Phosphorus (P) is a macronutrient that is associated with several metabolic functions, such as enzyme activation, hormonal control, formation of nucleic acids, starch, proteins, sucrose, glucose and also plays an important role in the process of energy transfer in cells, respiration and photosynthesis.
It is considered an element with low mobility in the soil, due to its “fixation” to clay minerals. It is not found in free form, but rather in combinations with oxides, calcium, iron and aluminum, which form compounds unavailable to plants.
Factors affecting soil phosphorus availability
The main forms of phosphorus found in soil solution are H ions.2DUST4– and HPO4–. In general, Brazilian soils have high levels of iron and aluminum oxides and kaolinite-type clay, in addition to a high degree of weathering and low levels of organic matter. The presence of these oxides results in the retention of phosphate ions, making P unavailable to plants.
For better understanding, the amount of phosphorus present in a soil is divided between inorganic (Pi) and organic (Po), depending on the nature of the compound in which this element is bound. According to Santos et al. (2008), the organic and inorganic fractions of phosphorus in the soil can act as a source or sink for the soil solution, which depends on its mineralogical characteristics and environmental conditions.
In addition to quantities, other factors such as clay content and type, pH, phosphate fertilization management and soil organic matter content also directly influence the availability of this element.
The main cause of the low availability of the element for plants is the great stability of phosphates in the solid phase of the soil, resulting from the formation of compounds that bind with high energy to colloids, especially to Fe and Al oxyhydroxides, constituents of the clay fraction that adsorb the most P (LEITE, 2015). Also according to Leite (2015), as a result of this, there is low efficiency of phosphate fertilization and the need to apply high doses of fertilizers to ensure crop profitability.
Furthermore, availability can also be affected by soil microbial activity. According to Conte (2001), cited by Souza Júnior et al. (2018), the amount of phosphorus in soil microbial biomass can be increased by adding fertilizers, as it acts as a P sink in the soil.
Relationship between organic matter and phosphorus
Organic matter (OM) is closely related to phosphorus availability, under two pillars: 1) it can adsorb phosphorus, or 2) it can block the binding sites that occur in clays and aluminum and iron oxides; which makes its availability in soils not fertilized with phosphates dependent exclusively on the cycling of organic compounds. According to Stevenson (1986), cited by Pereira (2009), for the phosphorus associated with soil organic matter to be used by plants, there must be conversion of organic P to inorganic P, via enzymatic mineralization.
It is known that organic acids from the metabolism of soil microorganisms responsible for the decomposition of organic matter contribute significantly to the solubilization of calcium phosphates. As stated by Zamuner et al. (2008), management systems that promote an increase in organic matter in the soil, such as the no-tillage system (NTS), contribute to the increase in more labile forms of P (which corresponds to the group of phosphate compounds capable of rapidly replenishing the soil solution when it is absorbed by plants or microorganisms, a definition suggested by Santos et al. (2008)), since the organic acids from the decomposition of OM block adsorption sites by coating them with iron and aluminum oxides. The cultivation of cover crops in NTS can favor the accumulation of OM in the soil and increase the efficiency of nutrient cycling.
Crops grown under NTS can substantially alter the dynamics of phosphorus, which is found in higher concentrations on the soil surface. The formation of P sites occurs as a function of the quantity and depth of application of phosphate fertilizers in the crop rotation and the frequency of rotation (YAMADA & ABDALLA, 2006).
Phosphorus deficiency
Phosphorus deficiency, especially at the beginning of the production cycle, can cause an irreversible reduction in crop development, even if the concentration of this mineral in the soil is increased to adequate levels. The first symptoms of phosphorus deficiency are especially noticeable in old leaves, due to the high mobility of this element in the plant. The purple coloration of the leaves is characteristic of this deficiency, as they begin to accumulate sugar in their tissues, which results in the synthesis of the anthocyanin pigment. In later stages of development, it can cause tissue necrosis.
Insufficiency of this mineral also results in a reduction in leaf area and number of leaves (due to leaf abscission). Other symptoms, according to Grant (2001), include a decrease in plant height, delayed leaf emergence and a reduction in sprouting and development of secondary roots, dry matter production and seed production.
It is worth remembering that soil analysis is the determining option for quantifying soil nutrients and should not, under any circumstances, be overlooked.
Which product does ILSA Brasil recommend?
ILSA Brasil's Gradual Mix line has a complete line of exclusive organomineral fertilizers, characterized by the presence of a high content of organic N and amino acids from AZOGEL® (hydrolyzed protein of animal origin) in combination with sources of mineral nutrients. It has several formulations, Gradual Mix 6-24-00 and the Gradual Mix 12-24-00 are the most suitable for increasing phosphorus levels.
Among the many benefits of these fertilizers, the following stand out: increased crop productivity; gradual release of nitrogen through the action of microorganisms, which allows this mineral to be made available throughout the production cycle; reduced losses of mineral nutrients due to the protective action of the high CTC organic matrix (AZOGEL); stimulation of microbial development and life in the soil and the presence of amino acids, which increase the plants' ability to withstand stress conditions.
Bibliographic References
CONTE, E. Acid phosphatase activity and accumulation forms through phosphate application in soil in the no-tillage system. Federal University of Rio Grande do Sul; 2001.
GRANT, CA; FLATEN, DN; TOMASIEWICZ, DJ; SHEPPARD, SC The importance of phosphorus in early plant development. Potafos, Piracicaba, nº 95, p. 1-5, 2001.
LEITE, JNF Organic and inorganic forms of phosphorus as a function of cover crops and nitrogen fertilization. UNESP, Jaboticabal, 2015. 57 p. (Dissertation)
LEITE, JNF; CRUZ, MCP da; FERREIRA, ME; ANDRIOLI, I.; BRAOS, LB Organic and inorganic fractions of phosphorus in soil influenced by cover crops and nitrogen fertilization. Brazilian Agricultural Research, Brasilia, v.51, n. 11, p. 1880-1889, 2016.
PEREIRA, HS Phosphorus and potassium require different management. Agricultural Vision, nº9, p.46-46, 2009.
SANTOS, DR dos; GATIBONI, LC; KAMINSKI, J. Factors affecting phosphorus availability and phosphate fertilization management in soils under no-tillage system. Science. Rural [online], vol.38, n.2, p.576-586, 2008.
SOUZA JÚNIOR, AA; DALL'ORSOLETTA, DJ BONFADA, EB; GATIBONI, LC The availability of added phosphorus depends on the soil clay content and reaction time. XII Southern Brazilian Meeting on Soil Science, Xanerê, 2018.
STEVENSON, FJ Cycles of soil. New York: Wiley-Interscience Publication, 1986.
ZAMUNER, EC; PICONE, LI; ECHEVERRIA, HE Organic and inorganic phosphorus in Mollisol soil under different tillage practices. Soil and Tillage Research, v.99, p.131-138, 2008.
YAMADA, T.; ABDALLA, SRS Phosphorus in Brazilian agriculture. Piracicaba: POTAFOS, 2006. 726 p.
Authors:
- Ex. Agr. Msc. Aline Tramontini dos Santos
- Agricultural Engineer Ana Elisa Velho
- Agricultural Eng. MSc, Thiago Stella de Freitas
