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ABSTRACT Land use changes profoundly impact the natural dynamics of soil phosphorus (P), potentially leading to decreased P concentrations. This study aimed to evaluate the different P fractions in soils from Paraguay Central Chaco under pristine and anthropogenic conditions. A randomized complete block design was utilized with two treatments (pristine and anthropogenic usage). Thirty-four composite soil samples were collected from the region at the layer of 0.00-0.20 m, followed by chemical fractionation of P into labile, moderately labile, and non-labile categories, further classified into inorganic and organic types. Collected data were analyzed using general and mixed linear models. Significant differences (p<0.05) were explored using Fisher’s least significant difference test for mean comparisons. Pristine soils consistently exhibited higher P levels across most evaluated fractions (labile, moderately labile, non-labile, and inorganic) compared to those affected by anthropogenic activities. Organic P fraction showed no significant differences. These findings highlight that converting pristine areas to agricultural use reduces soil P levels, posing significant implications for environmental management and agricultural productivity.

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ABSTRACT Phosphorus (P) is one of the most used nutrients in agriculture due to its high degree of interaction with the soil. It is susceptible to calcium precipitation in poorly weathered and alkaline soils, such as those in the Brazilian Semi-Arid region. Mehlich-1 is the most used extractor to evaluate P availability in this region. However, there are controversies regarding the efficiency of Mehlich-1 and the anion exchange resin (AER) has been an alternative extractor to evaluate P availability. However, AER has not yet proven its efficiency in this region. Additionally, other extractors such as Mehlich-3 and Olsen need to be evaluated. This study aimed to correlate soil properties in an alkaline environment with the P extracted by Mehlich-1, AER, Mehlich-3 and Olsen extractors and assess the performance of these extractors in predicting P availability for Urochloa decumbens in representative soils of the sub-middle São Francisco Valley. An experiment was carried out with samples of six representative soils from productive areas of the sub-middle São Francisco Valley, Brazil. Soils were incubated with increasing P rates and after 30 days, soil samples were collected for P determination by the extractors Mehlich-1, AER, Mehlich-3, and Olsen, relating this extraction to soil properties. Soils were seeded with U. decumbens to determine biomass production and P accumulated in plant biomass, correlating this accumulation with the P extraction capacity of the extractors. Exchangeable Ca2+ content and soil pH influenced the P extraction rate more than clay and P-rem content. Mehlich-1 extractor overestimated available P. Anion exchange resin was also influenced by soil properties and showed low prediction of P availability. In contrast, Olsen extractor was not influenced by soil properties, but showed low prediction of available P. The pH of Mehlich-3 extracts was little altered during P extraction in the different soils, with the extraction of P influenced by the exchangeable Ca2+ contents and pH. However, Mehlich-3 showed high performance in predicting P availability in alkaline environments, suggesting that soil properties such as exchangeable Ca2+ and pH should be considered when P availability is evaluated in alkaline soils.

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ABSTRACT Demand for phosphate fertilizers in Brazil, combined with its reliance on external sources, highlights the need to explore alternative phosphorous (P) sources for limed cultivated soils. This study aimed to characterize and evaluate the agronomic performance of phosphates from various sources, including national sedimentary (Arraias, Bonito, and Pratápolis) and igneous deposits (Catalão and Registro) imported sedimentary sources (Algeria, Bayovar, and Morocco), and residue-recovered sources (Bonechar and effluent recovered phosphate – ERCP). Phosphates underwent mineralogical and chemical characterization, including P solubility in different extractant solutions. A greenhouse experiment was conducted using an Oxisol with pH corrected to 6.3 in a completely randomized design. The experiment tested P sources at a rate of 160 mg kg-1, along with a treatment using triple superphosphate (TSP) as a reference source and a control without P addition. Two corn crops were grown for 45 days each, with measurements taken for P content and aboveground dry mass. Bonechar and ERCP exhibited high solubility in 2 % citric acid. Bonechar and sedimentary phosphates with solubility above 27 % in citric acid showed agronomic efficiency equivalent to TSP. In contrast, national phosphates subjected only to primary beneficiation processes displayed lower agronomic efficiency. The efficiency of low-water-soluble phosphates in soils with corrected pH is generally related to their solubility in citric acid, except for ERCP, which exhibited high solubility but low performance. This study highlights the potential of diverse phosphate sources to address P deficiency in Brazilian soils and emphasizes the importance of understanding their characteristics for effective fertilization strategies in agricultural soils.

