The rhizosphere is an area of soil surrounding plant roots in which soil's most reactions take place. The term "rhizosphere" was coined by Lorenz Hiltner, and it is 1-2 mm wide. The rhizosphere is divided into three zones: endorhizosphere, rhizoplane, and ectorhizosphere. The two dynamic properties of soil rhizosphere are root exudates and soil microbes. Root exudates are the chemical compounds that are secreted by roots and act as a source of food for soil microbes and play a pivotal role in soil microbe and plant interaction. These are low-and high-molecular-weight compounds. The root exudates are important for root-microbe and root-root communication. The other important aspect of rhizosphere is soil microbes. The soil microbes include bacteria, fungi, and actinomycetes. These organisms are important for both soil and fungi. The main aspect of this chapter is to give brief information about the underground world, and its future perspective is to understand soil microbe and plant interaction for enhancing sustainable agriculture. Studies on gene expression in the rhizosphere and the use of other molecular techniques like m-RNA, proteomics, labeled root compounds, stable isotope probes, and reporter technology will help in exploring underground undiscovered world.
The knowledge about the spatial distribution of soil organic carbon stock (SOCS) helps in sustainable land-use management and ecosystem functioning. No such study has been attempted in the complex topography and land use of Himalayas, which is associated with great spatial heterogeneity and uncertainties. Therefore, in this study digital soil mapping (DSM) was used to predict and evaluate the spatial distribution of SOCS using advanced geostatistical methods and a machine learning algorithm in the Himalayan region of Jammu and Kashmir, India. Eighty-three soil samples were collected across different land uses. Auxiliary variables (spectral indices and topographic parameters) derived from satellite data were used as predictors. Geostatistical methods—ordinary kriging (OK) and regression kriging (RK)—and a machine learning method—random forest (RF)—were used for assessing the spatial distribution and variability of SOCS with inter-comparison of models for their prediction performance. The best fit model validation criteria used were coefficient of determination (R2) and root mean square error (RMSE) with resulting maps validated by cross-validation. The SOCS concentration varied from 1.12 Mg/ha to 70.60 Mg/ha. The semivariogram analysis of OK and RK indicated moderate spatial dependence. RF (RMSE = 8.21) performed better than OK (RMSE = 15.60) and RK (RMSE = 17.73) while OK performed better than RK. Therefore, it may be concluded that RF provides better estimation and spatial variability of SOCS; however, further selection and choice of auxiliary variables and higher soil sampling density could improve the accuracy of RK prediction.
Biostimulants are organic products made up of peptides and amino acids which are readily available to plants. Changes in farming are being caused by agro-ecological practices that take into account biodiversity and the way soil works. In agriculture, biostimulants can be used to keep plant growth and productivity without use of chemicals. Biostimulants can be used to identify and enhance specific soil microorganisms and they can help them grow and thrive. Soil microbial activity and the activity of important plant growth hormones or enzymes are also considered to help crops grow and yield more. The words “soil health” and “soil tilth” aren’t new in the world of farming. Many factors, many of which are biological, affect the health of soil. With the application of biostimulants soil health gets improved by influencing soil health indicators. Chemical fertilizers affect soil environment, which ultimately affects the human and animal lives. Microbes in the soil called arbuscular mycorrhizal fungi (AMF) play an important role in maintaining long-term soil fertility by forming mutualistic relationships with the roots of food crops, which help them, grow and thrive. Plants thrive under biotic and abiotic stress, due to the activation of defense mechanisms through these substances. Biostimulants from seaweed extracts are very popular because they help plants to grow and be more resistant to stress. Repeated applications of biochar could make the soil more carbon-rich and productive, which could lead to more crop biomass and biological carbon sequestration over time. This review summarizes the description of biostimulants and their role in soil health.
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