Impact of planting dates and seeding densities on soil water depletion pattern, root distribution, and water productivity of industrial hemp

Industrial hemp (Cannabis sativa L.) has the potential to thrive in water-limited regions due to its deep roots and drought tolerance. However, little is known about hemp root dynamics and water productivity in the semi-arid West Texas. Therefore, this study investigates the impact of planting dates (P1- April 19th, P2- May 10th, and P3- June 6th) and seeding densities (SD1- 85, SD2- 1408, and SD3- 1972 thousand seeds ha⁻¹) on root growth, soil water depletion and water productivity of industrial hemp. The experiment was randomized in a blocked split-plot design. In 2023, P2 exhibited higher root length density, particularly fine roots compared to other planting dates. P2 also recorded the greatest soil water depletion during both years. Seeding densities showed comparable soil water depletion in 2022, but in 2023, SD2 depleted more water than SD1, while SD3 exhibited no significant differences in water depletion. P3 produced the lowest plant biomass, bast, and hurd fiber yields and their water productivity in both years. However, P3 demonstrated higher grain yield and grain water productivity in 2022, while P2 showed greater grain production in 2023, showing no significant difference in grain water productivity across plantings. Over both years, SD1 had the lowest production and water productivity for most of the yield parameters. In conclusion, May planting at higher seeding densities can enhance water productivity in West Texas conditions.