Biochar amendment is a good means of mitigating methane (CH4) and nitrous oxide (N2O) emissions. However, the effects of biochar amendment on N2O and CH4 reduction in soil under rotation with different soil moisture contents is not well understood. To understand CH4 and N2O flux from soil with biochar amendment under water-unsaturated and water-saturated conditions, a field experiment was conducted in a tobacco-rice rotation field in subtropical China to investigate N2O and CH4 emissions following soil amendment with tobacco straw biochar at rates of 0, 10, 40 and 80 t·ha−1 (B0, B10, B40 and B80, respectively). N2O and CH4 emissions were monitored by a closed-chamber method in the water-unsaturated tobacco (UT) and water-saturated rice (SR) seasons during the 2015 planting season. The soil pH increased from 5.4 in the control to 6.1 in the soil amended with biochar at 80 t·ha−1 in the UT season. During both the UT and SR seasons, with biochar amendment at 40 and 80 t·ha−1, the soil bulk density (BD) decreased, while the soil organic matter (SOM) and available potassium (Av. K) contents increased. N2O flux was significantly greater in UT than in SR in the controls but decreased with the application of biochar during both the UT and SR seasons. The cumulative CH4 emission decreased with the rate of biochar application and the methanotroph pmoA gene copy number in soils and increased with the methanogenic archaea 16Sr DNA gene copy number in soils during the rice-cropping season. These results indicated that biochar amendment could decrease methanogenic archaea and increase of methanotroph pmoA gene, which are the mechanistic origin for CH4 reduction.

Soil chemical degradation caused by acidity is a serious constraint to food production in most parts of the Tropics. It was in the bid to proffer solution to this that the present study was conceived. Anincubation study was conducted at the laboratory of Soil Science and Meteorology Department of Michael Okpara University of Agriculture Umudike. The aim was to ascertain the effect of amendments namely: Control (no amendment), Biochar, Ash, Lime, Biochar + Poultry Manure, Ash + Poultry Manure and Lime + Poultry Manure, on soil pH and exchangeable acidity of Sandstone, Shale and Alluvium. The rate of application was 1.43 g for the sole amendments and 0.72 g each for the combined amendments to give an equivalent of 2 t/ha. They were applied to 100 g of the soil and replicated three times in a Completely Randomized Design. The incubation study lasted for eighty-four days, the pH and exchangeable acidity were determined at fourteen days intervals. The result obtained revealed that all the treatments increased the soil pH and decreased the exchangeable acidity over the control. In all parent materials, applied Lime and Lime + Pm significantly (p < 0.05) gave the highest pH of 6.6, 6.9 and 7.2 for Shale, Sandstone and Alluvium respectively on the 28 th day of incubation which, was the time, the maximum pH value was attained. Biochar and Biochar + Pm were considered the appropriate amendments because the pH values they gave were towards neutral, unlike that of Lime and Lime + Pm that were towards alkaline. It is recommended that field trial of this work is conducted.

Various challenges face the sustainability of soil ecosystem.  This research was carried out to assess the impact of burning and application of cow dung on soil microbes.  Soil samples were taken from three different locations: Afugiri, Lodu and Umudike. The study comprised of two experiments.  The focus of the first experiment was to check the effect of slash and burn on soil pH, organic matter, microbial biomass phosphorus (MBP) and soil microbes. Result obtained showed that burning affected soil pH, organic matter and MBP and microbial population.  Burning reduced the organic matter content of soil, and increased soil pH.  The results of the microbial biomass showed that burning was disadvantageous to the sustainability of soil ecosystem.  However, in the second experiment, cowdung and fortified cowdung amendment were applied to determine the effect of organic amendment on soil microbes.  Cowdung significantly affected bacteria population and number of earthworm species. Bacterial species have more population than fungal species.  The results from this study indicate that burning in agricultural land increases soil pH, but have the capacity to destroy beneficial microbes and reduce those activities carried out by them.

Field trials and a pot experiment were conducted during the 2005 and 2006 cropping seasons at Michael Okpara University of Agriculture, Umudike, Nigeria, to assess the effect of various agricultural wastes ash on nutrient concentration, growth and yield of maize in a Haplic Acrisol. The treatments comprised palm bunch ash, kitchen residues ash, cocoa pod husk ash, saw dust ash, calcium carbonate, oyster shell ash and a control. Each of the ash was applied at five levels: 0, 2, 4, 6 and 8 tonnes per hectare. They were replicated three times in a split plot completely randomized design for the pot experiment and randomized completely block design for the field trials. The effects of the treatments were measured on nitrogen, phosphorus, potassium, calcium, and manganese and iron concentration in maize crop. Other plant parameters measured were maize height at 8 weeks after planting, stem diameter, stover weight and grain yield weight in the field trails. The results obtained showed that all the agricultural wastes significantly (P < 0.05) increased the concentrations of nitrogen, phosphorus, potassium and calcium. They also significantly (p<0.05) reduced the concentration of iron and manganese in the plant. The wastes applied significantly increased the plant height at 8 WAP, maize stem diameter, stover weight and grain yield. Among the treatments tested, 6t/ha of cocoa pod husk ash significantly (P<0.05) increased nitrogen concentration in the maize from 0.49 in the control to 5.17%. Plant height, stem diameter and stover weight were also increased by the application of 6t/ha of cocoa pod husk ash. While 4t/ha of kitchen residue ash, 4t/ha of oyster shell ash and 4 t/ha of cocoa pod husk ash significantly (P<0.05) increased the concentration of phosphorus from 1.01% to 4.98%, calcium from 0.4% to 6% and potassium from 0.19% to 0.42% respectively. The soil pH correlated negatively with iron and manganese concentration, positively with phosphorus and calcium concentration. These results show that maize can be grown successfully on Haplic Acrisol of the Southeastern Nigeria using waste from agricultural products.

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