IRRIGATION VOLUME AND FERTILIZER RATE INFLUENCE GROWTH AND LEACHING FRACTION FROM CONTAINER-GROWN GARDENIA JASMINOIDES^©

Over irrigating is a common problem in container-plant production because of poor uniformity and efficiency of irrigation systems (Fare et al., 1992) and the preference of growers to deal with the consequences of applying too much water vs. too little (Yeager et al., 2010). Along with this, many growers apply large amounts of fertilizer out of concern that lower fertilizer applications could negatively impact growth (Owen et al., 2008; Tyler et al., 1996). The combination often excessive irrigation and high fertilizer rates leads to significant leaching of fertilizers, which has a negative environmental impact as the leachate enters local ecosystems (Lea-Cox and Ross, 2001). Many states now have laws and regulations regarding nutrient runoff from nurseries necessitating that growers better manage the irrigation and fertilization applications (Beeson et al., 2004).
Growers have already adopted more effective irrigation practices including cyclic irrigation, drip irrigation, and grouping similar sized containers (Yeager et al., 2010; Tyler et al., 1996). Better management practices for fertilization and nutrient leaching have also been adopted, including using controlled-release fertilizers that last throughout the production period and monitoring substrate nutrient levels (Yeager et al., 2010). However, to irrigate and fertilize more efficiently more research is needed examining how plant growth is affected by reduced irrigation and fertilization.
It seems likely that fertilizer inputs can be reduced if irrigation is applied more efficiently because more efficient irrigation reduces leaching. With reduced leaching, more fertilizer remains in the container and available to the plant. Our objective was to determine how irrigation volume and fertilizer rate affect growth and leaching fraction of Gardenia jasminoides. Our hypothesis is that more efficient irrigation can reduce the fertilizer requirements without impacting plant growth, while reducing the leaching fraction.