Humans are currently confronted by many global challenges. These include achieving food security for a rapidly expanding population, lowering the risk of climate change by reducing the net release of ...greenhouse gases into the atmosphere due to human activity, and meeting the increasing demand for energy in the face of dwindling reserves of fossil energy and uncertainties about future reliability of supply. Legumes deliver several important services to societies. They provide important sources of oil, fiber, and protein-rich food and feed while supplying nitrogen (N) to agro-ecosystems via their unique ability to fix atmospheric N
2
in symbiosis with the soil bacteria rhizobia, increasing soil carbon content, and stimulating the productivity of the crops that follow. However, the role of legumes has rarely been considered in the context of their potential to contribute to the mitigation of climate change by reducing fossil fuel use or by providing feedstock for the emerging biobased economies where fossil sources of energy and industrial raw materials are replaced in part by sustainable and renewable biomass resources. The aim of this review was to collate the current knowledge regarding the capacity of legumes to (1) lower the emissions of the key greenhouse gases carbon dioxide (CO
2
) and nitrous oxide (N
2
O) compared to N-fertilized systems, (2) reduce the fossil energy used in the production of food and forage, (3) contribute to the sequestration of carbon (C) in soils, and (4) provide a viable source of biomass for the generation of biofuels and other materials in future biorefinery concepts. We estimated that globally between 350 and 500 Tg CO
2
could be emitted as a result of the 33 to 46 Tg N that is biologically fixed by agricultural legumes each year. This compares to around 300 Tg CO
2
released annually from the manufacture of 100 Tg fertilizer N. The main difference is that the CO
2
respired from the nodulated roots of N
2
-fixing legumes originated from photosynthesis and will not represent a net contribution to atmospheric concentrations of CO
2
, whereas the CO
2
generated during the synthesis of N fertilizer was derived from fossil fuels. Experimental measures of total N
2
O fluxes from legumes and N-fertilized systems were found to vary enormously (0.03–7.09 and 0.09–18.16 kg N
2
O–N ha
−1
, respectively). This reflected the data being collated from a diverse range of studies using different rates of N inputs, as well as the large number of climatic, soil, and management variables known to influence denitrification and the portion of the total N lost as N
2
O. Averages across 71 site-years of data, soils under legumes emitted a total of 1.29 kg N
2
O–N ha
−1
during a growing season. This compared to a mean of 3.22 kg N
2
O–N ha
−1
from 67 site-years of N-fertilized crops and pastures, and 1.20 kg N
2
O–N ha
−1
from 33 site-years of data collected from unplanted soils or unfertilized non-legumes. It was concluded that there was little evidence that biological N
2
fixation substantially contributed to total N
2
O emissions, and that losses of N
2
O from legume soil were generally lower than N-fertilized systems, especially when commercial rates of N fertilizer were applied. Elevated rates of N
2
O losses can occur following the termination of legume-based pastures, or where legumes had been green- or brown-manured and there was a rapid build-up of high concentrations of nitrate in soil. Legume crops and legume-based pastures use 35% to 60% less fossil energy than N-fertilized cereals or grasslands, and the inclusion of legumes in cropping sequences reduced the average annual energy usage over a rotation by 12% to 34%. The reduced energy use was primarily due to the removal of the need to apply N fertilizer and the subsequently lower N fertilizer requirements for crops grown following legumes. Life cycle energy balances of legume-based rotations were also assisted by a lower use of agrichemicals for crop protection as diversification of cropping sequences reduce the incidence of cereal pathogens and pests and assisted weed control, although it was noted that differences in fossil energy use between legumes and N-fertilized systems were greatly diminished if energy use was expressed per unit of biomass or grain produced. For a change in land use to result in a net increase C sequestration in soil, the inputs of C remaining in plant residues need to exceed the CO
2
respired by soil microbes during the decomposition of plant residues or soil organic C, and the C lost through wind or water erosion. The net N-balance of the system was a key driver of changes in soil C stocks in many environments, and data collected from pasture, cropping, and agroforestry systems all indicated that legumes played a pivotal role in providing the additional organic N required to encourage the accumulation of soil C at rates greater than can be achieved by cereals or grasses even when they were supplied with N fertilizer. Legumes contain a range of compounds, which could be refined to produce raw industrial materials currently manufactured from petroleum-based sources, pharmaceuticals, surfactants, or food additives as valuable by-products if legume biomass was to be used to generate biodiesel, bioethanol, biojet A1 fuel, or biogas. The attraction of using leguminous material feedstock is that they do not need the inputs of N fertilizer that would otherwise be necessary to support the production of high grain yields or large amounts of plant biomass since it is the high fossil energy use in the synthesis, transport, and application of N fertilizers that often negates much of the net C benefits of many other bioenergy sources. The use of legume biomass for biorefineries needs careful thought as there will be significant trade-offs with the current role of legumes in contributing to the organic fertility of soils. Agricultural systems will require novel management and plant breeding solutions to provide the range of options that will be required to mitigate climate change. Given their array of ecosystem services and their ability to reduce greenhouse gas emissions, lower the use of fossil energy, accelerate rates of C sequestration in soil, and provide a valuable source of feedstock for biorefineries, legumes should be considered as important components in the development of future agroecosystems.
