Ha-1 Of Biomass Research Articles

Increasing rye cover crop biomass production after corn residue removal to balance economics and soil health

Low or variable cover crop (CC) biomass production could limit CC benefits. Longer CC growing periods via late termination could increase CC benefits, especially under limited crop residue return. We studied whether early (2–3 wk before planting)- or late (at planting)-terminated winter rye (Secale cereale L.) CC maintains soil properties, crop yields, and farm income under 0%, 25%, 50%, 75%, and 100% corn (Zea mays L.) residue removal in rainfed and irrigated no-till in the U.S. Great Plains after 6 yr. Early-terminated CCs produced < 1 Mg ha-1 of biomass while late-terminated CCs averaged 1.6 Mg ha-1 at the rainfed site and 3.0 Mg ha-1 at the irrigated site. At the rainfed site, CC termination date did not affect soils, but ≥ 75% residue removal reduced soil organic matter (OM) fraction concentrations and 100% reduced mean weight diameter of water-stable aggregates (MWD) in the 0–5 cm depth. At the irrigated site, late-terminated CC increased MWD by 0.22 mm and OM concentration by 5.1 g kg-1 compared with no CC. At the same site, 100% residue removal reduced microbial biomass, while ≥ 50% removal reduced OM concentration by 7.6 g kg-1, available water, and MWD by 0.75 mm relative to no removal. Cover crops only partially offset the adverse effects of residue removal if biomass production was 3 Mg ha-1 yr-1. Corn yield was generally unaffected. High residue removal rates offset CC-induced reduction in net income. Overall, late-terminated CC partially maintains soil health indicators following residue removal and minimally impacts crop yields and economics.

USO DE BIOMASSA DE MERREMIA AEGYPTIA E DE CALOTROPIS PROCERA NO CULTIVO DO COENTRO EM AMBIENTE SEMIÁRIDO

ABSTRACT Green manuring with spontaneous species from the Caatinga has emerged as a viable alternative to supply vegetables with nutrients and thus increase their productivity. This study aimed to evaluate and estimate the maximum physical and economic efficiencies of coriander productive characteristics as a function of equitable biomass amounts of hairy woodrose [Merremia aegyptia (L.) Urban] and roostertree [Calotropis procera (Aiton) W. T.] in different cropping seasons. The experimental design was a randomized complete block with five treatments and five replicates. The treatments consisted of green manure amounts (16, 29, 42, 55, and 68 t ha-1 on a dry basis). A treatment without fertilization (control) was used in each experiment. The maximum agronomic efficiency (coriander green mass yield) was possible with the incorporation of equitable amounts of 49.56 t ha-1 of M. aegyptia and C. procera biomass, respectively. The maximum economic efficiency of production (evaluated in terms of net income and rate of return) of this leafy vegetable was achieved with the addition to the soil of 42.68 and 41.64 t ha-1 of biomass of these green manures, respectively. The net income and the rate of return optimized for these amounts of green manures were 30,243.92 R$ ha-1 and 2.79 reais for each real invested in the production of this leafy vegetable. The use of biomass from Merremia aegyptia and Calotropis procera from the Caatinga biome proved to be a viable technology for producers who practice the cultivation of coriander when monocropping in a semiarid environment.

Fall cover crop nitrogen uptake drives reductions in winter-spring leaching.

