Clay Amended Soilless Substrates: Increasing Water and Nutrient Efficiency in Containerized Crop Production

Current management practices in containerized crop production maximize plant growth by supplying adequate or excess nutrient and water inputs. In the United States, nursery production input use efficiency remains ≤ 50%, in part, because of the inert softwood bark used as a primary component of soilless substrate. One technique to increase input use efficiency would be to engineer a substrate that increases nutrient and water buffering capacity of the substrate. Clay may be such a component. Clay has been used in the past to generically describe an inorganic mineral aggregate to amend a peat- or bark-based soilless substrate that increased water and nutrient buffering capacity. Industrial mineral aggregates with various chemical composition, aggregate size, mineralogy, and temperature pretreatment have been used effectively as chemical absorbents, fertilizer carriers, or barrier clays to contain heavy metals. Experiments herein were conducted to determine which physical and chemical attributes of industrial mineral aggregate could increase input use efficiency in containerized crop production and at what amendment rate plant growth and water and nutrient use efficiency are maximized. Field experiments were conducted using Cotoneaster dammeri C.K. Schneid. "Skogholm" as an indicator plant for growth, net photosynthesis (P[subscript n]), stomatal conductance (g[subscript s]), and mineral nutrient content. Plant were potted into 14 L containers in a pine bark based (PB) substrate with known physical properties and grown for approximately 120 days in 2002, 2003, and 2004 on outdoor facilities in Raleigh, NC that allowed for collection of effluent and influent, which was used to calculate a water budget. In the laboratory, effluent NO₃-N, NH₄-N and dissolved reactive P (DRP) were quantified to determine effluent daily concentration and cumulative content which allowed for calculation of nutrient budgets. In 2002, a bentonite palygorskite industrial amendment with contrasting particle size and temperature pretreatment was evaluated for its effect on growth, and water and nutrient use efficiency. Substrate amended with a low volatile material (LVM) amended substrate leached 35% less dissolved reactive P (DRP) than the regular volatile aggregate amended substrate. In addition, a 0.25 to 0.85 mm aggregate amended substrate required 11 L less water applied per container when compared to 0.85 to 4.75 mm aggregate amended substrate. In 2003, 0% to 20% (by vol.) rate of the 0.25 to 0.85 mm LVM palygorskite bentonite mineral aggregate were compared. Plant growth and P[subscript n] increased curvilinearly and linearly with the maximum occurring at 12% and 11%, respectively. Container capacity and available water (AW) increased linearly with increasing amendment rate, whereas, unavailable water and air space decreased linearly with increasing rate of mineral aggregate. Water use efficiency of productivity and g[subscript s] was maximized at 11% clay amendment rate. Plant elemental nutrient content of P,…