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ABSTRACT Subtropical Oxisols have a high phosphate adsorption capacity and consequently lower phosphorus (P) availability. Therefore, correct management of phosphate fertilization in grain crop rotations is essential to increase the P-use efficiency and minimize potential environmental impacts. This study aimed to evaluate, in soils with medium and high initial P level, fertilization strategies (crop and system fertilization) and placement’s effects (banded P and broadcast) on soil available P, crop yield, and P use efficiency. Two field trials were installed on an Oxisol (Humic Hapludox – Latossolos) cultivated with a crop rotation with corn or soybean in the summer, and cereals in the winter. Crop yield, P use efficiency, and soil available P in the 0.00-0.10 and 0.10-0.20 m layers were evaluated during eight growing seasons. Three years of phosphate fertilization increased the P content of the 0.00-0.20 m layer above the critical level (8 mg dm-³) in the soil with medium initial P and maintained the P status above the critical level in the soil with high initial P. The P-rich environment in the 0.00-0.10 m soil layer was sufficient to support high-yield grain crops with low response to fertilization strategies and placement. However, four years of banded P fertilization on high initial P soil resulted in a greater increase in P content in the 0.10-0.20 m layer compared to broadcast P. In the field trial with medium initial available P content, there was a greater response to phosphate fertilization, leading to a significant increase in grain yields when compared to the control treatment with no P, especially for barley (50 % increase). Over four years of evaluation, banded P, regardless of the fertilization strategy (crop or system), proved effective in increasing crop yield (for one crop of black oat and three crops of corn) and P use efficiency (one crop of corn). System fertilization in a high P export environment should be adopted only in soils with available P content above the critical level and after at least four years of using diverse winter cover crops (grass + legume). Otherwise, P fertilization at every sowing (crop fertilization) remains more appropriate for intense grain production systems.

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ABSTRACT Growing off-season cover crops effectively enhances ecological diversity and improves nutrient cycling in agricultural systems, particularly when nutrient losses and low use efficiency are prominent. This study aimed to assess the interaction between different off-season cover crops and varying nitrogen (N) and phosphorus (P) application rates on common beans, soybeans, and corn yields, as well as on soil organic matter (SOM) and available P content (Mehlich-1) in a Cerrado loamy soil. The experiment was conducted as a strip-plot factorial design with three replications in Planaltina, Distrito Federal, Brazil, from 2017 to 2020 under a no-tillage system. A fallow control and different cover crops were assigned to the rows of the three blocks and cultivated during the off-season from February to May, including Urochloa ruziziensis, Crotalaria spectabilis, millet (Pennisetum glaucum L.), white oat (Avena sativa) and a mix of cover crops (white oat, millet, buckwheat [Fagopyrum esculentum Moench], and radish [Raphanus sativus L.]). Combinations of N and P rates were assigned to the columns of the blocks, and the effects of the interactions of the factorial were assessed on subsequently cultivated commercial summer crops, including soybeans (Glycine max L.) in the 2017/18, 2018/19, and 2020/21 seasons and corn (Zea mays L.) in the 2019/20 season. Furthermore, common beans (Phaseolus vulgaris L.) were grown during all winter cropping seasons from 2017 to 2020. Cover crops reduced the dependence of commercial crops on mineral N and P fertilizers, although response to increasing rates was still present. Moreover, the magnitude of this effect varied with the specific crop species and commercial crops. Among the cultivated species, U. ruziziensis and white oat; U. ruziziensis, white oat, millet, and the mix; and U. ruziziensis and C. spectabilis exhibited the greatest potential for increasing yield in beans; soybeans; and corn, respectively.

