Cultivation techniques

From Appropedia

Coursebook: Cultivation techniques Course from: 1st year of Herbalism Course year: 2005 - 2006 Education center: Syntra, Asse-establisment Teacher: Leo Van Crombrugge

Part 1: Soil science

[edit] The soil as a planting site

The word soil has 2 meanings:

the earthcrust: the study of the earth's crust = geology or geology
the planting site for a plant: the study of the soil as a planting site = soil science or pedology

Soil = the upper loose part of the earth's crust upto a depth that is of importance for the plant. The thickness of the soil varies in Belgium between a few cm (high Belgium) to 1-2 m (low and middle Belgium).

Soil is the medium or substrate through which the plant absorb their nutrients. This absorption is dependent on many factors such as:

the amount of water and air in the soil
the heat of the soil
Nutrition status and soil acidity

These factors determine whether a soil is aduquate or not.

[edit] Soil constituents

When we look at a clod of earth, we distinguish:

Solid constituents
Large and small cavities filled with air or water

[edit] Solid constituents

a. Mineral constituents Rock particles are created from large rocks due to weathering (wind, water, cold, ...). They are somtimes microscopic (powder-like in appearance). These mineral particles (dead material) form the skeleton of the soil, around which other components group to a complicated complex: the clay-humus complex.

b. Organic constituents These occur in the topsoil and are essentially waste from living organisms (plants and animals). These are further digested to humus in the soil, which is a black sticky substance that gives the soil its dark color. Organic ingredients make life possible in the soil.

c. Living constituents

Plants: especially plant roots
Animal organisms: moles, worms, insects
Micro-organisms: fungi and bacteria

These are important for:

the conversion into fertilizer
the formation of humus

[edit] Liquid constituents

Soil water is not pure but it is a solution of all several compounds of whom the most important are fertilizers. It is present in cavities and pores and unto sticky substances such as humus. It is one of the most important elements in the soil.

[edit] Gaseous constituents

Soil air has almost the same composition as atmospheric air

gas	soil air	atmospheric air
oxygen	19,2%	20%
Nitrogen	80,8%	78,95%
CO₂	0,2 - 0,7%	0,03%

Soil air contains 10 - 20 times more CO₂ as atmospheric air. This is caused by the digestion of organic matter and the respiration of the plant roots and soil organisms.

With an aduquate soil, the solid, liquid and gaseous constituents need to be present in a suitable composition.

[edit] Soil types

[edit] Particle size fractions

The solid constituents of the soil are more than 90% mineral particles of different sizes, ranging from a pebble to a microscopic particle (clay). The particles are classified according to their particle sizes (called fractions). We use the micron as a measuring unit. A micron is 0,001 mm or 1/1000th of a mm and is indicated by the Greek letter µ (pronounced mu). In the soil, one can distinguish the following fractions:

[edit] Soil texture

The whole of the different sizes of soil particles determine the particle size composition or soil texture. eg: 90% sand fractions and 10% clay fractions. Depending on which of the fractions dominate, we speak of a sandy, clayish, or loamy soil. These are the soil types.

The soils are divided in Belgium according to their composition.

Soils that have more than 30% organic material is called peat soil, those with more than 15% organic material are called humus soils.

[edit] Agricultural value

In practice, we speak of light and heavy soils, this relates to the manipulatability of the soil. Sandy, loam-sandy, and light sand-loamy soils are easiest to manipulate, these are light soils. Opposed to this are the clayish and loamy soils, which are more difficult to manipulate, these are heavy soils. As for the yield, it's the other way around. The lightest soils are the worst and require a heavy fertilization. Medium light soils such as sand-loamy and loamy soils give the highest yields and have the widest crop choice.

Some cultivations require specific soil types. A light soil supports asparagus (dry loam-sandy soil), Azalea (moderately dry sandy soil), begonia (dry light sand-loamy soil), outdoor vegetables (leek, carrot, cabbage) require light sand-loamy soils, seed onions and cabbage require a loamy to clayish soil.

[edit] Soil structure

By soil structure we mean the way how soil particles lay next to each other; seperatly or with fused unto each other to adhesive sets. This determines the number and the shape of the cavities in the soil or the ratio of soil/cavities.

