Volatile losses of sulphur from oven drying lucerne (Medicago sativa L.): Effects of sulphur,nitrogen, phosphorus and potassium supply

Lucerne was grown in nutrient solutions at adequate and “deficient”; levels of sulphur, nitrogen, phosphorus or potassium. Volatile losses of sulphur were then measured when shoots and roots were oven dried at 80°C for 48 hours.

Small but significant losses of sulphur occurred during oven drying. Losses from shoots ranged from 4.2 to 13.9 μgS/g dry weight, which represented from 0.38 to 0.66% of the total sulphur content of the shoot. Losses from roots ranged from 12.0 to 47.8 μgS/g dry weight, representing 0.82 to 1.77% of the total sulphur content of the root. Decreases in supply of nitrogen, phosphorus, potassium or sulphur generally decreased the amount of volatile sulphur lost by oven drying shoots. Losses from roots generally decreased when supply of sulphur decreased, but increased when nitrogen and potassium supply decreased, and were generally unaffected by phosphorus supply.

The organic sulphur concentration in the tissue was linearly correlated with absolute losses of sulphur (r = 0.799** for shoots; r = 0.822** for roots), the amount of sulphur lost per unit dry weight (r = 0.469* for shoots; r = 0.381* for roots) and the percentage of the total sulphur released as volatile sulphur (r = 0.937** for shoots; r = 0.970** for roots). By contrast, the total sulphur concentration in the tissue was linearly correlated only with the amount of sulphur lost per unit dry weight ( r = 0.704** for shoots; r = 0.723** for roots).