Cover crops can reduce nitrate leaching after cash crop harvest. Despite widespread cover crop implementation, there has been a limited effect on water quality in the Chesapeake Bay watershed. We hypothesize that typical timing for Maryland cover crop planting after cash crop harvest is too late to allow roots to take up substantial nitrate from the soil profile before it is leached by winter drainage water. Across four site-years (including sandy and silty soils), we compared various planting dates for a radish (Raphanus sativus L.)-crimson clover (Trifolium incarnatum L.)-triticale (Triticosecale) cover crop mixture. Also, across two site-years we compared early-planted pure rye, radish, and a three-species mixture with no cover. We measured cover crop biomass and N content and used tension lysimeters to measure deep soil porewater nitrate concentrations. Cumulative nitrate leaching was calculated from these concentrations and weather-based drainage estimates. Cover crops were planted on four dates over a 6-wk period. Overall, cover crops planted first, second, third, fourth, and no cover crop (just weeds) resulted in 3,340, 3,160, 1,600, 303, and 164kg ha-1 of biomass; biomass N accumulation of 65.5, 68.6, 44.0, 9.88, and 4.79kg N ha-1 ; and mean porewater concentrations of 2.71, 2.57, 4.72, 10.0, 17.1mg L-1 of nitrate-N, respectively. Over two site-years, the three-species mix performed as well or better than pure rye or radish. Early planting altered cover crop species proportions, increased cover crop productivity, and reduced nitrate leaching from agricultural fields.

Determination of the biomass stock in a mixed plantation of Pinus taeda L. and Pinus elliottii Engelm.

Mixed planting when well managed can be more efficient in the production of biomass and in the use of available resources, thus increasing the profits of planting. The objectives of this research were to quantify the biomass of a mixed plantation of Pinus taeda and Pinus elliottii, by the direct method and to verify the allocation of biomass between the components and the production of biomass per unit area of the mixed plantation and of the two species studied. From the forest census carried out in the mixed planting of 43.5 ha, at 16 years of age, the diametric distribution of the population was generated. Based on the diametric classes, 60 trees were randomly sampled by the direct method, 30 trees for each species. Then, the aerial biomass production in the different components of the tree for both species was evaluated and compared. Mixed planting produced 171.5 t ha-1 of biomass; the shaft represented more than 60% of the biomass. The biomass production in Pinus taeda was superior to Pinus elliottii. The biomass of branches, in turn, was significantly different between species. The stratified tree technique revealed that biomass production in the stand was lower than the biomass obtained by the direct method. In this technique, the biomass (t ha-1) was superior to Pinus elliottii, due to the frequency of individuals in the forest census being higher in the central diameter class, and the species having a larger number of individuals in the stand.

Evaluation of miscanthus productivity and water use efficiency in southeastern United States.

Second generation biofuels, such as perennial grasses, have potential to provide biofuel feedstock while growing on degraded land with minimal inputs. Perennial grasses have been reported to sequester large amounts of soil organic carbon (SOC) in the Midwestern United States (USA). However, there has been little work on biofuel and carbon sequestration potential of perennial grasses in the Southeastern US. Biofuel productivity for dryland Miscanthus × gigantus and irrigated maize in Georgia, USA were quantified using eddy covariance observations of evapotranspiration (ET) and net ecosystem exchange (NEE) of carbon. Miscanthus biomass yield was 15.54 Mg ha-1 in 2015 and 11.80 Mg ha-1 in 2016, while maize produced 30.20 Mg ha-1 of biomass in 2016. Carbon budgets indicated that both miscanthus and maize fields lost carbon over the experiment. The miscanthus field lost 5 Mg C ha-1 in both 2015 and 2016 while the maize field lost 1.37 Mg C ha-1 for the single year of study. Eddy covariance measurement indicated that for 2016 the miscanthus crop evapotranspired 598 mm and harvest water use efficiencies ranged from 6.95 to 13.84 kg C ha-1 mm-1. Maize evapotranspired 659 mm with a harvest water use efficiency of 19.12 kg C ha-1 mm-1. While biomass yields and gross primary production were relatively high, high ecosystem respiration rates resulted in a loss of ecosystem carbon. Relatively low biomass production, low water use efficiency and high respiration for Miscanthus × gigantus in this experiment suggest that this strain of miscanthus may not be well-suited for dryland production under the environmental conditions found in South Georgia USA.

