Potassium fertilization of rapeseed
Rapeseed is a basic oil plant in Poland and Europe. Winter rape with a yield of 3.5 t of seeds with the appropriate weight of straw uptakes 80 kg P2O5, 186 kg N and almost the same amount of potassium (180 kg K2O). In autumn, rapeseed plants absorb up to 25% of the potassium accumulated during the vegetation period. Plants well nourished with potassium develop a stronger root system in autumn and a thicker root.
Potassium has a positive effect on the plants condition during winter period, which significantly reduces wintering losses. Potassium also increases the resistance of plants to spring frosts, often occurring in May. This element takes part in the control of water management. It also participates in opening and closing crevices. Thanks to this, plants well supplied with potassium do better during periods of rainfall deficiency.
This component determines the use of nitrogen, so plants malnourished with potassium have problems with taking up this element, which limits the development of the assimilation surface of the plant, and this causes lower yields of dry matter of individual plant parts.
Potassium also takes part in the transformation and transport of assimilates. It has a positive effect on the formation of ATP - an energy carrier. It also stimulates the process of fat formation, and an increase of its content in seeds. It participates in protein accumulation. If there is not enough potassium nutrition, the protein content decreases regardless of the level of supply of nitrogen to plants. Plants well supplied with potassium are also more resistant to fungal diseases and pest infestation. Potassium also limits the lodging of plants. It also increases nectar secretion, which attracts rapeseed pollinating insects and contributes to abundant pods formation.
Recommendations for fertilizing rape with potassium:
The amount of potassium doses depends on the quality of the soil and its abundance in the available form of this nutrient as well as the expected grain yield and amounts to 50-180 kg K2O/ha in worse soil conditions and 60-180 kg K2O/ha on better soils. If manure is used under rape, potassium and phosphorus doses can be reduced by 25-30%.
Doses of phosphorus and potassium for winter rape, kg/ha (Wałkowski 2005)
|
Zasobność gleby | Soil suitability complex | |||||
|---|---|---|---|---|---|---|
| Wheat very good Wheat good Rye very good | Strong cereal-fodder Mountain wheat | Wheat not suitable Rye good
| ||||
| P2O5 | K2O | P2O5 | K2O | P2O5 | K2O | |
| Very low | 130 | 180 | 130 | 170 | 135 | 180 |
| Low | 95 | 160 | 90 | 150 | 95 | 150 |
| Medium | 60 | 140 | 50 | 130 | 65 | 120 |
| High | 50 | 70 | 45 | 80 | 40 | 70 |
| Very high | 40 | 60 | 35 | 50 | 30 | 50 |
| Expected yield, t/ha | above 3,5 | 2,5 – 3,5 | below 2,5 | |||
Rapeseed is a chlorine-neutral plant, so for its application a high concentration potassium salt should be used. It is best to apply the whole dose of potassium salt during sowing. Only in lighter soils, where there is a risk of leaching and large losses of potassium, 2/3 of the dose is applied in autumn and the remaining 1/3 in spring. Similarly, if for any reason potassium fertilization was not performed before rape sowing, it should be performed as early as possible in spring.
When determining the potassium dose, more attention should be paid to improving the soil's abundance in available potassium than to the amount of pre-sowing fertilization with this nutrient. The aim should be to ensure that the available potassium content of the soil is at least medium.
Written by dr inż. Arkadiusz Artyszak