Bishal K. Sitaula

CH4 uptake by temperate forest soil: Effect of N input and soil acidification

N fertilization and soil acidification effects on the uptake of atmospheric CH4 and soil CH4 concentrations were studied in lysimeter soil from a 100-y-old Scots pine forest in Norway. N fertilization with NH4NO3 significantly reduced the uptake of atmospheric CH4. Medium N application (30 kg N ha−1 y−1) resulted in a CH4 uptake rate which was 85 ± 3% of that in the control, while the uptake rate with high N (90 kg N ha−1 y−1) was 62 ± 2% of the control. The most acidic irrigation (pH = 3) increased CH4 uptake compared to pH 5.5 and 4 irrigations. This effect was the same at all N treatments (no interaction). The positive effect of acidification indicates that autotrophic NH4 oxidation is of minor importance for CH4 oxidation in soil. Increased soil moisture from 32 to 42% (v/v) significantly reduced CH4 uptake. CH4 uptake was observed during winter measurements, when the mean soil temperature was <1°C.

Nitrous oxide release from spruce forest soil: Relationships with nitrification, methane uptake, temperature, moisture and fertilization

Abstract The spatial variability in a homogeneous 63 yr old spruce forest stand was investigated with respect to potential release of N2O in relation to nitrification rate, N mineralization rate, CH4 uptake, organic C, total N and pH in soil under standardized laboratory incubation conditions. Soil samples were taken at random within a 100 m2 forest stand, and gas fluxes at three temperatures (3, 10 and 15°C) and two soil moisture contents (35 and 45% v/v) were measured. In addition, a number of other relevant factors was measured in each soil sample. There was large spatial variation in N2O release [coefficient of variation (CV)=up to 152%], nitrification rate (CV=65%) and N-mineralization rate (CV = 137%). Comparatively low spatial variations in organic C (CV=31%), total N (CV =29%), CO2 evolution (CV = 38%), CH4 uptake (CV = 37%) and pH (CV = 4.4%) were observed. The rate of N2O release was positively correlated with nitrification rate and negatively correlated with pH. The rate of CH4 uptake was negatively correlated (r = − 0.61) with nitrification rate. No significant correlation was observed between the N-mineralization rate and any of the variables measured. N2O fluxes measured at 10 and 3°C were 76% (±14%) and 17% (±4%) of that measured at 15°C, respectively. We found a significant increase in N2O accumulation by increasing the moisture content from 35 to 45%. Ammonium sulphate additions stimulated N2O release but not the nitrification. The investigation demonstrated large spatial variation in the rates of nitrification, N2O release, but it was difficult to identify regulating factors for this spatial variability.

N-fertilization and soil acidification effects on N2O and CO2 emission from temperate pine forest soil

The fluxes and soil atmospheric concentrations of N2O were studied in field lysimeters containing reestablished soil profiles from 100-y-old Scots pine (Pinus sylvestris) forest of Norway. The experiment was designed as a full factorial with 3 N-fertilization rates [0 (Control), 30 kg (Medium) and 90 kg (High) N ha−1 y−1] with NH4NO3 and 3 pH values of soil acidification (acid irrigation with pH 3, 4 and 5.5). The most acidic treatment (pH 3) significantly reduced both N2O fluxes and soil N2O concentrations. The highest N2O fluxes were observed in the intermediate pH treatment (pH 4). There was a significant increase in N2O release due to input of N. The average fertilizer-derived N2O-N emission during the summer period was 94 and 93 mg kg−1 of added NH4NO3-N d−1 for Medium N and High N, respectively. Surprisingly, despite a strong effect of acidification on the N2O flux, we could not find any significant interaction between acidification and N-fertilization. This means that N-deposition effects on the N2O fluxes will be more or less unaffected by previous acidification due to deposition of sulphuric acid. Soil acidification with the most acidic “rain” (pH 3) resulted in decreased CO2 fluxes and concentrations in soil.

Determinants of Farmers’ Adoption of Improved Soil Conservation Technology in a Middle Mountain Watershed of Central Nepal

This study explores different socio-economic and institutional factors influencing the adoption of improved soil conservation technology (ISCT) on Bari land (Rainfed outward sloping terraces) in the Middle Mountain region of Central Nepal. Structured questionnaire survey and focus group discussion methods were applied to collect the necessary information from farm households. The logistic regression model predicted seven factors influencing the adoption of improved soil conservation technology in the study area including years of schooling of the household head, caste of the respondent, land holding size of the Bari land, cash crop vegetable farming, family member occupation in off farm sector, membership of the Conservation and Development Groups, and use of credit. The study showed that technology dissemination through multi-sectoral type community based local groups is a good option to enhance the adoption of improved soil conservation technology in the Middle Mountain farming systems in Nepal. Planners and policy makers should formulate appropriate policies and programs considering the farmers’ interest, capacity, and limitation in promoting improved soil conservation technology for greater acceptance and adoption by the farmers.