Cultivating forage maize for biomass and bioenergy in a sub-boreal climate

The biomass potential of eight high yielding maize cultivars was studied in the sub-boreal climate of southern Finland. The effects of harvest date on lignin and sugar production, biomass yield, mineral element composition, bioenergy potential and soil nutrient management were determined in two years. The eight maize cultivars produced 17.6–33.3 t ha-1 of biomass. The ear fraction contained 50–60% of the biomass, and ash and mineral element composition of the plant fractions were significantly different (p &lt; 0.001), with more ash, Ca and S in the above-ear fractions of the plants than in the mid-stalk portions, whereas the C:N ratio was highest in the lower stalk. Cultivars with less lignin content produced more fermetable sugars. Despite the relatively cool growing conditions and short season of the sub-boreal region, maize has potential for use as biomass, for biofuel or other uses. The crop can be fractioned into ear and stalk, with the lower 20 cm of stalk left in the field to maintain soil organic matter content.

Mass and nutritional quality of upper and lower strata of tropical forages

The goal of this work was to evaluate the growth dynamics and chemical characteristics of the upper and lower strata of summer perennial grasses under a four cuts system. The experiment was conducted in a randomized block design, composed of 28 treatments in a factorial arrangement of 7x4, with four repetitions. The cultivars evaluated were Star Grass, Coast-cross, Tifton 68, Tifton 85, Jiggs, Roxinha and Quicuio. Each cultivar was cut when it reached 95% light interception. The cultivars Jiggs and Tifton 68 had the highest (P &amp;lt; 0.05) accumulation of dry biomass ha-1 during the four cuts, with productions of 21,348 and 21,016 kg ha-1, respectively. The ash content varied (P &amp;lt; 0.05) among species and times of cutting for both strata. Cellulose contents were significantly different in the upper stratum, with the highest concentrations found in cvs. Quicuio and Tifton 68 (39.12% and 38.07%, respectively). We found the highest levels of lignin (P &amp;lt; 0.05), for both strata, in cv. Quicuio. Cultivars Jiggs and Tifton 68 were the most appropriate for a management system of four cuts, displaying good chemical composition and high productivity.

Interference between Redroot Pigweed (Amaranthus retroflexus L.) and Cotton (Gossypium hirsutum L.): Growth Analysis.

Redroot pigweed is one of the injurious agricultural weeds on a worldwide basis. Understanding of its interference impact in crop field will provide useful information for weed control programs. The effects of redroot pigweed on cotton at densities of 0, 0.125, 0.25, 0.5, 1, 2, 4, and 8 plants m-1 of row were evaluated in field experiments conducted in 2013 and 2014 at Institute of Cotton Research, CAAS in China. Redroot pigweed remained taller and thicker than cotton and heavily shaded cotton throughout the growing season. Both cotton height and stem diameter reduced with increasing redroot pigweed density. Moreover, the interference of redroot pigweed resulted in a delay in cotton maturity especially at the densities of 1 to 8 weed plants m-1 of row, and cotton boll weight and seed numbers per boll were reduced. The relationship between redroot pigweed density and seed cotton yield was described by the hyperbolic decay regression model, which estimated that a density of 0.20–0.33 weed plant m-1 of row would result in a 50% seed cotton yield loss from the maximum yield. Redroot pigweed seed production per plant or per square meter was indicated by logarithmic response. At a density of 1 plant m-1 of cotton row, redroot pigweed produced about 626,000 seeds m-2. Intraspecific competition resulted in density-dependent effects on weed biomass per plant, a range of 430–2,250 g dry weight by harvest. Redroot pigweed biomass ha-1 tended to increase with increasing weed density as indicated by a logarithmic response. Fiber quality was not significantly influenced by weed density when analyzed over two years; however, the fiber length uniformity and micronaire were adversely affected at density of 1 weed plant m-1 of row in 2014. The adverse impact of redroot pigweed on cotton growth and development identified in this study has indicated the need of effective redroot pigweed management.

