Nutrient dynamics and crop productivity in lowland lateritic soil (aeu 10) under rice residue management practices

Abstract

The present investigation was undertaken at College of Agriculture Vellanikkara, Kerala Forest Research Institute Peechi, and Agricultural Research Station Mannuthy during 2017-2020. The experiment comprised of characterization of rice residues and their products for physical and chemical properties, an incubation experiment to study the kinetics of carbon mineralization, and a field experiment to evaluate the efficacy of rice residues and their products on lowland rice. Straw and husk, the important residues produced during the cultivation and processing of rice, respectively was procured from farmer’s field and further materials required for the research work viz., vermicomposted rice straw (VRS), vermicomposted rice husk (VRH), rice straw biochar (RSB), and rice husk biochar (RHB) were produced from the straw (RS) and husk (RH) using vermitechnology and pyrolysis. Recovery from vermicomposting was more (74.38 % for VRS and 70.03 % for VRH) than when the residues were converted into biochar through pyrolysis (19.86 % for RSB and 38.00 % for RHB). Vermicomposting and pyrolysis reduced the bulk density of raw materials. Rice residues and their products were alkaline, with biochar exhibiting the highest level of alkalinity (9.24 for RSB and 9.20 for RHB). The electrical conductivity increased both by vermicomposting and pyrolysis. Straw was comparatively superior to the husk in respect of C, N, K, Ca, Mg, Fe, Mn, Cu, and Zn. However, husk was superior in P, S, B, Si, cellulose, and lignin. Vermicomposting helped to concentrate the nutrients viz., N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn, B, and Si while reducing that of carbon, cellulose and lignin thereby narrowing down the C: N ratio. However, C: N ratio increased upon pyrolysis. Surface morphology of rice residues and their products were studied using scanning electron microscope (SEM). The SEM micrographs of straw and husk exhibited a complex morphology with cell wall composition. SEM micrograph of VRS showed highly fragmented, disaggregated and porous structure which could not be visualised in VRH, may be because the technology of composting using earthworms was more suited to decomposing rice straw than its husk. The SEM analysis showed that the structure of biochar was porous, fragmented and particles gave a broken or distorted appearance thus resembling the plant structure. The structural chemistry of rice residues and their products were analysed using fourier transform infra red spectrometer (FT-IR). Each peak is characteristic of correspondingfunctional group and it clearly explained the presence of C, H, O, N, and Si in the residues and products. Silicon, a major component in the chemical structure of rice material was illustrated by Si-O-Si and Si-H bond in FT-IR spectra. Vermicompost had significant level of nitrogen rich compounds and low level of aliphatic or aromatic carbon compounds compared to biochar, as confirmed by the FT-IR analysis. The FT-IR spectra of RSB and RHB revealed its aromatic and recalcitrant nature. The incubation experiment was conducted for 110 days at 15, 25, 35 and 45 oC to study the kinetics of carbon mineralization in lateritic soil over time, wherein the CO 2 evolution was determined at frequent intervals and the data were used for determination of carbon mineralization and mineralization kinetics. Lateritic soils (100g) collected from Agricultural Research Station Mannuthy, were treated with rice residues and their products (5t ha -1 ), FYM (5 t ha -1 ), and soil test based nutrient recommendation. An absolute control without the addition of organic/inorganic materials was also maintained. Dehydrogenase enzyme assay, enumeration of microbial population, and fractions of carbon were also undertaken at the end of incubation. Results of incubation experiment revealed that the amount of CO 2 –C mineralized during incubation increased with rise in temperature in all the treatments. The VRS treated soils registered higher mineralizable carbon at 15, 25, 35 and 45 oC. The rate of decomposition reaction was highest in soils that are treated with VRS and FYM. The highest activation energy was found in RHB amended soil (12.79 kJ mol -1 ) followed by RSB treated soil (12.71 kJ mol -1 ). Q 10 values represent the temperature dependency of the reaction. The results showed that all treatments had Q 10 values less than one. After incubation experiment, dehydrogenase activity as well as microbial population was found to decrease at 45 oC compared to the values at lower temperature. Comparatively, higher dehydrogenase activity and microbial population was registered in soils treated with VRS. The soils treated with VRS exhibited highest water soluble carbon (WSC), hot water extractable carbon (HWEC), microbial biomass carbon (MBC), and permanganate oxidizable carbon (POXC). However, biochar amended soils (RHB and RSB) registered higher value of total carbon. A field experiment was carried out to evaluate the efficacy of rice residues and their products in lowland with rice variety Uma as the test crop. The experiment consisted of ninetreatments with three replications viz., absolute control (T 1 ), Adhoc KAU organic POP (T 2 ), and treatments T 3 to T 9 comprised of soil test based nutrient recommendation along with FYM (T 3 ), VRH (T 4 ), VRS (T 5 ), RHB (T 6 ), RSB (T 7 ), RH (T 8 ), and RS (T 9 ) at 5t ha -1 . At weekly intervals Eh and pH were monitored. The soil and plant samples were collected at different stages of rice to analyse the effect of treatments on soil physical and chemical properties, fractions of nutrients in soil, nutrient content in plant, soil enzyme activity, and growth, yield and yield attributes of rice. Results of field experiment revealed that the application of residues and its products had a profound influence in lowering redox potential. The alkaline nature of rice residues and their products resulted in higher pH of experimental soil. Physical properties of post-harvest soil was improved by the application of T 6 and T 7 (soil test based nutrient recommendation + RHB and RSB). The application of T 5 (soil test based nutrient recommendation + VRS at 5 t ha -1 ) was superior in increasing the nutrient status of post-harvest soil viz., C, N, P, Ca, Mg, S, Fe, Mn, Zn, and Si. While, K content was superior in T 7 (soil test based nutrient recommendation + RSB at 5 t ha -1 ). Soils receiving combined application of soil test based nutrient recommendation and VRS at 5 t ha -1 (T 5 ) recorded the highest WSC, HWEC, MBC, POXC, inorganic-N and P fractions, fractions of Ca and Mg at all the stages of crop. However, total- C, total hydrolysable-N, organic-P, and Si fractions were higher in biochar amended plots. Soil receiving joint application of soil test based nutrient recommendation +RSB at 5 t ha -1 (T 7 ) was statistically superior in fractions of K at all stages. Enzyme activity (dehydrogenase, urease, and acid phosphatase) was found to be highest in T 5 (soil test based nutrient recommendation + VRS at 5 t ha -1 ), and it followed an increasing trend upto panicle initiation and thereafter it decreased in all treatments. The uptake of N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B and Si were also highest in T 5 . With respect to the growth, yield and yield attributes of rice, application of soil test based nutrient recommendation + VRS at 5 t ha -1 (T 5 ) had superior effect. To conclude, the study has brought out the tremendous potential of rice straw and husk based biochar in improving soil physical properties and in elevating the total carbon content. However, the integration of soil test based nutrient recommendation with vermicompostedrice straw at 5t ha -1 (T 5 ) proved outstanding in augmenting soil fertility and crop productivity in the highly weathered, nutrient poor acidic lateritic soils.