Methane oxidation potentials and fluxes in agricultural soil:Effects of fertilisation and soil compaction

We have studied the inhibiting effect offertilisation and soil compaction on CH4oxidation by measuring gas fluxes and soil mineral Ndynamics in the field, and CH4 oxidation rates inlaboratory-incubated soil samples. The fertilisationand soil compaction field experiment was establishedin 1985, and the gas fluxes were measured from 1992 to1994. Methane oxidation was consistently lower infertilised than in unfertilised soil, but thereapparently was no effect of repeated fertiliseradditions on the fertilised plots. The measuredmineral N in fertilised and unfertilised soil showedlarge differences in NH4+ concentrationsjust after fertilisation, but the levels rapidlyconverged because of plant uptake and nitrification.The CH4 oxidation rate did not reflect thesecontrasting mineral N patterns, suggesting that theCH4 oxidation capacity remaining in the soil thathad been fertilised since 1985 was largely insensitiveto ammonia in the new fertiliser. Thus, competitiveinhibition by ammonia may have been involved in theearly stage of the field fertiliser experiment, butthe CH4 oxidation remaining after 7 to 9 years ofcontinued fertilisation seems not to have beenaffected by ammonia. The substrate affinity of theCH4-oxidizing microflora appeared to be the samein both the fertilised soil and the unfertilisedcontrol, as judged from the response to elevatedCH4 concentrations (52 µl l−1) inlaboratory incubations. Soil compaction resulted in apersistent reduction of CH4 influx, also seen inlaboratory incubations with sieved (4-mm mesh) soilsamples. Since the sieving presumably removesdiffusion barriers created by the soil compaction, thefact that compaction effects persisted through thesieving may indicate that soil compaction has affectedthe biological potential for CH4 oxidation in thesoil.

Effects of soil compaction on N2O emission in agricultural soil

Abstract We have studied the effect of soil compaction on N2O fluxes in relation to gas diffusion and N fertilization in the field, and N2O release rates in laboratory incubated soil samples. The fertilization and soil compaction field experiment was established in 1985, and the gas fluxes were measured in the period from 1992 to 1994. N2O emission was higher in compacted than in uncompacted soil. This compaction effect was four times higher in the NPK-fertilized treatment compared to the unfertilized one. Soil compaction decreased gas diffusivity and this may have contributed for increased N2O emission. This increased N2O emission due to soil compaction in the field became non-significant after the compacted soil was sieved (2-mm mesh) and N2O emission rates were measured in laboratory incubations. The sieving presumably removed diffusion barriers and increased the oxygen supply compared with that under the soil compaction in field. This reversibility of field compaction effects indicates that the soil compaction does not permanently increase the biological potential for N2O production in the soil.

Analysis of the sustainability of upland farming systems in the Middle Mountains region of Nepal

This paper examines the sustainability of vegetable production systems as compared with traditional cereal cropping patterns in terms of their ecological suitability, economic profitability, social acceptability and institutional viability. An assessment was carried out using combined quantitative and qualitative data collected from on-farm experimental plots, soil and plant sample analysis, a household survey, focus group discussions and a workshop in Pokhare Khola Watershed of Middle Mountain Nepal. The study showed that adoption of vegetable farming improved the socio-economic condition of the upland farmers, particularly the poor, women and disadvantaged groups, in terms of their food security, farm income, resource accessibility, employment opportunity and social status. These indicators revealed that vegetable-based cropping patterns are economically profitable and socially acceptable and thus contribute somewhat to the sustainability of upland farming. However, such achievement has been made through intensive cultivation practices such as increased use of agrochemicals and hybrid seed, that have led to declining soil fertility and increasing dependency of farmers on external inputs in commercial vegetable production and, therefore, threaten the sustainability of mountain farming in the long run. Additionally, institutional mechanisms for vegetable production and marketing are minimal and do not squarely address problems of upland farming. To ensure environmentally and socially sustainable production, government policy and programmes should promote locally available resources for vegetable production and support market mechanisms which can be competitive in national and international markets.

Influence of slope aspect on soil physico-chemical and biological properties in the mid hills of central Nepal.

