Granular organic hydrosorbents increase water retention and resistance of boxwood seedlings during drought

Sufficient available water in the soil is critical for plant growth, especially soon after planting. Water absorbed by organic hydrosorbents has the potential to reduce drought stress after planting and improve seedling survival. This research evaluates the effectiveness of granular organic hydrosorbents (GOH) in increasing soil-water retention in a pot experiment with boxwood (Buxus sempervirens L.) seedlings. The leaf chlorophyll content was also evaluated to determine plant growth. The following fertilisers were used: GOH 1 comprised 50% biogas products and 50% wheat straw, and GOH 2 combined post-harvest grain, legume and oilseed residues. The fertilisers were applied to the bottom of the pot or mixed with the soil. Both types doubled the initial water retention compared to the control. While the control water retention dropped below zero after 18 days without watering, retention in the fertilised treatments ranged from 0.5 to 0.76 L. Re-watering part of the trial after the 18 days then induced increased retention to the initial levels in all treatments and the control. However, the fertilised plant's water retention was up to half a litre greater than in the control when the 62-day experiment ended. The effect of GOH application was also manifested in the chlorophyll content. In the no watering mode, the chlorophyll content was, on average, 20% and 13% higher in the treatments with GOH 1 and GOH 2 than in the control. In the watering regime, the application of GOH 1 and GOH 2 increased the chlorophyll content by an average of 31% and 26%, respectively. Finally, these trials established that the GOH applications significantly delayed boxwood-seedling drying and increased their water retention and chlorophyll content in unwatered and re-watered plants.