Impact of Integrated Application of Biochar and Nitrogen on Biochemical Composition of Maize and Wheat Crops

Abstract

Application of biochar and nitrogen not only improves cereal crops productivity but also the nutritional quality of grains. Field trials on the impact of biochar and N amendments on the soil physicochemical properties, microbial activity and nutritional and antinutritional components of maize and subsequent wheat crop was conducted in district Buner, Khyber Pakhtunkhwa, Pakistan during 2014-15. Biochar was applied at the rate of 0, 5, 10, 15 and 20 ton/ha along with N at the dose rate of 0, 100, 150 and 200 kg/h for maize and 0, 80, 120 and 200 kg/ha for wheat crop. The immediate effect of biochar and N amendments was assessed on the chemical composition of maize (cv. Azam) grains whereas the residual impact of biochar coupled with fresh application of N was determined on subsequent wheat (cv. Sahar) crop. The soil physicochemical properties and microbial activities were evaluated in the beginning, reproductive stage and at maturity of both crops. The crops were harvested at full maturity and the grains were analyzed for proximate composition, starch content, total protein and fractions, minerals, fatty acids, phytic acid and tannins contents. The average values of soil pH, electrical conductivity (EC), organic matter (OM), N, P, K and microbial biomass-carbon (MB-C), microbial biomass-nitrogen (MB-N) and C/N ratio of the composite soil before sowing of maize crop were found to be 8.2, 0.37dS/m, 0.95%, 1.74 mg/kg, 3.45mg/kg, 61.5mg/kg, 190 μg/g, 19 μg/g and 10.12 μg/g, respectively. The biochar and N levels significantly (p≤0.05) increased soil pH whereas soil OM was substantially enhanced only with biochar at the reproductive stage of maize. At maturity stage of maize crop, MB-C and MB-N were significantly affected by biochar and N treatments whereas soil pH, OM and EC were not significantly (p≥0.05) affected. Residual biochar significantly (p≤0.05) increased soil pH, OM, MB-C, MB-N and C/N at reproductive stage of wheat, while the effect of N levels was significant (p≤0.05) only for soil MB-C, MB-N and C/N ratio. At maturity stage of wheat crop soil OM, MB-C and C/N ratio was significantly (p≤0.05) increased with biochar residues and N applications, whereas soil pH and MB-N was only influenced by residual biochar. The proximate composition of maize grain was significantly (p≤0.05) affected by both biochar and N levels. Treatment combination of 20 t/ha biochar and 150 kg/ha N significantly (p≤0.05) increased the protein content of maize grains. Fat contents was higher with 20 t/ha biochar with no N and crude fiber content with no biochar and 200 kg/ha N application. Nitrogen free extract (NFE) was significantly (p≤0.05) increased with 15 t/ha biochar with no N application. Starch content of maize was highest with 15 t/ha biochar and 100 kg/ha N. Maximum amylose content (26.33%) was recorded in maize grains at treatment combination of 20 t/ha biochar with no N whereas amylopectin content was highest (77.02%) at 100 kg/ha N with no biochar. Maize grain albumin and globulin contents were highest at 20 t/ha biochar and 200 kg/ha N whereas glutelin and prolamine were highest with the application of 20 t/ha biochar and 120 xvi kg/ha N. Stearic acid, myristoleic, palmitoleic and linolenic acids contents were significantly (p≤0.05) higher at 20 t/ha biochar and 200 kg/ha N. Myristic acid content was highest (0.22%) with no biochar and 200 kg/ha N. Similarly, palmitic acid was maximum with the application of 10 t/ha biochar and 100 kg/ha N. The highest oleic acid content (35.15%) was found in maize grains at 10 t/ha biochar and 200 kg/ha N. Maize grain linoleic acid content was the highest (50.06%) with 15 t/ha biochar and 200 kg/ha N. Regarding minerals, maize grain K, P, Ca, Mg and Mn content were maximum at 10 t/ha biochar and 200 kg N/ha whereas the Cr and Ni contents were significantly (p≤0.05) higher at no biochar and 200 kg/ha N application. An increasing trend of phytic acid and tannins content of maize grains were observed with biochar and a reversal of the influence was noted with N application. Residual levels of biochar coupled with fresh application of N substantially influenced the chemical composition of wheat crop. The average wheat grain crude protein was highest with 20 t/ha biochar and 200 kg N/ha, while the average crude fat content was maximum at 20 t/ha biochar residues and no N. The highest average total starch content was recorded at 15 t/ha residual biochar and 120 kg N/ha, while amylose content was maximum at 20 t/ha biochar residues and no N. Average amylopectin content was highest at no residual biochar and 200 kg N/ha. Grain average albumin, globulin, glutelin and prolamine contents were highest at 20 t/ha biochar residues and 200 kg N/ha. Regarding fatty acid profile of wheat grains, the average values of myristic and stearic acids were highest at no residual biochar and at 200 kg N/ha. The average contents of palmitic acid, linoleic acid and linolenic acid were maximum at 15 t/ha biochar, while palmitoleic, oleic and cis- 11- eicosenoic acids were highest at 20 t/ha residual biochar. In response to N applications, the highest average values of palmitic acid, palmitoleic acid, cis- 11- eicosenoic acid and linoleic acid were obtained at 200 kg N/ha, whereas heptadecanoic acid and oleic acid were maximum at 120 kg N/ha. The grain average K, Ca, Mg and Mn contents were highest at 10 t/ha biochar residues and 200 kg N/ha. The highest average values of Fe, Cu, Cr and Ni were examined in wheat grains with the application of 200 kg N/ ha with no residual biochar. Grain P content was highest with 15 t/ha biochar residues and 200 kg N/ha. The wheat grain average phytic acid and tannins content were highest in the absence of N with 20 t/ha residual biochar. Overall, biochar application at the rate of 20 t/ha coupled with 200 Kg N/ha resulted in the highest concentration of majority of the nutrients in both maize and wheat grains. However, the concentration of antinutritional factors were lowest at 200 Kg N/ha in the absence of biochar. It was concluded that biochar amendments coupled with N application is an effective tool to enhance the nutritional quality of cereal grains.