The present study was carried out during two consequence growing years 2016 and 2017, to assess the effects of climatic, edaphic and water quality on growth characteristics, yield production, anatomical and physiological properties of walnut trees (Juglans regia L.) in northern parts of Erbil Province from three different locations. This investigation includes several aspects related to walnut trees such as influences of soil quality index and irrigated water quality index on walnut growth. Yield and physiology; in addition to the evaluating the nutritional status of leaves by using diagnosis and recommendation integrated system, and compensate nutrient deficit through using NPK fertilization to cultivated walnut seedlings and influences on morphological and anatomical component of tree. Finally, using walnut leaves and green husk extractions as allelopathic substances and application it as a bio-weeds against wheat, wild barley, and mustard rape. The differences between walnut orchard in various locations were compared by using different statistical approaches (Complete Randomized Design-CRD, Principal component analysis, Factorial analysis, Correlation coefficient test) and Duncan multiple comparison test at significant level (P≤0.05) was used to compare among mean values.
The results are summarized as:
Growth and yield characteristics:
1. Walnut trees height from Shaqlawa towards Malakan and Choman are increasing in ascending manner with values (11.1, 12.67 and 13.9m) and values (11.46, 13.3 and 15.68m) respectively for growing seasons 2016 and 2017.
2. Same manner increases in diameter breast height (DBH) and trees biomass following trees height were observed spatially and temporally.
3. Old trees are characterized by highest yield compared to young trees with productivity of 26.09 and 43.97 kg/trees respectively for 2016 to 23.53 and 40.68 kg/trees respectively for 2017, with statistically significant differences (P≤0.05) between both groups.
4. According to walnut growth indices the Malakan walnut trees recorded the highest relative growth rate (RGR), relative chlorophyll production rate (RCPR), and net assimilation rate (NAR) values (2588 mg/kg/d, 1480 mg/kg/d. and 3.633 g/cm2/d) respectively, which nearly four times higher than that of the other two locations.
5. The results show that the smallest average NBI values are 125.6 and 27.2 respectively for both studied years which was coincided by high walnut productivity.
6. The most limiting nutrient descending order as Fe>Na>Ca>K>P>N>Mg respectively for first-year samples, and N>Na>P>Fe>Mg>Ca>K respectively for the second year.
7. From the result of principal component analysis (PCA) it reveals that the nutrient concentration was explained in the low and high yield subgroups and the DRIS index by 61.95%, 87.75% and 58.67% respectively for the first-year and 79.22%, 60% and 65.95% respectively for the second-year sampling.
SQI and IWQI:
8. Soil quality index (SQI) values were varied from low (<0.5) soil type in location 2 (Malakan village), low (0.35) to moderate (0.72) in location 3 (Choman district) and from low (0.32) to high (0.83) soil type in location 1 (Shaqlawa district).
9. The values of irrigated water quality index (IWQI) was ranged from 0 for Shaqlawa site to highest value 1.48 in Malakan orchard, which coincided by high electrical conductivity (EC) and Sodium adsorption ratio (SAR) values.
Cultivated walnut seedlings and NPK fertilizer application:
10. Based on DRIS indices for the Fe had a negative index for all treatments and considered as a deficient nutrient.
11. The most limiting nutrient descending order was Fe>N>K>P>Na, respectively. The smallest nutrient balance indices (NBI) was 26663.7 for 200 mg/Kg treatment and produced dry shoot weight of 4.4g/plant.
12. Results indicated that 600 mg/Kg NPK dose improved the walnut plant growth of Shaqlawa, while 200mg/Kg and 400mg/Kg of NPK application were more productive for Malakan and Choman walnut plant growth characteristics respectively.
13. The inhibitory effect of walnut extract reduced germination % of wheat from 100% for control treatment to 83.3 and 53.3% for 15% treatment in both leaf and husk, respectively.
14. Seed vigor index of wheat was more influenced by husk than leaf extract, which reduced to 0.12 and 6.19% respectively. For wild barley and mustard rape inhibition percentage was 100%, and seed germination characteristics were completely reduced to zero.
Wheat seedling growth was not affected by foliar spraying of leaf and husk extract except for the weight of 1000seeds, which reduced to 3.21 and 3.18gm respectively in 15% treatment. While in wild barley, the reduction in plant length and length of the spike were observed for husk extract.