Abstract-Soil quality management helps to maintain biological productivity; air and water quality; and human habitation and health. As improper land management can deteriorate soil function, the evaluation of soil quality for different land use is necessary. To evaluate soil quality for different land use types in the Panchase area, soil quality index was computed on the basis of the soil management assessment framework. Protected forest has the highest soil quality index (0.95) followed by community forest (0.91), pasture (0.88), khet (0.81), and bari (0.79). Available phosphorus and soil organic carbon play major roles in making significant differences in the SQI among the different land use types. Less anthropogenic impact and vegetation in forest land result in better soil quality, whereas attempts to increase productivity in cultivated land degrade the soil quality. The proper application of fertilizer and giving priority to organic farming is recommended to improve soil quality.

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Biochars have potential to provide agricultural and environmental benefits such as increasing soil carbon sequestration, crop yield, and soil fertility while reducing greenhouse gas (GHG) emissions and nitrogen leaching. However, whether these effects will sustain for the long-term is still unknown. Moreover, these effects were observed mostly in highly weathered (sub-) tropical soils with low pH and soil organic carbon (SOC). The soils in northern colder boreal regions have typically higher SOC and undergo continuous freeze-thaw cycles. Therefore, effects of biochars in these regions may be different from those observed in other climates. However, only a few biochar studies have been conducted in boreal regions. We aimed to assess the long-term effects of biochars on GHG emissions, yield-normalized non-CO2 GHG emissions (GHGI), and N dynamics in boreal soils. For this, we collected data from four existing Finnish biochar field experiments during 2018 growing season. The experiments were Jokioinen (Stagnosol), Qvidja (Cambisol), Viikki-1 (Stagnosol), and Viikki-2 (Umbrisol), where biochars were applied, 2, 2, 8, and 7 years before, respectively. The GHG emissions, crop yield, soil mineral N, and microbial biomass were measured from all fields, whereas, additional measurements of plant N contents and N leaching were conducted in Qvidja. Biochars increased CO2 efflux in Qvidja and Viikki-2, whereas, there were no statistically significant effects of biochars on the fluxes of N2O or CH4, but in Qvidja, biochars tended to reduce N2O fluxes at the peak emission points. The tendency of biochars to reduce N2O emissions seemed higher in soils with higher silt content and lower initial soil carbon. We demonstrated the long-term effects of biochar on increased crop yield by 65% and reduced GHGI by 43% in Viikki-2. In Qvidja, the significant increment of plant biomass, plant N uptake, nitrogen use efficiency, and crop yield, and reduction of NO3−–N leaching by the spruce biochar is attributed to its ability to retain NO3−–N, which could be linked to its significantly higher specific surface area. The ability of the spruce biochar to retain soil NO3−–N and hence to reduce N losses, has implications for sustainable management of N fertilization.

The effectiveness of agricultural wastes as bioremediation materials is gaining research attention as a better option in mitigating the issue of crude oil effects in soil environment. In the present study, the growth performance of Telfairia occidentalis and Arachis hypogaea linn in crude oil polluted soil amended with plantain peels (PP) and cocoa pod husks (CPH) were investigated. Eight kilograms (8 kg) each of dried soil samples were collected and weighed into 60 polythene bags. The polythene bags except the pristine control were polluted with 80 ml of crude oil and allowed for 14 days of soil acclimatization. The treatments comprising of CPH and PP were amended after 14 days, using the following concentrations: 0, 100, 150 and 200 g and allowed to acclimatize for 60 days. T. occidentalis and A. hypogaea linn were cultivated immediately after treatment regimen. The pH of the amended and un-amended soil samples were observed to be at a range recommended for effective bioremediation of hydrocarbon polluted soil. The organic carbon content of the CPH amended soils were significantly reduced as compared to the PP amended soil. The phosphorus, nitrogen, potassium and other essential soil parameters evaluated were significantly high (P<0.05) in CPH amended soil than the PP amended soil. Crops grown in the rehabilitated soils possess a high adaptability in CPH amended soil than the PP amended soil. The amendments most preferably cocoa pod husks which tend to be more effective in the reduction of hydrocarbon content of the soil should be utilized in the enhancement of microbial degradation of crude oil product in soils.

A 15N tracing pot experiment was conducted using two types of wood-based biochars: a regular biochar and a Kon-Tiki-produced nutrient-enriched biochar, at two application rates (1% and 5% (w/w)), in addition to a fertilizer only and a control treatment. Ryegrass was sown in pots, all of which except controls received 15N-labelled fertilizer as either 15NH4NO3 or NH415NO3. We quantified the effect of biochar application on soil N2O emissions, as well as the fate of fertilizer-derived ammonium (NH4+) and nitrate (NO3−) in terms of their leaching from the soil, uptake into plant biomass, and recovery in the soil. We found that application of biochars reduced soil mineral N leaching and N2O emissions. Similarly, the higher biochar application rate of 5% significantly increased aboveground ryegrass biomass yield. However, no differences in N2O emissions and ryegrass biomass yields were observed between regular and nutrient-enriched biochar treatments, although mineral N leaching tended to be lower in the nutrient-enriched biochar treatment than in the regular biochar treatment. The 15N analysis revealed that biochar application increased the plant uptake of added nitrate, but reduced the plant uptake of added ammonium compared to the fertilizer only treatment. Thus, the uptake of total N derived from added NH4NO3 fertilizer was not affected by the biochar addition, and cannot explain the increase in plant biomass in biochar treatments. Instead, the increased plant biomass at the higher biochar application rate was attributed to the enhanced uptake of N derived from soil. This suggests that the interactions between biochar and native soil organic N may be important determinants of the availability of soil N to plant growth.