Abstract
The expansion of Brazilian agriculture has led to a heavy dependence on imported fertilizers to ensure the supply of the growing food demand. This fact has contributed to a growing interest in alternative nutrient sources, such as ground silicate rocks. It is necessary, however, to know the potential of nutrient release and changes these materials can cause in soils. The purpose of this study was to characterize six silicate rocks and evaluate their effects on the chemical properties of treated soil, assessed by chemical extractants after greenhouse incubation. The experimental design consisted of completely randomized plots, in a 3 x 6 factorial scheme, with four replications. The factors were potassium levels (0-control: without silicate rock application; 200; 400; 600 kg ha-1 of K2O), supplied as six silicate rock types (breccia, biotite schist, ultramafic rock, phlogopite schist and two types of mining waste). The chemical, physical and mineralogical properties of the alternative rock fertilizers were characterized. Treatments were applied to a dystrophic Red-Yellow Oxisol (Ferralsol), which was incubated for 100 days, at 70 % (w/w) moisture in 3.7 kg/pots. The soil was evaluated for pH; calcium and magnesium were extracted with KCl 1 mol L-1; potassium, phosphorus and sodium by Mehlich 1; nickel, copper and zinc with DTPA; and the saturation of the cation exchange capacity was calculated for aluminum, calcium, magnesium, potassium, and sodium, and overall base saturation. The alternative fertilizers affected soil chemical properties. Ultramafic rock and Chapada mining byproduct (CMB) were the silicate rocks that most influenced soil pH, while the mining byproduct (MB) led to high K levels. Zinc availability was highest in the treatments with mining byproduct and Cu in soil fertilized with Chapada and mining byproduct.
Highlights
The Brazilian production of potash salts covers only 8 % of the country’s requirements (Oliveira, 2008)
The technique consists of applying rock powder directly onto the soils; the competitiveness of this practice is directly related to the nutrient contents of the material and to the distance from the mining areas
These rocks might vary in quantity and sources of mineral elements they contain, but contribute to raise soil fertility, in the mid-to-long term, depending on the solubility and reaction with soil (Hilsinger et al, 1996; van Straaten, 2007). Rocks and their byproducts are, in general, sources of phosphorus (P), potassium, calcium (Ca) and magnesium (Mg), often including trace-elements, such as zinc (Zn) and copper (Cu), which are essential in plant nutrition (Leonardos et al, 1991, 2000; Wilpert & Lukes, 2003; Leonardos & Theodoro, 1999; Theodoro & Leonardos, 2006; Fyfe et al, 2006)
Summary
The Brazilian production of potash salts covers only 8 % of the country’s requirements (Oliveira, 2008). The world-wide demand has caused considerable price rises of conventional fertilizer sources, affecting the agricultural development, especially in tropical countries (Manning, 2010). To face this constraint, nutrient-rich rocks can be ground and used to reduce the dependence on imported sources. The technique consists of applying rock powder directly onto the soils; the competitiveness of this practice is directly related to the nutrient contents of the material and to the distance from the mining areas These rocks might vary in quantity and sources of mineral elements they contain, but contribute to raise soil fertility, in the mid-to-long term, depending on the solubility and reaction with soil (Hilsinger et al, 1996; van Straaten, 2007). Rocks and their byproducts are, in general, sources of phosphorus (P), potassium, calcium (Ca) and magnesium (Mg), often including trace-elements, such as zinc (Zn) and copper (Cu), which are essential in plant nutrition (Leonardos et al, 1991, 2000; Wilpert & Lukes, 2003; Leonardos & Theodoro, 1999; Theodoro & Leonardos, 2006; Fyfe et al, 2006)
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