ĐÁP ỨNG NHU CẦU PHÂN BÓN CHO CÂY TRỒNG

A deficiency of any single nutrient is enough to limit yield

( Justus von Liebig 1803-1873 )

General Principles 

of Fertilizer Application

  Mineral Fertilizers

¨ Plants are photo-autotrophs. Plants need light as energy for photo-synthesis. Other materials for photosynthesis are: Minerals, CO₂ and water. A deficiency of one, single mineral nutrient is enough to limit yield. 

¨ Macro Nutrient Minerals: Nitrogen, Ammonium, Urea, Nitrate, Phosphorus, Potassium, Calcium, Magnesium, 

¨ Micro Nutrient Minerals: Boron, Iron, Manganese, Zinc, Molybdenum, Copper, Cobalt. 

The Nutrient Requirement Growth needs Nitrogen and Phosphorus. Blooming and Ripening need Potassium. Stage of Development Nitrogen Phosphorus Potassium Growth  Very High High Low Blooming Normal High Very High Fruit Growth High High Normal Root & Tuber Growth High Normal High Ripening Low Low  High

  Balanced Fertilizers & Timely Applications of Fertilizers

 Balanced fertilizer use implies that:

¨ The different types of nutrients are supplied in the right proportion according to the plant's needs.

¨ All nutrient sources available to the farmer are taken into account, i.e. mineral fertilizers, farmyard manure, sewage sludge, crop residues etc. 

¨ The nutrient inputs to the soil equal the uptake by the plants. No nutrient deficiencies develop and the nitrate content in the soil is minimized at harvest. 

   Unbalanced fertilizer use, e.g. only applying nitrogen, can give yields below optimum, enhance the crop's susceptibility to insect and fungal damage, and reduce crop quality.

 Timely fertilizer use is:

¨ To fertilize when or just prior to the time the crop requires a heavy uptake of nutrients. This also minimizes the environmental impact of fertilizers.

¨ Fertilizers should not be applied outside and toward the end of growing season, or when there are warnings of heavy rains likely to be shortly after application 

  Efficiency of Fertilizer Application

¨ Basic Nutrient Uptake way to plants is through root system. Fertilizer has first dissolved in the soil solution and thus available for plants. That reason explains why water is important for efficient fertilizer application. The heavier dose of fertilizers the more water plants need for optimum growth. 

¨ Some of nutrients would be bonded or fixed to soil complex and become less available to plants. Only a small percentage (15-30%) of the applied phosphorus is used by the crop in the year of application. The rest stays in the soil pool and contributes to soil phosphorus availability for subsequent crops.

¨ Crops use nitrogen mainly in the nitrate form. Organic nitrogen and ammonium nitrogen are transformed to nitrate in days or, at most, a few weeks by microbes in the soil. Therefore most nitrogen in crops is taken up as soluble nitrate. The loss would happen in the form of Leaching of nutrients in soluble forms from fertilizers use.

¨ Excessive Fertilizer Application affects detrimentally to soils by unnecessary acidification, on crops by lodging, enhanced susceptibility to diseases, to water by leaching of enhanced concentration of soil solution, to air by gaseous emissions and on the economy: excessive application is an expense with no benefit.

  Organic Fertilizers

¨ Nutrients to plants are minerals. Plants can not use organic fertilizers directly. Organic manure has to be decomposed to simpler organic substances and then to minerals. This process is called Mineralization. Process of mineralization that allow organic substrates under controlled successive microbial decomposition become stabilized organic matter in the presence of oxygen is Composting.

¨ The process of mineralization is a long-term process. Organic fertilizers thus could be considered as Slow Released Fertilizers. The successive process of decomposition produces a chain of organic compounds that act as Chelating Agents, bonding with released minerals and making minerals available for plants. Other important products of mineralization process are Plant Growth Stimulants .

¨ Organic fertilizer is of plant residues. The content of minerals in residue, at level of few percents, is similar to that of originated crops. In order to return to soils the same quantity of minerals taken by harvest, roughly the same volume of organic fertilizers equal to that harvested  is needed. That's the reason explaining why organic fertilizer is too much bulky when applied as only source of fertilization.

¨ Best is to combine both organic and mineral fertilizers for highest yield with premium quality.