•Emissions of N2O and NH3 from cattle excreta on a Brachiaria pasture were compared.•Seasonal differences in N2O and NH3emissions from cattle excreta were assessed.•Fractions of N2O–N and NH3–N lost ...from urine were greater than from dung.•N2O emissions were greatest during the rainy season and minimal in the dry season.•Volatilization of NH3 was greater from urine than from dung and increased in the dry season.
Cattle ranching is one of the most important agricultural activities in Brazil. The impact of livestock on soil N2O emissions in Brazil has only been assessed using a Tier 1 approach of the IPCC guidelines, as there are no data available from field studies. Apart from the need for accumulating data for the development of proper direct N2O emission factors, we tested for possible differences between urine and dung as N2O sources and the difference in emissions between the dry and wet season. An area of Brachiaria brizantha at the Embrapa Rice and Bean Centre in the Cerrado (central savannah) region (Goiás state) was subdivided into plots where fresh cattle urine and dung were monitored for three consecutive periods (two in the rainy and one in the dry season) for N losses, principally N2O emissions and NH3 volatilization. 15N-labelled urine N was used in the first monitoring period for an N balance study which indicated that denitrification and NH3 volatilization were the most important processes for N loss. Percentages of N lost as N2O and as volatilized NH3 were greater for urine than for dung. In addition, N losses as N2O in the rainy season were much greater than during the dry season. Representing the Cerrado region and the extensive pasture systems common in this region, direct emission 0.007gN2O–Ng−1 (0.7%) excreta N, well below the EF3PRP of 0.020gNg−1 (2%) used by IPCC for cattle N in excreta. The fraction of excreta N lost as NH3 of ∼15% was in line with the IPCC guidelines. Disaggregation of emission factors for excreta type is recommended.
Primordial follicles, the main source of oocytes in the ovary, are essential for the maintenance of fertility throughout the reproductive lifespan. To the best of our knowledge, there are no reports ...describing the effect of anethole on this important ovarian follicle population. The aim of the study was to investigate the effect of different anethole concentrations on the in vitro culture of caprine preantral follicles enclosed in ovarian tissue. Randomized ovarian fragments were fixed immediately (non-cultured treatment) or distributed into five treatments: α-MEM+ (cultured control), α-MEM+ supplemented with ascorbic acid at 50 μg/mL (AA), and anethole at 30 (AN30), 300 (AN300), or 2000 µg/mL (AN2000), for 1 or 7 days. After 7 days of culture, a significantly higher percentage of morphologically normal follicles was observed when anethole at 2000 μg/mL was used. For both culture times, a greater percentage of growing follicles was observed with the AN30 treatment compared to AA and AN2000 treatments. Anethole at 30 and 2000 µg/mL concentrations at days 1 and 7 of culture resulted in significantly larger follicular diameter than in the cultured control treatment. Anethole at 30 µg/mL concentration at day 7 showed significantly greater oocyte diameter than the other treatments, except when compared to the AN2000 treatment. At day 7 of culture, levels of reactive oxygen species (ROS) were significantly lower in the AN30 treatment than the other treatments. In conclusion, supplementation of culture medium with anethole improves survival and early follicle development at different concentrations in the caprine species.
Conservation agriculture can provide a low-cost competitive option to mitigate global warming with reduction or elimination of soil tillage and increase soil organic carbon (SOC). Most studies have ...evaluated the impact of zero till (ZT) only on surface soil layers (down to 30 cm), and few studies have been performed on the potential for C accumulation in deeper layers (0-100 cm) of tropical and subtropical soils. In order to determine whether the change from conventional tillage (CT) to ZT has induced a net gain in SOC, three long-term experiments (15-26 years) on free-draining Ferralsols in the subtropical region of South Brazil were sampled and the SOC stocks to 30 and 100 cm calculated on an equivalent soil mass basis. In rotations containing intercropped or cover-crop legumes, there were significant accumulations of SOC in ZT soils varying from 5 to 8 Mg ha⁻¹ in comparison with CT management, equivalent to annual soil C accumulation rates of between 0.04 and 0.88 Mg ha⁻¹. However, the potential for soil C accumulation was considerably increased (varying from 0.48 to 1.53 Mg ha⁻¹ yr⁻¹) when considering the soil profile down to 100 cm depth. On average the estimate of soil C accumulation to 100 cm depth was 59% greater than that for soil C accumulated to 30 cm. These findings suggest that increasing sampling depth from 30 cm (as presently recommended by the IPCC) to 100 cm, may increase substantially the estimates of potential CO₂ mitigation induced by the change from CT to ZT on the free-draining Ferralsols of the tropics and subtropics. It was evident that that legumes which contributed a net input of biologically fixed N played an important role in promoting soil C accumulation in these soils under ZT, perhaps due to a slow-release of N from decaying surface residues/roots which favored maize root growth.
