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Knowledge of spatial variability of soil properties is important in precision agriculture as well as site specific nutrient management.

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A limiting factor in land application of sewage sludge is the resultant heavy metal accumulation in soils followed by biomagnification in the food chain, posing a potential hazard to animal and human health. In view of this fact, pot experiments were conducted to evaluate the effect of digested sludge application to soil on phytotoxicity of heavy metals such as Cd, Cr, Ni, and Pb to radish (Raphanus sativus L.) plants. Increasing sludge levels resulted in increased levels of DTPA-extractable heavy metals in the soil. Cadmium was the dominant metal extracted by DTPA followed by Ni, Pb, and Cr. The extractability of metals by DTPA tended to decrease from the first to the second crop. Dry matter yield of radish increased significantly as a function of increasing sludge treatments. Soil application of sludge raised the concentration of one or more heavy metals in plants. Shoots contained higher concentrations of Cd, Cr, and Ni than the roots of radish plants. Shoot concentrations of Cd, Cr, Ni, and Pb were within the tolerance levels of this crop at all rates of sludge application. Shoot as well as root concentration of Cd was above 0.5 mg kg −1 , considered toxic for human and animal consumption. The levels of DTPA-extractable Cd and Ni were less correlated while those of Cr and Pb were more correlated with their respective shoot and root contents. The results emphasize that accumulation of potentially toxic heavy metals in soil and their build-up in vegetable crops should not be ignored when sludge is applied as an amendment to land.

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Background: Potassium (K) availability in soil and plant uptake is restrained by the dynamic interactions among the different pools of K. Aims: To understand these interactions, a study was undertaken to assess the quantity–intensity (Q/I) and buffering characteristics of rainfed maize (Zea mays L.) growing soils. Ten contrasting soils were evaluated for K partitioning changes in exchangeable K (ΔEK) and non‐exchangeable K (ΔNEK) pools in the soil‐solution phase and buffering characteristics using a modified version of Q/I approach. Results: The partitioned Q/I isotherms showed strong adsorption with the increase in K concentration ratio (CRK) and the changes due to ΔEK were higher than changes due to ΔNEK. Total buffering capacity (PBCK) significantly correlated (r = 0.92, p <0.01) with clay content with a major share contributed by buffering capacity owing to non‐exchangeable K ( PBCΔNEK K ) rather than exchangeable K ( PBCΔEK K ). The fixation capacity (β) factor, the magnitude of added K converted into a non‐exchangeable pool, ranged from 41 to 63%, whereas release (α) factor, the magnitude of added K converted to the exchangeable pool, ranged from 19 to 36%. Both threshold solution K (CKr) and threshold exchangeable K (EKr) values were found to be high in Satran clay loam (S2) and lower in Doon silty clay loam (S3) soils. The equilibrium exchangeable K (EKo) was found close to minimum exchangeable K (Emin) in Doon silty clay loam (S3) and Babaweyl sandy clay loam (S1) soils and overall Emin constituted about 8.94 to 0.57% of the EKo. Conclusion: It may be concluded that K Q/I isotherm partitioning provides a valuable insight to assess the dynamic relations. The ratio of α/β (K recharge index) could be used to evaluate the K enrichment capacity of soil to K additions while EKr and Emin can be potentially useful in the elucidation of exchangeable K as K fertility index especially in soils with poor K fertilizer management.

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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