Light-Intercepting Characteristics and Growth of Tomatoes Cultivated in a Greenhouse Using a Movable Bench System

The objective of this study was to investigate the growth and light-intercepting characteristics of tomatoes when movable benches are used in their cultivation. We cultivated tomatoes in a greenhouse (168 m2) during summer (9 July–9 September 2018) under different furrow distances (F1.0 = 1.0 m and F1.6 = 1.6 m) and movable benches (M indicates that the furrow distance = 0.4–0.8 m). Compared to the other treatments, when the movable bench was used to the change furrow distance depending on the plant growth stage (M treatment), the percentage of canopy light interception increased to ~90% at the early stage of plant growth (~20 days after transplanting). The percentage of canopy light interception for different treatments increased in the order of M > F1.0 > F1.6, and it increased towards the end of cultivation. In addition, the yield per unit area exhibited the same trend. Therefore, the solar radiation inside a greenhouse can be efficiently intercepted by plants when movable benches are used. This indicated that it was possible to increase plant yield per unit area using movable benches in plant cultivation.

High Density and Uniform Plant Distribution Improve Soybean Yield by Regulating Population Uniformity and Canopy Light Interception

Optimizing the spatial distribution of plants under normal conditions of water and fertilizer is widely used by farmers to improve soybean yield. However, the relationship between soybean yield and spatial plant distribution in the field has not been well studied. This study examined the effect of planting density and plant distribution pattern on soybean plant growth, yield components, canopy light interception, and dry matter accumulation. We also analyzed the relationship between photosynthetic rate, dry matter accumulation, and yield under different planting densities and plant distribution. A two year field experiment was conducted during the 2018 and 2019 soybean planting seasons. Two planting densities (1.8 × 105 and 2.7 × 105 plants ha−1) and two plant distribution patterns (uniform and non-uniform plant spacing) were tested. Higher planting density significantly increased the canopy light interception and dry matter accumulation during soybean growth, leading to increased soybean productivity. The seed yield of soybean under higher planting density was 22.8% higher than under normal planting density. Soybean planted under uniform spacing significantly reduced the differences plant-to-plant. Uniform plant spacing significantly increased the canopy light interception and dry matter accumulation of the soybean population. In addition, the coefficient of variation of seed weight per plant between individual plants under uniform plant distribution decreased by 71.5% compared with non-uniform plant distribution. Furthermore, uniform plant distribution increased soybean seed yield by 9.5% over non-uniform plant distribution. This study demonstrates that increasing planting density under uniform plant distribution can be useful to obtain higher seed yield without increasing other farm inputs.

Importance of the description of light interception in crop growth models

Canopy light interception determines the amount of energy captured by a crop, and is thus critical to modelling crop growth and yield, and may substantially contribute to the prediction uncertainty of crop growth models (CGMs). We thus analyzed the canopy light interception models of the 26 wheat (Triticum aestivum) CGMs used by the Agricultural Model Intercomparison and Improvement project (AgMIP). Twenty-one CGMs assume that the light extinction coefficient (K) is constant, varying from 0.37 to 0.80 depending on the model. The other models take into account the illumination conditions and assume either that all green surfaces in the canopy have the same inclination angle (θ) or that θ distribution follows a spherical distribution. These assumptions have not yet been evaluated due to a lack of experimental data. Therefore, we conducted a field experiment with five cultivars with contrasting leaf stature sown at normal and double row spacing, and analyzed θ distribution in the canopies from 3-dimensional canopy reconstructions. In all the canopies, θ distribution was well represented by an ellipsoidal distribution. We thus carried out an intercomparison between the light interception models of the AgMIP-Wheat CGMs ensemble and a physically based K model with ellipsoidal leaf angle distribution and canopy clumping (KCell). Results showed that the (KCell) model outperformed current approaches under most illumination conditions and that the uncertainty in simulated wheat growth and final grain yield due to light models could be as high as 45%. Therefore, our results call for an overhaul of light interception models in CGMs.

Growth of Megathyrsus maximus cv. Mombaça as affected by grazing strategies and environmental seasonality. I. Tillering dynamics and population stability

In rotationally grazed pastures, the canopy light environment can be modulated through both grazing frequency and severity, and the magnitude of sward responses may differ according to forage species and its ability to use available resources. We hypothesised that the tall, tufted, fast-growing, tussock-forming species Mombaça guineagrass (Megathyrsus maximus (Jacq.) B.K.Simon & S.W.L.Jacobs cv. Mombaça) can modulate its tillering dynamics and change its persistence pathway according to grazing strategy and the availability of growth factors. Treatments corresponded to all combinations of two levels of pre-grazing canopy light interception during regrowth (95% and maximum) and two post-grazing heights (30 and 50 cm), and were allocated to experimental units according to a randomised complete block design with four replications. Measurements were performed throughout contrasting climatic conditions during four seasons from January 2001 to February 2002. A quite stable tiller population density presented regardless of the range of grazing frequency and severity used in the study. However, tiller appearance and death were strongly influenced (P < 0.001) by season of the year, with highest rates recorded during the two summers and lowest during autumn–winter. There was no conclusive evidence that the persistence pathway of Mombaça guineagrass changes within the grazing management strategies studied.

