Influence of Organic Fertilizer Sources and Application Rates on Onion Production in Georgia, USA

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Hanna Ibiapina de Jesus Department of Horticulture, University of Georgia, 1111 Miller Plant Sciences, Athens, GA 30602, USA

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Andre Luiz Biscaia Ribeiro da Silva Department of Horticulture, Auburn University, 124 Funchess Hall, Auburn, AL 36849, USA

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Bhabesh Dutta Department of Plant Pathology, University of Georgia, 2360 Rainwater Road, Tifton, GA 31793, USA

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Kate Cassity-Duffey Department of Horticulture, University of Georgia, 1111 Miller Plant Sciences, Athens, GA 30602, USA

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Timothy Coolong Department of Horticulture, University of Georgia, 1111 Miller Plant Sciences, Athens, GA 30602, USA

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Abstract

A range of organic fertilizers are available for vegetable crops; however, there is a lack of information regarding the performance and rates of organic fertilizers commonly used in the production of Vidalia onion (Allium cepa). Two commercial organic fertilizers, a mixed source organic fertilizer [MIX (10N–0.9P–6.6K)] and a pelleted poultry litter [PPL (5N–1.8P–2.5K)], were evaluated in two soil types at application rates of 0, 100, 150, 200, 250, and 300 lb/acre nitrogen (N) to determine their impact in the production of Vidalia onions in Georgia, USA, with the objective of determining an optimal fertilizer source and application rate. Field trials were conducted in the 2019–20 and 2020–21 growing seasons in Watkinsville, GA, USA (Cecil series sandy clay loam soil) and Tifton, GA, USA (Tifton series loamy sand soil) on certified organic land. There were significant interactions among location, year, and fertilizer application rate for total marketable yield. In Watkinsville, total marketable yields of onions at different N rates ranged between 1320 and 4565 lb/acre in 2019–20, and between 9951 and 28,749 lb/acre in 2020–21. In Tifton, total marketable yields ranged from 3776 to 9264 lb/acre and 7094 to 14,066 lb/acre in the 2019–20 and 2020–21 seasons, respectively. Aboveground onion N accumulation at harvest was affected by an interaction among location, study year, and fertilizer rate. The largest plant N accumulation was in Watkinsville in 2020–21, ranging from 26 to 50.8 lb/acre N in the 0- and 300-lb/acre N treatments, respectively. In 2020, there were no differences in soil inorganic N at harvest between plots receiving the MIX (9 lb/acre N) or PPL (9.8 lb/acre N) in either location. In 2021, soil inorganic N was greater in plots receiving the MIX fertilizer (14.8 lb/acre N) compared with the PPL fertilizer (11.2 lb/acre N). Yields increased linearly with additional fertilizer; therefore, an optimal application rate for organic fertilizers was not determined.

Vidalia sweet onions (Allium cepa) are an important crop for southeastern Georgia, USA. In 2021, there were more than 11,000 acres of onions grown with a farm gate value of $168 million, making them one of the top vegetable crops for the state (University of Georgia 2022a). Organic onion production represents roughly 7% of the total acreage of Vidalia onions, with ∼793 acres of certified organic onion production reported by the US Department of Agriculture (USDA 2019). This represents a value of more than $12 million, which continues to increase annually.

Recommendations for nitrogen (N) applications for conventional onion production in the Coastal Plain region of Georgia, USA, suggest the application of 100 to 130 lb/acre N (Coolong and Boyhan 2017). However, growers in the region have been able to achieve similar yields with reduced fertilizer N rates through the careful timing of applications (Tyson C, personal communication). Research conducted in Georgia during in the 2020–21 onion season reported average marketable yields of 38,700 lb/acre for conventionally grown onions with the application of 92 lb/acre N, indicating the potential for reducing N fertilizer rates while maintaining yields (Tyson et al. 2023). In organic vegetable production systems, the efficient application of fertilizers can be challenging because there is a lack of knowledge regarding the rate of N mineralization and plant availability of other nutrients in many organic products. The release of mineral N from organic fertilizers varies depending on the source material, soil characteristics, and environmental conditions (Calderón et al. 2005; Cassity-Duffey et al. 2018; Reganold and Wachter 2016). Failure to coordinate timing of N release from organic fertilizers with plant demand has the potential to reduce yields (Berry et al. 2002). Consequently, organic onion growers often over-apply fertilizers to ensure adequate levels of plant-available N during the entire growing season (Boyhan et al. 2007). However, over application of fertilizers can negatively impact flavor and storage quality of onion, particularly if there are high levels of available N at harvest (Coolong and Randle 2003; Díaz-Pérez et al. 2003; Gitaitis et al. 2008).

Organic onion growers in Georgia, USA typically use either fresh, noncomposted poultry litter [PL (applied in advance of planting)] or pelletized poultry litter (PPL) products as their primary nutrient source. Georgia is a leading poultry (broiler) producing state (USDA, National Agricultural Statistics Service 2022). There are ∼2 million pounds of PL, a mixture of feces, feathers, wasted feed, and bedding materials, produced annually and available for application to agricultural lands (Dunkley et al. 2011). Total N content of PL ranges from 2% to 4%, although only a portion of this will become available to plants during the subsequent cropping season. PL is also a significant source of phosphorus (P) and contains all other essential nutrients for plants (Chastain et al. 2001; Evers 1998). PL is a readily available fertilizer for organic onion production in Georgia; however, there are some drawbacks associated with its use, including high salinity levels that can reduce plant growth and environmental concerns due to the potential for pollution when PL is overapplied (Li-Xian et al. 2007; Sharpley 1997). Additionally, the risk of foodborne illnesses from PL is a concern in the production of vegetable crops. Onions, which grow partially within the soil, may be at high risk of contamination for foodborne pathogens (Islam et al. 2005; US Food and Drug Administration 2020).

In addition to PL, there are many commercial fertilizers available for certified organic vegetable production. These products are typically made from plant or animal byproducts that have been processed or composted for use in agriculture (Cassity-Duffey et al. 2020a). The N concentration of commercial organic fertilizers can vary widely with composition. Total N concentrations may range from 3% in alfalfa (Medicago sativa) meal to 13% and 15% in feather and blood meals, respectively (Cassity-Duffey et al. 2020a; Gale et al. 2006). Some fertilizers, such as blood meal and feather meal, release N relatively quickly, whereas others, such as alfalfa meal, are reported to be slower-release sources of N (Agehara and Warncke 2005; Gale et al. 2006; Hartz and Johnstone 2006). The pool of potentially mineralizable N can widely vary depending on the product type, but N mineralization rates are generally greater and more consistent for commercial organic fertilizers than for PL and composts (Cassity-Duffey et al. 2020a).

