GISdevelopment.net ---> AARS ---> ACRS 1989 ---> Agriculture & Soil Site mapping techniques for agricultural land D.D. Fraser and G.P. Ellis Land use planning division Department of land information Royal Melbourne of Technology (RMIT) Melbourne Austria Introdouction Whole farm planning may be described as the considerations of the total assets from the farm the soil water trees stock pastures crops and wild life and how to make the best use of them To efficiency manage a farm it is necessary to consider the whole area including areas surroundings the farm and to take in to account natural boundaries. In the making maps produced by analogue means have been used by land managers in a mostly quantitative manner. To assists in decision making. Computer technology has enabled analogue information to be converted in to a spatial form digital data and appreciate software has resulted in quantitative analysis ..The major limitation of using modern technology in whole farm planning however is the significant expense of collecting the original data at a suitably large scale . This paper will back look at some of the ways in which exciting data such as maps and aerials photographs .Along with field data can be overplayed enhanced and analyzed using computer assisted techniques. Main considerations In the process of preparing plans for agricultural units a number of factors are taken inn to account of these assisted techniques. Variability with regard to scale and accuracy of source information: In preparing a base map at a suitably large scale already existing information is typically accessed .The problem is that this information has been collected in many different ways and at any levels of accuracy some information for example precipitation may be levels of accuracy may be gathered at a regional level where as other information for example the positions of fence lines is known quite precisely the requirements isda successfully amalgamate and merge these various data sets. The smallness of the area to be covered When the area be managed is relatively small as is often the case then it is likely that existing information at a suitably large scale and with sufficient accuracy not be available .This may necessaries the collection of the required data by way of a field work program . In Australia the largest scale topographic mapping available is 1:250000 because of the graphic limitation of this scale map much detail is not shown that which is displayed is every generalized. The cost of producing understandable and relevant base maps Field work programs are quite often expensive to property carry out one way of cheaply and effectively producing base maps which carry useful information the purpose of agricultural management is to utilize over lapping aerial photography. Temporal aspect of agricultural land Agricultural land does not remain the some over long periods of time consequently and maps to be used for planning purposes must be systematically up graded with time so that they reflect the current or perhaps future state of the land rather than a past and obsolete view. Interactions between natural and man made systems In determinations the suitability of land for a particular use and the subsequent monitoring of the land for effective utilizations account must be taken of the interaction between the natural and man made systems .If nature is ignored inappropriate land use can result and this may lead to significant problems such as land degradation for example if step hills are cleared of vegetation a resultant rise in the water able may cause. Problem elsewhere. To assist in the solution of the difficulites outlined above it is suggested that the collect or convert data so that it is digital and to analyze the digital using computer technology is sensible procedure to follow. Data available for whole farm planning In the first instance data may be assembled and assigned to broad information classes this gives an overview with regard to the data currently available and permits a proper appraisal of requirements with regard to data collection. Broad subject areas related to farm planning are : Vegetation Soil Climate Land use Land systems Land capability Fauna habitat Hydrology Geology Administrative controls. Where ever possible historical data should be collected so that the impact of certain farm practices may be established by analysis changes in the natural environment both with in the area farmed and the surrounding areas. Data collection After carefully analyzing the data currently available and considering the purposes of the project, a data collection program is developed. Data collected typically includes : Maps Reports Photographs Imagery Ground control Data from specialized surveys The data gathered may be in the form of point source data such as bore hole information transect data such as for conductivity measurements or grid based data collection of original data should be undertaken according to guidelines which take the account the nature of the analysis and the statistical take to be applied to the data to give a measure of the accuracy of the results. Accuracy of the data The precision required of the data for large scale mapping is high and must be consistently high for all data sets used in the analysis often data from different sources with varying accuracy are brought together over a study area and conclusion are made based on an inappropriate meaning of data sets. Before data collection the accuracy requirements must be determined and only data collected at this level of precision