M.Sc.

The experiment was conducted during the period from May 2018 to December 2018 at Agronomy Farm, College of Horticulture, Vellanikkara, Thrissur to study the effect of planting density and seed tuber size on productivity of lesser yam. Seed tubers of 50 g, 100 g, and 150 g were planted at spacings of 50 x 50 cm (high density planting), 75 x 50 cm (medium density planting) and 75 x 75 cm (low density planting- recommended spacing), adopting factorial RBD. The treatments consisted of nine combinations of seed tuber size and spacing.
Growth characteristics like emergence percentage, number of sprouts per tuber, length of vine, number of tuber forming roots, number of leaves, leaf area, and total drymatter accumulation per plant were significantly influenced by seed tuber size. Large sized seed tubers (150 g) showed higher values for these parameters compared to that of medium or small sized tubers. In the initial growth stage of 45 days after planting (DAP), length of vine was significantly higher for large seed tubers. However by 90 DAP, all vines exhibited comparable length irrespective of seed size or spacing.
Spacing significantly influenced the leaf area index (LAI) as well as number of leaves per vine, and at peak vegetative growth (135 DAP), the highest leaf count of 591 leaves per vine was noticed in 150 g tubers planted at wider spacing of 75 x 75 cm. Total dry matter accumulation per plant was not significantly influenced by spacing.
Tuber forming roots could be observed even at 45 days after planting indicating early tuber initiation in lesser yam. The number of tuber forming roots increased upto 180 DAP, after which tuber bulking was noticed. Plants that emerged from large seed tubers produced more number of tuberous roots in the initial growth stage of upto 90 DAP. However at 135 DAP, plants from both 100 g and 150 g tubers were on par with respect to number of tuber forming roots. Plants at closer spacing of 50 x 50 cm produced higher number of tuber forming roots compared to wider spacing at 180 DAP. The crop growth rate (CGR), relative growth rate (RGR) as well as net assimilation rate




(NAR) were influenced by seed tuber size and spacing. Plants from larger seed tubers and closer spacing had higher CGR, RGR and NAR. Higher RGR was observed during the period from 135 to 180 DAP. Spacing had no influence on NAR at initial growth phase. However at later stages of observations, high density planting resulted in higher NAR. The highest NAR was observed at 45-90 DAP, after which a declining trend was observed.
The highest tuber yield was recorded from larger seed tubers of 150 g size (1270 g/vine), followed by 100 g (1053 g/ vine) and 50g seed tubers (929 g/vine), which differed significantly from each other. Spacing also had influence on tuber yield per plant and wider spacing resulted in significantly higher yield (1217 g), compared to 75 x 50 cm (1062 g) and 50 x 50 cm (972 g) spacings. Interaction effect also could be observed and performance of 150 g seed tuber at 75 x 75 cm was superior to others. It was also clear that neither the seed tuber size nor the spacing had influence on the number of small, medium or large sized tubers per plant or the length and girth of individual tubers. The trend in tuber yield per hectare was different as the yield is a function of number of plants per unit area. The highest productivity of 44.20 t/ha was realized when 150 g seed tubers were planted at a closer spacing of 50 x 50 cm. The combination of small seed tuber and wider spacing led to lower productivity in lesser yam (17.66 t/ha).Closer spacing resulted in higher cost of cultivation, but correspondingly yield per hectare was also high. The highest net profit of 5.31 lakhs per ha was realized when 150 g seed tubers were planted at 50 x 50 cm spacing, compared to 4.70 lakhs in the case of 50 g seed tubers and 4.34 lakhs from 100 g seed tubers at 50 x 50 cm.
Considering the easy availability of small seed tubers and higher net profit and B:C ratio, for realizing maximum productivity per unit area, it is advisable to go for high density planting in lesser yam with seed tubers of about 50 g or 100 g weight. This is especially important in a state like Kerala where availability of land is a major constraint in crop production.