Reactive Phosphate Rock Research Articles

Crops' Yield and Roots Response to Soil Phosphorus Distribution Resulting From Long-Term Soil and Phosphate Fertilization Management Strategies

We investigated labile P and roots distribution in the soil profile and their effect on phosphorus uptake and soybean and corn yield under different tillage systems and phosphate fertilization managements. In a long-term experiment fertilized with triple superphosphate (TSP) or reactive phosphate rock (RPR), where the fertilizer was band-applied in the crop row or broadcasted under conventional tillage (CT) or no-tillage (NT), we evaluated labile P (Bray-1) and root density distribution in depth, and crop yield, biomass production and P uptake by soybean (16th crop) and corn (17th crop). The soil disturbance in CT promoted more homogeneous soil P distribution while in NT there was a strong gradient in depth, with nutrient accumulation in the fertilizer application zone. In general, the average content of P in the 0–20 cm layer was similar for the two soil management systems and for the two application methods, but higher for TSP in relation to RPR. Root distribution of soybeans in NT and corn in both tillage systems showed a strong relationship with soil P distribution. The production of biomass, P uptake and grain yield of soybean in CT was influenced by phosphate fertilization management and generally presented lower performance than in NT, what did not occur for corn possibly due to a better P uptake efficiency compared to that of soybean. Greater stratification on the distribution of soil P and soybean and corn roots in NT did not represent any limitation on the nutrient uptake and yield of these crops, not even in the extreme case where the fertilizer was continuously broadcast on the soil surface. The influence of soil tillage management and phosphate fertilization was more evident in soybeans than corn.

Improved Alfalfa Phosphate Utilization Using Zeolite Amendments in Low pH Soil

Soil amendments are used to increase the solubility of phosphate rocks (PRs) such that they can supply phosphorus (P) to high P-demanding crops. Zeolites are naturally occurring aluminosilicate minerals that can solubilize PRs and increase P nutrient supply. This study sought to evaluate the effects of zeolite addition in PR mixtures in dry matter yield (DMY), nutrient accumulation, and alfalfa’s agronomic efficiency. The experiment was conducted in a greenhouse where treatments comprised of two zeolites types (clinoptilolite and stilbite), three P sources (triple superphosphate-TSP, Morocco PR, and Cajati PR), five P levels (0, 22, 44, 87, and 131 mg kg−1), and five zeolites ratios (w/w) based on P2O5 levels (0, 25, 50, 100, and 200%). Eleven cuts of alfalfa were taken to quantify DMY and P accumulation. Alfalfa dry matter yield and P accumulation increased due to P fertilization. Reactive PR (Morocco) was more effective than TSP to increase alfalfa DMY and P accumulation. Phosphorus levels in soil did not increase with reactive PR (Morocco) fertilization and zeolite amendment. Zeolite stilbite just increased P solubilization and accumulation by alfalfa plants in a 150–200% ratio (zeolite/PR) with the low-reactive PR (Cajati). Under this experiment’s conditions, zeolite was not an efficient amendment combined with P soluble and reactive PR sources to increase alfalfa DM yield and P accumulation. Large amounts of zeolite were necessary to provide the low-efficiency PR source solubilization to satiate alfalfa P demand.

Residual effects of rock phosphate on soybean growth at tidal swampland South Kalimantan

Phosphorus fertilizer application could be an option to improve soybean yield in Indonesia. As in tidal swampland, phosphate deficiency is one of the main obstacles in the soil because it fixates ferro as insoluble phosphates. This experiment aimed was to determine the residual effects of Reactive Phosphate Rock (RPR) in the second cropping season on soybean growth in tidal swampland of South Kalimantan. The experiment was conducted at Barambai Village, South Kalimantan. This study was set in a factorial randomized block design with sixth treatments and three replications. The treatments were farmer practice, P Fertilizer (SP 36), residual of RPR, residual of RPR with soluble P Bacteria, residual of RPR with mycorrhiza, residual of RPR with Rhizobium and Soluble P Bacteria. The residual effect of RPR treatments with rhizobium and soluble P bacteria in the second planting season gave higher plant height of soybean compared to farmer practice and SP 36 treatment. The residual effect RPR treatment with rhizobium increased soybean yield up to 40.9% compared to without RPR and microbe in second cropping season. The released soluble P derived from RPR is relatively slow, therefore the application of high-dose RPR increases crop production.

