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.     

Long-Term Wheat Residue Management and Supplementary Nutrient Input Effects on Phosphorus Fractions and Adsorption Behavior in a Vertisol

The management of crop residues coupled with external nutrient inputs is important for improving and conserving soil fertility and productivity. We assessed the long-term effects of three wheat residue management options (RMO) (residue burning, incorporation, and surface retention) in combination with three supplementary nutrient inputs (SNI) [control, fertilizer, and farmyard manure (FYM)] on phosphorus (P) fractions and adsorption behavior of a Vertisol under soybean–wheat system. Wheat residue incorporation and retention improved the labile inorganic P [sodium bicarbonate (NaHCO₃-P_i)] by 3.2 and 5.0 mg kg^?1 and the labile organic P (NaHCO₃-P_o) by 2.4 and 4.2 mg kg^?1, respectively, as compared to residue burning. The soils under residue incorporation and retention had 38 and 26% more moderately labile organic P [sodium hydroxide (NaOH-P_o)], respectively, than the soil under residue burning. The SNI either as fertilizer or FYM further enhanced NaHCO₃-P_i, NaHCO₃-P_o, and NaOH-P_o. In contrast, less labile P fractions [hydrochloric acid (HCl)-P and residual-P] remained unaffected by RMO and SNI treatments. Residue retention or incorporation decreased P adsorption over the residue burning for all the three nutrient inputs. The P-adsorption data fitted well to the Langmuir equation (R² ranged from 0.970 to 0.994). The P-adsorption maximum (b), bonding energy constant (k), differential P-buffering capacity (DPBC), and standard P requirement (SPR) were lower with residue incorporation or surface retention than with residue burning. The SPR followed the order residue burning > incorporation > retention for RMOs and control > fertilizer > FYM for SNI treatments. The NaHCO₃-P_i, NaHCO₃-P₀, and NaOH-P_o had negative correlation with P-adsorption parameters and showed positive correlation with soybean P uptake. Wheat residue incorporation or retention plus FYM could be an effective strategy for enhancing the P fertility of Vertisols under a soybean–wheat system.     

Growth,P uptake in grain legumes and changes in rhizosphere soil P pools

In soils with low P availability, several legumes have been shown to mobilise less labile P pools and a greater capacity to take up P than cereals. But there is little information about the size of various soil P pools in the rhizosphere of legumes in soil fertilised with P although P fertiliser is often added to legumes to improve N₂ fixation. The aim of this study was to compare the growth, P uptake and the changes in rhizosphere soil P pools in five grain legumes in a soil with added P. Nodulated chickpea (Cicer arietinum L.), faba bean (Vicia faba L.), white lupin (Lupinus albus L.), yellow lupin (Lupinus luteus L.) and narrow-leafed lupin (Lupinus angustifolius L.) were grown in a loamy sand soil low in available P to which 80 mg P kg⁻¹ was added and harvested at flowering and maturity. At maturity, growth and P uptake decreased in the following order: faba bean > chickpea > narrow-leafed lupin > yellow lupin > white lupin. Compared to the unplanted soil, the depletion of labile P pools (resin P and NaHCO₃-P inorganic) was greatest in the rhizosphere of faba bean (54% and 39%). Of the less labile P pools, NaOH-P inorganic was depleted in the rhizosphere of faba bean while NaOH-P organic and residual P were most strongly depleted in the rhizosphere of white lupin. The results suggest that even in the presence of labile P, less labile P pools may be depleted in the rhizosphere of some legumes.     

Transformation of fertilizer P in a Vertisol amended with farmyard manure

Availability, fixation, and transformation of added P were studied in a 16-week incubation experiment with a Vertisol amended with farmyard manure in pots with 500 g soil each. P availability, as measured by Olsen P, decreased for up to 8 weeks with various rates of added P, when no manure was applied. In the presence of farmyard manure, P availability decreased during the first 6 weeks and then showed a considerable increase from the 8th week onwards. P fixation increased for up to 8 weeks with the rates of P in the absence of manure. With manure application, P fixation increased only during the first 6 weeks and thereafter decreased continuously. Thus the presence of farmyard manure shortened the period of P fixation and promoted its availability. After 16 weeks of incubation, when manure and fertilizer P were applied together, P was transformed into labile organic (NaHCO₃–P), moderately labile organic P (NaOH-P), and calcium-bound inorganic P (HCl-P). When manure was not applied. P accumulated predominantly as labile inorganic (NaHCO₃–P), moderately labile inorganic (NaOH-P), and inorganic HCl-P. The application of farmyard manure enriched long-term P fertility through NaHCO₃–P and NaOH–P and a shortterm P supply as HCl-P. All fractions except inorganic NaOH-P showed good relationships with Olsen P.     

