Can dark septate endophytic fungi (DSE) mobilize selectively inorganic soil phosphorus thereby promoting sorghum growth? A preliminary study / ¿Los hongos endófitos septados oscuros (DSE) pueden movilizar selectivamente el fósforo inorgánico y promover así el crecimiento del sorgo? Un estudio preliminar

Abstract Phosphate fertilizers tend to precipitate with soil components, affecting fertilization efficiency and causing negative environmental effects. Soil microorganisms have been used to solve this problem. However, the ability of dark septate endophytic fungi (DSE) to dissolve phosphates and increase crop yield are not well known. The activity of DSE fungi capable of solubilizing reagent grade phosphates was studied in a Typic Hapludoll (Hapludol típico). The effect of the fungi on the inorganic phosphorus fractions was evaluated and an experiment was conducted in pots with sorghum as a crop. No fungal structures were found in the roots. Curvularia sp. aerial biomass and root length increased; however, P concentration was not affected. Although the results are not conclusive, they represent an advance in the potential use of DSE fungi as P solubilizers to treat crop nutrition.

Resumen Los fertilizantes fosfatados tienden a precipitar con componentes del suelo, lo que afecta la eficiencia de la fertilización y causa efectos negativos. Para resolver este problema se han utilizado microorganismos del suelo. Sin embargo, no se conoce bien la capacidad de los hongos endófitos septados oscuros (ESO) para disolver fosfatos y aumentar el rendimiento de los cultivos. Se estudió en un hapludol típico (typic hapludoll) la actividad de hongos ESO capaces de solubilizar fosfatos de grado reactivo. Se evaluó el efecto de los hongos sobre las fracciones de fósforo inorgánico y se realizó un experimento en macetas con sorgo como cultivo. No se encontraron estructuras fúngicas en las raíces. Curvularia sp. aumentó la biomasa aérea y la longitud radical, pero la concentración de fósforo no se vio afectada. Aunque los resultados no son concluyentes, representan un avance en el uso potencial de hongos ESO como solubilizadores de fósforo para tratar la nutrición de cultivos.

Can dark septate endophytic fungi (DSE) mobilize selectively inorganic soil phosphorus thereby promoting sorghum growth? A preliminary study.

Phosphate fertilizers tend to precipitate with soil components, affecting fertilization efficiency and causing negative environmental effects. Soil microorganisms have been used to solve this problem. However, the ability of dark septate endophytic fungi (DSE) to dissolve phosphates and increase crop yield are not well known. The activity of DSE fungi capable of solubilizing reagent grade phosphates was studied in a Typic Hapludoll (Hapludol típico). The effect of the fungi on the inorganic phosphorus fractions was evaluated and an experiment was conducted in pots with sorghum as a crop. No fungal structures were found in the roots. Curvularia sp. aerial biomass and root length increased; however, P concentration was not affected. Although the results are not conclusive, they represent an advance in the potential use of DSE fungi as P solubilizers to treat crop nutrition.

Phosphorus fractionation distribution in Guapimirim estuary: SE Brazil.

The Guapimirim estuary is the main tributary of Guanabara bay and is located in the northeast portion. Although it is protected, this estuary has been experiencing strong anthropogenic pressure, which has led to changes in the natural characteristics. Large amounts of sewage are dumped into the bay through tributaries, thereby changing the water and bottom sediment quality. One of the main elements of sewage is phosphorus. Despite its importance to life, a high concentration of this nutrient in the environment can result in eutrophication. This work describes the phosphorus distribution in its different fractions in the bottom sediment at 16 stations located in the main channel of the Guapimirim estuary. These results are correlated with data on grain size, organic matter and calcium carbonate content in the bottom sediment and with physicochemical parameters of the bottom water. The grain size decreases toward the mouth of the estuary, whereas the organic matter and carbonate content increase. The salinity increases significantly at 3.5 km upstream from the mouth, where there is also a notable increase in fine sediments; the same site is the mean position of the salinity front. The temperature and pH increase in the same direction. The Pinorg-total ranges between 3.18 and 7.13 µmol g(-1), increasing toward the mouth. The same trend is observed for the other phosphorus fractions P-Ca, P-Fe and P-f.a., which range from 0.68 to 1.91, 0.79 to 1.71 and 0.03 to 0.93 µmol g(-1), respectively. The P-Ca and P-Fe fractions are the most representative in the Pinorg-total, occurring at 26.3 and 26.0 %, respectively.