Yield and quality of elephant grass biomass produced in the cerrados region for bioenergy

The objective of this study was to evaluate the performance of two genotypes of elephant grass, fertilized with and without N, for biomass production for energy use under the edaphoclimatic conditions of the Cerrado. The genotypes Roxo and Paraíso, grown in a field experiment in a Latosol in the Cerrado region were evaluated for biomass yield, nitrogen accumulation, C:N and stem:leaf ratios, fibre, ash and P and K contents and calorific value. The accumulated dry biomass ranged from 30 to 42 Mg ha-1 and showed no response to nitrogen fertilization with the lowest biomass obtained by the genotype Paraíso and the highest by Roxo. The total N accumulation followed the same pattern as for dry matter, ranging from 347 to 539 kg N ha-1. C:N and stem:leaf ratio of the biomass produced did not vary with treatments. The fibre contents were higher in genotype Paraíso and the highest levels of ash in the genotype Roxo. The K content in the biomass was higher in genotype Roxo and P did not vary between genotypes. The calorific value averaged 18 MJ kg-1 of dry matter and did not vary with the levels of N in leaves and stems of the plant. Both genotypes, independent of N fertilization, produced over 30 Mg ha-1 of biomass under Cerrado conditions.

FLORÍSTICA, VOLUME E BIOMASSA LENHOSA DE UM FRAGMENTO DE MATA ATLÂNTICA NO MUNICÍPIO DE SANTA MARIA DE JETIBÁ, ESPÍRITO SANTO

Este trabalho teve como objetivo avaliar a florística, volume e biomassa em duas áreas de Mata Atlântica. Essas áreas estão localizadas na Reserva Biológica Sítio Palmares, no município de Santa Maria de Jetibá, Espírito Santo. Foram avaliadas 6 (seis) parcelas de áreas preservadas (mata primária) e 6 (seis) parcelas em uma área de regeneração natural com 33 anos de idade (mata secundária). Foram medidas todas as árvores com diâmetro a 1,30 m do solo (DAP) igual ou superior a 5 cm. Na área de mata primária foram encontradas 341 árvores distribuídas em 70 espécies e 32 famílias, que apresentaram DAP médio aritmético de 14,82 cm e área basal igual a 43,60 m2.ha-1, contabilizando 518 m3.ha-1 de fustes e galhos e 397.674 kg.ha-1 de biomassa lenhosa. A área de mata secundária apresentou 195 árvores classificadas em 17 espécies e 14 famílias, com DAP médio de 12,4 cm. Ainda, foram apresentados 12,5 m2.ha-1 de área basal, 93 m3.ha-1 de volume de madeira e 54.631 kg.ha-1 de biomassa lenhosa.

Broccoli yield in response to top-dressing fertilization with green manure and biofertilizer

The objective of this work was to evaluate the productive performance of broccoli under different top-dressing organic fertilizations. The experiment was conducted under protected cultivation, in a completely randomized design with four replications, with two plants per experimental unit. Broccoli seedlings were produced in a commercial substrate in styrofoam trays. The seedlings were transplanted to plastic pots containing 10.0 L of substrate made up of subsoil and organic compost at the ratio of 3:1 (v/v), respectively, which is equivalent to about 20.0 t ha-1 of organic compost at planting. After seedling establishment, the top-dressing fertilization treatments were applied: gliricidia biomass associated or not with liquid biofertilizer of cattle manure to the soil and bokashi. Two control treatments were established: one with mineral fertilization recommended for the crop and the other without top-dressing fertilization. The broccoli production was evaluated (commercial standard). Plants that received mineral fertilizer were more productive, however, they were not significantly different (p&gt;0.05), by Dunnet test, from the plants fertilized with 2.5 t ha-1 gliricidiabiomass (dry mass) associated with liquid biofertilizer (2.0 L m-2) applied to soil. Top-dressing fertilizations with only gliricidia, at 2.5 and 5.0 t ha-1 of biomass (dry mass), resulted in no significant increase in production of broccoli inflorescence. The use of bokashi in addition to gliricidia biomass and liquid biofertilizer reduced the efficiency of the fertilization compared with plants that received only gliricidia and liquid biofertilizer.

