Ph.d

Artocarpusheterophyllus Lam. (Jack tree) is a versatile tree species well-suited for the humid tropics, particularly for Kerala, Peninsular India. It is a key component in the traditional homegardens and farmlands of Kerala, primarily valued for the jackfruit, a unique delicacy of the region. Although the tree produces high-quality timber that is in great demand, it is rarely cultivated in Kerala with the primary aim of timber production. In this context, determining the optimal planting density becomes crucial, particularly when the goal includes producing quality timber and utilization of interspaces for integrating compatible intercrops with jack trees. In this backdrop, a field experiment was initiated in 2020 to evaluate the growth performance of jack trees at different planting spacing (3×3 m, 3×4 m, and 3×5 m) under randomized block design (RBD) with four replications, at Suhasini hills, Kerala Agricultural University, Thrissur, Kerala. After the first year of establishing the field, two shade-tolerant herbaceous spice crops viz. ginger and turmeric, were cultivated as intercrops along with black pepper trailed on the jack trees. The growth and productivity of spice intercrops were evaluated consecutively for two years 2021-2022 and 2022-2023 and compared with contiguous treeless control. The data revealed that tree height, crown attributes, GBH, collar diameter and branches increased consistently across all spacing regimes over the study period. Notably, trees planted at 3×3m spacing exhibited the maximum height growth (6.64 m), branch number (39) and crown cover (82.86%). However, the radial growth parameters such as diameter and basal area showed insensitivity to variable spacing regimes for jack during this early period of tree growth. The results from the study showed variable growth trends for black pepper under different tree spacing regimes, though many of such trends were non-significant. It is inferred that the intercropped black pepper is in the early phase of growth (one year) and the systems may take more time for inflicting competitive interactions for resources in short supply. Although all the growth parameters of turmeric and ginger remained non-significant across the planting spacing, there observed sizable variations under tree cover and treeless control. The yield of turmeric and ginger per meter square was not influenced by tree spacing and was comparable to the sole crop yields under treeless control. This is primarily due to the uniform availability of understorey PAR which was above 90% for all the spacing trial plots. However, the projected yield (Mg ha-1) of turmeric and ginger varied significantly with jack tree spacing. For instance, tree spacing 3×5 m recorded maximum (turmeric:15.83 Mg ha-1 and ginger: 11.69 Mg ha-1) while the tree spacing 3×3 m registered the minimum (turmeric: 7.41 Mg ha-1 and ginger: 5.71 Mg ha-1). The tree spacing exhibited insignificant effect on curcumin and oleoresin content of turmeric and ginger, during both the years respectively. The jack woodlot site and contagious control showed modest differences in soil bulk density and pH across the spacing during the two sampling periods. However, the soil under all spacing regimes noticed significantly higher organic carbon (3×3 m (0.667 %) > 3×4 m (0.661 %) > 3×5 m (0.641 %) than open treeless condition (0.56 %). The variation in the concentration of primary (N, P, K) and secondary nutrients (Ca Mg and S) across the tree spacing regimes and the comparable nutrient concentration in treeless open conditions depicted the considerable influence of trees in modifying soil-physico attributes of soil. Across all the spacing, tap root length did not show significant differences, although spacing at 3×3 m recorded the highest average length of 2.43 m followed by 2.36 m at 3×4m and 2.05 m at 3×5m. However, the trends were reverse with lateral root length which showed an increase with increasing tree spacing with highest lateral root length at 3×5m (275.25 cm). It was observed that leaves, twigs, stems and roots exhibit significant differences in biomass production across spacing with mean component biomass increased with increasing tree spacing. The results clearly revealed that wider spacing significantly enhanced carbon accumulation in component parts than the closer spacing at mean tree level and stand level. Results indicate promising trends toward optimizing the combined productivity of jack trees and understorey crops managed at variable planting spacing. The plentiful availability of resources including understorey light and nutrients may have created a non-competitive growth ambiance for intercrops which could be the reason for the marginal effect of tree spacing on growth and yield attributes. Therefore, it is concluded that jack tree has complementary interactions with intercrops during 2nd and 3rd year of growth. However, long term studies are required to get the more concluding results on tree growth, crops interactions and soil fertility changes.