Soil nutrient dynamics in a second rotation monocropped teak plantations

Abstract

Teak is considered the most valuable tropical timber species and is known as the "King of Timber". Kerala has 76,710 ha of pure teak plantation and 14,440 ha of teak plus softwood planting, accounting for 49.08 and 9.24 percent of the state's total plantation area, respectively. Kerala's teak plantations productivity has been declining and a large-scale drop in teak plantation productivity in the replanted teak regions, referred to as ‘Second rotation decline’ is being observed. In this context, a field study on “Soil nutrient dynamics in a second rotation monocropped teak plantations” was conducted in selected plantations from Thrissur and Chalakkudy Forest Divisions to investigate the quantity and intensity of soil nutrients among second rotation teak plantations. The study site was divided into five age classes (0-10, 10-20, 20-30, 30-40 and 40-50 years) and 6 replications (sample plots) were laid out in each age class forming a total of 30 sample plots (6 sample plots x 5 age classes). Sample plots of size 24m x 24m were laid randomly and total tree height and girth at breast height were measured in the field. Surface soil (0-30cm) samples were collected from each plot. Teak foliage sampling was done by collecting the index leaf (second fully opened leaf from the bud). Ground vegetation sampling was carried out by harvesting all vegetation from randomly laid out 1m x 1m plots from each sample unit. Soil sampling was also carried out from open barren lands from both the forest divisions. The collected soil was analysed for physical properties like particle size distribution/texture and chemical properties like soil pH, CEC, exchangeable bases, extractable acidity, organic carbon, quantity and intensity factors of N, P, K, Ca, Mg, S, Na, Fe, Zn, Cu, Mn, Al, Ni, Cd, Pb and also the critical limits with reference to teak. Quantity of C, N, P and K were estimated from teak foliage and ground vegetation following standard procedures. The results showed that among the plantations studied in Thrissur and Chalakudy divisions, there were differences in terms of soil chemical properties in 100 plantations of different age classes. However, definite pattern of concentration of elements with respect to the age of the plantations was lacking. The intensity factors of nutrients too showed no pattern or trend with reference to the age of the teak plantations. The variation in ion concentration in soil solution was not influenced by the quantity or labile pool of the element. The soils from teak plantations were observed to have more concentration of nutrients compared to barren land. All the observed soil parameters were well within the range required for the optimal growth of teak. However, there was also variation in terms of the concentration of the elements. Attempts to relate soil parameters to site productivity yielded no relevant associations, implying that the decline in productivity may be due to poor management rather than nutrient depletion. There was significant management inconsistency among the plantations, which significantly influenced the potential utilization of site resources for optimal teak development. Significant variation in the content of C, N, P and K were observed in teak foliage of various age classes. A decrease in N, P, and K content was observed in the foliage with an increase in age. The content of C, N, P and K in the ground vegetation samples of different age classes showed no pattern in trend with respect to the age of the teak plantations. Further extensive studies on the soils from teak plantations in the state in terms of ion activity to obtain better knowledge in terms of nutrient deficiency and toxicity with a particular focus on improving productivity of teak plantations is also required. The results of this study also point to an imperative necessity to study other factors apart from soil that affect teak productivity.