PURE NUTRIENT FACTS #6 Precision spreading Is your fertilizer at par with your spreader performance? CONTROLLING SPREADING, REDUCING COST New centrifugal spreaders promise working width of 24, 36 or 48 meters and even above. Matching the advantages of an extended working width with the need for precise control over spreading demands extreme mechanical performance of the fertilizer being used. Using low quality fertilizer can counterbalance your spreader performance. This aspect is often neglected. It is the subject of the present information.
PURE NUTRIENT FACTS Even spreading - why does it deserve your attention? Dual disc centrifugal spreaders have distinct spreading patterns. They vary as a function of construction principles and adjustable parameters such as pale position, length, inclination and rotational speed. In practice, however, it is the variation coefficient that results from superposition of several spreading patterns as the tractor moves back and forth in the field that determines spreading quality. How to ensure predictable results? A CLOSE LOOK TO SPREADING PATTERNS Spreading patterns of modern high performance spreaders are measured and optimized using computerized test benches. The exact repartition of the fertilizer alongside the tractor pathway and perpendicular to it can be measured and simulated for different parameters. Figure 1 shows a snapshot of a typical spreading pattern. The red arrow indicates the tractor movement. Fertilizer is spread in a characteristic croissant shaped pattern. Fertilizer deposit varies from low (blue) to high (red). - Figure 1: A typical spreading pattern profile of a modern centrifugal spreader [1] [2]. MEASURING VARIATION COEFFICIENTS The variation coefficient (CV) can be determined by field test. However, modern test benches for spreaders enable much more detailed computer simulations of spreading profiles and variation coefficients. Once the spreading pattern of a given fertilizer and spreader setting is recorded, the computer overlays these patterns as the (virtual) tractor moves forward (figure 1). Then the profiles from successive tractor paths are combined to establish the transversal spreading profile as well as the corresponding variation coefficient (figure 2). 1 - -1-1 SPREADABILITY OF FERTILIZER Different fertilizer qualities create different spreading profiles. Under optimum conditions, even spreading can be achieved with both, triangular and trapezoidal spreading profiles. However, they are not equally robust against perturbations such as tramline deviations. Figures 3 shows a triangular and a trapezoidal spreading profile, as well as the corresponding variation coefficients (CV) as a function of working width. In the case of the triangular profile, spreading parameters have been adjusted to a working width of 32 meters. The variation coefficient is at a minimum for this width. Even with deviations of the actual working width of +/- 3 meters, variations do not exceed %. In the case of the trapezoidal curve, the working width has been adjusted to 32 meters, too. However, the same deviation of tramlines result in a much higher variation, exceeding 1 %. A high spreading distance is not sufficient to ensure good results. The spreading pattern has a major impact on results. It depends on spreader configuration and on the mechanical characteristics of the fertilizer. For identical working widths, low density fertilizers favour trapezoidal spreading profiles, while high density fertilizers enable triangular profiles. High density fertilizers therefore result in lower variations. Distributed quantity (%) 12 1 7 2 1 1 Triangular profile -36-32 -28-24 -2-16 -12-8 -4 4 8 12 16 2 24 28 32 36 CV (%) 2 Distance from center of run (m) CV curve 2 3 3 4 2 4 1 1 Working width (m) Distributed quantity (%) 12 1 7 2 Trapezoidal profile -36-32 -28-24 -2-16 -12-8 -4 4 8 12 16 2 24 28 32 36 Distance from center of run (m) CV (%) 2 1 1 CV curve Figure 2: The overlapping of individual spreading patterns creates a more or less even distribution of fertilizer over the field. The variation coefficient measures the variability of observed application rates [3]. 2 3 3 4 2 4 1 1 Working width (m) Figure 3: Comparison of spreading profiles for identical working width of 32 meters. The triangular profile is much more robust against perturbations than the trapezoidal profile [4].