Direct application of reactive phosphate rock on improving maize yield in tidal swampland

Tidal swampland soil is characterized by low soil acidity and P availability, and high Al, Fe, S, and Na concentrations. Due to its productivity, tidal swampland needs an improved specific location technology. Reactive phosphate rock (RPR) which is characterized by its high reactivity and residual effect, and slow release is an option to overcome the P problem. The objective of this research was to study the effect of direct application of reactive phosphate rock in increasing maize yield in tidal swampland. The experiment was conducted at farmer’s field in Banyu Urip Village, Banyuasin District, South Sumatera. The research was arranged using randomized block design with four treatments and four replicates. The treatments consisted of farmers’ practice (P1), recommended single fertilizer (P2), recommended compound fertilizer (P3), and recommended RPR package (P4). The results showed that P4 treatment was able to improve plant growth and maize yield up to 25% compared to farmers’ practice. RPR package consists of RPR, dolomite, manure, Urea, and KCl of 1, 1, 2, 0.4, and 0.4 t ha−1, respectively, in tidal swamp land achieved maize production up to 8.25 t ha−1. This RPR package could be an applicable option in improving maize yield in tidal swamp land.

Efficacy of phosphate solubilizing Actinobacteria to improve rock phosphate agronomic effectiveness and plant growth promotion

In the rhizosphere, plant growth is facilitated by plant-growth-promoting rhizobacteria (PGPR). PGPRs like Actinobacteria can increase level of phosphate available to plants through P solubilization or mineralization. In this study we evaluated the ability of nine Phosphate Solubilizing Actinobacteria (PSA) to release P from rock phosphate (RP) and to promote maize growth and yield under in vitro and greenhouse conditions. Plate bioassay and pots culture experiment were conducted to investigate the effects of these PSA on maize plants development. High reactive rock phosphate (BG4, from Gantour phosphate mine, Morocco) and triple superphosphate (TSP) from Morocco were used as positive controls. BG4, is a reactive RP directly used to increase the P status of soil according to the Office Chérifien des Phosphates (OCP). For the other treatments, plants were grown in soil amended with low reactive RP obtained from the Khouribga phosphate mine (Morocco) and inoculated with selected PSA strains. Our findings have indicated that, PSA inoculation resulted in increasing of the assessed growth parameters and nutrient content in maize seedlings. Four of the tested strains (BC3, BC10, BC11 and P18) showed high performance efficiency in RP-solubilization and improved plant P nutrition and growth under low-P conditions i.e. amended with low reactive RP. Furthermore, inoculation with these latter strains also showed an important production of acid and alkaline phosphatase in the rhizosphere of the maize. The relative agronomic effectiveness (RAE) index showed that BC3(Streptomyces griseorubens) and BC11 (Norcardiopsis alba) increased the yield by 135.33 and 126.91% over the positive controls BG4. These strains can be considered as the most efficient to use rock phosphate as a crude phosphate fertilizer. Overall, our results demonstrate that PSA could constitute a promising solution to valorize low reactive RP in agriculture. The 16 S rRNA gene sequencing and phylogenetic analysis identified these isolates belong to Streptomyces and Nocardiopsis genera.