Soil legacy phosphorus after 10 years of annual dairy liquid manure application in a no-tillage system

The benefits of manure as a source of nutrients for plants and to improve soil quality are well-known. Monitoring of manure application is needed if environmental issues are to be prevented. In particular, the availability and accumulation of phosphorus (P) has to be subject to rigorous monitoring. This study aims to both evaluate the efficacy of the resin method in extracting inorganic labile P in soils under the long-term application of dairy liquid manure (DLM), and verify the influence of DLM on the recovery of applied P and soil legacy P. To realize our objectives, two long-term field experiments were established under a no-tillage system with annual DLM application on sandy clay loam (sandy Oxisol) and clayey (clayey Oxisol) soils. Treatment consisted of DLM applications (0, 60, 120, 180 m³ ha⁻¹ year⁻¹), independent of mineral fertilizer. Soil samples were taken from the 0–5, 5–10 and 10–15 cm layers after 10 years from the beginning of the trial. A single extraction with resin underestimated inorganic labile P; however, successive extractions were able to take up 43% and 26% of the total P in sandy and clayey Oxisols, respectively, whereas in a single extraction the take-up was 17% and 8% from the same soils, respectively. The resin method was more effective in extracting P from the sandy Oxisol. Thus, when interpreting soil P contents for fertilizer planning, the soil texture should be taken into account. DLM application decreased P recovered from applied P, ranging from 54% to 83% (sandy), and 43% to 67% (clayey), and substantially increased soil legacy P.     

Surface runoff phosphorus (P) loss in relation to phosphatase activity and soil P fractions in Florida sandy soils under citrus production

Phosphorus losses by surface runoff from agricultural lands have been of public concern due to increasing P contamination to surface waters. Five representative commercial citrus groves (C1-C5) located in South Florida were studied to evaluate the relationships between P fractions in soils, surface runoff P, and soil phosphatase activity. A modified Hedley P sequential fractionation procedure was employed to fractionate soil P. Soil P consisted of mainly organically- and Ca/Mg-bound P fractions. The organically-bound P (biological P, sum of organic P in the water, NaHCO₃ and NaOH extracts) was dominant in the acidic sandy soils from the C2 and C3 sites (18% and 24% of total soil P), whereas the Ca/Mg-bound P (HCl-extractable P) accounted for 45-60% of soil total P in the neutral and alkaline soils (C1, C4 and C5 soils). Plant-available P (sum of water and NaHCO₃ extractable P fractions) ranged from 27 to 61 mg P kg⁻¹ and decreased in the order of C3>C4>C1>C2>C5. The mean total P concentrations (TP) in surface runoff water samples ranged from 0.51 to 2.64 mg L⁻¹. Total P, total dissolved P (TDP), and PO₄³⁻-P in surface runoff were significantly correlated with soil biological P and plant-available P forms (p<0.01), suggesting that surface runoff P was directly derived from soil available P pools, including H₂O- and NaHCO₃- extractable inorganic P, water-soluble organic P, and NaHCO₃- and NaOH-extractable organic P fractions, which are readily mineralized by soil microorganisms and/or enzyme mediated processes. Soil neutral (55-190 mg phenol kg⁻¹ 3 h⁻¹) and natural (measured at soil pH) phosphatase activities (77-295 mg phenol kg⁻¹ 3 h⁻¹) were related to TP, TDP, and PO₄³⁻-P in surface runoff, and plant-available P and biological P forms in soils. These results indicate that there is a potential relationship between soil P availability and phosphatase activities, relating to P loss by surface runoff. Therefore, the neutral and natural phosphatase activities, especially the natural phosphatase activity, may serve as an index of surface runoff P loss potential and soil P availability.     

Phosphorus Fractionations in Acidic Piedmont Rice Soils

Piedmont lands in Bangladesh, India, Nepal, and many other Asian countries are important rice-growing soils, but most of the soils are potentially phosphorus (P) deficient because of low pH. Phosphorus fractions of rice-growing acidic piedmont soils were determined. Soil samples were amended with 100 and 200 mg P kg^?1 soil, and a control soil without P amendment was maintained. The samples were analyzed for the following fractions: solution P, labile pool [sodium bicarbonate (NaHCO₃) P], alkali-extracted inorganic pool [sodium hydroxide (NaOH) P_i], organic pool (NaOH P_o), acidic pool [sulfuric acid (H₂SO₄)?hydrochloric acid (HCl) P], and residual P. About 98% of the applied P in soils was extracted by the sequential extraction employed in the present experiment. The mean total P concentration in 10 acidic Piedmont soils was 247 ppm, of which only 0.12% was in solution, 8% labile (NaHCO₃), 16% NaOH-extracted inorganic, 32% resistant organic, 18% relatively recalcitrant acidic, and 25% residual. Application of P fertilizer increased mainly the labile P fraction, which would be easily available to wetland rice. Solution P was positively and significantly correlated with pH_KCl (r = 0.64, P < 0.05) and negatively correlated with clay (r = ?0.77, P < 0.01). A negative and significant correlation of NaHCO₃-P was observed with pH_H2O (r = ?0.62, P < 0.05). Solution P showed a negative and significant relationship with NaOH-P_i (r = ?0.63, P < 0.05). A significant and negative relationship of solution P was also observed with acid P (r = ?0.78, P < 0.01) and residual P (r = ?0.82, P < 0.01). The relationship of NaHCO₃-P with NaOH-P_i was positive (r = 0.70, P < 0.05) and significant. Similarly, a positive and significant relationship (r = 0.89, P < 0.01) between NaOH-P_i and acid P was observed, and acid P was positively and significantly correlated with residual P (r = 0.84, P < 0.01).     

Addition of organic and inorganic P sources to soil – Effects on P pools and microorganisms

Phosphorus deficiency is wide-spread due to the poor solubility of soil P and the rapid formation of poorly available P after P addition. Microbes play a key role in soil P dynamics by P uptake, solubilisation and mineralisation. Therefore a better understanding of the relationship between type of P amendment, microbial activity and changes in soil P pools is important for a better management of soil P. A P deficient soil was amended with two composts (low P or high P), two crop residues (low P or high P), and inorganic P (KH₂PO₄) at low and high P, and incubated for 56 days. Composts were added at 20 g kg⁻¹ resulting in a total P addition of 4.1 mg kg⁻¹ soil with the low P compost and 33.2 mg kg⁻¹ soil with the high P compost. The same amount of P was added with the other amendments (residues and inorganic P). All amendments increased cumulative respiration, but microbial biomass and the abundance of bacteria and fungi (assessed by phospholipid fatty acid analysis) increased significantly only in soils with organic amendments, with greater increases with residues. The concentration of the inorganic P pools NaHCO₃-P_i, NaOH-P_i and HCl-P increased significantly within 5 h after amendment, particularly with high P amendments. Over the following 56 days, labile inorganic P was converted mainly into non-labile inorganic P with inorganic P addition whereas labile and non-labile organic P was formed with organic amendments. It is concluded that organic P sources, particularly those with high P concentration can stimulate the formation of organic P forms in soils which may provide a long-term slow release P source for plants and soil organisms.     

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.     

Soil Colloidal P Release Potentials under Various Polyacrylamide Addition Levels

Anionic polyacrylamide (PAM) can prevent soil erosion, but its effect on fine particulate phosphorus (P), such as colloidal P, has not been thoroughly examined. The effects of PAM on the release potentials of water‐dispersible colloids (WDC) and total P, molybdenum‐reactive P (MRP), and molybdenum‐unreactive P (MUP) in the colloidal and truly dissolved phases (i.e., TP_coll, MRP_coll, MUP_coll, TP_truly, MRP_truly, and MUP_truly) from six soils across South China were tested in this study. The results showed that the release potentials of TP_coll in the control treatments were 6·9–46·1 mg kg⁻¹ and generally highest in sandy loam soil. Following low (12·5 kg ha⁻¹), middle (25 kg ha⁻¹), and high (50 kg ha⁻¹) levels of PAM application, the release potential of TP_coll decreased by 41·7, 63·2, and 77·4% compared to the control group, respectively. Additionally, PAM may trigger MRP_coll and TP_truly releases in sandy loam and/or silt soils, and for most soils, MRP_truly and MUP_truly showed the highest release potentials at middle or high PAM levels. A significant PAM application level by soil site interaction for the release potentials of WDC and colloidal P was observed. Multiple linear regression showed that the PAM rate combined with soil sand content can successfully predict the release potentials of WDC (R² = 0·552, p  < 0·001) and TP_coll (R² = 0·738, p  < 0·001). Our results suggest that PAM can effectively reduce the loss of soil colloids and colloidal P, while its effects are related to both application level and soil texture. Copyright © 2017 John Wiley & Sons, Ltd.     

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.     

The effect of soil phosphorus on particulate phosphorus in land runoff

Accumulation of surplus phosphorus (P) in the soil and the resulting increased transport of P in land runoff contribute to freshwater eutrophication. The effects of increasing soil P (19–194 mg Olsen‐P (OP) kg⁻¹) on the concentrations of particulate P (PP), and sorption properties (Q_max, k and EPCo) of suspended solids (SS) in overland flow from 15 unreplicated field plots established on a dispersive arable soil were measured over three monitoring periods under natural rainfall. Concentrations of PP in plot runoff increased linearly at a rate of 2.6 μg litre⁻¹ per mg OP kg⁻¹ of soil, but this rate was approximately 50% of the rate of increase in dissolved P (< 0.45 μm). Concentrations of SS in runoff were similar across all plots and contained a greater P sorption capacity (mean + 57%) than the soil because of enrichment with fine silt and clay (0.45–20 μm). As soil P increased, the P enrichment ratio of the SS declined exponentially, and the values of P saturation (P_sat; 15–42%) and equilibrium P concentration (EPCo; 0.7–5.5 mg litre⁻¹) in the SS fell within narrower ranges compared with the soils (6–74% and 0.1–10 mg litre⁻¹, respectively). When OP was < 100 mg kg⁻¹, P_sat and EPCo values in the SS were smaller than those in the soil and vice‐versa, suggesting that eroding particles from soils with both average and high P fertility would release P on entering the local (Rosemaund) stream. Increasing soil OP from average to high P fertility increased the P content of the SS by approximately 10%, but had no significant (P > 0.05) effect on the P_sat, or EPCo, of the SS. Management options to reduce soil P status as a means of reducing P losses in land runoff and minimizing eutrophication risk may therefore have more limited effect than is currently assumed in catchment management.     

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.     

Organic amendments differ in their effect on microbial biomass and activity and on P pools in alkaline soils

Organic amendments could be used as alternative to inorganic P fertilisers, but a clear understanding of the relationship among type of P amendment, microbial activity and changes in soil P fractions is required to optimise their use. Two P-deficient soils were amended with farmyard manure (FYM), poultry litter (PL) and biogenic waste compost (BWC) at 10 g?dw?kg^?1 soil and incubated for 72 days. Soil samples were collected at days 0, 14, 28, 56 and 72 and analysed for microbial biomass C, N and P, 0.5 M NaHCO₃ extractable P and activity of dehydrogenase and alkaline phosphomonoesterase. Soil P fractions were sequentially extracted in soil samples collected at days 0 and 72. All three amendments increased cumulative CO₂ release, microbial biomass C, N and P and activity of dehydrogenase and alkaline phosphomonoesterase compared to unamended soils. The increase in microbial biomass C and N was highest with PL, whereas the greatest increase in microbial biomass P was induced with FYM. All three biomass indices showed the same temporal pattern, with the highest values on day 14 and the lowest on day 72. All amendments increased 0.5 M NaHCO₃ extractable P concentrations with the smallest increase with BWC and the greatest with FYM, although more P was added with PL than with FYM. Available P concentrations decreased over time in the amended soils. Organic amendments increased the concentration of the labile P pools (resin and NaHCO₃-P) and of NaOH-P, but had little effect on the concentrations of acid-soluble P pools and residual P except for increasing the concentration of organic P in the concentrated HCl pool. Resin P and NaHCO₃-P_i pools decreased over time whereas NaOH-P_i and all organic P pools increased. It is concluded that organic amendments can provide P to plants and can stimulate the build-up of organic P forms in soils which may provide a long-term slow-release P source for plants and soil organisms.     