Precision spreading, pure benefit The effects of uneven spreading remain invisible in most cases. Only drastic variations are visible as dark and light stripes. However, losses set in long before any variation becomes visible to the naked eye. The cost of uneven spreading is mainly due to lost yield and lost quality. But the environmental burden and additional fertilizer cost shall not be neglected either. How to evaluate the cost of uneven spreading? SPREADING PROFILE AND YIELD PROFILE Figure 4 shows a typical cumulative spreading profile obtained with a trapezoidal configuration upon three fertilizer applications. The desired fertilization rate of 2 kg/ha has been applied on average, but the variation coefficient reaches 27 %. The mean yield is 79,9 dt/ha, whereas the potential yield amounts to 83,7 dt/ ha. The lost yield is 3,8 dt/ha, representing lost earnings of 76 / ha (at a wheat price of 2 /ha). CALCULATING YIELD LOSSES The yield losses due to spreading variations can be calculated using the fertilizer response curve. Figure 6 shows a typical response curve for wheat. The table 1 indicates the lost yield for different variation coefficients and fertilization at the agronomic optimum. For fertilization at the economic optimum, the variation coefficient has an even higher impact on yield. Fertilization kg N/ha 3 3 2 Maximum yield, 84 dt Mean Yield dt/ha 9 8 Yield [dt/ha] 9 8 7 - % Agronomic optimum - 1 % +1 % - 3 % +3 % 2 Mean 1 7 6 6 Yield loss Lodging risk 1 Working width Yield, 8 dt Fertilization 4 4 2 4 6 8 1 12 14 16 18 2 22 24 N [kg/ha] N-target: 2 kg/ha, 3 applications (cumulative spreading errors) Mean variation: 27 % Figure 6: The above fertilizer response curve for winter wheat was obtained from 28 field trials in Germany [6]. Figure 4: Cumulative spreading profile upon three fertilizer applications with urea and corresponding yield. The mean yield is diminished by 4 dt/ha due to a variation coefficient of 27 % and lodging []. coefficient [%] Yield [dt/ha] Lost yield [dt/ha] Lost yield [%] Lost earnings [ /ha] 83,7 1 83,3 -,4 -, - 8 2 82, -1,7-2, - 34 3 79,9-3,8-4, - 76 Table 1: The table above indicates the corresponding yield, lost yield and lost earnings for different variation coefficients. Lost earnings are calculated for a wheat price of 2 /t [6]. Figure : Marked color differences appear only when spreading variability exceeds 3 %, significantly reducing yield and increasing the risk of lodging []. Yield losses are aggravated if lodging occurs. Table 2 indicates expected losses for different crops and variation coefficients with and without lodging.
Crop Yield losses for a variation coefficient of 1 % 3 % No lodging Lodging Winter barley -,6 % -2,2 % - 8,6 % Summer Barley -,7 % -2,9 % - 1,8 % A study, conducted in Germany, compared the spreading loss of urea to calcium ammonium nitrate. The results are shown in the charts below. Even with a spreading width of only 21 meters, a mild breeze of 4 m/s resulted in 26 % variation of application rate with urea, whereas it was only 6 % with CAN! A spreading inaccuracy of 26 % is typically associated to yield losses above 2 % for winter wheat. Winter rye -,7 % -2,7 % - 18,2 % Winter oil seed rape -,9 % -3,6 % Table 2: Losses for different crops and different variation coefficients [6]. % yield loss 12 Calcium ammonium nitrate Ø 3,2-3,9 mm; 1, t/m 3 ; 27 % N Spreading width 21 m 6 % CONSEQUENCES OF UNEVEN SPREADING Spreading problems remain undetected in most cases. For variation coefficients below 2 % they remain barely visible to the naked eye, while yield drops already significantly. As soon as marked color differences appear, the variation coefficient already exceeds 4 %. Besides diminished yield and the risk of lodging, uneven spreading has other consequences on crops: Reduced and uneven quality (protein and oil content) Increased environmental burden (partial oversupply) Higher risk of infections Impaired threshing Higher desiccation cost AMMONIUM NITRATE OR UREA? Spreading nitrogen fertilizer precisely increases margin and reduces environmental burden. Using high quality fertilizers of known origin ensures good spreadability and even nutrient supply. However, when it comes to spreadability, fertilizer types are not equal. Ammonium Nitrate, due to a higher bulk density and lower nitrogen concentration, offers more homogeneous spreading characteristics than urea. Wind can further degrade spreading homogeneity with urea, resulting in significant local over- or undersupply. Quantity spread (%) 1 8 6 4 2 2 % yield loss Quantity spread (%) 12 1 8 6 4 2 % % 2 16 12 8 4 4 8 12 16 2 Spreading distance (m) single path spreading profile overall spreading profile Urea Ø 3,-3,3 mm;,7 t/m 3 ; 46 % N Spreading width 21 m 6 % 44 % Wind 4 m/s 26 % Wind 4 m/s 2 16 12 8 4 4 8 12 16 2 Spreading distance (m) Figure 7: Spreading errors, and therefore losses, are significantly higher with urea than with CAN. Even with a spreading width of only 21 m, a light breeze of 4 m/s causes a significant spreading error of 26 % with urea [7].
