Transcript Diapositiva 1

TOTAL AND EXTRACTABLE PHOSPHORUS CONCENTRATIONS AT DIFFERENT DEPTHS
IN A SOIL FERTILIZED WITH MANURE
R. DA SILVA DÍAS
1,
C. A. de ABREU
2,
R. M. MESTAS VALERO
1,
1
J. M. MIRÁS AVALOS & E. VIDAL VÁZQUEZ
1
1 University
of Coruña (UDC). Faculty of Sciences. A Zapateira 15008, La Coruña-Spain. E-mail: [email protected]
2 Agronomic Institute of Campinas (IAC).Barão de Itapura, 1481, Campinas, SP, Brazil. E-mail: [email protected]
INTRODUCTION
RESULTS
Phosphorus (P) is an essential element for plant and animal growth and its input has long been recognized as
necessary to maintain profitable crop and sustainable agriculture. However, intensification of crop and animal
farming in many areas has created regional imbalances in P inputs in feed and fertilizer and P output in farm
produce.
In many of these areas, soil P has built up to levels in excess of crop needs and now has the potential to enrich
surface runoff with P. This is the case in Galicia, northwestern Spain, where many cultivated soils analyzed were
ranked in categories with high or excessive of phosphate evels.
A number of extraction methods have been proposed to assess soil phosphorus availability. The extractable capacity
of these methods and their suitability depends on the type of soil and the degree of accuracy that we want to obtain.
OBJECTIVE
The aim of this work was to evaluate the effect of soil surface roughness on soil losses and
runoff for different tillage systems.
MATERIAL AND METHODS
The research was carried out in a plot located in
Ribadeo (Lugo Province, NW Spain).
Soil type: Umbrisol
The soil was classified as an Umbrisol.(WRB).
Soi texture: loam
Rotation was maize followed by winter cereal.
Rotation: maize and winter cereal
The study area was 625 m2.
 A total of 36 soil samples in 9 points at 4 different
depths: 0-5; 5-10; 10-20; 20-40 cm were collected.
Total P was determined after microwave digestion with
nitric acid, following USEPA method 3051.
Sampling: at 0-5, 5-10, 10-20 and 20- 40 cm depth
DETERMINATION OF AVAILABLE PHOSPHORUS
MEHODS
AER and O extractions
Mehlich-3 extraction
 Extractable P was assessed by :
- Mehlich-3 extraction followed by two different
determination techniques (ICP and colorimetry, M3-ICP
and M3-COL, respectively),
DETERMINATION
ICP-AES
Colorimetric
Colorimetric
Tukey’s test and Pearson’s r coefficient were used for
data analysis
All the methods, except anion
exchange resin, provided the highest
P concentrations at the 5-10 cm
depth, though they were not
significantly different than those
measured at the 0.5 and 10-20 cm
depths. At 20-40 cm depth, the
significantly lower P concentrations
were observed independently of the
method used
 Thresholds for excess P contents
using the Mehlich-3 and Olsen
methods have been reported as 31
and 21 mg kg-1, respectively. Our
results exceeded these thresholds in
every depth. However, they were
within the range reported by
Sharpley et al. (2004), who observed
P values fot total P ranging from 407
to 2480 mg kg-1 at a depth of 0-5 cm.
Depth
(cm)
P Total
(mg/kg)
P M3 (mg/kg)
COL
P AER
(mg/kg)
P OL
(mg/kg)
ICP
0-5
1793 a
664 a
598
583 a
154 a
5-10
1814 a
669 a
607 a
600 a
156 a
10-20
1633 ab
652 a
606 a
625 a
146 a
20-40
1453b
539 a
538 b
491 b
119 b
Mean P contents at sussesive depths. Total P= after microwave digestion,
M3=Mehlich-3 (ICP and COlL: Colorimetric), AER= Resin and Ol= Olsen.
Different letters in the column indicate significant differences (P < 0.05)
 The relatively high concentrations of P at the 20-40 cm depth can be attributed to
soil mixing during deep plowing.
 P values obtained by Mehlich-3 showed significant correlations with those from
the Olsen and resin methods (r values varied between 0.64 and 0.82). In addition, P
measured by Olsen and resin were significantly correlated (r = 0.69).
CONCLUSIONS
 Phosphorus accumulation in the studied soil suggests an intensive application of organic manures for several years.
 No significant differences were found between P concentrations at te 0-5 cm, 5-10 cm and 10-20 cm depth. Also relatively high
concentrations of P were recorded at the 20-40 cm depth, which are thought to be caused by deep plowing,
Based on our results it would be advisable to cease manure additions to the studied soil until the P level decreases.
- anion exchange resin (AER) extraction followed by
colorimetric determination
- Olsen (Ol). Extraction and colorimetric determination.
 Extracted amounts of P (Table 1)
were much higher than expected
and they were also relatively high
compared to those measured by
other researchers in these region.
Summary of methods used for extraction
and determination of available
phosphorus
REFERENCES
Sharpley, A.N., R.W. McDowell, and P.J.A. Kleinman. 2004. Amounts, forms, and solubility of phosphorus in soils receiving
manure. Soil Sci. Soc. Am. J. 68:2048–2057