Phosphorus Transformation in Soils Following Co-Application of Charcoal and Wood Ash

Phosphorus (P) is a vital soil macronutrient required by plants for optimum growth and development. However, its availability is limited because of fixation. The phosphorus fixation reaction is pH dependent. In acid soils, the predominance of aluminium (Al) and iron (Fe) oxides in both crystalline and amorphous forms reduces the solubility of soil inorganic P through fixation on positively charged surfaces and formation of insoluble Al and Fe precipitates. In alkaline soils, P readily reacts with calcium (Ca) to form sparingly soluble calcium phosphates. As a result, a large proportion of applied P may become chemically bound, whereas only a small fraction of soil P remains in the soil solution and available for plant uptake. To date, there is little information available on the use of charcoal with a highly negative charge and wood ash with high alkalinity to minimise P fixation in acid soils. Thus, this study examined the potential of the combined use of charcoal and wood ash to unlock P fixation in acid soils. Numerous studies have been conducted to identify effective approaches to improve P availability through the use of different types of soil amendments, regardless of whether P is organically or inorganically present. For example, to mitigate P fixation in acid soils, amendments such as compost and zeolite are used to reduce P sorption sites. These amendments have also been used to increase P uptake and crop productivity in P deficient acid soils by reducing soil acidity and the toxicity of Al and Fe. It is believed that long-term application of charcoal and sago bark ash can positively change the physical and chemical properties of soils. These improvements do not only reduce P fixation in acid soils, but they also promote an effective utilisation of nutrients through timely release of nutrients for maximum crop production.

Optimisation of Charcoal and Sago (Metroxylon sagu) Bark Ash to Improve Phosphorus Availability in Acidic Soils

Soil acidity is an important soil factor affecting crop growth and development. This ultimately limits crop productivity and the profitability of farmers. Soil acidity increases the toxicity of Al, Fe, H, and Mn. The abundance of Al and Fe ions in weathered soils has been implicated in P fixation. To date, limited research has attempted to unravel the use of charcoal with the incorporation of sago (Metroxylon sagu) bark ash to reduce P fixation. Therefore, an incubation study was conducted in the Soil Science Laboratory of Universiti Putra Malaysia Bintulu Sarawak Campus, Malaysia for 90 days to determine the optimum amounts of charcoal and sago bark ash that could be used to improve the P availability of a mineral acidic soil. Charcoal and sago bark ash rates varied by 25%, whereas Egypt rock phosphate (ERP) rate was fixed at 100% of the recommendation rate. Soil available P was determined using the Mehlich 1 method, soil total P was extracted using the aqua regia method, and inorganic P was fractionated using the sequential extraction method based on its relative solubility. Other selected soil chemical properties were determined using standard procedures. The results reveal that co-application of charcoal, regardless of rate, substantially increased soil total carbon. In addition, application of 75% sago bark ash increased soil pH and at the same time, it reduced exchangeable acidity, Al3+, and Fe2+. Additionally, amending acidic soils with both charcoal and sago bark ash positively enhanced the availability of K, Ca, Mg, and Na. Although there was no significant improvement in soil Mehlich-P with or without charcoal and sago bark ash, the application of these amendments altered inorganic P fractions in the soil. Calcium-bound phosphorus was more pronounced compared with Al-P and Fe-P for the soil with ERP, charcoal, and sago bark ash. The findings of this study suggest that as soil pH decreases, P fixation by Al and Fe can be minimised using charcoal and sago bark ash. This is because of the alkalinity of sago bark ash and the high affinity of charcoal for Al and Fe ions to impede Al and Fe hydrolysis to produce more H+. Thus, the optimum rates of charcoal and sago bark ash to increase P availability are 75% sago bark ash with 75%, 50%, and 25% charcoal because these rates significantly reduced soil exchangeable acidity, Al3+, and Fe2+.

