International Soil Tillage Research Organization

passage of sowing-machine.The loosening created by the former essentially results from the creation ofinternal mpture surfaces, the lifting of soil blocks falling after the passage of tines.This effect is emphasized by the flexibility of tines in spring steel. It is also interestingto point out the sorting effect of the implement, resulting from the falling of smallclods.111 tlic i~etiott of rotary e~lltiv:ttors, dynantic forces play :In in~portat~t role: soilclo~ls are broken 1111 hy ilic iri1p;ict sutldently . :tvplied -. by ;i rot.ni11r tine ant1 tricns~nit 3pan of the shock to their neighbours, which are split in7tum. So cmcks are propagatedin the environment.Table I. Evolution of soil porosity witit depth and with the treatments (%),Depth Spring-tine Row cultivator Rotary cultivator(cm) cultivator (h = 2.34) (h = 3.77)Before After Before Aftersowing sowing sowing sowingFrom Table I, it appears that porosity resulting from the passage of a rotary tillerwith h = 3.77 is considerably less than that of a rotary tiller with h = 2.34. The intensivesoil pulverization created by the rotors of the former was followed by an importantconsolidation of the crumbler roller. This consolidation is improved by the ridged rollerand measurements made after the passage of the sowing-machine show strong differencesin structure of the resulting tilth between plots corresponding to h = 2.34 and 3.77.Area and size dishiblition of pores determine various physical properties important toplants, they especially affect water infiltration rate and storage capacity. Fig. 4 gives areadistribution of pores, according to depth. They show that the highest proportion of pores islocated between 0.1 and 0.2 mm2. This proportion of rather small pores is greater for plotswith h = 3.77. Furthermore, the smaller standard deviation around the mean value of thearea suggest a greater homogeneity for these plots.Size of pores was measured by using a form factor C, which is represented by:.vE%C=2- with S the area and P the perimeter.P-For elongated pores, (L = 10 I), this ratio is < 0.60 while for very rounded pores, itis about 1. Fig. 5 gives the distribution of pores. From the computations relative to sizedistribution of pores, it appears that the most frequently encountered pores have a formfactor between 0.8 and 0.9, in the top layer as well as in deeper layers. One may considerthat more than 70 % of the pores have a C value comprised between 0.7 and 1, that is tosay they are rather rounded.