Management options to decrease phosphorus and sediment losses from irrigated cropland grazed by cattle and sheep

Published source details McDowell R.W. & Houlbrooke D.J. (2009) Management options to decrease phosphorus and sediment losses from irrigated cropland grazed by cattle and sheep. Soil Use and Management, 25, 224-233.
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This study is summarised as evidence for the following.

	Action	Category
	Amend the soil with non-chemical minerals and mineral wastes Action Link
	Reduce grazing intensity Action Link
	Amend the soil with formulated chemical compounds Action Link

Amend the soil with non-chemical minerals and mineral wastes

This controlled, replicated experiment in 2004-2008 on silt loam soil in New Zealand (McDowell & Houlbrooke 2009) found that applying alum (aluminium sulphate) after grazing of forage crops by cattle or sheep reduced phosphorus loss by 29% and 26%, and fine sediment loss by 16% and 43%, respectively, compared to normal forage crop grazing. Grazing cattle or sheep on forage crops increased phosphorus loss from fields by approximately 100% (1.3 kg/ha) and 33% (0.9 kg/ha) respectively, compared to normal sheep grazing on pasture (0.6 kg/ha). Forage grazing by cattle or sheep increased fine sediment loss by 1,000% (0.7 mg/ha) and 500% (0.4 mg/ha), relative to grazing pasture with sheep (0.06 mg/ha). Twenty-eight 10 × 25 m plots included four replicates of combinations of the following treatments: cattle or sheep grazing on winter forage crops (triticale Triticosecale Wittmack, then kale Brassica oleracea), sheep pasture, restricted grazing, or alum addition on the forage crops (20 kg/ha following grazing).
Reduce grazing intensity

A controlled, replicated experiment in 2004-2008 on silt loam soil in New Zealand (McDowell & Houlbrooke 2009) found that phosphorus loss from forage crop fields was reduced by 26% and 36%, and sediment loss by 35% and 53%, when cattle and sheep grazing was reduced to three/hours a day. Grazing cattle or sheep on forage crops increased phosphorus loss by approximately 100% (1.3 kg/ha) and 33% (0.9 kg/ha) respectively, relative to grazing sheep on pastures (0.6 kg/ha). Cattle or sheep grazing increased the amount of fine sediment washed from fields by 1,000% (0.7 mg/ha) or 500% (0.4 mg/ha), compared to grazing sheep on pastures (0.06 mg/ha). There were 28 plots (10 × 25 m) testing combinations of the following treatments: cattle or sheep grazing on winter forage crops (triticale Triticosecale Wittmack, then kale Brassica oleracea), sheep grazing on pasture, restricted grazing, and/or alum addition (20 kg/ha following grazing). Treatments were replicated four times.
Amend the soil with formulated chemical compounds

This controlled, replicated experiment in 2004-2008 on silt loam soil in New Zealand (McDowell & Houlbrooke 2009) found that applying alum (aluminium sulphate) after grazing of forage crops by cattle or sheep reduced phosphorus loss by 29% and 26%, and fine sediment loss by 16% and 43%, respectively, compared to normal forage crop grazing. Grazing cattle or sheep on forage crops increased phosphorus loss from fields by approximately 100% (1.3 kg/ha) and 33% (0.9 kg/ha) respectively, compared to normal sheep grazing on pasture (0.6 kg/ha). Forage grazing by cattle or sheep increased fine sediment loss by 1,000% (0.7 mg/ha) and 500% (0.4 mg/ha), relative to grazing pasture with sheep (0.06 mg/ha). Twenty-eight 10 × 25 m plots included four replicates of combinations of the following treatments: cattle or sheep grazing on winter forage crops (triticale Triticosecale Wittmack, then kale Brassica oleracea), sheep pasture, restricted grazing, or alum addition on the forage crops (20 kg/ha following grazing).