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ABSTRACT Sewage sludge (SS) from wastewater treatment has reasonable phosphorus (P) levels, which could be used as fertilizer in agriculture. However, SS-P content is lower than mineral fertilizers, which limits its operational application. The blend of organic and mineral material can increase the P content, formulating organomineral fertilizers (OMF) with higher P levels, enabling agricultural use. This study aimed to assess the agronomic efficiency and residual effect of organomineral fertilizers derived from SS as phosphorus sources for Urochloa brizantha. A greenhouse pot experiment was conducted to evaluate the successive cultivation of U. brizantha over eight cycles, with the following treatments: SS organic compost (SSC) powder; SSC pelletized (SSP), SSC+MAP pelletized (S+MAP) and SSC+AshDec® pelletized (S+ASD); AshDec® powder (ASD), monoammonium phosphate (MAP) and a control (no P). In each Urochloa cycle, height, tillering, shoot dry mass (SDM), and leaf P were evaluated. After eight cycles, the soil was subjected to P fractional analysis. Our results showed that tillering was higher in all treatments with P compared to control (No P). Shoot dry mass production in the first cycle was higher with S+MAP (21.8 g pot-1) than MAP (17.5 g pot-1), and after eight cycles, the accumulated SDM of all treatments (>140 g pot-1) was superior to MAP (132 g pot-1), except for S+ASD (118 g pot-1). No significant difference in plant height was observed. Total P uptake was higher in the treatments with recycled sources, however, plants fertilized with S+MAP accumulated more P during establishment, while SSC, SSP, and ASD promoted higher accumulation during 4 to 6 cycles. After eight cycles, soil labile P content was higher in treatments with OMFs compared to mineral sources, indicating a residual effect of organomineral fertilization. These results showed that SSC-derived OMFs are more efficient than conventional fertilizers if mixed with soluble mineral sources (MAP), but the same is not true with insoluble sources (ASD). Organomineral S+MAP can replace MAP, providing greater efficiency in forage establishment and a greater residual effect.

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ABSTRACT Natural phosphate rocks (PR) are characterized by low phosphorus (P) solubility in water. Acidulation is the normal method to raise P solubility of these materials, however, it increases the cost and causes operational issues. The aim of this study was to evaluate the agronomic efficiency of partially acidulated and micro-granulated Arraias phosphate rock, which has a lower P content (6.88 %) than normal apatite concentrates. Two experiments were carried out in a greenhouse at the University of Rio Verde, Goiás State, in which corn was grown in pots with two kg of red clayey Oxisol (Latossolo). Treatments for the first experiment were the natural Arraias phosphate rock; triple superphosphate (TSP); and three partially acidulated phosphate rock (PAPR) with 5, 10 and 15 % of H2SO4 relative to PR mass. Phosphorus diffusion from each fertilizer source was evaluated using Petri dishes filled with soil, with diffusion assessed at 1, 7, 14, 30, and 60 days after preparation. For the second experiment, treatments were 15 % PAPR granulated to average sizes of 0.25, 0.75, 1.50, and 2.4 mm. The agronomic efficiency of all variations of the PR was lower than the TSP. The 15 % PAPR treatment resulted in the highest corn dry mass yield among partially acidulated PR. The phosphorus diffusion radius was greatest with TSP, while diffusion from unacidulated Arraias rock phosphate was undetectable. Diffusion from acidified phosphate rocks increased with higher acidification rates. Granule size affected P absorption and, consequently, the agronomic efficiency of PAPR, but did not significantly influence its overall efficiency. Under the conditions of this study, partially acidulated and granulated phosphate rock was not an effective alternative to TSP.

