Balancing fuelwood and biodiversity concerns in rural Nepal

An agent-based model is developed to explore the pattern of fuelwood collection in an 1178 ha forest area in rural mountainous Nepal. The model relates fuelwood collection intensity and amount of dead wood available for collection to the diversity of polypore species, a group of strictly dead wood dependent fungi which can be used as indicators of the biodiversity associated with dead wood. By analysing scenarios of increased collection the model shows that the relative impact on polypore diversity is rising more rapidly than the time used for collection. This indicates that better market access in the future could potentially imply a major threat to biodiversity associated with dead wood.     

Redistribution of slurry components as influenced by injection method, soil, and slurry properties

The distribution of moisture, degradable C, and N after direct injection of slurry can affect the turnover and plant availability of slurry N. This study examined effects of injection method, soil conditions, and slurry properties on the infiltration of several slurry components under practical conditions. The water retention capacity of 22 pig and cattle slurries was quantified by dialysis at -0.016, -0.047, and -0.100 MPa. All slurries followed the relationship: relative water loss = 1/(1 + aVS[volatile solids]), indicating that retention of liquids in the slurry injection zone can be predicted from slurry VS and soil water potential. Two-disc injection and harrow tine injection were simulated (no slurry applied) in five trials. Two trials indicated that disc injection resulted in higher permeability compared with harrow tine injection. In a separate experiment, soil moisture and dissolved ions were monitored in and around injection slits amended with pig or cattle slurry. Moisture gradients, which were recorded with small printed-circuit-board (PCB) time-domain-reflectometry (TDR) probes, were temporally stable and reestablished following rainfall. Slit sections with pig and cattle slurry containing 13C-acetate and 15N-ammonium showed a shift in the 13C to 15N ratio of the injection zone within 24 h, which was explained by removal of dissolved C and/or retention of NH4+. Cattle slurry was more concentrated around the injection slit than pig slurry, and greater contact between slurry and soil was obtained with harrow tine injection. The heterogeneity of slurry C and N distribution after direct injection should be accounted for in models describing slurry N turnover.     

Biological degradation and greenhouse gas emissions during pre-storage of liquid animal manure

Storage of manure makes a significant contribution to global methane (CH4) emissions. Anaerobic digestion of pig and cattle manure in biogas reactors before outside storage might reduce the potential for CH4 emissions. However, manure pre-stored at 15 to 20 degrees C in buildings before anaerobic digestion may be a significant source of CH4 and could reduce the potential CH4 production in the biogas reactor. Degradation of energy-rich organic components in slurry and emissions of CH4 and carbon dioxide (CO2) from aerobic and anaerobic degradation processes during pre-storage were examined in the laboratory. Newly mixed slurry was added to vessels and stored at 15 and 20 degrees C for 100 to 220 d. During storage, CH4 and CO2 emissions were measured with a dynamic chamber technique. The ratio of decomposition in the subsurface to that at the surface indicated that the aerobic surface processes contributed significantly to CO2 emission. The measured CH4 emission was used to calculate the methane conversion factor (MCF) in relation to storage time and temperature, and the total carbon-C emission was used to calculate the decrease in potential CH4 production by anaerobic digestion following pre-storage. The results show substantial methane and carbon dioxide production from animal manure in an open fed-batch system kept at 15 to 20 degrees C, even for short storage times, but the influence of temperature was not significant at storage times of <30 d. During long-term storage (90 d), a strong influence of temperature on the MCF value, especially for pig manure, was observed.