*4.3. Total Soil N*

Overall, TSN content was not significantly improved following biochar application. However, significant difference was observed between experimental years. The TSN content in 2018 across treatments was lower than observed in 2019, probably due to the cumulative effect since treatments were applied to the same exact plots as in 2018. The TSN content observed at LCB was higher than that at Efaw. This is due to differences in soil type. Biochar effect was significant at the LCB site with a sandy loam soil but not at Efaw with silty clay loam. Across sites and years, an overall observed increase in TSN under biochar soil amendment was 3.7%. This finding is similar to the observations by Agegnehu et al. [25], using waste willow wood (*Salix* spp.) as biochar feedstock. Significant differences between TSN of FN treatment and NBC were not seen. The non-significant response of TSN to biochar application in the above scenarios is probably attributed to limited N in biochar from woody sources, and that was insufficient to support TSN increase within experimental periods and rates used in these studies. Total soil N is a quantity that builds up in soil over a period of time. To illustrate this viewpoint, Omara et al. [42] observed a significant trend in buildup of TSN in a long-term experiment where fertilizer N was applied on a yearly basis. Therefore, the element of time and rate of application, alongside N content of biochar, is paramount in explaining the behavior of TSN following biochar application. Contrary to these findings, Uzoma et al. [21] observed significant increase in TSN using dry cow manure biochar at similar rates as in the current study. Using dry cow manure biochar could have resulted to this significant difference in TSN buildup as compared to biochar from woody sources within the rates used in this study. With hard-wood biochar, Prommer et al. [16] reported significant increase in TSN following biochar application in combination with inorganic N compared to inorganic N alone. They could have seen the positive results due to high rate of biochar applied with up to 72 t ha−<sup>1</sup> compared to only 15 t ha−<sup>1</sup> as the maximum application rate of biochar used in the current study. The authors alluded that application of inorganic fertilizer-N in combination with biochar compensate for the reduction in organic N mineralization. Therefore, application rate and nature of biochar seems to play an important role in determining the rate of TSN increase following biochar application.
