The effect of 1-1 5 daily freeze/thaw cycles on aggregate stability ( S ) and aggregate-size distribution measured as mean-weight diameter (MWD) was investigated for loam, sandy loam and fine sandy loam (FSL) soils; and two aggregate-wetting procedures, spraywetting and vacuum-wetting, were compared. Initially, S and MWD decreased rapidly until about the fifth freeze/thaw cycle, thereafter change occurred progressively less rapidly reaching a minimum value at about the 10th cycle. Sand MWD in the loam, which had the greatest content of clay and iron oxides, decreased significantly less rapidly than in the other soils. The sandy loam, with the least clay but the most organic matter, was intermediate in behaviour. Macro-aggregate (>4.75 mm) content of the FSL decreased from 40% initially to 12% of total mass by the 15th cycle, while the micro-aggregate (<0.5 mm) content increased from 19% to almost 70% of total mass. In contrast, the loam retained many macro-aggregates, with a decrease from an 80% macro-aggregate content to 60% of total mass by the 15th cycle. With an average of about 40 freeze/thaw cycles occurring during a Prince Edward Island winter, S and MWD in both the sandy loam and the FSL will reach minima by the end of winter. In contrast, Sand MWD in the loam will not have reached a minimum by the end ofwinter. These results are related to the erosive behaviour of the three soils.Data on S and MWD of samples exposed to the two wetting procedures followed similar trends with number of freeze/thaw cycles (r =0.84 to 0.99); but spray-wetting gave less variable results than did vacuum-wetting and was a simpler procedure.
N. 1999. Soil organic matter quality and aggregate stability under eight potato cropping sequences in a fine sandy loam of Prince Edward Island. Can. J. Soil Sci. 79: 411-417. Soil degradation and soil organic matter (SOM) reduction have long been suspected to occur under intensive potato (Solanum tuberosum L.) production in Prince Edward Island. Thus, this study was conducted to evaluate the effect of eight potato cropping sequences involving barley (Hordeum vulgare L.), ryegrass (Lolium multiflorum L.), red clover (Trifolium pratense L.) and barley underseeded with red clover on aggregate stability and SOM properties of a Charlottetown fine sandy loam (Orthic Humo-Ferric Podzol). Total C and N, light-fraction (density < 1.7 g cm -3 ) C (LF-C) and light-fraction N (LF-N), microbial biomass C (MBC), carbohydrate content, alkaline phosphatase activity (APA) and aggregate stability were determined in the 0-to 15-cm soil layer in the 6th and 10th years of the trial. Average C and N contents were 20 to 27% greater in sequences that included 3 or 4 yr of potatoes and a high frequency of red clover than in a 9-yr potato sequence; and were attributed to the less frequent tillage and higher organic matter inputs associated with the forage component. The response for MBC, LF-C, LF-N and APA was greater than those for total C and N suggesting that the former parameters may better reveal SOM changes caused by variations in potato management than the latter. Light-fraction N was particularly sensitive to the inclusion of perennial legumes in the cropping sequence. Wet-aggregate stability was 33% higher after 6 yr in the sequence with 50% frequency of red clover than in the continuous potato system, but no effect was noted after 10 yr. The results of this study indicate that sequences which are limited to 30 to 40% of potatoes and have a high frequency of perennial forage such as red clover, lead to greater SOM content and quality of a Charlottetown fine sandy loam compared to continuous potatoes. Trends in aggregate stability generally followed those of SOM fractions but the effects were relatively smaller and varied with time. . La production intensive de pomme de terre (Solanum tuberosum L.) est souvent associée à la dégradation et la réduction de la matière organique des sols de l'Île-du-Prince-Édouard. Cette étude, effectuée sur un loam sableux fin de Charlottetown (Podzol humo-ferrique orthique), a évalué les effets de huit séquences culturales incluant la pomme de terre, l'orge (Hordeum vulgare L.), le ray-grass (Lolium multiflorum L.), le trèfle rouge (Trifolium pratense L.) en culture pure ou semé sous orge sur les propriétés de la matière organique et la stabilité des agrégats du sol. Les teneurs en C et N du sol entier et de la fraction légère (densité < 1.7 g cm -3 ) de la matière organique, les teneurs en biomasse microbienne et en glucides extraits à l'acide sulfurique, l'activité de la phosphatase alcaline et la stabilité des agrégats ont été déterminées dans la couche 0-15 cm de profondeur du sol dans la 6 e...