MANAGING GREENHOUSE ORGANIC WASTES: A HOLISTIC APPROACH

During the last decade, several sustainable management practices have been proposed by researchers and extension services. For greenhouse production, three main factors should be considered to reduce environmental burdens: 1) waste management, 2) nutrient emission, and 3) fossil energy use. Organic waste represents a significant source of biomass production for protected crops. Wastes such as 4.5 t tomato leaf biomass ha-1 week-1 are usually discarded in sanitary landfills or directed to other waste management sites such as composting sites or accumulated near the production facility thus constituting a phytosanitary problem. When drainage water from producing greenhouse vegetables is not recycled, nutrient emission into the groundwater may represent a major environmental impact (up to 3000-4500 m3 per ha of tomato wasted nutritive solution containing 4-10 t of nutrients such as nitrogen and phosphorus). Greenhouse culture production also uses a significant quantity of fossil fuel energy, in the form of heat (10-40% of production costs), CO2-enrichment, and fertilizers. Thus, management of significant quantities of organic solid and liquid waste produced by greenhouse crops as well as the use of renewable energy constitute a challenge that can be partly solved by more sustainable production systems. Our integrated closed-loop process recycles both solid and liquid organic waste, and converts the waste into renewable energy (CH4), CO2, and liquid and solid fertilizers. Organic waste products and drained water are then reintroduced into the irrigation system. This ensures minimal risks using biological processes such as anaerobic digestion and nitrifying bioreactor, artificial wetlands and passive bioreactors to reduce nutrient pollutants and sulfate content as well as risks associated to pathogens. The proposed integrated production system uses organic growing media or soil with organic fertilizers as well as liquid organic culture, and constitutes a sustainable organic production system achieving productivity levels as high as conventional growing systems.

Effect of Pre-Crop Type on Growth and Yield of Maize on Two Soils in the Guinea Savanna Zone of Ghana

Mucuna (black type) ( Mucuna pruriens var. utilis ), devil-bean ( Crotalaria retusa ), cowpea ( Vigna unguiculata ), maize ( Zea mays L.) and sorghum (Sorghum bicolor Moench.) were grown as preceding crops to maize in a Ferric Luvisol and a Haplic Luvisol in the Guinea savanna zone of Ghana in June 2001. Their effects on growth, grain yield and arbuscular mycorrhiza formation of the following maize in a rotational system were assessed. A non-fertilized weedy fallow treatment was also included as control. Each of the legume pre-crops received 40 kg P ha-1 and 30 kg K ha-1 whereas the cereals received 60-40-30 kg N-P-K ha-1. The legume biomasses were incorporated into the soil in June 2002, two weeks before maize was planted and grown to maturity. Each of the legumes produced over 5 t ha-1 of biomass within the cropping season. Devil-bean tended to be the most efficient in increasing maize grain yield (4.04 t ha-1 in the Ferric Luvisol and 1.2 t ha-1 in the Haplic Luvisol). This is probably due to its relatively higher mean shoot N accumulation across the two locations (214 kg N ha-1) and its greater stimulation of mycorrhizal fungal colonization (25.5%) in the following maize, especially in the Haplic Luvisol. Devil-bean and mucuna generally enhanced maize stover growth. Devil-bean can, therefore, produce significant benefits when used as a preceding crop to maize in a rotational system.

