When selecting fertilizers for soil fertilization before planting winter lettuce seedlings, it is important to know that lettuce is sensitive to high salt concentrations in the soil. This can cause leaf tip burn and, later on, loose heads of lettuce. Therefore, sulfate fertilizers should be used.
It is recommended to fertilize with NPK 5-20-30 + 26 SO3 at a rate of 50 g/m² or NPK 7-14-21 + 2 MgO + 18 SO3 at a rate of 70 g/m². Additionally, 15-20 g/m² of Urea 46% N should be added before planting.
The first fertilization should occur when the lettuce reaches the 6-7 leaf stage, using 10 g/m² of KAN 27% N + 4.8 MgO. The second fertilization is applied 2-3 weeks before harvest, also using 10 g/m² of KAN 27% N + 4.8 MgO. This means a total of 20 g/m² of KAN 27% N + 4.8 MgO is used in both fertilizations.
Example Calculation for Open Field Lettuce Fertilization Based on:
- Vegetation period from planting to harvest: 45 days,
- Two applications of KAN,
- Average yield: 30 t/ha,
- Using NPK formulation 5:20:30 S,
- Urea usage.
Nutrient Removal:
- 73 kg N/ha
- 29 kg P2O5/ha
- 126 kg K2O/ha
Fertilization Recommendation:
- 81 kg N/ha
- 82 kg P2O5/ha
- 232 kg K2O/ha
Fertilizers:
- NPK = 5:20:30 at 591 kg/ha
- N = Urea at 65 kg/ha
Top Dressing:
- 2 applications of 46 kg KAN/ha
Optimal NPK Fertilizer Formulation: 8:11:30
Nutrient Balance (Surplus or Deficit):
- N = 0 kg/ha
- P2O5 = 36 kg/ha
- K2O = -54 kg/ha
Calculation for Lettuce with the Same Parameters but Using NPK 5:14:20 Formulation:
Nutrient Removal:
- 73 kg N/ha
- 29 kg P2O5/ha
- 126 kg K2O/ha
Fertilization Recommendation:
- 81 kg N/ha
- 82 kg P2O5/ha
- 232 kg K2O/ha
Fertilizers:
- NPK = 5:14:20 at 679 kg/ha
- N = Urea at 55 kg/ha
Top Dressing:
- 2 applications of 46 kg KAN/ha
Optimal NPK Fertilizer Formulation: 8:11:30
Nutrient Balance (Surplus or Deficit):
- N = 0 kg/ha
- P2O5 = 13 kg/ha
- K2O = -28 kg/ha
