Comparative Analysis of Crop Methods and Harvest Season on Agronomic Yield and Spear Quality of Asparagus in Thailand

Asparagus (Asparagus officinalis L.) represents a high-value horticultural crop in Thailand with significant export potential; however, optimizing productivity in tropical environments requires a precise understanding of how cultivation practices and harvest seasons influence marketability. Here, a split-plot experiment arranged in a completely randomized design with three replications was conducted to examine how different crop methods and harvest seasons affect asparagus yield and quality in Lopburi Province, Thailand. The main plots were categorized by harvest season—summer, rainy, and winter—while the subplots included three crop methods: conventional, GAP, and organic. Summer produced the highest yield and asparagus with the greatest levels of total chlorophyll, phenolics, and DPPH radical scavenging activity compared to other seasons. Although the conventional methods yielded the most spears per plant, these spears contained higher levels of contaminants, including cadmium, lead, and nitrate. In contrast, spears from GAP and organic methods had higher phosphorus levels. However, no pesticide residues were found in any spear samples. Economically, the organic method had the shortest payback period, owing to lower production costs; despite a lower annual yield, stable market prices kept it profitable. In addition, organic soils had the highest levels of organic matter, nitrogen, and phosphorus. Overall, while conventional methods enhance the yield and certain qualities, organic farming, particularly when harvested in summer, yields the highest economic returns and the most sustainable system among those tested.