UTILISATION SURVEYS.

Manawatu Standard, Volume LVII, Issue 156, 3 June 1937, Page 5

UTILISATION SURVEYS.

SOIL DIVISION WORK. HAWKE'S BAY TESTS. Methods adopted in the utilisation survey of Hawke's Bay land undertaken by the Soil Survey Division of the Department of Scientific and Industrial Research were outlined in an addrevs to the sheep farmers' mocting at -Massey College yesterday by Mr L. J. Pohlen, who spoke in the absence of Dr L. Grange. Three main surveys—soil, farm management, ; and pasture —had been made in Hawke's Bay, he said. "During his lifetime, man alters the soil somewhat by ploughing and manuring," proceeded Mr Pohlen, "but the characteristics of the soil type remain sufficiently distinct for the soil type map to be accurate for many years. Other things being equal, each soil type should, for practical purposes, be uniform with regard t» topdressing requirements, the crops and pastures it will grow, and so on, and it follows that the more we ion correlate such factors with the soils—that is the more wo can tie down farm practice to the individual soil types, then the more comprehensive will be the information we can give the individual farmer about the methods cf farming his own particular soils. Then, again, the suitability of each soil for different types of farming according to the influence of economic factors such as transport will give him =omc definite information as to the most economical type of farming he can adept. HAWKE'S BAY LAND. "The main characters cf the soil profile may bo divided into two broad groups —physical and chemical. The physical characters are texture and structure, A clay soil i= not necessarily a poorly drained one, as -irrigators have found to their cost, because certain c'.iiys have a highly floculated nature which is expressed in a well dovoloped crumb structure, and this allows a high degree of aeration and well drained condition. In Hawke's Bay the leaching or washing out of chemical constituents—the plant foods, lime, phosphate, and potash—is very noticeable on older soils, although it has not proceeded to the same extent as in North Auckland and other high rainfall areas, except perhaps in the case of limostone soils in which a considerable depth of limestone must 'have been dissolved and removed to vieid the depth of residual soil now present. Each soil is the expression °f f , lts parent rock, climate, and vegetation. The soils of Hawke's Bay are relatively young and are therefore strongly influenced by their parent rocks. Forest soils have temporarily a high fertility, whilst fern o» -crub soils are naturally not so fertile. The rainfall, with its distribution over the year, \~ responsible for the texinral differentiation in the profile, but its action is modified by topography and parent rock. On flats or • entle slopes rainfall has its greatest effect, but where the slopes are steep and ho run-off greater, the textnral profde is 'c=s well developed. When the parent rock is coarse grained, as in sandstone or conglomerate, finer constiluneU are readily removed but in a fine grained parent material'such as mudstono, the downward movement of clay is rendered more difficult and (lie soil long remains immature. On steep slopes, too. slipping, particularly

*n mudstone sods, is -constantly removing “he mor.c developed profiles and exposing the parent rock beneath, so that these soils cmain immature and consequently fertile. As the plants depend largely on the finer material for their food supply, it will bo | seen that, well developed profiles are liaraclcristic of poorer and infertile soils because the clay and plant nutrients have been removed out of reach of the roots of the pasture. SOTE SURVEYOR S WORK. “This brief sketch of the soil characters 's perhaps sufficient to illustrate how the ncdologist or soil surveyor is able to disAnguish a soil profile by examining it with tn ordinary auger to a depth of 3 feel tod recognising its variations m tcxtuio. colour, moisture, structure, etc., as you go down through that. 3ft. The profile-;, w lie final criterion which distinguishes the .soil t.vpc. The pedologist is trained to observe factors associated with each soil ivpc and his ingenuity is always being called upon io help him to map rapid.y. He finds that soil types arc topographic units, and lie takes into account the contour, ruggedness, steepness, and so on of the hills, or the slight . depressions ot tne flat and innumerable minute ddforonees .in. the' topography undetected by any but the skilled observer. Ifc secs characteristic uasturc associations with each soil -VP 1 : • or perhaps a certain grass or wet'll that grows on one type and not on others, he notcs the occurrences of springs, of busn rnd its imposition, and by a number of distinctions lie conics to recognise the soil type by the look of it. . , "“Mapping when other information has been obtained, is then carried out, said Mr Pohlen. who added: “Each soil type is further examined in the laboratory, a,nd typical soil samples from different depths m each type are sent -to the Dominion Analyst and the chemical laboratory ol the Cawthron Institute. Here the soils are investigated from the chemical point ol view, and from the analyses considerable information is gathered about the lcitihtj Of the soil. The acidity, available potash, ohcephate, etc-., are determined. At Law-.ln-on. Institute the textures of the soils, as letermined by the pedologist in the field, are checked and the amount of sand silt, and clay in each eampltj is determined.