PURE NUTRIENT FACTS Fertilizer quality - Which parameters really matter? Centrifugal spreaders propel fertilizer granules in less than a tenth of a second to speeds that can exceed 1 km/h. Such high accelerations put severe mechanical strain on the granules. Fertilizers that do not withstand the extreme conditions of centrifugal spreaders will compromise yield and crop quality. More generally, the physical characteristics of fertilizer have a decisive impact on spreading performance and precision. Which are the physical characteristics that affect spreading? 9 KEY PARAMETERS FOR OPTIMUM SPREADABILITY A constant flow through the spreader, large spreading width, low transversal variability, and predictable results under all circumstances spreading performance depends on a number of parameters that fertilizer manufacturers need to control closely [8]. Density For the same diameter, the densest particles are projected at a wider distance. Density therefore affects application rate and working width. The density of a fertilizer shall be known and shall not vary. Density is measured as bulk density. It represents the mass of product contained in a given volume and includes the air between the granules. The higher the density, the better the spreading. Size Size is measured by two parameters: The mean size should be above 3,2 mm. For identical density, bigger particles will be projected farther as they are heavier. The size distribution (granulometric spread) indicates the variation of diameter between the smallest and biggest granules. If the variation is too big or too low, the distribution width is not optimal. A variation of,8 mm is recommended. Shape The more the granules are perfectly rounded and smooth, the better the aerodynamics and spreading trajectory. Aerodynamic resistance is measured as the Cx value. The lower the Cx value, the better the spreading. Distance [m] 18 16 14 12 1 2 7 1 12 1 Density [kg/m 3 ] Figure 8: The higher the density, the higher the weight and therefore the spreading distance (diameter = 3, mm; Cx =,44) at identical spreader settings [4] [9]. Distance [m] 18 16 14 12 1 8 6 1 2 3 4 6 7 Diameter [mm] Figure 9: The bigger the granule, the higher its weight and therefore the spreading distance (density = 83 kg/m 3 ; Cx =,44) at identical spreader settings [4] [9]. Distance [m] 16 14 12 1 8 6 Hardness The harder the granules, the less likely they crush during handling and under the impact of spreader blades. Crushed granules create unwanted dust and deteriorate granulometric spread. The spreading pattern becomes unpredictable. Hardness is measured by the force or weight required to crush the granules. Hardness shall exceed 3 kg (3 N). Flowability The flowability indicates how easily granules move under the impact of gravity, for example from the spreader hopper to the discs. Good quality fertilizers have a smooth surface and high flowability. Flowability is measured by the time needed for a sample of fertilizer to flow through a standardized funnel (EN 13299). Standard values range from 4 to 8 kg per minute. Dust content Fertilizer dust compromises spreadability, increases environmental burden and impacts working conditions in bulk storage areas. Dust results in over-fertilization along the tractor pathway. Dust also increases the risk of caking. The dust content of fertilizer is measured by separating dust from regular particles through airflow. Dust shall represent less than,1 % of weight. Abrasion resistance Friction and shocks cause abrasion of granules during handling. The mechanical resistance depends on the surface structure and particle strength. Fragments below 1,6 mm resulting from abrasion shall represent less than % of weight. Caking Under the effect of moisture, temperature and ongoing chemical reactions during handling and storage, fertilizer granules can stick together (caking). Caking impedes even flow and spreading. Surface treatment of fertilizer granules, low dust content and low humidity reduce the risk of caking. Composition Blended fertilizers are composed of different nutrients and each of these nutrients is represented as a different granule. Blended fertilizers tend to segregate during storage and in the spreader hopper. In addition, each granule is projected according to its specific mechanical characteristics. High precision, uniform spreading therefore cannot be achieved with blended fertilizers. Compound fertilizers with all nutrients contained in a single granule are always the first choice. CAN UREA 4, 1 1, 2 2, Air resistance (Cx) Figure 1: The lower the air resistance (low Cx), the higher the spreading distance (density = 83 kg/m 3 ; diameter = 3, mm) at identical spreader settings [4] [9]. Figure 11: CAN granules offer higher weight and density than urea prills, ensuring optimum spreadability.
