Journal ofAgricultural Engineering Vol. 44(3): July-September, 2007 Comparative Performance of Different Threshing Mechanisms on Pigeonpea Seed Quality Shiv K. Lohan, S. S. Jakhar and R. R S. Kharb ABSTRACT A study was conducted to compare hammermill, spike tooth and raspbar threshing cylinders at 3 combinations of cylinder speeds (400, 450, 500 rpm) and concave clearances (5, 10, 15 mm) for assessing quality ofthreshed pigeonpea seeds. Observations were recorded on the parameters namely, seed damage (%), efficiency (%), standard germination (%) and electrical conductivity (m mhos-'cm-'seed- I ). Maximum seed damage (16.54%) was observed when threshing was done by hammermill cylinder with the cylinder speed of 500 rpm and concave clearance of 5 mm. The threshing efficiency decreased (99 to 91 %) with decreasing the cylinder speed from 500 to 400 rpm and increasing the concave clearance from 5 to 15 mm. The minimum seed damage (3.5%) and maximum germination (82%) were found under low cylinder speed (400 rpm) and high concave clearance (15 mm) in raspbar and spike tooth threshing cylinder. The germination was found significantly and negatively associated with seed damage, threshing efficiency and electrical conductivity. The electrical conductivity of seed leachates increased as the cylinder speed increased and concave clearance decreased. Seed is the basic and most important input in modem agriculture. The use of quality seed gives maximum benefits to the farmers on their investment. Quality seed should have minimum damage, high germination and vigour. Among several factors affecting seed quality during production threshing is the most critical operation for a seed crop. The use of inappropriate machinery during harvesting and threshing usually results in mechanical damage, which is reflected by reduced germination and decreased storage life. Basic principles employed in threshing are shear, rubbing, impact and their combinations. The force applied by threshing cylinders usually results in splitting of cotyledons in legume crops and the seed damage may go up to 25% which is substantial loss in a seed production programme (Kamble and Panwar, 1984). The cleaning efficiency increased 83.4 to 93.5% with increasing cylinder speed in threshing of moongbean (Anwar et al.. 1991). The mechanical threshers utilizing either of the threshing mechanisms, cylinder speed and concave clearance, which are to be optimized for obtaining damage free seeds, maximum threshing and better physiological seed quality such as germination and electrical conductivity. Therefore, present study was undertaken with the objectives to have comparisons among hammermill, spike tooth and raspbar threshing cylinders for assessing seed quality of pigeonpea which rank second among pulses crops in India. MATERIALS AND METHODS Threshing performance is affected by several machine parameters viz. type of cylinder, moisture content of crop, cylinder speed, feed rate, concave clearance, blower speed, aspirator speed and labourer's skill. Therefore, evaluation was done to quantify the degree of influence of most important factors Le. cylinder speed and concave clearance. Every care was taken to ensure constant feed rate. The pigeonpea crop (variety Manak) was harvested at maturity, and sun-dried up to the moisture content of 10.5%. The dried crop/ plants were then threshed using three types of threshers having three threshing cylinders (hammer mill, spike tooth and raspbar) with three combinations of cylinder speeds (400, 450, 500 rpm) and three concave clearance (5, 10, 15 mm). The threshed seed was collected from the main outlet of thresher and subjected to take observations on seed damage, threshing efficiency. standard germination and electrical conductivity. The experiment was conducted using factorial completely randomized design (CRD). RESULTS AND DISCUSSION Effect on Seed Damage The seed damage increased with the increase in cylinder speed and decreased concave clearance in all the three types of cylinders (Fig. 1). Maximum damage (16.54%) was observed when threshing was done by hammer mill cylinder with the cylinder speed of 500 rpm and concave clearance of 5 mm. Minimum seed damage (3.5%) was observed when the threshing was done with raspbar Department of Seed Science and Technology, CCS Haryana Agricultural University, Hisar-125004