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ABSTRACT Determining soil phosphorus (P) buffer capacity (PBC) is crucial for establishing optimal P fertilizer rates in corrective fertilization practices. However, in subtropical regions, changes in soil chemical and physical properties, such as soil organic matter (SOM) accumulation and texture modifications, can significantly impact PBC values, altering soil adsorption capacity. Consequently, P rates recommended by generalized guidelines for soil correction in these regions may be insufficient to achieve the critical P level in the soil. This study aimed to define PBC, develop an equation for PBC estimation, and establish P rates for corrective fertilization in soils with high SOM and medium clay content under subtropical climate conditions in Brazil compared with CQFS-RS/SC (2016) recommendation. The study used 29 soils collected from the Serra Gaúcha region, Rio Grande do Sul state, Brazil. Soil samples were collected from native forest areas in the 0.00-0.20 m layer. After drying and sieving, the samples were subjected to incubation with phosphate rates for 30 days. Ten treatments, ranging from 0 to 300 % of the recommended P2O5 rate to increase P levels to high sufficiency levels were applied, with three replicates. After the incubation period, Mehlich-1 P (P_M1) levels were determined. The mean PBC value was 26.3 kg ha-1 P2O5, representing the rate required to increase P_M1 levels by 1.0 mg dm-3 in the soil. Terrain altitude was negatively correlated with PBC, while P_M1 showed a positive correlation with SOM content. An equation for estimating PBC was proposed [PBC (kg ha-1 P2O5) = 49.75 - 0.063A + 0.692Clay - 1.869P_M1]. The current corrective fertilization recommendations for the southern region of Brazil underestimate the P2O5 rates for very low and low classes in Serra Gaúcha soils by an average of 1.5 times. Therefore, we recommend adjusting phosphate fertilizer rates, monitoring soil P content, and maintaining SOM levels.

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ABSTRACT Corrective phosphate is a usual practice in poor soils to improve P levels and yield potential. However, the broadcast P application in soils with high P fixing capacity may have low efficiency. This study evaluated sugarcane yield response to corrective phosphate (broadcast application and incorporated) and in planting maintenance phosphate application in four sugarcane sites during three crop cycles in South-Central Brazil. The experimental design was a factorial 2 × 5: presence or absence of corrective phosphate and five rates of P2O5 as maintenance , with four repetitions. A reactive phosphate rock (Bayovar, 29 % of total P2O5, 14 % soluble in citric acid 2 %) was broadcast applied at a rate of 150 kg ha-1 P2O5, while monoammonium phosphate was used in planting furrow in rates varying from 0 to 200 kg ha-1 P2O5. Sugarcane stalk yield, total recoverable sugar, and sugar yield were evaluated in each site for three consecutive harvests with no re-application of P. Corrective phosphate fertilization combined with maintenance P statistically improved sugarcane yields in 4 of 12 sites-years, showing a yield gain of 4.2 Mg ha-1 compared to control. On the average of the literature review, corrective phosphate combined with maintenance P improved sugarcane yield of 7.8 Mg ha-1. In addition, the corrective P had a positive isolated effect in the other two ratoon cycles and a negative in one. maintenance P application isolated (rates of 100-200 kg ha-1 P2O5) improved sugarcane stalk yield in an average of three harvest, with a mean yield gain of 6.5 Mg ha-1. On average, of all cycles, the CP combined with maintenance P or the isolated practices (at the same rate) increased sugarcane yield from 92 Mg ha-1 of control to 97-98 Mg ha-1. Phosphorus fertilization slightly improved total recoverable sugar, so sugar yield improvement was most associated with yield enhancement. Corrective P combined with maintenance P can be a strategy for improving the sustainability of P usage in sugarcane production, including a potential reduction in P input in the cane-plant cycle, aligned to a positive residual effect on the ratoons.

