SSSAJ Journal of Natural Resources and Life Sciences Education
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published online 27 October 2006
Published in Soil Sci Soc Am J 70:2057-2064 (2006)
DOI: 10.2136/sssaj2005.0409
© 2006 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Du, Z.
Right arrow Articles by Chen, X.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Du, Z.
Right arrow Articles by Chen, X.
Agricola
Right arrow Articles by Du, Z.
Right arrow Articles by Chen, X.

Soil Fertility & Plant Nutrition

Potassium Movement and Transformation in an Acid Soil as Affected by Phosphorus

Zhenyu Du, Jianmin Zhou*, Huoyan Wang, Changwen Du and Xiaoqin Chen

State Key Lab. of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. Z. Du, current address: Institute of Soil and Fertilizer, Shandong Academy of Forestry, 42 East Wenhua Rd., Jinan 250014, China

* Corresponding author (jmzhou{at}issas.ac.cn)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
When P and K fertilizer are applied to soil at the same time, the movement and transformation of K may be affected by P. This study was conducted to quantify the effects of monocalcium phosphate (MCP) co-applied with KCl on the distance of K movement, the concentration of K in different forms and soil pH change at different distances from the fertilizer application site in an incubation experiment with an acid red soil from Yingtan, Jianxi province in southern China. Fertilizers of 0.5 g KCl alone or in combination with 0.98 g MCP were added to the surface of soil cylinders with a height of 150 mm and packed in wax blocks. The fertilizers and soil were incubated at field capacity moisture content for 7 and 28 d. Extraction and analysis of each layer (first 25 layers of 2 mm thickness and then 20 layers of 5 mm) from the interface of soil and fertilizer showed that the movement distance of K was not affected by the addition of MCP. However, the concentration of water-extractable K decreased and the concentrations of exchangeable and nonexchangeable K increased significantly near the fertilizer site in the presence of P. The application of MCP also slowed down the decrease of KCl-induced soil pH close to fertilizer site. The results suggested that the transformation of K in soil close to the fertilizer placement site was significantly affected by the addition of MCP, probably due to the reactions of MCP with Al and Fe in soil. The amounts of K in different forms in soil columns implied that the addition of MCP could reduce the bioavailability of K at the beginning of fertilizer application.

Abbreviations: AE-Al, acid-extractable Al • AE-Fe, acid-extractable Fe • AE-P, acid-extractable P • CEC, cation-exchange capacity • EX-K, exchangeable K • LSD, least significant difference • MCP, monocalcium phosphate • NE-K, nonexchangeable K • WE-K, water-extractable K • WE-P, water-extractable P


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
THE CHOICE OF FERTILIZER APPLICATION METHODS for a particular nutrient depends on the mobility of the nutrient in the soil. Phosphorus fertilizer applied to the soil typically moves only a short distance (Sharpley, 1986; Eghball and Sander, 1989). The movement of P in soil is primarily by diffusion (Barber et al., 1963). The rate and extent of P movement into soil from fertilizers depends on soil compaction, soil moisture, and P sorption capacity (Benbi and Gilkes, 1987). Potassium moves in soil through diffusion and mass flow, but diffusion is the most important mechanism involved in the movement of fertilizer K to absorbing roots. Potassium diffusion occurs in soil solution and is affected by several factors including volumetric moisture and temperature (Barber, 1985). Equilibrium exists between solution K and exchangeable K, and between exchangeable K and fixed K. Fixation and release is a reversible process that is dependent on the concentration of K ion on the clay surface, which in turn is dependent on the concentration of K ion in the soil solution (Foth, 1984). Clay minerals responsible for K fixation are 2:1 types such as vermiculite, illite, and montmorillonite (Dennis and Ellis, 1962; Page et al., 1967; Rich, 1968; Ross and Cline, 1984).

