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.
Soil type: Umbrisol
Soi texture: loam
Rotation: maize and winter cereal
Sampling: at 0-5, 5-10, 10-20 and 20- 40 cm depth
DETERMINATION OF AVAILABLE PHOSPHORUS
AER and O extractions
- 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.
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
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, J. M. MIRÁS AVALOS 1 & E. VIDAL VÁZQUEZ 1
1 University of Coruña (UDC). Faculty of Sciences. A Zapateira 15008, La Coruña-Spain. E-mail: [email protected]
2Agronomic Institute of Campinas (IAC).Barão de Itapura, 1481, Campinas, SP, Brazil. E-mail: [email protected]
- 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.
- 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.
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
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 research was carried out in a plot located in Ribadeo (Lugo Province, NW Spain).
- The soil was classified as an Umbrisol.(WRB).
- Rotation was maize followed by 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.
- Extractable P was assessed by :
- Mehlich-3 extraction followed by two different determination techniques (ICP and colorimetry, M3-ICP and M3-COL, respectively),
- anion exchange resin (AER) extraction followed by colorimetric determination
- Olsen (Ol). Extraction and colorimetric determination.
- Tukey’s test and Pearson’s r coefficient were used for data analysis
- 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).
Summary of methods used for extraction and determination of available phosphorus