls, New Brunswick (Environment Canada, 1982 ), less than 10 km from the site.

E Z. Cao et aL / Soil & Tillage Research 29 (1994) 23-34

27

Results and discussion

Estimation of l37Cs residual and soil erosion rates The measured 137Cs content, estimated soil redistribution, some soil parameters and average potato yields of 1991 and 1992 are listed in Table 1. The 137Cs content at the site varied from 188 Bq m -2 to 3359 Bq m -2, with most samples between 1000 and 3000 Bq m-2. The frequency distribution of 137Csloss classes observed at grid sample points at the site is presented in Fig. 2. The frequency distribution of 137Cs residue is asymmetrical and positively skewed, indicating that soil loss greatly exceeds soil gain. The site is not a closed system. Limited upslope runoff enters the site; however, at the downslope end there is a distinct outlet through which surface runoff leaves the site. When the total 137Cs redistribution from eroded areas to depositional areas was calculated for the entire site, approximately 41% of total 137Cs was estimated to have been lost from the site in runoff and sediments during the last 30 years. The distribution of soil m o v e m e n t (soil loss or gain ) at the site is shown in Fig. 3. The figure indicates that soil m o v e m e n t is closely related to the landscape. Most of the area (about 94% of the site) had been subjected to net soil loss, and soil gain (about 6% of the site) occurred in only three places. The net annual soil m o v e m e n t at the site ranged from 19.03 kg m -2 to - 4 . 3 4 kg m -2, with an average of 5.27 kg m -2 (52.7 t ha -1 ). The soil redistribution rates were grouped into the five classes defined for soil erosion by Coote et al. (1992): negligible (less than 0.60 kg m -2 year -1 ), low (0.60-1.09 kg m -2 y e a r - l ) , moderate (1.10-2.19 kg m -2 y e a r - l ) , high (2.20-3.29 kg m -2 year-1 ) and severe (at least 3.30 kg m -2 year- ~). The distribution frequency of these classes of soil m o v e m e n t are presented in Fig. 4; the figure indicates that 82% of the benchmark area was subjected to severe soil loss, and 6% to each of high and moderate soil loss. It is not possible, with the data available, to estimate the proportion of soil m o v e m e n t that was due to tillage rather than erosion. Other factors may have affected soil 137Cscontents, and could result in misleading soil loss or gain estimates. Such factors include land grading, fencerow removal, ditch construction or filling, etc. In the case of this site, aerial photographs were used to identify any of these activities during the period from 1960 to 1990. It appeared that a north-south fence was eliminated at 255-260 m distance from the zero line (Fig. 3 ). Some minor soil movement was also done along the field boundaries to create a shallow berm to divert most runoff originating outside the monitored area. The fence-row removal could have contributed to the area of soil accumulation at the 250-275 m zone of the site (Fig. 3 ), but this cannot be confirmed. It is unlikely, however,

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E Z. Cao et aL / Soil & Tillage Research 29 (1994) 23-34

Table 1 Soil parameters and potato yields at Site 20-NB Grid point

HO-75-35 HO-50-35 HO-150-35 HO-0-35 HO-275-35 HO-125-10 HO-100-35 HO-75-10 HO-25-35 HO-175-10 HO-75-60 HO-200-10 HO-125-35 HO-100-10 HO-0-10 HO-350-110 HO-350-60 HO-225-10 HO-350-10 HO-225-110 HO-325-85 HO-75-85 HO-175-35 HO-175-110 HO-325-35 HO-250-60 HO-225-35 HO-100-110 HO-225-60 HO-25-10 HO-325-110 HO-325-10 HO-275-10 HO-200-110 HO-75-110 HO-225-85 HO-125-85 HO-200-85 HO-250-10 HO-125-60 HO-350-35 HO-250-10 HO-300-35 HO-150-110 HO-150-10 HO-100-85 HO-300-10 HO-50-10 HO-100-60 HO-150-60

BD

~37Cs

(Mg m - 3 )

(Bq m - 2 )