The impact of some organic fertilizer sources on Vidalia onion production has been previously evaluated (Boyhan et al. 2010; Díaz-Pérez et al. 2018a, 2018b, 2021). Boyhan et al. (2010) reported no difference between two commercial organic fertilizers on yield of onion when fertilizers were applied at 150 lb/acre N. Díaz-Pérez et al. (2018a) reported a quadratic response of onion plant growth to application rates of organic fertilizer, with plant dry weights plateauing between 180 and 240 kg·ha−1 (160.6 and 214.1 lb/acre) N using a PPL fertilizer. In the same study Díaz-Pérez et al. (2018b) reported a quadratic response of bulb yield to organic fertilizer rate, although yield continued to increase with increasing N rate. Despite prior research, information regarding the performance of different organic fertilizers applied over a range of application rates for the production of organic onions is limited. Thus, the objective of this study was to compare the impact of a mixed source organic fertilizer (MIX) and a PPL product applied at multiple application rates in two soil types on Vidalia onion production.

Material and methods

Field experiments were conducted in Fall 2019 through Spring 2021 at the University of Georgia (UGA) Durham Horticulture Farm in Watkinsville, GA, USA (lat. 33°5′N, long. 83°3′W) and the UGA Horticulture Farm in Tifton, GA, USA (lat. 31°5′N, long. 83°5′W). The soil of the Watkinsville location is a Cecil sandy clay loam series (0% to 2% slope), whereas the Tifton location had a Tifton loamy sand series (USDA 2022). Before planting, average soil total N, organic matter, and pH were 0.21%, 1.80%, and 6.1, respectively, for the Tifton location and 0.31%, 3.10%, and 6.0, respectively, for the Watkinsville location (UGA Agriculture Environmental Services Laboratories, Athens, GA, USA). In the Watkinsville location, average preplant P (67 lb/acre) and potassium [K (223 lb/acre)] levels were considered high and high, respectively. In the Tifton location, average preplant P (79 lb/acre) and K (76 lb/acre) were considered high and medium, respectively (UGA 2020).

Plots were chisel plowed and harrowed before transplanting to a depth of ∼8 inches. After initial tillage and 2 d before planting, fertilizers were applied to plant beds that were ∼2 to 3 inches tall and spaced 6 ft center-to-center. Two commercial fertilizers, MIX [10N–0.9P–6.6K (All Season Organic Fertilizer; Nature Safe, Irving, TX, USA)] composed of feather-meat-bone-blood meal, and PPL [5N–1.8P–2.5K (Harmony Organic Fertilizer; Environmental Products LLC, Roanoke, VA, USA)] were applied to plots by hand at rates of 0, 100, 150, 200, 250, and 300 lb/acre N.

The MIX fertilizer contained 9.44% total N with 0.49% inorganic N, whereas the PPL fertilizer contained 4.36% total N with 1.04% inorganic N (Table 1). Ammonium levels were 0.14% in both fertilizers, whereas nitrate levels were 0.9% and 0.35% in the PPL and MIX fertilizers, respectively (Waters Agricultural Laboratories, Camilla, GA, USA). No additional fertilizer was applied during the growing season. Due to the nature of the organic fertilizers, levels of P and K were not balanced between the different application rates of the PPL and MIX fertilizers. Pre-plant P and K levels were either at high or medium levels for both locations.

Table 1.

Total nitrogen (N), ammonium (NH4-N), nitrate (NO3-N), total inorganic N, total carbon (C), and C/N ratio of pelleted poultry [PPL (5N–1.8P–2.5K)] and mixed-source organic [MIX (10N–0.9P–6.6K)] fertilizers used to grow organic onions (Allium cepa).

Table 1.

Fertilizer treatments were arranged in a randomized complete block design with four replications. Experimental units were 20 ft long and separated by 10-ft nonplanted buffers between adjacent plots within a bed. After application, fertilizers were incorporated to a depth of 6 inches using a tractor-mounted tiller. A planting wheel was used to make holes for onion plants on each bed. Beds received four onion rows spaced 12 inches apart with an in-row spacing of 6 inches, resulting in a population of 58,000 plants/acre.

Onion transplants of cultivar Granex Yellow PRR (Seminis Vegetable Seeds, Inc., St. Louis, MO, USA) were grown on a commercial certified organic farm for 8 weeks before planting. Onions were transplanted on 4 Dec 2019 and 2020 in the Watkinsville location, and 4 Dec 2019 and 3 Dec 2020 in the Tifton location. During the growing season, onions were overhead irrigated using sprinklers. Irrigation water volume was determined according to historical onion evapotranspiration and precipitation. Air temperatures and rainfall were monitored and recorded every 15 min using on-farm weather stations from the UGA weather network in each location (UGA 2022b). Weeds were controlled within plots using a tractor-mounted tine weeder (Aerostar-Classic 150; Einbock, Dorf an der Pram, Austria) in Watkinsville and hand cultivation in Tifton. No fungicide or insecticide applications were made during any growing season.

Soil samples (each comprising five subsamples) were collected from each plot at transplant and at harvest in both locations. After sampling, soil was air dried and tested for soil inorganic N content [ammonium (NH4+) and nitrate (NO3)] at a commercial laboratory (Waters Agricultural Laboratories). In 2020, onion shoot and bulb samples were collected at transplant and harvest for biomass estimation and N accumulation in each location. In 2021, plant samples were collected five times throughout onion growing season to monitor biomass and N uptake in each location. Samples consisted of two plants dried at 70 °C until a constant weight. Onion shoot and bulb dry weight were determined, and samples were ground and analyzed for plant total N content at a commercial laboratory (Waters Agricultural Laboratories). Aboveground N accumulation was calculated as the dry weight of plants multiplied by the tissue N concentration expressed in a percentage. Nitrogen uptake efficiency at harvest (NUPE) was calculated by the following equation: NUPE = total N taken up by the plant ÷ total N applied (Drost et al. 2002).

Onion plants were harvested on 1 May 2020 and on 7 May 2021 in Watkinsville, and on 1 May 2020 and 3 May 2021 in Tifton. Onions were hand-harvested, roots and tops were manually cut, and bulbs were left in the field for 48 h for curing. Bulbs were hand-graded by size and appearance as marketable and unmarketable according to USDA standards (USDA 2014). Subsamples of 20 marketable bulbs were cut in a longitudinal orientation and the number of bulbs with internal visual symptoms of sour skin (Pseudomonas cepacia) and center rot (Pantoea sp.) recorded.

Total yield (pounds per acre), soil inorganic N at harvest (pounds per acre), plant N accumulation at harvest (pounds per acre), plant N uptake during the season (pounds per acre), NUPE (percent) were analyzed using the Linear Mixed Model and Regression procedures from JMP Pro software (ver. 16.0; SAS Institute Inc., Cary, NC, USA). Year, location, organic fertilizer, N rate, and their interactions were analyzed as main factors, and block was considered a random effect. When statistically significant differences existed in the analysis of variance (P < 0.05), least-square means comparisons were performed using the Tukey’s honest significant difference test (α = 0.05). In 2019–20, four plots were removed from the statistical analysis due to poor plant survival.