Increase of nitrogen-use efficiency by phosphorus fertilization in grass–legume pastures

Forage legumes intercropped with grasses add nitrogen (N) to the production system and may increase forage yields. However, both phosphate fertilization and the solubility of phosphorus (P) sources may affect this contribution. This study aimed to evaluate the response of Guinea grass (Panicum maximum) intercropped with legumes and fertilized with phosphate fertilizers of different solubility. Guinea grass was grown as a single crop, fertilized or not with mineral N, and intercropped with Java (Macrotyloma axillare), or dwarf pigeon pea (Cajanus cajan); phosphorus was applied as triple superphosphate (P-TSP) or Bayovar (P-Bay), plus a control without phosphorus. The highest forage yield and N accumulation was observed in Guinea grass fertilized with N and P, with 70,364 and 60,036 kg ha−1of dry matter, resulting in 977 and 1004 kg ha−1 of N accumulated by the plants for P-TSP and P-Bay, respectively. The introduction of legumes increased the N accumulation but decreased yield of Guinea grass. The highest nitrogen use efficiency (NUE) was found with P fertilization, i.e., 56% and 54% for P-TSP and P-Bay, respectively. The use of legumes intercropped with Guinea does not improve the effectiveness of the reactive rock phosphate. Therefore, the introduction of legumes intercropping with Guinea grass may be an alternative to N fertilization only when P is not applied to low fertile soils. Broadcast and incorporated P fertilization by the time of Guinea grass sowing, not only increases forage yields but also results in higher NUE regardless of P fertilizer solubility.

Distribution of Soil Phosphorus Fractions as a Function of Long-Term Soil Tillage and Phosphate Fertilization Management

The forms in which phosphorus (P) accumulates in soils are dependent on management practices, fertilizer sources, and methods of application, which may promote distinct P solubility and plant uptake. We aimed here to evaluate how soil tillage and phosphate fertilization strategies affected soil P fractions over 17 years and to identify best management practices for improving labile P fractions. The experiment was conducted in a very clayey Rhodic Ferralsol (Oxisol) with initially very low P availability, during 17 years under soybean and corn, fertilized with 35 kg P ha?1 year?1 . Treatments were two soil management systems (CT-conventional tillage and NT-no-till) and four phosphate fertilization strategies (TSP ? triple superphosphate or RRP ? reactive rock phosphate, applied to the crop furrow or broadcast). Soil samples were taken at five depth layers, and organic (Po), inorganic (Pi), and total P (Pt) were determined by Hedley?s sequential fractionation. CT resulted in a more homogeneous distribution of Pi fractions throughout the soil profile, while under NT there was a steep depth gradient characterized by Pi accumulation in the fertilizer application zone. NT resulted in accumulation of Pi in more labile fractions and higher accumulation of Po physically protected by aggregation, both compared to CT. Also, under NT with RRP, there was a great accumulation of Pi associated with calcium (HCl Pi) compared to TSP, especially when the fertilizer was broadcast applied. An accumulation of Po down to 20 cm (CT) and 10 cm (NT) was also detected, compared to Cerrado natural soil. NT and RRP positively affected legacy P fractions and can be recommended as strategies to improve P fertilizer use efficiency. Keywords: no-tillage, P fractionation, legacy P, P source, P distribution

Long‐term phosphate fertilization strategies evaluation in a Brazilian Oxisol

AbstractThere are concerns related to the application of phosphate fertilizers to weathered soils that present low soil test phosphorus (STP) due to P adsorption in iron oxyhydroxides. Furthermore, long‐term trials are needed to evaluate crop response to corrective P fertilization and its interaction with different maintenance P fertilization strategies in these soils. An experiment involving the combination of three initial corrective P fertilization schemes (control without P correction or with the application of 105 kg P ha−1 as triple superphosphate [TSP] or reactive rock phosphate [RRP]), four P maintenance strategies (a control without the application of maintenance P, or 35 kg P ha−1 yr−1 as TSP, RRP, or a mix of both) and two application methods was cultivated during 16 yr at the Embrapa Cerrados experimental station in Planaltina, DF, Brazil. Corrective P fertilization promoted an early crop yield response. In contrast, high crop yields were only obtained in control treatments with no corrective P fertilization after soil P stocks were increased to a minimum level. With increasing P stocks, broadcast application resulted in slightly better yields. The required residual P stocks in soil to obtain high yields were estimated as equivalent to 113.6 and 205.2 kg P ha−1 for TSP and RRP, respectively. These values allow for STP contents to increase to critical levels, whose value for TSP of 4.1 mg kg−1 Mehlich‐1 P is below that recommended for the region, possibly due to the contribution of organic P forms in the long‐term no‐tillage system.