1.60 1.62 1.31 1.28 1.36 1.42 1.49 1.49 1.27 1.46 1.51 1.37 1.44 1.25 1.30 1.36 1.35 1.29 1.39 1.20 1.26 1.27 1.11 1.26 1.49 1.36 1.26 1.43 1.35 1.28 1.43 1.37 1.34 1.38 1.41 1.25 1.26 1.43 1.40 1.40 1.30 1.40 1.19 1.31 1.20 1.41 1.31 1.27 1.27 1.13

387 640 882 842 1292 1423 1838 953 1124 1493 1532 1282 1583 1250 1391 1367 1259 1431 1313 1361 1364 1264 1293 1399 1635 1681 1521 1727 1490 1372 1666 1602 1838 1637 1757 1830 1382 1956 1837 1721 188 2119 2000 2079 1941 2114 2124 2158 2106 2035

Soil loss (kg m - 2 y e a r - l ) 19.0 14.1 12.1 11.2 8.7 8.0 8.0 7.8 7.8 7.7 7.7 7.7 7.6 7.6 7.5 7.4 7.3 7.2 7.2 6.9 6.9 6.5 6.5 6.4 6.3 6.2 6.2 6.0 5.9 5.9 5.8 5.4 5.0 5.0 5.0 4.9 4.8 4.7 4.6 4.6 4.6 4.4 4.3 4.0 4.0 3.9 3.9 3.9 3.7 3.6

Soil C (%)

Soil P (#gg-l)

Yield (kg m - 2 )

0.85 1.38 1.68 1.97 1.58 1.82 1.37 1.68 1.72 1.51 1.95 1.56 1.88 1.79 1.68 1.84 1.58 1.81 1.81 2.13 2.38 2.34 2.13 1.74 1.90 2.33 1.71 1.94 2.25 2.02 2.32 2.26 2.06 2.10 1.99 2.51 2.42 1.98 1.85 2.30 1.80 1.79 1.91 2.09 1.99 2.15 1.99 2.09 2.05 2.17

96.4 132.4 125.4 98.9 156.8 190.9 201.4 191.2 138.6 213.2 126.6 156.8 127.6 213.2 96.6 153.0 174.0 190.4 176.4 93.2 117.8 134.8 146.8 207.6 173.0 118.6 188.0 138.9 190.0 149.0 130.5 200.0 163.5 175.3 161.9 178.2 147.8 190.3 225.5 182.7 140.0 201.8 197.9 111.0 147.0 166.2 184.2 174.6 213.0 156.4

2.78 2.67 3.95 3.38 3.72 3.90 3.40 2.74 3.25 3.96 3.89 3.79 3.28 3.10 3.46 3.16 4.11 4.02 3.93 3.42 3.93 3.59 4.29 3.24 3.48 4.05 3.73 3.52 4.13 3.66 3.56 4.65 4.43 3.35 3.36 3.64 3.51 3.82 3.89 4.53 3.45 3.92 3.71 3.22 4.28 3.97 4.19 3.43 4.71 4.54

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Y.z. Cao et al. /Soil & Tillage Research 29 (1994) 23-34

Grid point HO-325-60 HO-125-110 HO-350-85 HO-175-85 HO-250-110 HO-300-110 HO-300-85 HO-150-85 HO-200-60 HO-275-60 HO-300-60 HO-275-110 HO-250-85 HO-175-60 HO-275-85 HO-200-35

o~ v

t'--

( M g m -3 )

~37Cs ( B q m -1 )

1.29 1.27 1.39 1.18 1.28 1.43 1.33 1.24 1.33 1.30 1.36 1.25 1.32 1.23 1.52 1.37

2112 2168 2360 1983 2194 2463 2513 2371 2539 2579 2565 2670 3192 3304 3359 3058

BD

Soil loss (kg m - 2 year -1 ) 3.6 3.6 3.4 3.4 3.3 2.7 2.4 2.2 1.9 1.9 1.8 1.2 -2.9 -3.5 -3.8 -4.3

