Principles of Potash Use |
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Removal of Potash
Under-estimation of K offtake is one of the commonest causes for soil K levels to fall below target and emphasises the need to undertake careful estimations of the amount removed. Standard figures to calculate removal and therefore replacement needs are given below:
| Guidelines for calculation of phosphate and potash removal by crops | ||
|---|---|---|
| kg/t of fresh material | ||
| P2O5 | K2O | |
| Cereals - Grain only | 7.8 | 5.6 |
| Cereals - Grain & straw Cereals --- Winter wheat/barley |
8.6* |
11.3* |
| Cereals --- Spring wheta/barley | 8.8* | 13.7* |
| Cereals --- Winter/spring oats | 8.8* | 17.3* |
| Oilseed rape - Seed only | 14.0 | 11.0 |
| Oilseed rape - Seed & straw | 15.1* | 17.5* |
| Peas - dried | 8.8 | 10.0 |
| Peas - vining | 1.7 | 3.2 |
| Field Beans | 11.0 | 12.0 |
| Potatoes | 1.0 | 5.8 |
| Sugar Beet - Roots only | 0.8 | 1.7 |
| Sugar Beet - Roots & tops | 1.9 | 7.9 |
| Fodder Beet - Roots only | 0.6 | 4.0 |
| Fodder Beet - Roots & tops | 1.7 | 7.5 |
| Grass - fresh grass @ 15-20% DM | 1.4 | 4.8 |
| Grass - silage @ 25% DM | 1.7 | 6.0 |
| Grass - silage @ 30% DM | 2.1 | 7.2 |
| Grass - hay @ 86% DM | 5.9 | 18.0 |
| Kale | 1.2 | 5.0 |
| Maize - silage @ 30% DM | 1.4 | 4.4 |
| Swedes - roots only | 0.7 | 2.4 |
| Broad Beans | 1.6 | 3.6 |
| French Beans | 1.0 | 2.4 |
| Beetroot | 1.0 | 4.5 |
| Cabbage | 0.9 | 3.6 |
| Cauliflower | 1.4 | 4.8 |
| Onions - bulb | 0.7 | 1.8 |
| Sprouts - buttons | 2.6 | 6.3 |
| * offtake value is per tonne of grain or seed but includes nutrients in grain and straw | ||