INCREASE OF CROPS BY USE OF FERTILIZERS 21 



nitrogen or phosphorus on that crop and soil. Generally 

 speaking, Great Britain is not a country where marked 

 deficiencies of potash occur ; it is only on particular soils 

 that this element is needed. Potash appears to be partially 

 replaceable by other substances, such as soda, magnesia, and 

 lime ; it is possible that this replacement is sometimes due 

 to double decomposition in the soil. Over an average of 61 

 years at Rothamsted, the loss due to replacing potash by 

 soda is rather less than two bushels of grain per annum, and 

 the loss from replacing potash by magnesia is very slightly 

 greater. Similarly, about 3 cwts. of straw per annum 

 are lost by the same procedure. In comparison, the loss 

 due to leaving out farmyard manure is 23 bushels of grain. 

 It is, therefore, practicable on soils moderately supplied with 

 potash to go on farming for many years with few appli- 

 cations of potash. Where a farm is formed of very heavy 

 clay land, the judicious application of phosphates to land 

 under hay will indirectly remove a very large quantity of 

 the potash from the clay of the soil. Some of this potash 

 will return to the manure heap, and thence to the arable land, 

 provided that the manure heap is well cared for. Where, 

 however, a farmer has little heavy land, there is small chance 

 of his escaping the purchase of potash fertilizers if he wishes 

 to maintain the fertility of his fields. 



REFERENCES TO SECTION II. 



Lawes and Gilbert, /. Royal Agricultural Society, 1847, p. 226. 



Baguley, " The Phosphatic Nutrition of Plants," /. Agricultural Science, 

 vol. iv., part 3, p. 318. 



Smetham, " The Present Position and Prospects of the Chemical 

 Manure Industry," /. Society Chemical Industry, 1898, p. 980. 



Berry, " Results of Some Experiments with Farmyard Manure," Bull. 

 65, p. 177 ; West. Scot. Agric. Coll., Glasgow, 1914. 



Hall, " Fertilizers and Manures," p. 3 (Murray). 



Ingle, " Manual of Agricultural Chemistry," p. 108 (Scott, Greenwood). 



Russell, " Soil Conditions and Plant Growth," p. 33 (Longmans). 



Johnson, " How Crops Feed " (Orange Judd). 



Wibberley, " Farming on Factory Lines," p. 160 (Pearson). 



Leather, "Water Requirements of Crops in India" (Thackcr, Spiuk, 

 Calcutta). 