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ABSTRACT Phosphorus (P) is an essential macronutrient for plant growth, and its availability is often influenced by management systems adopted over time. Adopting management systems, such as no-tillage, combined with cover crops, can influence soil P availability through factors including soil organic matter accumulation. This study aimed to evaluate how management systems and cover crops influence different P fractions and organic matter. Furthermore, the effect of the time since the implementation of management systems on phosphorus (P) availability and soil organic matter accumulation was assessed. The study was conducted at an organic farm in Seropédica, Rio de Janeiro, Brazil. The soil was classified as Argissolo Amarelo with a sandy texture in the surface layer, corresponding to Ultisols. The experimental design was a randomized complete block design with three replications in a 2 × 6 factorial scheme, with two main plots representing the management systems (no-tillage and conventional tillage) and six subplots within each main plot: monocultures of pearl millet Pennisetum glaucum, sunn hemp (Crotalaria juncea), and jack bean (Canavalia ensiformis), two cover crop mixtures (100 and 50 % seed ratios of the aforementioned species), and a control subplot with spontaneous vegetation. Soil organic matter (SOM) particle size fractionation and P fractionation were analyzed at two-time points: the beginning of the experiment, in 2019, and four years later, in 2023. Four years later, the management systems increased the soluble phosphorus fraction (114-161 % across the evaluated layers) and decreased the occluded fraction (-23 to -43 %). However, within the management systems, higher values were observed for the occluded fraction and organic phosphorus, which may be correlated with the increase in soil organic matter fractions over time. Cover crops did not affect SOM accumulation and P availability. Soil management systems and time since adoption influenced phosphorus availability and soil organic matter accumulation. However, the timeframe was too short to observe the effects of cover crops.

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ABSTRACT Phosphorus is essential for plant metabolism. Although banana plants do not absorb large quantities, most of this mineral is exported together with the fruits, where the nutrients are related to sensory, nutritional, and technological qualities. Highly weathered soils, such as those found in most of Brazil, can immobilize phosphorus because of the cationic charges in iron and aluminum ions, making the element unavailable to plants and more challenging for phosphate fertilization. Brazil is the fourth-largest banana producer worldwide and plays an important role in national agribusiness. New banana cultivars are frequently introduced to address the adversities of banana farming and meet consumer expectations. This study aimed to evaluate the application levels of P2O5 in the BRS SCS Belluna banana plant in two crop cycles. A randomized block design with five blocks in a 6 × 2 factorial scheme was used. The first factor was the level of phosphorus application (P2O5), and the second factor was the crop cycle (first and second crop cycles). Variables related to plant vigor, production, and fruit quality were also evaluated. Shoot mass, plant height and diameter, number of photosynthetically active leaves, bunch yield, fruit mass, and nutritional aspects were analyzed. All plant biometric variables were positively affected by phosphate fertilization. Application of P2O5 promoted more vigorous banana plants with a larger number of leaves at the end of the crop cycle, and these variables were positively correlated with the production of bunches, fruit mass, and nutritional quality. The bunch yield per crop cycle increased by up to 84 % compared to the lowest level of P2O5 applied. In short, the BRS SCS Belluna banana plant responded well to phosphorus dosage, positively affecting plant vigor, which significantly influenced the production of bunches, fruit filling, and quality. The best results were achieved at P2O5 application levels close to the recommended reference level.

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ABSTRACT Phosphorus (P) is one of the most limiting elements for plant nutrition in tropical and subtropical soils due to its high binding energy on the surface of iron and aluminum oxides and hydroxides. Flooded rice cultivation occurs in lowlands, influencing redox reactions and P dynamics. This study aimed to evaluate the forms of phosphorus and their lability after soil reoxidation subsequent to a period of flooding for irrigated rice cultivation following four seasons of cultivation with soybean-ryegrass and corn-white clover succession in an Albaqualf (Planossolo) fertilized with triple superphosphate under no-tillage. The experiments were conducted in Albaqualf (Planossolo), in a 2 × 2 double factorial scheme, with factor 1 being P fertilization and factor 2 being flooding followed by drainage. Triple superphosphate was used as the P source. One of the experiments consisted of a soybean-ryegrass, and the other consisted of corn-white clover, cultivated for four years, with irrigated rice cultivated in the fifth year. Using TSP increased the soil P-labile fraction by 107 and 114 %, for soybean-ryegrass succession and corn-white clover succession, respectively. After the end of the flooding period and post-soil drainage, a reduction of 17 and 13 % was observed in the P-labile and P-moderately labile fractions, in soybean-ryegrass, respectively. And the same fractions in the corn-white clover succession decreased 12 and 5 %, respectively. Using P fertilizer increases the fractions of P-labile, P-moderately labile, and P-less labile in the soil. Soil drainage after rice cultivation reduces the fractions of labile and moderately labile phosphorus in the soil, regardless of the crop succession used.

