Phosphorus Availabilities Differ between Cropland and Forestland in Shelterbelt Systems

Shelterbelt systems play pivotal roles in providing goods and services to the rural community and the society at large, but phosphorus (P) cycling in shelterbelt systems is poorly studied, while P cycling and availability would be linked to the ecological function and services of shelterbelt systems. This study was conducted to understand how long-term (>30 years) land-use between cropland and forestland in shelterbelt systems affect soil P status. We investigated modified Kelowna (P<inf>Kelowna</inf>) and Mehlich-3 (P<inf>Mehlich</inf>) extractable P, P fractions (by sequential chemical fractionation), P sorption properties in the 0&ndash;10 and 10&ndash;30 cm soils and their relationship in six pairs of the cropland areas and adjacent forestland (each pair constitutes a shelterbelt system) in central Alberta. Both P<inf>Kelowna</inf> and P<inf>Mehlich</inf> in the 0&ndash;10 cm soil were greater in the cropland than in the forestland. The P<inf>Kelowna</inf> ranged from 10 to 170 and 2 to 57 mg kg&minus;1 within the cropland areas and forestland, respectively. The inorganic P fraction in the 0&ndash;30 cm depth was significantly related to P<inf>Kelowna</inf> (R2 = 0.55) and P<inf>Mehlich</inf> (R2 = 0.80) in cropland, but organic P fraction was not significantly related with neither P<inf>Kelowna</inf> nor P<inf>Mehlich</inf>. The iron (Fe) and aluminum (Al) associated P (Fe/Al-P) explained ~50% and ~45% of the variation of P<inf>Kelowna</inf> in the 0&ndash;30 cm soil in the cropland and forestland, respectively. The Fe/Al-P and organic P fractions in the 0&ndash;10 cm soil were greater in the cropland than in the forestland. The differences in availability and P forms depending on the land use type in shelterbelts suggest that P management needs to be land-use type-specific for shelterbelt systems.