# Effect of Biochar Application Depth on Crop Productivity Under Tropical Rainfed Conditions
## 4 Discussions
### Contingent Field Condition and Biochar Treatment Effects  
To quantify the effects of the contingent field conditions and the biochar application depth on the measured yield components, simple relational equations were developed. For this purpose, it was assumed that the effect of water logging, wherever it occurred, was the same. Similarly, the effect of pest damage, wherever it occurred, was the same too. Then while water logging and biochar application were yield-gain factors, pest damage was a yield-loss factor. With this, we then take the effect of water logging on the crop performance to be \(w\), that of pest damage be \(p\) and that of biochar depth be \(b\). Based on field observations, there was water logging in CK (\(CK\to w\)), water logging, biochar use and pest damage in TA (\(TA\to w+b-p\)), biochar use in TB (\(TB\to b\)) and then biochar use and pest damage in TC (\(TC\to b-p\)). It then becomes apparent that \(TA-TC=w\) and that \(CK-w=\overline{CK}\) (where \(\overline{CK}\) is crop yield without the effects of water logging, biochar use and pest damage). Also \(TC-TB=-p\) (where \(p\) is a yield loss factor and therefore negative). With \(w\) and \(p\) known, then \(b\) can be derived from \(TA\to w+b-p\); thus \(b=TA-\overline{CK}-w+p\). Note that TA, TB, TC and CK are used as defined earlier. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**MYV**} & \multirow{2}{*}{**BDT**} & \multirow{2}{*}{**Level**} & \multicolumn{5}{c}{**MYV Match**} \\ \cline{4-7}  & & & **TN** & **PW** & **PL** & **CW** & **SM** \\ \hline \multirow{3}{*}{TN} & TB & Highest & \(\surd\) & \(\surd\) & \(\times\) & \(\surd\) & \(\times\) \\  & TC & Lowest & \(\surd\) & \(\surd\) & \(\surd\) & \(\times\) & \(\surd\) \\  & TB & Highest & \(\surd\) & \(\surd\) & \(\times\) & \(\surd\) & \(\times\) \\  & TC & Lowest & \(\times\) & \(\surd\) & \(\surd\) & \(\times\) & \(\surd\) \\ \cline{2-7}  & TA & Highest & \(\times\) & \(\times\) & \(\surd\) & \(\times\) & \(\surd\) \\ \cline{2-7}  & TC & Lowest & \(\surd\) & \(\surd\) & \(\surd\) & \(\times\) & \(\surd\) \\ \cline{2-7}  & TC & Lowest & \(\surd\) & \(\surd\) & \(\surd\) & \(\times\) & \(\surd\) \\ \cline{2-7}  & \multirow{2}{*}{CW} & TB & Highest & \(\surd\) & \(\times\) & \(\surd\) & \(\times\) \\ \cline{2-7}  & TA & Lowest & \(\times\) & \(\times\) & \(\times\) & \(\surd\) & \(\times\) \\ \cline{2-7}  & TA & Highest & \(\times\) & \(\times\) & \(\surd\) & \(\times\) & \(\surd\) \\ \cline{2-7}  & TC & Lowest & \(\surd\) & \(\surd\) & \(\surd\) & \(\times\) & \(\surd\) \\ \hline \hline \end{tabular} Note that \(\overline{\text{TA}}\) = treatment A (with 10 cm biochar application depth), TB = treatment B (with 20 cm biochar application depth), TC = treatment C (with 30 cm biochar application depth) and CK is control treatment (with no biochar). The measured yield variables include TN = tiller number, PH= plant height, PW = plant weight, PL = plant length, CM = crop moisture content, SM = soil moisture content, \(\surd\) = a match, and \(\times\) = no match. Double underline means treatment with water logging (due to the development of sunken) and limited pest infestation whereas italicized bold means treatment with runoff (due to mounding) and high pest infestation.  
\end{table} 
Table 2: A table depicting the match of the biochar depth treatments (BDT) with the highest and lowest values of the measured yield variables (MYV) of NERICA-4 rice plant under tropical rainfed conditions. Using the above relations for plant weight (PW), there was 20.30% yield loss under TA due to pest damage, 36.84% yield loss under TB due to runoff (which indicates no water logging), 86.74% yield loss under TC due both to pest damage and runoff and then 14.86% yield gain under CK due to water logging. Similarly for plant length (PL), there was 4.98% yield loss under TA due to pest damage, 38.98% yield loss under TB due to runoff, 83.29% yield loss under TC due both to pest damage and runoff, and then 25.73% yield gain under CK due to water logging.