A study was made of the manner in which the movement of particles involved in saltation was initiated. The paths of flight of these particles while air borne were also studied.Evidence is presented to show initiation of movement can be caused by impulsive forces generated by differences in wind velocity, and by the distribution of particles, at the soil surface. Photographs of particles in saltation show that the paths of descent are nearly straight lines with an angle of incidence of about 6 ± 4 degrees. The data suggest that constant velocity in both the forward and downward directions is attained very quickly and that these velocities remain in essentially a constant ratio for most of the downward path.
A laborarory intestigation of a clay soil indicated that the pcrcentage .of aggregares ( I rnm ii diameter nrighi be increased, decreased or rlnaffccte-d by ii.-.r1'"s ^ni,hr.uing depending on'the initial moisture coirrcnt. thc initial sizc of soil"aggrcg"t"r "nt thi mettr-od of drying the sample. Little_or no ch-anges rn aggregare srze occurred if the initial mois-ture contcnt v'as at 15 atnlosphcres. At d.j ai-, aggregares rvhich u,crc.initialiy -coarse () ,i mnr).tendcd to break ao*,i Jigt tti-.uli.,.r .*por.d ro alrern_are frcezing end tlrau irrg ,foJlowed by air-dryin[ at room tempcrarure, O. t6e orlrcr 6arrd. a substanttal dccrease. tn
A mathematical relationship was developed which gives the amount of sand splashed from a splash cup when raindrop size and impact velocity are known. The amount of sand splashed was used as an index of the effective energy of the raindrops.This relationship is expressed as: G = KDV1.4 where G is the amount of sand splashed (gm.), K is a constant for the sand, D is the diameter of the drops (mm.), and V is the impact velocity of the drops (m./sec).
The wind velocity required to initiate movement of soil with varying amounts of standing wheat stubble and varying proportions of erodible and nonerodible soil aggregates was determined in a wind tunnel. The relationship between these variables was calculated as logeI = 6.0438 + 0.0001774 S + 0.02332 C where I is the initiating velocity in cm/sec as measured at a height of 30.5 cm above the soil surface, S is the amount of standing wheat stubble (approximately 15 cm tall) in kg/ha, and C is the percentage of soil aggregates greater than 1 mm in diameter in a soil sample.The wind velocity required to initiate erosion is proposed as an index of erodibility of farm fields.
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