Sudden changes in crop environment, as influenced by total solar eclipse

The Division of Agricultural Meteorology, at Pune of IMD conducted an experiment at Principal Evapotranspiration Observatory, Canning, W.B., during October, 1995 to study the sudden changes in crop environment. The present study revealed that both the crop canopy temperature and observatory temperature at different heights recorded sharp fall of around 2.0°C at 0900 hr (IST) on the eclipse day. The relative humidity (% ) increased sharply at 0900 hr (IST) on the eclipse day within crop canopy as well as within observatory. The soil temperature dropped suddenly at 10 and 20 cm depths of the subsoil and delayed reversal of the soil temperature gradient occurred on the eclipse day; the grass minimum temperature was 21.2°C. Bright sunshine hours reduced by 0.8 on 'the eclipse day as compared to the preceding and succeeding days. The wind during the eclipse period was almost calm between 0900 -0930 hr (IST). The daily total ET recorded on the eclipse day was the minimum. The rate of evapotranspiration was less than half as compared to the other days, as recorded at 0830 hr (IST) (0.2 mm) on the eclipse day, which was closely followed by that observed at 1130 hr (IST) (0.3 mm).

Variations in leaf temperature, plant internal resistance, photon requirement and transpiration of pigeonpea under bare and mulched soil conditions

ABSTRACT. The paper presents the results of an experiment conducted during 1992 and 1993 crop seasons at the farm of Gujarat Agricultural University, Anand on pigeonpea to determine variations in agro-meteorological characteristics of leaf transpiration leaf temperature plant diffusive resistance and quanta were considered at three levels within the crop canopy in mulched and unmulched fields. The anlilysis rewaled that leaf temperature is more in unmulched field where transpiration rates are lower than the mulched field. Stomatal resistance and the quantum requirements nearly match in both the treatments. Stomatal conductance attains large values in morning and evening hours.

Creating a Field-Wide Forage Canopy Model Using UAVs and Photogrammetry Processing

Alfalfa canopy structure reveals useful information for managing this forage crop, but manual measurements are impractical at field-scale. Photogrammetry processing with images from Unmanned Aerial Vehicles (UAVs) can create a field-wide three-dimensional model of the crop canopy. The goal of this study was to determine the appropriate flight parameters for the UAV that would enable reliable generation of canopy models at all stages of alfalfa growth. Flights were conducted over two separate fields on four different dates using three different flight parameters. This provided a total of 24 flights. The flight parameters considered were the following: 30 m altitude with 90° camera gimbal angle, 50 m altitude with 90° camera gimbal angle, and 50 m altitude with 75° camera gimbal angle. A total of 32 three-dimensional canopy models were created using photogrammetry. Images from each of the 24 flights were used to create 24 separate models and images from multiple flights were combined to create an additional eight models. The models were analyzed based on Model Ground Sampling Distance (GSD), Model Root Mean Square Error (RMSE), and camera calibration difference. Of the 32 attempted models, 30 or 94% were judged acceptable. The models were then used to estimate alfalfa yield and the best yield estimates occurred with flights at a 50 m altitude with a 75° camera gimbal angle; therefore, these flight parameters are suggested for the most consistent results.

Estimation of Site-specific Crop Coefficients for Major Crops of Lalgudi Block in Tamil Nadu using Remote Sensing based Algorithms

