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© 2004 Plant Management Network.
Accepted for publication 17 August 2004. Published 1 September 2004.

Winter Canola Survival and Yield Response to Nitrogen and Fall Phosphorus

Shawn P. Conley, Assistant Professor, Department of Agronomy, University of Missouri, Columbia 65211; David Bordovsky, Research Scientist, Texas A&M Chillicothe-Vernon Research and Extension Center, Vernon 76385; Charlie Rife, Research Assistant Professor, Department of Agronomy, Kansas State University, Manhattan 66506; and William J. Wiebold, Associate Professor, Department of Agronomy, University of Missouri, Columbia 65211

Corresponding author: Shawn P. Conley. conleysp@purdue.edu

Conley, S. P., Bordovsky, D., Rife, C., and Wiebold, W. J. 2004. Winter canola survival and yield response to nitrogen and fall phosphorus. Online. Crop Management doi:10.1094/CM-2004-0901-01-RS.

Abstract

The introduction of winter canola into the Great Plains will increase crop diversity and may increase profitability of existing cropping systems. In many parts of the region a major limitation of winter canola is winter survival. The objective of this research was to quantify the effect of nitrogen and phosphorus on winter canola survival and crop yield. Two locations in Missouri and one location in Texas were seeded to ‘Wichita’ winter canola in the 2001-2002 and 2002-2003 growing seasons. Fall N followed by spring N and fall P fertility treatments were applied in a randomized complete block factorial design. In Missouri, percent winter survival, bloom date, crop height, percent lodging, harvest maturity date, and grain yield response to N and P treatments varied among locations and years. Percent winter survival was greatest at Columbia, at 86 and 80% in 2002 and 2003, respectively. In contrast, grain yield was greatest at Novelty at 2100 and 2400 lb/acre in 2002 and 2003, respectively. In Texas, winter survival was greater than 85% in both years. Grain yield was 2900 and 990 lb/acre in 2002 and 2003, respectively. Shattering due to delayed harvest primarily caused decreased grain yield in 2003. Grain yield was greater at 50 lbs of fall N than when no fall N was applied. Fall P and spring N treatments had no influence on winter survival or crop yield. Our results suggest that winter canola can be successfully grown in the Great Plains and that proper management of N and P may increase winter survival and grain yield.

Introduction

Increased production of winter rapeseed (Brassica napus L.) in the Great Plains has been limited, in part, by winter survival concerns. Several crop management decisions including cultivar selection, planting date, plant density, and crop fertility may influence winter survival. Currently, the domestic market for rapeseed production is targeted at low erucic acid, low glucosinolate canola cultivars. The development of winter canola lines began in the 1980s. Early examples of these cultivars have proven to be less winter hardy than older, industrial-based cultivars (12). In the last decade however, a significant breeding effort has increased hardiness of both North American and European winter canola lines (15,16,17,18). Substantial research has also been conducted to characterize the effect of planting date on winter survival (3,11,13,20). The optimal planting date window for maximizing winter survival varies by geographic region within the Great Plains, however current recommendations suggest that winter canola should be planted six weeks before the average killing frost date (-4°C) in the region of interest (20).

Fall plant density will also play an important role in percent winter survival (19). Rife and Kochenower (19) reported increased levels of winterkill in thick stands when planted at optimum dates. They attributed this to natural thinning within the population; however, yield loss was not observed in these thinned stands. In contrast, Rife and Kochenower (19) observed an increase in winter survival, spring plant health, and grain yield in thin stands where plots were established two weeks prior to the optimum seeding date. They attributed this to a reduction in plant competition and the development of a more prostrate rosette. Few experiments, though, have quantified the effect of crop fertility on canola winter survival and crop yield in the Great Plains.

In winter wheat (Triticum aestivum L.), N timing and placement greatly influenced winter survival and crop yield. McKenzie et al. (10) reported that N fertilizer applied in the fall did not increase winterkill. They concluded that growers may apply all of the crop N requirements in the fall or apply a split-application of N to maximize crop yield. Also in winter wheat, Fowler and Brydon (4) stated that N placed near the seed at planting decreased winter survival and that winter damage to the crop was directly related to N rate.

N recommendations for winter wheat are approximately 1.75 lb/bu, whereas a winter canola crop requires N at approximately 3.0 lb/bu (14). Taking into account differences in yield potential between the two crops in the southern Great Plains region, the current N recommendation for winter canola is 30 to 40% of a wheat crop (20). Research pertaining to N application timing in canola has been inconsistent. Vullioud (22) found no advantage to splitting N applications whereas Anastasi et al. (1) reported a significant increase in grain yield when either two thirds or the entire N application rate was top dressed in the spring as opposed to the entire N rate applied at planting.

The application of fall N will stimulate fall growth, however excess fall growth may decrease soil moisture as well as move the growing point above the soil surface; both of which may reduce cold tolerance and decrease winter survival (3). Excess N may also be detrimental to seed oil content in winter canola (8). Therefore, when considering N management in winter canola it is critical to characterize the pattern of N uptake by the crop to maximize winter survival, grain yield, and oil content (7).

