Soil Phosphorus Management Based on the Agronomic Critical Value of Olsen P

Fertilizer phosphorus (P) is generally added to agricultural soils to meet the needs of crop production. In this study, the crop yield and soil Olsen P were measured every year (5–18 years) at 16 winter wheat (Triticum aestivum L.) –maize (Zea mays L.) crop rotation sites in cinnamon soil (Luvisols in FAO system). The mean agronomic critical value of Olsen P for maize was 14.2 mg kg^?1 and for winter wheat was 14.4 mg kg^?1 when using the Liner-plateau and Mitscherlich models. The change in soil Olsen P was positively linearly correlated with the P budget (P < 0.01), and an increase of 4.70 mg kg^?1 in soil Olsen P for each 100 kg ha^?1 of P budget in the 0–20 cm soil layer. A model of P fertilizer recommendation rate that integrated values of the change in soil Olsen P in response to P budget and the agronomic critical value of Olsen P was used, in order to adjust current levels of soil Olsen P to the agronomic critical value at the experimental sites over the next 5 years, P fertilizer application rate should be in the range of 0–87.5 kg P ha^?1.     

Phosphorus accumulation, leaching and residual effects on crop yields from long-term applications in the subtropics

The effects of 25 years of annual applications of P fertilizer on the accumulation and migration of soil Olsen‐P, and the effects of soil residual P on crop yields by withholding P application for the following 5 years, were evaluated in a subtropical region. Annual application of P fertilizer for 25 years to crops in summer (groundnut), winter (wheat, mustard or rapeseed) or in both seasons raised the Olsen‐P status of the plough layer (0–15 cm) from initially very low (12 kg P ha^?1) to medium (18 kg P ha^?1) and very high levels (40–59 kg P ha^?1), depending on the amount of P surplus (amount of fertilizer applied in excess of removal by crops) (r = 0.86, P ≥ 0.01). However, only 4–9% of the applied P fertilizer accumulated as Olsen‐P to a depth of 15 cm (an increase of 2 mg kg^?1per 100 kg ha^?1 surplus P) in the sandy loam soil. In the following 5 years, the raising of 10 crops without P fertilizer applications decreased the accumulated Olsen‐P by only 20–30% depending upon the amount of accumulated P and crop requirements. After 29 years, 45–256 kg of residual P fertilizer had accumulated as Olsen‐P ha^?1 in the uppermost 150 cm with 43–58% below 60 cm depth; this indicates enormous movement of applied P to deeper layers in this coarse textured soil with low P retention capacity for nutrients. Groundnut was more efficient in utilizing residual P than rapeseed; however, for both crops the yield advantage of residual P could be compensated for by fresh P applications. These results demonstrated little agronomic advantage above approximately 20 mg kg^?1 Olsen‐P build‐up and suggested that further elevation of soil P status would only increase the risk of environmental problems associated with the loss of P from agricultural soils in this region.     

Transformation and recovery of fertilizer phosphorus applied to five Quebec Humaquepts

Abstract

Improving phosphorus (P) fertilizer efficiency while minimizing environmental impacts requires better understanding of the dynamics of applied P in soils. This study assessed the fate of fertilizer P applied in Quebec Humaquepts. A pot experiment with five textural Humaquepts, each receiving 0 (P0), 10 (P10), 20 (P20) and 40 (P40) mg P kg^?1 soil was conducted under barley (Hordeum vulgare L.)-soybean (Glycine max L.) rotations. A modified Hedley procedure was used for soil P fractionation. The clayey soils reached a plateau of dry matter at less P applied than the coarser-textured soils. Plant P uptake, soil labile inorganic P (resin-P?+?NaHCO₃-P_i) and moderately labile inorganic P (NaOH-P_i) increased proportionally with P rate. The coarser-textured soils had lower contents of labile and moderately labile P_i, but a larger increase in labile P_i than the finer-textured soils after receiving P additions. The applied P was retained primarily as soil labile P_i, accounting for 43–69% of total soil recovery of applied P, compared to 20–30% recovered as moderately labile P_i, and 7–29% assumed to be sparingly soluble P (HCl-P?+?H₂SO₄-P). The labile P_i recovery of applied P was linearly depressed with clay content, compared to a quadratic relation for the moderately labile P_i recovery. The results suggest the importance of accounting for soil texture along with soil P adsorption capacity when assessing the efficiency of applied P, P accumulation in soils and subsequently P nutrient management.     

