Information

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

Level 1 General description

Purpose:

The purpose of this study was to compare P mobilisation by examining P forms and concentration in runoff from small-scale, high-intensity rainfall simulation and large-scale, low intensity simulations that have previously been shown to approximate natural runoff on hill-slopes.

Methods (brief)

Two rainfall simulation methods (LL, large plot, low rainfall intensity and SH, small plot, high rainfall intensity) were used to identify natural P concentrations in runoff.

Rainfall simulations (both LL and SH) were undertaken within large runoff plots that were themselves nested within larger grazing plots. Each LL simulation utilised a whole runoff plot, whereas the SH simulations were nested within the plot. The runoff plots were 50m long and 25m wide, on an average slope of 5% (± 0.5%), and were located in a mid-slope position.

For the LL artificial runoff events, over-head sprinklers were used to apply water to the whole runoff plot at a rate of 8 mm/h for 10 h. The SH rainfall simulations were carried out using a swinging boom simulator. Rainfall was applied to an area of 2 by 0.75m at rainfall intensity of 80 mm/h and continued for 20 min after the commencement of runoff. The SH and LL simulations were undertaken on consecutive days. Soil samples were collected after each simulation event. Total P and total dissolved P were determined by acidic persulfate digestion followed by colourimetric determination of P.

Key findings (brief)

The interaction method x 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 approximately 42 and 3 mm/h for the SH and LL methods, respectively.

Location

Camden (34.07oS, 150.69oE), 60 km south-west of Sydney.

Related studies

NA

Key references and sources of this data synthesis

These data summaries have been extracted from

      i. Dougherty WJ, Nash DM, Chittleborough DJ, Cox JW, Fleming NK. 2008. Small-scale, high-intensity rainfall simulation under-estimates natural runoff P concentration from pastures on hill-slopes. Australian Journal of Soil Research 46: 694 – 702.