English

Switchgrass (Panicum virgatum L.) is a native warm season perennial grass that has productive potential of up to 20 Mg ha-1 of biomass and it persists for decades when harvested once per year. Switchgrass provides excellent ground cover and soil stabilization once established and contributes to soil sequestration of new carbon. Slow establishment on newly reclaimed soil, however, provides for significant erosive opportunities thereby requiring initial soil stabilization with a cover crop. Several planting options were evaluated on two topsoil substitute soils. The planting options included: 1) an existing stand of bermudagrass (Cynodon dactylon L.) that was killed with glyphosate followed by disking in red oxidized topsoil substitute and prime farmland topsoil respread in 2007, 2) red oxidized topsoil substitute was seeded directly with switchgrass, 3) browntop millet (Panicum ramosum) was established with switchgrass, 4) or switchgrass was established in senescing browntop millet or wheat without tillage. Switchgrass was successfully established into a bermudagrass sod that had been killed with herbicides and disked as well as into a senescing stand of browntop millet or wheat. Significant soil erosion occurred on the disked area in 2008 leading to considerable repair work followed by planting wheat. Disked areas that did not erodemore » had an excellent stand of switchgrass with 23.3 plants m-2 in November, 2008. Eroded areas replanted in April, 2009 into senescing wheat had 46 plants m-2 by July, 2009. The area planted directly into newly respread soil in May, 2009 was eroded severely by a 75 mm thunderstorm and was repaired, disked and replanted to switchgrass and browntop millet. Switchgrass seeded with browntop millet had a sparse switchgrass stand and was replanted to switchgrass in August, 2009. Rainfall volumes from August, 2009 to October, 2009 totaled 750 mm, but new erosion damage in areas successfully planted to switchgrass has been minimal.« less

Efeito de adubos verdes na supressão de espécies de plantas daninhas

Este trabalho teve como objetivo avaliar o efeito de adubos verdes na supressão de plantas daninhas. O experimento foi instalado no Centro de Ciências Agrárias/UFSCar, localizado no município de Araras, São Paulo. O delineamento experimental foi de blocos ao acaso, em esquema fatorial (3 x 4 x 2), com quatro repetições, avaliando-se os efeitos de três quantidades de massa verde (40, 50 e 80 t ha-1) das espécies Crotalaria juncea, Canavalia ensiformis, Mucuna aterrima e Pennisetum glaucum, sob dois tipos de manejo (dispostas na superfície e incorporadas ao solo), na emergência e biomassa seca de duas espécies de plantas daninhas (Ipomoea grandifolia e Brachiaria decumbens).Adicionalmente, foram avaliadas testemunhas sem cobertura vegetal e amostras de solo coletadas de área com alta infestação de Panicum maximum. As avaliações foram feitas até os 30 dias após semeadura, determinando-se as plantas daninhas emergidas e a biomassa seca. M. aterrima foi a espécie mais eficiente na redução da germinação de I. grandifolia em todos os manejos utilizados. Para a espécie E. heterophylla, destacaram-se os tratamentos com P. glaucum e M. aterrima, principalmente quando se utilizaram 80 t ha-1 de biomassa, independentemente da forma de manejo. Para B. decumbens e P. maximum, as espécies P. glaucum e C. juncea foram as mais eficientes na redução da germinação.

Species Selection for Afforestation of Sub-Standard Soil Sites with Particular Reference to Biomass Production and Soil Rehabilitation

Performance of three, evenaged leguminous tree species (Acacia nilotica, A. auriculiformis and Pithecellobium duke) was evaluated on sodic soil sites (pH 9.6) at Biomass Research Centre, Banthra, Lucknow (north India). Species differed significantly in respect to plant survival, growth and productivity since beginning of its growth as observed at the age of five, 10 and, 15 years. Acacia nilotica had highest average girth at breast height (60.5 cm) and stand biomass (161 Mg ha-1) in spite of its lowest plants survival after 15 years of growth. A. auriculiformis ranked next to it with 131 Mg ha-1 productivity. Basal area ranged from 12.8 to 23 m2 ha-1 in different species. P. duke performed poorly as it had only 71 Mg ha-1 of biomass. Average leaf area per hectare in different species ranged from4,129 m2 ha-1 to 16,090 m2 ha-1 after 15 years of growth. A. nilotica also showed superiority in respect to energy content in woody biomass (2,467 GJ ha-1) and fuel wood value index (1694) as compared to the other two species. At the age of 15 years, litter accumulation over the soil surface resulted in marked reductions in soil pH, electrical conductivity, bulk density and sodium content, and increase in soil porosity, organic carbon and nitrogen content, particularly in the uppermost layer of the mineral soil (0-5 cm). A. nilotica exhibited greater efficiency in terms of soil amelioration followed by A. auriculiformis. The relative ranking of three species was A. nilotica > A. auriculiformis > P. duke, respectively. This indicated greater promise of A. nilotica for biomass production, energy harvest, and soil amelioration on degraded soil sites. Matching tree species to soil conditions needs serious considerations in order to expand site specific afforestation programs and to ameliorate vast tracts of degraded soil sites.