Soil C (%)

Soil P (/tgg -1 )

Yield

1.91 1.88 1.82 1.96 2.11 2.07 2.10 2.38 2.18 2.07 2.32 2.72 2.26 2.42 2.10 2.28

119.8 159.4 194.6 104.8 190.0 182.2 193.0 118.8 147.0 181.8 153.2 144.4 230.2 211.8 217.6 193.0

4.21 3.61 4.08 4.43 3.53 3.62 3.91 3.58 4.31 4.41 4.21 3.53 4.12 4.39 3.97 4.33

( k g m -2 )

20

15

O" IJ _

10

0

_

_

_

Cs-137 loss (%) classes Fig. 2. Distribution frequency of 137Cs loss classes observed at grid sample points at Site 20-NB (Class 10, 0 - 1 0 % loss; Class 20, 10-20% loss, etc.).

that soil disturbance other than erosion and tillage would have affected the remaining pattern of soil movement seen in Fig. 3.

Effects of erosion on soil quality and potato yield The relationships between soil redistribution (SR) and soil carbon (SC) and available phosphorus (SP) contents in the Ap horizon are shown in Figs. 5 and 6. The data indicate that soil carbon and soil phosphorus contents were

K Z, Cao et aL / Soil & Tillage Research 29 (1994) 23-34

30

353

288

j

255

i).cO '

~33 353

288

255

Fig. 3. Soil redistribution (kg m

-2

year- l ) estimated from 137Cs at Site 20-NB.

90 80

70

~ 5o ~ 3o 2O 10 0

Fig. 4. Distribution frequency of soil redistribution classes at Site 20-NB: N (negligible), less than 0.6 kg m -2 year-I; L (low), 0.60-1.09 kg m -2 year-l; M (moderate), 1.10-2.19 kg m -2 year-l; H (high), 2.20-3.29 kg m -2 year-1; S (severe), at least 3.30 kg m -2 year-i.

SC = 2 . 2 6

- 0.05 SR

(R = 0,67 **)

v

O

~2 ,---t u0l l

0 5

; Soil

redistribution

i;

15 (

kg

m-2

20

y-1

)

Fig. 5. Relationship between soil carbon content and soil redistribution at Site 20-NB.

K Z. Cao et al. ~Soil& Tillage Research 29(1994) 23-34

31

5O0

& 1

SP

=

185.6

-

4.15

SR

(R

=

0.43

**)

400

300

0 0 C~

lO0

,---I 0 u?

0 5

Soil

,

i

J

0

5

i0

redistribution

,

15

20

( kg m-2 y - 1 )

Fig. 6. Relationship between soil phosphorus content and soil redistribution at Site 20-NB.

negatively related to soil redistribution ( P < 0.01 ) when all sites are included (soil loss and gain). This means that although carbon and phosphorus from crop and animal residues, and fertilizers, respectively, have been incorporated into the soil, any carbon and phosphorus gains were less than the losses resulting from soil movement. There was no significant relationship between soil redistribution and soil exchangeable K content. Potato yields were negatively correlated with soil loss for both years for which yields have been measured ( 1991, P < 0.01; 1992, P < 0.01 ). The mean annual yield of potatoes was related to soil loss and gain as shown in Fig. 7. Similar relationships were also found between both 137Cscontent and soil loss and the specific gravity of the potatoes ( P < 0.05, data not shown). This suggests that the quality of the potatoes harvested may also have been affected by soil redistribution. These relationships between 137Cs (and also soil movement) and soil carbon, soil phosphorus and potato yields, indicate that soil erosion and soil displacement by tillage equipment have caused a redistribution of soil within the benchmark site, and it would appear that these processes have resulted in the impoverishment of the Ap in the 'eroded' areas. Figure 7 shows that there may be only marginal enrichment of the soils in the depositional areas. Indeed, as erosion and soil displacement by tillage proceed over many years, the quality of the soil in the source areas (i.e. the eroded areas) and the depositional areas will deteriorate as subsoil of lower organic and nutrient content in the source areas is incorporated into the Ap, and subsequently moved to the depositional areas. Records show that it was very dry in the early summer of 1991. Annual precipitation in 1991 was 1121 m m which was close to the long-term average annual precipitation of 1053 m m (1951-1980) (Environment Canada, 1982 ). However, in the early growing season, especially during June and July,

