Phosphorus

Phosphorus

1. essential, irreplaceable nutrient

   • Global P reserves limited
   • cannot be produced
   • P recycling
     • EU green paper
       • reduce Ag waste
       • promote P recycling from waste
   • crops also need K
     • too much K cause grass staggers

2. P lost from soils causes effects of eutrophication

   • loss of O2 in water
   • losses are sewage and agriculture
     • contribution from Ag increasing
       • controls on sewage increasing
     • 50-75% urban
     • 20-50% ag

3. need to maintain P for optimum yields

   • only apply where needed
     • not with 2m of watercourse
   • little or no P if index >3
     • index measures available P rather than total P
     • target index is 2
       • arable - 2 and 3 most common indices
         • grass - 1 and 2 most common
       • 10years to move an index
     • will leach above 4
   • yield increases up to index 2
     • critical value
     • crop yields eg potato increase upto index 3

4. consider reducing P content of animal diets

5. doesn't move in soil

   • roots need to find it to benefit
     • yet is required to create roots
       • starter P - next to seed
   • don't leave on soil
     • most P in top 1cm
       • plough to get P where most efficient

6. efficiency pH = 6.5

7. yields being maintained despite reduction in inputs

8. potatoes need a lot of P

   • but leave a lot of P
     • inefficient

9. for good N response need adequate P

   • maize benefits from fresh P
     • even if soil levels are high
     • more available

10. improving P efficiency

    • soil analysis
    • annual vs rotational application
    • placement
    • pH
    • erosion control
    • correct ratio of fert
    • adequate moisture
    • adequate supply of other nutrients

11. follow COGAP