Fracionamento das Formas de Fósforo em Terra Preta de Índio / Phosphorus Fractionation on “Terra Preta de Índio”

A Terra Preta de Índio (TPI) é rica em fósforo (P) e cálcio (Ca), por ser um solo de origem antrópica. A forma de P inorgânico mais comum nesse solo, é aquela formada com Ca, consequência da mineralização da hidroxiapatita da composição de ossos de animais descartado no solo. Para entender o processo de extração de P em TPI, como os extratores químicos, foi realizado um estudo do fracionamento das formas de P inorgânicas, em conjunto com os extratores Mehlich-1 (M1), Mehlich-3, Bray-1 (B1) e Olsen (OL), com objetivo de verificar o comportamento de extração das principais formas do P inorgânico pelos extratores M1, M3, B1 e OL. E para tanto, as amostras de solo coletadas na profundidade 0-20 cm, em oito sítios da Mesorregião do Centro Amazonense foram submetidas ao fracionamento de P pelo método proposto por Chang e Jackson em consorcio das extrações com M1, M3, B1 e OL. Os resultados das partições das formas de P foram caracterizados pela variação de todas as formas, de acordo com local amostrado. O extrator M1 retirou quantidades variadas de P-FL, P-Fe e P-Al, e influenciou principalmente na retirada do P-Ca. O OL possui a extrai preferencialmente o P mais disponível para a solução do solo. Portanto, a dinâmica de extração de P com o M1, M3, B1 e OL, está diretamente relacionada com a variabilidade dos teores das formas de P-FL, P-Fe e P-Al e P-Ca em solos antrópicos.

Sediment phosphorus fractionation and flux in a tropical shallow lake

Aim The aim of the present study is to evaluate the potential phosphorus (P) release from the sediment to the water column of a tropical shallow lake in the northeast of Brazil, based on the sediment P fractions and on the flux of P between water and sediment. Methods We used a sequential extraction method to analyse the different P fractions of the sediment of Lake Extremoz. We also carried out a 40-day microcosm experiment to analyse the flux of P between water and sediment. We did so by flooding 200g of sediment from the lake with 800 mL of 1.2 µm filtered lake water in 1 L beakers. Every 5 days we analysed: soluble reactive phosphorus (SRP), total phosphorus (TP), organic phosphorus (Org-P), dissolved oxygen (DO), temperature, and pH of the water. Results The largest fraction of P in the sediment of Lake Extremoz is Refractory-P, which is non-mobile. The main mobile fraction of this lake’s sediment is composed of P bound to Fe and Mn oxides (BD-P) which is redox sensitive. During the P flux experiment, the water was always oxic and with nearly neutral pH, however the temperature increased by almost 4 °C due to the increase of the temperature of the air. SRP, TP and Org-P concentrations in the water had a general decrease in the first 20 days. But, on the second half of the experiment, those concentrations increased and the fluxes of P from sediment to water, mainly Org-P, were positive. Even with this increase in concentrations, indicating a period of P release, overall fluxes were negative. Conclusions The main mobile fraction of the sediment is redox sensitive, therefore it has the potential to be released in case of oxygen depletion. Under current conditions, most of the P released by the sediment is in organic forms, indicating that, in the presence of oxygen, the balance of P between water and sediment is controlled by the effects of organisms on P as well as temperature.

Soil phosphorus fractionation after co-applying biochar and paper mill biosolids

In recent decades, there has been a growing interest in the recycling of organic materials such as paper mill biosolids (PB) and biochar for use as soil amendments. However, the benefits of co-application of PB and biochar and its effects on soil P availability remain unknown. An incubation study was conducted on two acidic soils to assess the effect of two PB types (2.5% w/w) co-applied with three rates (0%, 2.5%, and 5% w/w) of pine (Pinus strobus L.) biochar on soil P fractions. An unfertilized control and a mineral NP fertilizer were used as a reference. Soil P fractions were determined by Hedley procedure after 2 and 16 weeks of incubation. Material fractionation indicated that the PB containing the highest total P and the lowest Al content had the highest proportion of labile P, whereas most P in the biochar was in a stable form. The incubation study revealed that the P-rich PB increased P availability in both soils to a level comparable to mineral fertilizer at the end of the incubation. The addition of biochar to PB, however, did not affect soil P availability, but the highest rate induced a conversion of P fixed to Al and Fe oxides towards recalcitrant forms, particularly in the sandy loam soil. We conclude that co-applying biochar and PB could be more beneficial than application biochar alone and soils amended with such a mixture would be expected to release part of their P slowly over a longer period of time.