Based on research with other crops, P deficiency coupled with N by P imbalances may also affect canola winter survival and yield (5). In winter wheat, the application of fall N alone decreased winter survival whereas P alone or a balanced application of N and P increased winter survival (6). Lafond and Gan (9) reported that though seed placed P did not affect winter wheat stand, grain yield was increased. In spring canola, Brennan and Bolland (2) reported that yield increased as P rate increased. The objective of this experiment was to quantify the effect of N and P on winter canola survival and crop yield in the Great Plains.

Field Experiments in Missouri

Field experiments were initiated at two locations in the 2001-2002 and 2002-2003 winter growing seasons. The two locations were the University of Missouri Bradford Research and Extension Center located near Columbia, MO and the Greenley Memorial Research Center located near Novelty, MO. The soil type at Columbia was a Mexico silt loam (fine, smectic, mesic Aeric Vertic Epiaqualfs) with 2.6% organic matter and pH 7.1. The soil type at Novelty was a Putnam silt loam (fine, smectic, mesic Vertic Albaqualfs) with 2.7% organic matter and pH 6.2. The experimental design at each location was a randomized complete-block 4-×-4 factorial with four replications. The N treatments were fall N rates followed by spring N rates of 0/100, 34/66, 66/34, and 100/0 lb/acre. The P treatments were fall rates of 0, 5, 10, and 20 lb/acre. The N source was urea and the P source was triple superphosphate. The plot area was 100 ft².

‘Wichita’ canola was drilled in rows spaced 7.5 inches apart at a seeding rate of 8 lb/acre. Prior to planting in each year the ground was tilled using a field cultivator. Canola followed oat (Avena sativa L.) at Novelty and soybean (Glycine max (L.) Merr.) at Columbia in 2001. Canola followed winter wheat at both locations in 2002. Canola was seeded on 5 September and 12 September at Novelty in 2001 and 2002, respectively. Canola was seeded on 6 September and 10 September at Columbia in 2001 and 2002, respectively. Prior to planting, soil samples were taken to quantify residual N (ppm nitrate-N) and P (Bray-I) levels. At Columbia, initial N and P levels were 12 and 46, respectively, in 2002 and 22 and 55, respectively, in 2003. At Novelty, initial N and P levels were 15 and 28, respectively, in 2002 and 18 and 33, respectively, in 2003. Potassium was applied to the canola crop according to soil test recommendations provided by the University of Missouri Soil and Plant Testing Laboratory. Weed control was accomplished with a pre-emergence application of trifluralin.

Field Experiments in Texas

Field experiments were initiated in the 2001-2002 and 2002-2003 winter growing seasons at the Texas A&M Munday Research Station located near Munday, TX. The soil type at Munday was a Miles fine sandy loam (fine-loamy, mixed, superactive, thermic Typic Paleustalfs) with 0.8% organic matter and pH 7.5. The experimental design at Munday was a randomized complete-block 3-×-3-×-2 factorial with six replications. The factors were fall N, fall P, and spring N. The fall N treatments were 0, 25, and 50 lb/acre. The P treatments were fall rates of 0, 10, and 20 lb/acre. The spring N treatments were 25 and 50 lb/acre. The N source was urea and the P source was triple super phosphate. The plot area was 125 ft².

‘Wichita’ canola was drilled in rows spaced 10.0 inches apart at a seeding rate of 5 lb/acre. Prior to planting in each year the ground was tilled using a disk equipped with a drag. Canola was seeded following a fallow crop in each year. Canola was seeded on 19 September and 23 September at Munday in 2001and 2002, respectively. Prior to planting, soil samples were taken to quantify residual N (ppm nitrate-N) and P (Bray-I) levels. Initial N and P levels were 27 and 38, respectively, in 2002 and 8 and 52, respectively, in 2003. Soil tests indicated no potassium was needed in either year. Weed control was accomplished with a pre-emergence application of trifluralin. Insecticides were applied when needed to control aphid species.

Data Collection and Statistical Analysis

Fig. 1. Canola in bloom.

Visual estimates of percent winter survival were recorded each spring at green-up. Bloom date (date at which 50% of the plants have one or more open flowers) (Fig. 1) and harvest maturity date (date at which 90% of the plants have reached mature color) were recorded for each plot. Crop height, percent lodging, and percent shattering were recorded at harvest. Canola grain yield was adjusted to 8.5% moisture.

Analysis of variance statistics was performed using the PROC GLM procedure of SAS (21). Mean separations were accomplished using Fisher's protected LSD test. Bartlett’s test for homogeneity of variance was conducted prior to testing for year interactions. Comparisons among main N and P treatments were made using single degree of freedom contrasts. N and P treatment effects and all interactions were considered significant when P < 0.05.

