Biomass production of trees and grasses in a silvopasture system on marginal lands of Doon Valley of north-west India. 1. Performance of tree species

Bouldery riverbed lands occupy about one-third of the geographical area in Doon Valley of north-west India. These marginal lands need rehabilitation through establishment of silvopasture system for meeting the biomass requirements of resource-poor farmers. A study was carried out for 14 years (1980 to 1993) at Dehradun, involving four multi-purpose tree species viz. Albizia lebbek (L.) Benth., Grewia optiva Drumm., Bauhinia purpurea L. and Leucaena leucocephala (Lamk.) de Wit.; and two grass species viz. Chrysopogon fulvus (Spreng.) Chiov. and Eulaliopsis binata (Retz.) C.E. Hubb. Fifty and 75% of the tree crown was lopped once a year after four years of age. Tree survival decreased with age, and was highest with L. leucocephala (86.9% in 1993 of initial density of 625 trees ha⁻¹) and lowest with B. purpurea (49.3%). Canopy parameters of trees progressed differently, presumably due to their varying growth habits. The trees of A. lebbek were taller with more crown spread, whereas G. optiva had more crown height with lesser crown spread. Stem diameter growth of A. lebbek was highest followed by B. purpurea. Lopping intensity did not affect tree survival and also canopy growth in most years, but collar diameter and diameter at breast height (dbh) decreased significantly at the higher intensity of lopping. Intercropped grass species E. binata caused a greater adverse effect on the tree survival and growth parameters than C. fulvus. The biomass production (leaf and branch wood weight of lopped material) was highest at eight years of age in 1987 but showed no definite trend over the study period. Bauhinia purpurea produced the highest biomass and L. leucocephala the lowest, despite opposite trends in their survival. The performance of A. lebbek was on par with B. purpurea in the later years (1990--1993), but G. optiva was inferior despite its superiority in the early years (1984--1985). The effects of lopping intensity were not appreciable, but intercropping with E. binata decreased leaf and branch wood production significantly compared with C. fulvus throughout. However, the adverse effect was comparatively less pronounced on B. purpurea and A. lebbek than on G. optiva and L. leucocephala. The fibre yield of G. optiva also decreased due to intercropped E. binata compared with C. fulvus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Agroforestry for soil and water conservation in the western Himalayan Valley Region of India 2. Crop and tree production

A ten-year-study (1983 to 1992) conducted on nine 15 × 90 m runoff plots at 4% slope compared production efficiency of Leucaena leucocephala and Eucalyptus hybrid based agroforestry as well as monocropping landuse systems in the warm, subhumid climate of the western Himalayan region of India. Treatments for the first sequence were: monocropping systems of leucaena, eucalyptus, Chrysopogon fulvus grass and maize – wheat rotation, and alley cropping systems of grass and crops at 4.5 and 10.5 m alley widths with paired contour tree rows of leucaena and eucalyptus. In the second sequence, alley width increased to 22.5 m in 1989, grass was replaced by turmeric Curcuma longa and paired contour rows of leucaena hedges were introduced in monocropping systems of grain crops and turmeric. Integration of leucaena and eucalyptus trees with crops caused severe reduction of crop yields ranging from 21 to 92% for wheat grain, 59 to 69% for maize grain, 60 to 67% for dry grass and about 50% for turmeric rhizome depending upon the age of trees and alley width. The grain yield of crops stabilized at about 50% reduction with 22.5 m alley width. Total crop biomass (grain + straw) also revealed a similar trend; however, its magnitude of reduction was less severe than for grain. Production of biomass was much lower near the tree rows than in mid alleys. Managing leucaena as contour hedgerows eliminated crop yield reduction in alleys. Performance of grass and turmeric in alleys was not found to be satisfactory. Biomass produced from trees adequately compensated the crop yield reduction. Land equivalent ratios of agroforestry landuses were comparable or even better than monocropping systems indicating suitability of these systems for the western Himalayan valley region. This revised version was published online in June 2006 with corrections to the Cover Date.     

Biomass production and potential ethanol yields of shrub willow hybrids and native willow accessions after a single 3-year harvest cycle on marginal lands in central Minnesota,USA

Short rotation woody crops are being developed as a sustainable source of biomass for the production of bioenergy, biofuels, and bioproducts. With the potential increase in demand of biomass for energy in the future, there is a need to diversify and expand its source. In the present study, we evaluated the growth performance, biomass production, energy content, and potential ethanol yields of shrub willow hybrids and native willow accessions. Shrub willow hybrids cuttings were obtained from the State University of New York through its controlled breeding program while cuttings used for native willow accessions were collected naturally. At the end of one rotation, consisting of three growing seasons, we found that shrub willow hybrids outperformed native willow accession species (P = 0.0004), with an average survival rate of 80 and 39 %, respectively. Biomass production of shrub willow hybrids and native willow accessions ranged from 7.42 to 16.0 and from 0.69 to 1.83 Mg ha^?1 oven dry weight, respectively. The chemical composition (mass fraction % on dry basis) of willow hybrids and native willow accessions generally contained 39 % cellulose, 19 % hemicellulose, 25 % lignin, 1.4 % ash content, 17,500–18,500 kJ kg wood^?1, and 385 L Mg^?1 of theoretical ethanol yield. Energy content and potential ethanol yields on a dry weight basis did not vary between shrub willow hybrids and native willow accessions; however, the amount of biomass produced per unit land area is known to influence potential ethanol yields. Thus, we suggest that shrub willow hybrids offer promising potential as an alternative source of biomass. The results of our study suggest that four of the shrub willow hybrids evaluated have a greater potential for use as biomass energy crops on marginal lands in central Minnesota than the native willow accessions; hence, there is a need to test their potential at a larger scale.     

