## 3 Results and Discussion
### Residual Levels of Organochlorine Pesticides in Grain
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & **Without** & **Mineral** & **MBM \({}^{*}\) 1.0 t** & **MBM 2.0 t** & **MBM 3.0 t** & **Av. for** \\  & **Fertilization** & **Fertilization** & **ha\({}^{-1}\)** & **ha\({}^{-1}\)** & **ha\({}^{-1}\)** & **Ha\({}^{-1}\)** \\ \hline \multicolumn{7}{c}{Grain yield (t ha\({}^{-1}\))} \\
2014 & 4.75 \(\pm\) 0.30 \({}^{\mathrm{b}}\) & 4.06 \(\pm\) 0.23 \({}^{\mathrm{bcd}}\) & 3.98 \(\pm\) 0.11 \({}^{\mathrm{bcd}}\) & 3.83 \(\pm\) 0.23 \({}^{\mathrm{bcd}}\) & 2.74 \(\pm\) 0.33 \({}^{\mathrm{de}}\) & 3.87 \(\pm\) 0.18 \({}^{\mathrm{B}}\) \\
2015 & 2.42 \(\pm\) 0.16 \({}^{\mathrm{e}}\) & 3.41 \(\pm\) 0.41 \({}^{\mathrm{bde}}\) & 2.80 \(\pm\) 0.22 \({}^{\mathrm{cde}}\) & 3.03 \(\pm\) 0.12 \({}^{\mathrm{cde}}\) & 2.91 \(\pm\) 0.29 \({}^{\mathrm{cde}}\) & 2.91 \(\pm\) 0.13 \({}^{\mathrm{C}}\) \\
2016 & 3.96 \(\pm\) 0.22 \({}^{\mathrm{bcd}}\) & 7.97 \(\pm\) 0.30 \({}^{\mathrm{a}}\) & 4.64 \(\pm\) 0.47 \({}^{\mathrm{b}}\) & 7.11 \(\pm\) 0.39 \({}^{\mathrm{a}}\) & 6.87 \(\pm\) 0.14 \({}^{\mathrm{a}}\) & 6.11 \(\pm\) 0.38 \({}^{\mathrm{A}}\) \\
2017 & 1.12 \(\pm\) 0.08 \({}^{\mathrm{f}}\) & 3.87 \(\pm\) 0.26 \({}^{\mathrm{bcd}}\) & 3.05 \(\pm\) 0.34 \({}^{\mathrm{cde}}\) & 4.28 \(\pm\) 0.04 \({}^{\mathrm{bc}}\) & 4.21 \(\pm\) 0.16 \({}^{\mathrm{bc}}\) & 3.06 \(\pm\) 0.28 \({}^{\mathrm{C}}\) \\ Av. for Year & 3.06 \(\pm\) 0.37 \({}^{\mathrm{D}}\) & 4.83 \(\pm\) 0.49 \({}^{\mathrm{A}}\) & 3.62 \(\pm\) 0.24 \({}^{\mathrm{C}}\) & 4.56 \(\pm\) 0.41 \({}^{\mathrm{AB}}\) & 4.18 \(\pm\) 0.44 \({}^{\mathrm{B}}\) & \\ \hline \multicolumn{7}{c}{Lipid content (\%)} \\
2014 & 5.80 \(\pm\) 0.01 \({}^{\mathrm{cd}}\) & 5.12 \(\pm\) 0.01 \({}^{\mathrm{dede}}\) & 9.39 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 4.00 \(\pm\) 0.01 \({}^{\mathrm{fgh}}\) & 9.12 \(\pm\) 0.27 \({}^{\mathrm{ab}}\) & 6.68 \(\pm\) 0.50 \({}^{\mathrm{A}}\) \\
2015 & 3.71 \(\pm\) 0.06 \({}^{\mathrm{fgh}}\) & 2.79 \(\pm\) 0.01 \({}^{\mathrm{f}}\) & 2.83 \(\pm\) 0.01 \({}^{\mathrm{f}}\) & 2.26 \(\pm\) 0.01 \({}^{\mathrm{j}}\) & 5.52 \(\pm\) 0.06 \({}^{\mathrm{cd}}\) & 3.41 \(\pm\) 0.26 \({}^{\mathrm{C}}\) \\
2016 & 3.60 \(\pm\) 0.09 \({}^{\mathrm{gh}}\) & 2.27 \(\pm\) 0.13 \({}^{\mathrm{f}}\) & 4.39 \(\pm\) 0.86 \({}^{\mathrm{edg}}\) & 8.08 \(\pm\) 0.05 \({}^{\mathrm{b}}\) & 5.86 \(\pm\) 0.13 \({}^{\mathrm{c}}\) & 4.84 \(\pm\) 0.48 \({}^{\mathrm{B}}\) \\
2017 & 3.42 \(\pm\) 0.10 \({}^{\mathrm{gh}}\) & 2.91 \(\pm\) 0.07 \({}^{\mathrm{hij}}\) & 2.90 \(\pm\) 0.04 \({}^{\mathrm{hij}}\) & 8.52 \(\pm\) 0.02 \({}^{\mathrm{ab}}\) & 4.76 \(\pm\) 0.04 \({}^{\mathrm{def}}\) & 4.49 \(\pm\) 0.49 \({}^{\mathrm{B}}\) \\ Av. for Year & 4.13 \(\pm\) 0.25 \({}^{\mathrm{D}}\) & 3.27 \(\pm\) 0.28 \({}^{\mathrm{E}}\) & 4.88 \(\pm\) 0.72 \({}^{\mathrm{C}}\) & 5.71 \(\pm\) 0.69 \({}^{\mathrm{B}}\) & 6.31 \(\pm\) 0.44 \({}^{\mathrm{A}}\) & \\ \hline \end{tabular} \({}^{*}\)MBM—meat and bone meal. Values followed by the same letters do not differ significantly in [PERSON]’s (HSD) test (\(p<0.05\)).  
\end{table} 
Table 3: Grain yield (t ha\({}^{-1}\)) and lipid content (%) of maize grain (mean value and standard error). The DDT content of grain (Figure 6b) increased gradually in successive years with increasing soil DDT (Figure 5b). There is a close relationship between the residual levels of OCPs in soil and plants, and the rate of OCP uptake by plants is determined by the concentrations of these contaminants in soil [7; 14; 48; 60]. DDT levels in maize grain were highest in NPK treatments, mostly due to high DDT levels in 2016 and 2017 (Figure 7b). The content of DDE in maize grain was highest in unfertilized treatments and NPK treatments, whereas DDD levels were highest in 1.0 t ha\({}^{-1}\) MBM treatments (Figure 6b). On average, the lowest DDD and DDE concentrations in maize grain were noted in treatments fertilized with the highest MBM rates (2.0 and 3.0 t ha\({}^{-1}\)). The only exception was higher DDE concentration in grain in 2.0 MBM t ha\({}^{-1}\) treatments than in 1.0 MBM t ha\({}^{-1}\) treatments.