Chad W. Higgins’s research while affiliated with Oregon State University and other places

Agrivoltaic systems combine solar energy and agriculture, promoting dual land use. Although grazing sheep in these systems is common, research on intentionally designed pastures to increase production is lacking. This study seeks to compare the herbage growth and lamb production in simple, diverse, and legume pastures in an agrivoltaic system over 2 years in Oregon. Annual herbage production in diverse pastures (4583 kg DM ha ⁻¹ ) was comparable to simple pastures (4457 kg DM ha ⁻¹ ), but higher than legume pastures ( p < .05; 4023 kg DM ha ⁻¹ ) for the 2020/2021 growing season. In the 2021/2022 growing season, diverse pastures had a higher yield (4660 kg DM ha ⁻¹ , p < .05) than simple pastures (4052 kg DM ha ⁻¹ ), which were similar to legume pastures (3955 kg DM ha ⁻¹ ). Liveweight gain (LWG; g head ⁻¹ d ⁻¹ ) tended ( p = .06) to be higher from lambs in diverse and legume pastures compared to simple pastures in spring 2021. Liveweight production (LWP; kg ha ⁻¹ d ⁻¹ ) of legume pasture were greater ( P < 0.05) than other pasture types, while simple pastures had the lowest LWP during this period. In summer 2021, LWG tended to be greater in lambs grazing diverse versus simple pastures. No difference was detected (all p > .05) in LWG or LWP at any grazing period in 2022. Overall, efficiency of pasture production was greatly reduced by lower light availability in all pasture types. Diversification of pastures using forbs in agrivoltaics was a good strategy for greater herbage production, while the legume pastures had poor persistence.

The hydraulic conductivity of hemp stems under water-stress conditions was investigated to assess the impact on water transport from the root to the leaves. Water-stress conditions induce embolism (cavitation) in xylem channels, thereby affecting water flow. The percentage loss of water transfer ability within the xylem channels can be represented by a 19 'vulnerability curve' (VC). This study utilized an air injection technique to induce embolisms in the stem and measured the subsequent changes in hydraulic conductivity using a specialized measurement apparatus. The results revealed that the shape of the vulnerability curve for hemp was influenced by the xylem area, which is an atypical finding with no prior evidence in other plant species. The statistical analysis confirmed the significance of this effect (p-value=0.003 at 95% confidence intervals). Consequently, a non-traditional mathematical equation (simple power law) was developed to describe the relationship between pressure and xylem area. Furthermore, our findings demonstrated that hemp stems are more responsive to water stress compared to other plant species documented in previous literature. The minimum pressure (0.15 MPa) at which initial cavitation is observed and the maximum pressure (~2.4 MPa) at which all stem conductance is lost were among the lowest reported values, indicating that hemp growth may be significantly affected by deficit irrigation strategies. Thus, careful monitoring of the irrigation schedule is crucial, particularly for younger stems with smaller xylem cross-sectional areas. These insights into the hydraulic behavior of hemp can contribute to the development of improved irrigation strategies in agriculture, ultimately enhancing water-use efficiency and optimizing crop production.

In both agroforestry and agrivoltaics, crops are cultivated under the shade of a top story layer of trees and photovoltaic (PV) panels, respectively. However, the quality (i.e. spectral composition) of the transmitted radiation might differ between the two systems. Tree canopies are green and absorb different spectra selectively, while panels are black and thus should not alter the spectral composition of transmitted radiation. Consequently, plant growth and yield may differ depending on the spectral composition of light. In this study, the spectral composition of transmitted radiation (at ground level) was measured with a spectrometer along transects between adjacent rows of trees and PV panels. The transects crossed both sunlit and shaded areas. The radiation transmitted in sunlit areas was nearly identical, qualitatively and quantitatively, to the incident radiation above both systems. In the shaded areas, transmission was strongly reduced, as expected, and the spectral composition changed. Under tree canopies the percentage of green (G) and red (R) radiation decreased, while the percentage of blue (B) and violet (V) remained similar to the sunlit areas, and far-red (FR) increased sharply. Under the PV panels, both R and FR decreased, G remained similar, while B and V increased gradually from the edge of the shade towards the center of the shaded area. This changed the ratios between different spectra. For instance, the R:FR ratio under the panels varied with the position but remained close to the incoming radiation value (1.35), while under the trees it decreased to 0.35. The R:FR ratio decreased in close correlation (R² = 0.98) with the fraction of transmitted radiation, under the trees, but not under the panels. The B:R ratio increased in the shade in both systems, but more so in the panel system. G:R and B:G ratios also changed between and within systems, but less dramatically, while the B:FR ratio decreased at decreasing transmittance under the trees, but increased under the panels. The results indicate that even when transmitted radiation quantity is similar, radiation quality in the shaded areas may differ substantially between agroforestry and agrivoltaic systems. The higher R:FR and B fraction under PV panels shade may fail to induce shade adaptation responses in plants, unless low radiation level signals prevail over radiation quality signals in inducing such response.

