Mapping straw yield using on-combine light detection and ranging (lidar)

Wheat (Triticum aestivum L.) straw is not only important for long-term soil productivity, but also as a raw material for biofuel, livestock feed, building, packing, and bedding. Inventory figures in the USA for potential straw availability are largely based on whole states and counties. Site-specific information is needed to determine where sufficient straw is available for removal within farm fields. The objective of this study was to assess the accuracy and feasibility of light detection and ranging (lidar) measurements of crop height for predicting the straw yield of wheat at site-specific field locations and apply this information to determining where excess straw is available beyond soil conservation needs. An inexpensive lidar sensor was mounted on the top of a Case International Harvester 1470 combine and aimed to point forwards at a 45 degrees angle over the combine's reel. Lidar-measured crop height was correlated with manually measured crop height in small plots (r(2)=0.79) and was a good predictor of straw productivity across three farm fields (r(2)=0.85). Crop height was better correlated with straw yield than grain yield or grain protein concentration. Crop height predicted by lidar could then be used to estimate straw yield from a predetermined linear relationship between crop height and straw yield. A straw yield map was generated during harvest by programming the lidar sensor to compute the average of 91 readings in each scan. A map of harvestable straw was computed by subtracting the amount of straw required to maintain soil organic carbon from a map of total straw yield. Lidar is potentially useful for measuring crop biomass on a combine harvester and determining where in farm fields excess crop residue can be removed for commercial purposes. Further work with lidar is needed to resolve the issue of flying chaff.