[edit] Ratio of soil particles/pores

Pores are small openings that are located between the soil grains. The volume they occupy is called the pore volume. They are filled with air and/or water.

Large pores (>10µ) can not hold any water but drain let it go (draining pores)
Moderate pores (10 - 0,2µ) hold the water, and also make it available to the plant roots (available water)
Small pores (0,2µ) hold the water so fiercely that it is no longer absorbable by the plant roots (dead water)

The ratio between the soil particles/pores (air-water) determines the physical fertility of the soil.

[edit] Structure of the topsoil

Granular and crumb structure.

Grain structure: the soil grains are next to each other without any binding. One can compare them with a pile of grains. It is an inaduquate structure because there are too few holes for a good air-water ratio (pore volume 25%). Only extremely inaduquate soils have this structure.

Crumb structure: the soil grains stick together and form soil crumbs with rounded shapes pile together without any order, similar to breadcrumbs. It is an aduquate structure because the presence of binding substances (humus and clay) contain upto 60% pores so that c a good air-water ratio arises.

The structure of the soil changes regularly (even several times a year) of appearance due to agricultural activities, weather, ... Factors which improve the structure are: introduction of organic matter, tillage, natural phenomena (frost-thaw), crop rotation, workings of the soil organisms, ... Factors that worsen the structure are: precipitation, calcium deficiency, poor tillage, soils that are riden and walked upton (soil compression), ...

[edit] Humus in the soil

Large quantities of organic waste stream on top of and into the soil, such as plant remains (leaves, roots, stubbles, ...), animal waste (feces). In addition, the farmer also introduces tons of organic manure (stable manure, compost, ...) into the soil. After some time we retrieve nothing of these tons of organic substances, it vanished, consumed by the action of soil organisms (worms) and soil microorganisms (fungi and bacteria). These organisms feed on organic waste that they break it down into water, carbon dioxide (CO₂) and nutrients. It leaves only a residual product that cannot decompose further; this is called humus. The conversion process is called the humufication process. 1000 kg of manure leaves only a few grams of humus. Humus is a constantly changing mixture of organic compounds in various stages of decomposition. We distinguish between non-stable or nutrition humus which serves as food for microorganisms (the primary conversion) and stable humus with can be little or no further converted (final conversion). The humification is done by breathing or aerobic bacteria. When the soil contains too little air (due to too much water), the breathing bacteria can not develop and the plant waste is little converted. Peat is then formed (therefore so not introduce stable manure too deep into the soil). Besides air, these bacteria also require nitrogen for their nutrition. Organic material that contains too little nitrogen require the adding of nitrogen for a quick and smooth conversion. The C/N ratio determines the quality of the humus. Organic material with a C/N ratio lower than 30 will humificate smoothly. For the introduction of green manure (leguminous plants), the C/N ratio is 15-20, so the humus conversion poses no problem. With straw the C/N ratio is 80, here the humification requires the adding of nitrogen for a smooth humification process, if this is not done the bacteria will fetch all the required nitrogen from the surrounding soil and a nitrogen-depression could occur. Humus is a very fine colloidal substance = a substance whose molecules are too large to dissolve, but small enough to float in water. Due to the colloidal properties, humus is sticky. With soil analysis we determine not the humus but the carbon content from which we calculate the humus content.

$\%C\ X\ 1.72\ (2)=\%humus$

Role of humus:

With the humification, plant nutrients (N, P, K, ...) are released
Due to the colloidal properties, humus can hold water and nutrients (clay-humus complex) and it improves the soil structure.
Due to the dark color, humus accelerates the warming of the soil
Nutritional humus creates a rich bacterial life and a fertile soil

[edit] Water in the soil

[edit] Importance of water

It is necessary for: the plants: the germination of the seeds, the main component of the plant, solvent and transportation of the nutrients, the evaporation (transpiration), maintaining of the sapstream, ... the soil: heat control for the soil (water that evaporates takes heat with it (evaporation)), water influences the soil structure Total evaporation from soil and plant = evapotranspiration. the microorganisms: soil animals and microorganisms need a moist environment.

