Sulfur Leaching Rate Differs Based on Soil Characteristics in the Vidalia Region of Georgia, USA: Implications for Sweet Onion Production

Abstract

ABSTRACT Onion flavors arise from the enzymatically produced volatile sulfur-containing sulfinic acids created when onion cells rupture. The concentrations of these flavor-associated compounds depend on genetic and environmental factors, with soil sulfur (S) availability as a primary contributor. To understand how leaching influences S availability in soils of southeastern Georgia, a column leaching experiment was conducted over a 13-month period using soils from six historic Vidalia onion fields. Soil S in the A horizon ranged from 21–126 kg ha−1 and 126–261 kg ha−1 for plant available and total S, respectively, and 17–541 kg ha−1 for plant available S and 46–841 kg ha−1 of total S in the B horizon. Total S decreased 32% on average over the 13-month period, ranging from 10–65 kg ha−1. Unlike studies from other regions that determined that the overwhelming majority of soil S is organically bound, 16–64% of soil S in these soils was readily plant available, suggesting that in the sandy, low organic matter (OM) soils and thermic climate of southeastern Georgia, S retention is likely controlled by the combination of soil factors including, OM, amount and type of clay, and iron and aluminum content. While the amount of S decreased in all six soils, plant available S remained between 14–46 kg ha−1 in the A horizon, indicating it may take several seasons for soil S to appreciable decrease through leaching. Sweet onion producers like those in the Vidalia region should carefully monitor S additions to promote the production of low pungency onions.