Edwards, L. M. 2013. The effects of soil freeze–thaw on soil aggregate breakdown and concomitant sediment flow in Prince Edward Island: A review. Can. J. Soil Sci. 93: 459–472. The importance of aggregate size and integrity in soil productivity and crop production is paramount, and aggregate size reduction or increase invariably becomes a primary concern in such soil management practices as tillage and organic matter manipulation. In this regard, therefore, the present review looks particularly at the consequence of freeze–thaw cycling (FTC) on agricultural lands in Prince Edward Island (PEI) where an annual average of 40 cycles induce measurable aggregate breakdown with mixed consequences. On the one extreme, the consequences are manifest in increased soil erosion. On the other extreme, reduced (or reversed) soil compaction and improved seedbed conditions are welcomed consequences where temperature alternation breaks up hard pans or soil clods, or where the predominance of smaller aggregates can be an asset in seedbed environments, favouring improved crop emergence and early-spring establishment. In the PEI soils studied, the greatest changes in aggregate size distribution with FTC occurred in the largest and smallest size fractions wherein fractions <0.5 mm showed a 33% average increase while, simultaneously, the 4.75–9.5 mm fractions showed a 28% average decrease. This breakdown is reflected most contrastingly where FTCs to maximum (asymptotic) breakdown averaged up to 3.5 times for a loam as it did for a sandy loam or a fine sandy loam soil. This review also examines FTC in a broader agricultural and environmental context where it can potentially impact agro-sustainability. Where FTC effects on a fine sandy loam were measured in terms of erosion, there was a sediment mass increase of about 90% in interrill flow and about 25% in rill flow. Further, this review emphasizes methodology that has proven to be workable under the circumstances of PEI's dominant agricultural soils and the FTC research objectives that they helped to shape. It was considered important in this review, also, to highlight the need for expanded research (commencing with regional cooperation), particularly on frost depth, to feed into moisture-availability modelling towards improved clarity for end-user benefit.
, J. 1998. Measurement of rill erosion by snowmelt on potato fields under rotation in Prince Edward Island (Canada). Can. J. Soil Sci. 78: 449-458. Cool-period soil erosion from farmland in Prince Edward Island occurs predominantly through rilling mainly due to snowmelt. This is mostly evident on fields coming out of potatoes (Solanum tuberosum L.), a crop that is traditionally cultivated as part of a 2-yr rotation with cereal grains, or a 3-yr rotation with cereal grains and a forage crop for hay. Accurate assessment of snowmelt erosion (associated processes and effects) has been historically constrained by data inadequacy, particularly for rilling; and although a number of models have now been developed for estimating cool-period erosion, they still stand to benefit from the generation of actual field data. In the present study, actual volume measurements were made of erosion forms, for about 80 site-years, after the spring snowmelt in fields at various stages of potato rotation. Cool-period erosion, predominantly rills, amounted to about 30 t ha -1 for 2-yr and 3-yr rotations, thus an annual seasonal average of 15 t ha -1 and 10 t ha -1 , respectively. Potato fields left untilled over winter averaged about 20 t ha -1 which increased to 36 t ha -1 with fall ploughing. Sediment deposition in fields coming out of potatoes was 13.3 t ha -1 compared with the amount of 0.4 t ha -1 in fields coming out of forages and 1.6 t ha -1 in fields coming out of grain. Fields going into the winter in sod or stubble showed negligible erosion, averaging about 0.1 t ha -1 in spring. The results of this study demonstrate the dominant influence of cropping practice in the erosion process during the cool period, and the tendency for traditional computational procedures to underestimate soil loss.Key words: Cool-period erosion, rilling, rill volume, sediment deposition, soil-loss prediction, erosion mapping, crop rotation Edwards, L., Richter, G., Bernsdorf, B., Schmidt, R.-G. et Burney, J. 1998. Mesure de l'érosion en rigoles due à la fonte des neiges dans des champs à pomme de terre en rotation dans l'Île-du-Prince-Édouard au Canada. Can. J. Soil Sci. 78: 449-458. L'érosion des sols agricoles de l'Île-du-Prince-Édouard durant la période froide de l'année se manifeste le plus souvent par la formation de rigole due à la fonte des neiges. Elle s'observe particulièrement après une sole de pomme de terre (Solanum tuberosum L.), culture généralement pratiquée en rotation de deux ans avec une céréale ou de trois ans avec une céréale et une culture fourragère de fauche. L'évaluation de cette forme d'érosion (et des mécanismes et effets corollaires) a toujours été entravée par l'absence de données vraiment pertinentes, en particulier en ce qui concerne la formation des rigoles et bien qu'un certain nombre de modèles mathématique de prédiction aient été miss au point, on doit encore recourir aux données mesurées sur le terrain. Nos travaux consistaient à mesurer, sur environ 80 années-emplacements, le volume réel des formes d'érosion après ...
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