A brief review of slow-release fertilizer technology Slow-release nitrogen fertilizers can be separated into three broad categories. The first is “natural” organic fertilizer, with the N contained as a part of crop residue, animal waste, or other
Luz M. Reyes, Douglas C. Sanders, and Wayne G. Buhler
). Various types of slow-release fertilizers may extend the availability of nutrients, especially N, to the plant ( Maynard and Lorenz, 1979 ) and reduce N leaching losses from soil ( Wang and Alva, 1996 ). Research has been conducted with sulfur-coated urea
L. Carolina Medina, Jerry B. Sartain, and Thomas A. Obreza
Nutrient use efficiency, particularly for nitrogen (N) fertilizer, is still low despite significant improvements in crop production over the last few decades. Development of slow-release fertilizer (SRF) evolved as a potential way to enhance
Tim C. Knowles, Billy W. Hipp, and Mary Ann Hegemann
the slow-release N, P, and K formulations. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the Texas Agricultural Experiment Station. The cost of publishing this paper was defrayed in part by
William Terry Kelley
Despite some advantages, adoption of slow-release fertilizers in vegetables has been slow primarily due to cost. In crops fertilized with ground equipment, growers can make fewer trips through the field and assure fertilizer is present when conditions prevent application. With drip irrigation, some materials are difficult to inject, however, Nitamin is a new injectable liquid produced by Georgia Pacific. Thus, with plasticulture, growers can inject less frequently and potentially use lower rates. Granular and liquid formulations of slow-release fertilizer were tested on onions (Winter 2003–04), cabbage (Winter 2003–04) and pepper (Spring 2004) in Georgia. Combinations of traditional fertilizer with slow-release formulations and various rates of slow-release fertilizer alone were compared to a standard fertilizer program on these crops in separate experiments. The slow-release contains only N. So, other nutrients were held constant. Otherwise normal cultural practices were employed. Crops were harvested at maturity and data collected on yield and quality. In cabbage, with at least 50% of the standard N rate using the slow-release fertilizer, yields were comparable to the standard. Results on onions were similar with N rates of at least 75% of the standard for the liquid material; the granular formulation did not perform well. Split applications of slow-release fertilizer and combinations with standard fertilizer worked well for cabbage, but not for onions. Results on pepper, although inconclusive, indicated it was possible to get comparable yields at lower N rates with the slow-release material. Based on these results, lower N rates are possible on cabbage and onions with slow-release fertilizers which may make them economically feasible while providing application advantages to growers.
Bert T. Swanson, James B. Calkins, Daniel G. Krueger, and Theresa L. Stockdale
Media fertility is a critical factor in the successful production of container grown plants. Fertility treatments including fertigation and slow-release fertilizers (topdressed and incorporated) were compared. Fertility treatments were studied over a two-year period on a variety of deciduous and evergreen plant materials. Plant growth was quantified based on height, volume, branching, and quality. Soil fertility levels based on leachates were followed during the study. Nutrient release for incorporated fertilizers tested was variable although less so than when the same fertilizers were topdressed. Fertility treatment effects were species-dependent. Several incorporated, slow-release fertilizers, especially those high in nitrogen (Sierra 17-6-10, Sierra High N 24-4-6, Woodace Briquettes 23-2-0, Woodace 21-4-10), show promise for use in two-year container production systems.
Edward Bush, Jeff Kuehny, and Patricia Branch
Three slow-release fertilizer formulations (Osmocote 14–14–14, 18–6–12, and Nutricote 17–6–10) at three rates (1, 2, and 3 lb/yd3) were incorporated into 4 pine bark: 1 sand (by volume) media filling 1-gal nursery containers. Additional treatments included slow-release fertilizer formulations at 1 lb/yd3 fertigated with 100 ppm N 20–10–20 fertilizer. As fertilizer rates increased, vegetative height, width, and dry-weight accumulation generally increased for both pinched and no-pinch mum crops. Fertigated pinch and no-pinch mums were the largest plants with the greatest dry-weight accumulation for each fertilizer formulation. The high rate for all slow-release fertilizers produced the greatest vegetative growth for nonfertigated treatments. This research suggest that higher rates for incorporated slow-release fertilizers and/or fertigation are required to produce maximum vegetative growth.
