Mineral nutrient management strategies in containerized crop production are based on the “Sprengel-Liebig law of the minimum” (Epstein and Bloom, 2005) as noted by Lea-Cox and Ristvey (2003). Thus, excessive mineral nutrients are supplied to ensure plant growth is not restricted. The negative impacts (i.e., leaching and runoff) of this strategy are more pronounced in containerized crop production where nutrient uptake efficiencies are low because of the relatively inert substrates used as growing medium. This management strategy needs to be reconsidered as a result of economic and environmental concerns surrounding current production practices. Phosphorus losses are being investigated because P leaching or runoff can contribute to eutrophication, loss of aquatic biota, and hypoxia (Brady and Weil, 1999). The U.S. Environmental Protection Agency (USEPA) has proposed water quality criteria for maximum total P concentration to be 0.025 mg·L−1 or less within lakes or reservoirs (USEPA, 1986). Substrate solution P concentrations of 5 to 10 mg·L−1 are recommended currently by Best Management Practices (BMPs) (Yeager et al., 1997). These rates exceed the USEPA water quality criteria by 200- to 400-fold. Under current BMP recommendations, P uptake efficiency (PUE) ranges from 34% to 45% (Lea-Cox and Ristvey, 2003; Warren et al., 1995). Therefore, 55% or greater of applied P is not used by the plant in containerized production. Nursery management practices and infrastructure need to be adjusted to increase nutrient uptake efficiency and reduce nutrient loss. Warren and Bilderback (2005) reported irrigation management and nutrient uptake efficiency are directly interrelated. Unlike N, P leachate losses were unaffected by P application rate, but were affected by leaching fraction (LF) and P source. Tyler et al. (1996) decreased effluent P content by 58% when growing Skogholm cotoneaster (Cotoneaster dammeri Schnied. ‘Skogholm’) in a pine bark substrate with a low (0.0 to 0.2) versus high (0.4 to 0.6) LF.
Use of controlled-release fertilizers (CRFs) has increased mineral nutrient use efficiency by supplying nutrients corresponding with plant demand and minimizing pathways of losses (e.g., microbial transformation, soil fixation, and leaching), thus decreasing environmental impact (Shaviv and Mikkelsen, 1993). Warren et al. (1995) reported resin-coated CRF P resulted in the highest PUE (43%) by maintaining a low, constant rate of P loss at ≈1 mg·d−1 when Sunglow azalea [Rhododendron L. ‘Sunglow’ (Carla hybrid)] was grown in 3.8-L containers with a pine bark substrate. Lea-Cox and Ristvey (2003) suggested containerized P application be reduced 80%, thus making the optimal substrate solution P concentration 2 mg·L−1 or less and increasing PUE to 75% when adequate N was applied. This decrease in substrate solution P concentration has been reported not to affect plant growth (Lea-Cox and Ristvey, 2003). Implementing these suggested P reductions still result in P concentrations that remain 40- to 80-fold greater than USEPA criteria for public surface waters.
Current BMP recommendations are based, in part, on research conducted by Yeager and Wright (1982) who reported a 23% (1 g) increase in top dry weight Helleri holly (Ilex crenata Thunb. ‘Helleri’) when substrate solution P was increased from 0 to 10 mg·L−1. They also reported that root dry weight of Helleri holly was unaffected by P concentration. In contrast, Groves et al. (1998b) reported that current BMP substrate solution P recommendations could not be maintained when irrigating 3.8-L containerized Skogholm cotoneaster with 800 mL·d−1; however, top and root dry weight (Groves et al., 1998a) were maximized at 800 mL·d−1 although observed substrate solution P concentrations values fell to as low as 1.8 and 0.1 mg·L−1 P at 60 and 114 d after initiation of the experiment, respectively.
Another approach to reduce P losses and increase PUE is to modify the container substrate. Williams and Nelson (1997) investigated various clays (palygorskite and arcillite) and brick chips as precharged sources of P in peat:perlite substrates. The palygorskite clay absorbed 77% more P than the other materials. In a subsequent study, P leachate was reduced by amending the substrate with a precharged palygorskite (6% P leached) as compared with arcillite (18% P leached), brick chips (11% P leached), or a peat:perlite substrate (37% P leached) (Williams and Nelson, 2000). In a similar study, Zhang et al. (2002) used alumina-buffered P as a P source, which decreased effluent P60% or greater when compared with resin-coated P applied across four tree and shrub species grown in 7.6-L containers with a peat substrate. Therefore, our objective was to determine the effect of substrate amendment in combination with a 50% reduction in P application rate and leaching fraction on mineral nutrient and water efficiency and plant response when producing a containerized nursery crop in a pine bark-based substrate.
