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1.
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) Pi], organic pool (NaOH Po), 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 pHKCl (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 pHH2O (r = ?0.62, P < 0.05). Solution P showed a negative and significant relationship with NaOH-Pi (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-Pi was positive (r = 0.70, P < 0.05) and significant. Similarly, a positive and significant relationship (r = 0.89, P < 0.01) between NaOH-Pi and acid P was observed, and acid P was positively and significantly correlated with residual P (r = 0.84, P < 0.01).  相似文献   

2.
 Soil P availability and efficiency of applied P may be improved through an understanding of soil P dynamics in relation to management practices in a cropping system. Our objectives in this study were to evaluate changes in plant-available (Olsen) P and in different inorganic P (Pi) and organic P (P0) fractions in soil as related to repeated additions of manure and fertilizer P under a soybean-wheat rotation. A field experiment on a Typic Haplustert was conducted from 1992 to 1995 wherein the annual treatments included four rates of fertilizer P (0, 11, 22 and 44 kg ha–1 applied to both soybean and wheat) in the absence and presence of 16 t ha–1 of manure (applied to soybean only). With regular application of fertilizer P to each crop the level of Olsen P increased significantly and linearly through the years in both manured and unmanured plots. The mean P balance required to raise Olsen P by 1 mg kg–1 was 17.9 kg ha–1 of fertilizer P in unmanured plots and 5.6 kg ha–1 of manure plus fertilizer P in manured plots. The relative sizes of labile [NaHCO3-extractable Pi (NaHCO3-Pi) and NaHCO3-extractable P0 (NaHCO3-P0)], moderately labile [NaOH-extractable Pi (NaOH-Pi) and NaOH-extractable P0 (NaOH-P0)] and stable [HCl-extractable P (HCl-P) and H2SO4/H2O2-extractable P (resisual-P)] P pools were in a 1 : 2.9 : 7.6 ratio. Application of fertilizer P and manure significantly increased NaHCO3-Pi and -P0 and NaOH-Pi, and -P0 fractions and also total P. However, HCl-P and residual-P were not affected. The changes in NaHCO3-Pi, NaOH-Pi and NaOH-P0 fractions were significantly correlated with the apparent P balance and were thought to represent biologically dynamic soil P and act as major sources and sinks of plant-available P. Received: 23 October 1997  相似文献   

3.
Information concerning sources and sinks of available P in soil is needed to improve soil P management and protect water quality. This study, conducted from 1989 to 1998 on a Sultan silt loam soil (Aquantic Xerochrept), determined the annual P removal rate by corn (Zea mays L.) and P transformation as affected by P rate and winter cover cropping. Treatments included two P rates (0 and 44 kg P ha–1) applied to corn at planting each year. All cover crops received 19.6 kg P ha–1 at seeding each fall. Also included was a control without any cover crop and with no P addition. Corn yield and P uptake were affected by P fertilizer additions, but not by cover crops. A fairly constant amount of P was supplied from indigenous soil P when no external P was added. When the amount of P added exceeded that removed by corn, the excess P was converted mainly to NaOH-extractable inorganic P (NaOH-Pi). When the amount of P applied was below that removed by corn, indigenous soil NaOH-Pi acted as a source of available P for the plant. With no reduction of organic P (Po) extractable by NaOH or NaHCO3, the contribution from Po to the available P pool appeared limited. The role of NaOH-Pi in P availability in the soil was substantiated by its significant correlation with labile NH4Cl-extractable P (NH4Cl-P; r2 =0.60, P <0.001) or NaHCO3-Pi (r2 =0.81, P <0.001) pools. The NaOH-Pi for the soil reflected the changes in soil P resulting from past fertilizer P input and P removal by the crops.Scientific Paper Number 0005-34  相似文献   