Relationship between tree canopy height and the production of pasture species in a silvopastoral system based on alder trees

Silvopastoral systems in New Zealand that incorporate trees planted to control soil erosion on hills largely rely on the productivity of the pastoral system for financial returns. The effect on pasture productivity of increasing the tree canopy height by pruning Italian gray alder (Alnus cordata) was investigated by measuring the response of light, soil moisture, soil temperature, pasture production of major pasture species, and grazing behaviour of sheep. A split-plot design with four replicates was used. The main plot treatments were three levels of shade (81, 23, and 12% of available photosynthetic photon flux (PPF)), created by pruning 11 year old alder grown at the same density. The sub-plot treatments were four pasture mixes: perennial ryegrass (Lolium perenne), Yorkshire fog (Holcus lanatus), and cocksfoot (Dactylis glomerata), each sown with white clover (Trifolium repens), and cocksfoot sown with lotus (Lotus pedunculatus). Soil temperature was highest under light shade. Total herbage yield at 50 mm stubble height from October to May under heavy and medium shade was 60 and 80%, respectively, of the total herbage harvested under light shade. Cocksfoot had the greatest herbage yield, either with lotus or white clover. The tillering of perennial ryegrass was suppressed by shade more than for the other grass species making ryegrass unsuitable for use in this silvopastoral system. More sheep grazed in the light shade than in the heavy shade, but there was no difference in sheep preference for cocksfoot or Yorkshire fog. Lotus was grazed more frequently than white clover. Pruning of alder to increase canopy height has the potential to improve the productivity of the understorey pasture and its acceptability to sheep.     

Report of a 60 month study on litter production,changes in soil chemical properties and productivity under Poplar (P. deltoides) and Eucalyptus (E. hybrid) interplanted with aromatic grasses

Quantity of litter fall, its chemical composition, nutrient addition and changes in chemical constituents of soil were studied under agroforestry systems involving Populus deltoides and Eucalyptus hybrid tree with intercrops of Cymbopogon martinii Wats and Cymbopogon flexuosus Wats in the tarai tract of Kumaon hills of U.P. India. P. deltoides had significantly more diameter (63%) as compared to E. hybrid. There was decrease in herb (5.4%) and oil yield (15.4%) of grasses due to trees, but both the grasses did not affect the performance of trees. On an average, dry litter production of P. deltoides was 5.0 kg tree⁻¹ year⁻¹ where as of E. hybrid 1.5 kg tree⁻¹ year⁻¹. The litter of P. deltoides contained 1.3 times more N and 1.5 times P and K of E. hybrid. Addition of N, P and K through P. deltoides litter was 36.6, 91.6, and 69.9 per cent more than E. hybrid litter, respectively. Under these two canopies soil organic carbon was enhanced by 33.3 to 83.3 per cent, available N by 38.1 to 68.9 per cent, available P by 3.4 to 32.8 per cent and available K by 5.8 to 24.3 per cent over control (no tree canopy) in 0—15cm layer. P. deltoides plantation was superior to E. hybrib in enriching the soil.     

Biomass and net primary production of a <Emphasis Type="Italic">Pinus densiflora</Emphasis> forest established on a lava flow of Mt. Fuji in central Japan

We assessed the above- and below-ground biomass and net primary production (NPP) in a mature (85-year-old) Pinus densiflora forest established on a lava surface of Mt. Fuji in central Japan. The nitrogen (N) concentration of the forest soil was low (1.25%), and the mean soil carbon/nitrogen (C/N) ratio was 34.2; therefore, both plants and microorganisms would compete for N in our research forest. The total biomass was 192.62Mgha^–1, of which 67.28% was in the stems and 25.71% was in the roots. The fine-root biomass was 1.12% of the total biomass. The total NPP of the forest reached 11.89Mgha^–1 year^–1, which fell within the values reported for other cool temperate P. densiflora forests established on non-volcanic-related substrata. The below-ground production was about 39% of the total NPP; the value was relatively small under the conditions of low total N concentration and high soil C/N ratio. Our study suggested that P. densiflora could recruit and grow on geologically new substrata without increasing the allocation of its annual carbon budget to below-ground organs (i.e., roots).