FROM APPLIED PHOSPHATIC FERTILIZERS IN TWO LATOSOLS T. MURAOKA, A.E. BOARETTO
CENA, Piracicaba
W.B. SCIVITTARO EMBRAPA,
Pelotas E.C. BRASIL EMBRAPA, Belem Brazil
Abstract
The effectiveness of fluid (phosphoric acid, H3PO4 and 10-30-00 colloidal suspension, CS) and solid (monoammonium phosphate, MAP and triple superphosphate, TSP) fertilizers and the fate of fertilizer P to inorganic P fractions were evaluated in laboratory and in a greenhouse experiment. Corn plants were grown in pots (8 plants per pot; 3 replicates) containing 1 kg of two red-yellow Latosols with different phosphorus retention capacities, for three successive cycles (30 days each). The fertilizers were applied prior to the first sowing at rates of 0 (control), 70, 140 and 210 mg P2O5 kg-1 (0, 30.6, 61.2 and 91.8 mg P kg-1). Dry matter yield and total P were determined at each harvest time. Results showed no difference between the effects of fluid and solid phosphate fertilizers on dry matter yield and phosphorus uptake. However, the rates of phosphorus applied were significantly and positively related with dry matter yield and phosphorus uptake.
In both soils, the agronomic effectiveness of fluid and solid phosphate fertilizers was equivalent.
A laboratory experiment was carried out to measure the fate of P fertilizers converting into inorganic soil P fractions after incubation over a period of 30 days in both Latosols. Inorganic soil phosphates were fractionated and P derived from fertilizer was determined in each fraction. The larger parts of soil applied phosphates were recovered as aluminum (PAl ) and iron bound P (PFe) fractions. Only small quantities of fertilizer P were found as water soluble P, calcium bound P and occluded P. The P derived from H3PO4, MAP and CS was retained in more stable forms than that derived from TSP. The proportion of PAl to PFe was larger in soil B, which had less P fixing capacity, than in soil A. This result suggests that PAl fractions were more available to plants than PFe.
1. INTRODUCTION
Since the 1970’s research on agronomic evaluation of phosphorus sources has increased considerably in Brazil, due to the rising prices of soluble P fertilizers and the dependency of the country on external P supplies [1]. Therefore, the search for alternative phosphate fertilizers has been a constant concern [2].
The use of fluid fertilizers as an alternative for supplying phosphorus to crops is still very limited in Brazil. However, the perspectives of increasing its consumption are promising, due to the advantages offered in relation to solid fertilizers. Among these, the following can be considered: ease in storage and application, better uniformity in application, reduced losses, versality for formulations, less manual work on the product, and lower cost. Very little is known with respect to agronomic efficiency of fluid fertilizers. Nevertheless, according to Silva et al. [3], fluid and solid fertilizers have similar efficiency when applied at the same rate and conditions of application. The few studies carried out in Brazil have been only made with sugarcane [3,4,5]. Information on other crops is scarce.
137 Phosphate ions released by dissolution of soluble P fertilizers added to the soil do not remain stable.
They are converted into less soluble forms through a series of reactions with the soil components.
This phenomenon is known as P retention or fixation. According to [6], P retention is the process by which phosphate ions react with aluminum, iron and calcium ions of soil solution resulting in new phases in the system. These reactions take place in two stages. The first stage is the surface adsorption that is rapid occurring in a matter of minutes or hours. The second stage is slower and involves the migration of P to subsurface layers of adsorbed P, resulting in its occlusion [7].
The complex dynamics of soil phosphorus fixation processes results in a reduction of the P fertilizer utilization by the plants [8]. Therefore, knowledge of soil phosphate transformations is fundamental for establishing rational criteria and better management of phosphate fertilization [9].
The objectives of the present work were a) to evalaute in two Latosols the agronomic efficiency of some fluid and solid P fertilizer, using corn as a test crop in a greenhouse experiment, and b) to determine the fate of the applied P fertilizers into soil inorganic P fractions in the laboratory.