Borchardt, G. 1998 Smectites 675 728 Dixon J.B. & Weed S.B. Minerals in the soil environment 2nd Ed Book Series No. 1. Soil Sci. Soc. Amer Madison, WI
Chaves, M.M., Pereira, J.S., Maroco, J., Rodrigues, M.L., Ricardo, C.P.P., Osorio, M.L., Carvalho, I., Faria, T. & Pinheiro, C. 2002 How plants cope with water stress in the field? Photosynthesis and growth Ann. Bot. (Lond.) 89 907 916
Fonteno, W.C. & Bilderback, T.E. 1993 Impact of hydrogel on physical properties of coarse-structured horticultural substrates J. Amer. Soc. Hort. Sci. 118 217 222
Groves, K.M., Warren, S.L. & Bilderback, T.E. 1998a Irrigation volume, application, and controlled-release fertilizers: I. Effect on plant growth and mineral nutrient content in containerized plant production J. Environ. Hort. 16 176 181
Groves, K.M., Warren, S.L. & Bilderback, T.E. 1998b Irrigation volume, application, and controlled-release fertilizers: II. Effect on substrate solution nutrient concentration and water efficiency in containerized plant production J. Environ. Hort. 16 182 188
Havlin, J.L., Beaton, J.D., Tisdale, S.L. & Nelson, W.L. 1999 Soil fertility and fertilizers: An introduction to nutrient management 6th Ed Prentice Hall Upper Saddle River, NJ
Ku, C.S.M. & Hershey, D.R. 1992 Leachate electrical conductivity and growth of potted geranium with leaching fractions of 0 and 0.4 J. Amer. Soc. Hort. Sci. 117 893 897
Laiche A.J. Jr & Nash, V.E. 1990 Evaluation of composted rice hulls and a lightweight clay aggregate as components of container-plant growth media J. Environ. Hort. 8 14 18
Lea-Cox, J.D. & Ristvey, A.G. 2003 Why are nutrient uptake efficiencies so low in ornamental plant production? Proc. Southern Nursery Assoc. Res Conf., 48th Annu. Rpt 116 122
Milks, R.R., Fonteno, W.C. & Larson, R.A. 1989 Hydrology of horticultural substrates: I. Predicting physical properties of media in containers J. Amer. Soc. Hort. Sci. 114 53 56
Moll, W.F. & Goss, G.R. 1997 Mineral carriers for pesticides: Their characteristics and uses Standard Tech. Publ. 943. Amer. Soc. Testing and Materials West Conshohocken, PA
Murphy, J. & Riley, J.P. 1962 A modified single solution method for the determination of phosphate in natural waters Anal. Chim. Acta 27 31 36
Owen J.S. Jr 2006 Clay-amended soilless substrates: Increasing water and nutrient efficiency in containerized crop production North Carolina State Univ Raleigh, NC PhD Diss.
Shariatmadari, H. & Mermut, A.R. 1999 Magnesium- and silicon-induced phosphate desorption in smectite-, palygorskite-, and sepiolite-calcite systems Soil Sci. Soc. Amer. J. 63 1167 1173
Shaviv, A. & Mikkelsen, R.L. 1993 Controlled-release fertilizers to increase efficiency of nutrient use and minimize environmental degradation—A review Fert. Res. 35 1 12
Singer, A. 1998 Palygorskite and sepiolite group minerals 829 872 Dixon J.B. & Weed S.B. Minerals in the soil environment 2nd Ed Book Series No. 1. Soil Sci. Soc. Amer Madison, WI
Sonneveld, C., van den Ende, J. & van Dijk, P.A. 1974 Analysis of a growing media by means of a 1:1½ volume extract Commun. Soil Sci. Plant Anal. 5 183 202
Tyler, H.H., Warren, S.L. & Bilderback, T.E. 1996 Reduced leaching fractions improve irrigation use efficiency and nutrient efficacy J. Environ. Hort. 14 199 204
USEPA 1986 Quality criteria for water Office of Water Regulation and Standards, U.S. Environ. Protection Agency 440/5-86-001 Washington, DC
Warren, S.L. & Bilderback, T.E. 1992 Arcillite: Effect on chemical and physical properties of pine bark substrate and plant growth J. Environ. Hort. 10 63 69
Warren, S.L., Bilderback, T.E. & Tyler, H.H. 1995 Efficacy of three nitrogen and phosphorus sources in container grown azalea production J. Environ. Hort. 13 147 151
Williams, K.A. & Nelson, P.V. 1997 Using precharged zeolite as a source of potassium and phosphate in a soilless container medium during potted chrysanthemum production J. Amer. Soc. Hort. Sci. 122 703 708
Williams, K.A. & Nelson, P.V. 2000 Phosphate and potassium retention and release during chrysanthemum production from precharged materials: II. Calcined clay and brick chips J. Amer. Soc. Hort. Sci. 125 757 764
Yeager, T., Bilderback, T., Fare, D., Gilliam, C., Niemiera, A. & Tilt, K. 1997 Best management practices-guide for producing container-grown plants Southern Nursery Assoc Atlanta, GA
Yeager, T.H. & Wright, R.D. 1982 Phosphorus requirements of Ilex crenata Thunb. cv. Helleri grown in a pine bark medium J. Amer. Soc. Hort. Sci. 107 558 562
Zhang, Y., Kuhns, L., Lynch, J.P. & Brown, K.M. 2002 Application methods affects water application efficiency of spray stake irrigated containers J. Environ. Hort. 28 625 627