NITROGEN USE ON YIELD COMPONENTS AND STEM SHEARING STRENGTH OF CANOLA

Ali Esehaghbeygi¹, Bahram Hoseinzadeh², Shahin Besharati^3
1 Department of Farm Machinery, College of Agriculture, Isfahan University of Technology, Iran
² College of Agriculture, Shahrekord University, Iran
³ Department of Mechanics of Agricultural, Machinery Engineering, College of Agriculture, Shahrekord University, Iran

ABSTRACT

The effects of nitrogen fertilizer on the yield components and stem shearing strength of three canola (Brassica napus L.) varieties Okapi, Opera, and Zarfam were conducted in 2008. The amount of nitrogen fertilizer and variety had significant effect on plant height and biomass yield (P < 0.01), and only variety had significant effect on the length of petiole and siliques at 1% confidence (RCBD analyses with LSD 5% for means). Nitrogen fertilizer had no influence on the amount of seeds in canola siliques. Increased nitrogen fertilizer application enhances plant taller with lower stem diameters while, shearing energy will be decreased. There was no relationship between the cellulose content of the stem piths and level of nitrogen fertilizer. The Opera variety and the serrated knife yielded higher shearing strengths and shearing energy than others and knife tilt angle had significant effects on the stem shearing.

Key words: Canola, Yield, Silique, Stem shearing, Nitrogen.

INTRODUCTION

Growth and development of winter oilseed rape is more complicated to describe than that of cereals, because of some principal stages overlap widely [9]. Oilseed rape has a relatively high demand for nitrogen, because content of this nutrient in seeds and plant tissues is greater than in most grain crops [16]. Different results of nitrogen effects on canola yield and its components have been reported [1,5,12,13].

Studying the shearing strength of cutting stems can be of great import in the selection of proper design and operational parameters of harvesting machines. Studies of cutting energy requirements have been conducted on stalks of winter rape [14], hemp [3], pea [15], sunflower [7] and wheat [4]. These studies have shown that cutting energy is related to stem mechanical and physical properties. Furthermore, most cutting experiments have been conducted using pendulum type apparatus or shearing rig, which may not fully represent the cutting process using reciprocating knives. The main objective of the present study was to determine the shearing strength of canola stems, which can be used to measure power requirements associated with combine harvesting. In addition, the effects of nitrogen fertilizer on the yield components of three canola cultivars were investigated.

MATERIALS AND METHODS

Three varieties of winter canola (Brassica napus L.), Zarfam, Opera, and Okapi were cultivated in silty clay soil of Shahrekord University field with 45% clay, 40% silt, and 15% sand and pH 7.9 semiarid conditions. An average annual air temperature and relative humidity were -12 to 32°C and 50±24% in 2008, respectively. Canola was planted in rotation with potato and 50 plant m^-2 densities [12]. Soil moisture content was controlled by time domain reflectometry, TDR, model Trime-FM, in the depth of 0–500 mm at 0.5 MAW, management allowed depletion [8]. Due to the importance of nitrogen fertilizer effects on physical properties of canola stems [16] and yield [12]; first, one levels of nitrogen fertilizer 200 kg ha^-1, urea type were applied in three different stages [10], foliation (25%), stemming (50%) and blooming (25%). Other nutrition, phosphorous 70 kg ha^-1 and potassium 100 kg ha^-1 were added constantly in all treatments. RCBD analysis was performed to examine the effects of canola variety, two kinds of knives, smooth and serrated edge and three tilting angles (0, 25, and 50 degrees) on the shearing strength of canola stems with five replications, which fully represent the cutting process using reciprocating knives. For normalizing data, they were transmitted to logarithmic.

Second RCBD analysis was performed with suitable knives type and tilting angle to study the effect of canola variety and three levels of nitrogen fertilizer 125, 200, and 275 kg ha^-1 in three different stages, foliation (25%), stemming (50%) and blooming (25%) on the seed yield, plant height, biomass yield, length of petiole and siliques, 1000-seed weight and shearing strength of canola stems. A complete randomized block design was used in a factorial experiment with five replications and the statistical packages MINITAB, Ver.13.2. State College Pennsylvania, Minitab Inc. was used. Means were compared using LSD's multiple range tests (P < 0.05). Weed control with Trifluralin 2.5 lit ha^-1 before seed planting and Diazinon 2 lit ha^-1 for insects control in spring were used. A digital micrometer was used to measure silique dimensions with 0.01 mm accuracy. In addition, the cellulose content of the stem piths was calculated according to the method of Van-Soest [17]. The value for cellulose content has been mentioned by a number of researchers to be responsible for stem mechanical properties [14]. The cellulose concentration was calculated as the difference between Acid-detergent fiber (ADF) and acid-detergent lignin (ADL) concentrations. Samples of whole canola plants (at the blooming phase fully-filled with grains) used in the cutting test were obtained from the field at the time of harvesting. Samples were cut from 20 mm above soil surface and transferred to the laboratory. During the cutting test, the samples were stored in plastic bags to control stem moisture content. All the tests were performed over 12 days. To determine the average moisture content of the canola stem on the date of the test, the specimens were weighed and dried at 103°C for 24 h in the oven and then reweighed [2].