4.
The effect of different treatments on the fate of applied P was investigated in a long-term field experiment started in 1972–1973 following a maize–wheat sequence. The soil samples were collected after 29 years of continuous addition of mineral fertilizers and amendments such as farmyard manure (FYM) and lime. The total P content of all the treatments increased compared to the original soil; NaOH-inorganic P (Pi) (NaOH-Pi) representing Fe and Al-bound P was the dominant Pi fraction. At the beginning of the experiment (1972–1973), the various P pools could be quantitatively ranked in the following order: residual P>NaOH-organic P (Po)>NaOH-Pi>NaHCO3-Po>NaHCO3-Pi>HCl-P>H2O-P. As a result of continued P fertilization and cropping, the order changed as follows: residual P>NaOH-Pi>NaOH-Po>NaHCO3-Pi>NaHCO3-Po>HCl-P>H2O-P. Compared to the imbalanced mineral fertilizer application, the balanced as well as integrated application of nutrients resulted in significantly lower P adsorption capacity of soils. The Olsen extractable-P fraction (plant-available P) increased from about 12 mg kg–1 soil in 1972 to about 81 mg kg–1 soil in the treatments receiving P for the last 29 years.  相似文献   

5.
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-Pi) and moderately labile inorganic P (NaOH-Pi) increased proportionally with P rate. The coarser-textured soils had lower contents of labile and moderately labile Pi, but a larger increase in labile Pi than the finer-textured soils after receiving P additions. The applied P was retained primarily as soil labile Pi, accounting for 43–69% of total soil recovery of applied P, compared to 20–30% recovered as moderately labile Pi, and 7–29% assumed to be sparingly soluble P (HCl-P?+?H2SO4-P). The labile Pi recovery of applied P was linearly depressed with clay content, compared to a quadratic relation for the moderately labile Pi 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.  相似文献   

6.
旱地土壤微生物磷测定方法研究   总被引：42，自引：3，他引：42       下载免费PDF全文
介绍了国外关于土壤微生物磷测定方法的研究进展 ,讨论了常用的几种方法所存在的问题 ,介绍了主要操作过程要求。对我国 5种主要母质类型的土壤 (pH 3 .3～ 7.4,1molL- 1KCl)的对比研究表明 ,我国土壤采用氯仿熏蒸、0 .5molL- 1NaHCO3在 1∶2 0土水比提取测定无机磷 (Pi)、并以同时测得的培养土壤微生物的磷的回收率作为计算常数得到的结果最佳。测定的大多数南方土壤的微生物磷占土壤全磷的比例小于 1 .5 % ,微生物碳磷比值大于 3 0∶1 ,反映南方土壤磷的生物活性较低 ,土壤微生物对磷的作物供应调节能力不强。  相似文献   

7.
ABSTRACT

The formation of phosphorus (P) compounds including iron-P, aluminum-P and calcium-P in highly weathered tropical soils can be altered upon biochar addition. We investigated the effect of corn cob biochar (CC) and rice husk biochar (RH) pyrolyzed at three temperatures (300°C, 450°C and 650°C) on phosphorus (P) fractions of three contrasting soils. A 90d incubation study was conducted by mixing biochar with soil at a rate of 1% w/w and at 70% field capacity. Sequential P fraction was performed on biochar, soil and soil-biochar mixtures. Increase in most labile P (resin-Pi, NaHCO3-Pi) and organic P fraction (NaHCO3-Po + NaOH-Po) in CC and RH biochars were inversely related to increasing temperature. HCl-Pi and residual P increased with increasing temperature. Interaction of CC and RH with soils resulted in an increase in most labile P as well as moderately labile P (NaOH-Pi) fractions in the soils. CC increased most labile P in the soils more than RH. The increase in most labile P fraction in soils was more significant at relatively lower temperatures (300°C and 450°C) than 650°C. However, the increase in HCl-Pi and residual P of the soils was more predominant at high temperature (650°C). The study suggested that biochar pyrolyzed at 300–450°C could be used to increase P bioavailability in tropical soils.  相似文献   

8.
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-Pi)] by 3.2 and 5.0 mg kg?1 and the labile organic P (NaHCO3-Po) 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-Po)], respectively, than the soil under residue burning. The SNI either as fertilizer or FYM further enhanced NaHCO3-Pi, NaHCO3-Po, and NaOH-Po. 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-Pi, NaHCO3-P0, and NaOH-Po 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.  相似文献   

