Recycled Paper as a Growth Substrate for Container Spirea Production

Abstract

Spiraea japonica L. f. `Froebelii' were grown in 3.8-L containers filled with substrates consisting of recycled paper (RP) and pine bark at rates of 0%, 25%, 50%, 75%, or 100% (by volume) RP. Fertilizer treatments included 100% of the recommended rate of N as controlled release (CRF) or liquid fertilizer (LF) or both. The same amounts of N (as NO3--N and NH4+-N), P and K were supplied with each fertilizer treatment. Plants were irrigated in Fall 1996 based on substrate water-holding capacity and to achieve a 25% to 50% leaching fraction. In Spring 1997 regardless of substrate water holding capacity, plants were irrigated weekly initially, then twice weekly later in the study when plants were larger. Fertilizer treatment did not affect plant size, but plant diameter and shoot and root dry weight decreased as substrate RP concentration increased in Fall 1996. All plant size parameters measured decreased as substrate RP concentration increased regardless of fertilizer treatment in Spring 1997. In Fall 1996, shoot and root N concentration increased as CRF decreased (and LF increased), but substrate RP concentration did not affect shoot or root N concentration. In Spring 1997, shoot and root N concentration generally decreased as substrate RP concentration increased with 50% CRF, 50% LF, or 100% LF. Leachate NO3--N, NH4+-N and total N generally increased as CRF decreased but decreased as substrate RP concentration increased in both years. Substrate volume and percentage of air space decreased, but bulk density increased, as RP concentration increased. Although N leaching decreased as substrate RP concentration increased in both years, reasonable plant growth occurred only in those substrates containing ≤50% RP.