Resource management for source- sink modulation in chinese potato[Plectranthus rotundifolius (Poir.) Spreng.]

Abstract

The research work entitled ‘Resource management for source-sink modulation in Chinese potato [Plectranthus rotundifolius (Poir.) Spreng.]’ was undertaken at College of Agriculture, Vellayani during 2018 – 2021. The main objectives were to study the influence of planting methods, nutrient management practices and growth promoters on source-sink relationship, tuber yield and quality in Chinese potato, to assess the growth and yield responses of the crop to carbon dioxide (CO2) fertilization and to work out the economics. The investigation was carried out as two experiments: i) influence of planting methods, nutrient management practices and growth promoters on source - sink relationship, tuber yield and quality and ii) influence of CO2 fertilization on growth and yield responses in Chinese potato. The photo insensitive variety Suphala, released by Kerala Agricultural University (KAU), was used for the study. Experiment I was conducted during October 2019- February 2020 and repeated during 2020-2021 for confirmation. It was laid out in split plot design with five methods of planting as main plots and six combinations of two nutrient management practices and three growth promoters as sub plot treatments, in four replications. The methods of planting included were m1: bed method (30 cm x 15 cm), m2: bed method (30 cm x 30 cm), m3: ridge method (30 cm x 15 cm), m4: ridge method (30 cm x 30 cm) and m5: mound method (30 cm x 30 cm). The combinations comprised nutrient management practices (n1: 60:30:120 kg NPK ha-1 + PGPR Mix 1, n2: 60:30:120 kg NPK ha-1) and growth promoters (g1: humic acid @ 5 g L-1, g2: benzyl adenine @ 50 mg L-1 and g3: water spray). PGPR Mix 1 (2 %) was applied @ 5 g per plant, thrice, at the time of planting, 30 DAP and 60 DAP in n1 and growth promoters were sprayed 45 and 75 DAP. Other cultural operations were done as per package of practices of KAU. Bed method of planting at 30 cm x 15 cm (m1) produced significantly taller plants with higher leaf area index (LAI), dry matter production (DMP) and crop growth rate (CGR) in both the years. Planting at the wider spacing (30 cm x 30 cm) on beds (m2) or ridges (m4) resulted in higher and comparable values for number of branches and plant spread (N-S and E-W), while m2 showed superiority in the number of leaves and leaf area per plant at 45 and 90 DAP. The wider spacing, irrespective of the method of planting, revealed markedly higher relative growth rate (RGR) during 45-90 DAP and the trend remained similar in both years. Significantly higher net assimilation rate (NAR) between 45-90 and 90-135 DAP, and chlorophyll content were noted in m2. Higher chlorophyll content in m2 was on par with m4 during second year. Per plant tuber attributes (number of tubers, tuber yield, marketable tuber yield and average tuber weight) were found superior in bed planting at 30 cm x 30 cm. But, average tuber weight was comparable with m4 in the first year and with m4 and m5 in the second year. Per hectare tuber yields were significantly the highest in the bed method of planting at 30 cm x 15 cm spacing, during both the years with a pooled mean of 20.93 t ha-1. The treatment also showed the maximum uptake of N, P and K. Soil available N, P and K status were the highest in mound method at 30 cm x 30 cm (m5) and on par with m4 and m2. Bacterial, fungal and actinomycete population and dehydrogenase activity were higher in the bed/ridge method of planting at 30 cm x 15 cm spacing (m1 and m3). The combination of 60:30:120 kg NPK ha-1 + PGPR Mix 1 + humic acid (n1g1) resulted in significantly higher growth attributes (plant height, number of branches and plant spread) while at 135 DAP, n1g2 recorded the maximum number of leaves, leaf area per plant, LAI and delayed senescence in both the years. Physiological parameters (DMP, CGR, RGR, NAR) yield attributes, per hectare tuber yield, marketable tuber yield, percentage marketable tuber yield, N, P, K uptake, starch and protein content were superior in n1g1. The tuber yield and marketable tuber yield (pooled) were 21.10 and 18.34 t ha-1 respectively. Soil available N, P, K status, microbial count and dehydrogenase activity were markedly higher in treatments involving PGPR Mix 1 (n1) compared to that without PGPR Mix 1, nevertheless, remained comparable