Phosphorus distribution and availability in untreated and mechanically separated biogas digestates

Biogas digestates contain valuable nutrients but also have high water contents. Di-gestates were sampled from two different biogas facilities before and after solid-liquid separation and were analyzed with regard to their composition and phosphorus (P) fractions. Additionally, to investigate the P fertilizer effects of these digestates in comparison with undigested slurry or TripleSuper-P (TSP), they were applied in a pot experiment (6 kg soil per pot) in an amount corresponding to 200 mg P per pot in combination with various crops (amaranth, maize, maize + beans mixed cropping, sorghum). A separation of digestates resulted in higher P concentrations of the solid fraction in comparison with the liquid fraction. The proportion of the readily soluble P fractions (H2O-P, NaHCO3-P) to the total P was higher than 70 % in all digestates. The digestates increased P uptake of the tested crops and concentrations of bioavailable P in the soil to the same extent as highly soluble TSP. Activities of soil enzymes were lower after application of the digestates in comparison to unfermented slurry. The fertilizer management of digestates can be improved by a solid-liquid separation since the solid fraction showed a relatively high concentration of P resulting in a reduction in application doses required to meet the P demands of crops.

Phosphorus distribution and availability in untreated and mechanically separated biogas digestates

Biogas digestates contain valuable nutrients but also have high water contents. Di-gestates were sampled from two different biogas facilities before and after solid-liquid separation and were analyzed with regard to their composition and phosphorus (P) fractions. Additionally, to investigate the P fertilizer effects of these digestates in comparison with undigested slurry or TripleSuper-P (TSP), they were applied in a pot experiment (6 kg soil per pot) in an amount corresponding to 200 mg P per pot in combination with various crops (amaranth, maize, maize + beans mixed cropping, sorghum). A separation of digestates resulted in higher P concentrations of the solid fraction in comparison with the liquid fraction. The proportion of the readily soluble P fractions (H2O-P, NaHCO3-P) to the total P was higher than 70 % in all digestates. The digestates increased P uptake of the tested crops and concentrations of bioavailable P in the soil to the same extent as highly soluble TSP. Activities of soil enzymes were lower after application of the digestates in comparison to unfermented slurry. The fertilizer management of digestates can be improved by a solid-liquid separation since the solid fraction showed a relatively high concentration of P resulting in a reduction in application doses required to meet the P demands of crops.(AU)

Growth and accumulation of phosphorus by bean plants treated with foliar phosphate and phosphite / Crescimento e acúmulo de fósforo pelo feijoeiro tratado com fosfato e fosfito via foliar

Currently the use of phosphite as fungicide in agriculture or as a supplementary source of phosphorus (P) has been widespread, however little is known about its effects on phosphate nutrition of important crops such as bean plants. The present work aimed to evaluate the effect of foliar applied phosphite and phosphate on the growth and phosphated nutrition of the bean plant cultivated under low and adequate P supply conditions. The experiment was conducted in an entirely random layout, in factorial scheme 2 x 3 x 2, where two phosphate concentrations were combined in the nutrient solution (1.5 mg L-1 = low phosphorous and 20 mg L-1 = adequate phosphorous), three foliar application products: KH2PO3 (monobasic potassium phosphite), KH2PO4 (monobasic potassium phosphate) and KCl (potassium chloride) as control and two treatments referring to the number of applications (one application, at the appearance of the first trifoliolate leaf and two applications: one at the appearance of the first trifoliolate leaf and the other application at the pre-flowering), with four repetitions. Overall the dry matter, fosfatase activity, phosphorus content and phosphorus use efficiency was not were affected by the foliar application treatments. Under low readiness of that nutritient the application of foliar phosphite had a negative effect on these variables. It was concluded that foliar applied phosphite has a depressive effect on the growth of the bean plant under low supply of P. The foliar phosphite slightly affects the total concentration of P in the roots and shoots, especially under low P supply, and provides no changes in levels of soluble fractions of P in leaves under conditions of low or adequate supply this nutrient.

