Knowledge of site-specific crop parameters such as plant height, coverage and biomass density is important for optimising crop management and harvesting processes. Sensors for measuring crop parameters are essential pre-requisites to gather this information. In recent years, laser rangefinder sensors have been adopted in many industrial applications. In agricultural engineering, the potential of laser rangefinders for measuring crop parameters has been little exploited. This paper reports the design and the performance of a measuring system based on a triangulation and a time-of-flight laser rangefinder for estimating crop biomass density in representative crops under field conditions. It was shown that the mean height of reflection point is a suitable parameter for non-contact indirect measurement of crop biomass by laser rangefinder sensors. The main parameters for potential assessment were the coefficient of determination (R 2 ) and the standard error (RMSE) for the relation between crop biomass density and the mean height of the reflection point in crop stands from oilseed rape, winter rye, winter wheat and grassland during the vegetation period in 2006. For the triangulation sensor, R 2 was in the range from 0.87 to 0.98 and for the time-of-flight sensor in the range from 0.75 to 0.99 for both fresh matter and dry matter density. The triangulation sensor had a reduced suitability caused by masking effects of the reflected beam and because of limited measuring range. Based on the results of experiments and technical data, it was concluded that the time-of-flight principle has good potential for site-specific crop management.

No abstract

Th e leaf area index (LAI), as the ratio of the leaf area to a given unit of land area, is an essential parameter to describe plant productivity and make management decisions. Most methods for estimating the LAI are not suitable for practical agricultural management at the fi eld scale due to delayed availability of data, high costs, or inaccuracy at late growth stages. Th erefore, a new approach for rapid LAI mapping by ground-based laser rangefi nders mounted on a vehicle was evaluated. Two types of laser rangefi nders were tested in various confi gurations. Field trials were conducted to evaluate whether these sensors were capable of capturing temporal and spatial variability of LAI, biomass, and crop height. Crops included in the trials were winter wheat (Triticum aestivum L.), winter rye (Secale cereale L.), and oilseed rape (Brassica napus L. ssp. napus). Correlation coeffi cients ranging from 0.3 to more than 0.9 (Pearson's r) between sensor readings, LAI, and biomass were observed. Best correlations were achieved with the time-of-fl ight based rangefi nder in winter wheat. Th is study demonstrated that vehicle-based laser distance sensors off er potential for rapid mapping of LAI in crops. Th e sensors are robust and allow for real-time data processing. It is anticipated that they will become aff ordable in the near future, for example, due to mass production for collision avoidance in automobile industry. Th us, vehicle-based laser distance sensors might be used for precision agriculture applications like fertilizing, crop protection, and yield prediction.

In recent years, laser rangefinder sensors have been introduced to the practice and research of agricultural engineering. In research, laser rangefinders have been investigated in horticulture and agriculture. For vehicle-based determination of crop biomass, commercially available laser rangefinders have been analysed and tested to measure aboveground biomass in oilseed rape, winter rye, winter wheat, oats and grassland. Resulting from limited measuring range and fixed beam types, the laser rangefinder models that were investigated only partially met the specific demands for agricultural field and crop conditions. Therefore, a new laser rangefinder scanner (ibeo-ALASCA XT) was chosen. This sensor was specifically developed for driver assistance and autonomous guiding of road vehicles. The scanner was tested in 2008 focusing on the measurement of crop stand parameters in winter wheat under field conditions. The sensor achieved good results with reproducible measurements. Measuring from a stationary vehicle, the standard deviation for the measurements of crop height to characterise the crop stand was less than 3 mm in low, medium, and high biomass areas. The ground speed of the vehicle, ranging from 6 to 24 km h -1 , did not significantly influence the readings. For measurements in front of tractors and self-propelled machines (field sprayers, combines and forage harvesters), the sensor has to scan the crop stands at different inclination angles. It was shown that the inclination angle of the laser beam, which varied from 10°to 80°, significantly influenced the readings. Higher inclination angles resulted in apparent increased heights of the crop stand. For the functional relationship between reflection height levels (95th, 75th, 50th and 25th percentiles, and mean values) and crop biomass density, the coefficient of determination (R 2 ) was greater than 0.9.

Lady beetles (Coccinella septempunctata) are one of the most effective predators of aphids (Sitobion avenae). Therefore, the development of plant protection technologies that do not lead to their eradication within the field is necessary. With a sensor‐controlled field sprayer, which determined in real‐time the plant biomass of a heterogeneous winter wheat field and, based on these measurements, also controlled the amount of applied insecticide, a variable rate spraying program was implemented. The insecticide savings totaled 13.4% when compared to that of uniform spraying. An application of a high dosage led to a rapid die‐off of aphids. However, this same scenario did not occur in the areas that received a low dosage of insecticide. There, the aphids remained alive. It was observed that lady beetles colonized at first in these low dosage areas, where aphids were still present. Eventually 3 wk after insecticide application, aphids and lady beetles did not exist in the areas that received low insecticide dosages in the field. There, at this latter time the crop was mature. Now the aphids occurred in the high biomass areas, which were still green and not fully mature. The same scenario occurred for the lady beetles; as presence–absence sampling indicated that they followed their prey. The time‐dependent spatial variability of aphid and lady beetle occurrence were confirmed by GLIMMIX analysis which indicated a significant effect of the space–time interaction on their joint occurrence.