Nursery Crop Growth Response to Municipal Biosolids: Species Salt and Xeric Adaptation a Key Factor?

ABSTRACT

Growth responses of potted ornamental crops to municipal biosolids in the semiarid southwestern USA are not adequately known. In 10- to 11-wk greenhouse pot studies, we evaluated the effects of dried biosolids-amended growing media on four ornamental crop species: Garden chrysanthemum (Dendranthema Xgrandiflorum ‘Megan’), butterfly bush (Buddleia davidii ‘Nanho Blue’), Japanese honeysuckle (Lonicera japonica ‘Purpurea’), and blanket flower (Gaillardia Xgrandiflora ‘Goblin’). The biosolids were composted without bulking agents (100% sewage sludge) and incorporated into growing media at rates ranging from 0 to 593 kg m⁻³, or 0 to 72% by volume. Biosolids increased substrate pH from 5.8 to 7.2 and electrical conductivity (EC) from 2.6 to 47.3 dS m⁻¹. Any addition of biosolids (≥30 kg m⁻³) reduced total plant dry matter (DM) of chrysanthemum. Conversely, shoot DM of blanket flower and butterfly bush increased by four- to five-fold at biosolids rates of 59 to 148 kg m⁻³ (7 to 18% by volume) with corresponding increases in shoot N and P concentrations. Biosolids rates higher than 148 kg m⁻³ reduced top growth of the latter two species and of Japanese honeysuckle. For all species, growth reductions with excessive biosolids rates likely resulted from osmotic stress and specific NH₄ toxicity. However, based on the substantial growth stimulations at moderate biosolids rates, xeric and salt-adapted species, such as blanket flower and butterfly bush, may be ideally suited for expanding the use of highly saline biosolids at semiarid nursery production sites.

ACKNOWLEDGMENTS

We thank Eric Lopez and Doug Paczynski of the City of Las Cruces Utilities Division for providing the biosolids used in the study and in supplying information on the Jacob Hands Wastewater Treatment Plant. We also thank Jeff Harvey of Sunland Nursery, Inc. for providing plant materials and greenhouse growing space in the completion of the nursery crops study. The following undergraduate students of the course entitled “Ornamental Plant Production” provided technical support to the project: Dominick Carmack, Jared Chase, Amos Corrales, Jazmin Garcia, Edward Goodman, Alida Hunt, Mike Kilroy, Alejandrina Lopez, John Melvin, Kristen Ronning, and Vickie Vallee.

FUNDING

This study was supported, in part, by the New Mexico Agricultural Experiment Station.