Atualmente o uso de fosfitos na agricultura como fungicida ou como fonte suplementar de fósforo (P) tem sido amplamente difundido; contudo, pouco se sabe sobre seus efeitos na nutrição fosfatada em culturas importantes como o feijoeiro. No presente trabalho objetivou-se avaliar o efeito do fosfito e do fosfato, aplicados via foliar, sobre o crescimento e a nutrição fosfatada do feijoeiro em condições de baixo e adequado suprimento de P. O experimento foi conduzido em delineamento inteiramente casualizado, em esquema fatorial 2 x 3 x 2, combinando-se duas concentrações de fosfato em solução nutritiva (1,5 mg L-1 = baixo fósforo e 20 mg L-1 = fósforo adequado), três produtos de aplicação foliar: KH2PO3 (fosfito monobásico de potássio), KH2PO4 (fosfato monobásico de potássio) e KCl (cloreto de potássio) como testemunha e dois tratamentos referentes ao número de aplicações (aplicação única, no surgimento do primeiro trifólio e duas aplicações: uma no surgimento do primeiro trifólio e a outra aplicação no pré-florescimento), com quatro repetições. Em geral, a produção de matéria seca, a atividade da fosfatase ácida, os teores e a eficiência de utilização de fósforo não foram afetados pelos tratamentos de aplicação foliar sob suprimento adequado de P. Sob baixa disponibilidade desse nutriente, a aplicação de fosfito foliar teve efeito negativo sobre estas variáveis. Conclui-se a aplicação foliar de fosfito, comparado ao fosfato, tem efeito depressivo sobre o crescimento do feijoeiro sob baixo suprimento de P. O fosfito via foliar pouco afeta os teores totais de P, tanto nas raízes quanto na parte aérea, especialmente sob baixo suprimento de P, assim como não proporciona modificações nos teores das frações solúveis de P nas folhas, em condições de baixo ou adequado suprimento desse nutriente.

Growth and accumulation of phosphorus by bean plants treated with foliar phosphate and phosphite / Crescimento e acúmulo de fósforo pelo feijoeiro tratado com fosfato e fosfito via foliar

Currently the use of phosphite as fungicide in agriculture or as a supplementary source of phosphorus (P) has been widespread, however little is known about its effects on phosphate nutrition of important crops such as bean plants. The present work aimed to evaluate the effect of foliar applied phosphite and phosphate on the growth and phosphated nutrition of the bean plant cultivated under low and adequate P supply conditions. The experiment was conducted in an entirely random layout, in factorial scheme 2 x 3 x 2, where two phosphate concentrations were combined in the nutrient solution (1.5 mg L-1 = low phosphorous and 20 mg L-1 = adequate phosphorous), three foliar application products: KH2PO3 (monobasic potassium phosphite), KH2PO4 (monobasic potassium phosphate) and KCl (potassium chloride) as control and two treatments referring to the number of applications (one application, at the appearance of the first trifoliolate leaf and two applications: one at the appearance of the first trifoliolate leaf and the other application at the pre-flowering), with four repetitions. Overall the dry matter, fosfatase activity, phosphorus content and phosphorus use efficiency was not were affected by the foliar application treatments. Under low readiness of that nutritient the application of foliar phosphite had a negative effect on these variables. It was concluded that foliar applied phosphite has a depressive effect on the growth of the bean plant under low supply of P. The foliar phosphite slightly affects the total concentration of P in the roots and shoots, especially under low P supply, and provides no changes in levels of soluble fractions of P in leaves under conditions of low or adequate supply this nutrient.(AU)

