Influence of Irrigation Intervals and Mulching Treatments on Growth and Development of Paulownia tomentosa (Thunb.) Steud. Saplings in the Bazian District, Kurdistan Region, Iraq

The successful growth of Paulownia plantations depends on application of appropriate silvicultural techniques. Namely, irrigation management and soil moisture methods like mulching treatments are important. Therefore, this study investigates the effects of varied irrigation intervals, mulching treatments, their interactions on growth, biomass allocation, nutrient uptake, and physiological responses of 36 Paulownia tomentosa saplings under semi-arid conditions in Bazian district, Kurdistan Region of Iraq. A factorial experiment was conducted using three irrigation intervals (three, six, and nine days) with three mulching treatments (no mulch, hay mulch, and black plastic film).Results revealed that irrigation frequency had a dominant and statistically significant influence on morphological parameters. Frequent irrigation, especially every 3 days, improved stem height (127.66 cm), diameter (23.25 mm), and leaf number (21.77), with best results when combined with no or hay mulch. In contrast, irrigation every 9 days led to the weakest growth, regardless of mulching. Regarding biomass accumulation, frequent irrigation, every 3 days with hay, greatly boosted dry biomass (631.86 g) in all the plant parts. While mulching alone had little effect, with irrigation particularly hay mulch enhanced growth. Biomass ratios remained stable: treatments affected total biomass more than how distributed among plant parts.Nutrient uptake was significant by irrigation and mulching. Hay mulch improved nitrogen uptake (3.03%), black plastic mulch enhanced potassium absorption (0.383%). Phosphorus uptake was affected by irrigation. The highest nitrogen (3.23%) occurred under 9-day irrigation with hay, and the highest potassium (0.51%) under 3-day irrigation with black plastic. Protein14.98% and proline 8.92 µg/g levels, both were under 9-day irrigation with hay mulch. No significant changes for chlorophyll. Water use efficiency reached to highest (1.53 g/L) under 9-day irrigation with black plastic.Frequent irrigation promoting significantly growth and biomass, while mulching with hay improved nutrient use and physiological resilience when combined with irrigation in water-limited environments.