Tea yield and soil properties as affected by slope position and aspect in Lahijan area, Iran

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.