Phosphorus and K are important macronutrients, and are often co-applied in a band or on the soil surface directly. The interaction between P and K might influence their movement and bioavailability after co-application to the soil. The influences of K applied in combination with P on the behavior of P in soil have been investigated by various researchers (Bouldin et al., 1960; Isensee and Walsh, 1972; Ernani and Barber, 1991; Akinremi and Cho, 1993). However, there are fewer studies on K status as affected by P applied to soils. Earlier studies demonstrate that K can be retained when applied with P fertilizers in acid tropical and subtropical soils, possibly due to the increase in cation exchange capacity (CEC) of the soil as a result of the formation of aluminum-phosphates (Ayres and Hagihara, 1953; Perkins, 1958; Thorup and Mehlich, 1961). Zhou and Huang (1995) found that application of NH4H2PO4 fertilizer enhanced K release from three Chinese soils, that is, Oxisol, Alfisol, and Entisol, thus increasing their K-supplying rate. However, no reports have been published on the effect of MCP on the behavior of K from fertilizer in soil.

The nature of the reactions of phosphate fertilizers with soil constituents may vary with the distance from the fertilizer granule when P and K are applied together, due to the change in phosphate concentration and pH. This change might cause substantial alterations of soil constituents and subsequent K release. However, no research is available on the effect of applied P on the movement and transformation of K in the chemical environment surrounding the fertilizer sources.

The objective of this study was to investigate the effects of MCP applied in combination with KCl on the movement of K from the fertilizer sources and consequent changes in different K forms in an acid red soil, which is common in south of China.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
An acid red soil (Haplic Acrisol, FAO Soil Classification System) was collected from the top 15 cm of a cultivated layer in the Ecological Experiment of Red Soil, the Chinese Academy of Sciences (28°15'30''N, 116°55'30''E), located in Yingtan, Jiangxi province, China. Some selected chemical and physical properties of the soil are listed in Table 1. The clay minerals are dominated by kaolinite and hydrous mica, and also contain a small amount of vermiculite.


View this table:
[in this window]
[in a new window]
  		Table 1. Selected physical and chemical properties of the soil used.

 
Before incubation, the soil was air-dried and sieved using 1-mm mesh. The containers used for soil incubations in this study were wax columns, 150 mm in height with a cylindrical cavity having an internal diameter of 50 mm. These were prepared using the method of Khasawneh and Soileau (1969). The materials used to make wax column was the molten mixture of two parts of paraffin wax and one part of petroleum jelly. The wax column was closed on the bottom with two pieces of filter paper (Whatman 40, Whatman Inc., Clifton, NJ). Soil (360 g) was packed into each column to obtain a final bulk density of 1.22 g cm–3. To keep a constant bulk density, we filled and packed the soil in 3-cm intervals. More specifically, we calculated the weight of 3-cm depth of the soils based on the cross-sectional area of the wax column and the bulk density. The weighted soil was filled into the wax column and packed carefully to a depth of 3 cm. We brushed the soil surface to maintain a good contact with added soil and repeated the procedure. One filter paper, 49 mm in diameter, was placed on the soil surface to separate the soil from fertilizer. The wax blocks were next put on fine sand and wetted by capillary rise to a moisture content of 370 g kg–1 (field capacity, determined experimentally). The top and bottom of the packed wax blocks were covered with parafilm to prevent moisture loss (Fan and MacKenzie, 1993) after abandoning the filter papers covering the bottom and then allowed to equilibrate for 48 h at 25°C before P and K treatments were applied.

Fertilizer treatments were 0.5 g KCl alone or in combination with 0.98 g MCP. Reagent grade fertilizers were applied uniformly as finely ground materials (<1 mm) by spreading over the whole surface of the filter paper on the soil cylinder. Both K and P were at a rate of 0.26 g per column. This application is equivalent to the addition of 300 kg P2O5 ha–1 or 160 kg K2O ha–1 in a band 5 cm wide along one side of crop rows spaced 45 cm apart and were intended to simulate conditions similar to those near fertilizer granules or banding. A control treatment without application of P and K was also performed. Three replicates were used in a completely randomized design. Each treatment had six soil columns. Three were sampled after 7-d and three after 28-d incubation. The wax blocks were covered and then incubated vertically at 25°C. After 7 and 28 d, the filter paper on the soil cylinder was taken off for K analysis to evaluate the K retained by filter paper. The wax columns were sectioned into 25 slices, 2-mm thick, and then 20 slices, 5-mm thick, using a sharp stainless knife. The wax column was put on a wooden base of a self-designed apparatus (Fig. 1 ) and pushed by a screw rod with a 2-mm screw pitch. Each 2-mm thick slice was precisely extruded each time by turning the screw rod one circle each time. While being cut, the wax columns were fixed by turning clamps and fixing nut tightly.