Atualmente o uso de fosfitos na agricultura como fungicida ou como fonte suplementar de fósforo (P) tem sido amplamente difundido; contudo, pouco se sabe sobre seus efeitos na nutrição fosfatada em culturas importantes como o feijoeiro. No presente trabalho objetivou-se avaliar o efeito do fosfito e do fosfato, aplicados via foliar, sobre o crescimento e a nutrição fosfatada do feijoeiro em condições de baixo e adequado suprimento de P. O experimento foi conduzido em delineamento inteiramente casualizado, em esquema fatorial 2 x 3 x 2, combinando-se duas concentrações de fosfato em solução nutritiva (1,5 mg L-1 = baixo fósforo e 20 mg L-1 = fósforo adequado), três produtos de aplicação foliar: KH2PO3 (fosfito monobásico de potássio), KH2PO4 (fosfato monobásico de potássio) e KCl (cloreto de potássio) como testemunha e dois tratamentos referentes ao número de aplicações (aplicação única, no surgimento do primeiro trifólio e duas aplicações: uma no surgimento do primeiro trifólio e a outra aplicação no pré-florescimento), com quatro repetições. Em geral, a produção de matéria seca, a atividade da fosfatase ácida, os teores e a eficiência de utilização de fósforo não foram afetados pelos tratamentos de aplicação foliar sob suprimento adequado de P. Sob baixa disponibilidade desse nutriente, a aplicação de fosfito foliar teve efeito negativo sobre estas variáveis. Conclui-se a aplicação foliar de fosfito, comparado ao fosfato, tem efeito depressivo sobre o crescimento do feijoeiro sob baixo suprimento de P. O fosfito via foliar pouco afeta os teores totais de P, tanto nas raízes quanto na parte aérea, especialmente sob baixo suprimento de P, assim como não proporciona modificações nos teores das frações solúveis de P nas folhas, em condições de baixo ou adequado suprimento desse nutriente.(AU)

Phosphate fertilization and phosphorus forms in an Oxisol under no-till

Under no-till phosphorus (P) accumulates in a few centimeters of the topsoil layer. Plant residues left on the soil surface release P and organic acids, which may improve P availability and fertilizer efficiency, including both soluble (such as triple super phosphate) and less soluble sources (such as reactive natural phosphates). In this study, soybean response to P fertilizer and P forms in the top 40 cm of an Oxisol were evaluated after surface application of different phosphates in a 5-year-old no-till system. Treatments consisted of 0 or 80 kg ha-1 of total P2O5 applied on the soil surface, both as natural reactive phosphate (NRP) or triple super phosphate (TSP). In addition, 80 kg ha-1 of P2O5 were applied to subplots, in furrows below and beside the soybean (Glycine max L.) seeds, in different combinations of NRP and TSP. Soil samples were taken before and after the soybean growth, down to 0.40 m and soil phosphorus was chemically fractionated. The responses to NRP were similar to TSP, with an increase in P reserves at greater depths, even in non-available forms, such as P-occluded. After the soybean harvest, P-occluded levels were lower at the surface layer, but an increase was observed in the soluble, organic and total P down to 40 cm. An improved P distribution in soil depth, especially regarding the soluble and organic forms, resulted in higher soybean yields, even when the phosphates were applied to the soil surface.

Em semeadura direta o fósforo (P) acumula-se na camada mais superficial do solo, mas os resíduos deixados na superfície liberam P e ácidos orgânicos, que podem melhorar a disponibilidade e a eficiência de fertilizantes como o superfosfato triplo e fosfatos naturais reativos. Neste estudo, a resposta da soja à adubação com P e as formas de P até 40 cm de profundidade do solo foram avaliadas após a aplicação de fosfatos em um sistema conduzido em semeadura direta há cinco anos. Os tratamentos consistiram de 0 ou 80 kg ha-1 P2O5 total, aplicados na superfície do solo como fosfato natural reativo (FNR) ou superfosfato triplo (SFT). Nas subparcelas foram aplicados, no sulco de semeadura, 80 kg ha-1 de P2O5, em diferentes combinações de FNR e SFT. Amostras de solo foram coletadas até 0.4 m, antes e depois do cultivo da soja (Glycine max L.), para fracionamento do P. As respostas ao FNR foram semelhantes às do SFT, com aumento das reservas de P em profundidade, mesmo em formas não-disponíveis como P-ocluso. Após a colheita da soja, os teores de P-ocluso diminuíram na camada mais superficial, mas foi observado um aumento nas formas solúvel, orgânica e P - total em toda a espessura de solo estudada. A melhor distribuição do P no solo, principalmente em formas solúvel e orgânica, resultou em maior produtividade da soja, mesmo quando o fertilizante foi aplicado na superfície do solo.

