title: Salt as a mitigation option for decreasing nitrogen leaching losses from grazed pastures.
abstract: BACKGROUND
  The main source of nitrogen (N) leaching from grazed pastures is animal urine with a high N deposition rate (i.e. per urine patch), particularly between late summer and early winter. Salt is a potential mitigation option as a diuretic to induce greater drinking-water intake, increase urination frequency, decrease urine N concentration and urine N deposition rate, and thereby potentially decrease N leaching. This hypothesis was tested in three phases: a cattle metabolism stall study to examine effects of salt supplementation rate on water consumption, urination frequency and urine N concentration; a grazing trial to assess effects of salt (150 g per heifer per day) on urination frequency; and a lysimeter study on effects of urine N rate on N leaching.
  
  
  RESULTS
  Salt supplementation increased cattle water intake. Urination frequency increased by up to 69%, with a similar decrease in urine N deposition rate and no change in individual urination volume. Under field grazing, sensors showed increased urination frequency by 17%. Lysimeter studies showed a proportionally greater decrease in N leaching with decreased urine N rate. Modelling revealed that this could decrease per-hectare N leaching by 10-22%.
  
  
  CONCLUSIONS
  Salt supplementation increases cattle water intake and urination frequency, resulting in a lower urine N deposition rate and proportionally greater decrease in urine N leaching. Strategic salt supplementation in autumn/early winter with feed is a practical mitigation option to decrease N leaching in grazed pastures.
authors: AgResearch Ruakura, Hamilton, New Zealand.
authors: Stewart F
authors: SF
authors: Ledgard
authors: AgResearch Ruakura, Hamilton, New Zealand.
authors: Brendon
authors: B
authors: Welten
authors: AgResearch Grasslands, Palmerston North, New Zealand.
authors: Keith
authors: K
authors: Betteridge
mesh_terms: D000821:Animal Feed; D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D002417:Cattle; D003612:Dairying; D019587:Dietary Supplements; D004326:Drinking / Q000187:drug effects; D005260:Female; D065948:Grassland; D006801:Humans; D058751:Livestock / Q000378:metabolism*; D009584:Nitrogen / Q000652:urine*; D017673:Sodium Chloride, Dietary / Q000494:pharmacology*; D012987:Soil / Q000737:chemistry*; D014554:Urination / Q000187:drug effects
chemical_list: D017673:Sodium Chloride, Dietary; D012987:Soil; D009584:Nitrogen
keywords: cattle; grazed pasture; nitrogen leaching; salt; urination frequency