Effect of reactive phosphate rock to corn on acid sulphate soil in South Kalimantan

In South Kalimantan, acid sulphate soil rich in total phosphorus (P), but poor in available P, because of fixing. Most of the crops on the soil have a symptom of P deficiency. Reactive Phosphate Rock (phosphateR) was a slow-release P fertilizer and has a longer residual effect. This is to research on the effect of phosphateR to corn on acid sulphate soil in South Kalimantan. This research was carried out to determine the effects of reactive rock phosphate and planting method of corn on acid sulphate soil. This study used a factorial randomized block design with two factors. The first factor of P fertilizer, namely: P Fertilizer (SP 36), farmer practice, phosphate rock, phosphate rock + Manure, phosphate rock+ organic fertilizer+ phosphate rock+compost. The second factor is the planting method i.e: exsisting planting method (70x25 cm), Zig Zag Method (70x12,5 cm). The N and K doses are determined based on soil nutrient status. The results showed that phosphate treatment gave the weight of corncob where phosphate treatment with zig zag method reached 21% compared SP-36 with zig zag method treatment. And the lowest results are shown in the treatment of farmer practice with exsisting methods reached 10.07 t/ha corncob of weight.

Dynamics of residual phosphorus forms under different tillage systems in a Brazilian Oxisol

Phosphorus (P) accumulation in soil, mainly from decades of agricultural use with frequent additions of phosphate fertilizers, results in a large reserve of this nutrient that can be exploited by farmers. However, the dynamics of soil P forms under the residual effect of phosphate fertilization is still little known. In an experiment located at Embrapa Cerrados, in Planaltina, DF, Brazil, corn or soybeans were grown during the summer for 17 years, receiving 35 kg of P ha−1 year−1. The same area was then cultivated with corn for 4 more years without the supply of this nutrient, in order to characterize the behavior of P fractions accumulated in the soil and identify those that contribute most to crop nutrition when phosphate fertilization is interrupted. Changes in total P (Pt), organic P (Po), inorganic P (Pi), and labile P extracted by the Bray-1, Mehlich-1 and Olsen methods (organic and inorganic) and organic carbon (C) were evaluated by means of samples obtained before and after cultivation without P fertilization in different soil layers subject to no-till (NT) or conventional tillage (CT), previously fertilized with reactive rock phosphate (RRP) or triple superphosphate (TSP) which were applied by broadcast spreading or band-applied to the planting row. The superficial layers were most responsible for crop nutrition in NT, especially in the mode of broadcast application, while in CT the relative contribution of each layer was less stratified. There was a drastic reduction in the stock of almost all P fractions, except for Po which showed an increase, notably in soil cultivated under CT (22% in the 0–10 cm layer), although the C content was reduced. This suggests that the little available inorganic fractions, partially replacing the labile fractions, were responsible for the supply of P to crops. This replacement was more effective in NT, since it could sustain greater P offtake by crops, despite the similar reductions in labile P fractions observed in both systems.

Financial analysis of direct application of reactive phosphate rock fertilizer on corn farming on upland acid soils

Indonesia has extensive upland acid soils, which is around 99.6 million hectares spread across Sumatera, Kalimantan and Papua Islands. The use of upland acid soils for food crops is an urgent need because of the government’s self-sufficiency target, including corn. The level of nutrient in upland acid soils is relatively low so it requires adequate input of ameliorant, inorganic and organic fertilizers to produce high corn yield. A demonstration farm of corn based on the direct application of reactive phosphate rock (RPR) fertilizer was carried out in rainy season 2018/2019 by involving three farmer groups as cooperative farmers, with an area of 50 ha in Margosari village, Metrokibang subdistrict, Lampung Timur Regency. This paper presents the results of financial analysis of corn farming at the demonstration farm area. Data was gathered from 52 farmers (43.7% of the cooperative farmers) which randomly selected as survey respondents. The results of the analysis showed that balanced fertilization using RPR as much as 1 t ha−1 as a source of P fertilizer was financially benefited to farmers. The average corn productivity of hybrid varieties reached 14.357 t ha−1 and it gave an R/C ratio of 1.8.