Results and discussion

In 2019–20, cumulative rainfall was 38.5 inches in Watkinsville (Fig. 1A) and 24.7 inches in Tifton (Fig. 2A). In the 2020–21 season, rainfall totaled 21.0 inches (Fig. 1B) and 32.0 inches in the Watkinsville and Tifton locations, respectively (Fig. 2B). Multiple rain events of more than 2.0 inches were common in the Watkinsville location in the 2019–20 growing season and a single rainfall event of 6.4 inches occurred ∼1 week before harvest in Tifton for the 2020–21 growing season.

Fig. 1.
Fig. 1.

Average daily maximum and minimum air temperatures and accumulated rainfall in (A) 2019–20 and (B) 2020–21 for onion (Allium cepa) grown in Watkinsville, GA, USA; (°F – 32) ÷ 1.8 = °C, 1 inch = 2.54 cm.

Citation: HortTechnology 33, 4; 10.21273/HORTTECH05254-23

Fig. 2.
Fig. 2.

Average daily maximum and minimum air temperatures and accumulated rainfall in (A) 2019–20 and (B) 2020–21 for study location for onion (Allium cepa) grown in Tifton, GA, USA; (°F − 32) ÷ 1.8 = °C, 1 inch = 2.54 cm.

Citation: HortTechnology 33, 4; 10.21273/HORTTECH05254-23

Daily maximum and minimum air temperatures were greater in Tifton than in Watkinsville. Daily maximum temperatures averaged 69.3 °F in 2019–20 and 67.0 °F in 2020–21 in Tifton and 62.7 and 61.7 °F in 2019–20 and 2020–21, respectively, in Watkinsville. The 2019–20 growing season had 6 and 17 d of daily minimum air temperatures below freezing in Tifton and Watkinsville, respectively. In contrast, the 2020–21 growing season had more freeze events, with 14 and 31 d with daily minimum air temperatures below freezing in Tifton and Watkinsville, respectively.

Total marketable onion yields were affected by interactions between the fertilizer source and location (Table 2). An average total yield of 14,559 lb/acre was obtained with the use of the MIX fertilizer in Watkinsville. This was greater than the 10,470 lb/acre yield obtained with the use of the PPL fertilizer in the same location. In Tifton, total yields were 10,216 and 8336 lb/acre for the MIX and PPL fertilizers, respectively.

Table 2.

Effects of pelleted poultry litter [PPL (5N–1.8P–2.5K)] and mixed-source organic [MIX (10N–0.9P–6.6K)] fertilizers and location on total yield of organically grown onion (Allium cepa) in Watkinsville and Tifton, GA, USA.

Table 2.

Total marketable yield was also impacted by an interaction among location, application rate, and year (Fig. 3). Because there was not a significant four-way interaction, fertilizer sources were pooled by application rate. The total marketable yield of organic onions in both years and locations increased linearly with increasing N application rate. In Watkinsville, total yields of onions at different N rates ranged between 1320 and 4565 lb/acre in 2019–20, and between 9951 and 28,749 lb/acre in 2020–21. In Tifton, ranges of total yields were 3776 to 9264 and 7094 to 14,066 lb/acre in 2019–20 and 2020–21 seasons, respectively. Although yields in 2019–20 in both locations and yields in 2020–21 in Tifton were considerably lower than commercial yields for the region, in 2020–21 onion total yields in Watkinsville with the addition of 200 to 300 lb/acre N from organic fertilizers were comparable to the yield of onions receiving 134 lb/acre N of synthetic fertilizer (Díaz-Pérez et al. 2021). In the present study, we used a population of 58,080 plants/acre, as is typical for organic onions. However, many conventional farms in the region have adopted a population of 87,120 plants/acre. Further, in 2019–20, excessive rainfall in Watkinsville negatively affected developing plants, contributing to a reduction in onion populations. Although air temperatures were greater in 2019–20 compared with 2020–21, a rain event of 3.69 inches on 13 Dec 2019 coupled with 4 d with minimum air temperatures below freezing shortly after planting resulted in reduced transplant survival (data not shown) in some plots for the Watkinsville location. No differences in plant survival were noted among fertilizer treatments. Overall yield responses to fertilizer rates are similar to those reported by Boyhan et al. (2010), who reported a linear response of organic onion yields to increased preplant applications of PL. Díaz-Pérez et al. (2018a) reported a quadratic response of onion marketable yield to increasing rates of a PPL-based fertilizer, with application rates ranging from 0 to 240 kg·ha−1.

Fig. 3.
Fig. 3.

Effect of nitrogen (N) application rates on total marketable yield of organically grown onion (Allium cepa) in (A) Watkinsville and (B) Tifton, GA, USA, during the 2019–20 and 2020–21 growing seasons; 1 lb/acre =1.1209 kg·ha−1.

Citation: HortTechnology 33, 4; 10.21273/HORTTECH05254-23

Bulb disease was also evaluated at harvest; however, there were no bacterial diseases detected in any of the bulb subsamples in either location or study year (data not shown). Further, visual assessment of the study during growth indicated that very little to no disease was present at either location.

Soil inorganic N at harvest was impacted by the interaction between fertilizer source and year (Table 3). In 2020, there were no differences in soil inorganic N at harvest between plots receiving the MIX (9 lb/acre N) or PPL (9.8 lb/acre N) in either location. In 2021, soil inorganic N was greater in plots receiving the MIX fertilizer (14.8 lb/acre N) compared with the PPL fertilizer (11.2 lb/acre N). Nitrogen availability in soil varies with chemical composition of organic fertilizers (Cabrera et al. 2005; Cassity-Duffey et al. 2020a, 2020b; Sänger et al. 2010). Comparing different N sources, Agehara and Warncke (2005) reported that increasing soil moisture levels also enhanced N release from alfalfa pellets and PL but did not significantly affect N released from urea and blood meal. Moreover, the pattern of release also varied with composition of N sources; with mineralization of alfalfa pellets and PL increasing with high soil moisture levels during latter phases of incubation. In contrast, mineralization of blood meal was enhanced during the initial phase of incubation. Authors suggested that microbial communities responsible for N mineralization may be distinguished over time and are differentially impacted by soil moisture content.

Table 3.

Effect of pelleted poultry litter [PPL (5N–1.8P–2.5K)] and mixed-source organic [MIX (10N–0.9P–6.6K)] fertilizers and study year on soil inorganic nitrogen (N) at harvest for organically grown onion (Allium cepa) in Georgia, USA.

Table 3.

Rainfall levels in 2019–20 may have contributed to increased N leaching during the season, leading to the lack of significant differences in soil inorganic N between the MIX and PPL plots. However, with reduced rainfall in Watkinsville 2020–21, there was more soil inorganic N in MIX treated soils at harvest. The PPL fertilizer had more than twice the amount of inorganic N at application, suggesting that there was more readily leachable N at planting in the PPL compared with the MIX fertilizer. The N availability in soils is significantly influenced by precipitation and the resulting soil water dynamics. These effects are mediated through physical transport processes and microbial N transformations in the soil (Aranibar et al. 2004; Gu and Riley 2010). Using a modeling approach, Gu and Riley (2010) reported that precipitation patterns can have significant impacts on soil N cycling and losses, which were also influenced by soil texture and other soil characteristics. Increased N loss in 2019–20 could have also contributed to lower yields in that growing season. The process of pelletizing PL may also influence mineralization because it can create favorable conditions for microbial activity and the transformation of N to its inorganic form (Hadas et al. 1983). During a season without excessive rainfall, the MIX fertilizer may be subjected to less potential soil N leaching, particularly on the clay loam soils in the Watkinsville location.