Estimating Photosynthetically Active Radiation Intercepted by Almond and Walnut Trees using UAV-Captured Aerial Images and Solar Zenith Angle

Highlights Measurement of canopy light interception data using a ground-based mobile system. Using UAV-captured aerial images and zenith angle to estimate canopy light interception at different times of the day. Identifying boundaries of individual trees using the maximum likelihood estimator and the watershed algorithm. Abstract. Photosynthetically Active Radiation (PAR) absorbed by the leaves is a key piece of information to study the crop response to environmental conditions that could be used to estimate crop production potential. Canopies in a commercial orchard present differences in their capability to intercept light mainly due to the spatial variability in canopy development. There is a need for developing tools that could capture spatial variability in PAR interception to predict potential yield. Unmanned Aerial Vehicles (UAV) present an interesting alternative to provide this information, as they cover a larger area than ground-based systems in a shorter period with high spatial resolution. The objective of this study was to determine the relationship between the shadow of a tree derived from a ground-based canopy light interception scan obtained using a lightbar mounted on a mobile platform and that acquired from UAV Red-Green-Blue (RGB) images. Information acquired by an UAV was classified to separate canopy from its shadow, grass and sunlit soil using maximum likelihood estimator. Boundaries of individual trees were identified based on their positions using watershed transform algorithm. The relationship between canopy PAR interception data, sun angle in the sky (zenith angle), and the information derived from aerial images was analyzed. Coefficient of determination (R2) values of 0.92 and 0.88 were found for the multiple linear regression between PAR, the shadow area and the cosine of zenith angle obtained for almond and walnut crops, respectively. Moreover, R2 values of 0.81 and 0.86 were found for the relationship between the shadow’s area obtained underneath the canopy and the shadow’s area obtained from the UAV images and the cosine of the zenith angle for almond and walnut crops, respectively. The results show that the PAR interception can be estimated using the zenith angle and the area of the shadow, which can be obtained from a RGB aerial image. Keywords: Almond, Canopy segmentation, Image classification, PAR interception, Shadow area, UAV, Walnut.

115 Nitrogen fertilizer effects on above ground sward characteristics and beef heifer performance from native warm-season grass blends

A 2-yr study was conducted at Black Belt Research and Extension Center in Marion Junction, AL, to evaluate the effect of nitrogen (N) fertilizer application rate on forage production characteristics, nutritive value, and animal performance of beef heifers grazing a mixture of native warm-season grasses (NWSG) including big bluestem, little bluestem, and indiangrass. Six, two-hectare plots were randomly assigned to one of two treatments (0 or 67 kg N ha-1 applied in early April; n = 3 replications per treatment). Paddocks were continuously stocked with four weaned Angus × Simmental beef heifers (initial BW 288 ± 7 kg) from late May/early June through mid-to-late August during 2018 (73 grazing d) and 2019 (70 grazing d), respectively. Put-and-take cattle were used to manage forage to a target of 38 cm. Forage mass and canopy heights were collected every two weeks during the trial. Visual ground cover ratings, canopy light interception, and botanical composition were measured at the beginning and end of the trial in each year. Hand-plucked samples were collected every two weeks during the grazing trial to determine forage nutritional value. Data were analyzed using the PROC MIXED procedure in SAS 9.4, and differences were declared significant when P ≤ 0.05. Nitrogen fertilized NWSG had greater crude protein (P < 0.0001), sward heights (P = 0.0003), and canopy light interception at the beginning of the season (P = 0.0049) compared to non-fertilized paddocks. However, there were no differences (P ≥ 0.05) among N-fertility treatments for mean forage mass, heifer ADG, or BCS across the 2-yr study. Botanical composition data indicated that indiangrass decreased from 64% to 61% (P = 0.0022) and weed pressure increased from 11% to 15% (P = 0.0064) across the summer grazing season. Canopy light interception decreased by 51% from early June to August in fertilized NWSG and 26% in unfertilized paddocks, respectively. These data illustrate that NWSG systems may provide a viable grazing system in the summer months under reduced N inputs.

Quantification of light interception within image-based 3-D reconstruction of sole and intercropped canopies over the entire growth season

Background and Aims Light interception is closely related to canopy architecture. Few studies based on multi-view photography have been conducted in a field environment, particularly studies that link 3-D plant architecture with a radiation model to quantify the dynamic canopy light interception. In this study, we combined realistic 3-D plant architecture with a radiation model to quantify and evaluate the effect of differences in planting patterns and row orientations on canopy light interception. Methods The 3-D architectures of maize and soybean plants were reconstructed for sole crops and intercrops based on multi-view images obtained at five growth dates in the field. We evaluated the accuracy of the calculated leaf length, maximum leaf width, plant height and leaf area according to the measured data. The light distribution within the 3-D plant canopy was calculated with a 3-D radiation model. Finally, we evaluated canopy light interception in different row orientations. Key Results There was good agreement between the measured and calculated phenotypic traits, with an R2 >0.97. The light distribution was more uniform for intercropped maize and more concentrated for sole maize. At the maize silking stage, 85 % of radiation was intercepted by approx. 55 % of the upper canopy region for maize and by approx. 33 % of the upper canopy region for soybean. There was no significant difference in daily light interception between the different row orientations for the entire intercropping and sole systems. However, for intercropped maize, near east–west orientations showed approx. 19 % higher daily light interception than near south–north orientations. For intercropped soybean, daily light interception showed the opposite trend. It was approx. 49 % higher for near south–north orientations than for near east–west orientations. Conclusions The accurate reconstruction of 3-D plants grown in the field based on multi-view images provides the possibility for high-throughput 3-D phenotyping in the field and allows a better understanding of the relationship between canopy architecture and the light environment.