Nitrogen Uptake and Use Efficiency in Winter Camelina with Applied N

Abstract

Maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotations in the upper Midwest are highly productive. However, these narrow rotations are followed by a long winter fallow period. Over time, this has contributed to the loss of agroecological functioning, including increased ground water pollution from nitrate-nitrogen (NO₃–N). Winter camelina [Camelina sativa (L.) Crantz] is a third crop that could grow during this fallow period, but its nitrogen (N) use and efficiency are not well known. A study was conducted at three locations in the U.S. upper Midwest to determine the N uptake and use efficiency of winter camelina in response to applied N and N application timing. Agronomic efficiency (AE), internal efficiency (IE), and nitrogen recovery efficiency (NRE) tended to decrease with increasing N rates, especially beyond 67 kg N ha⁻¹ in most instances. Total N uptake ranged from 34 to 176 kg ha⁻¹ across N rates, and was on average 1.5 fold the applied rate. Based on the observed decline in N use efficiency with increasing N rates, an application rate of 67 kg N ha⁻¹ appears to balance efficient N use, high yield, and lower environmental risk compared to higher N rates.

1. Introduction

Upper Midwestern agriculture is dominated by the maize-soybean rotation. In 2023, Minnesota planted crops on over 50% of its 20 million total hectares, approximately 60% of which was planted in maize or soybean, producing over 11 billion USD [1]. This productive system has resulted in negative agroecological effects such as increased nitrate nitrogen (NO₃–N) leaching, greenhouse gas emissions, and soil erosion [2,3]. A major contributor of these negative environmental impacts is the fallow period from early fall to late spring. Lost NO₃–N comes at a significant cost to farmers in the form of lost input, estimated at 500 million USD and to their communities in the form of NO₃–N treatment of drinking water [4]. In addition to the environmental and economic costs, the fallow period is a lost opportunity for additional biomass or grain production.

Double cropping is a form of temporal intensification where two crops are harvested in a single season. This system may help farmers adopt more diverse and intensive rotations that can provide ecological benefit while also providing an economic return [5,6]. A variety of summer annual crops such as soybean, sunflower, and sorghum can be paired with a short season winter annual like camelina grown during the fallow period [5,7]. Additionally, the U.S. commercial aviation industry, Navy, and Airforce have a growing interest in crops that can be used to produce biofuel; winter annual oilseeds could meet some of that demand. Winter camelina has high seed oil and protein content with potential for incorporation as a third crop in rotations in the upper Midwest due to its short relative maturity and winter hardiness [5]. Camelina can be used to produce biodiesel similar to the more common and costly soybean and can fit into current production systems with existing machinery [8].

While double cropping with winter camelina could reduce some of the negative environmental impacts of conventional rotations, understanding of N uptake and use efficiency of any added crop in this high-N system is important for maximizing agronomic and ecological benefits [9,10]. Nitrogen use efficiency (NUE) indices are metrics to assess how well crops use N to achieve desired production outcomes [11]. Breeding for increased NUE is second only to drought when considering abiotic stress improvement for a crop [12]. Existing research on spring camelina fertilization in Minnesota showed that agronomic efficiency decreased from 4.28 to 1.29 kg kg⁻¹ as fertilizer N increased from 34 kg ha⁻¹ to 202 kg ha⁻¹. Additionally, residual soil N after spring camelina harvest increased from approximately 50 kg N ha⁻¹ in unfertilized plots to over 150 kg N ha⁻¹ in plots receiving the maximum fertilization rate of 200 kg N ha⁻¹ [13]. In a recent study [14], which provided the biomass, grain yield, and grain quality data used in this analysis, it was found that winter camelina yield increased by up to 1200 kg ha⁻¹ with N application rates ranging from 0 to 135 kg ha⁻¹. Additionally, residual soil N increasing by up to 24 kg N ha⁻¹ across these N rates. These studies illustrate the importance finding the right balance between providing needed N and considering the potential environmental consequences of applying higher N rates which could result in higher residual soil N.

Nitrogen uptake and use efficiency research on camelina has focused on the spring biotype (planted in spring and harvested in late summer) with a dearth of studies on winter biotypes (planted in fall and harvest in late spring) grown in the upper Midwest. The goal of this study was to determine the use efficiency and N in winter camelina. The hypothesis was that N fertilization and application timing affect the use efficiency and N in winter camelina. The objectives were to determine the N uptake and use efficiency of winter camelina in response to N application.