Soil residual nitrogen under various crop rotations and cultural practices

Crop rotation and cultural practice may influence soil residual N available for environmental loss due to crop N uptake and N immobilization. We evaluated the effects of stacked vs . alternate‐year crop rotations and cultural practices on soil residual N (NH₄‐N and NO₃‐N contents) at the 0–125 cm depth, annualized crop N uptake, and N balance from 2005 to 2011 in the northern Great Plains, USA. Stacked rotations were durum (Triticum turgidum L.)–durum–canola (Brassica napus L.)–pea (Pisum sativum L.) (DDCP) and durum–durum–flax (Linum usitatissimum L.)–pea (DDFP). Alternate‐year rotations were durum–canola–durum–pea (DCDP) and durum–flax–durum–pea (DFDP). Both of these are legume‐based rotations because they contain legume (pea) in the crop rotation. A continuous durum (CD) was also included for comparison. Cultural practices were traditional (conventional tillage, recommended seeding rate, broadcast N fertilization, and reduced stubble height) and improved (no‐tillage, increased seeding rate, banded N fertilization, and increased stubble height) systems. The amount of N fertilizer applied to each crop in the rotation was adjusted to soil NO₃‐N content to a depth of 60 cm observed in the autumn of the previous year. Compared with other crop rotations, annualized crop biomass N was greater with DCDP and DDCP in 2007 and 2009, but was greater with DDFP than DCDP in 2011. Annualized grain N was greater with DCDP than CD, DFDP, and DDFP and greater in the improved than the traditional practice in 2010 and 2011. Soil NH₄‐N content was greater with CD than other crop rotations in the traditional practice at 0–5 cm, but was greater with DDCP than CD and DDFP in the improved practice at 50–88 cm. Soil NO₃‐N content was greater with CD than other crop rotations at 5–10 cm, but was greater with CD and DFDP than DCDP and DDCP at 10–20, 88–125, and 0–125 cm. Nitrate‐N content at 88–125 and 0–125 cm was also greater in the traditional than the improved practice. Nitrogen balance based on the difference between N inputs and outputs was greater with crop rotations than CD. Increased N fertilization rate increased soil residual N with CD, but legume N fixation increased N balance with crop rotations. Legume‐based crop rotations (all rotations except CD) reduced N input and soil residual N available for environmental loss, especially in the improved practice, by increasing crop N uptake and N immobilization compared with non‐legume monocrop.     

Soil phosphorus dynamics in a Vertisol as affected by cattle manure and nitrogen fertilization in soybean‐wheat system

Repeated application of phosphorus (P) as superphosphate either alone or in conjunction with cattle manure and fertilizer N may affect the P balance and the forms and distribution of P in soil. During 7 years, we monitored 0.5 M NaHCO₃ extractable P (Olsen‐P) and determined the changes in soil inorganic P (P_i) and organic P (P_o) caused by a yearly dose of 52 kg P ha^—1 as superphosphate and different levels of cattle manure and fertilizer N application in a soybean‐wheat system on Vertisol. In general, the contents of Olsen‐P increased with conjunctive use of cattle manure. However, increasing rate of fertilizer nitrogen (N) reduced the Olsen‐P due to larger P exploitation by crops. The average amount of fertilizer P required to increase Olsen‐P by 1 mg kg^—1 was 10.5 kg ha^—1 without manure and application of 8 t manure reduced it to 8.3 kg ha^—1. Fertilizer P in excess of crop removal accumulated in labile (NaHCO₃‐P_i and P_o) and moderately labile (NaOH‐P_i and P_o) fractions linearly and manure application enhanced accumulation of P_o. The P recovered as sum of different fractions varied from 91.5 to 98.7% of total P (acid digested, P_t). Excess fertilizer P application in presence of manure led to increased levels of Olsen‐P in both topsoil and subsoil. In accordance, the recovery of P_t from the 0—15 cm layer was slightly less than the theoretical P (P added + change in soil P — P removed by crops) confirming that some of the topsoil P may have migrated to the subsoil. The P fractions were significantly correlated with apparent P balance and acted as sink for fertilizer P.     

