Phenotypic traits like plant height are crucial in assessing plant growth and physiological performance. Manual plant height measurement is labor and time-intensive, low throughput, and error-prone. Hence, aerial phenotyping using aerial imagery-based sensors combined with image processing technique is quickly emerging as a more effective alternative to estimate plant height and other morphophysiological parameters. Studies have demonstrated the effectiveness of both RGB and LiDAR images in estimating plant height in several crops. However, there is limited information on their comparison, especially in soybean (Glycine max [L.] Merr.). As a result, there is not enough information to decide on the appropriate sensor for plant height estimation in soybean. Hence, the study was conducted to identify the most effective sensor for high throughput aerial phenotyping to estimate plant height in soybean. Aerial images were collected in a field experiment at multiple time points during soybean growing season using an Unmanned Aerial Vehicle (UAV or drone) equipped with RGB and LiDAR sensors. Our method established the relationship between manually measured plant height and the height obtained from aerial platforms. We found that the LiDAR sensor had a better performance (R² = 0.83) than the RGB camera (R² = 0.53) when compared with ground reference height during pod growth and seed filling stages. However, RGB showed more reliability in estimating plant height at physiological maturity when the LiDAR could not capture an accurate plant height measurement. The results from this study contribute to identifying ideal aerial phenotyping sensors to estimate plant height in soybean during different growth stages.

Potential seed size in many crops including major cereals is determined during early seed developmental stages. However, the stage at which final seed size is determined in soybean (Glycine max [L.] Merr.) under field conditions is not known. Hence, this study was conducted with the main objective to assess seed growth dynamics under controlled and increased assimilate supply conditions during different seed filling periods using two maturity group soybean cultivars. Treatments consisted of a control, and a de-podding (pod removal) treatment at weekly intervals after the beginning of the seed filling stage up until physiological maturity. Only four to six pods were maintained per plant in de-podding treatments in order to provide a higher assimilate supply to remaining seeds. A higher assimilate supply until around the mid-seed filling stage increased unit seed weight in both the cultivars, indicating that the maximum seed size in soybean crops is determined during the mid-seed filling stage. The increase in seed weight under higher assimilate supply was associated with an extended seed filling duration and a uniform seed filling rate over a longer period. The results also suggested a possible source limitation during the early seed filling stage in soybean, indicating opportunities to improve its yield using supplemental inputs and other improved crop cultivation practices.

Core Ideas: Removal of aboveground biomass may affect soil C and N under sweet sorghum. The effect of cover crop and N fertilization on soil C and N under sweet sorghum was examined. SOC and STN were greater with vetch and vetch/rye mixture than other cover crops NH₄‐N was greater with rye and NO₃‐N greater with vetch/rye than other cover crops. Vetch and vetch/rye can enhance soil C and N storage and optimize N availability. Sustainable production of sweet sorghum (Sorghum bicolor [L.] Moench) grown for bioenergy production depends on practices that maintain soil C and N levels. The objective of this study was to evaluate the effect of winter cover crops (hairy vetch [Vicia villosa Roth], rye [Secaele cereale L.], hairy vetch/rye mixture, and the control [no cover crop]) and N fertilization rates (0 and 90 kg N ha⁻) on soil organic C (SOC), total N (STN), NH₄–N, and NO₃–N contents at the 0‐ to 30‐cm depth from 2010 to 2014 in the southeastern USA. Cover crop biomass yield and C content were greater with vetch/rye than vetch and the control and N content greater with vetch and vetch/rye than the control in 2013 and 2014. The SOC and STN at 0 to 5 cm were greater with vetch/rye than the control and at 15 to 30 cm were greater with vetch than vetch/rye. At 0 to 5 cm, SOC increased at 0.55 Mg C ha⁻¹ yr⁻¹ and STN at 0.06 Mg N ha⁻¹ yr⁻¹, regardless of treatments. At most depths, NH₄–N content was greater with rye than the control and greater with 0 than 90 kg N ha⁻¹, but NO₃–N content was greater with vetch/rye than rye. Because of greater cover crop C and N inputs, soil C and N stocks can be enhanced and N availability can be optimized by growing vetch and vetch/rye mixture cover crops to replace the stocks reduced by the removal of aboveground sweet sorghum biomass.

