The Rio Grande do Sul, the southernmost state of Brazil, occupies a prominent position in rice production in Brazil. According to the National Supply Company (Conab), in the 2011/2012 season rice production in the state accounted for 78% of Brazilian production. 1,053,000 acres of the crop were planted, harvested and 7.7396 million tons of grain. The main and most productive form of rice cultivation in the state is the lowland system. However, this form of cultivation can lead to solubilization of large amounts of iron before precipitate and forming chelate in the organic matter of the soil. (Ponnamperuma, 1972) .
The concentration of soluble iron, which, prior to the submergence of the soil, seldom exceeds 0.1 mg / L, can reach, in acid soils, to approximately 600 mg / L (Ponnamperuma et al., 1978). However, in extreme cases, values of up to 5,000 mg / L have been detected. (Hansen & van Breemen, 1978).
The main symptoms of toxicity by iron excess are bronzing of the leaves and the deposition of brown pigments, which can lead to growth retardation, low productivity, sterility and, in severe cases, death of the plant. Production losses resulting from toxicity by excessive iron can lead to losses of 15 to 20%; however, total losses were described in the literature (AUDEBERT; SAHRAWAT, 2000; Winslow et al., 1989). Once inside the plant, the excess iron not used for the metabolic needs of the plant needs to be stored, to prevent its toxicity. This is accomplished by various organic molecules, such as proteins, peptides, amino acids, organic acids and phosphate compounds such as phytic acid. (Briat; Lebrun, 1999).
The high affinity of phytic acid by iron leads to the formation of a chelate which is completely inert (GRAF et al., 1987). The high affinity and chelating ability of phytic acid to iron allows postulating that he can participate in the detoxification process in plants. This is strengthened by the observation of substantial quantities of phytate in roots of various species of plants (Briat & Lebrun, 1999). Based on these aspects, was conducted the application of a organic foliar fertilizer, Organic Bloom, in several lowland rice commercial producing areas of the western region of the State of Rio Grande do Sul.
The Organic Bloom is elaborate from solubilized nutrients of soy protein and rice bran, enabling the delivery of elements derived from plant own constitution, among them, phytic acid, which accounts for the results of inducing resistance to excess iron in irrigated rice. To evaluate the effects of Organic Bloom, in lowland rice, the Integrated System for Diagnosis and Recommendation (DRIS in portuguese) were used. This system considers the relationships between nutrients and compares with a pattern of high productivity, calculating an index for each nutrient and allowing to identify which are the most limiting and or excess elements.
The DRIS uses binary relationships between nutrients and turns the values of the concentrations at rates ranging from negative to positive. The smaller the index, if negative, will be most limiting nutrient deficiency, and the greater the index, if positive, will be more excessive nutrient. The index value of zero indicates that the nutrient is in better nutritional balance. (WALWORTH; SUMMER 1987).
In addition to the DRIS indices, we calculated the Nutritional Balance Index (NBI in portuguese), which results from the sum in module, the values of DRIS indices of each nutrient, indicating the nutritional status of the plant. The smaller the sum value, the less imbalance of nutrients, and therefore the higher the productivity of the crop. (WALWORTH; Sumner, 1987). In areas treated with Organic Bloom there was a marked reduction in symptoms associated with toxicity by iron excess (tanning leaves) which is corroborated by the findings, which indicate the leaf nutrient composition of rice plants treated and untreated with Organic Bloom, according to IBN and DRIS indices.
For those areas not treated with Organic Bloom, was observed a DRIS index for iron content of 22,77 and, after application of the product, the value fell to – 0.26; therefore stood at a value very close to zero, approaching to the better nutritional balance according to Walworth & Summer (1987). This allows postulate that the exogenous supply of phytic acid, through the application of the fertilizer Organic Bloom, potentiated the response of plants, as plants already used the mechanism against toxicity episodes of metallic elements (Briat & Lebrun, 1999).
Concomitantly with the reducing the toxic effects of excess of iron, in treated areas, the average gains in productivity was of 22 bags / hectare (1100kg). Characteristic which is enhanced by IBN values before application of the product of 47.47 and after application of the product of 9.95. In this sense, several studies show that IBN has high negative correlation with productivity (CRESTE & NAKAGAWA., 1997; Veloso et al, 2000; Son et MOURÃO al., 2002; Silva et al. 2003; Hoogerheide, 2005). It means, the lower the value, the higher the productivity. Thus, is recommended the use of organic foliar fertilizer, Organic Bloom, as an effective measure for controlling the toxicity of excess iron in crops subjected to lowland or irrigation, it promotes the improvement of health and productivity both conventional rice cultivation systems or organic, since Organic Bloom is a product certified by Brazilian Biodynamic Institute (IBD in portuguese) for use in organic production systems.
* Fabricio Barros Brum – Biochemical Pharmaceutical – Food Technologist
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