2. MATERIALS AND METHODS
The chemical and physical characteristics of two Latosols are described in Table I. After lime amendment to correct the soil pH to 6.0, using equivalent amounts to 10.8 and 3.9 t/ha of dolomitic lime for soils A and B, respectively, the soils were placed in 1 kg plastic pots. Four P sources were utilized in the study: phosphoric acid, H3PO4 (FA); 10-30-0 colloidal suspension in fluid form (CS), monoammonium phosphate (MAP), and triple superphosphate (TSP). The MAP and TSP were applied in powder form. Applied phosphate rates were 0, 70, 140 and 210 mg P2O5 per kg soil (0, 30.6, 61.2 and 91.8 mg P kg-1 soil). Experimental treatments were replicated 3 times.
Each pot also received additional fertilization consisting of 70 mg N and 120 mg K per kg soil (as ammonium nitrate and KCl) and 1 mL kg-1 soil of a mix of micronutrients. The P fertilizers were applied in a band at a 3 cm depth diametrically in the pots. Eight corn seeds were sown in each pot.
Corn was grown three consecutive times for 30 days each crop. The two successive crops also received N, K and micronutrients at the same rate applied at seeding. Supplements of N and K (160 mg N and 120 mg K/kg soil as ammonium sulfate and KCl) were applied to all three crops on a weekly basis, four times for N and twice for K. After harvest, plant samples were dried, weighed and ground for P analysis by colorimetry, after nitric-perchloric digestion.
For the soil P transformation study, 32P-labelled TSP, MAP, H3PO4 and 10-30-0 colloidal suspension in fluid form (CS) were used. Fertilizers were applied to 200 g of soil at a rate of 91.2 mg P kg-1 soil.
The fertilizers were labelled with 32P at a specific activity varying between 222 to 296 kBq/mg P.
Two Latosols were utilized, a very clayey texture alic Red Yellow Latosol(soil A) and a medium texture alic Red Yellow Latosol (soil B). The soils used were contained in plastic pots and incubated for one month after watering to saturation. During the period the soils were alternatively dried and moistened weekly.
After incubation, soil samples were analyzed for P inorganic fractions, according to [10]: water soluble P (PH2O), Al bound P (PAl), Fe bound P (PFe), Ca bound P (PCa) and occluded P. The 32P activity in each fraction was also determined [11] for identifying the fate of fertilizer P converted to various inorganic soil P fractions.
3. RESULTS AND DISCUSSION
Comparing the dry matter yield data over the 3 crops (Table II), the second crop had values smaller than others in the P fertilized treatment, which coincided with the growing period, when the temperature was the lowest. In the control treatment (without P), however, there was increase in dry matter yield from first to third crop, due probably to increasing availability of native P.
138
TABLE I. PHYSICAL AND CHEMICAL CHARACTERISTICS OF THE SOILS
Soil Sand Silt Clay pH P* Pfc** SiO2 Al2O3 Fe2O3 TiO2
---%--- --mg P cm-3-- ---%---
A 36 8 56 4.1 3 1118 19.0 19.2 19.7 6.5
B 86 0 14 4.2 2 525 2.6 4.1 2.1 0.7
* Resin extractable P
Soil H+Al Al3+ Ca2+ Mg2+ K+ OM
---cmol dm-3---%
A 15 1.4 0.39 0.13 0.11 6.3
B 6.1 0.7 0.25 0.10 0.10 2.9
** Pfc: fixing capacity
The dry matter yield and P uptake were significantly greater in soil B compared to soil A (Tables II and III) probably due to the lower P fixing capacity of soil A. There was no statistical difference amongst the P sources on dry matter yield and P uptake, showing the similarity on P efficiency to corn of the P fertilizers studied in liquid and solid form. The data confirm those obtained by Silva et al.[3], Korndorfer [4], Penatti [5], for sugarcane.
