The residual impact of straw mulch and biochar amendments on grain quality and amino acid contents of rainfed maize crop

The inability of humans and many farm animals to synthesize certain amino acids has long triggered tremendous interest in increasing the levels of these so-called essential amino acids in crop plants. Hence, a two-year field experiment was conducted to evaluate the effects of straw mulch (8 t ha(-1)) and biochar applied at various rates (0, 4, 12, 36 t ha(-1)) on the chlorophyll, photosynthesis, total nitrogen in soil, essential and nonessential amino acid (AA) contents of maize grain. The maize straw mulch and biochar significantly increased chlorophyll contents, photosynthesis rate of maize crop and total soil nitrogen. The application of biochar (12 t ha(-1)) increased the chlorophyll contents and photosynthesis rate and total soil nitrogen during both years. However, excessive biochar applications (more than 12 t ha(-1)) had negative effects on chlorophyll contents, photosynthesis rate of maize crop and total soil nitrogen of soil. The AAs were significantly affected by biochar, depending on the application rate. In conclusion, the application of straw mulch and biochar improved the rate of leaf chlorophyll contents, photosynthesis rate and amino acid contents in maize grain when applied at appropriate rates, but the effects were negative when biochar was overused.