t 535 ] 



Residues of many crops and shed leaves after harvest may 

 be considered as a kind of green-manure. In roots and 

 stubbles usually half of the quantity harvested is left, but in the 

 case of leguminous crops the residues are of equal value or of 

 double the value of the crop harvested, from a chemical or 

 manurial point of view. Root crops (potatoes, cabbages &c.) 

 leave very little residue behind and are therefore more 

 exhausting than other crops. Barley leaving little residue 

 should be considered an exhausting crop for the surface soil. 

 Lucerne, a perennial leguminous fodder crop, leaves as much 

 as 4 tons of crop residue in the top 10" of soil and it may 

 therefore be regarded as a very useful crop for fertilizing 

 soils. The residue of 4 tons of vegetable matter contains 

 over 100 Ibs. of N. 



856. Of other easily available nitrogenous manures may 

 be mentioned sea-weeds and aquatic weeds generally which 

 may be applied at the rate of 10 to 20 tons per acre. In 

 fresh state they contain 70 to 80 per cent, of water and 10 to 

 14 per cent, of ash which includes sand. The true ash is only 

 3 or 4 per cent. The nitrogen varies from '15 to '5 per cent, 

 usually about a quarter per cent. They are not so valuable 

 as farmyard manure, containing only half the proportion of 

 N, but young aquatic sea-weeds are richer in N and K 2 O. 

 The value of sea-weeds &c. is however greatly enhanced by 

 the presence of shells and animals and animal remains, which 

 raise the percentage of P 2 O 5 .and N. Where weeds are 

 available in large and inexhaustible quantities, it is advisable 

 to use them as fuel and then carefully collect the ashes for 

 manure. 



857. Straw is another readily available manure. The 

 value depending on the proportion of N and of ash. Straws 

 of cereals rarely contain more than -4 per cent, of N and 4 

 per cent, of ash. Straws of leguminous crops, however, often 

 contain as much as 2 per cent, of N. Straws are more valu- 

 able as cattle food than as manures, except barley straw, 