Response of Maize to Different Soil Residual Phosphorus Conditions

Large reserves of phosphorus (P) in Brazilian soils can be potentially used by crops. However, it is not well known how different tillage systems and past P fertilizer management strategies affect legacy P utilization. A trial was conducted in an Oxisol (Rhodic Haplustox) at Embrapa Cerrados, Federal District, Brazil to investigate the effects of different soil residual P conditions on maize yield. For 17 yr, annual summer crops were fertilized with 80 kg ha−1 yr−1 P2O5 in a split‐plot design consisting of eight treatments: no‐tillage system (NT) or conventional tillage (CT), fertilized with triple superphosphate (TSP) or reactive rock phosphate (RRP), applied to the crop furrow or broadcast. P fertilization was then discontinued and maize grown for 4 seasons relied on the residual soil P under NT or CT. Residual P use efficiency, calculated as a ratio between grain yield and total residual P in the soil, was greater under NT than CT, as a consequence of higher availability of P determined by Bray‐1, Mehlich‐1 and Olsen methods. Past use of RRP sustained better yields and higher residual P use efficiency, especially in NT, due to its lower solubilizing rate. P placement strategy did not change residual P use efficiency. We recommend assess amount of available P to identify sites in which residual P may sustain crop needs. Finally, the use of RRP, especially under NT, is a recommended management strategy for reducing phosphate fertilizer demand in heavily weathered soils of Central Brazil.Core Ideas No‐tillage system promotes efficient P use, especially after discontinued P supply. Due to slow solubilizing rate, reactive rock phosphate sustains better residual P availability. Fertilizer placement did not influence residual P use efficiency.

Radium in New Zealand agricultural soils: Phosphate fertiliser inputs, soil activity concentrations and fractionation profiles

Phosphate ores can contain high levels of 238U and its decay products. Of these decay products 226Ra is an important environmental contaminant, while 228Ra from 232 Th day may also be present, albeit at lower activity concentrations. Acid processing of phosphate ore to triple superphosphate elutes a large proportion of the 226Ra from the final product. However, fertiliser production in New Zealand generally avoids acid processing and instead uses single superphosphate and reactive phosphate rock to maintain crop yields, meaning that 226Ra is retained in the final product. As a first step towards characterising the human health impacts from fertiliser-borne radium, research was undertaken to identify loading and long-term accumulation of 226Ra and 228Ra in New Zealand agricultural soils, as well as the fractionation of 226Ra into different soil phases.Activity concentrations for 226Ra of up to 1.6 kBq/kg were determined in phosphate-containing fertilisers used in New Zealand. In contrast, 228Ra did not exceed 75 Bq/kg. Analysis of 40 New Zealand soils, covering a range of agricultural uses, showed activities of between (27–88) Bq/kg 226Ra and (21–102) Bq/kg 228Ra. Unexpectedly, there was also a strong correlation between the two radium isotopes. In 13 of the agricultural soils, all with very high available phosphate levels, the fractionation profile of 226Ra was determined. These data indicated that 226Ra largely remains immobile in the residual phase of the soil. Calcium and available phosphate were significantly correlated with binding of 226Ra into labile and non-labile fractions. Barium is also hypothesised to play a significant role in co-precipitating 226Ra into non-labile soil fractions. While a high percentages of 226Ra immobile in the non-labile fraction would allow for marked accumulation over time it may limit the availability for uptake into crops and thus the ionising radiation dose for consumers.