32

r.z. Cao et al. ~Soil& Tillage Research 29(1994) 23-34 6.0 P Y = 4.13

I

- 0.06 SR

(R = 0.51

**)

5.0

~ 4.0

JL

•

:"-7 (1)

•

2"0-5

5 Soil

redistribution

i0

1 ( kg

m -2

20 y-i

)

Fig. 7. Relationship between mean 1991-1992 potato yield and soil redistribution at Site 20NB.

the precipitation was much lower than the long-term mean. The precipitation in June 1991 (43.4 m m ) was approximately 49% of the 30 year mean (87.9 m m ) and that in July (42.8 m m ) was approximately 36% of the 30 year mean ( 117.4 m m ) for the region. However, this was partly compensated for by an unusually wet August so that growing season rainfall was approximately normal. In 1992, June and July were wetter than normal (June 125.4 ram, July 131.4 mm ), but the growing season total was, again, approximately normal. Since the yields at each grid location at the benchmark site were very similar in 1991 and 1992, it is unlikely that variability in moisture levels had much effect on the observed results. This had been suggested when the 1991 yields were first analyzed, as depositional areas might be expected to hold more moisture during the dry early growing season than the eroded slopes. However, the similar yields obtained under contrasting moisture conditions in 1992 suggest that the principal reason for the yield differences is probably soil redistribution. Because the yield results are for 1991 and 1992 only, it is not possible to determine whether such relationships are representative of long-term averages until several more years of yield monitoring have been completed. However, the soil loss estimates are the cumulative results of up to 30 years of erosion and tillage, and are therefore representative of long-term effects. The yields are a short-term indicator of the cumulative effect of soil processes that have occurred over many years. Conclusions

This study has demonstrated the utility of the 137Csmethod for estimating the cumulative effects of long-term soil erosion and tillage on soil redistribu-

Y.Z. Cao et aL / Soil & Tillage Research 29 (1994) 23-34

33

tion and on soil productivity for a soil benchmark site in New Brunswick that has been in intensive potato production since the early 1960s. Results indicate that the 137Cs residual in soil at the site varied from 188 to 3359 Bq m -2 and was mostly between 1000 and 3000 Bq m -2. During the last 30 years, approximately 41% of ~37Cs was lost from the site. Estimated soil redistribution rates varied from a loss of 19.03 kg m -2 year- 1 ( 190.3 t h a - ~ year- i ) to a gain of 4.34 kg m - 2 year- i ( 43.4 t h a - i year- i ), with an average of 5.27 kg m -2 year -i (52.7 t ha -i year - i ) soil loss. Grid soil samples of the Ap horizon indicated that about 94% of the area was subjected to soil loss, of which about 82% was severe, 6% was high erosion, and 6% was moderate, when compared with widely used soil erosion assessments. Regression analysis showed that 137Cs content was significantly positively related, and soil loss was significantly negatively related to soil carbon and soil phosphorus contents and potato yield. Yield relationships are for 2 years only. It is not possible to determine whether such relationships are representative of long-term averages until several years of yield monitoring have been concluded. However, to the extent that the present soil carbon and soil phosphorus contents are a reflection of many years of soil redistribution processes, the yields are a short-term indicator of within-site variability in soil productivity. It is concluded that soil m o v e m e n t by erosion and tillage over the last 30 years has had a detrimental effect on soil quality at this benchmark site in New Brunswick. This loss in soil quality is indicated by lower soil carbon and phosphorus contents in areas that have been subjected to soil loss. It is further concluded that the loss in soil quality reduced potato yields in 1991 and 1992 in these portions of the site.