Crop coefficient (Kc ) is an important parameter in estimating the crop water requirements during different crop growth stages. The Kc values for a particular crop are highly site and region-specific and need to be precisely determined for each agro-climatic region for better irrigation scheduling and improved water and crop productivity. The site-specific crop coefficients for paddy, sugarcane, and banana cultivated in Lalgudi block, Tiruchirapalli District, Tamil Nadu, India, were estimated using two remote sensing-based methods viz. NDVI-Kc linear regression technique and SEBAL actual evapotranspiration to reference evapotranspiration ratio approach (SEBAL-Kc ). The Kc values obtained by remote sensing methods were compared with FAO-56 Adjusted Kc (ClimAdj-Kc ) for local climatic conditions and FAO-56 tabulated reference Kc values (FAOTab-Kc ). Regression analysis revealed a good agreement between NDVI-Kc and ClimAdj-Kc for paddy (R2 =0.95), banana (R2 =0.93), and sugarcane (R2 =0.79). Compared to FAO56-Kc, the derived Kc values using NDVI-Kc were higher, while the SEBAL-Kc values were lower for all growth stages of paddy. For sugarcane crops, the FAO-56 Kc, NDVI-Kc, and ClimAdj-Kc for local climate were almost similar in all stages. In the case of bananas, NDVI-Kc and SEBAL-Kc were higher as compared to the FAO-56-Kc and ClimAdj-Kc. SEBAL approach performs well as it accounted for local climatic conditions and crop canopy changes, whereas NDVI considered only crop canopy. However, the SEBAL method is computationally intensive as compared to the NDVI-Kc method. The Kc values estimated in this study can be important in quantifying the crop evapotranspiration at regional and field scales, leading to better decision-making in irrigation scheduling.

Assessing the Capability and Potential of LiDAR for Weed Detection

Conventional methods of uniformly spraying fields to combat weeds, requires large herbicide inputs at significant cost with impacts on the environment. More focused weed control methods such as site-specific weed management (SSWM) have become popular but require methods to identify weed locations. Advances in technology allows the potential for automated methods such as drone, but also ground-based sensors for detecting and mapping weeds. In this study, the capability of Light Detection and Ranging (LiDAR) sensors were assessed to detect and locate weeds. For this purpose, two trials were performed using artificial targets (representing weeds) at different heights and diameter to understand the detection limits of a LiDAR. The results showed the detectability of the target at different scanning distances from the LiDAR was directly influenced by the size of the target and its orientation toward the LiDAR. A third trial was performed in a wheat plot where the LiDAR was used to scan different weed species at various heights above the crop canopy, to verify the capacity of the stationary LiDAR to detect weeds in a field situation. The results showed that 100% of weeds in the wheat plot were detected by the LiDAR, based on their height differences with the crop canopy.

Radiation Dynamics on Crop Productivity in Different Cropping Systems

Global demand for food has always been on the increase due to the increase of the population in this world. Intercropping is one of the alternatives of agronomic practices that is widely practiced in ensuring food security and enhancing yield stability. Strip, mixed, and relay intercropping can be practiced to increase crop production. In addition to achieving a successful intercropping system, factors such as suitable crops, time of sowing, maturity of the crop, and plant density need to be considered before and during planting. Besides, practiced intercropping becomes a useful cropping system to increase efficient resource utilization, enhance biodiversity, promote soil health, enhance soil fertility, erosion control, yield advantage, weed, pest, and disease control, insurance against crop failure, ecosystem and modification of microclimate, market instability, and increase farmers income. Crop productivity in any types of cropping system implemented relies primarily on the interception of photosynthetically active radiation (PAR) of crop canopy and conversion of intercepted radiation into biomass or known as radiation use efficiency (RUE). Both PAR and RUE are important measurements that have significant roles in crop growth and development in which the accessibility of these radiation dynamics is connected with the leaf area index and crop canopy characteristics in maximizing yield as well as total productivity of the crop component in intercropping systems.

Bi-directional exchange of ammonia above a corn crop canopy: from flux measurements to model parameterizations

<p>Emissions of ammonia (NH<sub>3</sub>) from agriculture have a significant impact on the environment. Its atmospheric transport and subsequent deposition has been shown to alter nutrient-poor ecosystems thereby reducing biodiversity. As the most abundant base in the atmosphere, NH<sub>3</sub> plays a key role in secondary aerosol formation impacting air quality and climate. Due to the lack of long term observations and challenges in performing NH<sub>3</sub> flux measurements, large uncertainties exist in both emission quantification from fertilized crop fields and in the bi-directional exchange of NH<sub>3</sub> with agroecosystems. We measured NH<sub>3</sub> fluxes above a corn field using the eddy covariance technique together with a quantum cascade laser spectroscopy analyzer over two consecutive growing seasons in 2017 and 2018. We found that after initial NH<sub>3</sub> emissions following fertilizer application, periods of both NH<sub>3</sub> emission and deposition with similar flux magnitudes prevailed throughout the growing seasons (ranging approximately between ±300 ng m<sup>-2</sup> s<sup>-1</sup>), highlighting the importance of the corn crop canopy for regulating the net NH<sub>3</sub> exchange. To evaluate the underlying processes of the NH<sub>3</sub> bi-directional exchange, a two-layer compensation point model was used. Based on the large range of environmental conditions encountered during the extensive flux measurements periods, the validity of different parameterizations could be assessed. In particular, processes regulating stomatal and non-stomatal flux pathways will be discussed.</p>

