Red soils are widespread throughout subtropical and tropical regions and are the most important resources for grain production in South China. Application of chemical fertilizers alone or chemical fertilizers combined with organic amendments is commonly practiced to improve physicochemical properties and fertility for red soils. This chapter summarizes the findings of a 22-year long-term field experiment conducted in the red soil region of south central China. Changes in soil pH, soil organic matter (OM), nitrogen (N), phosphorus (P), and aggregate distribution and stability as affected by the long-term fertilization treatments were examined and discussed. Combined application of chemical fertilizer and rice straw or pig manure significantly increased soil pH in the first 7 years, but soil pH decreased linearly at a rate of 0.04–0.07 unit yearly since then. Soil total N and total P content significantly increased during the long-term fertilization, and the effects of pig manure addition on N and P build-up were greater than that of rice straw addition. In contrast, soil total potassium (K) contents significantly decreased by the long-term fertilization. There was a significant difference between the effect of rice straw addition and pig manure amendment on various aggregate size distribution in the red soil.
Part of the book: Organic Fertilizers
The contamination of potentially toxic metals (PTMs) is widespread in the world and has negatively affected plants, humans, soil health, and environmental quality. Some metals are essential plant nutrients but they are also toxic to vegetation and aquatic live when present in high concentrations, such as Cu, Mn and Zn. Others (e.g., Pb, Cd, Cr, and As) are potential toxic metals for all organisms, and are not needed (or are toxic) for plant growth. This chapter summarizes the use of readily available biochars (BCs) to reduce PTMs phytoavailability in soils thus improving crop yields and to minimize its impact on the environment. The physicochemical and morphological properties of BCs as affected by feedstock sources and pyrolysis temperatures are discussed. The effectiveness of biochar rates on plant growth and metal fractions are also highlighted. Biochar has the potential to be used as a viable bioproduct for the remediation of contaminated soils since it reduces the phytoavailability of PTMs pollutants. Biochars produced from different feedstocks and at different pyrolysis temperatures present highly heterogeneous physicochemical and morphological properties, which can affect the effectiveness in the remediation of PTMs contaminated soils. Therefore, potential technologies need to be developed and research gaps still need to be overcome to optimize the use of BCs as a feasible alternative for remediation of metal contaminated soils.
Part of the book: Applications of Biochar for Environmental Safety