Crescimento e produtividade do inhame cultivado entre faixas de guandu em sistema orgânico

Growth and productivity of taro intercropped with pigeon pea hedgerows in organic system under different management was tested in Bom Jardim, upland region of Rio de Janeiro State, Brazil. A completely randomized block design was used with four replicates. The treatments consisted of unpruned hedgerows; hedgerows pruned with the biomass maintained on the soil surface; and hedgerows pruned with the biomass removed from the experimental area. The unpruned hedgerows system was shown to be advantageous by protecting taro leaves against sun burning and keeping the same productivity of the hedgerows pruned system. In addition, it represented an effective way to control weeds, reducing manual labor and costs of organic taro production in which herbicides are not allowed. The legume hedgerows pruned promoted a significant input of organic matter and nitrogen (6.58 t of dry biomass ha-1 and 159 kg of N ha-1) and the recycling of other nutrients, like 20 kg of P ha-1, 136 kg of K ha-1, 64 kg of Ca ha-1 and 16 kg of Mg ha-1.

Export of Nutrients in Plant Biomass Following Harvest of Eucalypt Plantations in Kerala, India

Pools of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were examined in the soil and above-ground plant biomass at the end of a 7 year rotation at two E. tereticornis lowland sites and two E. grandis highland sites in Kerala, India. Potential export rates of these nutrients were also examined for different biomass removal scenarios from the plantations. Pools of nutrients were measured in the above-ground components of the tree crop, forest floor and understorey, and in soil down to 1 m depth. At harvest, large quantities of biomass and nutrients are removed from eucalypt plantation sites, with the quantities of nutrients exported unlikely to be replaced through natural atmospheric and weathering inputs. Between 24 Mg ha-1 and 115 Mg ha-1 of biomass was exported in stem wood across the sites, and this increased to 40-145 Mg ha-1 in scenarios where all of the branches, bark and understorey were also exported. Stem wood had the lowest concentration of nutrients and had a relatively low export of nutrient per kg of biomass. On average, 54 kg, 12 kg and 65 kg of N, P and K were removed per hectare in stem wood only, equivalent to 0.46%, 0.17%, and 6.7%, respectively, of above- and below-ground (to 1 m depth) site pools. Export increased to 194 kg, 30 kg, and 220 kg of N, P and K per hectare if the branches, bark and understorey were also removed (equivalent to 1.6%, 0.5% and 24.7% of above- and below-ground site pools down to 1 m depth). Export of Ca and Mg was also high, with an average of 88 kg and 11 kg of Ca and Mg removed per hectare if only the stem wood was taken (3.12% and 1.34% of total above-ground and exchangeable below-ground to 1 m depth), increasing to 501 kg ha-1 and 66 kg ha-1 if the branches, bark and understorey were also removed (21.7% and 11.3% of total above-ground and available below-ground to 1 m depth). Removals of this magnitude represent a significant proportion of site nutrient pools and have the potential to reduce future plantation productivity unless steps are taken to promote retention of biomass and nutrients on site and/or replacement of nutrients through fertilizer application.