9.
Although many studies have examined the effect of different application rates of cattle manure, swine manure, and urea fertilizer on the distribution of phosphorus (P) fractions in soil, few studies have correlated P fractions in soil with inorganic P (Pi) and organic P (Po) in leachates. As part of a long-term field study, cattle and swine manures were applied to a loamy soil based on a nitrogen (N) content equivalent of 100 (low) and 400 (high) kg total N ha?1 yr?1 and were compared to urea fertilizer at 100 kg N ha?1 yr?1 and an unamended control soil. Readily available Pi [resin and sodium bicarbonate (NaHCO3)] was significantly greater in cattle manure– and swine manure–amended soil at a high application rate than in the control. With some exceptions, urea did not significantly affect P fractions in sequentially extracted P pools. Leaching of Pi and Po was at levels of environmental concern when cattle and swine manures were applied at the high application rate but not at the low application rate. Cattle manure had significantly greater concentrations of Pi and Po removed by leaching compared to swine manure, most likely because of its narrow N/P ratio and greater amount of P added. Positive correlations were observed between resin Pi and total leachate Pi and between NaHCO3-Pi and total leachate Pi, indicating the value of these measurements in predicting P mobility. The results suggest that a threshold (40 μg P g?1 of soil) must be exceeded before a positive correlation occurs.  相似文献   

10.
Purpose

The present study was designed to assess the potential effects of low-molecular-weight organic acids on the activation of inorganic phosphorus, obtain exact information on the acidity effect of proton and complex effect of organic anion in P availability, and determine the components among phosphorus fractions that contributed the most to inorganic phosphorus activation in black soil.

Materials and methods

Both oxalic and citric acids treated with different concentrations and pH values were carefully selected. The activating amounts of total inorganic phosphorus and individual phosphorus fractions were estimated. Path analysis was used to analyze the direct and indirect effects on inorganic phosphorus activation.

Results and discussion

The amount of total activating-Pi increased as the concentrations of oxalic and citric acids increased. When the concentrations were ≤?1.0 mmol L?1, oxalic acid exhibited a lower capability than citric acid in total activating-Pi, but when the concentrations were ≥?1.5 mmol L?1, oxalic acid exhibited a higher capability. The amount of total activating-Pi decreased as pH of LMWOAs increased. LMWOAs-induced Pi activation might be attributed to combine acidity and complex effects.

Conclusions

Correlation analysis showed that the activation of total Pi was significantly correlated with the activation of H2O-Pi, NaHCO3-Pi, NaOH-Pi, and HCl-Pi (p?<?0.05). Path analysis revealed that soil activating-H2O-Pi mainly affected Pi activation through an indirect path. The contribution of activating-NaHCO3-Pi alone was maximal on the total activating-Pi by both the direct and indirect effects, followed by activating-NaOH-Pi and activating-HCl-Pi.

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11.
This study was conducted to investigate the effect of time on chemical forms of P in 10 calcareous soils of western Iran. Phosphorus was added to soils at the rate of 200 mg kg?1 as KH2PO4. The samples were incubated for 1, 7, 15, 30, 60, 90 and 120 days at 25°C and constant moisture. After incubation, P was fractionated by the sequential extraction procedure: soluble and exchangeable P (NaHCO3-P) Al + Fe-P (NaOH-P), Ca-P (HCl-P) and residual P (Res-P). The distribution of added P into different fractions consisted of two phases involving initial rapid retention followed by a slow continuous retention. In general, the majority of the P applied entered mostly in the HCl-P and Res-P fractions. After 120 days incubation, the HCl-P fraction remained the most dominant in all soils. A combination of silt and sand content of the soils together explained between 88.5 and 83.3% of the variance inNaHCO3-P and HCl-P transformation rates, respectively, 76.6 and 72.8% of which is explained by silt alone. CaCl2-P and electrical conductivity (EC) together accounted for 66.3% of the variation in the rate constant of NaOH-P. The release rate of Res-P was not significantly related to soil properties.  相似文献   

12.
Potassium (K) fixation and release in soil are important factors affecting K availability to plants and the utilization efficiency of K fertilizer. Three typical soils (red soil, yellow cinnamon soil, and alluvial soil) were collected from the middle and lower reaches of Yangtse River, China, to study the K-fixation and K-release characteristics of the normal and K-exhausted soil. Results showed that K fixation of added K in K-exhausted soils were significantly (P < 0.05) greater than that of the normal soils. There were significantly (P < 0.05) negative correlations among K-fixation capacity, concentration of soil-available K, and K+ saturation. Irrespective of soil K exhaustion, K fixation of added K was in the order of red soil > yellow cinnamon soil > alluvial soil, but the cumulative amount of K released from the three soils during successive extractions with 1.0 mol L?1 nitric acid (HNO3) was in the opposite order. 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. The K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was lower in K-exhausted soil than in normal soil. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.  相似文献   

