Phosphorus Fertilizer and Grazing Management Effects on Phosphorus in Runoff from Dairy Pastures
- Warwick J. Dougherty *a,
- Paul J. Nichollsc,
- Paul J. Milhamab,
- Euie J. Havilahd and
- Roy A. Lawriea
- a New South Wales Dep. of Primary Industries, Locked Bag 4, Richmond, NSW, Australia 2753
c New South Wales Dep. of Primary Industries, Elizabeth Macarthur Agricultural Inst., PMB 8, Camden, NSW, Australia 2570
b Centre for Plant and Food Science, Univ. of Western Sydney, LB 1797, Penrith South DC, NSW, Australia 1797
d New South Wales Dep. of Primary Industries, Pasture Research Unit, PO Box 63, Berry, NSW, Australia 2535
Fertilizer phosphorus (P) and grazing-related factors can influence runoff P concentrations from grazed pastures. To investigate these effects, we monitored the concentrations of P in surface runoff from grazed dairy pasture plots (50 × 25 m) treated with four fertilizer P rates (0, 20, 40, and 80 kg ha−1 yr−1) for 3.5 yr at Camden, New South Wales. Total P concentrations in runoff were high (0.86–11.13 mg L−1) even from the control plot (average 1.94 mg L−1). Phosphorus fertilizer significantly (P < 0.001) increased runoff P concentrations (average runoff P concentrations from the P20, P40, and P80 treatments were 2.78, 3.32, and 5.57 mg L−1, respectively). However, the magnitude of the effect of P fertilizer varied between runoff events (P < 0.01). Further analysis revealed the combined effects on runoff P concentration of P rate, P rate × number of applications (P < 0.001), P rate × time since fertilizer (P < 0.001), dung P (P < 0.001), time since grazing (P < 0.05), and pasture biomass (P < 0.001). A conceptual model of the sources of P in runoff comprising three components is proposed to explain the mobilization of P in runoff and to identify strategies to reduce runoff P concentrations. Our data suggest that the principal strategy for minimizing runoff P concentrations from grazed dairy pastures should be the maintenance of soil P at or near the agronomic optimum by the use of appropriate rates of P fertilizer.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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