The hydraulic conductivity of hemp stems under water-stress conditions was investigated to assess the impact on water transport from the root to the leaves. Water-stress conditions induce embolism (cavitation) in xylem channels, thereby affecting water flow. The percentage loss of water transfer ability within the xylem channels can be represented by a ‘vulnerability curve’ (VC). This study utilized an air injection technique to induce embolisms in the stem and measured the subsequent changes in hydraulic conductivity using a specialized measurement apparatus. The results revealed that the shape of the vulnerability curve for hemp was influenced by the xylem area, which is an atypical finding with no prior evidence in other plant species. The statistical analysis confirmed the significance of this effect (p-value=0.003 at 95% confidence intervals). Consequently, a non-traditional mathematical equation (simple power law) was developed to describe the relationship between pressure and xylem area. Furthermore, our findings demonstrated that hemp stems are more responsive to water stress compared to other plant species documented in previous literature. The minimum pressure (0.15 MPa) at which initial cavitation is observed and the maximum pressure (∼2.4 MPa) at which all stem conductance is lost were among the lowest reported values, indicating that hemp growth may be significantly affected by deficit irrigation strategies. Thus, careful monitoring of the irrigation schedule is crucial, particularly for younger stems with smaller xylem cross-sectional areas. These insights into the hydraulic behavior of hemp can contribute to the development of improved irrigation strategies in agriculture, ultimately enhancing water-use efficiency and optimizing crop production. Highlight The hydraulic conductivity of hemp stems under water-stress conditions was investigated to assess the impact on water transport from the root to the leaves. The results revealed that the shape of the vulnerability curve for hemp was influenced by the xylem area, which is an atypical finding with no prior evidence in other plant species. Our findings demonstrated that hemp stems are more responsive to water stress compared to other plant species documented in previous literature. The minimum pressure (0.15 MPa) at which initial cavitation is observed and the maximum pressure (∼2.4 MPa) at which all stem conductance is lost were among the lowest reported values, indicating that hemp growth may be significantly affected by deficit irrigation strategies. Thus, careful monitoring of the irrigation schedule is crucial, particularly for younger stems with smaller xylem cross-sectional areas. These insights into the hydraulic behavior of hemp can contribute to the development of improved irrigation strategies in agriculture, ultimately enhancing water-use efficiency and optimizing crop production.

Animal grazing to control understory herbage growth in photovoltaics sites presents a substantial opportunity for animal and energy production within the same site. However, there is a paucity of information on the effect of field preparation method within solar arrays on the establishment and productivity of pastures. Thus, the current study investigated the effects of field preparation and shade within solar arrays on plant germination and subsequent herbage yield in an agrivoltaic system. The treatments were (i) tillage and plastic cover (TP), (ii) plastic cover only (P), and (iii) herbicide application prior to sowing (H). A diverse pasture mixture, comprised of perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), white clover (Trifolium repens L.), birdsfoot trefoil (Lotus corniculatus L.), chicory (Cichorium intybus L.), and plantain (Plantago lanceolata L.) was direct drilled within solar arrays in spring 2020. The experiment layout was a completely randomized plot design with three replicates. The pastures were harvested in fully shaded, partially shaded and non-shaded zones within solar arrays in each plot in July and October 2020. The average across the treatments herbage dry matter (DM) yield was 1127 kg DM ha⁻¹ and 1305 kg DM ha⁻¹ in July and October 2020, respectively. While the effect of establishment method was significant with plastic cover and tillage application resulting in the highest DM yield of 1547 kg DM ha⁻¹, the herbage yield in three shade zones within the solar arrays did not differ in July 2020. The herbicide application alone had the lowest DM yield at the establishment stage in summer. The effect of establishment method on forage DM yield was not significant in October 2020. However, a treatment×shade zone interaction was detected as the non-shaded, middle zone in herbicide only treatment had substantially lower DM yield than other two shade zones.

Agrivoltaics, which integrate photovoltaic power production with agriculture in the same plot of land, have the potential to reduce land competition, reduce crop irrigation, and increase solar panel efficiency. To optimize agrivoltaic systems for crop growth, energy pathways must be characterized. While the solar panels shade the crops, they also emit longwave radiation and partially block the ground from downwelling longwave radiation. A deeper understanding of the spatial variation in incoming energy would enable controlled allocation of energy in the design of agrivoltaic systems. The model also demonstrates that longwave energy should not be neglected when considering a full energy balance on the soil under solar panels.

The coverage of center pivot irrigation systems used around the world has increased. One potential factor driving their adoption is improved water application efficiency relative to some other sprinkler or surface irrigation approaches. Center pivot irrigation systems may be further improved by dynamic elevation spray application (DESA). DESA systems adjust the nozzle height in response to plant growth and canopy heterogeneities. The DESA approach is relatively new and there is uncertainty in its economic viability and worthiness of further investigation. Thus, an economic scenario analysis was performed to explore the potential economic benefits of DESA based on permutations of irrigation pivot efficiency without DESA, water-saving potential of DESA, and water cost. The weighted costs and benefits of the height-adjusted approach for a set of water cost savings scenarios showed the net return price with the water cost savings per season. We show that DESA could have economic viability at current component costs and is worthy of further investigation and refinement.