Fate of Carbon in Water-Stable Aggregates during Decomposition of 13C-Labeled Corn Straw

Fundamental knowledge about decomposition, fate of crop residue, and allocation of residue-derived carbon (C) in soil aggregates is essential to understand the C dynamics in soil. The incorporation of C derived from corn residue in water-stable aggregate fractions, particulate organic C (POC), and mineral-associated C (MAC) in soil were examined using the ¹³C tracer technique. Soil was treated with corn straw at the rate of 1% dry mass of soil brought to 66% of field capacity and incubated for 70 days at 25 °C. Samples were taken at 20, 35, and 70 days and analyzed for water-stable aggregates. Values for POC and MAC were analyzed for total C and ¹³C enrichment. The addition of corn straw caused a shift in the distribution of recoverable particles with significant decreases in <53-μm silts and clays, microaggregrates (53–250 μm), and smaller macroaggegates (250–2000 μm); however, the large macroaggegates (>2000 μm) increased significantly. Macroaggregates contained greater amount of C than microaggregates. The proportion of ¹³C recovered in the fractions <53 μm (silt and clay), 53–250 μm, and 250–2000 μm increased during decomposition of corn straw, whereas there was no significant change in >2000-μm fraction. Most (70–76%) of the soil organic C was affiliated with MAC (<53 μm). Carbon (¹³C) derived from corn straw decreased in POC but increased in MAC as decomposition proceeded. In the long term, microaggregate fraction appears to be involved in storage and stabilization of the C derived from corn straw and is important for soil quality and soil C sequestration point of view.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.     

Crop production impacts on soil phosphorus removal and soil test levels

An 8-year field study documented the impact of tillage, crop rotations, and crop residue management on agronomic and soil parameters at Brookings, South Dakota. The greatest annual proportion of above-ground biomass phosphorus (P) removed was from the grain (78–87% of total) although crop residue removed some P as well. Greater above-ground total biomass P (grain P + crop residue P) was removed from corn than from soybean and spring wheat crops mainly due to the greater corn grain biomass harvested. Cumulative above-ground biomass P removal was greatest for the corn-soybean rotation (214 kg P ha^?1), while it was lowest for the soybean-wheat rotation (157 kg P ha^?1). Tillage treatments within crop rotation or residue management treatments did not influence annual or cumulative P removal rates. Olsen extractable soil orthophosphate-P levels declined consistently through time from a mean of 40 µg g^?1 (2004) to 26 µg g^?1 (2011). Biomass P removal was calculated to be 15.7 ha^?1 yr^?1 to decrease Olsen extractable soil orthophosphate-P levels by 1 µg g^?1 yr^?1 over 8 years of the study.     

Effect of Chromium and Lead on Yield,Chemical Composition of Essential Oil,and Accumulation of Heavy Metals of Mint Species

A pot culture experiment was conducted to investigate the effect of increasing levels (30.0 and 60.0 mg kg^?1 soil) of chromium and lead on the yield, chemical composition of essential oil, and phytoaccumulation of heavy metals of three mint species (Mentha arvensis, M. piperita, and M. citrata). The fresh herbage yield of M. arvensis was not significantly affected by the application of chromium and lead, but its essential oil yield was significantly decreased by the application of chromium and lead as compared to the control. The fresh herbage, root yield, and essential oil yield of M. piperita were significantly increased and those of M. citrata were decreased by the increase in the levels of chromium and lead applications. The levels of α-pinene, β-pinene, sabinene, β-myrcene, limonene, menthone, and isomenthone in M. arvensis and M. piperita oil and of sabinene, pinene, and linalyl acetate in M. citrata oil were considerably affected by the application of chromium and lead to soils as compared to control plants. The concentrations of chromium in shoots and roots of mint species significantly increased as the levels of chromium in soil increased. The increases in the levels of lead in soil enhanced the concentrations of lead in the shoots and roots of mint species as compared to the control. The accumulations of chromium and lead were greater in the roots than in the shoots in all the three species of mint. Mentha piperita was found to be the most suitable crop for cultivation in the chromium- and lead-contaminated soils, followed by M. arvensis and M. citrata.     