Aboveground onion N accumulation at harvest was affected by an interaction among location, study year, and fertilizer rate (Table 4). The largest plant N accumulation was in Watkinsville in 2020–21, ranging from 26 to 50.8 lb/acre N in the 0- and 300-lb/acre N treatments, respectively. On-farm surveys in the Vidalia region have indicated an average above-ground N accumulation in plants at harvest of ∼66 lb/acre of N, although values can be greater than 100 lb/acre N in heavily fertilized fields (Coolong T, unpublished data). Nitrogen accumulation was greater in onion plants receiving organic fertilizer rates between 200 to 300 lb/acre N compared with plants that did not receive any fertilizer. Previously N accumulation in leaves and bulbs has been reported to be correlated with increasing N fertilization (Díaz-Pérez et al. 2003). In 2019–20 in Watkinsville, plant N accumulation increased with N application rate; however, it was not different in plants receiving between 0 to 250 lb/acre N fertilizer. As N accumulation is a function of total biomass and N concentration, this low N uptake was likely the result of low yields (total biomass) in Watkinsville in the 2019–20 growing season. In Tifton, plant N accumulation at harvest was unaffected by fertilizer application rate in 2019–20, whereas N uptake from onion plants increased with increasing N application rate in 2020–21. Aboveground N accumulation was lower in 2019–20 in both Watkinsville and Tifton locations, compared with 2020–21 for every treatment except for the 0-lb/acre N treatment in Tifton (Table 4). Díaz-Pérez et al. (2018b) reported that despite high fertilization rates, nutrient deficiencies were observed late in the season in organically grown onions in Tifton, GA, USA. These findings suggest that exclusive preplant application of organic fertilizers may result in leaching nutrients mineralized during the season.

Table 4.

Effect of the interaction among location, year, and application rate on aboveground plant nitrogen (N) accumulation at harvest for organically grown onion (Allium cepa) in Watkinsville and Tifton, GA, USA.

Table 4.

Aboveground N accumulation at harvest was also affected by an interaction between fertilizer source and location (Table 5). The accumulation of 27.0 lb/acre N was observed in plants receiving the MIX fertilizer in Watkinsville, followed by 20.4 lb/acre N accumulation in plants receiving the PPL fertilizer in the same location. In Tifton, there was no significant difference in plant N accumulation at harvest among fertilizer sources. Although N accumulation is a function of plant biomass (yield) and N concentration, it is possible that differences in plant N accumulation may be also linked to N availability, which can differ among fertilizers and is impacted by soil characteristics (Agehara and Warncke 2005; Cassity-Duffey et al. 2020a).

Table 5.

Effect of the interaction between pelleted poultry litter [PPL (5N–1.8P–2.5K)] and mixed-source organic [MIX (10N–0.9P–6.6K)] fertilizers and growing location on aboveground total nitrogen (N) accumulation at harvest for organically grown onion (Allium cepa) in Watkinsville and Tifton, GA, USA.

Table 5.

Plant N uptake was measured throughout crop development in 2020–21 season and was affected by an interaction among location, fertilizer source, and N rate. Despite the interaction, overall trends were similar among N rates; therefore, data corresponding to the midpoint application rate of 200 lb/acre N is presented in Fig. 4. Plant N uptake increased during the season and was greater for onions grown in Watkinsville compared with Tifton. In Tifton, there were no differences for N uptake between PPL and MIX fertilizers. However, in Watkinsville, N uptake in plants was greater for plants grown with the MIX fertilizer on 3 Feb 2021, when plants were actively growing vegetatively. On 1 Apr 2021, during the bulb swelling stage of onions, plants accumulated greater amounts of N with the MIX fertilizer compared with PPL. In onion, low N accumulation in the aboveground biomass is expected early in the season, but as bulb development is initiated, the N requirements increase, with N uptake only slowing during bulb maturation (Geisseler et al. 2022). It is important that N mineralization rates align with crop requirements, ensuring an efficient utilization of organic fertilizers.

Fig. 4.
Fig. 4.

Effects of the application of 200 lb/acre nitrogen (N) of pelleted poultry litter [PPL (5N–1.8P–2.5K)] and mixed-source organic [MIX (10N–0.9P–6.6K)] fertilizers on aboveground plant N uptake during the 2020–21 season for organic onions grown in (A) Watkinsville and (B) Tifton, GA, USA. Sample dates associated with the same letter and location are not significantly different according to Tukey’s honest significant difference test (P ≤ 0.05); ns = nonsignificant; 1 lb/acre =1.1209 kg·ha−1.

Citation: HortTechnology 33, 4; 10.21273/HORTTECH05254-23

There was a significant year by location by fertilizer source by rate interaction for onion NUPE (Table 6). Because NUPE is a function of dry matter accumulation (yield) values were low in 2020 in both study locations. In Watkinsville in 2019–20, NUPE for the MIX fertilizer averaged 4.40% to 8.11% in the 300- and 100-lb/acre N application rates, respectively, whereas the NUPE for the PPL product averaged 2.78%. In Tifton, NUPE values were similarly low. In 2021–22, NUPE were 50.44% and 20.99% for the MIX fertilizer applied at 100 lb/acre N in Watkinsville and Tifton locations, respectively. There were no differences in NUPE for the PPL applied in Watkinsville in either year; however, there were differences in NUPE for PPL in Tifton in both study years. In 2020–21, NUPE was significantly greater in both locations than in 2019–20 (data not shown). The NUPE values obtained in this study were considerably lower than those obtained by Drost et al. (2002) using a conventional urea-based fertilizer. Mineralization rates of both PPL and MIX products used in this study were previously determined in a soil incubation study using a Cecil sandy clay loam soil, which is the same soil as the Watkinsville location in the present study (Cassity-Duffey et al. 2020b). In that study, only 20% of organic N in the PPL mineralized after 99 d, whereas 60% of the organic N from the MIX product was available after 99 d. Further, the greater amount of inorganic N in the PPL product (23.8% of total N) may have leached early in the season, particularly with heavy rainfall. The NUPE (50.44%) obtained in Watkinsville in 2020–21 using the MIX product at 100 lb/acre N suggests that a large portion of the N that was likely mineralized and available was taken up by the plants. As would be expected, NUPE decreased with increasing N application rates. In the present study, the addition of MIX fertilizer to onion plants in the Watkinsville location may have favored plant N uptake by providing either a higher rate of N release or matching the release time with plant N-requirements.

Table 6.

