Óxidos de ferro e matéria orgânica na disponibilidade de fósforo no solo

Continuous crop expansion has led to a growing demand for phosphate fertilizers. A sound knowledge of the dynamics of phosphorus, and its interaction with iron oxides and organic matter, can be useful to develop effective strategies for sustainable management, especially in a scenario of increasing shortage of mineral phosphate resources. In this paper, we review the relationship of phosphate to iron oxides and organic matter, and its effect on phosphorus availability. Crops typically obtain phosphate from weathered minerals and dissolved fertilizers. However, the amount of phosphorus present in the soil solution depends on the extent to which it is adsorbed or desorbed by iron oxides, which may be influenced by interactions with organic matter. Therefore, systems for fertilizer recomendation based on methodologies considering interactions between soil components such as oxides and organic matter, and the phosphorus sorption capacity resulting from such interactions (e.g. residual P analysis), may be more reliable to ensure efficient, rational use of phosphate.A contínua expansão da produção agrícola tem levado a uma crescente demanda de fertilizantes fosfatados. O conhecimento da dinâmica do fósforo no solo e suas interações com óxidos de ferro e matéria orgânica podem ser uteis no desenvolvimento de estratégias eficientes para o manejo sustentável, especialmente em um cenário de crescente escassez de fontes de minerais fosfatados. Nesta revisão bibliográfica foi abordado a relação do fósforo com óxidos de ferro e matéria orgânica, e seu efeito na disponibilidade de fósforo. As culturas, normalmente, obtém fosfato de minerais intemperizados ou fertilizantes dissolvidos. No entanto, a quantidade de fósforo presente na solução do solo depende das reações de adsorção e dessorção por óxidos de ferro, as quais podem ser influenciadas por interações com a matéria orgânica. Portanto, os sistemas de recomendação de fertilizantes com base em metodologias que consideram as interações entre componentes do solo, tais como óxidos e matéria orgânica, e a capacidade de adsorção de fósforo, resultantes de tais interações (por exemplo, análise de P remanescente), pode ser mais confiável para garantir o uso eficiente e racional de fertilizantes fosfatados

Flue-cured tobacco and Cl rates : implications on yield, quality, and nutrient concentration

The increase in flue-cured tobacco (Nicotiana tabacumL.) yields in recent decadesdue to genetic improvements of new cultivars and management technologies mayincrease the plant demand for Cl, and the increased dry mass may dilute Cl concentra-tion, thereby reducing negative effects. This study evaluated the effect of increasingdoses of Cl on tobacco production, quality, and chemical composition of leaves, infour growing environments located at research stations where flue-cured tobacco isproduced in North Carolina. The treatments consisted of 11 rates of Cl (0, 11, 22,34, 45, 56, 67, 78, 90, 101, and 112 kg ha−1) in each growing environment, with fourreplications in a randomized complete block design. The yield and visual quality,total alkaloids, and reducing sugars concentrations of cured leaf were determined.In addition, the concentration of selected nutrients (N, P, K, Ca, Mg, S, and Cl) andnitrate (NO3−) in tobacco leaves was measured in five different periods. Rates of Clup to 112 kg ha−1did not reduce the productivity or quality of flue-cured tobaccoin any environment. The Cl rate required to reach the threshold of 1.0% Cl contentin cured leaf was site-specific, being surpassed even in the control treatment at onelocation, or with Cl rates higher than 34 and 90 kg ha−1in two environments. Inone environment, the Cl rates increased tobacco yield, probably due the direct effectof Cl as a nutrient. Although the increasing Cl rates increased the reducing sugarsconcentration, visual quality was not attenuated

Revisiting limestone quality for soil liming purpose

The quality of lime is generally estimated by traditional methodologies, which consist of coarse granulometry and chemical reactivity determinations. Performing a detailed chemical/min- eralogical and fine granulometric characterization is the objective of this study. Fifteen lime samples, from an original 52 commercial samples, were analyzed by their granulometric profile (GP) and chemical-mineralogical compositions to discuss limestone quality inside the tree group of tradi- tional efficiency neutralizing power (ENP) and Mg contents. The lime reactivity was estimated us- ing laser diffraction under water and acid solution (1 mol L−1 HCl). The grain-size distribution ranged from 0.563 to 1124 μm and the GP was associated with the chemical and mineralogical com- positions. Samples with high ENP (>99%) presented differences in GP regarding Mg contents. Lime with low ENP presents the most varied mineral assemblage, while calcite and dolomite were the predominant minerals in high-ENP samples. Samples containing high Mg were the most sensitive to the acid solution, suggesting great reactivity. This work contributes to a better understanding of limestone quality than routine analyses performed so far. Additionally, the use of the laser diffrac- tion method promotes a rapid lime reactivity test for liming purposes