Wendy Britton, E.J. Holcomb, and David J. Beattie
Four rates of two slow-release fertilizers were tested for optimum growth of five hosta cultivars: Hosta sieboldiana `Elegans', Hosta plantaginea `Aphrodite', Hosta `Jade Scepter', Hosta `Hadspen Blue', and Hosta `Francee'. Tissue-cultured hostas from 2.5-cm plugs were planted in 6-inch (15-cm) pots filled with a commercial soilless medium, and the slow-release fertilizer was dibbled into the medium at 0, 3, 6, or 12 g/pot. The plants were maintained for 4 months. Root and shoot fresh and dry weights were recorded at the end of the experiment. In addition, foliar nutrient analysis was conducted on `Aphrodite', `Francee', and `Jade Sceptor'. Overall, hostas grew best when the medium was amended with 3 g of either Osmocote 14N-6P-11.5K or Sierrablen 17N-6P-12K slow-release fertilizer.
Jong-Myung Choi and Paul V. Nelson
The structure of feather keratin protein was modified in attempts to develop a slow-release N fertilizer of 12 weeks duration or longer by steam hydrolysis to break disulfide bonds, enzymatic hydrolysis with Bacillus licheniformis (Weigmann) to break polypeptide bonds, and steam hydrolysis (autoclaving) to hasten mineralization followed by cross-linking of the protein by a formaldehyde reaction to control the increased rate of mineralization. Release of N in potting substrate within elution columns from ground, but otherwise untreated, raw feathers occurred mainly during the first 5 weeks with a much smaller release occurring from weeks 8 to 12. Steam hydrolysis resulted in an increase of N during the first 5 weeks and a decrease during weeks 8 to 11. Cumulative N release over 11 weeks increased from 12% in raw feathers to 52% for feathers steam hydrolyzed for 90 minutes. This favored an immediately available fertilizer but not a slow-release fertilizer. Microbial hydrolysis with B. licheniformis resulted in a modest reduction of N release during the first 5 weeks and a small increase during weeks 8 to 11. Both shifts, while not desirable for an immediately available fertilizer, enhanced the slow-release fertilizer potential of feathers but not sufficiently to result in a useful product. Steam hydrolyzed feathers cross-linked with quantities of formaldehyde equal to 5% and 10% of the feather weight released less N during the first 5 weeks, more during weeks 6 and 7, and less during weeks 9 to 12 compared to raw feathers. The first two shifts were favorable for a slow-release fertilizer while the third was not.
James B. Calkins and Bert T. Swanson
Media fertility, nutrient availability, and subsequently plant nutrition are critical factors that can be modified by growers to produce quality container-grown plants. The trend in container fertility has been toward incorporation of slow-release fertilizers; however, fertility release curves are variable and fertilizer longevity for many fertilizers is limited. Seventeen slow-release fertilizers were compared for longevity and plant performance over a 2-year production cycle using deciduous and evergreen plant materials. Plant growth was quantified based on height, volume, branching, dry weight, and quality. Soil fertility levels based on leachates were followed. Nutrient release for the incorporated fertilizers evaluated was variable. Fertility treatment effects were species-dependent. Several incorporated, slow-release fertilizers, especially those high in nitrogen and having extended release curves, including Nutricote 20–7–10, Scotts Experimental 24–6–10 and 26–6–11, Scotts Prokote Plus 20–3–10, Sierra 17–6–10, Sierra High N 24–4–6, Sierra Experimental 24–4–8, Woodace 21–4–10, Woodace 23–7–12, and Woodace Briquettes 23–2–0, show promise for use in 2-year container production systems.