Allometric equations for estimating above- and belowground biomass in Tea (Camellia sinensis (L.) O. Kuntze) agroforestry system of Barak Valley,Assam, northeast India

Tea (Camellia sinensis (L.) O. Kuntze) agroforestry has widespread implications for the earnings and food security for a large fraction of population in NorthEast India. It also has immense potentiality to act as a considerable reservoir of biomass carbon providing climate change mitigation options. In the present study an attempt was made to develop allometric equations for above- and belowground biomass estimation specific to Tea [C. sinensis (L.) O. Kuntze] in Barak Valley of northeast India. Relationships were developed through destructive sampling and regressing diameter alone and along height, wood density, crown area, branch count with biomass. Allometric power function equation and linear equivalents have been developed. Diameter singly could predict significantly aboveground biomass (AGB) root biomass (BGB) and total Tea biomass (TB) with over 95% accuracy. Whereas incorporation of height, crown area, wood density, branch count with diameter influenced the model in terms of modified coefficient of determination and minimized estimation errors. Branches, stem and leaves accounted 50, 21 and 6% of AGB respectively. Root biomass (BGB) contributed 23% of the total Tea bush biomass. The samples exhibited overall BGB/AGB ratio of 0.30 ± 0.08 and biomass expansion factor (BEF) by 4.23 ± 1.6. Biomass of different components significantly differs in varied diameter sizes.     

Interaction of willow (Salix) clones grown in polyclonal stands in short rotation coppice

Stool survival of Salix spp. clones is reduced when growing in polyclonal stands as compared to monoclonal stands. Stools growing in polyclonal stands show increased vigour with compensation of weak or dead stools from adjacent stools. In monoclonal stands the stools tend to be less vigorous but there is also less variation between stools. When a clone, which has become highly susceptible to rust infection, is included in the mixture, e.g. Salix burjatica Korso, it will die out completely within two years.     

Biomass and root stem production of a colony-forming willow (Salix interior) on highly disturbed,low fertility sites

This study describes biomass production, colony formation, and clonal spread via root stems (RS) of a wide-ranging North American willow species, Salix interior Rowlee (INT), one of the few willows that spread via vegetatively reproduced colonies, which can result in hundreds of upright stems arising from a shallow horizontal root network. Eight INT clones were tested in a common-garden experiment on two distinct site types (shale rock overburden and coarse gravel erosion sediments) with very low nitrogen and nutrients on a former coal mine site. Survival, height growth, aboveground biomass, and number of root stems (NRS) were quantified following 3 years of growth after establishment as rootless stem cuttings. Clonal differences were significant for survival and height at age 3. Survival was significantly greater on the coarse gravel outwash than shale rock overburden after the first and third year, but differences were only significant in the first year. There was a significant positive relationship between height growth and survival, both of which are indicators of plant vigor. Analysis of clonal variation in NRS showed an intermediate level of significance (P = 0.083), and a significant clone by site interaction (P = 0.024). On coarse gravel outwash, the more vigorous clones for height growth also produced more RS, indicating the absence of a potential trade-off in carbohydrate resource allocation between height growth of the ortet (mother plant) and its capacity for colony formation and spread via RS. It appears that RS quickly become independent sources of carbohydrate production. However, there was no relationship between clonal height growth and NRS on the rock overburden. Loose sand and gravel outwash deposits promoted a more rapid spread of the shallow horizontal root network than the less penetrable shale rock overburden that dominates this former coal mine site.     

Impact of different establishment methods in terms of tillage and weed management systems on biomass production of willow grown as short rotation coppice

To date little information is available on methods including soil preparation and weed control in SRC. For this purpose, in 2010, a field trial with willow cv. ‘Tordis’ was established in southwest Germany. Three different tillage systems (mouldboard plough, chisel plough + ley crop, no-till) were implemented in the establishment year in combination with eight chemical and mechanical weed management systems. Over a period of three years, plant and weed specific parameters were collected to determine the effect of tillage systems and weed treatments on final biomass production of willow. The highest biomass yields were obtained by mouldboard plough with chemical weed control (14.0 Mg ha⁻¹ dry matter) as well as by mouldboard plough with rotivation and band spraying of herbicides (14.2 Mg ha⁻¹ dry matter), followed by 13.7 Mg ha⁻¹ dry matter in no-till with broadcast application of herbicides. Chisel ploughing with ley crop led to lower willow yields in most weed treatments. It was assumed that chisel ploughing + ley crop would lead to a high competition for light, water and nutrients especially in the first year. Consequently, it is not recommended as an establishment method for willow. Additionally, mulching with wood chips and no weed management generally resulted in low biomass yields. Overall, the results suggest that the tillage system in combination with effective chemical or mechanical weed control is of major importance for the success of willow establishment.