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Title: Growth response, mineral nutrition, and water utilization of container grown woody ornamentals grown in biochar-amended pine bark

Author
item BASIRI, NASTARAN - University Of Tennessee
item WALKER, FORBES - University Of Tennessee
item FULCHER, AMY - University Of Tennessee
item Altland, James
item WRIGHT, WESLEY - University Of Tennessee

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2018
Publication Date: 3/1/2018
Citation: Basiri, N., Walker, F., Fulcher, A., Altland, J.E., Wright, W. 2018. Growth response, mineral nutrition, and water utilization of container grown woody ornamentals grown in biochar-amended pine bark. HortScience. 53(3):347-353. https://doi.org/10.21273/HORTSCI12643-17.
DOI: https://doi.org/10.21273/HORTSCI12643-17

Interpretive Summary: Greenhouse and nursery producers are facing increasing fertilizer costs and greater scrutiny toward nutrient use efficiency and retention. Developing management practices that make more efficient use of irrigation water is important for improving the sustainability of nursery crop production. Use of accurate, site-specific plant water use systems in support of precise application of water could improve water and nutrient use efficiency and proactively address nutrient and agrichemicals in container effluent by reducing runoff. The objective of this research was to provide a preliminary assessment of the effect of biochar amendment to a pine bark–based container substrate on water and nutrient leaching for a low and high water use woody species in combination with a precision irrigation system. A precision irrigation system in combination with biochar, a readily available, low cost substrate amendment, increased water holding capacity, reduced the water requirement for hydrangea and reduced leachate volume in both hydrangea and boxwood. Biochar application rate influenced irrigation frequency, which likely affected plant biomass for hydrangea, but the boxwood final dry weight was unaffected by biochar rate. The total amount of water leached and nutrients lost from hydrangea containers were lower in biochar amendment pots due to improvements in the water holding capacity of the substrate and fewer irrigation events in the biochar treatments. In the future, development of substrate water potential-based irrigation logic or schedules based on cues from the crop’s physiological status could help identify set points for on demand irrigation that exploit the water buffering capacity without exceeding it during irrigation cycles.

Technical Abstract: Container-grown nursery crops generally require daily irrigation applications and potentially more frequent applications during the hottest part of the growing season. Developing management practices that make more efficient use of irrigation water is important for improving the sustainability of nursery crop production. Biochar, a byproduct of pyrolysis, can potentially increase the water-holding capacity and reduce water and nutrient leaching. In addition, the development of sensor-based irrigation technologies has made monitoring substrate moisture a practical tool for irrigation management in the nursery industry. The objective of this research was to determine the effect of switchgrass biochar on water and nutrient-holding capacity and release in container substrates of Buxus sempervirens L. 3 Buxus microphylla (‘Green Velvet’ boxwood) and Hydrangea paniculata (Pinky Winky hardy hydrangea). Containers were filled with pine bark and amended with 0%, 10%, or 25% volume of biochar. Plants were irrigated when the volumetric water content (VWC) reached the water-buffering capacity set point of 0.25 cm3·cmL3. The sensor-based irrigation in combination with the low cost biochar substrate amendment increased substrate water-holding capacity and reduced irrigation requirements for the production of hydrangea, a high water use plant. Biochar application rate influenced irrigation frequency, which likely affected plant biomass for hydrangea, but boxwood dry weight was unaffected by biochar rate. Total irrigation applied was decreased by 32% in 10% biochar treatment without reducing hydrangea dry weight. However, in the 25% biochar treatment, total irrigation applied was reduced by 72%, whereas dry weight decreased by 50%. Biochar application reduced leaching volume and leaching fraction in both plants. Leachate analysis over the course of the 8-week experiment showed that the average mass of phosphate (PO4), potassium (K), and total carbon was greater in the leachate from containers that received 25% biochar compared with those receiving 0% or 10% biochar for both plant species. For hydrangea, mass of total nitrogen (TN) and nitrate (NO3) in leachate was not significantly affected by increasing the biochar rate. However, for boxwood, the mass of NO3 and TN was greater in the 25% biochar treatment leachate, whereas the mass of ammonium (NH4) was unaffected. In hydrangea, total nutrients lost from the containers was lower in biochar-amended containers (both 10% and 25% biochar) because of receiving a lower total volume of water. Amendment with biochar also affected concentration of phosphorus (P) and K, with the highest concentration in both leaf tissue and substrate from the 25% biochar application rate.