• No results found

Understanding soil analysis data

N/A
N/A
Protected

Academic year: 2023

Share "Understanding soil analysis data"

Copied!
60
0
0

Loading.... (view fulltext now)

Full text

Soil physical fertility represents the ability of the soil to store and conduct water, nutrients and gases. Soil organic matter is important for both chemical and physical fertility and should be an important part of any soil report.

F ORMS OF NUTRIENTS IN SOILS

It is directly involved in plant nutrition as a component of an essential metabolite or required for the action of an enzyme system (Mengel & Kirkby 1982). It is clear from nutrient functions that N, which is taken up by most higher plants in greater amounts than any other essential element, would not be utilized by the plant without the presence of Mo which may be the most absorbed element. a little.

Figure 1.  An illustration of the ‘Law of the minimum’ where copper (Cu) is the least available element,  resulting in only 60 per cent of the potential yield
Figure 1. An illustration of the ‘Law of the minimum’ where copper (Cu) is the least available element, resulting in only 60 per cent of the potential yield

S OIL P HYSICAL P ROPERTIES

There is a direct correlation between the dominant type of clay in the soil and the ability of the soil. A calculation of the lime requirement corresponding to the example below is carried out by the soil testing laboratory. These exchangeable Al+3 ions are again in equilibrium with dissolved Al+3 in the soil solution.

Therefore, the cation exchange capacity of the soil increases as the pH rises from 4.5 to 7.0. Ferdowsian & Greenham (1992) found high levels of salt stored in the soil profile in Upper Denmark (rainfall area 750 mm). In sandy soils, most of the CEC comes from clay and soil organic fractions.

Second, most P compounds are unavailable in soil because they are highly insoluble. In addition, high levels of Ca and Mg in the soil solution can reduce K uptake by plant roots. These changes depend on the pH and organic matter content, temperature and salt content of the soil.

Figure 3.  Major soil textural classes are defined by the percentages of sand, silt and clay (after Marshall  1947)
Figure 3. Major soil textural classes are defined by the percentages of sand, silt and clay (after Marshall 1947)

S OIL REACTION , P H

If the plant absorbs more cations (positively charged ions such as K+) than anions (negatively charged ions such as Cl), it releases H+ into the soil to maintain a. The mix of plant species that dominates a landscape under natural conditions often reflects the pH of the soil (Brady & Weil 2002). The long-term balance between the processes of acidification (production of H+) and alkalization (consumption of H+) in soil systems reflects the pH level of the soil.

From the pH buffer curve of the soil we find that we need 2.1 cmol of lime/kg of soil. Because of the H+ and Al3+ ions in the soil solution (this is the pH measured in field soil tests). ii) Exchangeable acidity: Involves the exchangeable Al3+ and H+ which is easy.

Figure 19 shows that, when the correlation between soil pH and nutrient availability is  considered as a whole, a pH range of about 5.5 to perhaps 7.0 seems to be best to promote  the availability of plant nutrients
Figure 19 shows that, when the correlation between soil pH and nutrient availability is considered as a whole, a pH range of about 5.5 to perhaps 7.0 seems to be best to promote the availability of plant nutrients

S ODICITY

This occurs only in certain acid sulfate soils and occurs from the oxidation of sulfur compounds. For most soils, except potential acid-sulfate soils, the total acidity that must be overcome to raise the soil pH to a desired value is equal to (Active acidity + exchangeable acidity + residual acidity). Most farmers in Western Australia treat soil acidity by applying one to two tonnes of lime sand per hectare. hectares on the topsoil.

The sodium absorption ratio (SAR) can also be used as an indicator of soil sodicity; shows the relationship between soluble sodium and soluble divalent cations, which can be used to predict the exchangeable sodium fraction of soil equilibrated with a given solution. In general, high sodium concentration (high ESP) is usually associated with high soil pH because Ca2+ and Mg2+ ions are usually precipitated out of soil solution by carbonate and bicarbonate ions.

