On-site Evaluation of Irrigation Management Practices in Container Nurseries in Alabama and the Effect of Leaching Fraction-based Irrigation on Fertilizer Longevity.

Abstract

Container production of ornamental plants is an important part of the green industry in Alabama. Container nursery growers rely on near daily irrigation and applications of fertilizers to produce marketable plants. Cultural practices lead to leaching of applied nutrients that could lead to eutrophication of surrounding watersheds, so efficient irrigation management is therefore an important part of reducing environmental harm as well as the loss of inputs from production systems. An on-site analysis of overhead irrigation systems was conducted at nine container nurseries in Alabama. Results of this study suggest that improving distribution uniformity (DU) is the most practical area to begin when improving irrigation practices in Alabama. The uniformity of plant size across all nurseries despite differing leaching fraction (LF) suggested that growers may be able to utilize lower volumes of irrigation to produce plants of salable size. A study was conducted to determine the effects of LF and control-release fertilizer (CRF) rates on plant growth and fertilizer longevity in container nursery conditions. A target LF of 5%, 25% or 35%, and a CRF rate of 50, 70, or 90g per container were assigned irrigation plots arranged in a completely randomized design with three replications, a total of 27 plots. Each plot contained four 2.91gallon (11 L) black plastic containers planted with a dwarf Japanese holly (Ilex crenata ‘Compacta’) liner. Plant growth index, percent fertilizer loss, and pour-throughs pH and electrical conductivity (EC) were recorded. LF and CRF rate had no effect on percent fertilizer loss and plant growth index and there were no interactions between LF and CRF rate. There were differences in pour-through pH among the LF treatments and differences in pour-through EC among the fertilizer rates, however, no significant trends for either. The results were likely inconclusive due to the containers overheating, as extreme heat stress on plant health compromised size index data, and heating of the media may have influenced the rate of fertilizer release. A study was then conducted to evaluate the effects of LF on the longevity of POLYON® CRF and leachate nutrient content in a greenhouse environment under six target LF treatments: 0.05, 0.15, 0.25, 0.35, 0.45, and 0.55. Results of this ten-week study indicate that reducing the LF did not influence the longevity of POLYON® CRF in a pine bark substrate, but that a lower LF may be useful in reducing nutrient runoff into the environment. The total amount of nutrients leached from the container was greater at higher LFs. The amount of dissolved nutrients left in the substrate decreased as the LF treatments increased, suggesting that at lower LFs, more nutrients may be available for plant uptake and that nursery producers could potentially reduce fertilizer rates when irrigating to lower target LFs.