Países que Presentaron y Superaron Conflictos de Supremacía Constitucional

Soil fertility is related to many aspects, including biotic and abiotic reactions and their interactions in an array of complex and dynamic processes. Biochar application may affect

154

soil parameters due to its specific properties and the changes that occur in soil after biochar addition, which may involve a range of soil physical and chemical properties as well as microbial activity (Atkinson et al., 2010; Lehmann et al., 2011). The changes in one or more of these parameters in soil after biochar amendment may indirectly affect other aspects in relation to soil fertility which denotes the complexity of the biotic and abiotic interactions and activities in soil.

When added at sufficient levels biochar seems likely to change the soil, but the degree and benefits/detractions from these changes appears to be partly based on the specifications of the biochar applied. Biochar can provide high micro-porosity and surface area which can a potential habitat for microorganisms in soil. Also their capacity to increase CEC enhances the retention of nutrient cations and their availability in the soil for microbes and plant uptake (Atkinson et al., 2010). The application of biochar could also improve irrigation management and water infiltration and enhance fertiliser treatment response in soil. Asai et al. (2009) investigate the effect of biochar on physical properties and rice green yields. Their experiments, conducted within upland conditions in ten sites at application rates from 0-16 t/h combined with different N and P fertilizer application rates, showed an improvement in the hydraulic conductivity and increased rice yields in sites with low P content and also higher responses in fertilised biochar treatments than fertiliser alone. Improving hydraulic conductivity and other physical characteristics in soil provides suitable conditions for the chemical interactions and microbial activity. Furthermore, because biochar has high resistance to the microbial degradation; the impact of biochar addition in soil could persist for a long time (Asai et al., 2009; Lehmann et al., 2009). The use of biochar as a soil amendment could be more beneficial in soils that have poor physio-chemical characteristics, such as sandy soils. An experiment conducted by Basso et al. (2013) suggested that biochar addition

155

increased water retention in soil by 23% compared to the control. The result also showed that bulk density of the control soil increased during the incubation time of the experiment by almost 3%, while bulk density of biochar-treated soils was 9% less than the control and constantly stable during incubation time. Biochar contribution and impact on soil physical properties such as soil stability and aggregation, water management, porosity and surface area indicate that understanding biochar functions and effects in soil would assist the use of particular biochars to suit specific agricultural soils to gain the maximum benefits from using biochar as a soil amendment (Sohi et al., 2010).

The implications of biochar addition on soil chemical properties are complicated and unpredictable because specific chemical properties of each biochar are affected by the pyrolysis conditions and feedstock used to produce the biochar (Unger et al., 2011; Kloss et al., 2012). Unger et al. (2011) conducted an incubation experiment to determine whether biochar produced under different reactions from different feedstocks would differentiate the influence of biochar on soil chemical properties. In this study, selected parameters were measured included total nitrogen, total organic carbon, ammonium nitrogen (NH4-N) and

nitrate nitrogen (NO3-N), the results suggested that the reaction conditions and organic

materials used to produced biochar will affect specific chemical properties which therefore influence soil parameters in the amended soils. It has been stated that biochar may increase pH in soil which influence nutrients availability in soil (Fowles, 2007). However, the impact of biochar on soil pH is dependent on the pH of the biochar itself and the liming capacity which varies between different biochars (Kookana et al., 2011; Lehmann et al., 2011).

The impact of biochar on biotic processes and related microbes has been discussed recently by many researchers; however there remains a limited understanding regarding the interaction between biochar amended soils and the normal vs heightened or changes in micro

156

biological processes (Lehmann et al., 2011). Biochar contains highly stable forms of vitrified carbon which potentially increases the C/N ratio and affects the microbial activity and nutrient cycling in soil (Nguyen et al., 2008; Kookana et al., 2011). Improvement of soil physical and chemical properties by biochar amendment may enhance microbial activity as it is likely to be source of nutrients and a suitable habitat for soil microorganisms. Investigating the effect of biochar addition on microbial biomass and activity, Kolb et al. (2009) added biochar to four different soils (Mollisol, Alfisol, Entisol, and Spodosol) at five application rates from 0 to 0.1 kg/kg-1 soil. Their results showed a significant increase in both microbial biomass and activity with increasing application rates. The same patterns of biochar impact were observed on microbial biomass, microbial activity and nutrient availability in all four soils but the microbial response to biochar varied depending on the differences in nutrient availability in each soil. Solaiman et al. (2010) found that phosphorus solubility increased in the presence of biochar due to an increase in mycorrhizal colonisation, however, the results showed a decrease in microbial respiration with increasing application rates in biochar amended soil (Thies and Rillig, 2009; Solaiman et al., 2010). In contrast, other studies have shown an increase in total respiration and respiratory rate, and a reduction in mycorrhizal colonization after biochar application (Treseder, 2004; Steinbeiss et al., 2009). The differences in biochars, application rates and type of soils are likely to have contributed to the range of effects of biochar on microbial communities.

The effect of biochar on soil fertility can be positive or negative depending on the quality of the biochar and application rates (Spokas et al., 2012), hence there are many aspects which still need to be investigated. Furthermore, changes in soil nutrients often occur over a long period of time and most of the studies reported in the literature were conducted over a relatively short time period. Hence longer term experiments with observations of plant

157

response are required for a comprehensive determination of the impact of biochar on soil fertility.