Biochar is a by-product of feedstock pyrolysis and is used as a carbon-rich amendment to improve soil physicochemical quality (Lehman and Joseph, 2009). From this study, application of rice husk biochar reduced soil acidity and it is in congruent with the earlier studies of Ghorbani et al. (2019) and Wu et al. (2020). This could be attributed to the alkalinity nature of biochar and specifically the increased buffering capacity of soil pH which culminated into improved plant growth (Guo et al., 2016).
Biochar has been reported to be superior to lime in reducing the effect of soil acidity, fruit quality and improving soil characteristics (Wu et al., 2020), its rich in organic carbon, active functional groups and special structure which enhance its ability to react and bind with toxic metals (Khan et al., 2017).
The E.CEC of the soil, basic cations and micronutrient values were elevated after biochar application. This is important as biochar cation exchange capacity (CEC) is germane in helping soil to retain nutrients, reduce fertilizer runoff, and improve soil water retention (Kharel et al., 2019). The increase in CEC and other properties have to do with the level of minerals present in the biomass or feedstock (Khan et al., 2017). This may also be attributed to considerable variation observed in the values of some of the elements like Manganese, Sodium, H+ and Copper.
However, % total carbon in biochar (3.70) was observed to be lower than the one present in the feedstock (6.59). This agrees with previous reports that during a slow pyrolysis, biochar helps in sequestering 50% of the initial carbon in comparison to low amount retained after pyrolysis (Mulabagal et al., 2015).
Biochar application at B1, B2 and B3 revealed significant increase in tomato height and stem girth across the weeks after transplanting compared to control. There were also significant differences in the leaf area and number of fruits at different biochar application rates compared to control. This is congruent with previous studies on tomato where biochar amendment was reported to reduce transient sodium ions by adsorption and released mineral nutrients such as potassium, calcium, and magnesium into the soil solution, which in turn have the potential in ameliorating salt stress and enhancing tomato production (She et al., 2018).
The role of biochar in improving soil quality and tomato production highlights the importance of biochar as a soil amendment to improve soil properties, particularly soil aggregation, soil biophysical properties, sink for atmospheric CO2, reduced nitrate leaching that ensure environmental sustainability (Ghorbani et al., 2019, Rahman et al., 2020).
Biochar amendments significantly increased the number of flower and fruits progressively at all growth rates at 12WAT. Thus, increasing the yield or tomato production. This is in line with earlier study that biochar application enhanced crop yield especially maize and tomato (Faloye et al., 2020 and Ronga et al., 2020).
Fruit weight is one of the most important parameters contributing in tomato yield. However, it was observed that the weight of tomato plant that received the biochar application at rate B3 (7.5 t/ha) greatly improved in comparison with the control. This agrees with previous study by Ronga et al. (2020) who observed higher mean value of fruit weight in tomatoes (82.67g) when biochar fertilizer was used compared to the control (65.33g).
Moreover, biochar amendment at B3 had highest influence on microbial biomass carbon, nitrogen and phosphorus at harvesting stage (302.30, 18.81 and 11.75 µg/g) compared to control (275.45, 15.30 and 10.49 µg/g respectively). The change in MBC shows the process of microbial growth, death and organic matter degradation. This is also applicable to microbial biomass nitrogen (MBN) and phosphorous (MBP) as biochar amendment had positive influence on nitrogen and phosphorous. The increase in MBC compared to decrease in MBN at harvesting stage indicated that biochar in soil acted as a carbon source rather than a nitrogen source for soil microbes and this could have consequences on nitrogen cycling (Zhang et al., 2014). Biochar treatment at B3 showed higher value of soil microbial biomass C: N: P ratios i.e. MBC > MBN > MBP and this could be attributed to the report that biochar could decrease the fraction of biomass nitrogen and phosphorous mineralized.