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Influence of lime and farm yard manure

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par Dieudonne MUGOBOKA
ISAE Busogo - Bachelor's Degree 2008
  

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2.3 Lime and organic matter on soil P availability, crop growth and yield

2.3.1 Meaning of soil amendment

Soil amendment is substance incorporated in soil to improve its physical and chemical conditions.

The amendments influence the soil reaction, especially in p H, its humus content, on the elimination of some impeding elements, on the modification of clay content, on the soil heating and on soil workability.

To amend a soil is to use a set of measures and techniques to improve its capacity of workability and yielding (Clement, 1981). 

 

2.3.2 Types of soil amendments

2.3.2.1 Organic amendments

They are used to maintain the humus stock in soil, increase water holding capacity, make soil se aggregates stable, improve soil structure, increase the availability of plant nutrients(P, Ca, Mg, K) ,stimulate microbial activity, and bring organic substances that are favorable to plant growth and development (Clement,1981).  

According to Bodet (20010), the organic amendments are fertilizers mainly composed combination carbonated compounds from plants, decomposable, used to maintain or restore soil organic matter store.

They are used to: 

Ø Improve the germination quality .especially in compact soil;

Ø Increase the capacity of soil to hold water and cations especially in sandy soils;

Ø Create favorable conditions to soil microorganisms;

Ø Improve soil workability and seeding conditions

The influence of organic matter on plant growth may be studied under two main headings, namely, its effects on physical condition of soil and the role of organic material in supplying nutrients to plants. The term organic matter has a very broad meaning because it includes all materials of vegetable and animal origin developing in or applied to the soil regardless of the stage of decomposition.

Thus, the term `'soil fraction'' known as humus, as well  the roots and tops of plants containing much easily decay able carbohydrate and protein material and in addition to the bodies of microorganism, worms, insects, and other animals, and also animal manures, and similar materials applied to the soil(Millar,2004).

According to Syers et al (1994), the organic matter level in soil is important in helping to maintain an active population of soil organisms to promote organic matter mineralization and pesticides decomposition, minimize development of pest organisms, promote and stabilize a favorable physical condition in the soil and promote the absorption of nutrients by plant roots. The effects of soil organic matter imply that the level of organic matter may be taken as indicator of the sustainability of soil management system. If the organic matter level falls away from an established ,satisfactory level for a given soil and land use system, the system is likely to be non sustainable.

All organic materials ,after they have been partially digested by the soil organisms, are gradually changed into dark -colored ,structure lees mass ,having colloidal properties and called `'humus''. The humus exerts a most important influence on soil productivity, and its value can be fully appreciated after the various physical, chemical and biological effects produced by it have been considered (Millar, 2004).

Organic matter is of extreme importance in regard to crop growing because of many useful effects it produces in soil, and many of these effects are purely physical.

Organic matter increases water retaining power of soils, decreases water runoff losses, improves aeration, especially on the heavier soils, and produces a better soil structure or tilth. Owing to the fact that organic matter decreases water -runoff losses, the damages done by either water and wind erosion is greatly reduced.

That portion of organic matter which has undergone considerable decomposition assumes colloidal properties for the most part and as such has a very high absorptive capacity of water. On the dry weight basis, humus may be considered in this case to act as a sponge, and it becomes obvious why it has the ability to hold several times its weight of water. Soil water is also retained in the small pores or air spaces between soil particles.

In the more sandy soil, these spaces frequently are too large for maximum water retention and humus tends partially to fill these large spaces and make them a more effective size for holding water. The humus also tends to pull the sand particles together, thereby increasing water retention. In heavy clay soils, the pore spaces between the mineral particles frequently are too small for the greatest moisture storage.

Organic matter improves this condition by forcing the soil particles apart, thus increasing the ability of those soils to retain water (Millar, 2004)

Organic matter improves the soil chemically by serving as store house or supply of plant nutrients element. As the organic matter decomposed, the plant food elements contained there in are gradually released.