Results in Missouri

Year by N and P interactions were significant (P < 0.001), therefore data were reported separately for each year (Tables 1 and 2). Within each year there were no N, P, or location interactions (P > 0.05), therefore data were pooled across main effects. In both years, percent winter survival was greatest at the Columbia location. Furthermore, bloom date and harvest maturity date were significantly earlier at Columbia. In contrast, canola grain yield was significantly greater at the Novelty location in both years. The canola crop was harvested prior to shattering in each year, however, significant lodging occurred at Columbia in 2003. Crop height differed between locations and years.

Table 1. Canola response to nitrogen and phosphorus fertilizer at Columbia and Novelty, MO in the 2001-2002 growing season.

 * LSD: Means within a column and treatment group were considered significantly different at alpha = 0.05.

Table 2. Canola response to nitrogen and phosphorus fertilizer at Columbia and Novelty, MO in the 2002-2003 growing season.

 * LSD: Means within a column and treatment group were considered significantly different at alpha = 0.05.

Results of N treatments were variable among locations and years (Tables 1 and 2). N treatments only affected crop height in 2002. In 2003, N treatments influenced percent winter survival, bloom date (Fig. 2), crop height, percent lodging, harvest maturity date, and crop yield. P treatments influenced crop height and crop yield in 2002 and percent winter survival in 2003. Single degree of freedom contrasts were used to compare the effect of split-N versus no split N, all fall N versus all spring N, and P versus no P treatments. In 2003, both bloom date and harvest maturity date were delayed in the all spring N treatment (0/100) when compared to the all fall N treatment (100/0) (P < 0.0001).

Fig. 2. Treatment effect on bloom date.

Results in Texas

Year by N and P interactions were not significant (P > 0.05), therefore data were pooled over years (Table 3). Percent winter survival and crop height were greater in 2003. Bloom date was significantly later in 2002. Percent lodging was also greater in 2002. Harvest maturity date was not collected. Canola grain yield was greater in 2002. Decreased grain yield in 2003 was due in part to increased pod shattering (Fig. 3) caused by delayed harvest.

Table 3. Canola response to nitrogen and phosphorus fertilizer at Munday, TX in the 2001-2002 and 2002-2003 growing seasons.

 * LSD: Means within a column and treatment group were considered significantly different at alpha = 0.05.

Fig. 3. Pod shattering in canola.

The application of fall N treatments decreased the bloom date and increased crop height (Table 3). Decreased bloom date with fall N was also observed in Missouri in 2003. Crop yield was greater when 50 lbs of fall N were applied when compared to the no fall N treatment. P and spring N treatments had no influence on any of the response variables in either year. Results of single degree of freedom contrasts were similar to those already reported for the Missouri experiments.

Winter Canola Survival and Yield Response to N and Fall P

One advantage of seeding winter canola in Missouri is that canola may mature and be harvested prior to winter wheat. An earlier maturity date may allow growers to plant double-crop soybean earlier. This may allow the soybean crop to have a prolonged growing season and potentially increased water availability for early season growth. At Columbia, the winter canola crop matured approximately two weeks prior to a typical wheat variety, whereas at Novelty the canola crop matured one week prior to a typical wheat variety. This indicates that double-crop soybean following winter canola in central Missouri may have an advantage over double-crop soybean following winter wheat. This advantage may be negligible in northern Missouri. A similar advantage did not exist in the Texas Rolling Plains where canola and wheat mature at approximately the same time. The rapid maturing of canola due to drastic changes in the crop environment is conducive to increased shattering in the Texas Rolling Plains and may explain the significant shattering loss at Munday in 2003.

Though winter survival was greater at Columbia, crop yield was greater at Novelty. Increased yield at Novelty suggests that winter canola may compensate for reduced winter survival. This may have been a result of increased pod number per plant due to greater branching; however we did not collect pod number per plant to verify this response (7).

Maximizing winter hardness of an adapted cultivar may be achieved by optimizing fall growth. Proper levels of fall growth are also important in maximizing grain yield. Additional growth achieved in the fall reduces the spring vegetative period which may allow for earlier crop development. This was evident in our experiment (Tables 2 and 3). As with winter wheat, a major contributor to reduced seed yield in canola is excessive heat during the grain fill period. Avoidance of heat stress by promoting an earlier flowering and maturity date may equate to increased grain yield.

The addition of canola to current production systems will increase crop diversity which may decrease grower risk associated with mono-crop production systems. Winter canola may also increase profitability and expand acreage of double-crop soybean. This research supports the current recommendation that sufficient N, either residual or applied, needs to be present in the fall to support adequate fall development. The economic benefits of a split application may be determined after evaluating the cost of an additional trip across the field in the spring, determining the potential for N leaching over the winter at a given location, and the possible consequences of excess N during a fall with excellent growing conditions. Through increased breeding efforts, proper seeding date, and correct fertility management, winter canola should be a viable rotation option for producers in the Great Plains.

Acknowledgments

This work was funded in part by the National Canola Research Program, United States Department of Agriculture, Cooperative States Research Program, Missouri Agriculture Experiment Station, Texas A&M Agricultural Experiment Station, and the Kansas State Agricultural Experiment Station.

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