Abstract
Organic agriculture plays a vital role in sustainable food production by improving soil health and enhancing the nutritional quality of horticultural crops. This study aimed to determine the optimal dose of vermicompost for the organic cultivation of blackberries in greenhouses. The experiment was conducted during the winters of 2024 and 2025 at the National Center for Organic Agriculture in Qassim, Saudi Arabia, using the blackberry cultivar Prime Ark 45. A randomized complete block design (RCBD) was used to evaluate five vermicompost doses, ranging from 0 to 2 kg per plant. Vermicompost application improved soil fertility by increasing organic matter and available N, P, and K, while reducing salinity and pH. The 1.5 kg/plant rate produced the highest soil and leaf nutrient levels (28–45% above the control), the greatest yield (4.54 kg/plant), and improved fruit physical and chemical qualities, including sugars, total soluble solids, anthocyanins, phenols, and vitamin C; acidity decreased. Increasing the rate from 1.5 to 2 kg/plant led to a decrease in yield and quality. In conclusion, the study suggests that 1.5 kg of vermicompost per plant is the optimal dose to maximize soil fertility, yield, and fruit quality in organic greenhouse blackberry production.