Maize Response to Leguminous Biomass Composted with Phosphate Rocks in the Northern Zone of Tanzania

A study was conducted to evaluate maize response to leguminous biomass composted with phosphate rocks (PRs) in a split plot design. Field experiments were conducted at Wang’waray Farmers Training Center (F.T.C) located in Babati District of Manyara region in the Northern zone of Tanzania between December 2013 and June 2015. Three leguminous (Crotalaria juncea, Lablab purpureus and Mucuna pruriens) strips were cultivated in 2013/14 to produce a biomass which was harvested at flowering to early podding stage and air dried. Air-dry biomass was composted with PRs from Minjingu (medium reactive PR) and Panda Hill (low reactive PR). Maize response to different treatments was evaluated across the field strips in 2014/15 season. The strips previously used to produce leguminous biomass were used as main plots and each strip was divided into seven subplots receiving different treatments at random. A medium term maize variety SC. 627 was used as a test crop. Average maize grain yields obtained from Crotalaria, Lablab and Mucuna strips reached 5.3, 4.5 and 4.0 t ha-1, respectively and were statistically different (P=.05). Application of Minjingu or Panda Hill PR alone didn’t increase maize grain yield above the control while Minjingu PR applied with urea or composted with biomass increased maize grain yield by 2.40 and 1.58 t ha-1, respectively above the control. Application of Panda Hill PR with urea or composted with biomass increased grain yield by 1.20 and 1.06 t ha-1, respectively above the control. The observed differences (0.82 and 0.14 t ha-1) were not statistically significant indicating that biomass composted with PR was as effective as the PR applied with urea.

The combination of Arachis pintoi green manure and natural phosphate improves maize growth, soil microbial community structure and enzymatic activities

We investigated the effect of the co-composting of Arachis pintoi (AP) as green manure with different sources of rock phosphate on maize growth and soil properties. Composts were prepared combining AP and different rock phosphates (simple superphosphate, apatite rock phosphate, reactive rock phosphate and thermophosphate), alone or in combination with AP. The incorporation of AP and natural phosphate was conducted in a greenhouse, and we investigated its effects on plant total dry matter, phosphorus absorption, microbial biomass carbon and phosphorus, total organic carbon, soil basal respiration, enzymatic activities (acid phosphatase, alkaline phosphatase and urease) and the soil microbial structure community. The application of natural thermophosphate phosphates with AP is an efficient management strategy for maize cultivation, with increases of more than 124% in maize dry matter, more than 300% in P uptake and 62% in soil microbial biomass carbon. The use of Arachis pintoi as green manure, combined with natural phosphate sources, represents an alternative fertilisation approach for maize cultivated on Entisols, enhancing the bioavailability of P from natural rock phosphate. It is a sustainable and financially attractive option to ensure the environmental integrity of cultivation, food and soil security.

Humic acid-phosphate fertilizer interaction and extractable phosphorus in soils of contrasting texture

Extractable phosphorus (P) in soil depends on soil test employed, reactivity of fertilizer and interaction of P added to the soil properties, including organic matter. The aim of this paper was to assess the contents of P extracted from Red Latosol (LVd) and Quartzarenic Neosol (RQ) samples, incubated with 0; 5; 10; 50 or 100 mg kg-1 C-humic acid (C-HA) and 400 mg kg-1 of P, via Araxa phosphate rock (AP), Bayovar reactive phosphate rock (BP) or single superphosphate (SS). Thus, it was adopted a five (C-HA concentrations) x three (P sources) factorial arrangement, using a randomized block design with three replications. The mixtures of soil, C-HA concentrations and P sources were incubated for 60 days; in sequence, the soil P was extracted by solutions of Bray-1, Mehlich-1 and Mehlich-3 and mixed ion exchange resin. In the LVd and RQ samples, the addition of C-HA reduced extractable phosphorus when the source was AP and BP. The levels of extractable P increased with the application of C-HA in RQ when the source was SS; the average concentration of 50 mg kg-1 C-AH provided the maximum extractable P by Bray-1, Mehlich-3 and mixed resin. The pH is the chemical attribute that most influence the extractable P content of the soil.

