Small-scale, high-intensity rainfall simulation under-estimates natural runoff P concentrations from pastures on hill-slopes

Soil Research - Tập 46 Số 8 - Trang 694 - 2008
Warwick J. Dougherty1,2, David Nash3, Jim Cox4, David J. Chittleborough2, Nigel Fleming5
1Current address: New South Wales Department of Primary Industries, Locked Bag 4, Richmond, NSW 2753, Australia.
2Soil and Land Systems, School of Earth and Environmental Sciences, University of Adelaide, SA 5005, Australia.
3Department of Primary Industries and eWater CRC, RMB 2460, Ellinbank, Vic. 3820, Australia.
4CSIRO Land and Water and eWater CRC, PMB 2, Glen Osmond, SA 5064, Australia.
5South Australian Research and Development Institute and eWater CRC, GPO Box 397, Adelaide, SA 5001, Australia.

Tóm tắt

Rainfall simulation is a widely used technique for studying the processes, and quantifying the mobilisation, of phosphorus (P) from soil/pasture systems into surface runoff. There are conflicting reports in the literature of the effects of rainfall simulation on runoff P concentrations and forms of P compared to those under natural rainfall runoff conditions. Furthermore, there is a dearth of information on how rainfall simulation studies relate to hill-slope and landscape scale processes and measures. In this study we compare P mobilisation by examining P forms and concentrations in runoff from small-scale, high-intensity (SH, 1.5 m2, 80 mm/h) rainfall simulation and large-scale, low-intensity (LL, 1250 m2, 8 mm/h) simulations that have previously been shown to approximate natural runoff on hill-slopes. We also examined the effect of soil P status on this comparison. The SH methodology resulted in lower (average 56%) runoff P concentrations than those measured under the LL methodology. The interaction method × soil P status was highly significant (P < 0.001). There was no significant effect of method (SH v. LL) and soil P status on P forms (%).The hydrological characteristics were very different between the 2 methods, runoff rates being c. 42 and 3 mm/h for the SH and LL methods, respectively. We hypothesise that the lower runoff P concentrations from the SH method are the result of a combination of (i) the P mobilisation being a rate-limited process, and (ii) the relatively high runoff rates and short runoff path-lengths of the SH method allowing for relatively incomplete attainment of equilibrium between P in the soil/pasture system and runoff. We conclude that small-scale, high-intensity rainfall simulation provides a useful tool for studying treatment effects and processes of mobilisation in pastures, but concentration and load data should not be inferred for natural conditions at larger scales without a clear understanding of the effects of the rainfall simulation methodology on the results for the system being studied.

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Soil Research

Tập 46 Số 8

694

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