Figure 1
View larger version (69K):
[in this window]
[in a new window]
  		Fig. 1. Diagram of sectioning apparatus.

 
Soil samples from each slice were analyzed for moisture content (Lu, 1999) and chemical composition. The chemical analysis involved several steps using procedures similar to Hao et al. (2002). First, 1.37 g of moist soil (equivalent to 1 g oven-dry soil) from each slice was weighed into a 15-mL centrifuge tube, 5-mL deionized water was added and the mixture was shaken for 10 min and centrifuged at 5000 x g (10 000 rpm) to separate the supernatant. Second, an additional 5 mL of deionized water was added to the residual soil samples in the centrifuge tubes and the supernatant was again extracted as described in the first step. The two extracts obtained from Step 1 and 2 were combined and termed as the water-extractable fraction. Third, the same sample was then successively extracted three times with 5 mL of 1.0 M HCl as described in Step 1. The three acid extracts were combined for the acid-extractable fraction. The concentration of K in water extractant was determined using a flame photometer (Model 6410, Shanghai Analytical Instrument Company, China). The concentration of Al and Fe in water and acid extractant was determined using an ICP (Inductively Coupled Plasma) apparatus. Concentration of P in extracts was determined by the ascorbic acid-ammonium molybdate method of Murphy and Riley (1962). The entire filter papers were extracted only with 1.0 M HCl as described above in Step 3 and analyzed for K using the flame photometer. For P, water was used as the extractant to provide information on the mobile phase, while the acid extractant was used to estimate sorbed phase (Akinremi and Cho, 1993; Hao et al., 2002).

To determine exchangeable K and non-exchangeable K, another 1.37 g of moist soil was extracted with 1.0 M NH4OAc. The exchangeable K was taken as the difference between the K extracted by 1.0 M NH4OAc and that extracted by water. Then, the residual soil sample was extracted with boiling 1.0 M HNO3 for 10 min. The concentration of K was determined using the flame photometer (Lu, 1999) and used to determine the non-exchangeable K.

The pH measurement of each slice was made using a thin combined glass/calomel electrode (Model 206-C, Shanghai San-Xin Instrument Co., China). Deionized water was added to a 15-mL centrifuge tube containing 1.0 g of moist soil from each slice at a soil/water ratio of 1/2.5. Soil and water were thoroughly mixed with a vortex mixer and the pH was determined after stirring for 10 min (Lu, 1999).

The data for each layer were analyzed as a completely randomized design. One-way ANOVA was used to evaluate the effects of fertilizer application on the concentrations of K in different forms and pH changes at each distance from the fertilizer application site at each incubation time, as well as the effects of fertilizer treatment on the amounts of different K forms from the added KCl at each incubation time. Multiple comparisons among the treatments were characterized using the LSD (least significant differences) test for each depth at each incubation time. For P data, unpaired t test was used to analyze difference for water-extractable P (WE-P) or acid-extractable P (AE-P) between KCl + MCP treatment and the control treatment for each depth at each incubation time. ANOVA, multiple comparisons, and t test were performed using Statistical Analysis System (SAS Institute, 1996). All results in figures and tables were given as means of three replicates on the basis of oven-dry soil.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Movement of Phosphorus
The movement of P applied together with K is important for evaluating the effects of P on K movement in soil columns. The amount of P in columns receiving MCP and KCl exceeding the values obtained for unfertilized soil in control was assumed to be from the fertilizer (Benbi and Gilkes, 1987; Fan and MacKenzie, 1993). Total P was calculated as the amount of WE-P plus that of AE-P. The amounts of P in different forms from fertilizer in each column were obtained by summing the quantities of P from MCP extracted from each slice of the column. Total P amount in each slice and the concentration distributions of WE-P and AE-P in soil columns receiving both MCP and KCl are presented in Tables 2 and 3. The distance of P movement in the red soil was relatively small. After 7 and 28 d, added P moved vertically to 24 and 28 mm, respectively. About 60 and 70% of added P were recovered in soil after 7 and 28 d, respectively. This indicated that added P moved faster within the first week, but then slowed in the subsequent 3 wk due to its strong affinity for soil particles and reactions with Al and Fe in soil. These measurements of P movement are comparable with those obtained by Fan and MacKenzie (1993) in a similar investigation. They observed that 77, 81, and 95% of the applied P moved into a Canadian acid soil from triple superphosphate with a movement depth of 20, 20, and 25 mm after 5, 10, and 20 d, respectively. The main physical and chemical properties of this Canadian soil included 56.8% clay, pH 5.0 (1: 2.5 soil/water suspension), 43 g kg–1 organic matter, and 18 kg ha–1 P (Mehlich No.3 extractant). Soil moisture was adjusted to 250 g kg–1 before the application of triple superphosphate. In their study, the total P retained in soil was calculated by summing the amount of soil solution P and that of sulfuric acid soluble P. The differences between these studies in the amount and distance of P movement can be attributed to the different characteristics of soils such as P adsorption/fixation capacities, water content, and bulk density. The latter two affect the tortuosity and hence the diffusion.