Aims Because of its high dry matter (DM) productivity, elephant grass (Pennisetum purpureum) is an ideal candidate for biomass production for biofuel production if low N fertilizer rates are used to ...avoid high fossil fuel inputs. The objective of this study was to investigate the potential of different elephant grass genotypes to obtain contributions of plant-associated biological N2 fixation (BNF). Methods Three field experiments with 4 or 5 different genotypes were conducted on low-fertility Acrisols, two in Rio de Janeiro State and one in Espirito Santo for the evaluation of DM and N accumulation and 15N abundance. Results DM and N accumulation rates of four genotypes in the two experiments in Rio State stabilized at high levels after 2 years of growth. In all experiments the spontaneously-occurring weeds in the plots were significantly higher in 15N abundance than the elephant grass genotypes. The lower 15N abundance of the elephant grass was shown not to be due to lower δ15N abundance at depth in the soil. Conclusions Four of the grass genotypes obtained between 18 and 70% of their N from BNF amounting to inputs of between 36 and 132 kg N ha−1 yr−1.
Beef cattle producers seldom use fertilizers for their pastures in tropical regions of Brazil. Slowly, this is changing but because of the need for repeated applications, N fertilizer is rarely ...applied. The introduction of a forage legume is an appropriate solution for this problem, but until recently adoption has been very low as the legumes generally have not persisted in the sward. We report research on how grazing management can affect the persistence of stoloniferous legumes in pastures of Brachiaria spp. and the problems of establishing and maintaining crown‐forming legumes such as Stylosanthes spp. With suitable management, milk or bovine carcass yields can be equal or greater from mixed than from grass‐alone pastures fertilized with 120 or 150 kg Nha‐1 year−1. In addition to savings in CO2 emissions from fossil fuels for the production and distribution of N fertilizers, nitrous oxide emissions from cattle excreta and legume residues are lower than those from N‐fertilized brachiaria grass monocultures. Other studies indicate that enteric methane emissions from cattle may be mitigated when forage legumes are included in their diet. The use of forage legumes in mixed pastures for tropical regions is emerging as a feasible strategy to keep meat and milk production at acceptable levels with reduced greenhouse gas emission rates.
Management swing potential for bioenergy crops Davis, Sarah C.; Boddey, Robert M.; Alves, Bruno J. R. ...
Global change biology. Bioenergy,
November 2013, Letnik:
5, Številka:
6
Journal Article
Odprti dostop
Bioenergy crops are often classified (and subsequently regulated) according to species that have been evaluated as environmentally beneficial or detrimental, but in practice, management decisions ...rather than species per se can determine the overall environmental impact of a bioenergy production system. Here, we review the greenhouse gas balance and ‘management swing potential’ of seven different bioenergy cropping systems in temperate and tropical regions. Prior land use, harvesting techniques, harvest timing, and fertilization are among the key management considerations that can swing the greenhouse gas balance of bioenergy from positive to negative or the reverse. Although the management swing potential is substantial for many cropping systems, there are some species (e.g., soybean) that have such low bioenergy yield potentials that the environmental impact is unlikely to be reversed by management. High‐yielding bioenergy crops (e.g., corn, sugarcane, Miscanthus, and fast‐growing tree species), however, can be managed for environmental benefits or losses, suggesting that the bioenergy sector would be better informed by incorporating management‐based evaluations into classifications of bioenergy feedstocks.
This study aimed to quantify nitrous oxide (N2O) and methane (CH4) emission/sink response from sugar cane soil treated with fertilizer nitrogen (N) and vinasse applied separately or in sequence, the ...latter being investigated with regard to the time interval between applications for a possible effect on emissions. The study was carried out in a traditional area of unburned sugar cane in São Paulo state, Brazil. Two levels of N fertilization (0 and 100 kg N ha–1) with no added vinasse and combined with vinasse additions at different times (100 m–3 ha–1 at 3 and 15 days after N fertilization) were evaluated. Methane and N2O fluxes were monitored for 211 days. On average, the soil was a sink for CH4, which was not affected by the treatments. Emissions of N2O were induced by N fertilizer and vinasse applications. For ammonium sulfate, 0.6% of the added N was emitted as N2O, while for vinasse, this ranged from 1.0 to 2.2%. Changes in N2O fluxes were detected the day after application of vinasse on the N fertilized areas, but although the emission factor (EF) was 34% greater, the EF was not significantly different from fertilizer N alone. Nevertheless, we recommend to not apply vinasse after N fertilization to avoid boosting N2O emissions.
Soil N2O fluxes are frequently assessed by the use of static chambers with a single daily sampling. In this study, two experiments were conducted in two contrasting climatic locations, one in ...Edinburgh, UK, and the other at Seropedica, Rio de Janeiro State, Brazil. Soil N2O fluxes were monitored every 6 h for 30 days during the summer in Edinburgh by the use of an automatic chamber system, and every 3 h for 5 days at Seropedica, using a manually-sampled static chamber. Air and soil temperatures were also measured at the same time as the N2O fluxes. The principal driver of N2O flux within any diurnal period was found to be soil temperature. Regression analysis showed that, for both places, the evenings (21:00-22:00 h) and mornings (09:00-10:00 h), were the times that the flux best represented the daily mean. The ability to work in daylight make the morning period the preferred one.
PDF