Acknowledgments The authors wish to acknowledge the assistance of J.-L. Daigle and V. H6bert for providing topographic surveys of the site, H. Ouellette for leasing and managing the site, K. Mellerowicz, S. Paradis and H. Cormier for assisting with potato yield sampling, P. von Bertoldi for operating the i 37Cs detector at the University of Guelph, and the soil laboratory at CLBRR. The authors also gratefully acknowledge the funding for the work provided by the NSCP-SQEP, managed by Dr. D.F. Acton, and for local funding provided by the CanadaNew Brunswick Soil Conservation Agreement, 1989-1992.

References Cao, Y.Z., Coote, D.R., Nolin, M.C. and Wang, C., 1993. Using 137Csto investigatenet erosion at two soil benchmark sites in Quebec. Can. J. Soil Sci., 73:515-526.

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r . z . Cao et al. ~Soil & Tillage Research 29 (1994) 23-34

Centre for Land and Biological Resources Research, 1992. Benchmark sites for agricultural land in Canada. CLBRR Brochure, CLBRR Contrib. No. 92-28, Research Branch, Agriculture Canada, Ottawa. Chow, T.L., Daigle, J.L., Ghanem, I. and Cormier, H., 1990. Effects of potato cropping practices on water runoff and soil erosion. Can. J. Soil Sci., 70:137-148. Coote, D.R., Dumanski, J. and Ramsey, J.F., 1981. An assessment of the degradation of agricultural lands in Canada. LRRI Contrib. No. 118, Agriculture Canada, Research Branch, Ottawa, 86 pp. Coote, D.R., Gordon, R., Langille, D.R., Rees, H.W. and Veer, C., 1992. Water erosion risk, Maritime Provinces. Publ. No. 5282/B, Agriculture Canada, Ottawa (map and report). De Jong, E., Villar, H. and Bettany, J.R., 1982. Preliminary investigations on the use of ~37Cs to estimate erosion in Saskatchewan. Can. J. Soil Sci., 62: 673-683. De Jong, E., Begg, C.B.M. and Kachanoski, R.G., 1983. Estimates of soil erosion and deposition for some Saskatchewan soils. Can. J. Soil Sci., 63:607-617. De Jong, E., Wang, C. and Rees, H.W., 1986. Soil redistribution on three cultivated New Brunswick hillslopes calculated from 137Csmeasurements, solum data and the USLE. Can. J. Soil Sci., 66: 721-730. Environment Canada, 1982. Canadian Climate Normals 1951-1980. Temperature and Precipitation: Atlantic Provinces. Atmospheric Environment Service, Environment Canada, Ottawa, 136 pp. Fox, M.G. and Coote, D.R., 1986. A preliminary economic assessment of agricultural land degradation in Atlantic and central Canada and southern British Columbia. LRRI Contrib. No. 85-70, Development Policy Directorate, Regional Development Branch, Agriculture Canada, Ottawa, 166 pp. Geng, G-Q. and Coote, D.R., 1991. The residual effect of soil loss on the chemical and physical quality of three soils. Geoderma, 48:415-429. Golden Software, 1990. Surfer, Version 4. Golden, CO, USA. Kachanoski, R.G., Miller, M.H., Lobb, D.A., Gregorich, E.G. and Protz, R.D., 1992. Management of farm field variability. I. Quantification of soil loss in complex topography. II. Soil erosion processes on shoulder slope landscape positions. Final Report. Technology and Evaluation and Development Soil Program, Soil and Water Environmental Enhancement Program, Agriculture Canada, Harrow, Ont. Saini, G.R. and Grant, W.J., 1980. Long-term effects of intensive cultivation on soil quality in the potato-growing areas of New Brunswick (Canada) and Maine (U.S.A. ). Can. J. Soil Sci., 60:421-428. Sheldrick, B.H. (Editor), 1984. Analytical Methods Manual. LRRI Contrib. No. 84-30, Land Resource Research Institute, Research Branch, Agriculture Canada, Ottawa, 190 pp.