Phosphate fertilization and phosphorus forms in an Oxisol under no-till

Under no-till phosphorus (P) accumulates in a few centimeters of the topsoil layer. Plant residues left on the soil surface release P and organic acids, which may improve P availability and fertilizer efficiency, including both soluble (such as triple super phosphate) and less soluble sources (such as reactive natural phosphates). In this study, soybean response to P fertilizer and P forms in the top 40 cm of an Oxisol were evaluated after surface application of different phosphates in a 5-year-old no-till system. Treatments consisted of 0 or 80 kg ha-1 of total P2O5 applied on the soil surface, both as natural reactive phosphate (NRP) or triple super phosphate (TSP). In addition, 80 kg ha-1 of P2O5 were applied to subplots, in furrows below and beside the soybean (Glycine max L.) seeds, in different combinations of NRP and TSP. Soil samples were taken before and after the soybean growth, down to 0.40 m and soil phosphorus was chemically fractionated. The responses to NRP were similar to TSP, with an increase in P reserves at greater depths, even in non-available forms, such as P-occluded. After the soybean harvest, P-occluded levels were lower at the surface layer, but an increase was observed in the soluble, organic and total P down to 40 cm. An improved P distribution in soil depth, especially regarding the soluble and organic forms, resulted in higher soybean yields, even when the phosphates were applied to the soil surface.

Em semeadura direta o fósforo (P) acumula-se na camada mais superficial do solo, mas os resíduos deixados na superfície liberam P e ácidos orgânicos, que podem melhorar a disponibilidade e a eficiência de fertilizantes como o superfosfato triplo e fosfatos naturais reativos. Neste estudo, a resposta da soja à adubação com P e as formas de P até 40 cm de profundidade do solo foram avaliadas após a aplicação de fosfatos em um sistema conduzido em semeadura direta há cinco anos. Os tratamentos consistiram de 0 ou 80 kg ha-1 P2O5 total, aplicados na superfície do solo como fosfato natural reativo (FNR) ou superfosfato triplo (SFT). Nas subparcelas foram aplicados, no sulco de semeadura, 80 kg ha-1 de P2O5, em diferentes combinações de FNR e SFT. Amostras de solo foram coletadas até 0.4 m, antes e depois do cultivo da soja (Glycine max L.), para fracionamento do P. As respostas ao FNR foram semelhantes às do SFT, com aumento das reservas de P em profundidade, mesmo em formas não-disponíveis como P-ocluso. Após a colheita da soja, os teores de P-ocluso diminuíram na camada mais superficial, mas foi observado um aumento nas formas solúvel, orgânica e P - total em toda a espessura de solo estudada. A melhor distribuição do P no solo, principalmente em formas solúvel e orgânica, resultou em maior produtividade da soja, mesmo quando o fertilizante foi aplicado na superfície do solo.

Phosphorus critical levels and availability in lowland soils cultivated with flooded rice

Lowland soils present a great potential for the flooded rice crop. This work aimed to estimate critical levels of P in waterlogged soils cultivated with rice using Mehlich 1 and anion exchange resin as soil-P extractors, compare the performance of these extractors as for the evaluation of the P availability, and study the soil-P fractions involved in the P nutrition of the rice crop. Studied soils consisted of four Histosols: Low Humic Gley (GP), Aluvial (A), Humic Gley (GH) and Bog Soil (O) which were previously cultivated with beans. The experimental design was completely randomized, in a factorial scheme, using four soils, five P rates (75, 150, 300, 500 and 800 mg dm-3) and two liming treatments (with and without liming), with three replicates. After 60 days of flooding, soil samples were submitted to P extraction by Mehlich 1 and resin, and phosphorous fractionation. Two rice plants were cultivated in pots containing 3 dm³ of waterlogged soils. The labile P and the moderately labile P of the soils contributed for rice nutrition. The two tested extractors presented efficiency in the evaluation of P availability for the rice cultivated in lowland waterlogged soils.