Most of the soil nitrogen supply exists in organic form. Nitrogen can not be held in organic combination. This organic nitrogen gradually undergoes conversion into nitrate under normal soil conditions, and in the absence of growing plants most of nitrate may leach out.

Decomposition of organic matter favors the release of plants food elements from the soil minerals. Various organic and inorganic acids are produced in soils when organic matter decays and they have a very pronounced dissolving effects on soil minerals. One of the important end products of organic matter decay is carbon dioxide gas. This gas dissolves in the soil water and forms carbon acids ,which is an effective dissolving agent for the soil minerals ,the dissolving effect of this carbonated water is several times that of pure water. After the organic matter has undergone considerable decay, it largely assumes the colloidal state.

The colloidal properties thus exhibited exert important physical and chemical effects which are directly concerned with soil productivity. The organic colloidal materials have a much greater Base Exchange Capacity per unity weight than do the colloidal minerals, and hence they may act as buffers in the soil, thereby retarding the process by which changes in soil reaction (acidity or alkalinity) are produced.

Furthermore, these colloidal substances have a strong ability to adsorb or hold on the constituents of fertilizers and nutrients released from minerals, thus decreasing their rate of loss by leaching (Millar, 2004). 

According to Pieters et al (2004), while our knowledge of the activity of soil microorganisms is in many aspects incomplete, it is known that, in addition to transforming organic nitrogen into nitrate and the fixing of atmospheric nitrogen, they profoundly affect the mineral plant food material.

Just how this is done cannot be fully explained in all cases, there is no doubt that in the decomposition of organic matter; mineral nutrients can be made available to crop plants. Jensen found that, 3 % of green manure and stable manure mixed with the soil and allowed to undergo partial decomposition increased the solubility of calcium and phosphoric acid in the soil from 30 to 100 %.

According to Paddock and Whipple (2003), when bone meal was subjected to the action of carbon dioxide, 2.11 %of the insoluble phosphoric acid was made soluble in an hour and 5.21 % in two hours. When the ground phosphate rock was treated in the same way ,0.16 %of insoluble phosphoric acid was made soluble in one hour and 0.28%% into two hours.

Magnesium phosphate similarly treated yielded in one hour 16.33% and in two hours 22.35 % of soluble phosphate acid. When green manures are turned under large quantity of carbon dioxide are produced and, since the soil solution acidulated by dissolving carbon dioxide is known tom act powerfully on soil mineral ,it is probable that the effect of green manure on the availability of rock phosphate is to be attributed to this by-product of micro organic activity.   

Organic matter improves the soil for the growth of microorganisms which, after all, are the agents whereby the plant food elements of the soil are kept in circulation.

It serves as a source of food and energy for the majority of the soil microorganisms. The soil may be considered as a factory operating to produce plant nutrients. The soil microorganisms may be considered as the power or driving force in this factory, and the soil organic matter as the fuel or energy for this power.

The organic matter is burned to carbon dioxide, water, ash, and various other products, the nature of which is determined largely by the degree of soil aeration .The organic matter constituents constantly are being burned in the soil shown by the continuous evolution or output of carbon dioxide. The complex constituent of organic matter, are simplified and nitrogen in the ammoniac form is released and changed to the nitrate form.

The energy stored in the compounds of growing plants for the most part eventually is either used or released by soil microorganisms whose activities within the soil make food elements available for a new generation of crop plants .

Thus, it can be said that, without the presence of organic matter to supply food and energy for the soil microbes, plant food elements of the soil could not be changed to usable forms.  

As noted by Stephens (2001), organic matter is broken down by organisms living in the soil, such as fungi, bacteria, algae, molds, insects and earthworms. In the process, nitrogen and other nutrients are converted to forms a plant can use. Nitrification is the term used for the conversion of organic nitrogen to available forms. Since nitrogen is the nutrient most often limiting plant growth, you must make sure that the following conditions exist in your soil (or compost pile) for good nitrification to occur:

Ø Nitrogen-rich materials

Ø Proper acidity (pH): 5.8 to 7.0

Ø Proper temperature over 50°F

Ø Good aeration

Ø Adequate soil moisture.

