# Effect of Biochar Application Depth on Crop Productivity Under Tropical Rainfed Conditions
## 4 Discussions
### Treatment Effect on Yield  
Based on the results, the number of tillers per hill was highest under TB, followed by TA, CK, and then TC. The increase in the number of tillers in successive time periods (2 weeks in this case) were strongly correlated (\(r>0.85\)), but only significantly different (\(p=0.05\)) for the period from the 6 th to the 8 th week and then from the 8 th to the 10 th week (Figure 3a,b). Tillering was not completely consistent with biochar application depth, probably due to field contingencies (pest damage and water logging) under the tropical rainfed condition. For the shoot system, increase in plant height in successive time periods (also 2 weeks in this study) was strongly correlated (\(r>0.96\)), except for the period between the 8 th and 10 th weeks (\(r=0.41\)). Also 2-tailed T-test showed that the differences in the increase in height between the successive time periods were significant at the 0.05 confidence interval. On average, plant height was highest under CK (control treatment), followed by TB, TC, and TA (Figure 3c,d). Like tillering, plant height was not completely consistent with biochar application depth and probably affected by the same contingent field conditions. For plant length (which is the total length for root, shoot and panicle), it decreased with increasing biochar application depth (Figure 4). However, plant length under CK (no biochar) was higher than \begin{table}
\begin{tabular}{l l l l l l l l l l} \hline \hline \(R^{2}\) & TN & GW & SW & SL & RW & RL & PW & PL & CM \\ \hline TN & 1.00 & & & & & & & & \\
**GW** & 0.89 & 1.00 & & & & & & & \\
**SW** & 0.84 & 0.99 & 1.00 & & & & & & \\
**SL** & 0.19 & 0.91 & 0.93 & 1.00 & & & & & \\
**RW** & 0.94 & 0.94 & 0.99 & 0.96 & 1.00 & & & & \\
**RL** & _0.00_ & 0.89 & 0.91 & _1.00_ & 0.96 & 1.00 & & & \\
**PW** & _0.90_ & _1.00_ & 1.00 & _0.95_ & 1.00 & _0.97_ & 1.00 & & \\
**PL** & 0.19 & 0.91 & 0.93 & 1.00 & 0.97 & 1.00 & 0.98 & 1.00 & \\
**CM** & 0.14 & 0.88 & 0.92 & 1.00 & 0.96 & 1.00 & 0.98 & 1.00 & 1.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A table of correlativity of yield component variables of NERICA-4 upland rice. In the table, TN = tiller number, GW = grain weight, SW = shoot weight, SL = shoot length, RW = root weight, RL = root length, PW = panicle weight, and PL = panicle length and CM crop moisture content. that under TC (30 cm biochar depth). On average, the rice plant increased from root to panicle (cut from the last leaf base) and then to shoot (without panicle). Genetically, rice shoot is longest, followed by panicle and then root (Figure 4). The approximate ratio of panicle-to-root was 1:2, shoot-to-panicle was 1:3, and panicle-to-shoot was 1:5. The observed field contingencies included water logging, which was highest in CK (where there was no tillage), followed by TA (10 cm tillage depth plus biochar), but no water logging in TB (20 cm tillage depth plus biochar), but even mounding in TC (30 cm tillage depth plus biochar). The differential water logging condition was because with no tillage (CK), the bamboo canes around the plots caused sunken beds to develop. Under TA, the addition of only 1 part of biochar to 20 parts of dug-out soil to the depth of 10 cm increased little the backfill volume and therefore sunken beds also formed after using separation bamboo canes. Under TB, the increase in volume due to the mixing of the 20-cm depth of soil with biochar caused the bed to just level out with the separation canes and there was therefore no water logging. Finally, under TC, the increase in volume due to the mixing of 30 cm depth of excavated soil with biochar cause mounding above the separation canes, causing runoff. As a key factor for rice growth, the differential water conditions of the treatment plots affected the crop yield. Also, because no buffer plots were put around the treatment plots, pest out outbreak affected more the peripheral TA (which bordered on vegetable plots) and TC (which bordered on bush) treatment plots.