Phosphate fertilization strategies for soybean production after conversion of a degraded pastureland to a no-till cropping system

A considerable area of previously degraded pastureland in Brazil is appropriate for agricultural use, mostly for soybean cultivation. These degraded soils can be restored by establishing no-till systems which should protect the soil, enhance nutrient cycling, and be economically feasible. One of the main challenges when performing agricultural operations in these soils is soil phosphorus (P) status, due to the low levels and difficult management of this nutrient in highly weathered soils. This is mainly related to a lack of information regarding the best management strategy with respect to fertilizer sources and their placement and time of application. We hypothesized that applying P to the cover crop, rather than to the soybean furrow, is a better strategy for the production system, because it would improve P recycling and soil cover and guarantee better timing and operational efficiency in soybean sowing. A 4-year field trial examined the effect of P application (44kgPha−1year−1) using various P sources (RPR – Reactive Phosphate Rock, TP – Thermophosphate and TSP – Triple Superphosphate) at different times (black oat furrow or soybean furrow), on a sandy loam Oxisol of a degraded pastureland in Southern Brazil. A black oat (Avena strigosa Schreb) – soybean (Glycine max L. Merrill) cropping sequence was used for 4years after no-till establishment. Soil P content, plant nutrient uptake, black oat dry biomass yield, and soybean grain yield were assessed. Soil P content increased from 2.5 to 13.3mgdm−3 (0–0.20m depth) on average across all times and sources of P application after 4years. Different application times resulted in a residual P for black oat (when P was applied to soybean furrow) and soybean (when P was applied to black oat furrow). Soybean exhibited better use of residual P (based on nutrient uptake and grain yield) than black oat (based on effects on nutrient uptake and biomass yield). Black oat P uptake was positively correlated with soybean P uptake (r=0.71, p<0.01) and soybean yield (0.69, p<0.01). The use of the TSP source led to a greater P-use efficiency, which was about 67kg of black oat dry biomass for each kg of P applied to the black oat sowing furrow, and about 40kg of soybean grain for each kg of P applied to the sowing furrow of black oat or soybean. Compared to TSP, less soluble phosphate sources (RPR and TP) led to a two to three times lower P-use efficiency. Results suggest that, on a previously degraded sandy loam Oxisol, P application to cover crop boosts P recycling and improves soybean yield by improving soil cover, and increases operational efficiency at sowing, even at low soil P levels. The use of water-soluble P sources should be preferred over less-soluble sources for the application on cover crop furrow.

Solubilization of Bay&amp;#243;var Natural Phosphate Rock under the Drain Effect of Calcium and Phosphorus at Two Levels of Acidity

Natural phosphate rock (NP) solubilization in soils is dependent on the soil pH and its power to remove or drain (sink effect) P and Ca of the solution that is in equilibrium with the NP. The aim of this work was to evaluate the effect of acidity and P- and Ca-sinks on the solubilization of bayovar reactive rock phosphate (a phosphorite). Samples of this NP in aqueous suspension were placed in a cassette (Slide-A-Lyzzer G2 Dialysis Cassette) compartment and immersed in a beaker containing 150 mL of an aqueous solution with pH adjusted at 4.5 or 6.0, where P- and Ca-sinks individually or in their combinations, were applied. The tested sinks were: Anionic Resin (AR); Cationic Resin (CR); Mixed Resin (MR: AR + CR); Goethite (Goe); Goe + AR; Goe + CR and one control (NP only) in five replicates. Beakers (experimental units) were shaken for 12 h daily, at 130 rpm, until completing 30 days of equilibrium. The suspensions were filtered to extract solution-P from the residue on the filter paper; the labile-P was extracted from this residue using 0.8 mol·L-1 NH4Cl in 2 mol·L-1 HCl and, finally, the remainder P in the same residue together with the filter paper were subjected to nitric-perchloric acid digestion, to determine the P-residual in the extract. Goe caused greater solubilization of the NP, indicating that this P-sink was more effective than AR, causing similar or greater solubilization than CR. AR and CR, in a similar way, significantly restricted the trait characteristic of Goe (p < 0.05), at both pH values, in the solubilization of NP. Although Goe generally caused greater solubilization of the NP, it also caused the lower formation of labile-P. The CR presented, in general, the highest contents of solution-P, thus it triggered solubilization of NP without the immobilization of the solution-P, unlike the one with the AR that adsorbs it. In the lower pH condition (4.5), the solubilization of NP tended to be higher than at pH 6.0, although in a little effective way, compared to the effects of the sinks.