or higher should be used data should never be compiled at a smaller scale than the final map product required. Data collection and analysis Where ever possible it is prefer able to use existing data and to carry out a limited field checking process which take the accuracy of the existing data .it is also necessary to determine whether or not the various data sets are able to be successfully and property integrated it is useful to recognize natural sub means areas of the farms based on the simarliarty of measured values of a selected variables depending on the criteria adopted this allows management plans to be constructed in harmony with the natural boundaries typical variables used to define sub areas are soil type slope and vegetation cover. Once data has been assembled assessed and digitized analysis using a computer begins the analysis looks at data set in turn and determine the information that the can be boundaries and with what accuracy it is possible to then look at relationships between data sets. The transformation of data in to useful information may establish the existence of areas requiring the collection of additional data. For the purpose of analyzing the physical factors affecting whole farm planning the following data set may be considered. Digital elevation model of area can be derived from grid placed over a topographic map or from controlled aerial photographs the DERM can be draped with other map thematic information such as land use. Insolation overlay showing amount of sun light reaching an area using an image analysis system the sun angle can be altered to simulate the isolation for the four seasons . Aspect overlay can be produced from the topographic data using image analysis . Slope overlay derived from the topographic data. Topographic over lay can be used to relate other thematic information to height at selected coordinated. Digital aerial photograph frame grabbed from a video image allows a high resolution general feature over lay to the part of the imagery and also be draped over the DEM. Anaglyph map from conjugate aerial photographs created by super imposing blue red image of one photo graph and a reed image of the other photograph filtered glasses are than used to view a three dimensional image. Stereo screen image image from each of two conjugate aerial photographs are displayed simple enhancements of the images can be plotted and viewed using a stereoscope. Orthophotomaps provide geometrically rectified images which can be adjusted to other over lays more easily than can uncertified aerial photographs. vegetation classification of airborne scanner imagery the high resolution of this allows accurate mapping of vegetation with a minimum amount of around survey the vigor of the vegetation can also be determined by classification. Survey control points with the use go global positioning system technology an area of farmland 20 kilometers by 20 kilo can be provided with 50 points to be metre accuracy from a single days work this control can then be used relate all over lays matter what the source to an accurate system. Fences roads and drainage lines can be digested from large scale topographic maps from aerial photographs vector to raster conversation may be necessary. Geological map if at a suitable scale can be digitized as one layer. Soils map may require original data to be collected at grid intersections using a soil auger. Topographic map may used to provide basic natural and cultural details as well height information. Land capability map will provide polygons which display the erosion risk and other characteristics of the land which may impose constraints on farm developments. Reports on studies already under taken in the area will provide textual; information which scan in the interpretation of correlation between the spatial referenced data see displayed graphically. Infiltration readings collection at selected points using infiltration rings allows the change point between infiltration and classification of air borne scanner will enable this points data to be expressed in areal extent.. EMI conductivity readings collected along transects allow the salinity of the soil to be detrmined along with the soil grain size. A classification of air borne scanner imagery will enable these transects to be expressed in areal extent. Conclusions Planning and managing agricultural land require an understanding of the nature and man made influence on the land it is necessary to represent these influence spatially so that a management map can be created the boundaries of the management zones displayed should take in to account the variation in significant data sets and the correlations between the data sets. Mapping at such large scales means that data may not be readily available at the required accuracy, over the whole area. The techniques outlined above allow conventional data sources to be manipulated using computer assisted methods, so that with limited ground surveys, registered overlays may be established and suitable hardcopy maps and related graphics can be produced as an aid to the management of agricultural land. Refferences Garrett B.K., 1988, Whole Farm Planning, principles and options, Department of Conservation, Forests and Lands, Victoria, Australia. Rice Center for Community design and Research, Houston, Texas, 31 May 1974 " Environmental Analysis for Development Planning, Chambers, County, Texas. vol. An approach to Natural Environmental Analysis " Prepared for National Science Foundation, Washington, D C Research Applied to National Needs, PB -268 745.