For both soils, fertilizer P was recovered mostly as aluminum and iron bounded P (PAl and PFe).
The contribution of other P fractions such as Ca bound P (PCa), Al and Fe occluded P (Poccl), and water-soluble or weekly soluble P (PH2O) were very small (Table IV). These results could be attributed to the predominance of iron and aluminum oxides with high affinity for phosphate ions in these acid Latosols.
Comparing PAl and PFe, the aluminum bound phosphate was responsible for a larger part of the fixed P. This fact suggests a higher concentration and solubility of aluminum phosphate containing compounds in soil in relation to iron phosphate compounds. In the course of time, part of the PAl is converted to PFe due to the lower solubility of iron bound phosphates. Ultimately, P may be converted to occluded iron and aluminum phosphates [12]. These processes explain the small recovery of the applied phosphates in the occluded P fraction, indicating that the period of contact fertilizers: soil was not sufficient for the P retention reactions to be completed. The ratio PAl to PFe was larger in soil B, which is a less P fixing soil, than in the high P-fixing soil A, suggesting that the PAl fractions are more available to plants than PFe.
139 TABLE II. EFFECT OF P SOURCES AND RATES ON CORN DRY
MATTER YIELD OF CORN GROWN IN THREE SUCESSIVE CROPS IN TWO LATOSOLS
---Crop---
P source(1) P rate I II III Total
mg kg-1 P2O5 ---g pot-1--- ---Soil A---
0 3.99 4.79 5.27 14.05
FA 70 4.74 4.55 5.20 14.49
140 6.56 4.78 6.08 17.42
210 7.55 4.54 6.18 18.27
0 4.02 4.41 6.21 14.64
CS 70 5.14 4.71 6.51 16.36
140 6.38 4.50 6.26 17.14
210 7.58 5.03 6.03 18.64
0 4.14 4.71 6.11 14.96
MAP 70 5.10 4.30 6.17 15.57
140 5.75 4.84 7.11 17.70
210 9.92 4.97 5.96 20.85
0 4.21 4.44 5.44 14.09
TSP 70 5.32 4.87 5.43 15.62
140 5.84 5.51 6.03 17.38
210 6.34 4.94 6.14 17.42
---Soil B---
0 4.28 4.74 6.00 15.02
H3PO4 70 6.44 5.64 6.18 18.26
140 7.22 6.12 8.02 21.36
210 8.02 7.10 8.41 23.53
0 3.99 4.99 5.46 14.44
CS 70 6.79 5.07 6.39 18.25
140 7.52 6.28 7.88 21.68
210 8.86 6.53 8.68 24.07
0 4.49 4.55 5.84 14.88
MAP 70 6.06 5.30 6.82 18.18
140 7.04 6.01 8.12 21.17
210 8.04 6.36 8.80 23.20
0 4.02 4.61 6.21 14.84
TSP 70 6.10 5.46 6.38 17.94
140 7.24 6.47 8.49 22.20
210 8.15 7.01 8.51 23.67
FA= H3PO4; CS= colloidal suspension (10-30-00); MAP= Monoammonium phosphate;
TSP= Triple superphosphate.
