TILLAGE OPERATIONS AND MANURING 109 



be benefited by the application of these artificial manures is a 

 question which should be determined by experiment, and for 

 this purpose one or two rows of each crop should be separately 

 treated. 



Lime, in the form of marl, ground limestone, or freshly slaked 

 lime, may generally be applied with advantage at intervals of 

 about four years. Lime tends to be washed by rain from the 

 upper soil into the subsoil. In soil which has been heavily 

 manured with farmyard manure or decayed vegetation for 

 some years there is generally an accumulation of organic acids, 

 especially humic acid, which may seriously affect the healthy 

 action of the roots and arrest the work of the soil bacteria. In 

 such a case the application of lime will neutralise the free acid 

 of the soil and render the soil sweet. 



Of almost greater importance than the chemical character 

 of the soil is its physical condition, and this is capable of almost 

 indefinite improvement by tillage properly carried out at the 

 proper time, and by the application of decaying vegetable matter 

 and lime. Digging, hoeing, raking, and pressing are the four 

 chief methods employed in gardening for the improvement of 

 the physical condition of the soil, and these will now be con- 

 sidered in some detail. 



The object of digging is to provide a moderately firm soil 

 in which the roots of the plants can spread freely, and to admit 

 air, moisture, and carbonic acid, which act chemically upon 

 the insoluble reserve mineral matter of the soil, rendering it 

 available for absorption by the roots. Boys should be instructed 

 how to hold the spade properly, how to use their strength to 

 the best advantage in driving the spade into the ground and in 

 lifting the soil, and how to place the soil so as to have a fairly 

 level surface. The method of full trenching has been already 

 described. Bastard trenching, or double digging, consists of 

 cultivating the soil to a depth equal to that of twice the spade's 

 depth. As in full trenching, the ground to be double dug is 

 marked off into rectangles one yard wide (see Fig. 52). 



The whole of the top spit in the rectangle ACDB is dug out, 

 placed in a wheelbarrow, and transferred to the other end of 

 the plot beyond GH. The second spit of ACDB is then dug 



