Fertiliser
Nutrient analyses of the soil and irrigation water before planting, plus one to two plant analyses of the youngest mature leaves during growth are recommended. This will provide information on nutrients that are deficient or toxic and allow adjustment to the fertiliser program. Some nutrients in the fertiliser programs suggested in this webpage may be deleted or reduced if it is obvious that sufficient quantities are present in irrigation water, soil, compost or fertilisers from previous cropping.
Using compost in the rotation or before planting at up to 50 cubic metres per hectare will be beneficial. It will supply nutrients, organic matter, and help retain moisture in the soil. Apply phosphorus, magnesium and trace elements to sandy soils before planting (see Table 2).
Table 2 Fertilisers and application rates for sandy soils before planting
|
| Application rate |
|---|---|
| Superphosphate | 800 |
| Magnesium sulphate | 50 |
| Manganese sulphate | 25 |
| Borax | 18 |
| Iron sulphate | 18 |
| Copper sulphate | 18 |
| Zinc sulphate | 16 |
| Sodium molybdate | 2 |
Starting one week after planting, apply side dressings of nitrogen as urea (70kg/ha) each fortnight until the start of bulbing. Bulbing starts six to eight weeks before harvest when the base of the stem is 1.5 times the diameter of the main stem and small cloves can be seen internally in cross-section. Late applications of nitrogen will result in excessive side shoots.
Apply topdressings of muriate of potash (85kg/ha) with the fortnightly application of nitrogen until bulbing, with two applications of potash (without nitrogen) after bulbing.
On fertile soils, garlic can be grown with much lower applications of fertiliser.
On alkaline soils, extra trace elements may be necessary after planting and before bulbing. Zinc is the main trace element required and applied as zinc sulphate as a foliar spray at 4g/L. Symptoms of zinc deficiency in garlic include stunting of plants and yellowing of young (inner) leaves which develop burnt tips.
Manganese sulphate applied at 8g/L may also be needed. Manganese deficiency is seen as streaking of younger leaves and leaf twisting around the stem axis.
Do not apply excess fertiliser. Nitrogen, phosphorus and potassium are readily leached through sandy soils by rainfall and irrigation and can cause groundwater pollution in rivers and estuaries. Excess fertiliser will also result in side shoots in the garlic.