S ALINITY (EC)

For example, a soil that has a CEC of 12 cmol(+)/kg indicates that 1 kg of the soil can hold 12 centimoles of H+ ions and can exchange this amount of charges with the same number of charges from any other cation. This can also indicate to some extent how strongly an individual cation is held on the soil colloids. In all methods, however, the adsorbed cations must be replaced by a single exchange cation such as Ba2+, NH4+, or Sr2+, and then the CEC is calculated either from the amount of the exchange cations used for replacement, or from the amounts of each of the replaced cations originally held at the soil exchange sites (usually Ca2+, Al3+, Mg2+, K+ and Na+).

If the pH of the soil is less than the pH of the buffer solution, then pH-dependent exchange sites that would be negatively charged at pH 7.0 or 8.2 will also be measured. Removing excess acidity by applying lime would in most cases improve the base saturation of the soil.

Table 9.  factors for converting EC 1:5  to EC e  for  different soil texture
Table 9. factors for converting EC 1:5 to EC e for different soil texture

O RGANIC M ATTER (OM)

The resistant or stable part of soil organic matter contributes mainly to cation exchange capacity and color. Evidence that soil structure improves and becomes more resistant to degradation as soil organic matter content increases. Losses of soil organic matter and aggregate stability are considered standard features of unsustainable land use.

Much of the impact of organic matter on soil health is achieved by stimulating soil microorganisms. The process is based on the oxidation of organic matter in the soil with dichromate in the presence of sulfuric acid.

Figure 20.  Soil high in organic matter is granulated and has significantly  lower bulk density compared to soil low in organic matter
Figure 20. Soil high in organic matter is granulated and has significantly lower bulk density compared to soil low in organic matter

N ITROGEN (N)

In general, organic matter contains about 50 percent organic carbon, so multiplying organic carbon (OC) by two gives a good estimate of organic matter. The durability of organic matter depends on the rate of decomposition, which exposes more surface area for interaction. However, partially decomposed organic matter provides an important source of energy and nutrients for soil microorganisms and also helps soil compaction.

Soils with low organic matter require more artificial nitrogen than soils rich in organic matter. The ideal organic matter content is around 4 to 6 percent, but this is difficult to achieve in low-rainfall areas, where average organic matter is usually in the 1 to 3 percent range.

S ULPHUR (S)

P HOSPHORUS (P)

Although the actual dosage depends on economic considerations, the soil survey forms a good basis for fertilization planning. For example, a P-Recovery of 50 percent means that if 10 kg of phosphorus is introduced into the soil as fertilizer, only 5 kg is available for the plants. The Phosphorus Retention Index is used to assess the soil's ability to leach or 'fix' phosphate applied as a water-soluble fertilizer.

The plant yield response curve for Colwell P (see below) varies with soil type, particularly influenced by the P adsorption characteristics. When the P binding capacity of a soil is not saturated, a large portion of the applied P will be fixed by the soil and for optimal crop yield it will require much higher doses of P fertilizer than the.

C ALCIUM (C A )

Calcium can be supplied as agricultural gypsum, lime or dolomite and also in calcium and rock phosphate fertilizers. Measurement of exchangeable and soil solution Ca is the basis of diagnostic soil tests for Ca. For example, exchangeable Ca can be expressed as a percentage of CEC (Ca saturation) or as the ratio of Ca to Mg.

Soil solution Ca is often expressed as a Ca activity ratio, which is the ratio of Ca activity to the sum of the activities of all major cations in solution. Calcium will also suppress manganese uptake, so a deficiency can be caused by the application of gypsum.

Table 13.  Analytical data for topsoik and subsoil of acid soils (Bruce et al. 1989 )
Table 13. Analytical data for topsoik and subsoil of acid soils (Bruce et al. 1989 )

M AGNESIUM (M G )

P OTASSIUM (K)

Surprisingly, these critical values ​​in surface soils are similar for most agronomically important plant species and are generally around 0.2-0.5 cmol(+)/kg or 80-200 ppm for Australia in general, and around the 60 ppm for mostly duplex soils in WA. This is due to the fact that there are more exchange surfaces in a high CEC soil, so a higher amount of potassium is also available. Symptoms first appear on the oldest leaves, speckled along their entire length, and in severe cases spread rapidly to the tip and margins.