View this table:
[in this window]
[in a new window]
  		Table 2. Distribution of applied P with distance from fertilizer placement in the soil column treated with monocalcium phosphate and KCl after 7 d.

 

View this table:
[in this window]
[in a new window]
  		Table 3. Distribution of applied P with distance from fertilizer placement in the soil column treated with monocalcium phosphate and KCl after 28 d.

 
Soil pH Changes
Soil pH decreased as a result of KCl application (Fig. 2 ). However, the reduction was modified by added MCP. Compared with KCl alone, the addition of MCP with KCl increased soil pH at 0- to 2-mm distance from the fertilizer site by 0.30 and 0.45 units after 7 and 28 d, respectively. This increase extended to 9 and 11 mm at 7 and 28 d, respectively, which were within the distance of P movement from the fertilizer site. The reason why a pH difference between KCl and KCl + MCP treatments was not observed as deep as P movement was probably due to the buffer capacity of soil.


Figure 2
View larger version (19K):
[in this window]
[in a new window]
  		Fig. 2. Changes of pH in soil columns treated with KCl alone (K) or in combination with monocalcium phosphate (PK) at different incubation periods. Vertical bars represent standard deviation (n = 3).

 
Although KCl is neutral in water solution, applying KCl reduced the pH of this red soil through cation exchange. In this red soil, a large portion of the acidic cations on the soil surface could be displaced by K ions resulting in a soil pH decrease (Wang et al., 2003). The significant change in soil pH close to fertilizer site after the addition of MCP with KCl probably was a result of Al-P interactions. Aluminum ions in soil solution could make soil pH decrease due to hydrolysis. As Al ions precipitated with P after addition of MCP, the amount of Al ions involved in hydrolysis was decreased. Therefore, the decrease of soil pH induced by KCl application was buffered to a certain extent. Another possible explanation is exchange of H2PO4– and OH– on soil surfaces, which would slightly increase soil pH (Zhu, 1982).

Movement of Potassium and Water-extractable Potassium
The concentrations of water-extractable K (WE-K) contained in soil sections with increasing distance from the fertilizer application site are shown in Fig. 3 . The addition of MCP did not change the depths of K movement, which were 60 mm after 7 d and 110 mm after 28 d of incubation.


Figure 3
View larger version (25K):
[in this window]
[in a new window]
  		Fig. 3. Distributions of water-exchangeable K (WE-K) in soil columns treated with KCl alone (K) or in combination with monocalcium phosphate (PK) at different incubation periods. Vertical bars represent standard deviation (n = 3).

 
The addition of MCP with KCl decreased the concentration of WE-K at 0- to 60-mm distance from fertilizer site in columns after 7 d and 0 to 110 mm after 28 d. Statistical analysis using LSD test indicated that the differences in WE-K concentration at the same distance from fertilizer site were all significant (P < 0.05) at the same incubation period.

