For onions, soils need to be well structured and fertile to maximize growth and produce high yields.
Seedbed condition is critical, particularly if crops are being grown from seed. A fine, consolidated seed zone is required for maximum germination and good establishment.
Rooting is generally poor. Onions have sparse root systems with short lengths and few root hairs. Thus, it is important to maintain nutrient and soil moisture availability within the shallow rooting area. Research suggests that water uptake is restricted to the top 10 inches of soil. While onions can survive long periods of drought stress, water availability is critical for growth and high yields of quality crops. Read on investing on drip irrigation here
Under drought stress, onions are more likely to split or form double and multiple bulbs.
Onions have a high water requirement, usually around 3 inches of water per week. However, late season irrigation can delay maturity and lead to skin cracking. See how well small scale farmers are performing here
When grown on particularly light soils, inter-row guard crops of barley or wheat, or the use of straw helps minimize erosion.
Clods and stones will hinder growth, herbicide efficiency and mechanical harvesting, so heavy or stony soils are usually avoided.
Soil pH is normally in the range of 6-7, but on organic soils, onions can be grown down to pH’s of 4 it is therefore necessary to do a soil analysis to know the conditions of your soil.
Nitrate and sulfate forms of fertilizer are preferable.