PhD

A field experiment was undertaken at Vellanikkara, Thrissur in a seven year old bamboo (Dendrocalamus strictus (Roxb.) Nees) stand planted at 4x4, 6x6, 8x8, 10x10, and 12x12 m spacings to assess rhizosphere competition and understorey (turmeric, ginger and chittaratha) productivity, to explore the root activity and distribution pattern in bamboo, to determine the understorey photosynthetically active radiation (PAR), leaf area index of bamboo (LAI) and aboveground biomass production, nutrient uptake and carbon sequestration as a function of planting density. Detailed investigation on the physico-chemical attributes of the soil was also done.
Results reveal that understorey turmeric and ginger height, shoot length, number of tiller and leaves were significantly lesser due to close spacings (4x4 and 6x6 m) of bamboo, but NPK uptake, dry matter production, rhizome yield and oleoresin content were significantly higher in wider spacings (10x10 and 12x12 m) of bamboo. The chittaratha responded better in control plot followed by widest spacing (12x12 m) of bamboo. Due to competition of bamboo about 89% decline in 32P absorption by turmeric at closest spacing (4x4 m) of bamboo as compared to sole turmeric plot. The recovery of 32P by bamboo from the treated turmeric was significantly decreased with increasing distance from the turmeric beds. The recovery of 32P by bamboo in > 8x8 m spacings was nil. The other factors attributed to reduction in growth and yield of understorey crops may be high LAI of bamboo and low understorey PAR. The LAI of bamboo in 4x4 m spacing was 678 % higher compared to 12x12 m spacing. At 12 noon the understorey PAR increased from 107 µmol/sec per m2 in 4x4 m to 1019 µmol/sec per m2 in 12x12 m spacings of bamboo against the overstorey PAR (1033 µmol/sec per m2).
The maximum rooting intensity of bamboo was within 0-30 cm soil depth and up to 4.45 m lateral distance under all the spacings. However, in wider spacings (10x10 and 12x12 m) the roots were distributed beyond 30 cm depth and spread laterally up to 8.75 m. The deeper spread of roots in wider spacings may enable clumps to capture nutrients that would otherwise be leached from the upper horizons of the soil profile. The root activity of bamboo was studied by 32P at varying depths (50 cm and 1 m) and lateral distances (50 cm, 1 m and 2 m). At closest spacing (4x4 m), the 32P absorption by bamboo (15th DAA) at 50x50 cm depth and lateral distance was significantly higher (809 cpm) which gradually decreased by placing 32P beyond 1 m (448 cpm) and 2 m lateral distances (196 cpm). However, in wide spacings (12x12 m) the lateral spread of active roots were more at greater depth (1 m); this helps pumping of soil nutrients from the deeper layers.
The bulk density of soil increased with increasing depth of soil and spacings of bamboo. The N, P and K content of soil significantly decreased with increasing spacing of bamboo. Closest spacing (4x4 m) of bamboo recorded maximum amount (2109 kg/ha) of total N and 10x10 m spacing had lowest (1430 kg/ha). The available P at surface soil (0-20 cm) ranged from 12.86 kg/ha under bambooless control plot to 21 kg/ha at closest spacing. The available P up to 1 m soil depth was highest (42 kg/ha) in closest spacing and decreased with increasing spacing of bamboo. The total available K up to 1 m depth of soil in closest spacing was 35% higher compared to widest spacing. The amount of soil organic carbon (SOC) in the whole soil at 0-20 cm was highest (11.50 Mg/ha) due to 4x4 m spacing and lowest (6.61 Mg/ha) due to widest spacing (12x12 m). The total SOC up to 1 m depth in closest spacing declined by 143% compared to widest spacing. The SOC in silt and clay fraction (<53 µm) was highest (16 Mg/ha) in closest spacing (4x4 m) and lowest (5.20 Mg/ha) in bambooless control plot at 20-50 cm soil depth. The SOC in macro sized fraction (>250-2000 µm) in closest spacing was 9 Mg/ha at 0-20 cm depth; this decreased to 2.27 Mg/ha at 80-100 cm depth.
Due to decrease of bamboo spacing from 12x12 to 4x4 m, the clump DBH decreased from 1.61 to 1.06 m. The crown spread, number of live culms and MAI of bamboo also increased due to increasing spacing. Due to closest spacing (4x4 m), culm wood biomass decreased by 54% compared to widest spacing (12x12 m) of bamboo. The twig biomass recorded maximum (28%) at 6x6 m and 8x8 m spacing of bamboo and minimum (19%) in closest spacing. The total aboveground biomass in closest spacing was 112 kg/clump which increased to 271 kg/clump due to 12x12 m spacing. At stand level, the culm wood biomass was maximum (49 Mg/ha) in densest stand (625 clumps/ha); this decreased to 11.49 Mg/ha due to least dense stand (69 clumps/ha). The twig and leaf biomass reduction in least dense stand was 206% and 114% compared to densest stand. The total aboveground biomass at densest stand was 274% more compared to least dense stand. Nutrient removal at harvest from the site depends on both nutrient concentration of different plant parts and biomass yield. Nutrient concentration (NPK) in aboveground biomass under all the spacings of bamboo decreased in the order of: leaf>twig>culm wood>dried wood. The total N accumulation in the aboveground biomass was highest (323 kg/ha) in densest stand and lowest (108 kg/ha) in least dense stand. Aboveground biomass P accumulation in densest stand increased by 161% than the least dense stand. The total amount of K accumulated in aboveground biomass ranged from 354 kg/ha in densest stand to 157 kg/ha in the least density of 69 clumps/ha. Higher amount of NPK was retained mainly in the culm wood followed by twig, leaf and dried wood mass. However, dense stands can store significantly higher amount of nutrients in its biomass. The carbon partitioning among the aboveground parts in bamboo show that almost 57-68% was in stem, whereas twigs, leaf and dried wood stored 20-30%, 4-8% and 3-6% in all the spacings of bamboo. The C storage in culm wood varied from 35 kg/clump at closest spacing to 79.12 kg/clump in widest spacing of bamboo. The consistent increase in aboveground C stock with increasing spacings of bamboo might be due to more number of culms per clump and in turn higher dry matter production. At stand level, the total C accumulation in the aboveground biomass was highest (32 Mg/ha) in densest bamboo stand compared to 8.85 Mg/ha in the least dense stand.
The study clearly revealed that wider spacings (10x10 and 12x12 m) of bamboo are ideal for better growth and productivity of understorey crops. Even though chittaratha perform best in open condition, among the varying spacings of bamboo, the widest spacing (12x12 m) of bamboo is best. The dense stands of bamboo had the potential of higher aboveground biomass production, nutrient storage and carbon accumulation. However, the study recommends wider spacings (12x12 m) for clump-wise biomass production/C storage and nutrient uptake.