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ABSTRACT Exploring different fertilization strategies in an integrated crop-livestock system (ICLS) can enhance soil phosphorus (P) availability and improve soil quality, ultimately leading to higher yield. This study aimed to evaluate different fertilization strategies in ICLS and their effects on soil P fractions, soil quality and soybean grain yield in a tropical soil. Initiated in 2019, the experiment tested four fertilization strategies: 1) Conventional fertilization with P and K applied at soybean sowing (CF); 2) CF + N fertilization in the pasture phase (CF+N); 3) System fertilization with P and K applied in the pasture phase (SF) and; 4) SF + N fertilization in the pasture phase (SF+N). Nitrogen fertilization in the pasture (CF+N and SF+N) increased soil P availability by up to 32 %. Additionally, SF+N increased the contents of total and inorganic P extracted with NaOH and HCl by up to 12, 49 and 59 %, respectively, compared with CF. A similar trend was observed for the P legacy index, where SF was approximately 4.1 times higher than the CF. The metabolic quotient was also enhanced, and microbial biomass carbon (BMC) was increased in system fertilization treatments. However, soil physical properties, such as weighted mean diameter and geometric mean diameter, remained unaffected by the fertilization strategies. Soybean grain yield was 16 % higher in the treatment with SF+N, compared with CF, indicating that both the P and K fertilization strategies and the presence of N in the pasture can alter soybean yield. Soybean crop benefits from the enrichment of N in the soil via fertilization in the pasture phase, and, when combined with system fertilization, the benefits are enhanced by the greater availability of P, total P, and the index of legacy P in the soil.

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ABSTRACT Eucalyptus genus exhibits high nutrient use efficiency, but the phosphorus (P) balance in the soil under Eucalyptus stands is often negative, mainly due to higher P exportation in the wood after forest harvesting when compared with fertilization inputs. We evaluated the effect of phosphate fertilizers with varying solubilities and technologies on P balance and use efficiency in Eucalyptus, focusing on organic P (Po) mineralization. A randomized complete block design, with four blocks and six treatments, was used to test the P sources both as single sources and in mixtures. The P balance was calculated by considering fertilization as input and wood harvest as output. By adding P stocks from the soil and trees, we estimated the potential number of rotations (PNR). Relative agronomic efficiency (RAE), recovered P (Rec-P), and P use efficiency (P-UE) were also estimated. Before the experiment, soil P stocks were higher when P contents obtained through fractionation were considered. Phosphorus balance was positive in treatments with rock phosphate when considering total P applied. Organic P significantly influenced PNR, with increases ranging from one to four rotations. The P-UE was higher when soluble P was used. Treatments fertilized with phosphate complexed with humic substances had higher Rec-P and RAE. Soluble phosphate fertilizers promote high wood production but fail to meet long-term P needs due to their rapid uptake and depletion, resulting in negative P balance. In contrast, rock phosphate maintained positive P balances, suggesting it can sustain soil fertility and have a long-term effect on multiple rotations (legacy P), promoting sustainability. Nevertheless, Po is essential for soil fertility and P availability in Eucalyptus stands, contributing more than routine analysis suggests. It should therefore be considered in sustainable fertilizer management to ensure the long-term productivity and economic viability of Eucalyptus plantations.

