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Onions are recognized as having a high S requirement of 0.3 to 0.9 percent, depending on plant part tested. Sulfur increases the content of oils that impart flavor in onion (Chang et al., 1988). Onions remove about 100 lb of S per acre. Garlic bulb yield and concentration of flavor components
in volatile oil are improved with S fertilization (Beaton, 1966). The
highest yields of garlic (Allium sativum) have been obtained with
SOP (Laske, 1962). There were more consistently high yields under adverse
weather conditions as well as greater dry matter content when SOP was
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Potash
improves the yield and quality of onions by accelerating growth and improving
ripening without bolting. Larger bulb diameter and greater solids are
the result of adequate K. Sufficient K also reduces sprouting in storage,
thus increasing onion storage life. Onion roots are somewhat sensitive
to salts, so SOP is often recommended. (Chloride-containing fertilizers
raise the water content of onion bulbs and reduce onion storability).