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«Tea yield and soil properties as affected by slope position and aspect in Lahijan area, Iran F. Khormalia,*, Sh. Ayoubia, F. Kananro Foomania, A. ...»

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International Journal of Plant Production 1(1), March 2007

ISSN 1735-6814


This is a refereed journal and all articles are professionally screened and reviewed.


Tea yield and soil properties as affected by slope position

and aspect in Lahijan area, Iran

F. Khormalia,*, Sh. Ayoubia, F. Kananro Foomania, A. Fatemib,

Kh. Hemmatic

a Department of Soil Science, cDepartment of Horticulture, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

b Tea Research Center, Lahijan, Iran ∗Corresponding author. Email: Khormali@yahoo.com Accepted 3 January 2007; Published online 24 February 2007.

Abstract Soil genesis, physico-chemical properties and tea yield were investigated along different hillslope positions in the major tea cultivation area of Iran, i.e. Lahijan, Gilan Province. Land suitability was also determined for the tea production in this hilly region. Four different slope positions i.e., summit, shoulder, backslope and toeslope were sampled on three slope aspects following the profile description. Tea leaf was also sampled in those positions as an index of tea yield. The results of the soil genesis studies presented a catenary evolution in which the well developed Cambisols (Hapludepts) were formed mainly on summit positions and non-developed Regosols (Udorthents) were formed on less stable segments of shoulder and backslope. In toeslope, where the groundwater saturates the soil profile, hydromorphic properties were dominant and Gleysols (Endoaquepts) were formed. Some soil physico-chemical and morphological properties such as solum thickness, thickness of the epipedons, clay content, organic carbon, total nitrogen, carbonate, and exchangeable magnesium were significantly different on different slope positions in the near surface layers.

However the differences were not reflected in the tea yield. Land suitability evaluation in different landforms in the three aspects showed that the soils were marginally suitable and non-suitable for tea production. The most limiting factors were climatic factors especially the mean minimum temperature during the coldest month of the year. Shoulder and backslope positions showed the lowest suitability due to higher slope gradient and lower organic carbon and soil depth. Tea yield as determined by leaf dry weight showed no significant differences in different slope positions. Moreover, different aspects had also a non-significant role regarding the soil properties and tea production. It is believed that in this humid region the effects of slope aspect and position are rather annihilated due to the uniform density of the vegetation and soil moisture.

Keywords: Tea cultivation; Slope positions; Aspect; Soil property.

100 F. Khormali et al. /International Journal of Plant Production (2007) 1: 98-111 Introduction Lahijan region in Gilan Province is considered as the major tea producing area in Iran.

Understanding the soil limiting factors for the production of this important plant would help policy makers for the sustainable planning and management of the soils. Tea is mainly cultivated in the hill slopes in Lahijan area. Stability of the landform directly influences the soil properties and consequently the soil productivity. Among many landform parameters, effect of slope position and aspect on the variability of soil quality attributes and yield were little studied. There are many studies carried out on the relationship of soils and geomorphic surfaces. Pierson and Mulla (1990) studied the soil properties on different slope positions and concluded that soils formed on footslope and toeslope positions contained higher organic carbon and aggregate stability compared to summit position.

Walia and Chamuah (1990), investigated some soil parameters e.g. soil texture, organic matter content, pH, kind and the presence of surface and subsurface horizons in four pedons formed on flood plains, piedmont plains, hillslopes and lowlands and showed that soils of piedmont plains were the most suitable for tea production due to higher acidic conditions and Al3+ activity. Floodplains and lowlands were shown to be non-suitable due to their poor drainage conditions. Brubaker et al., (1993), studied the soil properties highly related to landform position and found significant differences among 13 properties. Sand, silt, pH, calcium carbonate content, and exchangeable Ca2+ and Mg2+ mostly decreased down the slope. Young and Hammer (2000) found that most of the soil properties were similar between ridge and shoulder positions. Differences were minimal within the backslope. Backslopes differed from ridges and shoulders, with more argillic horizon clay, thinner epipedons, and less organic C, lower pH and base saturation, and less silt on a clayfree basis. Color patterns suggest that backslopes are wetter than ridges and shoulders, with more redoximorphic activity and organic matter accumulation on ped faces. Tsui et al., (2004) reported that the slope aspect and gradient can control the movement of water and soil material on a hillslope and hence contribute to the spatial differences of soil properties.

The studied transect was divided into three slope positions: summit, backslope and footslope, each with a different floristic composition and structure. Their results showed that organic carbon, available N, available K, extractable Fe and exchangeable Na were highest on the summit, while pH, available P, exchangeable Ca and Mg were significantly higher on the footslope at 0–5 cm soils. Similar patterns were observed at subsurface 5–15 cm depth soils. Soils were reported to have properties such as redder color, moderate to high acidity, lower than 50% base saturation in the argillic horizon, in the sloping landscapes (Bhaskar et al., 2004). Soils of the upper slope positions had higher available Fe, Mn, Cu and Zn. These soils were classified as Ultisols and Entisols while soils of valleys were of Inceptisols order. Soils particles 0.5 mm in diameter decreased downslope, and those of 0.05 and 0.5 mm formed a larger soil fraction in the midslope position other than summit or footslope. Total organic C, N and P in the middleslope soil were the lowest among the soils in the three topographic positions (Chen et al., 2002).

The term of land evaluation has been used to describe many concepts and analytical procedures, but most frequently its main objective is to appraise the potential of land for alternative kinds of use by comparison of the requirement of land use with the resources offered by the land (Dent and Young, 1981). Land evaluation is now well established as an F. Khormali et al. / International Journal of Plant Production (2007) 1: 98-111 101 important component of the broader field of resource assessment (Messing et al., 2003).