Effects of pelleted poultry litter [PPL (5N–1.8P–2.5K)] and mixed-source organic [MIX (10N–0.9P–6.6K)] fertilizers applied at different rates for nitrogen uptake efficiency (NUPE) of organically grown onion (Allium cepa) in Watkinsville and Tifton, GA, USA in 2020 and 2021.

Table 6.

Conclusions

The total yield of organic onions increased with increasing organic fertilizer rates as would be expected, although NUPE significantly decreased with increasing application rate. Onions grown in the Watkinsville location had a greater N aboveground accumulation compared with those grown in Tifton. Further, the relatively high level of inorganic N in the PPL fertilizer would have been available early in the season when onions may have had low N requirements (Coolong et al. 2004). Higher N accumulation at harvest and plant N uptake over the season was obtained with the application of MIX fertilizer compared with the application of PPL fertilizer. In 2020–21, the total yield of Vidalia onions in Watkinsville, GA, USA was significantly higher with the use of MIX fertilizer and was comparable to yields of onions receiving conventional synthetic fertilizers (Díaz-Pérez et al. 2021). Overall, there were no effects of fertilizer treatments in onions grown in Tifton, GA, USA. Our findings suggest that the MIX fertilizer may be more effective than the PPL fertilizer for organic onion production in some seasons. Further, NUPE of the PPL product in all locations and years suggest that less N from the PPL product was taken up by onions during the cropping season. Although yields increased linearly with application rate, a low NUPE, particularly for the PPL fertilizer, suggests that high N application rates of these organic are inefficient.

Units

TU1

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    • Export Citation
  • Cabrera ML, Kissel DE, Vigil MF. 2005. Nitrogen mineralization from organic residues: Research opportunities. J Environ Qual. 34(1):7579. https://doi.org/10.2136/sssaj2004.0361.

    • Search Google Scholar
    • Export Citation
  • Calderón FJ, McCarty GW, Reeves JB. 2005. Analysis of manure and soil nitrogen mineralization during incubation. Biol Fertil Soils. 41:328336. https://doi.org/10.1007/s00374-005-0843-x.

    • Search Google Scholar
    • Export Citation
  • Cassity-Duffey K, Cabrera M, Gaskin J, Franklin D, Kissel D, Saha U. 2020a. Nitrogen mineralization from organic materials and fertilizers: Predicting N release. Soil Sci Soc Am J. 84(2):522533. https://doi.org/10.1002/saj2.20037.

    • Search Google Scholar
    • Export Citation
  • Cassity-Duffey K, Cabrera M, Franklin D, Gaskin J, Kissel D. 2020b. Effect of soil texture on nitrogen mineralization from organic fertilizers in four common southeastern soils. Soil Sci Soc Am J. 84(2):534542. https://doi.org/10.1002/saj2.20039.

    • Search Google Scholar
    • Export Citation
  • Cassity-Duffey K, Moore A, Satterwhite M, Leytem A. 2018. Nitrogen mineralization as affected by temperature in calcareous soils receiving repeated applications of dairy manure. Soil Sci Soc Am J. 82(1):235242. https://doi.org/10.2136/sssaj2017.02.0044.

    • Search Google Scholar
    • Export Citation
  • Chastain JP, Camberato JJ, Skewes P. 2001. Poultry manure production and nutrient content. In: Confined animal manure managers certification program manual: Poultry version. https://www.clemson.edu/extension/camm/manuals/poultry/pch3b_00.pdf. [accessed 25 Feb 2023].

  • Coolong T, Boyhan G 2017. Onion production guide. Univ Georgia Coop Ext Bull 1198.

  • Coolong TW, Kopsell DA, Kopsell DE, Randle WM. 2004. Nitrogen and sulfur influence nutrient usage and accumulation in onion. J Plant Nutr. 27:16671686. https://doi.org/10.1081/PLN-200026010.

    • Search Google Scholar
    • Export Citation
  • Coolong TW, Randle WM. 2003. Ammonium nitrate fertility levels influence flavour development in hydroponically grown ‘Granex 33’ onion. J Sci Food Agr. 83(5):477482. https://doi.org/10.1002/jsfa.1398.

    • Search Google Scholar
    • Export Citation
  • Díaz-Pérez JC, Bautista J, Gunawan G, Bateman A, Riner CM. 2018a. Sweet onion (Allium cepa L.) as influenced by organic fertilization rate: 1. Plant growth, and leaf and bulb mineral composition. HortScience. 53(4):451458. https://doi.org/10.21273/HORTSCI12791-17.

    • Search Google Scholar
    • Export Citation
  • Díaz-Pérez JC, Bautista J, Gunawan G, Bateman A, Riner CM. 2018b. Sweet onion (Allium cepa L.) as influenced by organic fertilization rate: 2. Bulb yield and quality before and after storage. HortScience. 53(4):459464. https://doi.org/10.21273/HORTSCI12360-17.

    • Search Google Scholar
    • Export Citation
  • Díaz-Pérez JC, da Silva ALBR, Valdez-Aguilar LA. 2021. Seasonal plant growth, leaf and bulb mineral nutrients, and bulb yield and quality under chemical, mixed, and organic fertilization in sweet onion (Allium cepa L.). J Plant Nutr. 45(2):153167. https://doi.org/10.1080/01904167.2021.1952227.

    • Search Google Scholar
    • Export Citation
  • Díaz-Pérez JC, Purvis AC, Paulk JT. 2003. Bolting, yield, and bulb decay of sweet onion as affected by nitrogen fertilization. J Am Soc Hortic Sci. 128(1):144149. https://doi.org/10.21273/JASHS.128.1.0144.

    • Search Google Scholar
    • Export Citation
  • Drost D, Koenig R, Tindall T. 2002. Nitrogen use efficiency and onion yield increased with a polymer-coated nitrogen source. HortScience. 37(2):338342. https://doi.org/10.21273/HORTSCI.37.2.338.

    • Search Google Scholar
    • Export Citation
  • Dunkley CS, Cunningham DL, Harris GH. 2011. The value of poultry litter in south Georgia. Univ Georgia Coop Ext Bull 1386.

  • Evers GW. 1998. Comparison of broiler poultry litter and commercial fertilizer for coastal bermudagrass production in the southeastern US. J Sustain Agric. 12(4):5577. https://doi.org/10.1300/J064v12n04_06.

    • Search Google Scholar
    • Export Citation
  • Gale ES, Sullivan DM, Cogger CG, Bary AI, Hemphill DD, Myhre EA. 2006. Estimating plant-available nitrogen release from manures, composts, and specialty products. J Environ Qual. 35(6):23212332. https://doi.org/10.2134/jeq2006.0062.

    • Search Google Scholar
    • Export Citation
  • Geisseler D, Ortiz RS, Diaz J. 2022. Nitrogen nutrition and fertilization of onions (Allium cepa L.)—A literature review. Scientia Hortic. 291. https://doi.org/10.1016/j.scienta.2021.110591.

