Alfalfa has high fertility requirements (Table 3-2). For more information on the nitrogen, phosphorus and potassium requirements of alfalfa, see the fertility section of Chapter 5, Cool-season Perennials.
Sulphur
Sulphur (S) deficiency is being observed more frequently on alfalfa in Ontario with significant reductions in yield. The appearance of sulphur deficiency is similar to nitrogen deficiency with general yellowing of the plants. Sulphur availability varies from year to year according to temperature and rainfall. Sulphur, like nitrogen, can be leached below the root zone. Sulphur in manure is in the elemental form, which is more slowly available than sulphate fertilizers.
Sulphur deficiencies are more likely to occur in Northwestern Ontario, (where soil is upwind of major industrial centres) on low organic matter soils, and soils that have not had a manure application for several years. Tissue sampling of alfalfa is a diagnostic tool used to predict whether there will be a response to applying S (see Table 3-3). If required, apply 6 kg/ha of S per tonne (5 lb/acre of S/ton) of expected dry matter yield. Sulphur must be in the sulphate form to be utilized by plants, so application of sulphate-S provides a more immediate yield response. Applying elemental-S bulk, blended with other fertilizer, is a cost-effective long-term method of providing S.
| One Production Year (3 cuts) | Lifetime (10 cuts) | |||
| Metric | Imperial | Metric | Imperial | |
| Yield | 7.78 tonnes DM/ha | 3.47 tons DM/acre | 25.34 tonnes DM/ha | 11.30 tons DM/acre |
| Nitrogen Removal | 244 kg/ha | 218 lb/acre | 793 kg/ha | 708 lb/acre |
| Phosphate Removal | 50 kg/ha | 45 lb/acre | 164 kg/ha | 146 lb/acre |
| Potash Removal | 233 kg/ha | 208 lb/acre | 758 kg/ha | 676 lb/acre |
Boron
Boron (B) is important for alfalfa, but application is not required on all soils. A deficiency shows up mainly on high-pH, sandy soils. Boron applications are often advised on sandy soils and, in particular, the sandy loam and loam soils in the area east of the Niagara Escarpment up to and including Frontenac County. Boron deficiency is seen most frequently on droughty soils under dry conditions.
As boron deficiency becomes more visual, the youngest upper leaves of the plant become yellow to red in different plants (Figure 3-4). Growth can be severely stunted and winter hardiness reduced.
Boron deficiency can usually be corrected or prevented by an application of 1.0–2.0 kg/ha (0.9–1.8 lb/acre) of boron broadcast with the other fertilizer (e.g., potash). Boron should not be banded at seeding.