2. Materials and Methods

2.1. Experimental Sites

Field experiments were conducted at three Minnesota locations from fall 2018 to fall 2020. Locations included the University of Minnesota Southwest Research and Outreach Center (SWROC; 44°14′02.20″ N 95°18′6.87″ W) near Lamberton, MN, University of Minnesota West Central Research and Outreach Center (WCROC; 45°35′37.17″ N 95°52′42.63″ W) near Morris, MN, and the Swan Lake Research Farm (SLRF; 45°41′04.2″ N 95°47′58.9″ W) of the USDA-ARS near Morris, MN. Soil properties vary across locations (

Table 1. Average properties in the 0 to 30 cm depths of soil at the three experimental sites in 2018.

Site	Textural Class	OM	pH	CEC	NO3–N	Bray P	K	Ca	Mg
		%		meq 100 g−1	ppm
SWROC	Clay loam	3.5	6.4	19	3.8	8	116	2402	581
WCROC	Clay loam	6.5	5.8	27	5.5	13	149	3002	594
SLRF	Loam	3.0	7.4	20	5.9	11	166	3095	467

), representing the agricultural soils in the region. Dominant soils were characterized as Normania loam (fine-loamy, mixed, superactive, mesic Aquic Hapludolls) and Amiret loam (fine-loamy, mixed, superactive, mesic Calcic Hapludolls) at SWROC, Nutley Flom clay loam (fine, smectitic, frigid chromic Hapluclerts and fine-loamy, mixed, superactive, frigid Typic Encloaquolls) at WCROC, and Barnes loam (fine-loamy, mixed, superactive, frigid Calcic Hapludolls) at SLRF [15].

The region has a continental climate with long, cold winters with short, wet springs and summers. The 25-year long-term average (LTA) temperatures and rainfall are 7 °C and 737 mm at SWROC and 5.8 °C and 670 mm at WCROC and SLRF. The USDA climate hardiness zones are 4b at SWROC and 4a at WCROC and SLRF (USDA-ARS). Long-term air temperature and precipitation data were obtained from the National Oceanic and Atmospheric Administration [16].

2.2. Experimental Design

The experiment was a completely randomized design in a 2 × 5 factorial. Factor A consisted of two N fertilization strategies: a spring-only application (Time 1) and a fall-spring split application (Time 2, 33% fall and 67% spring). Factor B consisted of five N fertilizer rates (0, 33, 67, 100, 135 kg ha⁻¹); plots were 3 m × 5 m with four replications.

2.3. Agronomic Management

Every year at each of the three sites, winter camelina was planted following small grains, which allowed for timely planting in the fall. Additionally, small grains helped reduce residual soil N creating a lower and more even soil N. Herbicides trifluralin N-dipropyl-4-(trifluromerhyl) aniline and glyphosate [N-(phosphonomehtyl) glycine] at 2.0 kg a.e. ha⁻¹ were used at SWROC and SLRF, respectively, with no preplant herbicide used at WCROC, due to planting soon after harvest and tillage of previous crop. Winter camelina cultivar, Joelle (USDA), was drill-seeded at a rate of 9 kg ha⁻¹ at SWROC and WCROC and 8 kg ha⁻¹ at SLRF. Rows were planted 19 cm apart and camelina was planted in mid-September to early October in SWROC and WCROC and early September to mid-September at SLRF.

Winter camelina is typically fertilized in early spring. However, since small grains are often fertilized at planting, a fall-spring split fertilization application timing was compared with a spring only. The fall portion of the fall-spring split N application (Time 2) was applied in corresponding plots at preplanting and incorporated. The spring only application (Time 1) was applied in all plots at the inflorescence emergence stage (BBCH50). Fertilizer used was N_trt-30-30, (where N_trt represents the N treatment amount) as urea (NH₂–CO–NH₂) triple superphosphate (P₂O₅) and muriate of potash (K₂O). Camelina was harvested when >90% of silicles were brown and dry.

2.4. Data Collection

Due to weather conditions, trials at SWROC and WCROC in 2019 produced limited data compounded by errors in sample processing for N analysis. Additionally, no data were collected at WCROC during the 2020 growing season due to difficulties during the COVID-19 pandemic. As a result, the study includes two years (2019 and 2020) of data from SLRF and SWROC and one year (2019) from WCROC. Above-ground biomass at maturity was harvested within a 1 m² quadrat. Biomass was oven-dried at 60 °C to a constant weight and threshed for grain yield using a belt thresher (Almaco, BT14 Belt Thresher, Nevada, IA, USA). Biomass and grain were ground and analyzed for N using an Elementar Vario EL Cube (Elementar Americas Inc., Ronkonkoma, NY, USA).

Nitrogen use efficiency indices included nitrogen recovery efficiency (NRE), agronomic efficiency (AE), and internal efficiency (IE). Additionally, the nitrogen exported in grain (NE) and total N uptake (NU) were calculated. Nitrogen uptake is the total N uptake of the biomass at physiological maturity (Equation (1), kg ha⁻¹). Nitrogen recovery efficiency is the ability of mature above ground biomass to capture N compared to a non-fertilized control (Equation (2), kg kg⁻¹). Agronomic efficiency measures the increase in grain yield per unit of N applied compared to a non-fertilized control (Equation (3), kg kg⁻¹); Internal Efficiency indicates how efficiently the N taken up by the crop is converted into grain yield (Equation (4), kg kg⁻¹). Finally, NE is the amount of N removed from the system in the harvested grain (Equation (5), kg ha⁻¹) [17,18].

$$\mathrm{N}\mathrm{U}=Biomass\times {Biomass}_N$$

(1)

$$\mathrm{N}\mathrm{R}\mathrm{E}=\frac{{NU}_{Nrate}-{NU}_{N0}}{N_{applied}}$$

(2)

$$\mathrm{A}\mathrm{E}=\frac{{GrainYield}_{Nrate}-{GrainYield}_{N0}}{N_{applied}}$$

(3)

$$\mathrm{I}\mathrm{E}=\frac{GrainYield}{NU}$$

(4)

$$\mathrm{N}\mathrm{E}=GrainYield\times {GrainYield}_{N\%}$$

(5)

2.5. Statistical Analysis

All data were analyzed using R statistical software v2023.06.2 (Posit 2023, Boston, MA, USA). Nitrogen exported, NU, AE, NRE, and IE were analyzed using the linear mixed effects model ANOVA to determine significant effects and interactions. Year, fertilization application time, and N rate were considered fixed effects. Regression analysis was performed to find the functional relationship between a given variable and N rate using the least squares method. Models were used that minimized the sum of the squared errors and showed the highest r² values. Parameters and fixed effects were assessed for linear or quadratic relationships. Locations were analyzed independently due to the significant effects of location. Assumptions of normality and constant variance of model residuals were visually assessed. If a combined analysis showed significant interactions, response variables were separated for ANOVA. Post hoc analysis was conducted using Tukey’s honest significant difference (HSD) with the ‘agricolae’ package at p ≤ 0.05 to determine means separation for variables by treatment.

3. Results and Discussion

3.1. Weather Conditions

Weather conditions during the experimental years were described in depth in a recent study [14]. At all three locations, monthly average air temperatures were below the LTA by 2 to 3 °C in fall of 2018. The 2019 year was consistently colder than the LTA (Figure 1a). In 2020, the temperatures were closer to the LTA than previous years, but during the inflorescence emergence and flowering stages for camelina (April and May), air temperatures were 4 to 5 °C colder. Precipitation was higher than the LTA at all locations in 2019 and at SWROC in 2020, with a drier-than-average year in 2020 in both Morris locations. At SWROC in 2019, 80 mm more precipitation fell than the LTA in April, with 100 mm more in the fall after planting. This excessive fall precipitation potentially caused spring waterlogging stress for the 2020 crop, which may have contributed to lower grain and biomass yields. The sites at WCROC and SLRF experienced similar high rainfall in 2019, receiving 190 mm above the LTA. Precipitation in 2020 at SWROC was 32 mm higher than the LTA from January to July. Precipitation in 2020 at the Morris locations was lower than the LTA, with over 100 mm less from late-winter to late-spring (Figure 1b).

3.2. Nitrogen Uptake and Nitrogen Exported with Winter Camelina

Total N uptake was affected by year and N rate at SLRF and by N rate at SWROC (

Table 2. Significance of F values for fixed effect sources of variation for total N uptake, N exported in grain, agronomic efficiency (AE), nitrogen recovery efficiency (NRE), and internal efficiency (IE) by nitrogen rate (kg N ha⁻¹) of winter camelina grown at three locations from 2018 to 2019 and 2019 to 2020.

Location	Source of Variation	N Uptake	N Exported	AE	NRE	IE
SWROC	Year (Y)	−	***	***	−	−
	Application time (AT)	ns	ns	ns	ns	ns
	Nitrogen rate (NR)	***§	***	***	ns	*
	Y × AT	−	ns	ns	−	−
	Y × NR	−	ns	ns	−	−
	AT × NR	ns	ns	ns	*	ns
	Y × AT × NR	−	ns	**	−	−
WCROC	Year (Y)	−	−	−	−	−
	Application time (AT)	−	**	ns	−	−
	Nitrogen rate (NR)	−	***	***	−	−
	Y × AT	−	−	−	−	−
	Y × NR	−	−	−	−	−
	AT × NR	−	*	ns	−	−
	Y × AT × NR	−	−	−	−	−
SLRF	Year (Y)	***	***	ns	ns	***
	Application time (AT)	ns	ns	ns	ns	ns
	Nitrogen rate (NR)	***	***	***	ns	ns
	Y × AT	ns	ns	ns	ns	*
	Y × NR	ns	ns	ns	ns	*
	AT × NR	ns	ns	ns	ns	ns
	Y × AT × NR	ns	ns	ns	ns	ns

SWROC = Southwest Research and Outreach Center near Lamberton MN; WCROC = West Central Research and Outreach Center in Morris, MN; SLRF = Swan Lake Research Farm in Morris, MN. ^§ Variables with ***, **, and * are significant at the 0.001, 0.01, and 0.05 levels. ns denotes not significant and − denotes not available.

). Significant differences between N rates were found in both locations in 2020; N uptake was highest at or above the rate of 100 kg N ha⁻¹ at SWROC and at or above the rate of 67 kg N ha⁻¹ at SLRF (

Table 3. Effect of fertilizer N and application timing on total N uptake, N exported in grain, agronomic efficiency (AE), nitrogen recovery efficiency (NRE), and internal efficiency (IE) by N rate (kg N ha⁻¹) of winter camelina grown at three Minnesota locations from 2018 to 2019 and 2019 to 2020.

Location	Year	N Rate	N Uptake	N Exported		AE		NRE		IE
		(kg ha−1)				T1 †	T2	T1	T2	T1	T2
SWROC	2019	0	−	61 c		−	−	−	−	−	−
		33	−	76 bc		11.4 ab	19.0 a	−	−	−	−
		67	−	93 ab		13.8 a	9.9 b	−	−	−	−
		100	−	99 a		9.4 ab	9.2 b	−	−	−	−
		135	−	89 ab		4.8 b	6.9 b	−	−	−	−
	2020	0	93 c	40 c		−	−	−	−	13.7 a
		33	138 b	56 b		15.7 a	10.0 a	78 a	33 a	13.0 a
		67	147 b	61 b		6.3 b	9.4 a	26 b	47 a	13.2 a
		100	175 a	74 a		7.8 b	8.0 ab	34 ab	61 a	13.1 a
		135	176 a	67 ab		4.1 b	5.4 b	37 ab	43 a	11.5 a
WCROC	2019	0	−	63 b	98 b	−		−	−	−	−
		33	−	93 a	108 ab	19.6 a		−	−	−	−
		67	−	100 a	109 ab	11.0 b		−	−	−	−
		100	−	96 a	105 ab	6.3 b		−	−	−	−
		135	−	114 a	122 a	7.3 b		−	−	−	−
SLRF	2019	0	75 a	50 b		−		−		14.3 A §	12.6 A
		33	78 a	64 ab		9.0 a±		28
		67	98 a	80 a		6.5 a
		100	98 a	60 ab		3.2 b
		135	115 a	68 ab		1.8 b
	2020	0	34 c	11 b		Year NS, 2020 combined with 2019		Year and N rate NS, 2020 combined with 2019		8.2 B	10.4 A
		33	50 bc	27 a
		67	57 ab	29 a
		100	60 ab	28 a
		135	68 a	28 a

SWROC = Southwest Research and Outreach Center near Lamberton MN; WCROC = West Central Research and Outreach Center in Morris, MN; SLRF = Swan Lake Research Farm in Morris, MN. † T1 denotes fertilization Time 1, one application in spring; T2 denotes fertilization Time 2, split (33%) fall and (67%) spring. Data centered between strategies show that the strategy was not significant. ± Year was not significant for AE at SLRF, and the single set of data by N rate represent averages per treatment across years 2019 and 2020. For a given location and year, means followed by different letters within a column are significantly different at p ≤ 0.05. § Upper case letters are used for significant differences for strategies.

). At SLRF in 2020, total N uptake increased with an increase in fertilizer N, but differences were not significant beyond the rate of 67 kg ha⁻¹. At all locations and years, a quadratic relationship best described the response of winter camelina to fertilizer N. At SLRF, total N uptake increased 52% across N rates in 2019 and 97% in 2020. At SWROC, total N uptake increased 89% across N rates. Results from SWROC showed higher total N uptake compared to SLRF in either year. In this study, total N uptake across fertilizer N rates ranged from 34 to 176 kg ha⁻¹. These are higher than N uptake results in spring camelina which ranged from 10 to 132 kg N ha⁻¹ as reported by Malhi et al. [19] and 55 to 100 kg ha⁻¹ as reported by Johnson et al. [13]. The lowest N uptake in the current study was obtained in 2020 at SLRF while the highest was reported in 2020 at SWROC. At SWROC, total N uptake was higher than applied N in all N rates, suggesting that N mineralization during the season may have supplied additional N to winter camelina, a possibility also reported in a N fertilization study of spring camelina also conducted at SLRF in 2014 and 2015 [13]. Similarly, a study conducted in South Australia on canola, a close relative of camelina, reports that its N uptake was nearly double the amount of N applied [20].

Nitrogen exported was affected by N rate in all instances except with the fall-spring split application at WCROC in 2019 (Table 2). Nitrogen exported was significantly affected by year at SWROC and SLRF and by the N rate × application time interaction at WCROC. Significant differences between N rates were observed in every instance and a quadratic relationship best described the response of winter camelina grain N to fertilizer N. At SWROC and SLRF, the N exported from the 33 and 67 kg ha⁻¹ rates was significantly higher than in the unfertilized control. At WCROC, in Time 1, all rates were significantly higher than the control while in Time 2 only the highest rate was (Table 3). Among locations, N exported was highest at WCROC in 2019, where it ranged from 98 to 122 kg ha⁻¹, followed by SWROC from 40 to 99 kg ha⁻¹, and SLRF from 11 to 68 kg ha⁻¹. Nitrogen exported in 2019 was higher than 2020, mostly due to higher grain yield due to better growing conditions (mostly rainfall) at N fertilization. Most results from this study were within 23 to 72 kg ha⁻¹ reported for irrigated spring camelina for conditions in Arizona [21] and 50 to 67 kg ha⁻¹ reported for spring camelina by Johnson et al. (2019) [13]. Results from 2020 at SLRF were the lowest of the study due to low yields likely caused by a lack of spring soil moisture. In Minnesota, maximum winter camelina growth and canopy cover occurs during late spring (April–May). Low precipitation levels, such as at SLRF in 2020, could lead to reduced N uptake and grain yield.

3.3. Nitrogen Use Efficiency of Winter Camelina

Nitrogen recovery efficiency was significantly affected by the N rate × application time interaction at SWROC only (Table 2). At SWROC, NRE decreased sharply beyond the 33 kg N ha⁻¹ rate. Significant differences were found only in 2020, specifically with the spring-only application, between the 33 and 67 kg N ha⁻¹ rates (Table 3). The NRE was highest at lower and middle rates of applied N, but these differences were significant in only one instance. In this instance (Time 1 at SWROC in 2020), the NRE at 33 kg N ha⁻¹ was approximately double that of the higher rates because of high N scavenging at the 0 and 33 kg N ha⁻¹ rates which resulted in similar N uptake to the higher N rates. At SLRF, the low NRE value of 6% was due to little difference in biomass weight and N content between the 33 kg ha⁻¹ rate and the non-fertilized (control) treatments at SLRF in 2019. These results are similar to those reported for a study on spring camelina in Saskatchewan and Alberta, Canada, which averaged 35% NRE across N rates and declined 21% between the lowest and highest N rates (25 to 200 kg N ha⁻¹) [19]. Similar results were found in a camelina fertilization study in the desert of Nevada that reported the highest NRE at the lowest N application rate of 22 kg N ha⁻¹ and quickly declined with rates up to 90 kg N ha⁻¹ [22].

Agronomic efficiency was affected by the year × N rate × application time interaction at SWROC and by N rate at the SLRF and WCROC locations. Internal efficiency was affected by N rate at SWROC and by the year × N rate and year × application timing interactions at SLRF (Table 2). At all locations, AE declined at N rates beyond 33 kg N ha⁻¹ with significant differences and a quadratic relationship to N application found in all instances. Similarly, a quadratic relationship was found for the IE response to N rate at SWROC and SLRF. Significant differences were only found between strategies at SLRF in 2020, where IE was lower in the Time 1 (Table 3). In instances with significant differences between N rates, nitrogen use efficiency indices typically declined with N rates above 67 kg N ha⁻¹ (Table 3). For instance, AE decreased as much as 60% from 33 to 67 kg N ha⁻¹ and 50% from 67 to 100 kg N ha⁻¹; NRE declined in the Time 1 by as much as 64% between 33 and 67 kg N ha⁻¹ at SWROC; IE showed significant differences in Time 1, being 21% lower than the Time 2 in 2020 at SLRF. The AE of winter camelina in this study ranged from 1.0 to 19.6 kg kg⁻¹. Similarly, studies on spring camelina have reported AE values ranging from 1.3 to 24.8 kg kg⁻¹. Also, it is reported that the AE of spring camelina declines with increasing N rates, often exhibiting linear or quadratic relationships [13,19,22,23]. The IE of winter camelina from this study ranged from 6.2 to 18.8 kg kg⁻¹, similar to the 12.4 to 20.9 kg kg⁻¹ range reported for a spring camelina study conducted in Arizona [21]. Similarly, in a N fertilization × genotype study of spring canola, NRE was found to be highest at 0 and 100 kg N ha⁻¹ rates while IE was found to be highest at the 0 and 50 kg N ha⁻¹ rates [24].

Application timing was rarely significant in this study, possibly due to a flexible N requirement for this crop. This has also been found in a South Australia N fertilization × irrigation study of spring canola which found no significant differences between applications timings [25]. Additionally, there was generally a lack of significance for NRE at SLRF and for IE at both SWROC and SLRF. Nitrogen uptake at SLRF showed only minor significant differences, likely reducing the chance of finding differences in NRE and IE. At SWROC, while N uptake showed significant differences, it increased proportionally with yield, resulting in no response of IE across N rates. This suggests that winter camelina may use higher rates of N to produce more biomass rather than increasing grain yield. Considering the high N uptake (up to 4 fold the applied N rate in one instance) along with declining NUE, these results further indicate that winter camelina uses excess N primarily for biomass production (Table 3).

These results suggest that winter camelina could be managed as part of a sustainable cropping system if lower rates of N are applied, or it could be used as an excellent cover crop due to its effective uptake of N in the fall and spring. This is particularly beneficial for cold climates where cover crop options are currently limited. However, at high rates of N, winter camelina may contribute to N leaching, an issue already observed in maize and soybean rotations. Currently, winter camelina has received relatively low breeding investment compared to crops like canola or maize. Increased funding may lead to significant improvements in yield, NUE and other traits further strengthening its inclusion an role in sustainable cropping systems.

4. Conclusions

This study compared the effect of N-fertilization rates and application timing on winter camelina N uptake and use efficiency. Fertilizer application timing did not affect nitrogen uptake or the response and magnitude of nitrogen use efficiency. Nitrogen uptake was as high as 176 kg N ha⁻¹ and averaged 1.5 fold the applied amount, demonstrating that winter camelina is capable of up taking N. Nitrogen uptake was consistently higher than applied N at SWROC where soils are heavier, but not consistently at SLRF which has sandier soil. Although N uptake increased with increasing N rate in some cases, nitrogen use efficiency declined at higher rates. The most significant decreases in nitrogen use efficiency were observed in agronomic efficiency across all locations. Considering nitrogen use efficiency results and the yield increase from moderate application rates, a fertilization rate of 67 kg N ha⁻¹ for winter camelina in Minnesota could provide a balance of high yield and efficient nitrogen use.