Os solos de várzea apresentam-se com um grande potencial para o cultivo do arroz irrigado por inundação. No presente trabalho, objetivou-se estimar os níveis críticos de P pelos extratores Mehlich 1 e resina em solos de várzea cultivados com arroz sob inundação e identificar as frações de P que estão contribuindo para a nutrição fosfatada do arroz. Foram utilizados quatro solos de várzea pré-cultivados com feijoeiro: Glei Pouco Húmico (GP), Aluvial (A), Glei Húmico (GH) e Orgânico (O). O experimento foi em delineamento inteiramente casualizado, em fatorial 4 x 5 x 2 com três repetições, sendo: quatro solos, cinco doses de P (75, 150, 300, 500 e 800 mg dm-3) e dois níveis de calagem: ausência e presença. Após 60 dias de inundação, coletaram-se amostras dos solos para a determinação do P por Mehlich 1 e resina e fracionamento de P. Cada parcela constituiu de um vaso de 3 dm³ em que cultivaram-se duas plantas. As formas de P lábeis e pouco lábeis dos solos contribuíram para a nutrição fosfatada do arroz. Os dois extratores demonstraram eficiência na avaliação do P disponível para o arroz.

Phosphorus critical levels and availability in lowland soils cultivated with flooded rice

Lowland soils present a great potential for the flooded rice crop. This work aimed to estimate critical levels of P in waterlogged soils cultivated with rice using Mehlich 1 and anion exchange resin as soil-P extractors, compare the performance of these extractors as for the evaluation of the P availability, and study the soil-P fractions involved in the P nutrition of the rice crop. Studied soils consisted of four Histosols: Low Humic Gley (GP), Aluvial (A), Humic Gley (GH) and Bog Soil (O) which were previously cultivated with beans. The experimental design was completely randomized, in a factorial scheme, using four soils, five P rates (75, 150, 300, 500 and 800 mg dm-3) and two liming treatments (with and without liming), with three replicates. After 60 days of flooding, soil samples were submitted to P extraction by Mehlich 1 and resin, and phosphorous fractionation. Two rice plants were cultivated in pots containing 3 dm³ of waterlogged soils. The labile P and the moderately labile P of the soils contributed for rice nutrition. The two tested extractors presented efficiency in the evaluation of P availability for the rice cultivated in lowland waterlogged soils.

Os solos de várzea apresentam-se com um grande potencial para o cultivo do arroz irrigado por inundação. No presente trabalho, objetivou-se estimar os níveis críticos de P pelos extratores Mehlich 1 e resina em solos de várzea cultivados com arroz sob inundação e identificar as frações de P que estão contribuindo para a nutrição fosfatada do arroz. Foram utilizados quatro solos de várzea pré-cultivados com feijoeiro: Glei Pouco Húmico (GP), Aluvial (A), Glei Húmico (GH) e Orgânico (O). O experimento foi em delineamento inteiramente casualizado, em fatorial 4 x 5 x 2 com três repetições, sendo: quatro solos, cinco doses de P (75, 150, 300, 500 e 800 mg dm-3) e dois níveis de calagem: ausência e presença. Após 60 dias de inundação, coletaram-se amostras dos solos para a determinação do P por Mehlich 1 e resina e fracionamento de P. Cada parcela constituiu de um vaso de 3 dm³ em que cultivaram-se duas plantas. As formas de P lábeis e pouco lábeis dos solos contribuíram para a nutrição fosfatada do arroz. Os dois extratores demonstraram eficiência na avaliação do P disponível para o arroz.