Submitted to: Transactions of the ASAE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/10/1996
Publication Date: N/A
Citation: Interpretive Summary: Yield maps are used to show the actual amount of crop harvested in each section of large fields. As each row is harvested, the crop is weighed, and yield per unit land area calculated, such as pounds/sq. ft. In row crops like potatoes, it is easy to follow the rows and make one pass over each row. It doesn¿t matter if two rows, four rows, or more, are harvested don each pass, it is clear how many rows the resulting crop yield came from and therefore, how much land area should be used in the yield/area calculation. In a crop like wheat, the rows are spaced too closely together to easily follow the row. The farmer makes one full width pass through the field, then overlaps each neighboring pass a little in order to harvest the entire crop in a manner similar to the way a lawn is mown. Each pass might be a little wider or a bit narrower than the previous one. This creates a problem when trying to decide how much ground area to distribute the wheat yield over in the yield map. If the yield is spread over too wide a pass, the yield is underestimated. If the yield is spread over too narrow a pass, the yield is overestimated. A software program was created to keep track of which rows have already been harvested. If a succeeding pass overlaps already harvested rows, the already harvested area is not counted when calculating yield/unit land area. This has resulted in much more accurate yield maps for closely spaced crops, such as wheat. Accurate yield maps can then be used to identify areas of the field that have outstanding crop yield and areas that have poor yield. The areas of good yield can be studied to determine what contributed to the high production. Areas of poor growth can be studied for ways to improve crop performance.
Technical Abstract: In harvesting narrow row or broadcast crops such as wheat, the actual combine cut width can vary significantly within a field. Assuming a constant combine cut width in the whole field to calculate crop yields will give incorrect results. In this study, a bitmap method is developed to determine the effective combine cut width from GPS positions of the combine ein the field. The method consists of first initializing a bitmap that represents the pre-harvest crop conditions in the field, and then progressively updating the bitmap to represent the up-to-date crop conditions during the harvest process. The effective combine cut width at each time step is derived by manipulating the changes of the bitmap during that time period. An example application of the method is shown with yield data for 1994 spring wheat. The average cut widths among combine passes varied from 1.18m to 2.24m, compared with a desired cut width of 1.52m. The accuracy of the resulting yield maps was greatly improved by the bitma method.