Comportamento de herbicidas com efeito residual em diferentes coberturas na cultura do feijoeiro

O objetivo deste trabalho foi avaliar o comportamento de herbicidas com efeito residual em diferentes tipos de cobertura vegetal no sistema plantio direto, antes da semeadura do feijoeiro. Cada herbicida foi aplicado isoladamente em cinco diferentes coberturas, totalizando 20 ensaios. Os herbicidas e as respectivas doses, em kg ha-1, foram: diclosulan (0,0125), sulfentrazone (0,300), dimethenamid (1,125) e S-metolachlor (1,152). Em Santo Antônio de Goiás utilizou-se a cobertura de Pennisetum glaucum seco e plantas daninhas secas (Commelina benghalensis e Bidens pilosa) no Sistema Integrado de Controle (SIC); e na localidade de Santa Helena de Goiás empregou-se a cobertura de sorgo seco no SIC e Pennisetum glaucum verde e plantas daninhas verdes (C. benghalensis e B. pilosa) no sistema Aplique e Plante, nos anos agrícolas de 1999 e 2000. Cada ensaio constituiu-se de 0, 2, 4, 6, 8, 10, 12, 14, 16, 18 e 20 t ha-1 de biomassa com diferentes coberturas vegetais, as quais receberam os cinco herbicidas, separadamente, no delineamento inteiramente casualizado, com três repetições. A quantificação dos herbicidas no solo foi determinada em bioensaio, usando-se o Sorghum bicolor como planta-teste. Os resultados obtidos indicaram que diclosulan e sulfentrazone foram encontrados no solo acima de 80% da dose aplicada, independentemente da quantidade e do tipo da cobertura do solo. Para dimethenamid e S-metolachlor, até aproximadamente 50% das doses aplicadas foram detectadas no solo com 8 t ha-1 de palha.

Retaining Forest Biomass by Reducing Logging Damage

Global concern over rising atmospheric concentrations of carbon dioxide is stimulating development and implementation of policies aimed at reducing net greenhouse gas emissions by enhancing carbon sinks. One option for reducing net emissions is to lessen damage to residual forests during selective logging, thereby retaining additional carbon in biomass. A pilot carbon offset project was initiated in Sabah, Malaysia, in 1992 in which a power company provided funds to a timber concessionaire to implement guidelines aimed at reducing logging damage; in doing so, the utility gained potential credit towards future emissions reduction requirements. To quantify the carbon retained due to this effort, we compared dipterocarp forests logged according to reduced-impact logging guidelines with forests logged by conventional methods in terms of the above- and below-ground biomass both before and after logging. Prior to logging, the forest stored approximately 400 Mg biomass ha-1, 17 percent of which was belowground. High volumes of timber were removed from both of the logging areas (mean CNV = 154, RIL = 104 m3ha-'). Forty-one percent of the unharvested trees <60 cm DBH were severely damaged (uprooted and crushed) from logging in conventional logging areas in contrast to 15 percent in reduced-impact logging areas. Approximately 18 and 12 percent, respectively, of the remaining residual trees in conventional and reduced-impact logging areas suffered less severe damage (e.g., crown or bark damage). Mortality rates of the less severely damaged trees in all DBH classes were higher during the first year in conventional logging areas than in reduced-impact logging areas. One yr post harvest, conventional and reduced-impact logging areas contained biomass equivalent to about 44 percent and 67 percent of pre-logging levels, respectively. Approximately 62 percent of the difference in carbon retention was due to fewer trees killed in the reduced-impact logging areas; the remaining 38 percent was due to a lower mass of branches, stumps and waste wood from felled trees in reduced-impact logging areas. Mortality of damaged trees in both areas may contribute to net decreases in biomass for several years after logging. More and larger trees remained undamaged where reducedimpact logging was practiced, hence future biomass increment and yields of marketable timber are expected to be greater in the reduced-impact logging areas than in conventional logging areas.