Table : Characteristics of soil organic and associated effects on soil properties and plants.

Properties

Effects on soil

Effect on plants

Color

O.M imparts dark color in soil

Can increase surface soil temperature and advance germination and seeding growth

Water retention

O.M retains 20 times its weight in water.

Increase water availability to plant by improving water holding capacity, especially in sandy soils, also increase infiltration.

Chelating

Form stable complexes with Fe2+, Mn2+, Ca2+ and other cations.

Enhance availability of micronutrients to plants.

Interaction with Clay

Helps cement soil particles in aggregates

Enhances plant growth by improving soil structure, which enhance gas exchange ,water infiltration and root proliferation through  soil 

Solubility in water

Humus is insoluble in water due to its association with clay, some organic compounds

Soluble organic compound complexes with nutrients can leach through the profile, moving nutrients from the soil surface to subsoil areas.

Buffering capacity

Exhibits p H and nutrients buffering

Help buffer changes in  p H and nutrients solution

Cations exchange

The total C.E.C ranges from 300 to 1400 meq/100gr

O.M may increase CEC 20to70%

Mineralization

O.M decomposition yields CO2 and nutrients

Increase nutrients availability

 Source: Havlin (2005)

 

As has already been pointed out, soil organic matter has its origin for most part in the plants. Its accumulation in any soil at any particular time represents the difference between the quantities of plant residues and decay activities of microorganisms. This organic material, regardless of its origin, is found in soil in all stage of decomposition. It may vary from the fresh material to that which has undergone extensive chemical changes. It may occur as leaf or vegetable mold, peat, muck, or humus depending on the nature and extent of changes it has undergone. 

The decomposition of organic matter is a biochemical process and is brought about primary by microorganisms, the most important of which in most soils are bacteria, fungi, and actinomycetes. The decomposition of organic matter is extremely variable and complex which also vary constantly.  

Table : Composition (%) of humus from different source of organic matter.

Erreur ! Source du renvoi introuvable.                                 Manures

Nutrients

Cow manure

Green clover

Oat straw

Carbon

41.95

54.22

54.30

Hydrogen

6.65

3.40

2.48

Nitrogen

6.16

8.24

2.50

Oxygen

45.63

3.14

40.74S

 

Source: Pieters (2004)

Since the decomposition of organic matter in the soil is a biochemical process, any factor that affects the activities of the soil organisms will necessarily affect the rate of organic matter decay.

Several influential factors which have a bearing on the rate of organic matter decomposition may be placed in the three following groups: factors concerned with the nature of plant material (including such points as the kind of plant, age of plant and chemical composition), soil factors (including aeration, temperature and fertility) and

climatic factors (the effect of moisture and temperature are particularly influential).

Humus denotes the soil organic matter which has undergone extensive decomposition.

It is a homogeneous compounds, it has no definite chemical composition. It is a dark colored, homogeneous mass, consisting of plant and animal materials together, with the synthesized cell substances of soil organisms.

Humus is not sticky, dynamic in soils; it is a continually undergoing change. It has been pointed out that, during the decomposition of plant and animal residues, in soils, some organic constituents are more readily attacked than others and some are extremely resistant to decomposition. The starches, sugars, proteins, and amino-acids are rapidly attacked by a great variety of organism and associated with these changes, is a considerable synthesis of microbial cell substance. The cellulose and especially hemi cellulose are decomposed rapidly by a rather large variety of micro-organisms (Millar, 2004).  

Figure : Processes involved in fresh organic matter decomposition into humus. 

             Fresh organic matter

Erreur ! Source du renvoi introuvable. 

Decomposition

           Fine organic matter

Erreur ! Source du renvoi introuvable. 

Humification


 

Erreur ! Source du renvoi introuvable. Erreur ! Source du renvoi introuvable.          Humus    Mineralization             Mineral elements 

Source: FAO (1982)

 

Considering their organic matter content, the nature of the organic matter and the applied doses, some farm yard manure are considered as organic amendments. The farm yard manure improves, with the character of organic amendment, improves physical properties of soil when it is incorporated in soil). 

