Ploughing-down v spreading P&K fertiliser
DO we lose anything by ploughing down P and K fertiliser, rather than spreading on to a prepared seedbed?
THE short answer is no. But then you have to consider the soil indices for both phosphorus and potassium and the depth of ploughing.
Most growers will have a soil analysis carried out every five years, or possibly three years in some cases. Most soils are soil index 2 or above for these. At index three we are talking about maintenance dressings only from time to time and I dont think it will make any difference at all how P and K are introduced. At index one, more regular applications are needed but, again, there should be little difference in application methods.
However, it is important to keep the nutrient level of the topsoil high, so growers should not be ploughing too deeply in an index one situation. It is very rare to get a response to P & K application because the aim is to supply a maintenance dressing.
If it is a new field, if growers are not sure of the indices, then they do need to get a soil analysis.
THE grower wont lose much on the potash side as long as he isnt ploughing down below the rooting depth; it might be important to have the nutrient in the topmost layer for a shallow-rooting crop such as lettuce. Top dressing may place the phosphorus in the top 4-5mm, where it can be beneficial to some crops because of the even distribution.
For a suga- beet grower, however, ploughing down potash rather than incorporating wont make a difference.
With phosphorus there might be a difference. Ploughing for sugar beet is normally done in the previous autumn for spring seeding, so there is a possibility of some phosphate being lost over the winter.
However, the act of ploughing down doesnt cause problems as long as you dont plough below the rooting depth of the crop, which can be quite extensive for crops such as wheat and sugar beet, certainly below the 300mm to which most people will plough.