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In recent years digital sensors have been successfully integrated on board Unmanned Aerial Vehicles (UAV) to assess crop vigour, vegetation coverage, and to quantify the 'greenness' of foliage as indirect measurements of crop nitrogen status. The classical approach of precision agriculture has involved the use of multispectral sensors onboard UAV and the development of numerous vegetation indices associated with vegetation parameters, such as the mostly used Normalized Difference Vegetation Index (NDVI). However, the main negative issue when dealing with multi and hyper-spectral reflectance measuring tools is their high cost and complexity from the operational point of view. As a low-cost alternative, vegetation indices derived from Red Green Blue (RGB) cameras have been employed for remote-sensing assessment, providing data on different stress conditions and species. Digital images record information as amounts of RGB light emitted for each pixel of the image; however, the intensity of red and blue will often alter how green an image appears. To simplify the interpretation of digital colour data, recent studies have suggested converting RGB values to the more intuitive Hue, Saturation, and Brightness (HSB) colour spectrum, and then into a single measure of dark green colour, the Dark Green Color Index (DGCI). In this study, NDVI acquired by a ground-based handheld crop sensor and by a multispectral camera mounted on board a UAV has been compared with DGCI calculated from images taken with a commercial digital camera on board a UAV, trying to quantify the colour of turfgrass that had received different nitrogen (N) rates. The objectives of the trial were to study an affordable easy-to-use tool evaluating the relationship among NDVI, DGCI and leaf nitrogen content on turfgrass. [ABSTRACT FROM AUTHOR]

Satellite remote sensing of leaf nitrogen (N) content is an interesting technique for agricultural crops for both economic and environmental reasons since it allows the monitoring of fertilization, and hence can potentially reduce the application of N according to real plant needs. The objective of this trial was to compare the N status in different turfgrasses using both remote multispectral data acquired by GeoEye-1 satellite and two ground-based instruments. The study focused on creating a N content gradient on three warm-season turfgrasses, (Cynodon dactylon × transvaalensis‘Patriot’,Paspalum vaginatum‘Salam’,Zoysia matrella‘Zeon’), and two cool-season (Festuca arundinacea‘Grande’,Lolium perenne‘Regal 5’). The linear gradient of applied N ranged from 0 to 342 kg ha−1for the warm-season and from 0 to 190 kg ha−1for the cool-season turfgrasses. Proximity and remote-sensed reflectance measurements were acquired and used to determine the normalized difference vegetation index (NDVI). Our results proved that proximity-sensed NDVI is highly correlated with data acquired from satellite imagery. The correlation coefficients between data from the satellite and the other sensors ranged from 0.90 to 0.99 for the warm-season and from 0.83 to 0.97 for the cool-season species. ‘Patriot’ had a clippings N content ranging from 1.20% to 4.1%, thus emerging as the most reactive species to N fertilization. As such, the GeoEye-1 satellite can adequately assess the N status of different turfgrass species and its spatial variability within a field, depending on the N rates applied. In future, information obtained from satellites could allow precision fertilizer management on sports fields, golf courses, or other extended green areas. [ABSTRACT FROM AUTHOR]

High turfgrass wear resistance and recovery are the most sought after characteristics in turfgrass species when used for sports turf, but they are also very important in home gardens and public parks. Several wear resistance investigations have been conducted in field conditions in recent years, but these investigations involved the use of machinery and techniques that are not able to segregate the plant wounding and death effects from soil compaction effects that are generally associated with turfgrass wear. The same can be said of wear recovery investigations, with an extensive use of agronomical machinery for field trials. This study focussed on the wear resistance and recovery of mature swards of Cynodon dactylon (L.) Pers. var. dactylon × C. transvaalensis Burt-Davy cv. Tifway 419, Zoysia matrella (L.) Merr. cv. Zeon and Paspalum vaginatum Swartz. cv. Salam and a typical sports-type mix of Lolium perenne L. (cvv. Speedster 35% and Greenway 35%) + Poa pratensis L. (cvv. SR2100 15% and Greenknight 15%). The goal of this trial was to evaluate turfgrass wear resistance and recovery devoid of climatic and soil effects and thus, sward growing, wear simulation and recovery were conducted in controlled environment. Furthermore, wear simulation was conducted with FIFA-approved, numerical control machinery (Lisport). Wear resistance and recovery data was plotted against results from laboratory investigations on key tissue constituents. Zoysia matrella proved to be the most wear resistant, but the slowest in recovery, whereas the bermudagrass hybrid showed the exact opposite behaviour. Lignin and carbohydrate concentrations proved to be the two factors most closely correlated with wear resistance and recovery respectively. These two classes of compounds were present in an equilibrium that was species specific, with a frequent mutual exclusion between lignin and starch concentrations that deserves further investigation at the intra-specific level. [ABSTRACT FROM AUTHOR]

