Considering the arid and low-rainfall climatic conditions of South Khorasan province and the necessity for cultivating low-water-demanding and industrial medicinal plants, guar was selected as a medicinal crop to evaluate the effects of planting date and density on its biochemical properties and quality traits of guar seeds. A split-plot design with three replications was employed in 2023 at two locations: Birjand and Sarayan, South Khorasan province, Iran. Treatments included three planting dates (May 12th, June 12th, and July 13th) as main plots and five plant densities (10, 20, 30, 40, and 50 plants/m²) as subplots. Analysis of variance revealed that planting date significantly affected seed yield, oil content, protein content, galactomannan content, carbohydrate content, total ash, and protein yield. Notably, delayed planting resulted in a substantial decrease in seed yield (by approximately 52.36%), carbohydrate content, galactomannan content, total ash, protein yield, and oil yield. Plant density also significantly influenced seed yield, oil content, protein content, galactomannan content, carbohydrate content, phosphorus content, total ash, protein yield, and oil yield. The highest seed yield (2125.3 kg/ha) was observed with a June 12th planting date at a density of 30 plants/m². Both planting date and density significantly affected yield and seed quality, with optimal results for protein, galactomannan, carbohydrate, and oil content achieved with the June 12th planting date and a density of 30 plants/m². This combination, likely benefiting from a longer growing season and favorable climatic conditions, yielded the highest seed yield. These findings demonstrate the potential of guar as a low-input crop for sustainable cropping systems in arid climates like South Khorasan, offering significant benefits for regional agriculture. |