Changes in P fractions and sorption in an Alfisol following crop residues application

With the emphasis on sustainable agriculture, attention has been increasingly turning to recycling of crop residues as a component of fertility management strategies for tropical soils. We assessed the effects of soybean residue (SR) and wheat residue (WR) applied either alone or in combination with fertilizer P (FP) on dynamics of labile P, distribution of P fractions, and P sorption in a semiarid tropical Alfisol by conducting a 16 w long incubation experiment. The amount of P added through crop residues, FP or their combinations was kept constant at 10 mg P (kg soil)^–1. Addition of SR or WR resulted in net increase of labile inorganic (P_i) and organic P (P_o) and microbial P throughout the incubation period, except that the WR decreased labile P_i during first 2 w due to P_i immobilization. The P immobilization associated with WR addition was, however, offset when fertilizer P was combined with WR. Generally, the increases in labile‐P fractions were larger with the SR and SR+FP than with the WR and WR+FP. The sequential fractionation of soil P at the end of 16 w indicated that a major part of added fertilizer P transformed into moderately labile and stable P fractions as evident from the increased NaOH‐P_i and HCl‐P in the FP treatment. In contrast, the addition of SR and WR alone or in combination with FP favored a build‐up in NaHCO₃‐P_i and ‐P_o and NaOH‐P_o fractions while causing a decrease in NaOH‐P_i and HCl‐P fractions. The addition of these crop residues also effectively decreased the P‐sorption capacity and hence reduced the standard P requirement of the soil (i.e., the amount of P required to maintain optimum solution P concentration of 0.2 mg P l^–1) by 24%–43%. Results of the study, thus, imply that soybean and wheat crop residues have the potential to improve P fertility of Alfisols by decreasing P‐sorption capacity and by redistributing soil P in favor of labile‐P fractions and promoting accretion of organic P.     

Phosphorus balances for arable soils in Southern England 1986–1999

The behaviour of P in a range of English arable soils was examined by plotting the change in resin P in the topsoil (ΔPres) at the end of a 3‐ to 5‐year period, against the P balance over the same period (fertilizer P applied minus offtake in crops, estimated from farmers’ reported yields and straw removal). Based on the assumption that values for offtake per tonne of crop yield used for UK arable crops are valid averages, 20–60% of ΔPres was explained by the balance. Applying excess P fertilizer increased Pres, and reducing P fertilizer use decreased it; typically 3–4 kg P ha^?1 was required for each mg L^?1ΔPres (6–8 kg ha^?1 for each mg L^?1 of Olsen P). About half the P balance seems to be resin extractable and this differed little between soil groups, except in cases of very low P (index 0) in which the P buffering was stronger, and on very high P soils (index 4/5) when buffering was less. However, on calcareous soils and red soils, when fertilizer was applied in accord with offtake, Pres fell by up to 4 mg L^?1 year^?1 (2 mg L^?1 yr^?1 olsen P) and to prevent this an extra 3–10 kg P ha^?1 year^?1 fertilizer was required. But on most non‐calcareous soils, replacing offtake maintained Pres, with perhaps slight rises on soils of low clay content or greater organic matter content. In soils under arable rotations, the apparent recovery of P from fertilizer was often around 100%, falling to 85% on Chalk soils and 75% on medium–heavy soils on limestone or Lower Chalk. The fate of the ‘missing’ P needs clarification. The case for corrections to current P fertilizer recommendations in the UK on certain soil types is discussed.     