A commercial single sickle knife section for mowers, trapezoidal shape with 76 mm base length and 55 mm height, and a countershear with 0.2 mm gap as the double shear test (Fig. 1). This simulated a single edge cutting process of a reciprocating knife of the cutterbar. To measure the shearing strength of the stem, an apparatus was constructed to hold the countershear and the canola sample, so that it would be possible to cut the stem under a constant speed with a Hounsfield universal testing machine under a load cell 5 kN. Following other similar studies, the perpendicular cutting method was employed in the present study to determine the cutting forces of the biological materials [3]. The knife section was attached onto the moveable crosshead and the specimen was positioned on the specimen support so that it was cut at a constant cutting speed of 200 mm min^-1 approximately 20 mm from the base to approximate the typical cutting height used in field harvesting operations. The mesh-grid method was used for determining the cross sectional area of the stem. Assumption the canola stems were homogenous from the rind to the center, which had no specific pith and circular cross section, the shearing strength of the stem was determined by dividing the shearing force into two section areas of the stem sides. The shearing energy was calculated by integrating the curves of shearing force and displacement [3] using the Curve expert 1.3, Hyams computer program.

RESULTS AND DISCUSSION

The analysis of variance shows that canola variety and knife type, and tilt angle of knives had significant effects on stem shearing strength at 1% and 5% confidence, respectively (on one level of nitrogen fertilizer, 200 kg ha^-1). The effects of tilting angle can be explained by the change of contact area between the knife and the stem, while cutting has accrued and by the physical properties of stem tissues (Tab. 1). With the low correlation coefficient between moisture content and shearing force, it is obvious that the short-range changes in moisture content during the experiment (52% to 60% w.b.) have no effect on canola stem shearing force. Energy consumption can be reduced by choosing the appropriate knife for shearing canola stems (Tab. 2). Greater engagement of the serrated edge knife with the stem than with the smooth one and the increase in friction are the main causes for increasing energy consumption by 23%.

Second RCBD analysis with suitable knives type and tilting angle was performed to study the effect of canola variety and three levels of nitrogen fertilizer on the shearing strength of canola stems and crop yield revealed that the levels of nitrogen fertilizer had no significant effects on stem shearing strength; however, canola variety (P < 0.01) (Tab. 3) and the levels of nitrogen fertilizer had significant effects on the shearing energy (Fig. 2), plant height and biomass yield (P < 0.01) (Tab. 4). Plant height and biomass yield increased with increasing nitrogen fertilizer while, shearing energy decreased. More nitrogen utilization efficiency in canola cultivars produced larger plant biomass [16] so, changing stem diameter in taller plant, and different development of collenchymas and peculiarities of stem architectonics, causes different strength [15]. There was positive relationship between shearing force and cellulose or ADL content. Results showed that canola variety had significant effect (P < 0.01) on petiole length and siliques. By counting the seeds inside each silique, it was observed that nitrogen fertilizer had no significant effect on the amount of siliques seed and the weight of each 1000-seeds (Tab. 4). Meanwhile, Saleem [13] showed that the yield and yield attributes were significantly influenced both by nitrogen levels. Improved N-management strategies in winter oilseed cropping, should account for site-specific biological, chemical and physical soil conditions [6,12]. The average number of seeds in each silique was 24 similar to that reported by Morgan [11]. The magnitudes of the biomass yield and plant height in Okapi were higher than Opera and Zarfam, respectively (Tab. 4).

The maximum value of shearing strength and used energy was recorded for the Opera stems, while Zarfam and Okapi had the minimum value among the three varieties studied (Tab. 5). This difference is due to differences in physical and physiological properties of stem varieties. For example, Zarfam stems are thicker, while Okapi stem is thinner but more solid. The values of shearing strength for the canola stems were lower than those of hemp (3.1–3.8 MPa) [3] but higher than that of sunflower (0.187–1.07 MPa) [7]. Of the 135 canola stem cuts, the values for F-max ranged from 74 to 190 N averaging out to 93 N, which is far lower than that of hemp (67–555 N) [3].

Chemical analysis of piths revealed that the cellulose content of the pith from Zarfam was slightly higher than that of Opera, while that of Okapi was significantly lower. Therefore, cell wall flexibility in Okapi must be lower [18]. In other words, the low cellulose content in Okapi causes cellulose micro-fibrils to be more strongly linked to each other. On the other hand, shearing strength increases with increasing stalk diameter [3,15]. The cross sectional area of canola stem varied greatly within Opera, Okapi, and Zarfam, respectively. Nitrogen fertilizer enhances plant growth. Taller plants, however, have lower stem diameters and shearing energy will be decreased [14]. The average cross sectional area of canola stem varied greatly within the field, 138.8 mm² for Okapi, 167.3 mm² for Opera, and 134.5 mm² for Zarfam. These values are within the range of hemp diameters (6–16 mm) reported by Chen [3]. The shearing force of canola stem increased with increasing cross sectional area of canola stems, R² = 0.81 (Fig. 3). The effects of stem diameter on maximum cutting force and cutting energy observed in the present study were consistent with those reported by Chen [3] and Skubisz [15], who reported that both the cutting energy and maximum cutting force were directly proportional to the cross sectional area of hemp and pea stalks, respectively.

CONCLUSIONS

Nitrogen fertilizer had no significant effect on the amount of siliques seed and the weight of each 1000-seeds and stem shearing strength. The levels of nitrogen fertilizer had significant effects on the shearing energy, plant height and biomass yield. Plant height and biomass yield increased with increasing nitrogen fertilizer while, shearing energy decreased. Canola variety had significant effect on petiole length and siliques. The magnitudes of the yield and plant height in Okapi were higher than Opera and Zarfam, respectively. Canola variety, type and tilt angle of knives had significant effects on stem shearing strength. Selection of smooth edge knife type plays a significant role in economizing on cutting force requirements. Selection of suitable tilt angle of the knife, zero-degree decreases the shearing force of canola stems. Increased nitrogen fertilizer application enhances plant growth, while decreases shearing energy. Taller plants, however, have lower stem diameters and shearing energy will be decreased.

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Accepted for print: 29.09.2010

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