Short-chain soluble polyphosphate fertilizers increased soil P availability and mobility by reducing P fixation in two contrasting calcareous soils

Short-chain polyphosphate fertilizers have been increasingly applied in agriculture, but little is known about the chemical behaviors of polyphosphate in soils. Herein, a cylinder experiment was carried out to investigate the influences of different P types (i.e., mono-ammonium phosphate (MAP), phosphoric acid (PA) and ammonium polyphosphate (poly-P)) and their application methods (single vs split) on the mobility and availability of P in soil through a column millimeter-scale slice cutting method; meanwhile a soil microcosm experiment (560-day) was conducted to investigate the effects of different P types on phosphorus dynamic transformation. Polyphosphate addition significantly increased P mobility. The average distance of P downward movement (81.5 mm) in soil profile in the poly-P application treatment increased by 33.6% and 81.1%, respectively, compared to the MAP and PA treatments. Different P application methods also markedly influenced phosphorus mobility. For instance, the average distance of P vertical movement in the split P application treatment was 21.2% higher than in the single application treatment, indicating that split P addition significantly increased P downward movement. Moreover, polyphosphate application decreased soil P fixation by blocking the transformation of the applied-P from labile to recalcitrant forms (HCl-P and residual-P). Overall, our findings provide meaningful information to current phosphorus fertilization practice in increasing soil P mobility and bioavailability. We suggest that polyphosphate could be regarded as an alternative P source used in agriculture, and split polyphosphate application is recommended as an effective P fertilization strategy.

Micorrizas arbusculares e absorção de fósforo em função da capacidade de fixação de fósforo do solo e da competição com a microbiota

Fungos micorrízicos arbusculares (FMA) se associam às raízes das plantas e incrementam a absorção de fósforo (P), macronutriente com baixa mobilidade no solo. A capacidade de fixação de P do solo e a competição com a biota heterotrófica afetam sua disponibilidade para plantas. Visando avaliar a contribuição dos FMA na absorção de P em solos com capacidade crescente de fixação ou em situação de competição com a biota foram realizados experimentos em vasos compartimentalizados cultivados com braquiária associada a FMA, contendo substrato marcado com 32P. Foram quantificadas a massa seca das plantas, o conteúdo e a atividade específica do P. No experimento 1 avaliou-se a absorção de P por raízes e hifas de FMA ou somente por hifas em solos com alta, média e baixa capacidade fixação de P. No experimento 2 avaliou-se a absorção de P por raízes e hifas de FMA ou somente por hifas em solos com alta e baixa capacidade fixação de P em situação de competição com a biota do solo ativada por fontes de carbono. O aumento da capacidade de fixação de P pelo solo resultou em diminuição de massa seca, conteúdo de P e atividade específica nas plantas. No solo com alta fixação de P, plantas com absorção exclusiva por hifas de FMA tiveram aumento da massa seca e conteúdo de P. Em situação de competição, houve diminuição na massa seca e no conteúdo de P nas plantas. Plantas com absorção por raízes e hifas de FMA tiveram maior atividade específica de P. Arbuscular mycorrhizae and phosphorus uptake in soils as a function of adsorption capacity and competition with microbiota A B S T R A C TArbuscular mycorrhizal fungi (AMF) are associated with plant roots and increase the absorption of phosphorus (P), macronutrient with low soil mobility. Soil P fixation capacity and competition with heterotrophic biota affect its availability. To evaluate the contribution of AMF to P uptake in soils with increasing fixation capacity or in competition with biota, experiments were carried out in compartmentalized pots cultivated with AMF-associated Brachiaria decumbens containing 32P-labeled substrate. Plant dry mass, content and specific activity of P. were quantified. In experiment 1, the absorption of P by roots and hyphae of AMF or only by hyphae in soils with high, medium and low P. fixation capacity was evaluated. In experiment 2, the absorption of P by roots and hyphae of AMF or only by hyphae in soils with high and low P fixation capacity in competition with carbon-activated soil biota was evaluated. Increasing P fixation capacity by soil resulted in decreased dry matter, P content and specific activity in plants. In soil with high P fixation, plants with exclusive absorption by FMA hyphae had increased dry matter and P content. In a competition situation, there was a decrease in dry matter and P content in plants. Plants absorbed by roots and hyphae of AMF had higher P-specific activity.Keywords: 32P, P-soil fixing, AMF, extraradical mycelium, hyphal absorption