    • Search Google Scholar
    • Export Citation
  • Gitaitis RD, Gent DH, Schwartz HS. 2008. Leaf streak and bulb rot, p 58. In: Schwartz HF, Mohan SK (eds). Compendium of onion and garlic disease and pests (2nd ed). APS Press, St. Paul, MN, USA.

  • Gu C, Riley WJ. 2010. Combined effects of short term rainfall patterns and soil texture on soil nitrogen cycling—A modeling analysis. J Contam Hydrol. 112(1-4):141154. https://doi.org/10.1016/j.jconhyd.2009.12.003.

    • Search Google Scholar
    • Export Citation
  • Hadas A, Bar-Yosef B, Davidov S, Sofer M. 1983. Effect of pelleting, temperature, and soil type on mineral nitrogen release from poultry and dairy manures. Soil Sci Soc Am J. 47(6):11291133. https://doi.org/10.2136/sssaj1983.03615995004700060014x.

    • Search Google Scholar
    • Export Citation
  • Hartz TK, Johnstone PR. 2006. Nitrogen availability from high-nitrogen-containing organic fertilizers. HortTechnology. 16(1):3942. https://doi.org/10.21273/HORTTECH.16.1.0039.

    • Search Google Scholar
    • Export Citation
  • Islam M, Doyle MP, Phatak SC, Millner P, Jiang X. 2005. Survival of Escherichia coli O157: H7 in soil and on carrots and onions grown in fields treated with contaminated manure composts or irrigation water. Food Microbiol. 22(1):6370. https://doi.org/10.1016/j.fm.2004.04.007.

    • Search Google Scholar
    • Export Citation
  • Li-Xian Y, Guo-Liang L, Shi-Hua T, Gavin S, Zhao-Huan H. 2007. Salinity of animal manure and potential risk of secondary soil salinization through successive manure application. Sci Total Environ. 383(1-3):106114. https://doi.org/10.1016/j.scitotenv.2007.05.027.

    • Search Google Scholar
    • Export Citation
  • Reganold JP, Wachter JM. 2016. Organic agriculture in the twenty-first century. Nat Plants. 2(2):18. https://doi.org/10.1038/nplants.2015.221.

    • Search Google Scholar
    • Export Citation
  • Sänger A, Geisseler D, Ludwig B. 2010. Effects of rainfall pattern on carbon and nitrogen dynamics in soil amended with biogas slurry and composted cattle manure. J Plant Nutr Soil Sci. 173(5):692698. https://doi.org/10.1002/jpln.200900254.

    • Search Google Scholar
    • Export Citation
  • Sharpley AN. 1997. Rainfall frequency and nitrogen and phosphorus runoff from soil amended with poultry litter. J Environ Qual. 26(4):11271132. https://doi.org/10.2134/jeq1997.00472425002600040026x.

    • Search Google Scholar
    • Export Citation
  • Tyson C, Jackson D, da Silva ALBR, Edenfield J, Shirly A, Bowen D, Thigpen D, Clark D, Powell S, Tanner S, Greene S. 2023. UGA variety trial report for the 2020–21 Vidalia onion crop season. 2022 Vidalia Onion Extension and Research Report. Univ Georgia Coop Ext Bull AP114-1. https://site.extension.uga.edu/vidaliaonion/2023/04/2022-vidalia-onion-research-extension-report/. [accessed 17 Apr 2023].

  • University of Georgia. 2020. Fertilizer recommendations by crops. http://aesl.ces.uga.edu/cropcodelist.pdf. [accessed 7 Apr 2023].

  • University of Georgia. 2022a. 2021 Georgia farm gate value report. Univ. Georgia Coop Ext Serv Bul. AR 22-01. https://caed.uga.edu/publications/farm-gate-value.html. [accessed 25 Feb 2023].

  • University of Georgia. 2022b. Watkinsville and Tifton Georgia climate data. http://www.georgiaweather.net/. [accessed 20 Feb 2023].

  • US Department of Agriculture. 2014. United states standards for grades of Bermuda-Granex-Grano type onions. US Dept Agric, Washington, DC, USA.

  • US Department of Agriculture. 2019. Census of Agriculture—2019 Organic survey. https://www.nass.usda.gov/Publications/AgCensus/2017/Online_Resources/Organics/. [accessed 25 Feb 2023].

  • US Department of Agriculture. 2022. Soil survey. Web soil survey—Soil survey of Oconee and Tift counties, Georgia. https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx. [accessed 28 Mar 2023].

  • US Department of Agriculture, National Agricultural Statistics Service. 2022. Poultry—Production and value 2021 summary. https://downloads.usda.library.cornell.edu/usda-esmis/files/m039k491c/dr2703010/v405tf48t/plva0422.pdf. [accessed 17 April 2023].

  • US Food and Drug Administration. 2020. 2020 Recalls of food products associated with onions from Thomson International, Inc. due to the potential risk of Salmonella. https://www.fda.gov/safety/major-product-recalls/2020-recalls-food-products-associated-onions-thomson-international-inc-due-potential-risk-salmonella. [accessed 25 Feb 2023].

  • Fig. 1.

    Average daily maximum and minimum air temperatures and accumulated rainfall in (A) 2019–20 and (B) 2020–21 for onion (Allium cepa) grown in Watkinsville, GA, USA; (°F – 32) ÷ 1.8 = °C, 1 inch = 2.54 cm.

  • Fig. 2.

    Average daily maximum and minimum air temperatures and accumulated rainfall in (A) 2019–20 and (B) 2020–21 for study location for onion (Allium cepa) grown in Tifton, GA, USA; (°F − 32) ÷ 1.8 = °C, 1 inch = 2.54 cm.

  • Fig. 3.

    Effect of nitrogen (N) application rates on total marketable yield of organically grown onion (Allium cepa) in (A) Watkinsville and (B) Tifton, GA, USA, during the 2019–20 and 2020–21 growing seasons; 1 lb/acre =1.1209 kg·ha−1.

  • Fig. 4.

    Effects of the application of 200 lb/acre nitrogen (N) of pelleted poultry litter [PPL (5N–1.8P–2.5K)] and mixed-source organic [MIX (10N–0.9P–6.6K)] fertilizers on aboveground plant N uptake during the 2020–21 season for organic onions grown in (A) Watkinsville and (B) Tifton, GA, USA. Sample dates associated with the same letter and location are not significantly different according to Tukey’s honest significant difference test (P ≤ 0.05); ns = nonsignificant; 1 lb/acre =1.1209 kg·ha−1.

  • Agehara S, Warncke DD. 2005. Soil moisture and temperature effects on nitrogen release from organic nitrogen sources. Soil Sci Soc Am J. 69(6):18441855. https://doi.org/10.2136/sssaj2004.0361.

    • Search Google Scholar
    • Export Citation
  • Aranibar JN, Otter L, Macko SA, Feral CJ, Epstein HE, Dowty PR, Eckardt F, Shurgart HH, Swap RJ. 2004. Nitrogen cycling in the soil–plant system along a precipitation gradient in the Kalahari sands. Glob Change Biol. 10(3):359373. https://doi.org/10.1111/j.1365-2486.2003.00698.x.