The WE-K concentration reduction in soil columns as affected by the addition of MCP was probably due to the reaction of K and P with Al and Fe. As the dissolution of MCP, H3PO4 was formed resulting in a solution pH of about 1.5 near the fertilizer grain (Lindsay and Stephenson, 1959; Sample et al., 1980). Other soil minerals in contact with the H3PO4 may be dissolved, increasing the concentration of cations such as Al and Fe near the fertilizer (Lehr et al., 1959; Lindsay and Stephenson, 1959; Low and Black, 1947). A part of K in soil solution would be precipitated with P and Al as the non-crystal analog of taranakite (Lindsay et al., 1962). Precipitation of P, rather than adsorption processes would dominate the process due to the very high initial P concentration (van Riemsdijk et al., 1984). As a result, the concentration of WE-K could be reduced because of the formation of K-bearing precipitations. It is worth noting that some Ca ions from MCP could displace K ions on the sorption sites simultaneously, which would result in higher WE-K concentration in soil solution. Probably, this increase of WE-K was insufficient to offset the decrease of WE-K induced by precipitations.

Exchangeable Potassium
Adding MCP with KCl increased the concentration of exchangeable K at the 0- to 18-mm distance from the fertilizer site after 7 d, but reduced EX-K concentration at the 28- to 40-mm distance (Fig. 4 ). After 28 d, EX-K profiles followed a pattern similar to that at 7 d. As affected by the addition of MCP, the EX-K concentration was higher at the 0- to 30-mm distance, but lower at the 50- to 105-mm distance. Statistical analysis using LSD test indicated that the differences in exchangeable K between two treatments at these two depths were all significant (P < 0.05).


Figure 4
View larger version (24K):
[in this window]
[in a new window]
  		Fig. 4. Distributions of exchangeable K in soil columns treated with KCl alone (K) or in combination with monocalcium phosphate (PK) at different incubation periods. Vertical bars represent standard deviation (n = 3).

 
A possible explanation for the results is the reaction of P with Al. The application of KCl on the soil surface provided K ion in soil column. The K ion in soil solution displaced Al ion on the exchange sites. In the soil columns treated with KCl and MCP, the higher Al ion concentration in the vicinity of a high P concentration increased the interaction between the two ions. At the same time, this interaction promoted more Al ion to be exchanged by K ion, which led to higher EX-K concentrations. The phosphate ion is capable of neutralizing positive charges of Fe hydroxides in the clay fraction generating electronegative sites (Mekaru and Uehara, 1972), which could also explain why MCP increased K adsorption. Another possible explanation is the competition between Al (Fe) ion and K ion. When KCl alone was added in this acid soil containing kaolintie, soil pH was reduced below 4 close to the fertilizer site (Fig. 2). As a result, kaolinite was decomposed and thus more Al and Fe ions existed in solution (Lindsay, 1979). Those can compete with the K ion on the exchangeable sites. In contrast, when MCP was co-applied with KCl, the P precipitated with Al (Fe) and then less of these ions were left in solutions. In addition, the pH close to the fertilizer site was a bit higher after the addition of MCP than only KCl, which caused less dissolution of kaolinite. As a result, less Al and Fe ions competed with K ion on the sorption sites. Therefore, adding MCP with KCl increased EX-K concentration in soil close to fertilizer site.

Nonexchangeable Potassium
The distributions of nonexchangeable K (NE-K) in soil column are presented in Fig. 5 . Because the K-fixation ability of red soil is relatively low (Xie et al., 2000), the concentration of NE-K increased only a little in the zone close to the fertilizer site after the addition of KCl. However, the addition of MCP with KCl greatly increased the NE-K concentration close to fertilizer site after both the 7- and 28-d incubation. The maximum concentration of NE-K occurred at 2–6 mm from the surface of the soil column.


Figure 5
View larger version (22K):
[in this window]
[in a new window]
  		Fig. 5. Distribution of nonexchangeable K in soil columns treated with KCl alone (K) or in combination with monocalcium phosphate (PK) at different incubation periods. Vertical bars represent standard deviation (n = 3).

 
When MCP was applied with KCl, the much higher concentration of NE-K close to the fertilizer site was believed to be derived from newly formed precipitations containing K. After the reaction between MCP and soil, a certain amount of K would be precipitated with P and Al as the non-crystal analog of taranakite, but not yet converted to the acid-insoluble crystalline form (Hao et al., 2002). Zhou (1995) also found the concentration of 1 M HNO3 extractable K was greatly enhanced in Oxisol by the application of MCP. Taranakite has been identified in soils as a reaction product of phosphate fertilizer (Lindsay et al., 1962). As the concentration of K ion in the soil-fertilizer reaction zone decreases, taranakite becomes unstable and its solubility increases (Lindsay, 1979). The formation of taranakite in soil can result in the transformation of K from the readily available form to the slowly available form and thus affect the dynamics and bioavailability of K in soils to plants, especially in the immediate vicinity of phosphate fertilizer bands. This transformation may reduce the rate of K supply at the early stage of plant growth.