Digital soil class mapping in Brazil: a systematic review

In Brazil several digital soil class mapping studies were carried out from 2006 onwards to maximize the use of existing maps and information and to provide estimates for wider areas. However, there is no consensus on which methods have produced superior results in the predictive value of soil maps. This study conducts a systematic review of digital soil class mapping in Brazil and aims to analyze the factors which can improve the accuracy of digital soil class maps. Data from 334 digital soil class mapping studies were grouped and analyzed by Student’s t-test, Wilcoxon-Mann-Whitney test and Kruskal-Wallis test. When conventional maps were used for validation, the studies showed average values of 63 % and when field samples were used, 56 % for Overall Accuracy. Studies compatible with the Planimetric Cartographic Accuracy Standard for Digital Cartographic Products (PEC-PCD) averaged between 4 % and 15 % higher accuracy than those of the incompatible group. There seems to be no evidence that increasing the number of variables and samples results in more accurate soil map prediction, but studies using variables related to four soil-forming factors enhanced accuracy. From a density of 0.08 MU km–2 and upwards, it became more difficult for studies to obtain greater accuracy. Artificial neural network classifiers and Decision Tree models seem to be producing more accurate digital soil class maps

IMPACTO DA FERTILIZAÇÃO NITROGENADA EM PASTAGENS PERENES NA CONTAMINAÇÃO DOS RECURSOS NATURAIS

Muitas das unidades de produção familiar (UPF) do Norte do Rio Grande do Sul (RS) são baseadas na intensificação e concentração de sistemas produtivos, principalmente a suinocultura e a bovinocultura de leite. Nessas UPF costuma-se utilizar altas e frequentes doses de dejetos animais e fertilizantes químicos nitrogenados, muitas vezes acima da demanda de N exigida pelas pastagens perenes, aumentando o risco de contaminação ambiental pela transferência de N para os mananciais aquáticos. Neste trabalho avaliou-se a relação entre as doses de N total aplicadas anualmente via fertilizantes orgânicos e químicos, em pastagens perenes, e as concentrações das formas de N (N-NO3 ‒ , N-NO2 ‒ e N-NH4 +) na água lixiviada e escoada, no solo e no tecido das pastagens. Para isso, foram monitoradas 14 unidades agropecuárias familiares de produção leiteira na região do Médio Alto Uruguai do RS nos anos de 2014 e 2015. As doses de N total aplicadas nas pastagens variaram de 45 a 2.000 kg de N ha‒1 ano‒1. Dez UPF aplicam doses de N 1,25 a 10 vezes maiores que as recomendadas. A quantidade de N aplicada via fertilizante apresentou correlação positiva e significativa com o teor de N-NO3 ‒ na água lixiviada. Em duas ocasiões a água lixiviada apresentou teores de N-NO3 ‒ acima dos níveis críticos para a saúde humana (10 mg L‒1) em UPF que aplicaram entre 5 e 10 vezes a quantidade de N recomendada. A quantidade de N aplicada nas pastagens perenes foi o fator que mais influenciou o teor das formas de N na água lixiviada e escoada, no solo e na pastagem, enfatizando o potencial de contaminação da água pelo uso excessivo do fertilizante nitrogenado

Crop response to gypsum application to subtropical soils under no-till in Brazil : a systematic review

The use of gypsum to improve the root environment in tropical soils in the southeastern and central-western regions of Brazil is a widespread practice with well-established recommendation criteria. However, only recently gypsum began to be used on subtropical soils in South of Brazil, so available knowledge of its effect on crop yield is incipient and mainly for soils under no-till (NT) systems. Avaiable studies span a wide range of responses, from a substantial increase to a slight reduction in crop yield. Also, the specific conditions leading to a favorable effect of gypsum application on crop yield are yet to be accurately identified. The primary objectives of this study were to examine previously reported results to assess the likelihood of a crop response to gypsum and to develop useful recommendation criteria for gypsum application to subtropical soils under NT in Brazil. For this purpose, we examined the results of a total of 73 growing seasons, reported in 20 different scientific publications that assessed grain yield as a function of gypsum rates. Four different scenarios were examined, by the occurrence or not of high subsurface acidity (viz., Al saturation >20 % and/or exchangeable Ca 3 cmolc dm-3) failed to increase crop yield, irrespective of the soil water status. Under these conditions, high gypsum rates (6-15 Mg ha-1) may even reduce grain yield, possibly by inducing K and Mg deficiency. On the other hand, applying gypsum to soils with high subsurface acidity increased yield by 16 % in corn (87 % of cases) and by 19 % in winter cereals (83 % of cases), whether or not the soil was water-deficient. By contrast, soybean yield was only increased by gypsum applied in the simultaneous presence of high soil subsurface acidity and water deficiency (average increase 27 %, 100 % of cases)

Effect of anthropic activities on aoil geochemistry in toposequences of the Rio Grande do Sul Plateau, Brazil

A gestão agrícola e ambiental eficaz depende da compreensão da variação do conteúdo total dos elementos químicos no solo. Neste trabalho (i) foram determinados os teores totais de elementos químicos em solos de duas topossequências localizadas no planalto do Rio Grande do Sul e, (ii) foi avaliada a influência dos usos antrópicos e relevo na geoquímica do solo. As amostras foram coletadas em nove pontos de amostragem e em cinco camadas de solo, num total de 45 amostras. A concentração elementar (flúor a urânio) foi determinada utilizando um espectrômetro de fluorescência de raios-X por dispersão de comprimento de onda, em pastilhas de solo previamente peneiradas em malha de 53 μm e pren- sadas. Foram estabelecidas as concentrações basais de 35 elementos químicos para os solos do planalto do Rio Grande do Sul, cujo material de origem são arenitos da formação Tupanciretã. O teor total de elementos químicos variou com a posição na encosta (ambiente de perda e deposição de material); com a intensidade da influência antrópica (adição de fertilizante, manejo do solo e drenagem da área úmida) e; com a condição hidromórfica do solo ao longo das toposse- quências.Efficient agricultural and environmental management depends upon the good understanding of the variation in the total contents in soil chemical elements. In this study (i) determine the total contents of chemical elements in soils of two toposequence located in the Rio Grande do Sul plateau and, (ii) the influence of anthropic uses and relief in soil geochem- istry. Soil samples were collected at nine sampling points and five soil layers for a total of 45 samples. The elemental concentrations (fluorine to uranium) was determined using a wavelength dispersive X-ray fluorescence spectrometer with pressed soil pellets, pre-sieved in 53 μm and pressed. The basal concentrations of 35 chemical elements were established for the soils of the Rio Grande do Sul plateau, whose material of origin are fluvial sandstones of the Tupanciretã For- mation. The chemical element levels varied according to the position in the slope (environment of loss and deposition of material); the intensity of the anthropic influence (addition of fertilizer, soil management and drainage of the wet area); and the hydromorphic condition of the soil along the topossequences

Release of phosphorus forms from cover crop residues in agroecological no-till onion production

Cover crops grown alone or in association can take up different amounts of phosphorus (P) from the soil and accumulate it in different P-forms in plant tissue. Cover crop residues with a higher content of readily decomposed forms may release P more quickly for the next onion crop. The aim of this study was to evaluate the release of P forms from residues of single and mixed cover crops in agroecological no-till onion (Allium cepa L.) production. The experiment was conducted in Ituporanga, Santa Catarina (SC), Brazil, in an Inceptisol, with the following treatments: weeds, black oat (Avena sativa L.), rye (Secale cereale L.), oilseed radish (Raphanus sativus L.), oilseed radish + black oat, and oilseed radish + rye. Cover crops were sown in April 2013. In July 2013, plant shoots were cut close to the soil surface and part of the material was placed in litterbags. The bags were placed on the soil surface and residues were collected at 0, 15, and 45 days after deposition (DAD). Residues were dried and ground and P in the plant tissue was determined through chemical fractionation. The release of P contained in the tissue of cover crops depends not only on total P content in the tissue, but also on the accumulation of P forms and the quality of the residue in decomposition. The highest accumulation of P in cover crops occurred in the soluble inorganic P fraction, which is the fraction of fastest release in plants. Black oat had the highest initial release rate of soluble inorganic P, which became equal to the release rate of other cover crop residues at 45 DAD. Weeds released only half the amount of soluble inorganic P in the same period, despite accumulating a considerable amount of P in their biomass. The mixtures of oilseed radish + rye and oilseed radish + black oat showed higher release of P associated with RNA at 45 DAD in comparison to the single treatments