As leaves die back from the tip and edges, a spear-shaped pattern of green remains.

C OBALT (C O )

B ORON (B)

The absorption of B by plant roots is determined by its concentration in the soil solution and correlates well with the assessment of plant toxicity and response to a wide range of soils (Aitken & McCallum 1988). Soil testing is difficult due to high spatial variability and high B concentrations in the subsoil, which is more difficult to sample. Scattered across the field, toxic patches of pine occur irregularly, stunting growth and causing low yields.

B reacts more strongly with clay than with sandy soil, which makes clay soil a better buffer for B in the soil solution than sandy soil. Unlike all other essential plant nutrients, B is mainly present in the soil solution as non-ionized boric acid, B(OH)3, which under high soil pH conditions is only slightly deprotonated (dissociated).

I RON (F E )

M ANGANESE (M N )

Determining the Mn status of field soils for adequate plant growth requires measurement of water-soluble plus. Time of sampling, field conditions at the time of sampling, time taken for and conditions of drying and storage prior to analysis can all affect test values. The reducibility of the oxides is related to the exposed surface area of ​​these oxides.

There are quite large differences between species and cultivars of the same species in their tolerance to toxicity and deficiency. Mn concentration in plants can also be suppressed in soils with high potassium content or after applications of calcium or potassium.

C OPPER (C U )

However, there is no clear link between the mechanism of tolerance to toxicity on the one hand and tolerance to deficiency on the other. Organic matter and Fe and Al oxides in WA soils have been reported to strongly bind Cu and influence its availability to plants (Brennan 1986). Copper deficiency can be caused by an excess of molybdenum in the soil, and the availability of iron and copper to plants is affected by soil pH.

The desired content of Cu in ammonium oxalate extracted soil is higher than 0.8 ppm. The desired level in DTPA extracted soil is around 0.2-0.3 ppm (Ross Brennan, DAFWA, pers. comm.).

Z INC (Z N )

M OLYBDENUM (M O )

In soil, Mo occurs in clay minerals, bound to organic matter and in soil solution. The soil solution Mo is readily available to the plant, followed by MoO42 which is poorly held on the surface of clay or secondary minerals, while Mo held in primary mineral structure is only sparingly soluble and considered unavailable to the plant. At the time of sampling, tissue tests may be able to diagnose Mo deficiency in some crops.

Symptoms of Mo deficiency are difficult to detect in the field, however the middle leaves show yellow speckled spots or streaks and appear limp and water stressed. Physiological effects such as flagellar constriction are often mistaken for a symptom of Mo deficiency.

S ODIUM (N A )

A LUMINIUM (A L )

Base saturation percentage: The degree to which the adsorption complex of a soil is saturated with exchangeable cations other than hydrogen and aluminum. Exchangeable sodium percentage: The extent to which the adsorption complex of a soil is occupied by sodium. Permeability, soil: The penetration of water and gases through a large mass of soil or a layer of soil.

A review of the utility of relative bulk density values ​​in soil structure and compaction studies, Soil Tillage Research 53: 71-85. In: Lal R, Blum WH, Valentine C and Stewart BBA (eds), Methods for assessing soil degradation.

Figure

Table 1.  Average nutrients contained in 1 tonne of grain of different crops.  Note that
Figure 1.  An illustration of the ‘Law of the minimum’ where copper (Cu) is the least available element,  resulting in only 60 per cent of the potential yield
Table 2.  Classification of plant nutrients
Table 3.  Some physical properties of the major soil texture classes  Texture class  Size (mm)  Number of particles
+7

References

Related documents

58 QUANTIFYING SOIL CARBON SEQUESTRATION IN KIWIFRUIT ORCHARDS: DEVELOPMENT OF A SAMPLING STRATEGY M Deurer1, H Rahman2, A Holmes2, S Saunders2, B E Clothier1 and A Mowat3 1The