Physical land evaluation is concerned with assessing whether a particular use of a group of uses could be supported by the land resource. In the agricultural context, it involves comparing a crop's physical requirements for growth with the land's inherent or managed properties and provides a performance index such as suitability index (Bouma, 1999).

Three adjacent hillsopes with different aspects in the Lahijan area were considered to study some selected soil quality attributes, soil development and land suitability for tea production and relate the effects of slope aspect and position on the spatial variability of soils properties and tea yield.

Methods and Materials Site setting and sampling The study area is a hilly region of Kate Chal, 2 Km from Lahijan, lying between 37° 10´ 59" northern latitude and 50° 2´ 44" eastern longitude (Figure 1). The climate of the region is humid with the mean annual precipitation of 1312 mm and mean minimum and maximum temperatures of 19.5 and 2.8 °C, respectively. The mean humidity is 77.5% and the annual evapotranspiration is 884 mm. The soil moisture and temperature regimes are udic and thermic, respectively. The major geological formations are composed of thick sedimentary and metamorphic rocks of Tertiary and Quaternary periods. The coastal plain lying between Alborz mountain ranges and Caspian Sea is composed of marine, river and aeolian deposits of varying thicknesses. Three adjacent north, south and east slope aspects were selected and summit, shoulder, backslope and toeslope positions were sampled after describing the soil profiles (Figure 1). The soils were then classified according to Soil Taxonomy and World Reference Base for Soil Resources (Soil Survey Staff, 2006; WRB 2006).

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Figure 1. Study area and the slope positions sampled (SU: Summit, SH: Shoulder, BS: Backslope, TS: Toeslope) 102 F.

Khormali et al. / International Journal of Plant Production (2007) 1: 98-111 Laboratory analyses TS Particle-size distribution was determined after dissolution of CaCO3 with 2N HCl and decomposition of organic matter with 30% H2O2. After repeated washing to remove salts, samples were dispersed using sodium hexametaphosphate for determination of sand, silt and clay fractions by the pipette method (Day, 1965). Alkaline-earth carbonate was measured by acid neutralisation (Salinity Laboratory Staff, 1954). Organic carbon was measured by wet oxidation with chromic acid and back titration with ferrous ammonium sulphate (Nelson, 1982). Soil pH was measured in a saturation paste and electrical conductivity (total soluble salts) was determined in a saturation extract (Salinity Laboratory Staff, 1954). Cation exchange capacity (CEC) was determined using sodium acetate (NaOAc) at pH 8.2 (Chapman, 1965). Basic cations were determined using ammonium acetate at pH 7 (Salinity Laboratory Staff 1954). Total N and available P were determined by Kjeldahl and Olsen (Olsen, 1953) methods. The soluble K and Na were measured by flame photometer and soluble Ca and Mg were determined by titration with EDTA (Salinity Laboratory Staff, 1954).

In order to study the tea green leaf production, leaves were sampled in 1.5m2 areas with three replications in each slope position. The samples were put in bags and taken to the lab for oven dry weight determinations. For land suitability evaluation, soils located in different positions were physically evaluated for tea production by comparison of the tea production requirements with land characteristics using three different comparison methods including (i) simple limitation method, (ii) number and intensity of limitations and (iii) parametric method. Parametric methods included Storie and Square root methods (Sys et al, 1991a).

The FAO guidelines for land evaluation (FAO, 1976) and land evaluation procedure constructed by Sys et al., (1991a) were used. Tea production requirements were prepared in literature cited (Sys et al., 1993) integrated with farmer’s communications. Statistical analyses were carried out on the data after the test of normality done by KolmogorovSmirnov using SPSS software (SPSS Inc, 1999) through analyses of variance. The means of soil quality parameters, in different slope positions were compared with their tea yield.

Results and Discussions

Table 1 presents the classification of the soils formed on different slope positions and aspects according to the Soil Taxonomy (Soil Survey Staff, 2006) which is based mainly on the presence of diagnostic horizons and soil moisture regimes. Soils are mostly classified as Inceptisols and Entisols. As seen, soils are all well drained except the toeslope position, which shows gley patterns and therefore classified as Endoaquepts. Due to the high slope gradient, cambic horizons are the most developed ones and there is not a significant difference among different slope positions and aspects with regard to the development of the soils. This similarity could mainly be explained by the fact that the whole study area receives high precipitation and there is no significant difference among different aspects and slope positions regarding the moisture content which is considered as a main soil forming factor. Moreover, the effect of erosion on different slope positions is highly reduced due to the dense anchorage made by tea roots.

F. Khormali et al. / International Journal of Plant Production (2007) 1: 98-111 103 Table 2 shows some physical, chemical and morphological properties of the soils. The most important feature observed, is the clay illuviation process shown as Bt horizon mainly in the summit positions. The higher stability and consequently higher infiltration in this position have provided favourable conditions for the downward leaching of clay. The clay content differences with the upper horizon however, do not meet the requirements for the argillic horizon and therefore considered as cambic horizon. Majority of the studied soils are acidic and pH increases with depth due to the leaching of bases from upper horizons.

Organic carbon is highest in the surface layers and decreases regularly with depth. The soils are poor in N and K. The texture is mainly sandy loam and sandy clay loam. The calcium carbonate content of the soils shows it's high depletion from upper horizons evidenced by having no effervescence with dilute HCl. There is no salinity or sodicity in the area. The drainage condition of the soils is well drained except the toeslope position which is poorly drained.

Table 1. Classification of the soils according to the Soil Taxonomy.

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