Amounts of Potassium from Fertilizer in Different Forms
Since the extraction method using boiling 1 M HNO3 obviously involved a rather drastic treatment of the mineral components of soil, and the freshly precipitated reaction products involving P, K, Al, and Fe are vulnerable to acid extraction (Sample et al., 1979), the sum of K amounts in soil slices extracted by 1.0 M ammonium acetate and 1 M HNO3 above that from unfertilized soil were assumed to represent total K from fertilizer applied in this study. The WE-K and EX-K were considered to be available for plant growth. In this experiment, the amounts of WE-K plus EX-K above that from unfertilized soil were assumed to the available K from added fertilizers.

The data in Table 4 showed that nearly all the K moved into the soil column was recovered. The addition of MCP significantly reduced the amount of WE-K, but increased the amount of EX-K or NE-K at 7 or 28 d. The recovery of K was not complete. This might have been due to the incomplete extraction of K by boiling 1 M HNO3. However, above 93% of the added K was accounted for in all the columns. Addition of MCP with KCl significantly reduced the amount of available K maintaining in the soil column. The result may imply the addition of MCP could reduce the bioavailability of K after the fertilizer application.


View this table:
[in this window]
[in a new window]
  		Table 4. Mass balance of K moved into soil column from fertilizer{dagger}.

 
Acid-extractable Aluminum and Iron
The addition of MCP with KCl resulted in significant variations of Al and Fe concentrations extracted by 1 M HCl. In this experiment, acid-extractable Al (AE-Al) and acid-extractable Fe (AE-Fe) is assumed to represent the fraction of Al and Fe that had been precipitated with P as the non-crystal analog of variscite and strengite, but not yet converted to the acid-insoluble crystalline forms which cannot be extracted by 1 M HCl. Close to the fertilizer placement site, the concentrations of AE-Al and AE-Fe were higher and steadily decreased with increasing distance from the fertilizer site as affected by the addition of MCP with KCl (Fig. 6 ). The distribution of AE-Al and AE-Fe in soil columns treated with MCP and KCl followed a pattern similar to that of the acid extractable P in soil column, which indicated that the changes of AE-Al and AE-Fe were the results of added P and confirmed the formation of new non-crystal precipitations that could be extracted by 1 M HCl.


Figure 6
View larger version (26K):
[in this window]
[in a new window]
  		Fig. 6. Distributions of acid-extractable Al (AE-Al) and acid-extractable Fe (AE-Fe) in soil columns treated with KCl alone (K) or in combination with monocalcium phosphate (PK) at different incubation periods. Vertical bars represent standard deviation (n = 3).

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
An experiment was conducted with KCl and MCP applied to an acid soil to study the effects of P on K concentrations in various forms in soil close to the fertilizer application site. Results showed that both EX-K and NE-K concentrations were elevated near the fertilizer site by the addition of P. However, the concentrations of water-extractable K decreased significantly. In this reaction, some readily available K from fertilizer apparently was transformed to less available form. These changes possibly were the results of the release of Al and Fe from cation exchange sites by added K, the dissolution of Al and Fe oxides and hydroxides during MCP reaction with soil matrices, and the formation of new precipitates. Similarly, MCP slowed down the decrease of soil pH close to fertilizer site induced by applied KCl. The depth of K movement was not affected by MCP application. The amounts of K in different forms moved into soil implied that the addition of MCP could reduce the bioavailability of K at the beginning of fertilizer application.


   ACKNOWLEDGMENTS
 
The authors acknowledge the financial support of the National Natural Science Foundation of China (No. 40071051) and the National Key Basic Research Support Foundation of China (No.G1999011802).

Received for publication December 16, 2005.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 





This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Du, Z.
Right arrow Articles by Chen, X.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Du, Z.
Right arrow Articles by Chen, X.
Agricola
Right arrow Articles by Du, Z.
Right arrow Articles by Chen, X.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome