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Nitrogen doses and sources applied as top-dressing in onion crops grown under no-tillage and conventional tillage systems

ABSTRACT

Nitrogen (N) fertilization effectiveness in onion depends on N source, as well as on soil type and management system. The aim of the study is to investigate the effect of N sources and doses applied as top-dressing on bulb yield, leaf N contents and on the postharvest conservation of onion bulbs grown under no-tillage (NTS) and conventional tillage (CTS) systems. Three experiments were carried out: two in Lebon Régis County-SC, under NTS; and one in Caçador County-SC, under CTS. The herein tested N sources comprised urea, ammonium nitrate, calcium nitrate and ammonium sulfate, in combination to N doses applied as top-dressing (70, 140, 210, 280 and 350 kg N ha-1) in addition to the control, without N. The N sources did not affect yield parameters, leaf N content and post-harvest onion losses. The maximum technical efficiency in bulb yield was observed at N doses of 195.8 and 258.4 kg ha-1 in the no-tillage system (NTS) and at 270.7 kg N ha-1 in the CTS. The NTS enabled maximum yield at N dose 47% lower than the officially recommended one. Maximum relative commercial yield was associated with 31.1 g kg-1 of leaf N.

Keywords
Allium cepa ; urea; calcium nitrate; ammonium nitrate ammonium sulfate

INTRODUCTION

Nitrogen (N) is the nutrient mostly absorbed by onion plants (Kurtz et al., 2016Kurtz C, Pauletti V, Fayad J & Vieira Neto J (2016) Crescimento e absorção de nutrientes pela cultivar de cebola bola precoce. Horticultura Brasiliera, 34:279-288.); however, it is the element mostly influencing crop yield, bulb quality (Kurtz et al., 2013Kurtz C, Ernani PR, Pauletti V, Menezes Junior FG & Vieira Neto J (2013) Produtividade e conservação de cebola afetadas pela adubação nitrogenada no sistema de plantio direto. Horticultura Brasileira, 31:559-567.) and disease incidence (Pfeufer & Gugino, 2018Pfeufer EE & Gugino BK (2018) Environmental and management factors associated with bacterial diseases of onion in Pennsylvania. Plant Disease, 102:2205-2211.). Crops producing 37.34 t ha-1 of bulbs extract 101.4 kg ha-1 of N from the soil; 58.3 kg ha-1 (57%) of this total is exported through bulb harvesting (Kurtz et al., 2016Kurtz C, Pauletti V, Fayad J & Vieira Neto J (2016) Crescimento e absorção de nutrientes pela cultivar de cebola bola precoce. Horticultura Brasiliera, 34:279-288.). This value represents a significant amount of exported N, which must be replenished to help maintaining soil fertility (Moraes et al., 2016Moraes CC, Araujo HS, Factor TL & Purquerio LFV (2016) Fenologia e acumulação de nutrientes por cebola de dia curto em semeadura direta. Revista de Ciências Agrárias, 39:281-290.).

Nitrogen fertilization can significantly increase bulb yield. According to Kurtz et al. (2012)Kurtz C, Ernani PR, Coimbra JLM & Petry E (2012) Rendimento de cebola e conservação pós-colheita em função da dose e do parcelamento de nitrogênio. Revista Brasileira de Ciência do Solo, 36:865-875., maximum economic returns observed in three cycles under CTS were recorded at N doses ranging from 116 kg ha-1 to 142 kg ha-1 in medium-texture soil presenting medium organic matter (OM) content, as well as at 249 kg ha-1 of N in sandy soil presenting low OM content. Maximum economic return in NTS was observed at N doses ranging from 102 kg ha-1 to 131 kg ha-1 (Kurtz et al., 2013Kurtz C, Ernani PR, Pauletti V, Menezes Junior FG & Vieira Neto J (2013) Produtividade e conservação de cebola afetadas pela adubação nitrogenada no sistema de plantio direto. Horticultura Brasileira, 31:559-567.). Resende & Costa (2014)Resende GM & Costa ND (2014) Dose econômica de nitrogênio na produtividade e armazenamento de cultivares de cebola. Horticultura Brasileira, 32:357-362. observed the highest commercial yield at N dose of 161.4 kg ha-1. On the other hand, excess N induces exuberant vegetative plant growth due to increased protein synthesis and water content, a fact that reduces plant resistance to diseases and bulb quality (Robles & García, 2013Robles EJ & García MFE (2013) Respuesta de niveles crecientes de NK en la producción de cebolla (Allium cepa L.) var. “Roja Arequipeña”. Scientia Agropecuaria, 4:15-25.). According to Kurtz et al. (2016)Kurtz C, Pauletti V, Fayad J & Vieira Neto J (2016) Crescimento e absorção de nutrientes pela cultivar de cebola bola precoce. Horticultura Brasiliera, 34:279-288., maximum nutrient absorption rates were concentrated at bulbing stage, at 73 days after transplantation.

