Water retention curves are essential for the parameterization of soil water models such as HYDRUS. Although hydraulic parameters are known for a large number of mineral and natural organic soils, our knowledge on the hydraulic behavior of cultivated Histosols is rather limited. The objective of this study was to derive characteristic water retention curves for a large cultivated peatland with lettuce (Lactuca sativa L.) and vegetable farming in southern Quebec, Canada. A comparison showed that the van Genuchten model its better to the water retention data obtained with a Tempe pressure cell experiment than the Groenevelt-Grant model in terms of residual sum of squares; however, the difference in performance was quite small due to the high number of iterations used for itting. Finally, an agglomerative cluster analysis of 85 peat samples allowed us to deine two distinct water retention curves, where the irst water retention curve described samples of relatively shallow (<150 cm) Histosols with an organic content <0.89 and a bulk density >0.3 g cm −3 , and the second curve characterized samples of the deepest (depth 150-230 cm) Histosols with an organic content of up to 0.97 and a bulk density >0.3 g cm −3 , which are the soils that suffered a more dramatic transformation as a result of agriculture. This characterization allows for a multitude of applications, including parameterization of the HYDRUS model for soil water movement, and presents an essential tool for the optimization of water management in cultivated peatlands.Abbreviations: BFGS, Broyden-Fletcher-Goldfarb-Shanno.

Organic soils are an excellent substrate for commercial lettuce (Lactuca sativa L.) farming; however, drainage accelerates oxidation of the surface layer and reduces the water holding capacity, which is often lethal for crops that are sensitive to water stress. In this case study, we analyzed 942 peat samples from a large cultivated peatland complex (18.7 km2) in southern Quebec, Canada, and demonstrated from spatial and temporal patterns that agriculture resulted in a compacted layer below the root zone. We grouped the samples based on the year in which the corresponding fields were created on the previously undisturbed peatland (cutoff years 1970, 1980, 1990, and 2000) and discovered that bulk density has continued to increase, partly due to the overburden pressure, while organic matter has continued to decline since the fields were reclaimed and drained in phases between 1955 and 2006. Saturated hydraulic conductivity (Ks) in the upper 20 cm was remarkably lower on fields older than 10 yr (p = 0.0973 for Wilcoxon rank test), with more samples having a Ks < 2.0 × 10−3 yr. Soil water available capacity (SWAC) was between approximately 5 and 33 cm on fields reclaimed after 2000, while samples from fields reclaimed before 2000 had a lower SWAC between 2 and 23 cm (groups discernable at p = 0.0203). It is possible, however, that the greatest rate of change in Ks and SWAC occurred within even a year of reclamation. The results of this study call for active measures to reduce organic soil degradation such as reducing tillage and on‐field traffic or following a crop rotation scheme.

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Lettuce is an important crop in Canada, mainly grown in South West Quebec muck soils. Lettuce is sensitive to water stress during periods of high crop water requirements, which result in important yields decrease mainly due to tip burn. This physiological disorder can be controlled by adequate irrigation, which is affected by spatial distribution patterns of water needs at different field scales. Such patterns result from spatial variability of soil properties and water drainage, and from evapotranspirative processes affecting local crop water needs at a given time. This study aimed at evaluating irrigation management performances (water and energy consumption, leaching and yield) for Romaine lettuce in a Histosol at two spatial scales, local and global (0.5 and 7 ha). Three field experiments were performed during summers 2010 and 2011 at two sites of 7 ha presenting a high spatial variability in available water (AW). The set up was divided into three zones equipped with wireless tensiometers. The critical irrigation threshold for initiating irrigation was −30 kPa for a low (< 4mm) potential evapotranspirative (ET) demand and −15 kPa for a higher ET (> 4 mm) [1]. Results indicated that local irrigation management has resulted in marketable yield increase of 16.5 to 18.2% depending on years, but resulted in 21.2 to 23.6% more water (and consequently energy) use with respect to global management. Higher frequency and quantity of applied irrigation water has resulted in higher tracer leaching in the second year in the local irrigation management approach.