Chemical Analysis of Soils

January 30, 2014
By Krishiworld

Chemical Analysis of Soils


The chemical analysis of soils or of plants growing on them constituents the modern method of determining the fertility status of a soil. Such analysis give information on the relative abundance or scarcity of the different nutrients required by crops from the soil, but they give no indication regarding the exact quantity, of fertilizer that may be applied to make good the deficiency. The dependability of this, method can, however, be increased a great deal by co-ordinating its results with those obtained from field experiments.


Facilities for rapid soil-testing have been made available in almost all states and can be availed of. At the same time, a very large number of fertilizer experiments with different crops on a variety of soils are conducted annually in all parts of the country under a comprehensive scheme. The results of these field experiments, when calibrated against those of rapid soil tests, will make the latter purely dependable. This will then be a valuable aid in the hands of extension workers in furnishing advice to farmers regarding fertilizer practices.


It is also sometimes possible to obtain a clue to the nutrient deficiences of soil with the help of deficiency symptoms in plants, as described already. However, a correct deagnosis of deficiency symptoms needs extensive experience. Furthermore, such symptoms in plants appear long after the actual occurance of nutrient deficiency in the soil. Therefore, such soil deficiencies must be diagnosed and remedied much earlier by adopting other means.


How much fertilizer to apply.In a vast country, such as India, possessing a wide variety of climatic and soil conditions, no definite quantity of any fertilizer can be prescribed as an optimum dose even for one and the same crop for all regions. each state in the country has conducted fertilizer investigations for the last 50 years and accumulated information on the manurial requirements of principal crops under local conditions. Therefore, for specific fertilizer practices in relation to particular crops and soils, the state agricultural department should always be consulted.


For determining the quantities of fertilizers from the recemmended rates of application N,P or K, or vice versa, the following conversion factors may be used :

Conversion factors determining quantities of fertilizers

 

Qunatity Multiplied by Gives corresponding quantity of
Nitrogen 4.854 Ammonium sulphate
Nitrogen 2.222 urea
Nitrogen 3.846 Ammonium sulphate nitrate
Nitrogen 4.000 Ammonium chloride
Nitrogen 3.030 Ammonium nitrate
Phosphoric acid(P2O5) 6.250 Superphosphate, single
Phosphoric acid(P2O5) 12.222 Superphosphate, double
Phosphoric acid(P2O5) 2.857 Dicalcium phosphate
Phosphoric acid(P2O5) 5.000 Bone meal, raw
Potash (K2O) 1.666 Muriate of potash
Potash (K2O) 2.000 Sulphate of potash
Ammonium sulphate .206 Nitrogen
Sodium nitrate 0.155 Nitrogen
Urea 0.450 Nitrogen
Ammonium sulphate nitrate 0.260 Nitrogen
Ammonium chloride 0.250 Nitrogen
Ammonium nitrate 0.330 Nitrogen
Superphosphate, double 0.450 Phosphoric acid(P2O5)
Dicalcium phosphate 0.350 Phosphoric acid(P2O5)
Bone meal, raw 0.200 Phosphoric acid(P2O5)

uriate of potash
0.600 Potash (K2O)
sulphate of potash 0.500 Potash (K2O)


Considerations governing the use of fertilizers.It may be stressed that in order to secure the maximum response to fertilizers, the crop should be irrigated immediately, following their application and at suitable intervals thereafter. The response of a crop under arid and semi-arid conditions is usually uncertain and relatively small. It is, therefore, advantageous to restrict the use of chemical fertilizers mainly ti irrigated lands and areas of assured rainfall.


It must also be borne in mind that the maximum profit from the use of fertilizers depends on many factors, such as the nature of soil, the kinds of crop grown, the climate (in relation to soil, the kinds of crops growth), the prices of fertilizers, the market price of the agricultural produce and so no. All these factors must be given due consideration to secure the most economic results. Changes in one or more of them are bound to influence the economic results. changes in one or more of them are bound to influence the economics of fertilizer use. The use of fertilizers is also subject to the ‘law of diminishing returns’. This means that the rate of increase in the crop yield decreases after a certain point is reached regarding the quantity of fertilizer used, and consequently the value of the additional yield finally becomes less than the cost of the fertilizer. Usually, the smaller applications of fertilizers produce greater percentage increase of yield than larger applications.


It should also be exphasized that an adequate supply of nutrients is only one of the factors that determine crop yield and that the application of fertilizers is not the sole means of making good the nutrient deficiencies in soils and plants. Equal attention must be paid to the other soil and crop-management practices to ensure good tilt, proper drainage, the required soil reaction, soil conversion, good land use, a suitable crop rotation, adequate organic matter in the soil and satisfactory soil micro-organism activity. Each one of these plays a vital role in determining the eventual productioin. the neglecting of one or more or these factors leads to a reduction in yield and created the need for still heavier manuring. Finally, manuring should not only be balanced in itself, but should also be designed to supplement the good effects of proper land use and beneficial soil management.

Conversion factors

 

Distance 1 mile = 1760 yards = 5,280 feet
1 metre = 1.0936 yards = 39.37 inches
1 yard = 0.9144 metre
1 foot = 0.3048 metre
1 inch = 2.54 centimetres
Area 1 acre = 4840 sq yards = 43,560 sq feet
1 guntha = 1/40thacre = 1089 sq ft = 33′ * 33′
1 acre = 0.4047 hectare
1 hectare = 2.471 acres
1 sq mile = 640 acres
Weight 1 long ton = 2,240 pounds
1 short ton = 2,000 pounds
1 metric ton = 1000 kilograms = 2204.6 pounds
1 long ton = 28 maunds(approx.)
1 1 maund = 80 pounds(approx.)
1 metric ton = 1.1023 short tons
1 metric ton = 0.9842 long ton
1 short ton = 0.9072 metric ton
1 long ton = 1.0161 metric ton
1 pound(avoir) = 453.6 grammes = 0.4536 kg
1 hundred-weight(cwt) = 112 pounds = 50.8 kg
1 kilogramme = 2.2046 pounds
Weight per area 1 lb per acre = 1.12 kilogrammes per hectare
1 cwt per acre = 125.6 kilogrammes per hectare
Capacity 1 gallon (Imp.) = 4.5461 litres
1 gallon (U.S.) = 3.7853 litres
1 gallon (Imp.) = 0.1604 cft
1 litre = 0.2200 gallon (Br.)
1 litre = 2642 gallon(U.S.)
1 bushel = 56 lb (potaoes)
1 bushel = 56 lb (barley)
1 bushel = 60 lb wheat
1 bushel = 42 lb (oats)
1 gallon (Imp.) water weighs 10 lb
1 cft of water weighs 62.3 lb
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