Identifying sensitive plant growth stages is vital for effective crop management. Defoliations is a widely used technique to assess the crop sensitivity to decreased assimilate supply in many crops including soybean [Glycine max (L.) Merrill]. Previous studies suggest that soybean is vulnerable to defoliations across different growth stages. However, the most sensitive soybean growth stage to defoliation is not clearly understood as previous studies have tested the effect of defoliation at one or few growth stages. Hence, this study was conducted with defoliations (67% leaf removal) across different soybean growth stages between vegetative stage (V4) to physiological maturity (R7) using two soybean cultivars from different maturity groups. Defoliation at most growth stages reduced soybean yield parameters, with the greatest reduction occurring during the early seed development stages (R5 to R5 + 1 week). The results from this study suggest that the early seed development stage is the most sensitive stage to defoliation induced assimilate limitations in soybean. Therefore, avoiding stresses which limit photoassimilates availability particularly during early seed-filling stage, is critical for maintaining soybean productivity.

Soybean is a globally important legume crop which fulfills most of its nitrogen (N) requirement through Biological Nitrogen Fixation (BNF) in symbiosis with Bradyrhizobium species, thereby reducing dependence on synthetic fertilizers and supporting more sustainable production systems. This review synthesizes current knowledge on the mechanism, capacity, and regulation of BNF in soybean, including nodule formation, nitrogenase activity and response to soil and environmental conditions. The evidence shows that BNF can provide a substantial share of the crop’s N uptake, although high-yielding systems frequently experience the “N gap”, which is a difference between a higher crop demand and a lower N supplied from BNF and existing soil reserves. This can be partially managed with strategies like inoculation, co-inoculation, re-inoculation or judicial application of N. This review further highlights the advances in microbial inoculant technologies, plant growth-promoting rhizobacteria (PGPR), soybean breeding and genetic engineering aimed at improving BNF stability, efficiency and capacity across different soil environments. Overall, the maximization of soybean BNF has strong potential to reduce synthetic fertilizer use, improve yield and seed quality, and enhance the economic and environmental sustainability of soybean-based systems.

Due to limited information, identifying suitable cannabidiol (CBD) dominant industrial hemp (Cannabis sativa L.) cultivars and optimal planting date are critical for hemp commercialization for CBD production in Florida. Two field trials were conducted with seven cultivars planted on three different dates from late April to late June. The cultivars were received from two different suppliers (Kentucky and Colorado) representing their adaptation. Plant growth parameters such as plant height and green canopy cover were recorded at 2−3 weeks intervals during crop growth. Temporal CBD and Δ‐9‐tetrahydrocannabinol (THC) concentrations in developing flowers were analyzed weekly beginning two weeks after flowering until maturity. The final floral biomass yield was measured at harvest. CBD and THC concentration curve over crop growing season varied among the tested cultivars. High positive correlations between CBD and THC concentrations (R² = 0.88−0.98) were observed in all cultivars. This resulted in similar CBD/THC ratios across all planting conditions. Earlier planting resulted in higher CBD, THC, and floral biomass yield in a few cultivars, with no significant effect in most cultivars. Cultivars adapted in Kentucky performed better compared to Colorado in floral biomass and CBD yield. However, THC concentrations in the cultivars adapted in Kentucky mostly exceeded the acceptable legal threshold (0.3% THC) at harvest. Results indicate cultivar performance was affected more by genetics compared to planting date. Screening more cultivars adapted to regions of similar latitudes and environmental conditions is necessary to identify suitable hemp cultivars for Florida or similar climatic conditions.