تاثیر توپوگرافی بر ویژگی های خاک، عملکرد و کیفیت چای در منطقه ی لاهیجان

توپوگرافی به عنوان یکی از فاکتورهای خاکسازی از طریق تاثیر بر توزیع آب در بخش های مختلف زمین‌نما و همچنین اثر بر ویژگی های‌ خاک می‌تواند از عوامل مهم و موثر بر عملکرد و کیفیت محصول باشد. این مطالعه به منظور بررسی اثر توپوگرافی بر ویژگی های خاک، عملکرد و کیفیت چای در منطقه لاهیجان استان گیلان انجام شد. به این منظور از یک ترانسکت در شیب شمالی و یک ترانسکت در شیب جنوبی باغات چای منطقه، چهار موقعیت شیب انتخاب شد. در هر موقعیت شیب یک پروفیل حفر شد و در سه پلات اطراف آن نمونه‌برداری خاک از مرکز هر پلات (عمق صفر تا 30 سانتی‌متر) و نمونه‌برداری برگ سبز چای در هر پلات انجام گرفت. ویژگی‌های فیزیکی و شیمیایی خاک، عملکرد و کیفیت چای بر اساس روش‌های استاندارد تعیین شدند. نتایج نشان داد که بیشترین درصد ماده آلی، ازت و فسفر خاک مربوط به موقعیت پنجه شیب می باشد و مقدار رطوبت اشباع جهت شمالی به طور معنی داری بیشتر از جهت جنوبی است. همچنین بیشترین مقدار عملکرد و ویژگی های کیفی چای شامل درصد تئافلاوین، تئاروبیجین، رنگ و شفافیت چای مربوط به موقعیت پنجه شیب دامنه شمالی می‌باشد. نتایج همبستگی نشان داد که ازت و ماده‌ آلی خاک دو پارامتر مهم و موثر بر عملکرد و کیفیت چای می‌باشند. بر طبق نتایج ارزیابی کیفی تناسب اراضی منطقه مطالعاتی، مهمترین عوامل محدود کننده شامل شرایط اقلیمی به ویژه حداقل درجه حرارت سردترین ماه و توپوگرافی (شیب) برای کشت چای در منطقه می‌باشدکه در موقعیت شانه شیب و شیب پشتی، پایین‌ترین کلاس تناسب (n) را موجب شده است.

Effect of topography on soil properties, yield and quality of tea in Lahijan region

Introduction As one of the pedogenic factors, topography can be an important and effective factor on yield and quality of crop performance through affecting water distribution and soil properties in different landscape positions. This factor affects soil properties by changing the altitude, steepness and slope direction of lands. Understanding the soil limiting factors for the production of crop would help policy makers for the sustainable planning and management of the soils.  Among many landscape parameters, effect of slope position and aspect on the variability of soil quality attributes and yield were little studied. This study aims to investigate the effect of topography on soil properties, yield and quality of tea in Lahijan, Guilan province. Materials and Methods Four slope positions were selected from one transect in the northern slope and one transect in the southern slope of tea gardens in Lahijan, Guilan province. In each slope position, one profile was drilled. Soil samples (0 to 30 cm depth) and green tea leaves were collected from in three plots (2 m2) around each profile. Physicochemical soil properties, yield and quality of tea were determined according to standard methods. So, this study was carried out in a factorial arrangement based on the completely randomized design with two factors, including slope position (summit, shoulder, backslope and toeslope) and slope aspect (northern and southern) with four replications. The data were analyzed by using SAS and graphs were plotted with the help of Excel program. Qualitative land suitability was also determined using simple limitation and parametric methods for tea production in this hilly region. Results and Discussion The results showed that slope position significantly affected some soil physical and chemical properties including silt content, electrical conductivity, total nitrogen, organic matter, available potassium and phosphorus. The highest content of organic matter, nitrogen and phosphorus in the soil of toeslope position can be attributed to soil erosion and transferred from top of the slope and their accumulation in this situation. The highest values of clay was found in the in the northerntoeslope position. The saturated water content in soil of the northern aspect was significantly higher than the southern aspect. The analysis of data showed that the interaction effect of slope positions and aspects on the yield and qualitative characteristics of tea, including the theaflavin, thearubigin, total color and brightness was statistically significant. Yield was the highest (3112 kg/ha) and the lowest (1762 kg/ha) in the northerntoeslope and southernshoulder positions, respectively. The highest amount of theaflavin, thearubigin, total color and brightness were related to the northerntoeslope position. The northern aspect of all slope positions had more yield than the southern aspect that have contributed to higher amount of organic matter and saturated water content in northern aspect. Correlation analysis revealed that tea yield, thearubigin and brightness were significantly positively correlated with soil organic matter (P value < 0.05) also tea yield, theaeflavin and total color positively correlated with soil nitrogen (P value < 0.05). Also, theaflavin was significantly and positively correlated with thearubigin (P value < 0.05). This correlation is probably due to the presence of common chemical precursors for the formation of two substances as well as the transformation of theaflavin to thearubigin as one of the path for the thearubigin formation. According to the land suitability evaluation, the climatic factors especially the minimum temperature during the coldest month of the year is the most important limiting factor for tea cultivation in the study area. Another limiting factor was related to the topography (slope), which caused the lowest suitability class (N) in the shoulder and backslope positions. Conclusion Overall, the results showed that higher soil quality in northerntoeslope aspect lead to an increase in yield and quality of tea. The correlation results showed that soil nitrogen and organic matter are two important and effective parameters on the yield and quality of tea. This findings showed that the need to consider physiological characteristics of specific variety and the soil moisture and nutrients status in requirements tables for tea cultivation. Investigations on the soillandscape relationship revealed that there is a strong link between the soil properties and the slope positions and aspects. More detailed studies would be helpful for the management of the sloping geomorphic surfaces.