[edit] Types of water in the soil

Soil water: in a well water is present at a certain depth = soil water. The depth to which the groundwater is present is called the the groundwater table. The part below the groundwater table is the groundwater zone; all pores are filled there with water. In temperate countries, the groundwater table rises in the winter and falls in the summer. The cause of this lies in the evapotranspiration. In the summer, the plant and soil evaporation exceeds the rainfall, so the water table drops. In the winter, the evaporation is reduced and the rainfall is greater than the water consumption, so the water table rises. Capillary water: water from the groundwater table rises up through the small pores between the soil grains. These fused pores are fine tubes which extend upto the surface. These fine tubes are called capillaries. The water that rises trough here is called capillary water. The zone above the groundwater table to where the capillary water rises is called the capillary zone. Its thicknesss depends on the soil type. Water will rise high but only slowly in clay, and will not rise high but fast in sand. Just above the groundwater table, the capillary zone contains much water = closed capillary zone (roots die off). Above it is the open capillary zone, only the fine pores are filled there with water. Hanging water: The portion above the capillary zone contains water that, during seepage, kept hanging in the fine pores or got stuck in the colloidal particles. (sandy soils have little or no hanging water, clayish and loamy soils have a lot therof)

[edit] Water content of soil

Saturation: All pores are filled with water, there remains no room for air. Maximum water content = saturation Field capacity: From a saturated soil layer, water is draint downwards. This takes up to the mement when there is a balance between the suctionforce of the medium and small pores and the force of gravity of the water. The large pores are filled with air, the small and medium are filled with water. The maximum watercontent - drainage water = field capacity Wilting point: The water present at field capacity is only partially absorbable by the plant (available water). Water in the finest pores is so strongly bound that it can not be absorbed by the plants (dead water). A soil with only non-absorbable water = wilting point. Field capacity - available water = wilting point

[edit] Soil acidity

[edit] Definition of pH

The acidity of a solution is determined by the amount of H⁺ions. In an acid solution the H+ ions are greater than 10^-7 gram/liter. In a neutral solution they are equal to 10^-7 gram/liter. In an alkaline solution they are smaller than 10^-7 gram/liter. Due to the low values, the concentration is often expressed in the pH-value. A solution with a concentration of 10^-5 (0,00001) has a pH = 5. Therefore a pH = 5 is 10 times more acidic than a pH = 4.

[edit] pH in soil science

We find the acidity of the soil by measuring the H⁺ ions using a liquid that had sufficient time in contact with the soil. pH-water or the current acidity-level: when we dissolve the soil in distilled water and then measure the pH thereof, we measure the free H⁺ ions that are in the solution. pH-KCl or the total acidity level: when we dissolve the soil in a KCl-solution, we measure not only the free H⁺ ions, but also those ions who got stuck into the soilcolloïds (clay-humus complex). The difference between pH-KCl and pH-water =exchange acidity level. pH-KCl is always 0,5 to 1 pH unit lower. For professional purposes, pH-KCl is increasingly measured as pH-water fluctuates somewhat according to the seasons. (towards summer, the pH drops)

How to measure the pH

Litmus paper
- blue in alkaline medium (pH 7)
- red in acid medium (pH 7)
With electronic pH-meter = introduce electrode in solution

[edit] Soil type and pH

For all soil types, we must be state that the best pH-water is between 6 and 8. As the soil gets lighter, the pH needs to be lower.

	pH/H₂O	pH/H₂O
sandy soil	5,7 - 6,3	average at about 6
sand-loamy soil	6,3 - 7,0	average at about 6,5
loamy soil	7,0 - 7,5	average at about 7,0
clayish soil	7,5 - 8,0	average at about 7,5

Cultivation and pH Most vegetables prefer a weakly acid to neutral soil pH = 6 to 7. Typical heathland plants such as Erica and Azaleas prefer a pH = 4-5. At a pH below 5,5 diseases start to occur because the absorption and conversion of the nutrients is disturbed or even impossible.

A high pH is rare, a low pH is frequently encountered in Belgium.