among n1g1, n1g2 and n1g3. Land configuration (bed/ridge) with planting at wider spacing and inclusion of PGPR and humic acid proved superior with respect to the number of branches, leaves per plant and leaf area. Leaf area index was significantly the highest in m3n1g1 in the first year and m1n1g1 in the second year at 90 DAP. The combination m4n1g1, produced the maximum number of tubers per plant (23.8) in the first year on par with m2n1g1 (23.6), whereas during the second year it was the highest (25.0) in m2n1g1. Maximum per plant tuber yield (189.48 and 198.95 g), marketable tuber yield (170.37 and 179.45 g) and percentage of marketable tubers (73.06 and 70.67) were noted in m2n1g1 during both years. The treatment combination m1n1g1 recorded the highest DMP and per hectare tuber yield with a pooled mean of 23.38 t ha-1. The percentage of marketable tuber yields increased by nearly 10 per cent over m1n2g3 in the two years. Potassium uptake was the highest in m1n1g1 and remained comparable with m1n1g2 in the second year. Irrespective of growth promoters applied, inclusion of PGPR Mix 1 (n1) resulted in higher soil available P and K status in the widely spaced planting and the maximum dehydrogenase activity and microbial counts were enumerated in the closely spaced planting on beds (m1). Bed method of planting at 30 cm x 15 cm spacing along with application of 60:30:120 kg NPK ha-1 + PGPR Mix 1 + humic acid (m1n1g1) was the most profitable resource management practice, pooled mean of economics of cultivation revealed maximum net returns and BCR of ₹ 651296 ha-1 and 3.83 respectively. The CO2 fertilization study was conducted in trenches (2 m x 1 m x 1 m) in completely randomized design with six treatments (substrates for CO2 evolution) replicated thrice, during November 2019- July 2020 and October 2020- March 2021. The treatments included, s0: no substrate, s1: cow dung, s2: coir pith, s3: cow dung + coir pith (2:1), s4: s2 + Pleurotus 1g kg-1 + N + P (2% w/w) and s5: s3 + Pleurotus 1g kg-1 + N + P (2% w/w). Cuttings of Chinese potato were planted directly in soil in the first year and in grow bags during the second year. Organic substrates (as per treatment) were spread at the trench base to a thickness of 5 cm, taking precautions to avoid direct contact of the substrates with the cuttings planted directly in soil. The trenches were kept covered with a dome prepared of 200 μ uv stabilised polythene sheet fixed on a metal frame, daily from 4.00 pm to 10.30 am. In all the substrate applied treatments, maximum release of CO2 (501 to 858 ppm) occurred during the first two weeks of application and thereafter it declined. The highest peak of CO2 concentration (858 ppm) at two weeks of application was observed in s5 followed by s3, (752 ppm). Relatively higher air and soil temperatures were observed in trenches during both the years of study. Significantly higher growth attributes at 30 DAP were observed in plants grown in the trench filled with cow dung and coir pith in 2:1 ratio (s3) comparable with treatments containing cow dung and additives (s5). The superiority of s5 on growth attributes were evident at the later stages of growth. Chlorophyll contents (1.147 and 1.193 mg g-1) were maximum in s3 applied trenches at 45 DAP, whereas s5 recorded superior values at 90 DAP (1.153 and 1.193 mg g-1). Initiation of senescence was significantly earlier in CO2 fertilized plants and the highest biomass per plant was recorded in s5. Nevertheless, despite an increased above ground biomass with elevated CO2, tuber development was not observed in any of the treatments. Based on the results of the experiments, it could be concluded that bed/ ridge method of land preparation with planting at 30 cm x 30 cm spacing in combination with an NPK dose of 60:30:120 kg ha-1 + PGPR Mix 1 + humic acid significantly improved the growth parameters (source) and yield attributes (sink) in Chinese potato. A closer planting (30 cm x 15 cm) on beds and application of 60:30:120 kg NPK ha-1 through chemical fertilizers, PGPR Mix 1 (2 %) @ 5 g per plant thrice, as basal, 30 and 60 DAP along with foliar sprays of humic acid @ 5 g L-1 (45 and 75 DAP) can be recommended for superior marketable tuber yields, higher net returns and B: C ratio. The results of the CO2 fertilization study indicated that elevated CO2 enhanced the vegetative growth in Chinese potato at the expense of tuber development.