Nitrogen cycling in pastoral livestock systems in Sub-Saharan Africa: knowns and unknowns

Pastoral systems are the dominant livestock production system in arid and semiarid regions of sub-Saharan Africa (SSA). They are often the only form of agriculture that can be practiced due to unfavorable climate and soil fertility levels that prevent crop cultivation. Pastoralism can have negative impacts on the environment, including land degradation, greenhouse gas emissions and other gases to the atmosphere, soil erosion, water pollution and biodiversity loss. Here, we review the current knowledge on nitrogen (N) cycling, storage, and loss pathways, with an emphasis on identification of N emission hotspots. Our review reports a large uncertainty in the amount of N lost as ammonia from excreta and manure storage, as well as N losses via nitrate and DON leaching. We also found that another major N loss pathway (18%), soil N2 emissions, has not yet been measured. In order to summarize the available information, we use a virtual pastoral farm, with characteristics and management practices obtained from a real farm, Kapiti Research Station in Kenya. For outlining N flows at this virtual farm, we used published data, data from global studies, satellite imagery and geographic information system (GIS) tools. Our results show that N inputs in pastoral systems are dominated by atmospheric N deposition (~80%), while inputs due to biological nitrogen fixation seems to play a smaller role. A major N loss pathway is nitrogen leaching (nitrate > DON) from pastures (33%). Cattle enclosures (bomas), where animals are kept during night, represent N emissions hotspots, representing 16% of the total N losses from the system. N losses via ammonia volatilization and N2O were four and three orders of magnitude higher from bomas than from the pasture, respectively. Based on our results, we further identify future research requirements and highlight the urgent need for experimental data collection to quantify nitrogen losses from manure in animal congregation areas. Such information is needed to improve our understanding on N cycling in pastoral systems in semiarid regions and to provide practical recommendations for managers that can help with decision-making on management strategies in pastoral systems in semiarid savannas

Respuesta de la respiración del suelo a la temperatura y humedad del suelo en sistemas forestales mediterráneos

La respiración del suelo es uno de los mayores flujos en el ciclo global de carbono y supone unas 80-98 Pg C año-1, por lo que cambios en las condiciones de los suelos pueden tener grandes efectos en las emisiones globales de carbono a la atmósfera. Esto hace que sea importante conocer y entender los mecanismos que influyen en la respiración de los suelos. La temperatura del suelo se ha reconocido como uno de los factores principales que influyen en la respiración del suelo aunque la humedad del suelo no es menos importante, sobre todo en climas como el mediterráneo donde es uno de los factores ecológicos más importantes. El objetivo del trabajo es determinar la relación que tienen la temperatura y la humedad del suelo con la respiración del mismo, y valorar si la gestión forestal influye en dicha relación

Nitrogen form and concentration interact to affect the performance of two ecologically distinct Mediterranean forest trees

Most studies examining inorganic N formeffects on growth and nutrition of forest trees have beenconducted on single species from boreal or temperateenvironments, while comparative studies with species fromother biomes are scarce. We evaluated the response of twoMediterranean trees of contrasting ecology, Quercus ilex L.and Pinus halepensis Mill., to cultivation with distinctinorganic N forms. Seedlings were fertilized with differentNH4?/NO3- proportion at either 1 or 10 mM N. In bothspecies, N forms had small effects at low N concentration,but at high N concentration they markedly affected theplant performance. A greater proportion of NH4? in thefertilizer at high N caused toxicity as it reduced growth andcaused seedling death, with the effect being greater in Q.ilex than in P. halepensis. An increase in the proportion ofNO3- at high N strongly enhanced growth relative to lowN plants in P. halepensis but had minor effects in Q. ilex.Relatively more NH4? in the fertilizer enhanced plant Pconcentration but reduced K concentration in both species,while the opposite effect occurred with NO3-, and these effects were enhanced under high N concentration. We conclude that species responses to inorganic N forms were related to their ecology. P. halepensis, a pioneer tree, had improved performance with NO3 - at high N concentration and showed strong plasticity to changes in N supply. Q. ilex, a late successional tree, had low responsiveness to N form or concentration.Ministerio de Educación y CulturaMinisterio de Ciencia e InnovaciónComunidad de Madri

Can the dehesa system work as a carbon sink? Analysis of the case of the Dehesón del Encinar.

Agroforestry systems are considered multi-purpose systems, aimed towards achieving an increased and more efficient use of natural resources. This acquires greater relevance in Mediterranean areas where high yield is compromised and non-timber goods and services are the main ecosystems products. The dehesa is a well-known agroforestry system that occupies more than 3.10 6 ha in the Iberian Peninsula. In spite of their importance, there is a lack of knowledge of multiple issues regarding the ecosystem functioning and dynamics. One of the potential services of the dehesa is CO2 fixation which should be incorporated into the management planning. In this work the potential of dehesas as C sink is analysed in the framework of a Spanish Research National Plan project carried out in several dehesa system locations in Spain

Nitrate leaching and soil nitrous oxide emissions diminish with time in a hybrid poplar short-rotation coppice in southern Germany

