Utilization of biochar from different bioresources for soil health and crop production

Abstract

The study entitled “Utilization of biochar from different bioresources for soil health and crop production” was carried out during 2021-2023 in the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani and Integrated Farming System Research Station, Karamana. The objectives of the study were characterization of biochar produced by pyrolytic conversion of bioresources generated in farming systems and assessing their influence on soil health and crop production. The study comprised of four parts viz., production and characterization of biochar from different bioresources, bioassay study for selection of best four biochar, incubation experiment to study the nutrient release pattern and field evaluation of the effect of biochar on crop performance and soil health. Biochar was produced from seven different organic residues viz., teak leaf, coconut leaf, banana pseudostem, crop residue of vegetables, Eichhornia crassipes, Limnocharis flava and Colocasia esculenta, by the process of pyrolysis and the synthesized biochar were analysed for physical and chemical properties using standard procedures. Temperature of pyrolysis and residence time for various organic residues ranged between 250-5000C and 30-120 minutes, respectively. Highest recovery percentage of 46.53 % was recorded for coconut leaf biochar and lowest, 24.93 % for E. crassipes. Teak leaf biochar recorded the highest bulk density (0.48 Mg m-3) and EC (4.70 dS m-1), while banana pseudostem biochar had a higher water holding capacity (327.74 %). The produced biochar has an alkaline characteristic, with pH values ranging from 8.19 (C. esculenta biochar) to 10.40 (Banana pseudostem biochar). CEC (14.10 cmol kg-1), total carbon (67.52 %), N (1.34 %), K (2.24 %), S (0.33 %) and Zn (69.37 mg kg-1) content were highest for banana pseudostem biochar while P (0.77 %), Mn (173.76 mg kg-1), Cu (37.12 mg kg-1) and B (47.40 mg kg-1) were highest for L. flava biochar. Calcium (0.57 %) and magnesium (0.43 %) content were highest for crop residues of vegetable biochar while iron (2314.15 mg kg-1) content was highest in biochar produced from C. esculenta. C: N ratio was highest in C. esculenta biochar (128.35) and lowest in banana pseudostem biochar (50.38). 159 Bioassay study was carried out for 28 days using okra seedlings to select best four biochar for field study. The biochar produced from seven different bioresources were mixed with 2 kg soil @ 0.5 and 1 % w/w basis and FYM @ 1 % w/w basis and 10 okra seeds were placed in each pot. Coconut leaf, banana pseudostem and L. flava biochar recorded the highest germination percentage (96.67 %) and it was on par with biochar derived from crop residues. Banana pseudostem biochar recorded the highest values for shoot length (33.04 cm) and shoot biomass (2.23 g plant-1) and it was on par with L. flava biochar and FYM treated soil. Root length (23.97 cm), root biomass (0.60 g plant-1) and root volume (4.90 cm3) of the okra seedlings were highest in L. flava biochar treated soil and it was found to be on par with crop residue of vegetables biochar and FYM supplied treatments. Teak leaf biochar applied @ 1 % recorded the lowest values for germination percentage, shoot length, shoot biomass, root length, root biomass and root volume. Based on the results obtained from bioassay study, four biochar viz., coconut leaf, banana pseudostem, crop residue of vegetables and L. flava were selected for the incubation and field experiments. The nutrient release pattern from the selected four biochar was monitored after incorporation to soil based on a 90 day incubation study. Biochar and FYM were added @10 g kg-1 of soil. Periodic sampling and analysis of samples were done at 0, 30, 60 and 90 days of incubation. The incubation study revealed a slow and sustained release of nutrients from biochar. Biochar treated soils showed significantly higher value for pH and EC compared to FYM treated soil till the end of the incubation period. The pH was significantly higher for banana pseudostem biochar treated soil while EC was higher in soil applied with crop residue of vegetables biochar. During initial period of incubation, the mean values for available N, K, S and Zn content were highest for FYM treated soil but as incubation period progressed, banana pseudostem biochar treated soil recorded the highest values. The mean value for P, Fe, Cu and B were significantly higher for FYM treated soil during initial period and later stages, it was for L. flava biochar applied soil. Similarly, exchangeable Ca and Mg content were highest in FYM treated soil during initial period and as incubation period progressed, the crop residue of vegetables biochar treated soil recorded the highest values. A field experiment was conducted during 2023 to compare the effect of biochar from different bioresidues and FYM application on soil health and crop production using okra as the test crop. The treatments consisted application of selected four biochar viz., coconut leaf, banana pseudostem, crop residue of vegetables and L. flava biochar @ 25 t ha-1 along with 100 and 75 % of recommended dose of fertilizers (RDF) and FYM @ 25 t ha-1 along with 100 % RDF and soil with 100 % RDF only. The physical, chemical and biological properties of soil were markedly improved by the application of biochar. Reduction in bulk density, increase in water holding capacity, pH, EC, CEC, organic carbon and nutrient availability were observed with biochar application compared to FYM incorporation. Banana pseudostem biochar application recorded the highest values for organic carbon (1.92 %), available N (334.56 kg ha-1), K (258.45 kg ha-1), S (23.27 mg kg-1), Zn (3.73 mg kg-1) and dehydrogenase (192.78 µg of TPF g-1 soil 24 h-1) and microbial biomass carbon (81.97 mg kg-1) content of post harvest soil. Available P (91.78 kg ha-1), Fe (132.08 mg kg-1), Mn (34.89 mg kg-1) Cu (2.77 mg kg-1) and B (0.667 mg kg-1) content were higher in soil applied with L. flava biochar. Biochar application had significantly influenced the biometric and yield parameters of okra. Plant height, biomass yield and fruit yield were highest in treatments supplied with banana pseudostem biochar and it was on par with the treatments received L. flava biochar. Nutrient content of index leaf at harvest also indicated the beneficial effect of biochar in comparison to FYM and conventional fertilizers. Plant biometric attributes, fruit yield and soil health parameters for biochar application @ 25 t ha-1 and RDF at 100 and 75 % were on par. The highest B: C ratio (1.70) was recorded in treatment supplied with banana pseudostem biochar @25 t ha-1 along with 75 % RDF, which indicated that 25 % reduction in fertilizer application is possible through biochar application. There was 21 % increase in yield by banana pseudostem biochar application compared to FYM. It may be inferred that physico-chemical properties of biochar varies with the source material and their assessment for phytotoxicity is essential for ensuring the safety for agricultural use. Coconut leaf biochar, banana pseudostem biochar, crop residues of vegetable biochar and L. flava biochar had ideal physical and chemical 161 properties that qualify them to be used as good soil amendments which improve the soil physical, chemical and biological properties. FYM and biochar application had a positive effect on soil properties during incubation and field study. However biochar application exhibited sustainable effects than FYM. From the study, it can be concluded that banana pseudostem biochar @ 25 t ha-1 along with 75 % RDF is the economically viable and best treatment.