Physio-engineering Properties of Seeds and Fertilizers for Design of Site-specific Seed Cum Fertilizer Applicator

Field experiment on nutrient dynamics was conducted in the year 2022-23 and 2023-24 at the research farm of Indian Council of Agricultural Research (ICAR)-Indian Agricultural Research Institute (IARI) in New Delhi. Maize seed dimensions varied significantly across varieties, with mean length ranging from 8.24 mm (Kaveri Hybrid 25K55) to 12.42 mm (PUSA HQPM-5). Geometric mean diameter (GMD) and sphericity, indicators of seed shape, ranged from 7.00-7.53 mm and 0.64-0.77 mm, respectively. Coefficients of variation for GMD and sphericity were consistently below 10%. The angle of repose, reflecting flow behavior, ranged from 37.01˚ (PUSA HQPM-5) to 38.53˚ (Kaveri Hybrid 25K55). The coefficient of static friction, highest for wood (0.59) and lowest for mild steel (0.53), suggests mild steel as a preferred material for seed hopper construction. Bulk density of maize varieties ranged from 727 to 811 kg/m³, with PUSA VIVEK exhibiting the lowest (754 kg/m³) and PUSA HQPM-5 the highest (808 kg/m³). True density varied from 1053 to 1192 kg/m³, with PUSA VIVEK showing the lowest and PUSA HQPM-5 the highest values. Coefficients of variation for both bulk and true densities were consistently below 3%. Fertilizer particle dimensions also varied, with mean length, breadth, and thickness ranging from 4.01-4.34 mm, 3.56-3.73 mm, and 2.69-3.43 mm, respectively. DAP exhibited the highest length (5.04 mm), NPK fertilizer the highest breadth (4.34 mm), and NPK complex the highest thickness (3.75 mm). GMD ranged from 3.47-3.63 mm across all fertilizers, while sphericity ranged from 0.81 (DAP) to 0.91 (NPK complex). Bulk density of fertilizers varied from 753.77±11.40 kg/m³ (Urea) to 1236.02±12.36 kg/m³ (NPK fertilizer). True density of DAP was lower (1379.76±24.9 kg/m³) compared to SSP (1950±21.97 kg/m³). The angle of repose ranged from 35.29±0.58˚ (DAP) to 33.32±0.68˚ (SSP), with field-used NPK fertilizer showing the highest bulk density (1236.02±13.62 kg/m³) and an angle of repose of 32.46±1.42˚. These findings provide valuable insights into the physical properties of maize varieties and fertilizer, with implications for seed and fertilizer handling, storage, and agricultural machinery design.