Added value from Yara Yara (formerly Norsk Hydro) was the first company to produce nitrogen fertilizers by industrial processes in 19. Since then, we have gathered extensive knowledge about fertilizer production and application. Today, we promote safe and sustainable practices for the whole fertilizer industry. Our factories rate among the most efficient in the world. Precision farming technologies developed by Yara reduce fertilizer input and increase farmer incomes. Fertilizer from Yara is always a sure choice. SUPERIOR QUALITY Yara strives to be among the best companies in terms of product quality, environmental respect as well as employee health and safety. All our European factories are certified according to internationally respected standards: ISO 91 Quality Management System ISO 141 Environmental Management System OHSAS 181 Occupational Health and Safety Management System Yara consequently adopts the standards and programs set forth by the International Fertilizer Association (IFA) and the European Fertilizer Manufacturers Association (EFMA). Our factories deliver fertilizers of highest physical and chemical quality. Catalysts developed by Yara drastically cut GHG emissions from fertilizer production and our factories rate among the most energy efficient in the world. PURE NUTRIENTS Fertilizers from Yara are pure nutrients for efficient and sustainable agriculture. Made from pure raw materials and using modern production technologies, we ensure that our fertilizers offer precise dosage and spreadability, stable quality, low environmental impact and high return on investment. Yara fertilizers are referenced by all major spreader manufacturers. Design: bb&b Photos: Yara / Ole Walter Jacobsen 4/21 For further information about nitrate fertilizers, get the complete nitrate fertilizer brochure from www.yara.com For multimedia contents on farming, visit our YouTube channel: www.youtube.com/ yarainternationalasa ABOUT YARA Nitrate fertilizer Optimizing yield, preserving the environment. Yara International ASA is an international company headquartered in Oslo, Norway. As the world s largest supplier of mineral fertilizers for more than a century, we help to provide food and renewable energy for a growing world population. Yara provides quality products, knowledge and advice to farmers. Please do not hesitate to contact one of our local agronomists for further information. LITERATURE [1] IRSTEA (212) : Épandages des matériaux organiques et minéraux. Montoldre, France. [2] E. Piron, D. Miclet, L. Leveillé et al (21): Mineral spreader eco-design: method and real application examples. AgEng 21, International Conference on Agricultural Engineering, Clermont-Ferrand, France. [3] Yara internal communication: From factory to field, properties and handling of Yara fertilizers. [4] E. Piron, D. Miclet (213): Recent technological developments in fertilizer spreading. Irstea, Clermont-Ferrand, France. [] Yara internal communication (213): Streubarkeit von NPK und anderen Düngern. [6] Yara internal communication (213): Düngerstreuen- welche Faktoren beeinflussen die Streuqualität? [7] Stamm R. (26): Streufehler bei Seitenwind. DLZ Agrarmagazin 1:26 [8] COMIFER (29): Guide d optimisation de l épandage des engrais minéraux solides. La Défense, France. [9] Adapted from: A. Colin (1997): Study of mineral fertilizer centrifugal spreading. PhD Thesis, Université de Technologie de Compiègne, France. Yara International ASA Drammensveien 131 N-277 Oslo, Norway Tél : + 47 24 1 7 Fax : + 47 24 1 7 1 www.yara.com