140
TABLE III. EFFECT OF P SOURCES AND RATES ON P UPTAKE BY CORN GROWN IN THREE SUCESSIVE CROPS IN TWO LATOSOLS
---Crop---
P source(1) P rate I II III Total
mg kg-1 P2O5 ---mg pot-1--- ---Soil A---
0 3.95 4.04 3.76 11.75
FA 70 5.41 4.30 4.00 13.71
140 8.49 4.26 5.20 17.95
210 10.36 4.28 5.16 19.80
0 4.11 3.88 4.61 12.60
CS 70 5.54 4.50 4.89 14.93
140 7.84 4.13 4.69 16.66
210 11.67 4.67 5.19 21.53
0 3.97 3.81 4.31 12.09
MAP 70 5.50 3.90 4.76 14.16
140 7.18 4.40 5.32 16.90
210 9.70 4.82 5.05 19.57
0 4.13 3.88 3.96 11.97
TSP 70 5.81 4.36 4.27 14.44
140 7.79 5.09 4.81 17.69
210 8.83 4.49 4.60 17.92
---Soil B---
0 4.39 4.23 4.59 13.21
H3PO4 70 8.50 5.10 5.27 18.87
140 11.96 6.02 6.51 24.49
210 15.58 7.18 7.09 29.85
0 4.15 4.44 4.20 12.79
CS 70 9.14 4.62 5.23 18.99
140 13.91 6.03 6.30 26.24
210 19.44 6.44 7.21 33.09
0 4.35 3.96 4.24 12.55
MAP 70 7.19 4.98 4.86 17.03
140 12.20 5.95 6.82 24.97
210 17.19 6.18 7.59 30.96
0 4.06 3.97 4.08 12.11
TSP 70 7.83 5.21 5.03 18.07
140 11.76 6.35 6.95 25.06
210 14.42 6.99 7.71 29.12
FA = H3PO4; CS = Colloidal suspension (10-30-00); MAP= Monoammonium phosphate; TSP = Triple superphosphate.
141 The data of Table IV also show the significant effect of P sources on the inorganic P fractions.
The effect is more pronounced in soil B that probably occurred due to the higher recovery of the applied phosphate in this soil.
The P recovery in all fractions in soil B and in PH2O and PAl in soil A was significantly larger for TSP than the values obtained for other sources. Nevertheless, these differences are small in terms of alterations in soil P fertility levels, and thus, it may be concluded that fluid and solid fertilizer P have similar fate in the Latosols studied.
TABLE IV. PHOSPHORUS DERIVED FROM THE FERTILIZER IN DIFFERENT P INORGANIC FRACTIONS OF TWO LATOSOLS AS AFFECTED BY P SOURCES
P inorganic fraction*
P Source PH2O PAl PFe PCa Poccl.
---mg P g-1 soil--- Soil A
TSP 0.8 a 41.4a 17.4 1.1 2.0
H3PO4 0.3b 36.3bc 16.2 1.2 2.0
MAP 0.4b 38.6ab 16.2 0.9 1.6
CS 0.3b 32.4c 15.1 1.2 1.7
CV % 27 6 13 20 19
Soil B
TSP 2.9 a 102.6 a 15.4 a 1.1 a 0.4 a
H3PO4 1.5c 51.2c 6.4c 0.4c 0.1b
MAP 2.4b 77.3b 12.0b 0.8b 0.1b
CS 1.7c 50.6c 8.1c 0.4c 0.1b
CV % 11 12 8 23 29
*PH2O= water soluble P; PAl = Al bound P; PFe= Fe bound P; PCa= Calcium bound P;
Poccl.= Occluded P. The values in the same row followed by the same letter are not significant.
4. CONCLUSIONS
1. No significant differences in dry matter yield and P uptake of corn were found for the fluid and solid P fertilizer sources studied.
2. Corn dry matter yield and P uptake showed a linear response to the increasing P rates. These effects were more pronounced in soil B, due to its lower P-fixing capacity.
3. In both Latosols, the agronomic efficiency of fluid and solid fertilizers was equivalent, demonstrating the potential for the application of fluid P sources for annual crops such as corn.
4. In the one-month incubation experiment, the larger proportion of soil-applied P sources was recovered as aluminum and iron bound P fractions. Only small quantities of P were found as water soluble P, calcium bound P and occluded P. The ratio PAl to PFe was larger in soil B, with less P-fixing capacity.
142
ACKNOWLEDGEMENTS
Financial and technical support of the International Atomic Energy Agency (IAEA) under research contract BRA-7500 is greatly acknowledged.
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143 PHOSPHATE FERTILIZERS WITH VARYING WATER-SOLUBILITIES
APPLIED TO AMAZONIAN SOILS: I. AGRONOMIC EFFICIENCY OF