13.
Yao  Yihan  Cao  Shanzhi  Gong  Xueliu  Singh  Bhupinder Pal  Fang  Yunying  Ge  Tida  Wang  Hailong  Li  Yongfu 《Journal of Soils and Sediments》2022,22(10):2640-2653
Purpose

Intensive long-term management practices in forest ecosystems can markedly influence soils’ physicochemical and microbial properties. However, their effects on the magnitude of nutrient pools and activities of enzymes regarding nutrient cycling in subtropical forest soils remain unclear. This study aimed to examine effects of long-term intensive management (organic mulching and chemical fertilization) on concentrations of different C, N, and P fractions and activities of enzymes involved with nutrient cycling in a subtropical Lei bamboo (Phyllostachys violascens) forest soil.

Materials and methods

Soil samples were taken from a chronosequence of Lei bamboo forests with intensive management spanning 0, 5, 10, and 15 years. Concentrations of various forms of C, N, and P, as well as activities of β-glucosidase, cellobiohydrolase, urease, protease, and acid phosphatase were measured.

Results and discussion

The results revealed that the concentrations of different classes of C (water-soluble organic C, hot-water-soluble organic C, and readily oxidizable C), N (NH4+-N, NO3?-N, and water-soluble organic N), and P [resin-inorganic P (Pi), NaHCO3-Pi, NaHCO3-organic P (Po), NaOH-Pi, NaOH-Po, HCl-Pi, and residual-P] were enhanced markedly with prolonged duration of intensive management. Furthermore, activities of β-glucosidase, cellobiohydrolase, urease, protease, and acid phosphatase were increased following a 5-year treatment, while they were markedly reduced from 5- to the 15-year treatments. The 15 years of intensive management significantly reduced microbial biomass C and N concentrations by 8.2% and 31.9%, respectively, compared to the control.

Conclusions

We concluded that long-term intensive management led to the accumulation of C, N, and P, while it negatively impacted microbial biomass and activities of enzymes involved in nutrient cycling in subtropical Lei bamboo forest soils. Consequently, a reduction in chemical fertilizers should be considered toward the long-term sustainable development of subtropical Lei bamboo forests.

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14.
Shen  Yan  Duan  Yinghua  McLaughlin  Neil  Huang  Shaomin  Guo  Doudou  Xu  Minggang 《Journal of Soils and Sediments》2019,19(7):2997-3007
Purpose

Calcareous soils are characterized by high pH and phosphorus (P) fixation capacity. Increasing application of P fertilizer recently has significantly improved soil P concentration, especially available P (Olsen-P) and inorganic phosphate (Pi) fractions. However, there are few data available on the ability of soils with different initial Olsen-P levels to continuously supply P (i.e., P desorption capacity) to crops without additional P fertilization and on which Pi fraction exerts the greatest influence on P desorption capacity.

Materials and methods

Five soils with different initial Olsen-P levels (0.5, 14.3, 38.4, 55.4, 72.3 mg kg?1, hereafter refer as OP1, OP2, OP3, OP4, and OP5) but similar other soil properties were selected to evaluate the capacity of P desorption and its relationship with Pi fractions. Soil P was sequentially extracted once daily for 16 consecutive days using Olsen solution.

Results and discussion

The content and proportions of dicalcium phosphate fraction (Ca2-P), octacalcium phosphate fraction (Ca8-P), aluminum phosphorus fraction (Al-P), and iron phosphorus fraction (Fe-P) in Pi increased significantly with the increase of initial Olsen-P (P?<?0.01). Applied P fertilizer was mostly stored as Ca8-P in the soil. Soil P desorbed reached an equilibrium after 16 extractions for all soils, and P desorption capacity (12–358 mg kg?1) showed a significant linear relationship with initial Olsen-P (P?<?0.01), with an increase of 4.2 mg kg?1 desorbed P per 1 mg kg?1 increase of initial Olsen-P. Ca2-P exerted the conclusive effect on P desorption in the first four extractions, but Ca8-P played a more important role in the 16 extractions.

Conclusions

Ca8-P was the greatest potential pool for P desorption after Ca2-P was depleted. P desorption capacity was significantly linearly related to initial Olsen-P (P?<?0.01). Different fertilizer use strategies were developed based on P desorption capacity for soils with different initial Olsen-P levels. The present study provided basic data on how to reduce effectively the application amount of chemical P fertilizer.

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15.
The aim was to evaluate eight methods of boron (B) extraction in different soils from Córdoba and Sucre, Colombia. 37 samples were collected at a depth of 0–20 cm and carried to Soil and Water Laboratory of University of Córdoba for its chemical characterization. The available boron was extracted with the following methods: modified hot water, calcium chloride (CaCl2) 0.05, hydrochloric acid (HCl) 0.05, barium chloride (BaCl2) 0.006, manitol 0.05 + CaCl2 0.01, Ca(H2PO4)2H2O 0.008 in mol L?1, mehlich-1 and ammonium acetate (NH4OAc) (1.0 mol L?1, pH = 7.0). The major quantity of boron was extracted with mehlich-1, HCl 0.05 mol L?1 and hot water, extracting 0.36, 0.29 and 0.26 mg kg?1, respectively. The extracting solution that correlated with the hot water method was HCl 0.05 mol L?1 (r = 0.81); followed by Ca(H2PO4)2H2O 0.008 mol L?1 (r = 0.62) and mehlich-1 (r = 0.54). According to characteristic and heterogeneity of soils, we recommend HCl method to extract available boron.  相似文献   

16.
This study was conducted to investigate changes in P-fractions, bio-available P (CAL-P), citric acid extractable P, acid phosphatase activity and microbial biomass C and N during incubation of mature biogenic compost (MBC), immature biogenic compost (IBC) or immature sheep manure compost (ISC) not amended with P or amended with rock phosphate (RP, 7.6% P) or triple-superphosphate (TSP, 19.5% P). Incubation was performed at 20?°C in darkness under aerobic conditions. Samples were collected for laboratory analysis at the start of incubation (D-0) and after one, six and 26?days during incubation (D-1, D-6, D-26). Addition of soluble P fertilizer (TSP) led to a threefold increase in all P fractions in comparison to compost without TSP; even a “priming effect” could be observed, promoting conversion of non-labile to labile P. Moreover, addition of TSP lowered biological activity, especially acid phosphatase activity (P-ase), due to already high concentrations of readily available P. In general, P fractions (bicarbonate extractable Pi (NaHCO3-Pi) and bicarbonate extractable Po (NaHCO3-Po) and sodium hydroxide extractable Po (NaOH-Po)) increased during incubation until day 6 at the expense of NaOH-Pi fraction, which decreased. Generally, RP-derived P showed little or no effect on P fractions during the entire incubation period and only led to slightly increased CAL-P and Citric-acid-P levels. Fertilizer effects on labile P fractions were most enhanced with ISC. IBC enhanced microbial growth and P-ase, thereby enhancing conversion of labile into moderate labile NaOH-Po.  相似文献   

17.
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-Pi pools decreased over time whereas NaOH-Pi 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.  相似文献   

18.
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 (Pi) and organic P (Po) and microbial P throughout the incubation period, except that the WR decreased labile Pi during first 2 w due to Pi 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‐Pi 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‐Pi and ‐Po and NaOH‐Po fractions while causing a decrease in NaOH‐Pi 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.  相似文献   

19.
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20.
Quantity–intensity relations of potassium (K) were worked out for guava orchard soils. Equilibrium activity ratio of potassium (ARe k) ranged from 0.46?×?10?3 to 21.30?×?10?3 (mol L?1)0.5. The majority of the samples had less than 1?×?10?3 (mol L?1)0.5, indicating K depletion in these soils due to continuous K mining. ARe k was significantly and positively correlated with available forms of K, K saturation percentage, labile K (KL), and specific-site K (KX) and negatively correlated with free energy of exchange (–ΔG). The potential buffering capacity (PBC0 K) of K varied from 8.8 to 286.2 cmol kg?1/(mol L?1)0.5. PBC0 K was positively and significantly correlated with clay content. Sixty percent of the soils had ΔK0 values of less than 0.1 cmol kg?1. High KG (Gapon selectivity coefficent) indicated high affinity for K in these soils. Leaf K was positively and significantly correlated with ΔK0, KL, and KX and negatively correlated with –ΔG.  相似文献   

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