Effect of soybean crop structure on large crabgrass (Digitaria sanguinalis) growth and seed dormancy

Crop-weed interactions are affected by the environment alterations resulting from the crop presence, such as modifications in temperature, light quality and quantity and moisture conditions that could modify the weed performance. The objectives of this work were to study 1) how soybean [Glycine max (L.) Merr.] crop structure modifies the environment under the canopy and large crabgrass [Digitaria sanguinalis (L.) Scop.] plant structure, biomass and seed production and dormancy and 2) the relative importance of these environmental changes on the weed characteristics. A field experiment in a completely randomized block design with five replicates was performed to evaluate narrow and wide inter-row spacing, and soybean maturity group III and IV. Measured variables were intercepted solar radiation (RAD), R-FR ratio, humidity, minimum, maximum and alternating temperatures, as well as, weed biomass, tillers per plant, weed height and seed dormancy. Crop canopy reduced solar radiation, R-FR ratio, daily average maximum and alternating temperatures. Soybean presence reduced the weed biomass, tillers and seeds per plant and seed dormancy. High solar radiation intercepted by the crop during the reproductive phase was the main environmental variable related to reductions in weed biomass, tillers per plant and fecundity. The combination of low temperature and solar radiation received by developing seeds was more related to seed dormancy than the rest of the variables. Crop management decisions focused on the fact that keeping the crop canopy alive during more time by the end of the season, would not only reduce the weed growth but also seed dormancy.

Inter-row Cultivation Timing Effects on Waterhemp (Amaranthus tuberculatus) Control and Sugarbeet Yield and Quality

The invasion of waterhemp into northern sugarbeet growing regions has prompted producers to re-integrate inter-row cultivation into weed management programs as no currently registered herbicides can control glyphosate-resistant waterhemp POST in crop. Inter-row cultivation was a common weed control practice in sugarbeet until the release of glyphosate-resistant sugarbeet cultivars in 2008 made the use of inter-row cultivation unnecessary. In the late 2010s, producers began again to use inter-row cultivation to remove weeds that glyphosate did not control, but producers need information on the effectiveness and safety of inter-row cultivation when used with soil residual herbicide programs. Efficacy and tolerance field experiments were conducted in Minnesota and North Dakota from 2017 to 2019. Results from the efficacy experiment demonstrated cultivation improved waterhemp control 11% and 12%, 14 and 28 DAT, respectively. Waterhemp response to cultivation was dependent on crop canopy and precipitation after cultivation. Cultivation had minimal effect on waterhemp density in three environments, but at one environment, near Galchutt, ND in 2019, waterhemp density increased 600% and 196%, 14 and 28 DAT, respectively. Climate data indicated Galchutt, ND in 2019 received 105 mm of precipitation in the 14 days following cultivation and had an open crop canopy which likely contributed to further weed emergence. Results from the tolerance experiment demonstrated root yield and recoverable sucrose were not affected by cultivation timing or number of cultivations. In one environment, cultivating reduced sucrose content by 0.8% regardless of date or cultivation number, but no differences were found in three environments. In-season cultivation can damage/destroy leaf tissue which is likely responsible for the reduction in sucrose content. Results indicate cultivation can be a valuable tool to control weeds that herbicide cannot, but excessive rainfall and open crop canopy following cultivation can create an environment conducive to further weed emergence.