    • Search Google Scholar
    • Export Citation
  • Berry PM, Sylvester-Bradley R, Philipps L, Hatch DJ, Cuttle SP, Rayns FW, Gosling P. 2002. Is the productivity of organic farms restricted by the supply of available nitrogen? Soil Use Manage. 18:248255. https://doi.org/10.1111/j.1475-2743.2002.tb00266.x.

    • Search Google Scholar
    • Export Citation
  • Boyhan GE, Hicks R, Torrance R, Hopkins C, Riner C, Hill R, Paulk T. 2007. Organic Vidalia onion production: The basics of what works, what you can do and what you can’t. https://hdl.handle.net/10724/33582. [accessed 25 Feb 2023].

  • Boyhan GE, Hicks R, Torrance R, Riner CM, Hill CR. 2010. Evaluation of poultry litter and organic fertilizer rate and source for production of organic short-day onions. HortTechnology. 20(2):304307. https://doi.org/10.21273/HORTTECH.20.2.304.

    • Search Google Scholar
    • Export Citation
  • Cabrera ML, Kissel DE, Vigil MF. 2005. Nitrogen mineralization from organic residues: Research opportunities. J Environ Qual. 34(1):7579. https://doi.org/10.2136/sssaj2004.0361.

    • Search Google Scholar
    • Export Citation
  • Calderón FJ, McCarty GW, Reeves JB. 2005. Analysis of manure and soil nitrogen mineralization during incubation. Biol Fertil Soils. 41:328336. https://doi.org/10.1007/s00374-005-0843-x.

    • Search Google Scholar
    • Export Citation
  • Cassity-Duffey K, Cabrera M, Gaskin J, Franklin D, Kissel D, Saha U. 2020a. Nitrogen mineralization from organic materials and fertilizers: Predicting N release. Soil Sci Soc Am J. 84(2):522533. https://doi.org/10.1002/saj2.20037.

    • Search Google Scholar
    • Export Citation
  • Cassity-Duffey K, Cabrera M, Franklin D, Gaskin J, Kissel D. 2020b. Effect of soil texture on nitrogen mineralization from organic fertilizers in four common southeastern soils. Soil Sci Soc Am J. 84(2):534542. https://doi.org/10.1002/saj2.20039.

    • Search Google Scholar
    • Export Citation
  • Cassity-Duffey K, Moore A, Satterwhite M, Leytem A. 2018. Nitrogen mineralization as affected by temperature in calcareous soils receiving repeated applications of dairy manure. Soil Sci Soc Am J. 82(1):235242. https://doi.org/10.2136/sssaj2017.02.0044.

    • Search Google Scholar
    • Export Citation
  • Chastain JP, Camberato JJ, Skewes P. 2001. Poultry manure production and nutrient content. In: Confined animal manure managers certification program manual: Poultry version. https://www.clemson.edu/extension/camm/manuals/poultry/pch3b_00.pdf. [accessed 25 Feb 2023].

  • Coolong T, Boyhan G 2017. Onion production guide. Univ Georgia Coop Ext Bull 1198.

  • Coolong TW, Kopsell DA, Kopsell DE, Randle WM. 2004. Nitrogen and sulfur influence nutrient usage and accumulation in onion. J Plant Nutr. 27:16671686. https://doi.org/10.1081/PLN-200026010.

    • Search Google Scholar
    • Export Citation
  • Coolong TW, Randle WM. 2003. Ammonium nitrate fertility levels influence flavour development in hydroponically grown ‘Granex 33’ onion. J Sci Food Agr. 83(5):477482. https://doi.org/10.1002/jsfa.1398.

    • Search Google Scholar
    • Export Citation
  • Díaz-Pérez JC, Bautista J, Gunawan G, Bateman A, Riner CM. 2018a. Sweet onion (Allium cepa L.) as influenced by organic fertilization rate: 1. Plant growth, and leaf and bulb mineral composition. HortScience. 53(4):451458. https://doi.org/10.21273/HORTSCI12791-17.

    • Search Google Scholar
    • Export Citation
  • Díaz-Pérez JC, Bautista J, Gunawan G, Bateman A, Riner CM. 2018b. Sweet onion (Allium cepa L.) as influenced by organic fertilization rate: 2. Bulb yield and quality before and after storage. HortScience. 53(4):459464. https://doi.org/10.21273/HORTSCI12360-17.

    • Search Google Scholar
    • Export Citation
  • Díaz-Pérez JC, da Silva ALBR, Valdez-Aguilar LA. 2021. Seasonal plant growth, leaf and bulb mineral nutrients, and bulb yield and quality under chemical, mixed, and organic fertilization in sweet onion (Allium cepa L.). J Plant Nutr. 45(2):153167. https://doi.org/10.1080/01904167.2021.1952227.

    • Search Google Scholar
    • Export Citation
  • Díaz-Pérez JC, Purvis AC, Paulk JT. 2003. Bolting, yield, and bulb decay of sweet onion as affected by nitrogen fertilization. J Am Soc Hortic Sci. 128(1):144149. https://doi.org/10.21273/JASHS.128.1.0144.

    • Search Google Scholar
    • Export Citation
  • Drost D, Koenig R, Tindall T. 2002. Nitrogen use efficiency and onion yield increased with a polymer-coated nitrogen source. HortScience. 37(2):338342. https://doi.org/10.21273/HORTSCI.37.2.338.

    • Search Google Scholar
    • Export Citation
  • Dunkley CS, Cunningham DL, Harris GH. 2011. The value of poultry litter in south Georgia. Univ Georgia Coop Ext Bull 1386.

  • Evers GW. 1998. Comparison of broiler poultry litter and commercial fertilizer for coastal bermudagrass production in the southeastern US. J Sustain Agric. 12(4):5577. https://doi.org/10.1300/J064v12n04_06.

    • Search Google Scholar
    • Export Citation
  • Gale ES, Sullivan DM, Cogger CG, Bary AI, Hemphill DD, Myhre EA. 2006. Estimating plant-available nitrogen release from manures, composts, and specialty products. J Environ Qual. 35(6):23212332. https://doi.org/10.2134/jeq2006.0062.

    • Search Google Scholar
    • Export Citation
  • Geisseler D, Ortiz RS, Diaz J. 2022. Nitrogen nutrition and fertilization of onions (Allium cepa L.)—A literature review. Scientia Hortic. 291. https://doi.org/10.1016/j.scienta.2021.110591.

    • Search Google Scholar
    • Export Citation
  • Gitaitis RD, Gent DH, Schwartz HS. 2008. Leaf streak and bulb rot, p 58. In: Schwartz HF, Mohan SK (eds). Compendium of onion and garlic disease and pests (2nd ed). APS Press, St. Paul, MN, USA.

  • Gu C, Riley WJ. 2010. Combined effects of short term rainfall patterns and soil texture on soil nitrogen cycling—A modeling analysis. J Contam Hydrol. 112(1-4):141154. https://doi.org/10.1016/j.jconhyd.2009.12.003.

