Phosphorus

Phosphorus

essential, irreplaceable nutrient
1. Global P reserves limited
2. cannot be produced
3. P recycling
  1. EU green paper
    1. reduce Ag waste
    2. promote P recycling from waste
4. crops also need K
  1. too much K cause grass staggers
P lost from soils causes effects of eutrophication
1. loss of O2 in water
2. losses are sewage and agriculture
  1. contribution from Ag increasing
    1. controls on sewage increasing
  2. 50-75% urban
  3. 20-50% ag
need to maintain P for optimum yields
1. only apply where needed
  1. not with 2m of watercourse
2. little or no P if index >3
  1. index measures available P rather than total P
  2. target index is 2
    1. arable - 2 and 3 most common indices
      1. grass - 1 and 2 most common
    2. 10years to move an index
  3. will leach above 4
3. yield increases up to index 2
  1. critical value
  2. crop yields eg potato increase upto index 3
consider reducing P content of animal diets
doesn't move in soil
1. roots need to find it to benefit
  1. yet is required to create roots
    1. starter P - next to seed
2. don't leave on soil
  1. most P in top 1cm
    1. plough to get P where most efficient
efficiency pH = 6.5
yields being maintained despite reduction in inputs
potatoes need a lot of P
1. but leave a lot of P
  1. inefficient
for good N response need adequate P
1. maize benefits from fresh P
  1. even if soil levels are high
  2. more available
improving P efficiency
1. soil analysis
2. annual vs rotational application
3. placement
4. pH
5. erosion control
6. correct ratio of fert
7. adequate moisture
8. adequate supply of other nutrients
follow COGAP

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