Potential of Red Edge Spectral Bands in Future Landsat Satellites on Agroecosystem Canopy Green Leaf Area Index Retrieval

Vegetation biophysical parameter retrieval is an important earth remote sensing system application. In this paper, we studied the potential impact of the addition of new spectral bands in the red edge region in future Landsat satellites on agroecosystem canopy green leaf area index (LAI) retrieval. The test data were simulated from SPARC ‘03 field campaign HyMap hyperspectral data. Three retrieval approaches were tested: empirical regression based on vegetation index, physical model-based look-up-table (LUT) inversion, and machine learning. The results of all three approaches showed that a potential new spectral band located between the Landsat-8 Operational Land Imager (OLI) red and NIR bands slightly improved the agroecosystem green LAI retrieval accuracy (R2 of 0.787 vs. 0.810 for vegetation index approach, 0.806 vs. 0.828 for LUT inversion approach, and 0.925 vs. 0.933 for machine learning approach). The results of this work are consistent with the conclusions from previous research on the value of Sentinel-2 red edge bands for agricultural green LAI retrieval.

Spatiotemporal Attributes and Crop Loss Associated with Tan Spot Epidemics in Baby Lima Bean in New York

Tan spot, caused by the pycnidial fungi Didymella americana and Boeremia exigua var. exigua, is a foliar disease affecting processing baby lima bean production in New York. Tan spot epidemics are prevalent, occur annually, and may result in substantial defoliation. The disease is controlled by the prophylactic application of fungicides to maximize green leaf area. Information on yield losses due to tan spot on baby lima bean yield and the benefits of fungicide applications is needed to justify investments in disease management. Four small-plot, replicated trials were conducted over 2 years in commercial baby lima bean fields to evaluate the efficacy of fungicides for tan spot control at Piffard and Leicester, NY. Applications of pyraclostrobin or boscalid significantly reduced tan spot incidence and severity compared with nontreated plots, and increased the number of leaves per stem. In 2016, the increase in green leaf area associated with fungicide application was also documented in canopy reflectance values at 830 nm. Despite the decrease in tan spot incidence and corresponding increase in crop health obtained from fungicides, this effect did not translate into significant increases in pod yield. This finding suggested that the relationship between green leaf area and yield is highly variable in baby lima bean. The spatial and spatiotemporal patterns of naturally occurring tan spot epidemics were also characterized in baby lima bean fields across western New York using disease incidence data collected in transects and grids. The spatial pattern of data collected in transects was analyzed using median runs analysis. Disease incidence data collected in two-dimensional grids were analyzed to quantify spatial pattern using spatial analysis by distance indices (SADIE). The association function of SADIE was used to quantify the spatiotemporal patterns of tan spot epidemics after crop emergence and at harvest. These findings suggested that tan spot is likely to initiate at relatively frequent, randomly positioned foci, and that subsequent, limited spread results in significant local aggregation. Hypotheses for inoculum sources and recommendations for tan spot control in baby lima bean fields in New York are discussed.

Quality and yield response to the control of Mycosphaerella graminicola in wheat as affected by nitrogen rate and cultivar bread-making characteristics

Septoria leaf blotch (SLB), caused by Mycosphaerella graminicola, reduces yield and grain quality of wheat (Triticum aestivum L.) by affecting the photosynthetically active area of the crop. This might influence grain protein concentration (GPC) and affect bread-making parameters. Nitrogen (N) fertilisation is required to achieve high yields in wheat; however, it may enhance the development of foliar diseases such as SLB. The aim of this study was to evaluate the effect of fungicide and N rate on SLB severity, green-leaf-area duration, grain yield and bread-making parameters in three wheat cultivars differing in bread-making characteristics. Two field experiments were conducted during 2009 and 2010 in a split-split-plot design with three fungicide treatments (triazole, triazole–strobilurin, nil) as main plots, three N fertiliser rates as subplots and three cultivars as sub-subplots. Fungicides significantly reduced the area under disease-progress curve (AUDPC) and this was associated with increased yield, which varied among cultivars. The AUDPC was lower in the higher N-rate treatments. Fungicide applications and increasing N rates extended green-leaf-area duration. GPC increased in untreated plots and it was reduced with applications of triazole–strobilurin fungicide. GPC reduction caused by this type of fungicide tended to be lower when the rate of N increased. The two cultivars with low bread-making characteristics showed a tendency to greater reductions in GPC with both fungicide types. Regarding quality variables, only tenacity and dough strength were reduced by the triazole-strobilurin fungicide. On average, for all treatments, tenacity, water absorption and dough development time were higher in the best quality group cultivars.