Accurate internal representation of eye position in saccade planning

Fixation position changes slightly after each blink (Lau & Maus, 2019). We investigated whether these changes affect subsequent saccades. We tested if the oculomotor system uses an internal representation of eye position to plan a saccade. Naïve participants (N = 12) made 10° visually-guided (VG) and memory-guided (MG) saccades to a dot target presented to the left or right of fixation. Participants blinked once (blink) or remained fixated (no-blink) before an auditory cue instructed them to saccade to the target. We hypothesized that if participants had access to an eye position signal at the onset of their saccade, blink-induced position shifts should be corrected for. The alternative hypothesis was that without such an internal eye position signal, blink-induced position shifts should correlate with landing positions. This was not the case either in VG or MG saccades. Saccades started more forward from fixation for MG than VG saccades and landed more backward of the target for MG than VG saccades. Blinking did not contribute to these positional differences. Instead, blinks enlarged both saccade amplitudes. MG amplitudes were also smaller than VG amplitudes. We found no correlation between starting and landing errors across saccades. Hence, start position changes did not influence saccade landing errors. Our results suggest that to plan accurate saccades, the oculomotor system uses an internal representation of eye position that is updated after each blink. Although blinking was introduced to increase eye position changes, it did not influence saccade starting nor landing positions.

Improving soil phosphorus availability and yield of Zea mays l. using biochar and compost derived from agro-industrial wastes

Tropical soils such as Ultisols fix phosphorus (P) because of their characteristically high contents of aluminium and iron. Organic amendments could be used to mitigate P fixation. This study aimed to: i) improve soil P availability, nutrients uptake, and yield of Zea mays L. using biochar and pineapple leaf residues compost; and ii) determine if the use of biochar and pineapple leaf residues compost could exert a residual effect on P. Two cycles of field trials were carried out and the test crop used was Zea mays L. hybrid F1. At harvest, the plants were harvested, partitioned into leaves and stems, and analysed. Soil samples were also collected and analysed. The results suggest that the soil total P, available P, inorganic P, and organic P recovered from the treatments with the organic amendments were higher compared with the nonorganic amendments. The availability of soil macro-nutrients in the soils and Zea mays L. yield were higher in the treatments with the organic amendments in the first and second field trials. Amending chemical fertilisers with organic amendments have a larger residual effect than chemical fertilisers only and can be used to ameliorate P fixation of acid soils to improve maize production on acid soils.

“Fix and assay”: separating in-cellulo sphingolipid reactions from analytical assay in time and space using an aldehyde-based fixative

Fixation of fluorescent sphingolipid-loaded cells enables cell metabolism and assay readout to be separated in time and space.

Effectiveness of a rock phosphate solubilizing fungus to increase soil solution phosphate impaired by the soil phosphate sorption capacity

Available phosphate (P) deficiency in tropical soils has been recognized as a major factor that limits soil quality and plant performance. To overcome this, it is necessary to add high amounts of soluble P-fertilizers; however, this is inefficient and costly. Alternatively, rock phosphates (RP) can be used, but their low reactivity limits their use. Phosphate solubilizing microorganisms (PSM) can enhance RP dissolution and, thus, improve the RP agronomic effectiveness as fertilizer. Nonetheless, their effectiveness may be impaired by the soil P fixation capacity. An experiment was carried out to assess the in vitro effectiveness of the fungus Mortierella sp. to dissolve RP in an axenic culture medium and, thus, enhance the solution P concentration in the presence of aliquots of soils with contrasting P fixation capacity. The results showed that the fungus was capable of lowering the medium pH from 7.7 to 3.0 and, thus, dissolving the RP. The presence of soil aliquots in the medium controlled the effectiveness of the fungus to increase the concentration of the soluble P. In the presence of soils with a low or medium P sorption capacity, the concentration of the soluble P was high (63.8-146.6 mg L-1) in comparison with the inoculated (soilless) treatment (50.0 mg L-1) and the uninoculated control (0.7 mg L-1). By contrast, with very-high P fixing soil aliquots, the concentration of the soluble P was very low (3.6-33.1 mg L-1); in addition, in these soils, the fungus immobilized more P into its mycelia than in soils with a low or medium P fixation capacity. The capacity of a soil to fix P seems to be a good predictor for the effectiveness of this fungus to increase the soluble P concentration via RP dissolution.