    • Search Google Scholar
    • Export Citation
  • Hadas A, Bar-Yosef B, Davidov S, Sofer M. 1983. Effect of pelleting, temperature, and soil type on mineral nitrogen release from poultry and dairy manures. Soil Sci Soc Am J. 47(6):11291133. https://doi.org/10.2136/sssaj1983.03615995004700060014x.

    • Search Google Scholar
    • Export Citation
  • Hartz TK, Johnstone PR. 2006. Nitrogen availability from high-nitrogen-containing organic fertilizers. HortTechnology. 16(1):3942. https://doi.org/10.21273/HORTTECH.16.1.0039.

    • Search Google Scholar
    • Export Citation
  • Islam M, Doyle MP, Phatak SC, Millner P, Jiang X. 2005. Survival of Escherichia coli O157: H7 in soil and on carrots and onions grown in fields treated with contaminated manure composts or irrigation water. Food Microbiol. 22(1):6370. https://doi.org/10.1016/j.fm.2004.04.007.

    • Search Google Scholar
    • Export Citation
  • Li-Xian Y, Guo-Liang L, Shi-Hua T, Gavin S, Zhao-Huan H. 2007. Salinity of animal manure and potential risk of secondary soil salinization through successive manure application. Sci Total Environ. 383(1-3):106114. https://doi.org/10.1016/j.scitotenv.2007.05.027.

    • Search Google Scholar
    • Export Citation
  • Reganold JP, Wachter JM. 2016. Organic agriculture in the twenty-first century. Nat Plants. 2(2):18. https://doi.org/10.1038/nplants.2015.221.

    • Search Google Scholar
    • Export Citation
  • Sänger A, Geisseler D, Ludwig B. 2010. Effects of rainfall pattern on carbon and nitrogen dynamics in soil amended with biogas slurry and composted cattle manure. J Plant Nutr Soil Sci. 173(5):692698. https://doi.org/10.1002/jpln.200900254.

    • Search Google Scholar
    • Export Citation
  • Sharpley AN. 1997. Rainfall frequency and nitrogen and phosphorus runoff from soil amended with poultry litter. J Environ Qual. 26(4):11271132. https://doi.org/10.2134/jeq1997.00472425002600040026x.

    • Search Google Scholar
    • Export Citation
  • Tyson C, Jackson D, da Silva ALBR, Edenfield J, Shirly A, Bowen D, Thigpen D, Clark D, Powell S, Tanner S, Greene S. 2023. UGA variety trial report for the 2020–21 Vidalia onion crop season. 2022 Vidalia Onion Extension and Research Report. Univ Georgia Coop Ext Bull AP114-1. https://site.extension.uga.edu/vidaliaonion/2023/04/2022-vidalia-onion-research-extension-report/. [accessed 17 Apr 2023].

  • University of Georgia. 2020. Fertilizer recommendations by crops. http://aesl.ces.uga.edu/cropcodelist.pdf. [accessed 7 Apr 2023].

  • University of Georgia. 2022a. 2021 Georgia farm gate value report. Univ. Georgia Coop Ext Serv Bul. AR 22-01. https://caed.uga.edu/publications/farm-gate-value.html. [accessed 25 Feb 2023].

  • University of Georgia. 2022b. Watkinsville and Tifton Georgia climate data. http://www.georgiaweather.net/. [accessed 20 Feb 2023].

  • US Department of Agriculture. 2014. United states standards for grades of Bermuda-Granex-Grano type onions. US Dept Agric, Washington, DC, USA.

  • US Department of Agriculture. 2019. Census of Agriculture—2019 Organic survey. https://www.nass.usda.gov/Publications/AgCensus/2017/Online_Resources/Organics/. [accessed 25 Feb 2023].

  • US Department of Agriculture. 2022. Soil survey. Web soil survey—Soil survey of Oconee and Tift counties, Georgia. https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx. [accessed 28 Mar 2023].

  • US Department of Agriculture, National Agricultural Statistics Service. 2022. Poultry—Production and value 2021 summary. https://downloads.usda.library.cornell.edu/usda-esmis/files/m039k491c/dr2703010/v405tf48t/plva0422.pdf. [accessed 17 April 2023].

  • US Food and Drug Administration. 2020. 2020 Recalls of food products associated with onions from Thomson International, Inc. due to the potential risk of Salmonella. https://www.fda.gov/safety/major-product-recalls/2020-recalls-food-products-associated-onions-thomson-international-inc-due-potential-risk-salmonella. [accessed 25 Feb 2023].

Hanna Ibiapina de Jesus Department of Horticulture, University of Georgia, 1111 Miller Plant Sciences, Athens, GA 30602, USA

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Andre Luiz Biscaia Ribeiro da Silva Department of Horticulture, Auburn University, 124 Funchess Hall, Auburn, AL 36849, USA

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Bhabesh Dutta Department of Plant Pathology, University of Georgia, 2360 Rainwater Road, Tifton, GA 31793, USA

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Kate Cassity-Duffey Department of Horticulture, University of Georgia, 1111 Miller Plant Sciences, Athens, GA 30602, USA

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Timothy Coolong Department of Horticulture, University of Georgia, 1111 Miller Plant Sciences, Athens, GA 30602, USA

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Contributor Notes

Funding for this research was provided US Department of Agriculture, National Institute of Food and Agriculture Project No. GEOW-2019-03518 (Evaluation of integrated Bacterial Disease Management Options for Organic Onion Production in the Southeastern and Northcentral United States).

T.C. is the corresponding author. E-mail: tcoolong@uga.edu.

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  • Fig. 1.

    Average daily maximum and minimum air temperatures and accumulated rainfall in (A) 2019–20 and (B) 2020–21 for onion (Allium cepa) grown in Watkinsville, GA, USA; (°F – 32) ÷ 1.8 = °C, 1 inch = 2.54 cm.

  • Fig. 2.

    Average daily maximum and minimum air temperatures and accumulated rainfall in (A) 2019–20 and (B) 2020–21 for study location for onion (Allium cepa) grown in Tifton, GA, USA; (°F − 32) ÷ 1.8 = °C, 1 inch = 2.54 cm.

  • Fig. 3.

    Effect of nitrogen (N) application rates on total marketable yield of organically grown onion (Allium cepa) in (A) Watkinsville and (B) Tifton, GA, USA, during the 2019–20 and 2020–21 growing seasons; 1 lb/acre =1.1209 kg·ha−1.

  • Fig. 4.

    Effects of the application of 200 lb/acre nitrogen (N) of pelleted poultry litter [PPL (5N–1.8P–2.5K)] and mixed-source organic [MIX (10N–0.9P–6.6K)] fertilizers on aboveground plant N uptake during the 2020–21 season for organic onions grown in (A) Watkinsville and (B) Tifton, GA, USA. Sample dates associated with the same letter and location are not significantly different according to Tukey’s honest significant difference test (P ≤ 0.05); ns = nonsignificant; 1 lb/acre =1.1209 kg·ha−1.

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