Nowadays, there is large supply of N sources available in the market; these sources vary in concentration, chemical N form and association with other nutrients. Overall, many of these fertilizers present high cost per nutrient unit, a fact that increases production costs. In addition, there are losses associated with each of these sources; they result from leaching (Wang et al., 2019Wang Y, Ying H, Yin Y, Zheng H & Cui Z (2019) Estimating soil nitrate leaching of nitrogen fertilizer from global meta-analysis. Science of the Total Environment, 657:96-102.), volatilization (Huang et al., 2016Huang S, Weisheng LV, Bloszies S, Shi Q, Pan X & Zeng Y (2016) Effects of fertilizer management practices on yield-scaled ammonia emissions from croplands in China: A meta-analysis. Field Crops Research, 192:118-125.) and denitrification (Alsina et al., 2013Alsina M, Borges ACF & Smart DR (2013) Spatio temporal variation of event related N2O and CH4 emissions during fertigation in a California almond orchard. Ecosphere, 4:01-21.) processes, as well as influence N availability in the soil and N-use efficiency by plants.

Systems based on seedling production in flower beds and on subsequent seedling transplantation prevail in Southern Brazil (Kurtz et al., 2013Kurtz C, Ernani PR, Pauletti V, Menezes Junior FG & Vieira Neto J (2013) Produtividade e conservação de cebola afetadas pela adubação nitrogenada no sistema de plantio direto. Horticultura Brasileira, 31:559-567.). However, there has been fast expansion of no-tillage seeding in recent years; this system has been adopted in approximately 20% of production fields. It mainly happens due to scarcity of, and high cost with, manpower to perform seedling transplanting operations (Epagri, 2013Epagri - Empresa de Pesquisa Agropecuária e Extensão Rural de Santa Catarina (2013) Sistemas de produção para cebola: Santa Catarina. Florianópolis, Epagri. 106p.).

Conventional tillage system (CTS) is the traditional soil preparation method adopted for onion crops; however, it leads to intense soil physical (Vizioli et al., 2021Vizioli B, Cavalieri-Polizeli KMV, Tormena CA & Barth G (2021) Effects of long-term tillage systems on soil physical quality and crop yield in a Brazilian Ferralsol. Soil and Tillage Research, 209:104935.), chemical (Thomaz & Antoneli, 2020Thomaz E & Edivaldo A (2020) Long-term soil quality decline due to the conventional tobacco tillage in Southern Brazil. Archives of Agronomy and Soil Science, 67:01-13.) and biological (Bhaduri et al., 2017Bhaduri D, Purakayastha TJ, Patra AK, Singh M & Wilson BR (2017) Biological indicators of soil quality in a long-term rice–wheat system on the Indo-Gangetic plain: combined effect of tillage-water-nutrient management. Environmental Earth Sciences, 76:202.) degradation. Thus, the onion no-tillage system (NTS) - which performs seeding without turning over the soil, crop rotation and cover crops - is a soil management alternative that should be implemented by technicians, researchers and producers due to broad benefits provided by this system to different ecosystems. Cover crops used in onion NTS in Santa Catarina State, Southern Brazil, were efficient in recovering and increasing total organic carbon contents, as well as in improving soil physical quality (Loss et al., 2015Loss A, Basso A, Oliveira BS, Koucher LP, Oliveira RA, Kurtz C, Lovato PE, Curmi P, Brunetto G & Comin JJ (2015) Carbono orgânico total e agregação do solo em sistema de plantio direto agroecológico e convencional de cebola. Revista Brasileira de Ciência do Solo, 39:1212-1224.).

Nitrogen management in CTS, mainly in onion no-tillage sowing in NTS, is an important research demand to help defining the N doses and sources to be applied, mainly due to increase in the adoption of these techniques in Santa Catarina State, which is the largest onion producer among Brazilian states (IBGE, 2023IBGE - Instituto Brasileiro de Geografia e Estatística (2023) Produção de Cebola. Available at: https://www.ibge.gov.br/explica/producao-agropecuaria/cebola/br. Accessed on: October 8th, 2023.
https://www.ibge.gov.br/explica/producao...
). The aim of the current study was to assess the effect of N sources and doses, applied as top-dressing, on onions planted based on no-tillage seeding, under conventional tillage and no-tillage management systems.

MATERIALS AND METHODS

Two experiments - called experiments 1 and 2 - were carried out in the 2016/2017 planting season; one experiment - called experiment 3 - was carried out in the 2017/2018 planting season. Experiments 1 and 2 (at coordinates: -26.911225 S and -50.766628 W; and -26. 846680 S and -51.077776 W, respectively) were implemented in Lebon Régis County/SC. Experiment 3 (at coordinates: -26.904108 S and -50.751973 W) was implemented in Caçador County/SC. All experiments were carried out in typical Dystrophic Bruno Nitosol (Embrapa, 2013Embrapa – Empresa Brasileira de Pesquisa Agropecuária (2013) Sistema brasileiro de classificação de solos. 3ª ed. Brasília, Embrapa. 353p.). Based on Köeppen’s classification, the climate in the experimental region is of the Cfb type – i.e., temperate, humid mesothermal, with mild summer (Alvares et al., 2013Alvares CA, Stape JL, Sentelhas PC, Gonçalves JLM & Sparovek G (2013) Köppen’s climate classification map for Brazil. Meteorol Z, 22:711-28.). Climatic data were collected in meteorological stations located 100 m away from the experiments (Figure 1).

Figure 1
Daily rainfall rate, minimum and mean temperatures recorded throughout the months in two years of experiments.

Soil samples were collected from the 0-20 cm soil layer at experiments’ implementation time (Table 1). Soil acidity was corrected based on limestone application (PRNT 80%); fertilizations with phosphorus and potassium were performed based on the CQFS-RS/SC (2016)CQFS - Comissão de Química e Fertilidade do Solo - RS/SC (2016) Manual de adubação e calagem para os estados do Rio Grande do Sul e de Santa Catarina. 11ª ed. Porto Alegre, Sociedade Brasileira de Ciência do Solo – Núcleo Regional Sul. 376p. to achieve crop yield of 70 t ha-1.

Table 1
Chemical attributes of, and clay content in, soils used in all three experiments conducted in the 2016 and 2017 crop seasons

Experiments were carried out based on a randomized block design, with 4 repetitions. Experiment 1 has followed factorial arrangement 3x4+1; it combined 3 N sources (urea, ammonium nitrate and calcium nitrate) and 4 N doses applied as top-dressing (70, 140, 210 and 280 kg ha-1), in addition to the control treatment (without N application) – this experiment comprised 13 treatments, in total. Experiments 2 and 3 have followed factorial arrangement 4x5+1; it comprised 4 N sources (ammonium sulfate was added to the N sources of experiment 1) and 5 N doses applied as top-dressing (N dose of 350 kg ha-1 was added to N doses adopted in experiment 1), in addition to the control treatment (without N application as top-dressing) – these experiments comprised 21 treatments, in total. Nitrogen sources presented the following compositions: urea (UR, 45% of N), calcium nitrate (CN, 15.5% of N and 19% of Ca), ammonium nitrate (AN, 32% of N) and ammonium sulfate (AS, 21% of N and 22% of S). All experiments were 3.0-m wide and 5.0-m long, spacing between rows was 0.30 m and usable area was 1.2 m2.

Experiments 1 and 2 were conducted in no-tillage (NTS) soil management system; they comprised previous soybean crop in Summer, which was followed by black oat crop used as cover crop in Fall. Black oat was sown in April in both crop seasons and managed through desiccation before stem elongation (phenological stage V6), at 30 days before onion sowing. Experiment 3 was implemented in area subjected to conventional tillage system (CTS), after subsoiling and double harrowing procedures. Onion sowing density was set at 26 seeds / meter; thinning was carried out at 60 days after sowing (DAS) and left a final population comprising 550 thousand plants ha-1. In total, 20 kg N ha-1, 370 kg ha-1 of P2O5 and 60 kg ha-1 of K2O were applied in the sowing furrow via formulated fertilizer, at sowing time. Top-dressing comprised the application of 120 kg ha-1 of K2O divided into two equal doses at 45 and 80 DAS. Top-dressing N doses were split into 5 doses applied at 45 (25% of N), 80 (25% of N), 110 (30% of N) and 140 (20% of N) DAS (CQFS-RS/SC, 2016CQFS - Comissão de Química e Fertilidade do Solo - RS/SC (2016) Manual de adubação e calagem para os estados do Rio Grande do Sul e de Santa Catarina. 11ª ed. Porto Alegre, Sociedade Brasileira de Ciência do Solo – Núcleo Regional Sul. 376p.).

Experiments 1 and 2 have used onion cv. Mulata, whereas experiment 3 used onion cv. Salto Grande. Onion seeds were treated with fungicides pyraclostrobin and thiophanate methyl, as well as with insecticide fipronil. Invasive plants, pests and diseases were controlled based on spraying with chemical products registered for onion crops in the Ministry of Agriculture.

The last fully expanded leaf was collected from 10 plants at bulbing stage (at approximately 90 DAS) for leaf N content determination purposes. Leaves were dried in forced air circulation oven, at 65 ± 5 °C, until they reached constant mass; then, they were ground in Wiley mill. Samples were digested with sulfuric acid, and the N content in them was determined in micro-kjeldahl still (Tecnal, TE-0363, Brazil), based on Tedesco et al. (1995)Tedesco MJ, Gianello C, Bissani CA, Bohnen H & Volkweiss SJ (1995) Análise de solo, planta e outros materiais. 2ª ed. Porto Alegre, Ufrgs. 174p..

Bulbs were harvested at 170 DAS, when approximately 80% of plants showed shoot popping. Plants’ shoot was cut; bulbs were placed in plastic boxes and stored in shed at room temperature for approximately 10 days, for pre-curing purposes. Subsequently, bulbs were separated into commercial and non-commercial classes, based on Maara (1995)MAARA - Ministério da Agricultura, Abastecimento e Reforma Agrária (1995) Portaria nº 529, de 18 de agosto de 1995. Norma de identidade, qualidade, acondicionamento, embalagens e apresentação da cebola. DOU 01/09/1995, Seção 1, p.94.. All commercial bulbs were placed in plastic boxes, stored in shed at room temperature and evaluated again after 150 days in order to determine post-harvest losses (%).

Data were subjected to analysis of variance and to regression analysis for quantitative data; bifactorial comparisons between N doses and sources were performed. All analyses were carried out in R software (R Development Core Team, 2020R Development Core Team (2022) R: A language and environment for statistical computing. Available at: https://www.R-project.org/. Accessed on: December 10th, 2022.
https://www.R-project.org/...
). Regressions were applied to adjust the polynomial degree in order to establish the maximum technical efficiency (MTE) and economic efficiency (MEE) of the variables of interest, based on equation 1:

y = a ± b 1 x ± b 2 x 2 (1)

Equation 2 was used to estimate the MTE:

M T E = b 1 : 2 b 2 (2)

Equation 3 was used for the estimation of the MEE:

M E E = t w b 1 2 b 2 (3)

Where: t is the value of the input (nitrogen source) and w is the marketable value of the product (onion).

The average price of UR, CN, AN and AS in the year 2016 was US$0.77, 6.18, 1.34 and 1.91 kg-1 of N, respectively, and US$0.86, 6.76, 1.47 and 2.09 kg-1 of N, in the year 2017 (Conab, 2021aConab - Companhia Nacional de Abastecimento (2021a) Relatório de Insumos Agropecuários. Available at: https://www.conab.gov.br/info-agro/precos. Accessed on: June 21rst, 2023.
https://www.conab.gov.br/info-agro/preco...
). The average price of a kilogram of marketable onion in the years 2016 and 2017 was US$0.19 kg-1 (Conab, 2021bConab - Companhia Nacional de Abastecimento (2021b) Preço da cebola. Available at: http://sisdep.conab.gov.br/precosiagroweb/. Accessed on: June 21rst, 2023.
http://sisdep.conab.gov.br/precosiagrowe...
).

Critical leaf N level was estimated through the regression equation obtained by associating MTE with leaf N contents.

RESULTS AND DISCUSSION

Climate differed between the two crop seasons (Figure 1), since there were considerably higher and better distributed rainfall events in 2016 (780 mm) than in 2017 (564 mm).

Nitrogen sources tested in experiment 1 – i.e., urea, ammonium nitrate and calcium nitrate, which were added with ammonium sulfate in experiments 2 and 3 - did not show difference in commercial bulb yield (Figure 2), post-harvest losses (Figure 3), distribution in commercial classes (Figure 4) and leaf N levels (Figure 5). Lack of N sources’ effect on onions was also reported in other studies (Sullivan et al., 2001Sullivan DM, Brown BD, Shock CC, Horneck DA, Stevens RG, Pelter GQ & Feibert EBG (2001) Nutrient management for onions in the Pacific Northwest. Oregon, Oregon State University. 28p.; Boyhan et al., 2007Boyhan GE, Torrance RL & Hill CR (2007) Effects of nitrogen, phosphorus, and potassium rates and fertilizer sources on yield and leaf nutrient status of short-day onions. HortScience, 42:653-660.). According to the aforementioned authors, splitting top-dressing N applications into smaller doses, based on the N demand curve, is more important than the used N source.

Figure 2
Doses of maximum technical efficiency (MTE) and maximum economic efficiency (MEE) for commercial onion yield in the three experiments, at different N doses (70, 140, 210, 280 and 350 kg ha-1) applied as top-dressing and treatment without N application. *: Significant at 5% probability level.
Figure 3
Post-harvest losses based on N doses (70, 140, 210, 280 and 350 kg ha-1) and sources (calcium nitrate (Ca(NO3-)2), ammonium nitrate (NO3NH4), ammonium sulfate ((NH4NO3)) and urea applied as top-dressing, and on treatment without N application in onion crop grown under NTS in experiment 2. *: Significant at 5% probability level.
Figure 4
Onion production rate in five commercial classes based on nitrogen rates (70, 140, 210, 280 and 350 kg ha-1) applied as top-dressing and treatment without N application, in all three experiments. Different letters indicate differences between treatments (Tukey, 0.05).
Figure 5
Leaf nitrogen contents based on N doses (70, 140, 210, 280 and 350 kg ha-1) applied as top-dressing and treatment without N application, in onion crop grown in all three experiments - experiment 1 does not present treatment with N dose of 350 kg (Statistical significance level at 5%).

The tested N sources provide different N concentrations in their amide (e.g., urea), ammoniacal (e.g., ammonium sulfate) and nitric (e.g., calcium nitrate) forms. Some studies have evidenced positive effect of N source combinations on species belonging to genus Allium. Gamiely et al. (1991)Gamiely S, Randle WM, Mills HA & Smittle DA (1991) Onion plant growth, bulb quality, and water uptake following ammonium and nitrate nutrition. Hortscience, 26:1061-1063. have shown that nitrate and ammonium supply at ratio 1:3 has favored the production of onion leaves, roots and bulbs. NH4-NO3- applications to Allium tuberosum, at ratios 50:50 and 75:25, were the most suitable for the species quality and growth (Sun et al., 2014Sun YD, Luo WR & Liu HC (2014) Effects of different nitrogen forms on the nutritional quality and physiological characteristics of chinese chives seedlings. Plant, Soil and Environment, 60:216-220.). The application of calcium nitrate and ammonium nitrate in two crops investigated in the state of Georgia (USA) has increased the total weight of onions when N concentrations increased from 84 kg ha-1 to 168 kg ha-1, in comparison to results recorded for sodium nitrate, potassium sodium nitrate and potassium nitrate (Batal et al., 1994Batal KM, Bondari K, Granberry DM & Mullinix BG (1994) Effects of source, rate, and frequency of N application on yield, marketable grades and rot incidence of sweet onion (Allium cepa L. cv. Granex-33). Journal of Horticultural Science, 69:1043-1051.). In addition, the aforementioned authors have shown that ammonium nitrate was capable of increasing the production of onions belonging to larger diameter classes.

Nitrate is the main N form absorbed by onions (Geisseler et al., 2022Geisseler D, Ortiz RS & Diazc J (2022) Nitrogen nutrition and fertilization of onions (Allium cepa l.) – a literature review. Scientia Horticulturae, 291:110591.). Moreover, soil and climate features in sub-tropical regions favor amide and ammoniacal N transformation into NO3- (Silvia & Bohannan, 2016Silvia P & Bohannan BJM (2016) Ecology of nitrogen fixing, nitrifying, and denitrifying microorganisms in tropical forest soils. Frontiers in Microbiology, 7:1045.). Therefore, the tested N sources may have supplied different NH4-NO3- rates to onion plants, and they did not affect onion plants’ growth and yield.

Urea N losses due to NH3 volatilization may have been minimized by irrigation after fertilizer application (Viero et al., 2015Viero F, Bayer C, Vieira RCB & Carniel E (2015) Management of irrigation and nitrogen fertilizers to reduce ammonia volatilization. Revista Brasileira de Ciência do Solo, 39:1737-1743.). Soil acidification promoted by ammonia sources (Bindraban et al., 2015Bindraban PS, Dimkpa C, Nagarajan L, Roy A & Rabbinge R (2015) Revisiting fertilisers and fertilisation strategies for improved nutrient uptake by plants. Biology and Fertility of Soils, 51:897-911.) has also shown insignificant negative effects on results in the present study. The addition of Ca and S deriving from calcium nitrate and ammonium sulfate sources, respectively, did not have impact on the current results. Soil Ca and S contents (Table 1) were higher than the critical values recommended by CQFS-RS/SC (2016) for onion - 4.0 cmolc cm-3 and 15 mg dm-3, respectively.

Maximum technical efficiency (MTE) in experiment 1 was achieved at N dose of 195.8 kg ha-1; it recorded commercial onion production of 79,410.7 kg ha-1 (Figure 1). On the other hand, MTE in experiments 2 and 3 was achieved at higher N doses - 258.4 kg ha-1 and 270.7 kg ha-1 –; these experiments recorded commercial onion yield of 65,491.2 kg ha-1 and 56,391.2 kg ha-1, respectively. On the other hand, maximum economic efficiency (MEE) in experiment 1, 2 and 3 was achieved at N dose of 183.1, 230.1 and 235.0 kg ha-1, respectively. The difference between the doses of MTE and MEE, were 12.7, 28.3, and 35.7 kg N ha-1. This reduction in fertilizer application causes the decrease of only 1,885.0, 200.7 and 235.7 kg ha-1 of marketable onion, respectively in experiment 1, 2 and 3.

CQFS-RS/SC (2016) recommends using 288 kg ha-1 of N for expected onion yield of 70.000 kg ha-1. MTE doses obtained in experiments 2 and 3 in the present study were close to the official recommendation, mainly if one takes into consideration that CQFS-RS/SC (2016) has suggested reducing the N dose by up to 25% in consolidated no-till system, as observed in experiment 2. However, MTE in experiment 1 was achieved at N dose 47% lower than the recommended one. Experiment 1 was conducted under CTS, whose management is well-known for increasing the efficiency of N applied in these production systems (Silva et al., 2020Silva PCG, Tiritan CS, Echer FR, Cordeiro CFS, Rebonatti MD & Santos CH (2020) No-tillage and crop rotation increase crop yields and nitrogen stocks in sandy soils under agroclimatic risk. Field Crops Research, 258:107947.; Yang et al., 2020Yang H, Ngkun Wu G, Mo P, Chen S, Wang S, Xiao Y, Ma H, Wen T, Guo X & Fan G (2020) The combined effects of maize straw mulch and no-tillage on grain yield and water and nitrogen use efficiency of dry-land winter wheat (Triticum aestivum L.). Soil and Tillage Research, 197:104485.), mainly by increasing OM and N availability and by improving soil quality (Tiritan et al., 2016Tiritan CS, Bül LT, Crusciol CAC, Carmeis Filho ACA, Dirceu M, Fernandes DM & Nascente AS (2016) Tillage system and lime application in a tropical region: soil chemical fertility and corn yield in succession to degraded pastures. Soil and Tillage Research, 155:437-447.; Daigh et al., 2018Daigh ALM, Dick WA, Helmersc MJ, Lal R, Lauer JG, Nafziger E, Pederson CH, Strock J, Villamil M, Mukherjee A & Cruse R (2018) Yields and yield stability of no-till and chisel-plow fields in the midwestern us corn belt. Field Crops Research, 218:243-253.).

Assumingly, the higher performance of plants subjected to lower N doses in NTS is explained by N produced by soybean and black oat straw decomposition – these crops were precursors to onion sowing. This N likely replaced most of the applied mineral N. According to Kurtz et al. (2016)Kurtz C, Pauletti V, Fayad J & Vieira Neto J (2016) Crescimento e absorção de nutrientes pela cultivar de cebola bola precoce. Horticultura Brasiliera, 34:279-288., the estimated N uptake by onions reached 409 mg plant-1, which corresponded to N extraction of 101.4 kg ha-1. The aforementioned authors have pointed out that the amount of absorbed N was 35.2% higher than that added by mineral fertilization; this finding highlights the important contribution of soil organic matter in N supply.

Experiments 1 and 3 did not show difference in onion losses after storage for approximately 150 days. However, storage losses presented quadratic increase associated with calcium nitrate source and linear increase associated with urea in experiment 02 (Figure 3). Post-harvest losses reached approximately 20% at the highest N doses.

Class-2 bulbs, which have low commercial value, recorded increased participation in commercial yield due to lack of N in experiments 2 and 3 (Figure 4). Class-4 bulbs, which have high commercial value, recorded increased participation in commercial yield due to N application in experiments 1 and 2. However, N application in experiment 1 reduced the participation of class-3 onions in commercial yield. According to Rodrigues et al. (2015)Rodrigues GSO, Grangeiro RLC, Negreiros MZ, Silva AC & Novo Júnior J (2015) Quality of onion due to nitrogen doses and planting times. Revista Caatinga, 28:239-247., class-3 and -4 onions are commercially desirable, since these classes are preferred by the consumer market and enable producers to get higher marketing price. These very same authors recorded yield by 86% in these two onion classes, and considered 168 kg ha-1 of N as the efficient dose to be applied to this crop type.

