Vidalia Onion Yield as Influenced by Biodegradable Mulch and Cultivar

This study aimed to determine the effect of biodegradable mulch on Vidalia onion bulb yield in three sweet onion cultivars.

Material and Methods

The experiment was conducted at the University of Georgia Vidalia Onion and Vegetable Research Center near Reidsville, GA, and at the Horticulture Farm on UGA’s Tifton campus in the winter of 2021–2022. Two weeks before planting, the soil received the equivalent of 150 lb/acre of nitrogen (N) from chicken manure. Onion seedlings were transplanted on Dec. 16, 2021.

Plants were grown on beds (6 ft center to center) with four rows (7 in. apart) and an in-row plant spacing of 5 in. Beds were uncovered or covered with film mulch. There were two lines of drip tape per bed. The experimental design was a randomized complete block with four replications. There were nine treatment combinations (three mulches with three cultivars).

Mulch treatments were black plastic mulch, biodegradable mulch, and bare soil. The cultivars evaluated were ‘Candy Joy’, ‘Macon’, and ‘Vidora’.

Plants were harvested when about 30% of the plant necks had collapsed (tops down). Onions were graded into marketable and unmarketable according to USDA grading standards. The bulb numbers and weights were recorded. After grading, a subsample of 10 marketable bulbs per replication was used to determine soluble solids content (SSC), dry matter content, and pungency (measured as pyruvate concentration). Total phenols were determined to measure antioxidant capacity (expressed as gallic acid equivalents.

Results

Location

Marketable and total-bulb number and yields, percentage of marketable bulbs, and bulb weight were higher in Reidsville than in Tifton, while cull yield was higher in Tifton than in Reidsville (Table 1).

The incidence of doubles was higher in Reidsville than in Tifton, while sour-skin incidence was the highest in Tifton. Leaf N was higher, while phosphorus (P) and potassium (K) were lower in Tifton than in Reidsville (Table 2). Bulb SSC, total phenols, and pungency were higher in Reidsville than in Tifton (Table 3).

Mulch

Plastic mulch had the highest weed control, followed by biodegradable mulch. Marketable yield, total yield, and individual bulb weight were highest on plastic mulch and lowest in bare soil (Table 1). Cull yield and the incidence of bulb sour skin were the highest on plastic mulch. Leaf nutrients were unaffected by mulch treatments, except for manganese (Mn), which was reduced in bare soil (Table 2). Bulb SSC was the highest on biodegradable mulch and the lowest on plastic mulch (Table 3).

Cultivar

Marketable yield was highest in ‘Macon’ and lowest in ‘Candy Joy’ (Table 1). There were no leaf nutrient differences among cultivars (Table 2). Bulb SSC was highest in ‘Macon’ and lowest in ‘Vidora’, while the dry matter was lowest in ‘Macon’ (Table 3). ‘Macon’ also had the highest total phenols and pungency.

Conclusion

Marketable and total yields and bulb size were the highest on plastic mulch. Onion yield was the highest on plastic mulch. Plants on biodegradable mulch had higher yields and lower weed pressure than those in bare soil. The reduced weed pressure in the plastic mulch plots may partially explain the enhanced bulb yields. Among cultivars, marketable bulb yields were the highest in ‘Macon’ and the lowest in ‘Candy Joy’.