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ABSTRACT Phosphorus (P) plays a crucial role in plant metabolism. However, its specific effect on biomass and stalk production in energy cane in tropical soil regions has not yet been fully clarified. This study aimed to evaluate the effect of P application rates on energy cane yield under two water regimes, determine critical soil P levels, and propose interpretive classifications for agronomic and fertilization recommendations. The experiment was conducted in containers in a controlled environment in a randomized block design with four P application rates (0, 60, 180, and 300 kg ha-1 of P2O5 applied as triple superphosphate), two water regimes (full irrigation and water deficit irrigation), and two energy cane varieties (Vertix 2 and Vertix 3) in a 4 × 2 × 2 factorial arrangement with three replications. The following factors were analyzed: biometric evaluations, stalk yield, gross sugar yield, definition of critical soil P levels, and classifications of soil P levels. The application rate of 180 kg ha-1 of P2O5 provided the best crop growth and yield (174 Mg ha-1 for Vertix 3 and 181 Mg ha-1 for Vertix 2). Critical soil P levels under the water deficit irrigation and full irrigation conditions, respectively, were 18 and 29 mg dm-3 P for the linear model, 19 and 29 mg dm-3 P for the quadratic model, and 23 and 31 mg dm-3 for the Inverse Mitscherlich model. Soil P levels for deficit irrigation and full irrigation were classified as very low (up to 16 mg dm-3, under both irrigation conditions), low (16–23 or 16–31 mg dm-3, resp.), intermediate (24–29 or 32–60 mg dm-3, resp.), high (30–58 or 61–120 mg dm-3, resp.), and very high (>58 or >120 mg dm-3, resp.). Energy cane has a higher P nutritional requirement compared with conventional sugarcane, highlighting the need to revise the phosphorus fertilization recommendation criteria. Therefore, the definition of specific P critical levels and content classifications for energy cane is essential to optimize fertilizer use efficiency, reduce environmental impacts, and promote more sustainable production systems.

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ABSTRACT Although Brazilian soils contain considerable reserves of total P, accumulated by constant phosphorus (P) application, most of it is preserved in non-labile and moderately labile fractions, which could not be efficiently exploited so far. This study aimed to evaluate microorganisms capable of accessing less available P fractions in two soils with different textures. A greenhouse experiment in a completely randomized design, in a factorial arrangement (2 × 5) with four replications, was carried out in the municipality of Bandeirantes, Paraná. The regional climate was classified as humid subtropical (Cfa) and the average temperature during the experimental cycle was 25.6 °C (max. 40 °C, min. 15 °C). Water was added to maintain humidity at around 60 % of the maximum water retention capacity (MWRC). The first factor consisted of two different-textured soils (sandy and clayey), taken from areas with little human interference. The second factor comprised the soybean treatments: T1 – control (no inoculation nor P fertilization); T2 – mineral fertilization (triple superphosphate); T3 – seeds inoculation with Bacillus strains; T4 – inoculation with arbuscular mycorrhizal fungi (AMF); T5 – co-inoculation with Bacillus and AMF strains. Response variables related to the agronomic performance of soybean were analyzed (shoot and root dry weight; number of pods per plant; nodulation; P content and P accumulation in shoot and roots), as well as variables related directly with microbial performance (degree of AMF colonization and soil available P content (Mehlich-1), an indicator of the P desorption dynamics of the microorganisms). In the sandy soil, AMF proved more effective in raising levels of available P (Mehlich-1) than the control. However, under the experimental conditions, the microorganisms did not significantly increase P availability in clayey soils. Nevertheless, AMF inoculation proved to be a promising possibility of improving P availability in soybean. Regardless of the soil texture studied — sandy or clayey —, the results of inoculation or co-inoculation were equivalent or superior to those of triple superphosphate fertilization and consistently better than those of the control, for most response variables.

