Biosolids and the need for Potash |
Additional potash requirements for crops receiving biosolids
For average-yielding crops assuming no other manure is applied
Fertiliser policy should be tailored to individual situations taking into account: rotation, crop grown, yield,
treatment of residues such as straw, soil type and soil fertility level. Refer to other PDA leaflets or to the MAFF
RB209 recommendations for precise guidance for individual crops. Check soil nutrient status every 4-5 years by
soil analysis.
| soil K index | |||||||||
| kg/ha K2O | 0 | 1 | 2- | 2+ | 3 | 4 | |||
| Cereals | |||||||||
| Straw returned | |||||||||
| winter cereals (8 t/ha) | 95 | 70 | 45 | 20 | 0 | 0 | |||
| spring cereals and oats (7 t/ha) | 90 | 65 | 40 | 20 | 0 | 0 | |||
| Straw removed | |||||||||
 |
-winter cereals (8 t/ha) | 145 | 120 | 95 | 70 | 25 | 0 | ||
| -spring cereals (7 t/ha) | 145 | 120 | 95 | 70 | 25 | 0 | |||
| -all oats (7 t/ha) | 170 | 145 | 120 | 95 | 50 | 0 | |||
| Oilseed rape | 90 | 65 | 40 | 20 | 0 | 0 | |||
| Linseed | 75 | 50 | 25 | 0 | 0 | 0 | |||
| Peas and Beans | 90 | 65 | 40 | 20 | 0 | 0 | |||
| Potatoes | |||||||||
| Earlies, seeds (30t/ha) | 220 | 195 | 170 | 145 | 50 | 0 | |||
| Maincrop, 2nd earlies (50t/ha) | 350 | 325 | 300 | 275 | 150 | 0 | |||
| Sugar Beet (60t/ha) |
150 |
125 |
100 |
75 |
0 |
0 |
|||
| (Assuming sodium is also applied) | |||||||||
| Fodder Beet (65t/ha) | 310 | 285 | 260 | 235 | 175 | 0 | |||
| Forage Maize (40 t/ha) | 230 | 205 | 180 | 155 | 110 | 0 | |||
| Kale (40 t/ha) | 250 | 225 | 200 | 175 | 130 | 0 | |||
| Grass | |||||||||
| Reseeding | 120 | 80 | 60 | 40 | 0 | 0 | |||
| Grazing only | 60 | 30 | 20 | 0 | 0 | 0 | |||
| Hay | |||||||||
| 1 cut + grazing | 140 | 115 | 90 | 65 | 20 | 0 | |||
| Silage | |||||||||
| 1 cut + grazing | 200 | 170 | 140 | 120 | 30 | 0 | |||
| 2 cuts + grazing | 320 | 270 | 230 | 180 | 70 | 0 | |||
| 3 cuts + grazing | 370 | 320 | 280 | 190 | 90 | 0 | |||
|
|||||||||
Conclusion
The application of biosolids to agricultural land makes a useful contribution to the recycling of nitrogen and phosphate, and completes natural carbon cycles. However, biosolids are seriously imbalanced nutritionally because of their low potash content. Where they are used additional potash is required and there is frequently only a need to apply a straight potash fertiliser to balance the N and P in the biosolids. Serious soil fertility and crop yield problems will usually arise if this balancing potash is omitted. Potash is firmly held in most soils so there is considerable flexibility in timing the applications of this essential nutrient. (see Timing of Potash).