The intrinsic resistance of plant tissue to several biomechanical stresses, including tensile stress, is a decisive factor in determining the wear resistance of a turfgrass species. Lignin, dry matter, starch, sugars and silica are some of the tissue constituents that have been associated with leaf and stem mechanical resistance, whereas little information is available concerning stolons and rhizomes. These organs not only enable C4 turfgrass species lateral growth, soil colonisation and injury recovery, but are also key constituents of mature swards. This study consisted in an extensive investigation on the effective leaf, stolon and rhizome tensile strength of Cynodon dactylon (L.) Pers. var. dactylon × C. transvaalensis Burt-Davy cv. Tifway 419, Zoysia matrella (L.) Merr. cv. Zeon and Paspalum vaginatum Swartz. cv. Salam, as measured with a Fédération Internationale de Football Association (FIFA)-approved dynamometer and correlating the results with laboratory investigations on key tissue constituents. Tensile strength per unit area was influenced by both tissue constituents and tissue dimension. In rhizomes and stolons, tissue breakage usually occurred in the area at the intercalary meristem at the apical zone in the immediate proximity of a node. Older tissues had higher tensile strength owing to their higher levels of lignification. Lignin was the principal constituent determining tissue tensile strength and as such it could be used as a turfgrass wear resistance predictor in the cultivar breeding stages. Stolon total soluble sugars were generally inversely proportional to lignin content and, therefore, can also be considered clear markers of tissue mechanical strength. Silica was found to have no influence on the mechanical properties tissues. [ABSTRACT FROM AUTHOR]

High turfgrass wear resistance and recovery are the most sought after characteristics in turfgrass species when used for sports turf, but they are also very important in home gardens and public parks. Several wear resistance investigations have been conducted in field conditions in recent years, but these investigations involved the use of machinery and techniques that are not able to segregate the plant wounding and death effects from soil compaction effects that are generally associated with turfgrass wear. The same can be said of wear recovery investigations, with an extensive use of agronomical machinery for field trials. This study focussed on the wear resistance and recovery of mature swards of Cynodon dactylon (L.) Pers. var. dactylon×C. transvaalensis Burt-Davy cv. Tifway 419, Zoysia matrella (L.) Merr. cv. Zeon and Paspalum vaginatum Swartz. cv. Salam and a typical sports-type mix of Lolium perenne L. (cvv. Speedster 35% and Greenway 35%)+Poa pratensis L. (cvv. SR2100 15% and Greenknight 15%). The goal of this trial was to evaluate turfgrass wear resistance and recovery devoid of climatic and soil effects and thus, sward growing, wear simulation and recovery were conducted in controlled environment. Furthermore, wear simulation was conducted with FIFA-approved, numerical control machinery (Lisport). Wear resistance and recovery data was plotted against results from laboratory investigations on key tissue constituents. Zoysia matrella proved to be the most wear resistant, but the slowest in recovery, whereas the bermudagrass hybrid showed the exact opposite behaviour. Lignin and carbohydrate concentrations proved to be the two factors most closely correlated with wear resistance and recovery respectively. These two classes of compounds were present in an equilibrium that was species specific, with a frequent mutual exclusion between lignin and starch concentrations that deserves further investigation at the intra-specific level.

The intrinsic resistance of plant tissue to several biomechanical stresses, including tensile stress, is a decisive factor in determining the wear resistance of a turfgrass species. Lignin, dry matter, starch, sugars and silica are some of the tissue constituents that have been associated with leaf and stem mechanical resistance, whereas little information is available concerning stolons and rhizomes. These organs not only enable C4 turfgrass species lateral growth, soil colonisation and injury recovery, but are also key constituents of mature swards. This study consisted in an extensive investigation on the effective leaf, stolon and rhizome tensile strength of Cynodon dactylon (L.) Pers. var. dactylon×C. transvaalensis Burt-Davy cv. Tifway 419, Zoysia matrella (L.) Merr. cv. Zeon and Paspalum vaginatum Swartz. cv. Salam, as measured with a Fédération Internationale de Football Association (FIFA)-approved dynamometer and correlating the results with laboratory investigations on key tissue constituents. Tensile strength per unit area was influenced by both tissue constituents and tissue dimension. In rhizomes and stolons, tissue breakage usually occurred in the area at the intercalary meristem at the apical zone in the immediate proximity of a node. Older tissues had higher tensile strength owing to their higher levels of lignification. Lignin was the principal constituent determining tissue tensile strength and as such it could be used as a turfgrass wear resistance predictor in the cultivar breeding stages. Stolon total soluble sugars were generally inversely proportional to lignin content and, therefore, can also be considered clear markers of tissue mechanical strength. Silica was found to have no influence on the mechanical properties tissues.