Effects of Drip-Tape Spacing, Discharge and Irrigation Duration on Wheat Germination, Root Development, Yield and Water Productivity during Establishment Irrigation

Effects of Drip-Tape Spacing, Discharge and Irrigation Duration on Wheat Germination, Root Development, Yield and Water Productivity during Establishment Irrigation
Extend Abstract:
1- Background and Objectives
Water scarcity and successive droughts are the major challenges facing agricultural sector in Iran. Given the country's limited water resources, efficient irrigation management is essential in both surface and pressurized irrigation systems. The development of pressurized irrigation methods plays a key role in improving water productivity, and approximately three million hectares of Iran’s agricultural land have so far been equipped with modern irrigation systems. Among these, drip-tape irrigation has gained considerable importance for wheat production owing to its high application efficiency and adaptability to row crops. Most previous studies on drip-tape systems for wheat have focused on economic aspects, cost-reduction strategies, and the effect of lateral spacing on initial investment costs. Although wheat is the most strategic crop for food security in Iran, and research interest in drip-tape irrigation of wheat has increased due to water shortages, no study has yet specifically addressed the management of the first (establishment) irrigation and its effects on germination, stand establishment, grain yield, and water productivity. Proper management of this initial irrigation is critical for uniform seed germination and early crop establishment; poor management of this stage can cause substantial water loss and reduced yield. The present study was therefore conducted to investigate the combined effects of lateral spacing, drip discharge rate, and duration of the first irrigation on germination, root development, grain yield, and water productivity of wheat under drip-tape irrigation.

2- Methodology
A field experiment was carried out during the 2021–2022 cropping season at Zarghan Agricultural Research Station, northeast of Shiraz, Iran. The experiment was laid out as a split-split plot design based on a randomized complete block with three replications. Main plots were assigned to lateral spacing (50 cm – L1 and 75 cm – L2), subplots to dripper discharge rate (4 L/h/m – Q1 and 8 L/h/m – Q2), and sub-subplots to first irrigation duration (6 h – T1, 12 h – T2, and 18 h – T3). Each plot measured 3 m wide ×10 m long; six tape lines were installed in the 50 cm spacing treatment, and four lines in the 75 cm treatment, with 1.2 m between treatments was and 2 m between replicates. Wheat cultivar "Sirvan" was sown following standard local practices. Traits measured included number of germinated seeds, root length and volume, grain yield, and irrigation water productivity (WP). Data were statistically analyzed using ANOVA and Duncan’s multiple range test at the 5% probability level, and biplot analysis was employed to examine correlations among the traits.

3- Findings
Results indicated that lateral spacing, discharge rate, and irrigation duration all significantly influenced the germination percentage, emergence uniformity, and root characteristics (P ≤ 0.05 or P ≤ 0.01). The highest germination rate, emergence uniformity, root volume, and final plant stand were obtained with treatment L1Q2T3 (50 cm lateral spacing, 8 L/h/m discharge rate, 18-hour irrigation duration). However, the highest grain yield (6.2 t/ha) was recorded in treatment L1Q2T1, which combined the same close lateral spacing (50 cm) and high discharge rate (8 L/h/m) with the shortest irrigation duration (6 hours). Among the three factors, only discharge rate had a statistically significant effect on final grain yield, while irrigation duration showed no significant effect on yield. Biplot analysis (PCA) revealed strong positive correlations between root length, final plant density, water productivity (WP), and grain yield. The highest WP (0.89 kg/m³) was achieved in treatment L1Q1T1 (50 cm spacing, 4 L/h/m discharge, and 6-hour irrigation (, demonstrating that high water-use efficiency can be attained even with a lower discharge rate when lateral spacing is minimized and irrigation duration is kept short.

4- Conclusion
Efficient management of first irrigation in drip-tape systems is critical for uniform wheat germination and stand establishment in arid and semi-arid regions. This study demonstrated that reducing lateral spacing and increasing emitter discharge rate had significantly greater effects on early seedling development, root growth, and soil water distribution uniformity than prolonging irrigation duration. Although extended irrigation enhanced emergence uniformity, it did not increase final grain yields. From both agronomic and water productivity standpoints, the optimal strategy involves closer lateral spacing (50 cm) combined with higher discharge rate (8 L/h/m) is recommended for wheat production under drip-tape irrigation, especially in water-scarce environments. Further research is suggested to validate and refine these findings across diverse soil textures and climatic conditions.
Keywords: Establishment irrigation, Discharge rate, Drip-tape irrigation, Lateral spacing, Water productivity, Wheat, Yield.