Distribution of Inorganic and Organic Phosphorus Fractions in Two Phosphorus-Deficient Soils as Affected by Crop Species and Nitrogen Applications

It is desirable to know the distribution of phosphorus (P) fractions in soil so that plants may use P efficiently. Here we report the dynamics of inorganic and organic P in P-deficient black and rice soil cropped by soybean, white lupin, and maize supplied with nitrogen (N) inputs by N fixation and urea fertilizer. Inorganic P fractions of the three cropped soils could be ranked as O-P (organic phosphorus) > Al-P (aluminum phosphorus) > Fe-P (iron phosphorus) > Ca₁₀-P (calcium-10 phosphorus) > Ca₈-P (calcium-8 phosphorus) > Ca₂-P (calcium-2 phosphorus), irrespective of soil type. The potential of various inorganic P fractions to plant nutrition differed between soybean and white lupin. The percentage of total P present as inorganic P was affected by crop, soil type, and N source. In black soil, the change of organic P fraction induced by N fixation was larger than by urea application. The moderately labile organic P (MLOP) concentration was not affected significantly by soil type and crop species, and it was probably the main P source to the inorganic P fraction because the correlation between the two pools was high (r = 0.945; P < 0.05). Crop species differed in their uptake of inorganic and organic P from soil. Though P fraction concentrations varied between black soil and rice soil, their response to crop species and N source was similar. The amounts of P removed from soil were affected by N source. The right choice of crop species and the application a suitable N source may increase crop yield and P uptake by plant in P-deficient soils.     

Relationship of Soil Phosphorus Pools with Bray 1 Phosphorus in Some Acid Soils of Central Southern Cameroon

We measured phosphorus (P) chemical pools of genetic horizons of five representative pedons from central southern Cameroon. Our objectives were to assess the relative abundance of P pools and to empirically model their interrelations and contributions to a P availability index. The fractionation scheme followed a modified Hedley sequential procedure with anion exchange resin, 0.5 M sodium bicarbonate (NaHCO₃; Pi and Po), 0.1 M sodium hydroxide (NaOH; Pi and Po), 0.5 M hydrochloric acid (HCl; Pi), and 2 M sulfuric acid (H₂SO₄) after soil ignition at 550 ^oC. Resin P, sodium bicarbonate (NaHCO₃-P; Pi and Po), and HCl-Pi–extractable pools accounted for 1.0, 5.7 and 0.7 % of total P (TP) respectively. The NaOH-P and residual P pools measured through 2 M H₂SO₄ emerged as the largest and most variable pools, accounting for 86.2% of TP. The relative abundance of extracted P pools decreased in the order resin P < NaHCO₃-P ≤ HCl-P < NaOH-P < H₂SO₄-P. Bray 1 P was significantly correlated with all P pools except NaHCO₃-Pi, NaOH-Pi, and residual pools.     

水磷一体化对磷素有效性与磷肥利用率的影响

水肥一体化是发挥水肥耦合效应提高养分效率的重要途径,然水磷一体化研究较少。本文在模拟滴灌条件下研究了液体磷肥和固体颗粒磷肥(TSP)及其不同施用方法对土壤磷移动性、各形态无机磷含量动态变化的影响,比较了玉米磷素营养与磷肥利用率对不同磷源及其施用方式的响应,旨在提出滴灌条件下磷肥高效利用的最优策略。研究结果表明:1)与TSP肥料分次施用相比,液体磷肥分次施用更能提高土壤磷素有效性,在各土层Ca2-P与树脂磷(resin-P)平均含量分别提高12.4%与21.6%,且可显著提高磷在土壤中的移动性(P0.05),resin-P含量的垂直下降幅度降低56.5%;2)与TSP分次施用相比,液体磷肥分次施用的土壤中高活性无机磷含量(Ca2-P、resin-P及Na HCO3-P之和)占无机磷总量的比例提高21.0%,而低活性无机磷含量(Ca10-P与residue-P之和)占无机磷总量的比例则下降10.1%,说明液体磷肥分次施用可减小磷肥在土壤中的固定转化;3)玉米地上部干物质、叶片吸磷量和植株磷素累积吸收量均对不同磷源与施用方式有明显响应(P0.05),液体磷肥分次处理的玉米生物量、吸磷量及肥料利用率分别比TSP肥料分次处理提高27.1%、34.6%及61.4%。水磷一体化施用可提高磷在土壤中的移动性和有效性,减少磷的固定转化,显著改善玉米磷素营养,并明显提高磷肥利用率。     

Importance of heterotrophic nitrification and dissimilatory nitrate reduction to ammonium in a cropland soil: Evidences from a 15N tracing study to literature synthesis

