Influence of Diameter Class and Field Conditions on Nutrient Cycling under Toona ciliata M. Roem Trees in North-Western Himalaya

摘要

The aim of the present study is to report the variation in soil and plant nutrients, leaf litter deposition and microbial biomass, and their cycling under four different diameter classes and two field conditions of Toona ciliata trees growing under natural conditions in mid hills of Himachal Pradesh, India. Soil samples from two directions of each distance, i.e., 1 m from the tree trunk (E~(1)), half way to the crown radius (E~(2)), perimeter of the crown radius (E~(3)) and double the crown radius (E~(4)) in two different field conditions, i.e., cultivated field (C~(1)) and uncultivated field (C~(2)), were taken and mixed to form one composite sample. The collected soil samples were tested in the laboratory for different parameters through standard procedures. The results revealed that soil physico-chemical characteristics improved inside the tree canopy compared to outside. Bulk density and pH increased from the lowermost diameter class to the uppermost classes with successive increase in the diameter from 20 to 30 cm to >50 cm diameter at breast height (DBH) trees. Significantly higher nitrogen (480 kg ha_(−1)) and bulk density (1.18 g cm_(−3)) were recorded in cultivated fields. Soil organic carbon (2.30%) and soil carbon density (52.20 t ha_(−1)) showed significantly higher values in uncultivated bunds. Higher microbial biomass was recorded in the soil towards uncultivated bunds under the canopy of higher diameter class. The amount of nutrients (g m_(−2)) added to the soil due to the leaf litter accumulation were in the range of 29.9–45.5 (g m_(−2)) in carbon, 1.49–2.27 (g m_(−2)) in nitrogen, 0.061–0.092 (g m_(−2)) in phosphorus, 3.27–4.97 (g m_(−2)) in potassium, 3.27–4.97 (g m_(−2)) in calcium, 0.039–0.059 (g m_(−2)) in iron, 0.003–0.005 (g m_(−2)) in manganese and 0.001–0.002 (g m_(−2)) in copper. The study concludes that growing of this tree species in mid hill environmental conditions will make important contribution by improving the soil and nutrient conditions, and can be a source of fertility which would improve crop production and livelihood.