Hybrid poplar short-rotation coppices (SRC) provide feedstocks for bioenergy production and can be established on lands that are suboptimal for food production. The environmental consequences of deploying this production system on marginal agricultural land need to be evaluated, including the investigation of common management practices i.e., fertilization and irrigation. In this work, we evaluated (1) the soil-atmosphere exchange of carbon dioxide, methane, and nitrous oxide (N$_{2}$O); (2) the changes in soil organic carbon (SOC) stocks; (3) the gross ammonification and nitrification rates; and (4) the nitrate leaching as affected by the establishment of a hybrid poplar SRC on a marginal agricultural land in southern Germany. Our study covered one 3-year rotation period and 2 years after the first coppicing. We combined field and laboratory experiments with modeling. The soil N$_{2}$O emissions decreased from 2.2 kg N$_{2}$O-N ha$^{-1}$ a$^{-1}$ in the year of SRC establishment to 1.1–1.4 kg N$_{2}$ON ha$^{-1}$ a$^{-1}$ after 4 years. Likewise, nitrate leaching reduced from 13 to 1.5–8 kg N ha$^{-1}$ a$^{-1}$. Tree coppicing induced a brief pulse of soil N$_{2}$O flux and marginal effects on gross N turnover rates. Overall, the N losses diminished within 4 years by 80% without fertilization (irrespective of irrigation) and by 40% when 40–50 kg N ha$^{-1}$ a$^{-1}$ were applied. Enhanced N losses due to fertilization and the minor effect of fertilization and irrigation on tree growth discourage ist use during the first rotation period after SRC establishment. A SOC accrual rate of 0.4 Mg C ha$^{-1}$ a$^{-1}$(uppermost 25 cm, P = 0.2) was observed 5 years after the SRC establishment. Overall, our data suggest that SRC cultivation on marginal agricultural land in the region is a promising option for increasing the share of renewable energy sources due to its net positive environmental effects

Strategies for GHG mitigation in Mediterranean cropping systems. A review

In this review we aimed to synthetize and analyze the most promising GHGs mitigation strategies for Mediterranean cropping systems. A description of most relevant measures, based on the best crop choice and management by farmers (i.e., agronomical practices), was firstly carried out. Many of these measures can be also efficient in other climatic regions, but here we provide particular results and discussion of their efficiencies for Mediterranean cropping systems. An integrated assessment of management practices on mitigating each component of the global warming potential (N2O and CH4 emissions and C sequestration) of production systems considering potential side-effects of their implementation allowed us to propose the best strategies to abate GHG emissions, while sustaining crop yields and mitigating other sources of environmental pollution (e.g. nitrate leaching and ammonia volatilization)

Root trenching: a useful tool to estimate autotrophic soil respiration? A case study in an Austrian mountain forest

We conducted a trenching experiment in a mountain forest in order to assess the contribution of theautotrophic respiration to total soil respiration and evaluate trenching as a technique to achieve it. We hypothesised that the trenching experiment would alter both microbial biomass and microbial community structure and that Wne roots (less than 2 mm diameter) would be decomposed within one growing season. Soil CO2 eZux was measured roughlybiweekly over two growing seasons. Root presence and morphology parameters, as well as the soil microbial community were measured prior to trenching, 5 and 15 months after trenching. The trenched plots emitted about 20 and 30% less CO2 than the control plots in the Wrst and secondgrowing season, respectively. Roots died in trenched plots, but root decay was slow. After 5 and 15 months, Wne root biomass was decreased by 9% (not statistically diferent)and 30%, (statistically diVerent) respectively. When wecorrected for the additional trenched-plot CO2 eZux due to Wne root decomposition, the autotrophic soil respiration rose to »26% of the total soil respiration for the Wrst growing season, and to »44% for the second growing season.Soil microbial biomass and community structure was not altered by the end of the second growing season. We conclude that trenching can give accurate estimates of the autotrophic and heterotrophic components of soil respiration, ifmethodological side eVects are accounted for, only

Aboveground soil C inputs in the ecotone between Scots pine and Pyrenean oak in Sierra de Guadarrama

Aboveground litterfall from Pyrenean oak (Quercus pyrenaica Willd. a semi-deciduous species), mixed Pyrenean oak-pine and pine (Pinus sylvestris L.) forest stands was surveyed in two sites in a Mediterranean mountain area during a period of 36 and 29 months, respectively. Separation in different litterfall fractions was performed, and C content of each fraction was measured to calculate the C flux to the soil due to litterfall. Our results showed that litterfall input was higher in pine stands than in Pyrenean oak stands (1.8-2.4 Mg C ha–1 year–1 at pine plots and 0.9-1.4 Mg C ha–1 year–1 at oak plots) and mixed plots showed intermediate values. Needles or leaves contributed about 50% to total litterfall, underpinning the importance of the rest of materials in the soil C input. The seasonal pattern showed a maximum in Pyrenean oak stands in autumn-early winter, while the pine stands had the maximum in summer, which is in consonance with the physiology of fall of broadleaves and coniferous trees in these latitudes , but clearly differs from needle-shed in Central and Northern Europe. A dry-spring year corresponded to a lower leaf fall during the following autumn, and leaf abscission came some weeks earlier than a year with a rainy spring

El “trenching” como método de separación de las componentes de la respiración de suelos forestales

Técnicas como el trenching permiten la separación de las componentes de la respiración de suelos forestales. Sin embargo, dicha técnica lleva asociada una serie de alteraciones sobre el suelo que es preciso analizar para evaluar de forma más precisa sus resultados. En este estudio se realizó un experimento comparando parcelas en las que se había efectuado un trenching con otras no tratadas, tomando muestras periódicamente con las que llevar a cabo un seguimiento de la evolución de las raíces y de los diferentes grupos de microorganismos edáficos. Para esta última tarea, se analizaron los ácidos grasos fosfolipídicos (PLFAs), que poseen un alto valor como identificadores de bacterias, hongos, actinomicetos y micorrizas arbusculares. Quince meses después de haber realizado el trenching, el volumen y longitud de las raíces presentes no había cambiado significativamente respecto a las parcelas control; los PLFAs asociados a microorganismos no sufrieron variaciones de importancia. En base a estos resultados, se puede concluir que, al menos hasta 15 meses después de la realización del trenching, las posibles mediciones de flujos de CO2 en parcelas trenching y control resultarían válidas para valorar la contribución de las componentes heterótrofa y autótrofa de la respiración del suelo