Ruzigrass Grown in Rotation with Soybean Increases Soil Labile Phosphorus

Crop rotations with species able to solubilize soil P can result in improved P availability for subsequent crops. Ruzigrass [Urochloa ruziziensis (R. Germ. and C.M. Evrard)] has been shown to increase soil available P, but there are few studies on its effect on soil P forms and how growing ruzigrass interacts with P fertilization, which is important in defining fertilization strategies. This study aimed to investigate soil P fractions resulting from cropping ruzigrass in rotation with soybean [Glycine max (L.) Merr.] fertilized with broadcast triple superphosphate (TSP) or reactive rock phosphate (RRP) and TSP applied to soybean furrows under no‐till. Soil samples were taken after ruzigrass desiccation and before soybean planting from long‐term experimental plots in Botucatu, in southeastern Brazil. Phosphate management included RRP and TSP broadcast on the soil surface, and TSP applied to soybean furrows, in the presence or absence of ruzigrass. Broadcast TSP increased labile (anion exchange resin‐extractable P) and moderately labile P fractions extracted with 0.1 M NaOH, whereas RRP increased moderately labile P extracted with HCl. There was no interaction between phosphate management configurations. Regardless of phosphate management, the presence of ruzigrass resulted in a lower residual‐P concentration in deeper soil layers and higher concentrations of labile and moderately labile P in the uppermost soil layers. Ruzigrass introduction into the cropping system resulted in higher soil labile P content compared with fallow, probably because it can take up moderately labile soil P fractions that are recycled into the system, regardless of the P fertilization strategy.Core Ideas Ruzigrass grown in soybean off‐season affects soil fertility. Soil P cycling by ruzigrass may result in benefits to next crops. Agronomic efficiency of phosphate fertilizers may be improved by ruzigrass.

Can phosphorus fertilizers sparingly soluble in water decrease phosphorus leaching loss from an acid peat soil?

AbstractThe potential risk of phosphorus (P) loss in surface run‐off can be decreased using sparingly soluble forms of P fertilizer (e.g. reactive phosphate rock (RPR)). However, it is unclear whether RPR can decrease P loss in leachate, especially when applied to soils with a small anion storage capacity (viz. P sorption capacity) and pH. Our hypothesis was that at low soil pH, the solubility of RPR would increase and result in P losses in leachate similar to those receiving single superphosphate (SSP), but at higher pH, less P would be lost from soils receiving RPR than SSP. Lysimeters containing a crushed, sieved acid mesic Organic (viz. peat) subsoil (30–60 cm) were limed to pH 4.5, 5.5 or 6.5 and treated with SSP or RPR at rates of 0, 50, 100 or 200 kg P/ha. Lysimeters were sown with ryegrass and watered over 12 months under controlled conditions and the leachate collected. Losses of filtered (&lt; 0.45 μm) reactive inorganic P (FRP) and unreactive or organic P (FUP) in leachate were greatest for pH 4.5 treatments and least for the pH 6.5 treatments. The difference in FRP and FUP leachate losses in RPR‐ and SSP‐treated soils was smaller at pH 4.5 and 5.5, and increased at pH 6.5 as losses from soils receiving RPR decreased compared to those receiving SSP. The results suggest that RPR can be used as a strategy to decrease P losses in leachate from an acid Organic soil with small P sorption capacity when limed to &gt; pH 5.5.