This study assessed the influence of slope aspect and land use on soil physio-chemical and biological properties (soil quality indicators) on contiguous south- and north-facing slopes of the mid hills in central Nepal, having the same climate, vegetation and parent material. In each aspect, two treatments (agriculture and forest) were chosen and four replicates taken for each treatment. Soil sample collection and microarthropod extraction was done according to the standard methodology: soil core samples (10 × 10 × 5 cm) and extraction with the modified Berlese–Tullgren funnel. The investigated soil variables were temperature, moisture, faunal abundance and diversity, organic matter, organic carbon, bulk density and pH. Except in a few cases, all considered soil properties showed significant differences between aspects and land use. Soils of the north-facing slope had higher SOC content, moisture, faunal abundance and diversity, and lower temperature and pH. Variations due to topographic aspect induced varied microclimates, causing differences in faunal abundance and diversity; soil moisture, temperature and organic matter trends affected soil fertility and ultimately soil quality. Further studies are required to clarify the complex interactions between soil properties (physio-chemical and biological), vegetation and slope aspect in Nepal, as well as to develop soil biological indicators as a tool to assist in sustainable land management.

Health and environmental costs of pesticide use in vegetable farming in Nepal

There is a growing concern of pesticide risks to human health, natural environment and ecosystems. Many previous economic valuations have accounted health aspects or environmental components, but rarely combined; thus, overall risk assessment is partially distorted. The study, conducted close to the capital of Nepal, addressed the health effects of pesticides on small-scale farmers and evaluated the monetary risks of pesticide use on human health and environmental resources. We also aim to establish the relationships among valuation methods. The paper adopts cost of illness, defensive expenditure and contingent valuation willingness to pay approach. The study concluded that the methods used for valuing pesticide risks to human and environmental health are theoretically consistent. The exposed individuals are likely to bear significant economic costs of exposures depending on geographical location, pesticide use magnitudes and frequency. Individuals are willing to pay between 53 and 79% more than the existing pesticide price to protect their health and environment. The integrated pest management training is less likely to reduce health costs of pesticide exposure, although it leads to higher investment in safety measures.

Profile carbon and nutrient levels and management effect on soil quality indicators in the Mardi watershed of Nepal

Abstract Soil organic carbon (SOC) and nutrient stocks in the soil profile (0–80 cm) in four dominant land uses [forest, upland maize and millet (Bari), irrigated rice (Khet), and grazed systems)] and 0–15 cm depth along elevation gradient 1000 to 3000 m, and aspects in the Mardi watershed were measured. Soil properties at 0–15 cm depth were also measured in undisturbed forest, forest with free grazed system, managed forest, and grassland to compare the soil quality index (SQI) of topsoils. The SOC and nutrient concentration decreased with increasing profile depth. The SOC and N contents in the 0–15 cm depth of forest soils were significantly greater than the corresponding depth in upland maize and millet, irrigated rice, and grazed systems. On the other hand, available P and K concentrations at the same depth were significantly greater in upland maize and millet compared to irrigated rice, grazed system, and forest land uses. The SOC and N stocks (0–15 cm) increased from agricultural land at the valley bottom at about 1000 m above mean sea level (a.s.l.) (24 and 3 Mg ha−1) compared to undisturbed forest (74 and 5.9 Mg ha−1) at 2600 m a.s.l, demonstrating the effects of cover and elevation. Both SOC and N stocks decreased sharply in grassland (54 and 4.5 Mg ha−1) at elevations of 2600 to 2800 m a.s.l. compared with undisturbed forest. Above 2800 m a.s.l. the cover type changed from grass to coniferous forest, and the SOC and N stocks steadily increased at the summit level (3200 m a.s.l.) to 65 and 6.9 Mg ha−1, respectively. Slope and aspect significantly affected SOC with the northwest aspect having significantly higher concentrations (46 g kg−1) than other aspects. Similarly, SOC concentration at the lowest slope position (39 g kg−1) was significantly higher than the middle or upper positions (25 and 13 g kg−1). Integrated soil quality index (SQI) values varied from 0.17 to 0.69 for different land uses, being highest for undisturbed forest and lowest for irrigated rice. The SQI demonstrated the degradation status of land uses in the following ascending order: irrigated rice > grazed system > forest with free grazing > upland maize and millet > managed forest > grass land > undisturbed forest. The irrigated rice, grazed system, upland maize and millet, and freely grazed forestlands need immediate attention to minimize further deterioration of soil quality in these land uses.