How to Maximise Onion Dry Matter Content

Most common bulb onions have 10-12% dry matter. Shallots have a very high dry matter content - between 16 and 35% - compared to 7-15% for onions. Onions grown for dehydration require higher dry matters of 17-20%. They are usually made from white-fleshed onions, but chives and leeks can also be processed in such a manner. Nitrogen and potassium are the most important nutrients to influence dry matter content of onion bulbs.

Crop Nutrition and Onion Bulb Dry Matter Content

Nitrate x Ammonium Nitrate

Trials confirm that a balance between nitrate and ammonium-N is most effective at promoting onion leaf and bulb growth. However, during later stages of growth, nitrate forms provide higher dry matters in the bulb.

Potassium

Potassium is particularly important where high N rates have been applied (if high yielding systems). In these situations, increasing dry matter and sugar accumulation in the bulb helps maintain yield.