The farm yard manure contains some acid compounds, susceptible of liberating H+ ions (H2CO3,NH4,H2SO4,etc...) and basic compounds, susceptible of retaining H+ ions(HCO3,CO3,NH3,SO2- ,Ca(OH)2,Mg(OH).The use of farm yard manures was thought to increase the soil acidity;

In contrast, this was true only the use of farm yard manure containing much ammonia. In this case, the experiment conducted by ITCF (1982-1990) has shown that the use 330kg /year of lime has not been sufficient to maintain a p H on initial level in the treatments that has received ammonitrate 33.5 %.Thus, the total or partial replacement on ammonitrate by farm yard manure has contributed to the increase of initial p H. 

The effect of farm yard manure on soil p H depends on its chemical composition and transformations that happens after its incorporation in soil; In some cases, there is an increase of soil p H or alkalinization, i.e. fixation of H+ by anions such as OH- .In other cases, there is a decrease of soil p H or acidification i.e. liberation of H+ in the soil. The mineralization of organic P is a particular case; it rends  to increase p H in acidic soils by formation of complexes compounds with aluminum, and  decrease soil p H in alkaline soils by formation of apatite   (Bodet, 2001).

In the arable land, the p H can be maintained by compensate the annual bases losses (OH-,HCO3-,SO4- ,NH3, etc.. ) which neutralize the acids (H2SO4,Hcl,,HNO3, Fe3+,Al3+ etc.).These losses comprise the exportation and leaching. This concerns soils susceptible of acidification (which does not contain CaCO3) (Bodet, 2001,). 

The wealth of farm yard manure in mineral elements is reflected by the plant wealth in mineral. The analysis shows that in the same leaps, the composition of farm yard manure is not homogeneous; the nitrogen and phosphoric acid content are generally more from the bottom to the top consequently.

According to FAO (1977), the experiments done in the station has shown that 2.17% of N, 1.3%of P2O5   of dry matter in the bottom layer of the heap, while the top layer contained 1.82%of N and 0.8% of P2O5 of dry matter. 

Major characteristics of FYM

Ø Residual effects are only fairly strong;

Ø Relative high moisture;

Ø Imbalanced nutrients but high in organic matter; and

Ø Low in mineral nutrients but high in organic matter.

Compost is the result of aerobic decomposition of biodegradable organic matter, producing compost. Composting is the decaying of food, mostly vegetables or manure. The decomposition is performed primarily by facultative and obligate aerobic bacteria, yeasts and fungi, helped in the cooler initial and ending phases by a number of larger organisms, such as springtails, ants, nematodes and oligochaete worms.

Composting can be divided into home composting and industrial composting. Essentially the same biological processes are involved in both scales of composting; however techniques and different factors must be taken into account. 

Green manuring is the practice of turning into the soil undecomposed green plant tissue. The function of a green manure crop is to add organic matter to the soil. As a result of the addition, the nitrogen supply of the soil may be increased and certain nutrients made more readily available, thereby increasing the productivity of the soil.  

According to Warman (2001) green manure offers the following benefits:


·        Increases organic content of soil;

·        Increases nutrient availability;

·        Improves the tilth of soil,

·        Restricts growth of weeds,

·        Helps in pest control and 

·        Increases biological activity in the soil

Agronomists have argued that green manuring will increase either the humus content or the supply of available nitrogen in the soil, but rarely both at the same time. The humus content is only increased appreciably if material fairly resistant to decomposition is added to the soil (high Carbon: Nitrogen ratio), and this type of plant material is typically low in nitrogen (less than 1.5 per cent on a dry-weight basis).

The available nitrogen supply is only increased if readily decomposable material high in nitrogen, such as immature green plants, is incorporated into the soil. The amount of organic matter that may accumulate will vary with the soil, climatic conditions, and the age and type of crop.

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