• Rock phosphate is the basic raw material for the production of the phosphatic fertilizers.
• Water-soluble sources of fertilizer P are recommended for crops grown on alkaline soils.
• SSP was the first P fertilizer manufactured in India.
• Single superphosphate contains 16-22% P 2O5 of which 90% is water soluble.
• SSP is a mixture of monocalcium phosphate and calcium sulphate (gypsum).
• SSP contains 8-11% sulphur and 18-21% calcium.
• When SSP is added to soil it is converted into insoluble dicalcium phosphate in alkaline soils.
• In acidic soils SSP is converted into iron and aluminium phosphates.
• Enriched compost with super phosphate is the super-digested compost.
• Triple super phosphate contains 44-52% P2O5.
• Dicalcium phosphate contains 53% P2O5.
• Monoammonium phosphate contains 12% N and 61% P2O5.
• DAP is available in two grades 16-48-0 and 18-46-0.
• Ammonium phosphate sulphate contains 16% N and 20% P2O5.
• Nitrophosphate contains P2O5, half in water soluble form and half in citrate soluble form.
• Bone-meal is suitable for acid soils and long duration crops.
• Basic slag is suitable for acid and near neutral soils, but not for alkaline soils.
• Basic slag contains 14-18 % P2O5 of which 80 per cent is citrate soluble.
• Rock phosphate contains 25 – 39 % P2O5 and 33-36% Ca.
• Phosphocompost is a cheaper source of P than DAP.
• Phosphocompost/ N-enriched phosphocompost is produced by the use of PSM’s namely Aspergillus awamori, Pseudomonas striata and Bacillus megaterium.
POTASSIUM
• Potassium management in Indian agriculture has been traditionally overlooked because of high fertilizer cost and anomalous crop response to fertilizers in majority of Indian soils.
• Most crops absorb as much or more K than they absorb N from the soil.
• About 70-75% of the K absorbed is retained by leaves, straw and stover and the rest is found in grains, fruits, nuts etc.
• Potassium activates more than 60 enzymes and is directly or indirectly involved in all major plant growth processes.
• Potassium promotes the transport of photosynthates to storage organs of crops.
• Potassium is essential for the formation and translocation of sugars in plants and is of utmost importance for crops like sugarcane, sugarbeet, sweet potato and other tuber crops.
• Potassium is important in making plants more resistant to lodging.
• Potassium improves the quality of crops and prolongs their shelf life.
• Soil K exists in 4 forms a) Soil solution K (0.1-0.2%) b) Exchangeable K (1-2%) c) Fixed or non-exchangeable (1-10%) d) Structural or mineral (90-98%)
• Forms of soil K in the order of their availability to plants and microbes are Solution > exchangeable > fixed (non-exchangeable) > mineral
• Exchangeable (available) K is generally <1% of the non exchangeable K.
• Soil solution K, exchangeable K and non-exchangeable K contribute to plant K uptake.
• Most of the total K in soils is in the mineral form, mainly as K bearing primary minerals such as muscovite, biotite and feldspar.
• Mineral K comprises about 98% of the total K.
• Exchangeable K is generally higher in Vertisols and vertic type soils and in the fine-textured alluvial soils than in red and lateritic soils, acidic alluvial soils with kaolinite as dominant clay mineral, and light textured alluvial soils.
• Antagonistic interactions of K may occur between K and Ca or K and Mg.
• K application resulted in reduced uptake of Fe, B and Mo and increased the utilization of Zn, Cu and Mn.
• Potassium application is known to correct Fe toxicity in rice grown on Fe-rich acid soils, as it improves metabolic activity and Fe excluding power of plant roots.
• Increasing level of K supply decreases the Fe content in paddy.
• Low soil temperature reduces available soil K and its absorption by plants.
• Leaching losses are a problem in sandy soils in high-rainfall areas, under such conditions split application of K is a possible solution.
• Canada has the largest reserves of K.
• Germany dominated world potash market for 75 years.
• Langbeinite contains Mg and S in addition to K.
• Deficiency of K is seen on leaf-margins.
• For optimum growth, the N:K ratio in straw in cereal crops should be between 1.1 and 1.4.
• All the foodgrain crops require more potash than nitrogen for production of 1 tonne of grain.
• Potassic fertilizers are grouped in two forms chloride form and non chloride form.
• Potassium chloride belongs to the first group.
• Potassium sulphate, potassium magnesium sulphate, potassium nitrate etc. belong to the second group.
• Potassium chloride is unsuitable for sugar crops, tobacco and potato.
• Potassium chloride or muriate of potash is the most common and cheap fertilizer among potassic fertilizers.
• KCl contains 58-60 % K2O.
• KCl is suitable for most of the crops except sugarcane, sugarbeet, potato and tobacco.
• In sugar crops, accumulation of sugar is affected due to chloride ion present in the fertilizers.
• Higher content of chloride in tobacco leaf reduces its burning quality.
• KCl or muriate of potash is suitable for acidic and heavy soils but not for alkaline soils.
• Potassium sulphate contains 48-50% K2O and 17.5 % Sulphur.
• Potassium sulphate can be safely applied to any crop including sugarcane, sugar beet and tobacco.
• Potassium magnesium sulphate is a double salt of potassium sulphate and magnesium sulphate and contains 22 % K2O and 11% Mg and 22% S.
• Potassium nitrate or saltpeter or nitre contains 13 % N and 44% K2O.
• Potassium polyphosphate contains 56% P2O5 and 24% K2O.
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