Table 1. Peters 20–20–20 (Peters) and Osmocote 14–14–14 (Osmocote) treatment levels used in experiments to enhance growth of pawpaw (Asimina triloba) seedlings in containers.
| Treatment designations (Peterslevel)z | Amount applied [mg·L-1 (ppm)] | Treatment designations (Osmocotelevel)y | Amount applied (kg·m-3) |
|---|
| Expt. 1. Slow-release and weekly liquid-feed fertilizer application |
| Control | 0 | Control | 0.00x |
| Medium | 250 | Low | 0.13 |
| High | 500 | Medium | 0.26 |
| | High | 0.81 |
| Expt. 2. Slow-release fertilizer application only |
| | Control | 0.00 |
| | A | 0.81 |
| | B | 2.22 |
| | C | 4.43 |
| | D | 8.86 |
| | E | 17.7 |
Table 2. Leaf number and plant height of pawpaw (Asimina triloba) seedlings grown in a greenhouse with three levels of soluble fertilizer [Peters 20–20–20 (Peters)] and four levels of slow-release fertilizer [Osmocote 14–14–14 (Osmocote)].
Fertilizer Leaves Plant ht (cm)
Osmocotez
[mg·L-1 (ppm)] (no.) Controlz Low Medium High Response
Petersz
250 7.7 16.7 15.3 16.9 19.1 Q**
500 8.3 18.7 15.4 18.7 22.3 Q**
Response L** L** NS L** L**
Osmocote
Control 6.9 13.6y 14.0 16.6 18.6 Q**
Control 7.0
Low 6.8
Medium 8.1
High 8.8
Response L**
Peters × Osmocote NS **
Block NS **
ments, pawpaw seed was harvested from open-pollinated half-sib trees at the Keedysville, Md., orchard at the Western Maryland Research and Education Center. Seed was stratified at 5 °C (41 °F) for 3 months and was sown to a 3-cm (1.2-inch) depth in moist Pro-Mix BX potting substrate in 5 × 6.4 × 25.4-cm (2 × 2.5 × 10-inch) Roottrainers (Hummert Intl., Earth City, Mo.) with a volume of 740 cm³ (45 inch³). The initial electrical conductivity (EC) of Pro-Mix BX substrate was determined to be 1.02 dS·m⁻¹ and the nitrate (NO₃)⁻ concentration at 18 mg·L⁻¹ by the University of Kentucky Division of Regulatory Services (Lexington). Seedlings were grown in a white-washed glass greenhouse under a 16-h photoperiod supplemented by high-pressure sodium lights. At noon on a representative sunny day on 27 Apr. 2000, photosynthetic photon flux (PPF) was measured at 1200 μmol·m⁻²·s⁻¹ at canopy level using a LI-185B photometer with a Q7072 quantum sensor (LI-COR, Inc., Lincoln, Nebr.) with the supplemental lights on.
EXPERIMENT 1. SLOW-RELEASE AND WEEKLY LIQUID-FEED FERTILIZER APPLICATION. A greenhouse experiment was conducted to examine early growth and development of container-grown pawpaw seedlings with both slow-release and weekly liquid-feed fertilizer applications. A split plot experimental design was used with main plots of three levels of liquid-feed fertilizer of 0 (control), 250, or 500 mg·L-1 Peters 20–20–20 (Peters) water-soluble fertilizer plus soluble trace elements (Scotts Co., Marysville, Ohio) that were applied once each week and subplot treatments at four levels of Osmocote 14–14–14 (Osmocote) 3-to 4-month release product (Scotts
Table 3. Growth characteristics of pawpaw (Asimina triloba) seedlings grown in a greenhouse with three levels of soluble fertilizer [Peters 20–20–20 (Peters)] and four levels of slow-release fertilizer [Osmocote 14–14–14 (Osmocote)].
| Osmocotez |
| Petersy | Control | Low | Medium | High | Response | Control | Low | Medium | High | Response |
|---|
| [mg · L-1 (ppm)] | Root dry wt (g) | Shoot dry wt (g) |
| Control | 1.01x | 0.99 | 1.25 | 1.46 | Q** | 0.56 | 0.54 | 0.85 | 1.31 | Q** |
| 250 | 1.06 | 1.20 | 1.44 | 1.42 | Q** | 0.89 | 0.84 | 1.05 | 1.71 | Q** |
| 500 | 1.25 | 1.05 | 1.61 | 1.56 | Q** | 1.24 | 0.94 | 1.76 | 2.31 | Q** |
| Response | L* | NS | L** | NS | | L** | L** | L** | L** | |
| Peters × Osmocote | | | ** | | | | | ** | | |
| Block | | | ** | | | | | ** | | |