Vol. XIII. Xo. 



THE AGKICULTURAL NEWS. 



.301 



STUDENTS' CORNER. 



DYNAMICS OF A PLOUGH.* 



Tlu' (lirec-tii)ii of tlic various fori-fs at work in <lra\viiig 

 ami resisting tlio plough are in general little nnilerstond. 

 The result is that, though a plough is one of the siniijlest uf 

 machines, iniplenient makers have jirohably more trouljle over 

 the ploughs tliey make tlian they have over all their line.s of 

 maimfacture. These troubles are umltiplied by the great 

 (livergeneo in .soils, as to l>()th type and condition, to be dealt 

 with, the varying depths and widths nf fuirows ploughed, and 

 by the different methods adopted for the yoking of the horses 

 and the variation in number of these emiiloyed. 



Fig. '). 



In endeavouring to explain the dynamics of a plough 

 I shall in the first place, for the sake of sim]jlicity, deal with 

 a single-furrow lever plough of the New Zealand type, liaving 

 three wheels, and shall assume that it is being used in 

 ploughing lea land in gooil, tirni condition, and that the 

 funv.w is 1 1 inches wide l)y 61 inclics deep. 



A phrtigh may l>e considered as a kind of a planing toul, 

 the share and coulter forming the <'ntters, the.se sheariiig off 

 from the ground a rilibon of sciil the furrow; the mould- 

 board and the upper .surface of the share combined forming 

 a twisted wedge whereby this ribbon is rolled over, firstly on 

 its lower right hand corner until it has completed a quarter 

 of a revolution and reaches the vertical po.sition as shown in 

 Fig. 5, and secondly, l)y rolling it .still further over upon what 

 was originallj' its right-hand upper corner till it lies at an 

 angle shown in Fig. 6. 



Fl<:. 6. 



The i-esistaiu-es to the al)ove work are many, but the 

 three principal are: (1) that of the coulter making the 

 vertical cut; (2) that of the share cutting off the .sole of the 

 furrow; an<l (.3) that of the mould-bdard, which lifts, .stretches, 

 and rolls the furrow over until it falls by gravity into its 

 place against the preceding furrow at the angle incidental to 

 its deiith and width. 



The circular coulter, having to 

 roots near the surface fi-oin the .solid 

 the plough when at work by an 



■nt through the tough 

 opposes the advance of 

 upward and liackwaid 



thrust. The proportion of the total draught of the plough 

 reipiired to overcome this resistance (resistance =:a force 

 acting in opposition to another force) is probably about 

 ■20 per cent. The share is also a cutting-tool, but as in this 

 case it is 6i inches lielow the surface it meets with fewer roots 

 than the coulter. In addition to cutting the .sole of the furrow 

 the share acts as the advance guard of the 'twi.sted wedge' and 

 it has to lift about 50 per cent, of the weight of the furrow 

 some 3i iivches or -f inches until it reaches the forward 

 end of the mould-board. The .sliare opposes the advance of 

 the ijlough when at woi-k liy a thrust backwards, downwards, 

 and to the right. A fair estimate of the share resistance is 

 40 per cent, of the total draught, leaving another 40 per cent, 

 to the mould-board in raising, twisting, stretching and push- 

 ing o\er the furrow. The mould-board's pressure in opposi- 

 tion is backwards, downwards at the front, and to the left 

 throughout the remaining length. The.se proportions are 

 estimated only; there are no means of separating them to 

 ascertain their actual amounts. Their relative amounts will 

 vary largely under different circumstances. 



This article will be continued in the next issue of the 

 Aijricultural Ne>"s. 



Questions for Candidates. 



1>RELIMINAKV QUESTIONS. 



(1) \Vhy is the .soil round a tree, under ordinary <.'on- 

 ditions, higher than the surrounding soil? 



(2) Why does recently germinated corn possess a sweet 

 taste? 



(3) How do pod-bearing plants help to enrich the .soil 

 in nitrogen? 



INTEE5IEI>I.\TE QUESTION.S. 



(1) De.scrilie the structure of any root that you have 

 examined. 



(2) Give an account of the exports of the colony in 

 which you live. 



(3) .State how you employ published agricultural 

 matter in <'onnexion with your work. 



KIN.\L liUESTIONS. 



.f 



the employment of 



(1) Give your exjicrience 

 a nur.sery on an estate. 



(2) From a consideration of the imp.irts of the colony 

 in which you live, sh(nv how the conditions may be improved 

 by a greater local production of useful foodstuffs. 



(3) Di.scuss the n.sefnlne.ss of agricultural literature to 

 the planter. 



*Froni the Jouiiiul of AgrioiUuie of New Zealand for Jum 

 20, 1014. 



The Rlwdesia Aijricultural Jaiirnal ior .Tune 1914 eon- 

 tains an illustrated account of a maize reaper and binder at 

 work in that country. The machine certainly seems t<i 

 perform its work efficiently if one can judge from the photo- 

 graphs. The introduction of this class of machinery, though 

 possibly not in itself an economy, will undoubtedly facilitate 

 the better working of the llhodesian farms since the present 

 methods lead to a delay of ploughing. When the crop is cut 

 with a reaper and binder it is said that the ploughs can 

 tollow immediately and the land being still moist, deeper 

 ploughing can be practised and the soil moisture thereby 

 conserved. 



