What Crops Grow on

In order to grow, crops need water, light, carbon, oxygen and minerals. Air provides oxygen and carbon dioxide, which is the source of carbon, and plants fix it through photosynthesis. Soil provides the reserves of water and mineral elements that nourish plants, and it is a true biological reactor that shelters a complex ecosystem. Soil recycles organic matter into mineral elements that can be reused by plants and provide farmers with good yields.

    1, Soil

    Soil is made up of the following substances :

    - Organic matter

    - humus

    - Fine and very active elements (clay)

    - Coarse siliceous or calcareous elements

    - Iron, aluminum, calcium

    - Water and air, 50% of its volume

    In agriculture, soil plays a crucial role in crop nutrition because it:

    - retains the soil solution

    - fixes certain nutrients; and

    - it is home to microorganisms that help convert non-absorbable elements into elements that can be directly absorbed by plants.

    Each soil is a unique biotope with its own physical, biological and chemical characteristics. The supply of nutrients depends on these.

2, The Role of Nitrogen

Nitrogen is an essential element for photosynthesis, which allows the conversion of minerals into plant tissue. Nitrogen is present in the air, but plants cannot take it up in gaseous form, except for legumes (alfalfa, clover, peas, etc.). In the soil, nitrogen is present in organic or mineral form (ammonium, nitrate). Organic nitrogen (residues from crops already harvested, organic fertilizers, etc.) must be converted to nitrate by microorganisms in the soil in order to be used by plants; this is known as mineralization. Basically, it is nitrate that provides nitrogen nutrition to plants. The nitrogen cycle depends on climatic conditions and the microorganisms in the soil. Nitrate is rarely retained by the soil, so it must be added when plants are ready to take up nitrate or to promote mineralization to avoid leaching into groundwater. Nitrogen is a growth and quality factor that affects the protein content of plants.

3, Role of Phosphorus

Phosphorus is essential for plant growth. It is present in the soil as phosphate: either dissolved in water, immobilized on soil particles, or in mineral or organic form. When roots take up phosphate dissolved in water, the immobilized molecules are gradually released. Organic phosphorus mineralizes slowly. However, these exchanges are very slow. The phosphorus cycle depends to a large extent on the physical and chemical properties of the soil. Potato, vegetable and sugar beet crops have the greatest phosphorus requirements. Usually, the short-term bioavailability in the soil is limited because phosphorus ages very quickly in the soil. Acidic soils rich in free iron and aluminum fix soluble phosphorus very quickly, as do soils rich in calcium and/or magnesium.

4, The Role of Potassium

Potassium plays a key role in the formation and storage of sugars. It also helps plants to withstand cold, drought and disease. Potassium in the soil solution is retained by humus or clay; potassium in minerals is only released very slowly. As with phosphorus, the cycling of potassium depends on the physical and chemical properties of the soil, but it is always bioavailable. Not all crops have the same potassium requirements, for example potatoes, vegetables and sugar beets have a greater need for potassium than cereals. In general, potassium additions should be done before planting.

5, Functions of Other Elements: Calcium, Magnesium, Sulfur, Trace Elements

The main function of calcium and magnesium is to improve the soil structure and they are applied in the form of soil conditioners. Sulfur is necessary for protein synthesis, and certain fertilizers provide sulfur in the form of sulfates. Cruciferous plants (cabbage, rape, etc.), garlic, onions and leeks have the greatest demand for sulfur. It can be supplied in other, less oxidized forms, but only with market authorization. Trace elements (copper, manganese, zinc, boron, molybdenum, iron, etc.) are involved in plant nutrition in very small doses, however, deficiencies of any of these elements can lead to vegetative disorders. These deficiencies are caused either by insufficient levels or by the unavailability of the element.