Future climate change is predicted to influence soil moisture regime, a key factor regulating soil nitrogen (N) cycling. To elucidate how soil moisture affects gross N transformation in a cultivated black soil, a ¹⁵N tracing study was conducted at 30%, 50% and 70% water-filled pore space (WFPS). While gross mineralization rate of recalcitrant organic N (N_rec) increased from 0.56 to 2.47 mg N kg⁻¹ d⁻¹, the rate of labile organic N mineralization declined from 4.23 to 2.41 mg N kg⁻¹ d⁻¹ with a WFPS increase from 30% to 70%. Similar to total mineralization, no distinct moisture effect was found on total immobilization of ammonium, which primarily entered the N_rec pool. Nitrate (NO₃⁻) was mainly produced via autotrophic nitrification, which was significantly stimulated by increasing WFPS. Unexpectedly, heterotrophic nitrification was observed, with the highest rate of 1.06 mg N kg⁻¹ d⁻¹ at 30% WFPS, contributing 31.8% to total NO₃⁻ production, and decreased with WFPS. Dissimilatory nitrate reduction to ammonium (DNRA) increased from near zero (30% WFPS) to 0.26 mg N kg⁻¹ d⁻¹ (70% WFPS), amounting to 16.7–92.9% of NO₃⁻ consumption. A literature synthetic analysis from global multiple ecosystems showed that the rates of heterotrophic nitrification and DNRA in test soil were comparative to the forest and grassland ecosystems, and that heterotrophic nitrification was positively correlated with precipitation, soil organic carbon (SOC) and C/N, but negatively with pH and bulk density, while DNRA showed positive relationships with precipitation, clay, SOC, C/NO₃⁻ and WFPS. We suggested that low pH and bulk density and high SOC and C/N in test soil might favor heterotrophic nitrification, and that C and NO₃⁻ availability together with anaerobic condition were crucial for DNRA. Overall, our study highlights the role of moisture in regulating gross N turnover and the importance of heterotrophic nitrification for NO₃⁻ production under low moisture and DNRA for NO₃⁻ retention under high moisture in cropland.     

Rice-residue biochar influences phosphorus availability in soil with contrasting P status

ABSTRACT

Thermo-chemical conversion of crop residues to produce biochar is an emerging strategy in the context of sustainable phosphorous (P) use and residue management. An incubation study for 90 d was conducted to investigate the effects of rice-residue biochar (0, 10, 20 and 40 g kg^?1) in combination with inorganic-P (KH₂PO₄) (0, 25 and 50 mg kg^?1) on phosphorous availability in medium- and high-P status soils. Increasing biochar addition rates alone or in combination with inorganic-P resulted in a significant increase in P pools, i.e. plant available P or Olsen-P (from 8 to 132 mg kg^?1 in medium-P and 15 to 160 mg kg^?1 in high-P soils), microbial biomass P and various mineral-bound inorganic-P fractions in the order (Ca-P > organic-P > Al-P > loosely held/soluble-P > Fe-P > reductant soluble-P). Further, lower phosphatase activity (19–50%) with increasing rates of biochar addition in both soils elucidates the ability of biochar to act as a long-term source of available P in the experimental soils. The results demonstrate that rice-residue biochar can directly or indirectly enhance the status of available P in soils and hence can be used as a beneficial amendment to meet the crop P demand.     

The impact of sugarcane filter cake on the availability of P in the rhizosphere and associated microbial community structure

This study aimed to evaluate the interaction between filter cake (FC), and phosphorus fertilizers with differing solubility on the growth and P nutrition of sugarcane. Effects of soil amendment with FC on different soil P fractions and influence on microbial community structure in the rhizosphere were also assessed. Two glasshouse experiments were conducted with completely randomized block designs. The first experiment evaluated rates of FC using a factorial design (5 × 2): 0, 2.5, 5, 10 and 15 g FC kg^?1 soil applied as either broadcast in bulk soil or in the planting furrow. The second experiment used a factorial design (2 × 3): without and with FC (5 g kg^?1 soil, dry basis), both without P (NP) and with P supplied as either triple superphosphate (TSP) or as rock phosphate (RP), both at the rate of 78.4 mg kg^?1 based on total P. Microbial community structure was determined using TRFLP and dynamics of soil P by Hedley fractionation. Filter cake applied at increasing rates in the absence of P was effective in increasing shoot growth and P uptake by plant, particularly when applied to bulk soil as compared to furrow application. Also, FC improved P uptake and increased the availability of labile inorganic P in the rhizosphere and modified the structure of fungal and bacterial communities, whereas only bacterial and archaea communities were influenced by P fertilizer use. Filter cake was more effective when combined with RP, with increased growth and P utilization and thus can be considered as a feasible and practical option for farmer use in substitution to TSP, a more expensive source.