Leaf N levels recorded quadratic increase due to the application of increasing N doses as top-dressing, in all three experiments (Figure 5). Maximum estimated values reached 37.9 g kg-1, after the application of 185.9 kg N ha-1 in experiment 1; 28.9 g kg-1, after the application of 288.6 kg N ha-1 in experiment 2; and 28.9 g kg-1, after the application of 329.5 kg N ha-1 in experiment 3. Differences between cultivars and different climates between crop seasons can explain these variations. Nitrogen application has also increased N content in onions in studies carried out by Kurtz et al. (2012)Kurtz C, Ernani PR, Coimbra JLM & Petry E (2012) Rendimento de cebola e conservação pós-colheita em função da dose e do parcelamento de nitrogênio. Revista Brasileira de Ciência do Solo, 36:865-875., who observed maximum N levels of 40, 35 and 32 g kg-1 after the application of 237, 136 and 150 kg N ha-1, respectively, in three consecutive onion crops. Rodrigues et al. (2018)Rodrigues GSO, Grangeiro RLC, Lima JSS, Chaves AP, Bezerra Neto F, Medeiros JF & Novo Júnior J (2018) Onion yield as a function of nitrogen dose. Revista de Ciências Agrárias, 41:46-51. recorded maximum estimated value for leaf N content equal to 32.7 g kg-1 at N dose of 168 kg ha-1, and 41.2 g kg-1 at N dose of 67 kg ha-1, in two different experiments. Relative commercial yield recorded quadratic increase due to leaf N content (Figure 6) - maximum commercial yield was obtained at leaf N content of 31.1 g kg-1.

Figure 6
Association between leaf N contents and relative commercial yield in 3 experiments conducted with different N sources and doses.

CONCLUSIONS

Nitrogen, ammonium nitrate and sulfate, calcium nitrate and urea sources did not affect onion yield parameters, leaf N content and postharvest losses;

The maximum technical efficiency recorded for bulb yield was observed at N doses of 195.8 kg ha-1 and 258.4 kg ha-1 in the no-tillage system (NTS) and at N dose of 270.7 kg ha-1 in the conventional tillage system (CTS).

Onion postharvest losses took place as N doses deriving from calcium nitrate and urea sources increased in NTS.

Maximum relative commercial yield was associated with 31.1 g kg-1 of leaf N.

ACKNOWLEDGMENTS, FINANCIAL SUPPORT AND FULL DISCLOSURE

We thank the anonymous reviewers for their contribution to manuscript. This article was supported financially by Santa Catarina State Agricultural Research and Rural Extension Agency (Epagri). No potential conflict of interest was reported by the authors.

REFERENCES

  • Alsina M, Borges ACF & Smart DR (2013) Spatio temporal variation of event related N2O and CH4 emissions during fertigation in a California almond orchard. Ecosphere, 4:01-21.
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  • Batal KM, Bondari K, Granberry DM & Mullinix BG (1994) Effects of source, rate, and frequency of N application on yield, marketable grades and rot incidence of sweet onion (Allium cepa L. cv. Granex-33). Journal of Horticultural Science, 69:1043-1051.
  • Bhaduri D, Purakayastha TJ, Patra AK, Singh M & Wilson BR (2017) Biological indicators of soil quality in a long-term rice–wheat system on the Indo-Gangetic plain: combined effect of tillage-water-nutrient management. Environmental Earth Sciences, 76:202.
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Publication Dates

  • Publication in this collection
    11 Dec 2023
  • Date of issue
    2023

History

  • Received
    12 May 2022
  • Accepted
    05 July 2023
Universidade Federal de Viçosa Av. Peter Henry Rolfs, s/n, 36570-000 Viçosa, Minas Gerais Brasil, Tel./Fax: (55 31) 3612-2078 - Viçosa - MG - Brazil
E-mail: ceres@ufv.br