Assessing the Feasibility of Olsen P and P Sorption Parameters in Acidic Soils

Plant-available phosphorus (P) and P adsorption capacities are important for crop growth in acidic soils. Olsen P test, which is based on extraction with bicarbonate for predicting the amount of soil P available to plants, was used in this work. Soil P-adsorption capacities were determined by Langmuir line equation. The purpose of this work was to examine the suitability of Olsen P for predicting phytoavailable P and P sorption parameters in acid soil. To this end, we (i) assessed the phytoavailable P by successively pot-cropping rice and (ii) P adsorption characteristics of soil and their relation with Olsen P. Plant-available P, estimated by Olsen P in tested soil, was correlated to labile P. Qm (phosphorus sorption maximum) was negatively correlated with K (P sorption strength). P buffering capacity of soils was P3 (the highest P rate) >P2 (the second highest P rate) >P1 (the lowest P rate) >P0 (no P adding) after 75 day’s rice growth, which indicated P replenishment capacity was different among P treatments. This also suggested that P of plant uptake may decrease soil buffering capacity, especially for soils that contained relatively lower amounts of P. Qm and K were not significantly correlated to Olsen P. Degree of P saturation and Olsen P shared the similar trend with the change of P application rates and sampling dates. We concluded P status in soil can be characterized by degree of P saturation and Olsen P in tested soil. They were able to explain P status from both agronomic and environmental aspects.

Abbreviations: Qm, P sorption maximum; K, P sorption strength; P3, highest P rate in soil; P2, second highest P rate in soil; P1, lowest P rate in soil; P0, P adding in soil.     

Correction and standardization of critical limit of zinc for maize (Zea mays L.) crop: Bangladesh perspective

Abstract

Critical limit (CL) determination of zinc (Zn) is very important for predicting response of maize crop to its application in soils and for the crop’s actual fertilizer requirement. This study was conducted at Bangladesh Agricultural Research Institute, Gazipur, to determine the CL of Zn for maize grown in 20 soils collected from the five Agro–Ecological Zones during January to March, and April to June of 2017. The available Zn content of soils and maize biomass were estimated utilizing the extraction method with 0.005?M diethylene triamine pentaacetic acid (DTPA). During January to March and April to June 2017, the amount of DTPA extractable Zn in different soils ranged from 0.60–3.25?mg?kg^?1 and 0.50–1.68?mg?kg^?1, respectively. During both periods of crop growth (January to March and April to June, 2017), the soil available zinc was negatively significantly correlated with soil pH, available P, exchangeable Ca, exchangeable Mg and positively significantly correlated with relative dry matter (DM) yield. Soil Zn also positively significantly correlated with maize tissue Zn content (r?=?0.521*). However, the CL of Zn were estimated to be 0.84?mg kg^?1 in soils and 26.1?mg kg^?1 in maize tissue for maize cropping as determined by Cate and Nelson’s (1965 Cate, R. B., and L. A. Nelson. 1965. A rapid method for correlation of soil test analysis with plant response data. International soil testing series technical Bulletin No. I North Caroline State University, Agricultural Experiment Statistics, Releigh, USA, pp. 135–136. [Google Scholar]) graphical procedure. Maize crop may respond to Zn application in soils containing Zn at/below the above level. This data may be used for predicting plant response to Zn fertilizer and development of crop Zn nutrition guide for maximum production.     

Impact of manure application on forms and quantities of phosphorus in a Chinese Cambisol under different land use

Purpose

It is critical to understand the effect of manure application on the availability of phosphorus (P) and the potential environmental contamination by runoff and leaching. However, previous studies generally focused on cultivated soil layer in single cropping systems. The aim of this study was to evaluate the effect of manure application on soil P forms and quantities to the 200 cm depth in a Chinese alkaline Cambisol in different cropping systems and the potential environmental implications.

Materials and methods

The sampling site, Shunyi District, is located in the peri-urban area of Beijing in the North China Plain, where large quantities of manure generated from intensive animal operations have been applied to agricultural fields. A field survey was carried out before sampling to identify soil sampling sites with long-term manure application and an adjacent area receiving no manure used for the same crop production. Soil samples from three cropping systems (vegetables, cereals, and trees) were vertically collected to a depth of 200 cm with the following depth increments: 0–20, 20–60, 60–90, 90–120, 120–160 and 160–200 cm. Soil samples were analyzed for plant-available P (Olsen P) and various P fractions by sequential P fractionation. Degree of P saturation (DPS) was also determined.