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ABSTRACT Phosphorus in agriculture is an essential, limited, and strategic resource, and its sustainable management is a global challenge. Phosphorus (P) recovery as struvite (NH4MgPO4.6H2O) from manures and municipal and agro-industrial wastewaters has been considered one of the most sustainable technologies, based on the circular economy, to face challenges regarding P reserves and its use for conventional fertilizer production. Struvite is a slow-release P-fertilizer (5 % N, 12 % P, 10 % Mg), which could significantly reduce the Brazilian dependency on fertilizer imports. We found a large number of recent studies that show its predominant application for temperate and Mediterranean regions. However, its potential as a fertilizer and better use for subtropical and tropical regions, such as Brazilian agriculture, is still unknown. We highlight that: (i) crop responses reported were quite variable with few field studies carried out; (ii) the crop yield expected may be on average 10 % below those in soluble P sources; (iii) a potentially high residual effect should be effectively measured; (iv) promising use of struvite mixed with soluble P-fertilizers to produce high yields; (v) higher efficiency than manure, composts or phosphate powder rocks. In fact, there is a lack of studies carried out on subtropical and tropical soils and climates; none were found in Brazil. Therefore, the lack of studies on Brazilian soils is a barrier to a precise evaluation of struvite as a fertilizer for Brazil’s agricultural systems, especially for acidic Oxisols and no-till systems. Finally, struvite production from swine wastewater can expand in specific states in the South, Southeast, and Midwest of Brazil, where the swine production is concentrated. Struvite production technology might be easily adopted and affordable for medium- to large-scale confined swine operations, which could yield some 300,000 Mg of struvite per year.

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ABSTRACT Dynamics of phosphorus (P) distribution, availability, and accumulation in reservoirs are influenced by land use and management. This study aimed to evaluate the total P (TP) content in soil aggregates formed under different vegetation cover types and agricultural crops, analyze the inorganic and organic forms of P with different degrees of lability, evaluate the percentage of P adsorbed (P ads), and, investigate the interactions between the soil aggregate P-fractions evaluated and their physical and chemical properties. Three different cultivated areas (banana, BN; coffee, CF; and cocoa, CC) and a reference model (forest fragment, FS) were evaluated at three different points on an agricultural property. The areas are located on sloping terrain, as is most commonly the case in southeastern Brazil. Soil aggregates measuring 8.0–4.0 mm were selected from the 0.00-0.10 and 0.10-0.20 m topsoil layers. The following P fractions were sequentially extracted: SOLP (CaCl2), M3P (Mehlich-3), OHPi, OHPo (NaOH), HClP (HCl), OCLP (sulfuric digestion of the residual), and TP (the sum of all extracted P fractions). In addition, P adsorption potential was determined based on the percentage of P adsorbed (P ads). All P fractions correlated with the aggregate properties determined, including weighed average diameter, sand, silt, and clay contents, pH(H2O), ∆pH, total organic carbon, labile organic carbon, and humic substances. Phosphate fertilization, in association with soil properties in the cultivated areas, has led to an increase in TP levels and accumulation of non-labile P (OCLP) and moderately labile P (OHPi and OHPo) in the soil aggregates. A higher percentage of P ads was observed for the aggregates in the FS and CF areas. The CF area was closely associated with higher OHPi levels in the aggregates at 0.00-0.20 m soil layer; the CC area was closely associated with the highest TP and OCLP values in the aggregates at 0.00-0.20 m soil layer. The BN and CC areas were strongly associated with the SOLP, OHPo, and HClP fractions in the aggregates at 0.10-0.20 m soil layer. Interactions were observed among the properties associated with aggregation, particularly among SOLP, OHPo, P ads, soil acidity, and sand, silt, and clay contents. The edaphic property showing the highest number of correlations with P fractions was fulvic acid-carbon. This study highlights the need for changes in the type of phosphate fertilization and for the adoption of a more diverse agricultural matrix in terms of plant species in cultivated areas, especially in the CF areas.