President Rodrigo R.
Duterte emphasized the conduct of soil analysis in the country during his first
State of the Nation Address (SONA) on July 15, 2016. He said that “we shall
also conduct a nationwide soil analysis to determine areas most suitable for rice
farming to optimize production with the use of effective soil rehabilitation
and fertilization.”
As an effect of this
presidential pronouncement, many people including professionals from various
academic fields have been wondering what soil analysis is. Several readers of
this blog suggested that I write about this topic hence, this article.
Soil analysis refers
to the measurement of soil physical, chemical, and biological properties. It is
done, depending on the type of soil analysis, for the following purposes: 1) to
evaluate the origin and formation of the soil; 2) to assess the level of contamination
of the soil; 3) to characterize the soil as a habitat of soil organisms; 4) to
assess the soil fertility status, and 5) to evaluate the soil’s suitability for
certain crops. Soil analysis is generally synonymous with soil testing. The
major steps of soil analysis are soil sampling (and field soil examination) and
laboratory analysis.
 |
| Soil profile examination and sampling to evaluate the origin of the soil |
The first type of
soil analysis is the most difficult and complex type. It is carried out by soil
specialists called pedologists. It
involves detailed field description of the soil using standard procedures such
as the Guidelines for Soil Description (4th edition by Jahn et al., 2006)
published by FAO, Rome. Soil description is done on newly dug soil pit at least
1.5m deep or fresh road cuts. The collection of soil samples for intensive
laboratory analysis is done on every soil layer (soil horizon) down to the
bedrock. Laboratory analyses include the physical, chemical, and mineralogical
properties of the soil. Geochemical analysis of rock samples is also necessary.
The second type is
conducted by soil scientists interested in soil pollution or contamination.
Soil samples are usually collected in areas where soil contamination is
suspected. Soil sampling is done at random or at fixed intervals. Only the topsoil layer (0-10 or 0-20 cm) is sampled using a soil auger or a similar sampling
tool. Soil samples are analyzed for their contents of soil pollutants (e.g.
heavy metals) and are compared with published threshold values to know if the
sample is contaminated or not.
 |
| Soil sampling to assess the contamination of Taft River in E. Samar |
The third type of
soil analysis is conducted to know if the soil is favorable for certain soil
organisms of interest (e.g. earthworms). This is popular among soil ecologists.
Soil samples are collected usually from the topsoil layer and then they are analyzed
for soil physical and chemical properties. Correlation analysis is then done
between the population of the soil organism and the different soil properties
to know which among the soil properties influences the population of the
organisms.
The fourth type is
the most well-known and commonly done type of soil analysis to support crop
production. The main purpose is to know if the soil is fertile or not.
Specifically, it is performed to assess, using high-tech laboratory equipment, if the soil contains sufficient amounts of
the essential nutrients required by plants (crops) to grow well and produce
good yield (grain, tubers). The essential nutrients that the plant takes up from
the soil include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca),
magnesium (Mg), sulphur (S), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn),
molybdenum (Mo), boron (B), chlorine (Cl) and nickel (Ni). Since N, P, and K are
required by the plant in the largest amounts, these three are usually the nutrients
that are of limited supply in the soil. So farmers need to know how much of
these nutrients must be applied to the soil through fertilizers. The final
result of this type of soil analysis is a fertilizer recommendation.
 |
| Soil sampling for fertility evaluation |
The fifth and last
type of soil analysis is carried out to assess if a certain soil is suitable
for crops such as rice, corn, vegetables, fruit trees, and others. This
involves field soil examination to know the soil’s texture, structure,
drainage, slope, and depth using the methods of the first type of soil analysis.
The soil samples are analyzed for soil chemical properties such as soil pH,
organic matter content, nutrient holding capacity as well as the amounts of the
major nutrients (similar to the third type of soil analysis). The soil
properties are then matched with the ecological requirement of the crop. The
final result is a suitability map or table showing suitable crops for each
soil. It also indicates the soil constraints (or problems) if a crop is grown
in soil that is not suitable for that particular crop.
From the president’s
pronouncement, it looks like that he meant the fifth type of soil analysis. Due
to the tremendous amount of field and laboratory works, it cannot be done by
the Bureau of Soil and Water Management alone. It needs the participation of
universities with strong soil science program throughout the country such as
Central Luzon State University, University of the Philippines Los Banos,
Visayas State University, Central Mindanao State University, and University of
Southern Mindanao.
 |
| Soil science students at VSU performing laboratory analysis of soil samples |
The laboratory step
of soil analysis or soil testing is tedious, time-consuming, and costly because
the chemicals and apparatus required are very expensive. Although there are
some rapid soil test kits available, they are not reliable. Also, the laboratory
analysis has to be done according to accepted procedures and by trained personnel.
Examples of accepted procedures of laboratory analysis of soils are:
Carter M.R. and E.G.
Gregorich (Eds.). 2008. Soil Sampling and Methods of Analysis (2nd ed). CRC
Press, Boca Raton.
International Soil
Reference and Information Center (ISRIC). 1995. Procedures for Soil Analysis
(L.P. Van Reuwijk, Editor). Wageningen, the Netherlands.
Jones J. B. Jr.
2001. Laboratory Guide for Conducting Soil Tests and Plant Analysis. CRC Press,
Boca Raton.
Margesin R. and F.
Schinner(Eds.). 2005. Manual for Soil Analysis – Monitoring and Assessing Soil
Bioremediation. Springer Verlag, Berlin.
Pansu M. and J.
Gautheyrou. 2006. Handbook of Soil
Analysis. Mineralogical, Organic and
Inorganic Methods. Springer Verlag, Berlin.
Schlichting E., H.P.
Blume and K. Stahr. 1996. Bodenkundliches Praktikum (Soil Science Practicum).
Blackwell Wissenschaftsverlag, Berlin.
Sparks D.L., A.L.
Page, P.A. Helmke and R.H. Loeppert (Eds.). 1996. Methods of Soil Analysis Part
3—Chemical Methods. Soil Science Society of America, Madison, Wisconsin.
Westerman R.L.
(Ed.). 1990. Soil Testing and Plant Analysis (3rd ed). Soil Science Society of
America, Madison, Wisconsin.
