SOIL ANALYSIS AND ITS INTERPRETATION 341 



All are arable soils. The chalk pastures on the .South 

 Downs usually contain less than 'Oi per cent, of available 

 potash {e.g. the Patching soil), and they respond to potassic 

 manures. It will be observed that '015 per cent, is insuffi- 

 cient in East Kent where the rainfall is 23 inches, whilst 'Oio 

 per cent, suffices in West Sussex under 10 inches higher rain- 

 fall and generally better water-supply in the soil. 



Phosphoric Acid. — Generally speaking, the largest amount 

 of phosphoric acid is found in chalk soils, 0'2 to 0*25 per cent, 

 being present; about 0*15 to 02 per cent is found in good 

 loams ; sandy loams contain about O'l per cent, while poor 

 clay pastures and poor sands contain still less. Little if any 

 direct connection can be traced between the phosphoric acid 

 and the productiveness ; in general it tends to increase as the 

 clay, fine silt, and silt increase — the poor clay pastures form 

 a readily explained exception — but it does not appear to be 

 closely associated with any one fraction like the potash. The 

 amounts of " available " phosphoric acid vary enormously ; 

 Kentish hop gardens commonly contain from -05 to '18 per 

 cent.; well-farmed arable soils contain some "015 per cent, 

 while in poor worn-out pastures the quantity may sink as low 

 as '002 per cent. In most cases these quantities are insuffi- 

 cient for some of the crops grown, especially where high 

 quality or feeding value is aimed at ; hop growers regularly^ 

 and, they maintain, profitably, apply phosphates to gardens 

 already containing "05 per cent, of available phosphoric acid, 

 whilst arable farmers use them for swedes when "Oi 5 per cent, 

 or sometimes even more, is present. The exceptions to this 

 rule are the light soils sufficiently provided with moisture and 

 a forward climate ; on these the need for phosphates appears 

 to be less. But in all cases where much purchased food is fed 

 on the land phosphates appear to be of advantage to the suc- 

 ceeding crop. 



Rainfall does not appear to have so marked an effect in 

 controlling the need for phosphates as it has for potassic 

 manures. The explanation is to be found in the fact that 

 phosphates are useful both in dry and in moist situations : 



