BY CALVIN CHONG AND GLEN LUMIS, DEPARTMENT OF PLANT AGRICULTURE, UNIVERSITY OF GUELPH, PRINCIPAL RESEARCHERS; AND ZAHIDUL ALAM AND JENNIFER LLEWELLYN, AFFILIATED RESEARCHERS
Forsythia growth in response to different controlled-release fertilizer (CRF) rates (Nutricote 18-6-8 100-d at 2, 4, and 6 kg.m-3) and placements (incorporation and topdress) under three irrigation regimes [drip-irrigated low (25 per cent) leaching fraction (DrLoLF), hand-sprinkled low (25 per cent) leaching fraction (HsLoLF), and hand-sprinkled high (50 per cent) leaching fraction (HsHiLF)] were studied to determine the best fertilizer-irrigation regime which minimizes fertilizer and water usage and NO3-N runoff from container culture. In a parallel study, forsythia growth was also examined including dibbled fertilizer placement with same CRF rates but with single or split doses and under drip irrigation only. The experiment was carried out at the University of Guelph research facilities and hand-sprinkling was used as a simulation of overhead irrigation.
Fertilizer placement
Fertilizer placement had a significant effect on plant growth and NO3-N concentration in the leachate. Incorporation was better than topdress, however, dibble fertilizer was superior to both incorporation and topdress, in this order. Maximum growth of forsythia occurred at a rate of 4.7 kg.m-3 (calculated) with dibbling, with a savings of 22 per cent fertilizer whereas with incorporation and topdress, maximum growths were not achieved even at 6 kg.m-3 (maximum rate tested). This means that about 22 per cent of the CRF can be saved through dibbling, compared to incorporation and topdress application, without sacrificing plant growth. However, single application of the entire amount of CRF, dibbled, at time of potting may be toxic to plug-rooted liners with exposed roots but not to potted liners.
Irrigation methods
Irrigation system type and CRF placement greatly influenced plant growth and NO3-N leaching depending on irrigation volume and leaching fraction (LF). When CRFs were topdressed, overhead irrigation proved to be essential for better utilization (wetting) of the applied fertilizer, resulting in good growth.
When CRFs were topdressed and placed under drip irrigated methods, the CRF was under-utilized and reduced plant growth resulted. Drip irrigation proved to be useful when CRFs were dibbled or incorporated, which resulted in greater top dry weight, reduced LF, and reduced NO3-N leaching. Despite fertilizer placement method, overhead irrigated plants recovered more quickly after potting than drip irrigated plants but overhead irrigated plants with high leaching fraction had lower top dry weights.
Leachate results
NO3-N concentration in leachate varied from as low as two per cent, to as high as 34 per cent, depending on the rate of CRF, CRF placement and irrigation method. As was expected, topdress application of CRF under drip irrigation resulted in the lowest NO3-N concentration in the leachate. Incorporation of CRF under overhead irrigation with high LF (50 per cent) resulted in the highest concentration of NO3-N in the leachate. Under drip irrigation, at a rate of 6 kg/m3 and 22 × 22 spacing, NO3-N leachings were 76, 85 and 22 kg/ha respectively for dibbled, incorporated and topdressed CRF. With similar CRF rate and spacing, NO3-N leachings were 116 and 152 kg/ha respectively for incorporated and topdressed CRF when plants were overhead (hand-sprinkled) irrigated with high LF. Split application of CRF greatly reduced leachate concentration of NO3-N compared to a single application. CRFs were mostly under-utilized with split application (second application is a topdress) under drip irrigation and often resulted in reduced plant growth.
Management strategies
A survey of irrigation water use was conducted at several commercial nurseries in Ontario. Data on irrigation cycle length, total water applied (based on sprinkler output) interception efficiency (IE) and leaching fraction (LF) was carried out to create a database on water use and efficiency of overhead irrigation systems in container nursery production.
LF and IE varied greatly from one commercial nursery to another (1-53 per cent and 25-41 per cent). Depending on canopy growth and size, pot spacing was compressed and LF and IE were measured again. If LF was still high (>25 per cent), growers were asked to reduce the irrigation cycle length. By making these small shifts in management practices, we were able to demonstrate water savings and improved IE over the growing season. The results of this survey have already fostered improvements in irrigation management at individual commercial nurseries.
It should be noted that two factors impacted on the research reported here. Sadly, Professor Calvin Chong, the principal researcher, became seriously ill in November of 2006 and remains on long term disability. Also, Professor Glen Lumis retired in May of 2006. Dr. Zahidul Alam, post doctoral fellow, coordinated and carried out much of the research, especially in year two. Jennifer Llewellyn, OMAFRA Nursery Crops Specialist, gave significant contributions towards planning and execution of the project, especially in year two.
To download an in-depth report in PowerPoint format, including detailed data, please visit www.horttrades.com/leachate.
Acknowledgements: This research was supported through the Canada-Ontario Research and Development Program (CORD). Funding partners include the Ontario Horticultural Trades Foundation, Agriculture and Agri-Food Canada, the Ontario Ministry of Agriculture, Food and Rural Affairs and the Agricultural Adaptation Council.