Results and discussion

Soil calcium bound P was the most abundant P fraction, followed by the residual P. Organic P only accounted for less than 5 % of total P in most of the soils. Manure application increased the levels of inorganic P (Pi), with higher proportions of Pi in labile forms than stable forms. After manure application for 8–15 year, available P (Olsen P) and DPS values of the 0–20 cm layer in all sites exceeded the threshold for Olsen P (60 mg?kg^?1) and DPS (30 %) and the risk of P loss by runoff is expected to significantly increase. The DPS values were generally lower than 30 % below 20 cm, indicating a minimal risk of P loss via leaching from deeper soil.

Conclusions

The results indicated that in typical peri-urban areas of the North China Plain, the on-going practice of manure application not only increased the size of each of the labile and non-labile P pools, but also caused a shift in the relative sizes of the different pools, regardless of the cropping systems. However, contrary to what was expected, soil P loss through surface runoff would be a greater concern than leaching following long-term manure amendment.     

Limitations of the Olsen method to assess plant-available phosphorus in reclaimed marsh soils

The aim was to assess the ability of bicarbonate-extractable P (Olsen P) to estimate total plant-available P (TPAP) in reclaimed marsh soils (Aeric Endoaquepts) which differed widely in P buffering capacity (PBC). Total plant-available P was estimated as the cumulative P uptake for a final concentration of 0.02 mg P/L in the soil solution which is the typical P requirement for field crops. The Olsen P estimated for that concentration was adopted as the critical level for crop production. We found that TPAP was better predicted by anion exchange resin-extractable P (AER-P) (65% of variance accounted for) than by Olsen P, probably because the effectiveness of the AER depends on the soil P buffering capacity, a factor that greatly influences the availability of P to plants. The critical Olsen P level was found to depend on those soil properties affecting the relationship between sorbed P and P in soil solution, viz. the P buffering capacity of soil, the Na/Ca mole ratio in the 1:1 soil:water extract, which explained 63 and 84% of the variance in the critical level, respectively, and the affinity of the sorbing surfaces for P. These properties must be taken into account when using Olsen P as the P index for fertilizer management.     

Evaluation of phosphorus management practices in East Mediterranean altered wetland soils

In this study, we re‐examined the common practice of intensive P fertilization in altered wetland soils even when soil test (Olsen‐P) indicates sufficient P levels (>10 mg/kg). We tested the effects of P fertilization on crop performance and P leaching in 36 lysimeters (1.5 m³) filled with peat, marl or alluvial materials and compared a new bone‐char‐based fertilizer to the common superphosphate. The lysimeter experiment consisted of the two fertilizer types, two application rates and a typical crop rotation of setaria (Setaria italica), pea (Pisum sativum) and tomatoes (Lycopersicon esculentum). By the end of each crop rotation, the yield was evaluated relative to P‐fertilization rates and soil‐test P. P fertilization resulted in increased Olsen‐P, soil‐solution P and P loss through leachates and a slight quality yield advantage in pea and tomato with no increase in yield of any crop. P budget calculations showed that plant uptake was not affected by the amount or type of applied P. We concluded that P fertilizer application should be significantly reduced because of limited crop response and increased P concentrations in leachates that may increase P loss to waterways especially in the marl soils. The ABC Protector exhibited slow P release, but its environmental implications should be further studied.     

Using diffusive gradients in thin films technique for in-situ measurement of labile phosphorus around Oryza sativa L. roots in flooded paddy soils

