LABOURS ON THE SOIL. 199 



becomes lessened in capacity, and the soil can neither be moved to the 

 proper depth nor sufficiently mixed. All roots of trees or bushes 

 ought to be carefully picked out as the work proceeds, as they become 

 fruitful centres for generating fungi. But small stones, brickbats, &c. 

 should be left, as they tend to make heavy soils porous, and to 

 consolidate those that are too light. 



Trenching. The object of deep trenching is to increase the depth of 

 soil fit for plants, by which means it becomes a larger reservoir of air, 

 moisture, and manure ; and in the case of plants which do not per- 

 manently occupy the soil, it admits of entirely changing the surface, so 

 as to bring up fresh soil every time the ground is trenched. The plot 

 to be trenched is marked out by a line, exactly in the same manner as 

 in digging ; but instead of a narrow furrow, which suffices for that 

 operation, a trench at least as broad as the depth to which the ground 

 is to be moved, say from two to three feet, is marked off and opened, 

 the soil being wheeled to the place of finishing, as in digging. The 

 next point to determine is, whether the whole of the soil to be moved 

 is to be equally mixed together ; whether the subsoil only is to be 

 mixed, and the surface soil still kept on the surface ; or whether the 

 surface is to be laid in the bottom of the trench, and the subsoil laid 

 on the top. 



In trenching ground that is to be cropped with culinary vegetables 

 for the first time, the whole of the soil turned over should be equally 

 mixed together, manure or compost being added and incorporated at 

 the same time. When the ground of a kitchen-garden has been 

 originally trenched in this manner to the depth of three feet, a fresh 

 surface may be exposed for cropping every year, by trenching one year 

 two spits, and the next three. Top and bottom and middle will thus 

 exchange places in rotation. 



In the operation of trenching, when the object is to reverse the 

 surface, the firm soil is loosened, lifted, and thrown into the trench in 

 strata, which, when completed, will hold exactly the reverse positions 

 which they did in the firm ground ; but when the object is to mix the 

 soil throughout, or when the surface soil is to be kept uppermost, the 

 face of the surface of the moved ground must be kept in a sloping 

 position, in order that every spitful thrown on it may be deposited in 

 the proper place, with a view to mixture. To secure space enough 

 for the thorough admixture on the slope, a trench four feet wide will 

 be used, as the soil should be bodily removed from one side and laid 

 at the opposite side, ready to fill up the last trench. " Ridge trench- 

 ing" is the term applied when the surface of the moved soil, instead of 

 being smoothed and levelled, is laid up in the form of a ridge, in order 

 to benefit by exposure to the atmosphere. Whatever mode of trenching 

 may be adopted, it is of great importance that the bottom of the trenches 

 should either be level, or form one or more regularly inclined planes, 

 in order to carry off the superfluous water of the surface soil. 

 In a very retentive subsoil, if the bottom is trenched irregularly, 

 the places marked a, b 1 c, in fig. 160, would retain stagnant water 



