Leaching fraction-based irrigation schedule, coir-amended pine bark improve sustainability of H. paniculata ‘Jane’ production

Authors: FESSLER, L - University Of Tennessee; Owen Jr, James - Jim; WRIGHT, W - University Of Tennessee; XIAOCUN, S - University Of Tennessee; KRAUSS, C - University Of Tennessee; Altland, James; FULCHER, AMY - University Of Tennessee

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: In the United States (U.S.), nursery producers typically aim to irrigate to a depth of approximately 19 to 25 mm of water daily. This can total up to 180 cubic meters of water applied per hectare every day. With over 30,000 irrigated horticultural operations in the U.S., this adds up to significant water usage. Leaching fraction-based irrigation (LF; ratio of drainage water to water applied on a container basis) has the potential to significantly reduce water use and leachate during nursery container production. Incorporation of LF-based irrigation reduced water use by up to 60% and reduced container effluent by up to 96% compared to the grower’s standard of irrigating two hours every other day, demonstrating the potential that LF-based irrigation to improve irrigation efficiency. Substrate components can be strategically selected to maximize water holding capacity. Traditional pine bark substrate has relatively low water holding capacity. Fibrous substrate components, such as coconut coir, have a much greater water holding capacity. The addition of just 20% (by vol.) of coir added to pine increased water retention from 39% to 44% while addition of 65% coir by volume, to pine bark increased water retention to 59%. The objective of this research was to determine the effect of the grower’s standard irrigation practice versus LF-based irrigation scheduling and the addition of coconut coir amendment to pine bark-based substrate on water use, plant growth, and crop quality. Coir-amended substrates under both irrigation regimes had greater amount of maximum water retention and retained more water throughout the day. The LF-based irrigation zones used 74% less water per irrigation event on average than the standard irrigation zones, which is paralleled in irrigation run time. Cumulatively, the LF-based zones used 47% less water on average across the two seasons than the standard irrigation zones. This translates to average savings of over 10,000 L per zone or more than 1.7 million L per hectare per season, and reduced fuel expense and extended pump life. LF-based irrigation reduced leachate volume by 82%, compared to standard irrigation. These results indicate that the LF-based irrigation system can reduce irrigation and related inputs while maintaining acceptable growth and quality and that coir can be a beneficial substrate amendment.

Technical Abstract: Two irrigation systems, standard and leaching fraction-based, and two substrates, 100% pine bark and 35% coconut coir/65% pine bark, were used in the production of Little Lime® hydrangeas (Hydrangea paniculata ‘Jane’). The purpose of this study was to determine the effect of these treatments on total water use, irrigation efficiency, substrate moisture, growth index, and plant quality. The standard irrigation system simulated the grower’s normal practice operating for two hours every other day, applying 33 mm of water per irrigation event. The LF-based irrigation system aimed to maintain a 15% LF by using real-time leachate and irrigation volumes to calculate the irrigation run time each day. Growth index measurements were taken at the beginning and end of each season. Plant quality ratings were taken at the end of the 2019 season. Leachate and irrigation volume, volumetric water content (VWC), and water use were recorded daily throughout the season. Increase in growth index was greater in zones with coir than without coir (p = 0.0354) and increase in growth index was also greater in leaching-fraction based irrigation zones than standard irrigation zones (p = 0.0018). Plant quality did not differ among the four zones (p > 0.05). LF-based irrigation reduced LF and leachate volume by 40% and 82%, respectively, compared to standard irrigation (p = 0.0111 and p = 0.0005, respectively). Both maximum and minimum daily VWC were greater in the LF-based zone with coir than the standard zone without coir (p < 0.0001). Cumulative water use was reduced by nearly 50% in LF-based zones compared to standard irrigation zones (p < 0.0001), yet there was no negative impact on growth index or plant quality. These results indicate that the LF-based irrigation system can reduce irrigation and related inputs while maintaining acceptable growth and quality and that coir can be a beneficial substrate amendment.