Behavior of phosphorus(P) in flooded rice soil is controlled by iron(Fe) redox cycling in root-zone. In this study, we applied a novel approach—the diffusive gradients in thin films(DGT) technique—for investigating the in-situ distribution of labile phosphorus(P) and Fe in close proximity to Asian rice(Oryza sativa L.) roots at submillimeter to millimeter spatial resolutions during the seedling and booting stages. We conducted a seven-year field experiment under rice-wheat rotation with different P fertilizer treatments. The results showed a significant and strong positive relationship of the average DGT-labile P concentration with soil Olsen P(R2= 0.77, P < 0.01) and with rice total P concentration(R²= 0.62, P < 0.05). Furthermore, results on one-and two-dimensional changes of DGT-labile P indicated that fertilization only in the wheat season produced sufficient amounts of labile P in the flooded paddy soils, similar to when fertilizer was applied only in the rice season;dissolved P concentrations, however, were lower. A co-occurrence and significant positive correlation(P < 0.01) between DGT-labile P and Fe indicated Fe-coupled mobilization of P in flooded paddy soils. These results collectively indicated that the DGT technique provided information on in-situ distribution of labile P and its variability in close proximity to rice roots. This suggests that the DGT technique can improve our understanding of in-situ and high-resolution labile P processes in paddy soils and can provide useful information for optimizing P fertilization.     

Long-Term Effects of Tillage and Manure Applications on Soil Phosphorus Fractions

Application of manure on the basis of crop nitrogen (N) need increases the level of soil phosphorus (P), which is concern for deterioration of surface water quality. Soil samples were collected from a long-term field study to investigate the impact of crop N need–based manure application on soil P fractions and P adsorption and release kinetics. The field experiment was initiated in 1990. The soil was moderately well-drained Kennebec (fine silty, mixed, mesic Cumulic Hapludolls). No-tillage (NT) and conventional-tillage (CT) treatments were established in main plots, and subplots had five N treatments, including a control, and annual application of 84 or 168 kg N ha^?1 applied as ammonium nitrate (NH₄NO₃) or beef (Bos taurus) manure. Manure at the high N application rate had significantly greater Bray 1 P under NT than under CT at 0- to 5-cm soil depth. Nitrogen fertilizer treatments were not significantly different than the control for Bray 1 P. Continuous application of manure at the high N rate significantly increased all Hedley P fractions; however, the major increase was observed in high bioavailable P pools [iron oxide (FeO) P and sodium bicarbonate (NaHCO₃) P_i] and hydrochloric acid (HCl) P fractions. Soil organic P (P_o) pools, including both labile (NaHCO₃-P_o) and resistant [sodium hydroxide (NaOH) P_o], were increased by application of N from any source, suggesting biomass production and return of residue to soil surface was the responsible factor. Continuous application of manure based on N need also significantly increased FeO-P, NaHCO₃-P_i, and HCl-P fractions at lower soil depths (5–15 and 15–30 cm). Results from the P-adsorption study suggest that ability of soil to adsorb additional P was decreased by manure application and that EPC₀ was increased. Maximum desorbable P was observed for manure treatments under NT, although the release constant k (h^?1) was significantly less than with fertilizer N treatments.     

Assessing soil P fractions changes with long-term phosphorus fertilization related to crop yield of soybean and maize

Long-term P Fertiliser application increases soil phosphorus (P) labile fractions, which can be associated with crop P uptake and grain yield and are useful to improve fertilizer recommendations. Research aims were to evaluate in long-term experiments with different P Fertiliser application in a Mollisol and a Vertisol: (a) the changes of soil P fractions and (b) the relationship between soil P fractions with long-term P Fertiliser application, with accumulated apparent P budget, grain P, total P uptake, soybean (Glycine max L.Merr.) and maize (Zea mays L.) grain yield. Soil P fractions were measured after 1 and 9 year since the beginning of the long-term experiments. Experiments included an initial Fertiliser application rate of 200 kg P ha⁻¹ and annual P Fertiliser application rate of 36 kg P ha⁻¹. Bray1-P, total, organic, and inorganic P in fine (<53 μm) and coarse (>53 μm) (CF) soil fractions, and in NaHCO₃ extract were measured. Initial P Fertiliser application increased inorganic and total P fractions. However, Bray1-P, total P in NaHCO₃ extract and in the CF were the fractions that most increased with continuous long-term P Fertiliser application in both sites. In the Mollisol, maize grain yield was unrelated to long-term P Fertiliser application. In the Vertisol, total P in NaHCO₃ extract, and total and organic P in the CF were more closely related to soybean grain yield than Bray1-P. We proposed soil P indices of labile inorganic and organic P that showed close relationships with soybean grain yield and may be useful to improve the diagnosis of P soil fertility.