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Learn about essential macro and micro elements, nitrogen cycle, soil analysis, and nutrient testing for optimal plant growth and crop yield in agricultural science.
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Leaving Certificate Agricultural Science Soil 6 – Soil Fertility
Soil Fertility • All plants require certain elements and minerals to carry out functions in the plant. • These minerals allow for proper growth of the plant. • A lack of the minerals results in a deficiency disease or stunted growth. • An essential element is defined as “a chemical element required for the normal growth of the plant”. • Some elements are required in large amounts and they are called macro elements. The others are called micro elements and are only required in small amounts.
Nitrogen • Nitrogen is an important component of plant proteins, chlorophyll and nucleic acids; therefore it is vital for growth, photosynthesis and cell reproduction. • It is the most important and widely used fertiliser element. • A deficiency in N causes sharp reductions in crop yields. • When N is abundant in soil, the crop grows quickly, is dark green in colour and fruits and seeds have high protein levels. • When N is short, growth is restricted and the plant goes yellow.
The Nitrogen Cycle The significant parts of the Nitrogen Cycle are as follows: i. Fertiliser Application Organic and Inorganic fertilisers contain N in Urea, Ammonium and Nitrate forms. ii. Nitrogen Fixation Nitrogen fixation is the process of changing atmospheric nitrogen into other; simpler forms (e.g. NH4+) Rhizobium bacteria are found on root nodules on legumes convert Nitrogen into a usable form. (E.g. Clover) iii. Organic Matter Breakdown When organic matter or manure is applied to soil, the complex forms of N in the material are converted in NH4+
The Nitrogen Cycle iv. Nitrification Nitrification is the conversion of NH4+ (Ammonium) into Nitrates using O2 v. Plant Uptake The uptake of NO3- by plants completes the cycle – N begins at plants and end at plants. vi. De-nitrification and Leaching De – Nitrification occurs in wet, anaerobic or waterlogged soils. It results in a loss of N from the soil and its conversion to N2O or Nitrous Oxide and N2 gas.
Soil Analysis Soil must be analysed to measure its fertility and the fertiliser requirements. It involves three steps: Soil Sampling • Soil must be sampled in various areas of the field considering different coloured areas & sloped areas. • Take a minimum of 25 samples, usually in a W shape throughout the field are taken at root level. • Mixing all of these samples makes a composite sample.
Soil Analysis Soil Analysis Soil analysis generally means determining lime requirements, available P and available K. Most testing is carried out by Teagasc, in their soil testing lab at Johnstown Castle. Interpretation of soil analysis The results of the soil analysis are compared to previous reference tests carried out by Teagasc. This allows the technician to give guidelines for the farmer on P and K application and liming requirements.
