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place at once, and soluble phosphates are apt to get washed 

 away before complete precipitation takes place. In such soils 

 therefore it is best to apply phosphates in a less soluble form. 

 Soils poor in lime treated with super may get too acid, and 

 lose in absorptive power and capacity for nitrification. On 

 the whole, it is better especially for India, to use finely divided 

 bone-dust or mineral phosphates without dissolving them 

 with sulphuric acid, though more marked immediate result is 

 obtained from the use of super. 5 maunds of super per acre 

 is the best quantity to use for root-crops and 2i maunds for 

 cereals. A crop of 150 maunds of potatoes takes up only 

 about 10 Ibs. of ?2O 5j while. 5 maunds of bone-dust adds 

 about 90 Ibs. of P^O 5 to the soil. 



902. In estimating the amount of soluble phosphates, 

 cold water should be uniformly used. Phosphate of Allumi- 

 num is less soluble in hot water than in cold and when it 

 is in solution in water it is precipitated by heating. In 

 estimating the amount of reduced phosphate, the substance 

 should be treated with a neutral solution of Ammonium 

 Citrate (Sp. gr. rog2). This has little action on insoluble 

 phosphates but it dissolves those that have been once soluble 

 and then become precipitated. The precipitated phosphates 



from the slag of iron foundries are very rich in dicalcium 

 phosphate, the proportion being equivalent to 32 per cent, of 

 PgOs or 78 per cent, of Ca 3 P 2 O. The whole of this is 

 soluble in a solution of Ammonium Citrate. On soils rich 

 in humus, basic slag, therefore, acts as a very rich manure. 



903. Effect of phosphatic manures. Phosphatic manures 

 hasten the development of young plants, make them so 

 healthy that they resist the attack of insect pests which thrive 

 better on weakly plants. They also hasten maturity, increase 

 the flowering and fruiting tendencies of plants, and assist in 

 the elaboration of sugar and starch. 



904. Available phosphates. According to Dr. Dyer of 

 London, there should be at least 300 to 400 Ibs. of available 



