الفهرس 
Design of a combined machine for seedbed preparation for onion
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Abstract
This study aimed at designing combined machine for seedbed preparation in one trip and evaluating its performance technically and economically under different operating conditions. The effect of the combined machine on some soil physical properties was studied. The design and implementation of the proposed model of the combined machine which consists of seven tines chisel plow as primary tillage equipment, packer roller as secondary tillage equipment, and two ridger tines for making a terrace. The combined machine has been tested and evaluated at the experimental station, Faculty of Agriculture, Cairo University, Giza Governorate, Egypt, under three levels of soil moisture contents (23% - 18% - 9.5%), three-working forward speeds (3.85- 4.69 - 5.30 km/h) and two depths of the tillage (15 and 25 cm). Actual field capacity, field efficiency, fuel consumption, wheel slip percentage, and brake horsepower were measured. The effect of combined machine on some soil physical properties (bulk density - total porosity - hydraulic conductivity {u2013} soil aggregates and size distribution) was studied. The most important results were increasing of actual field capacity of combined machine compared with the traditional method of seedbed preparation for onion crop, the highest value of actual field capacity was 1.98 fed/h compared with the traditional method 1.23 fed/h. Combined machine had lowest wheel slip percentage under different operating conditions, the minimum value of wheel slip percentage was 5.39% at 23% soil moisture content, 3.85 km/h and 15cm depth. The results showed an increase in field efficiency and decreasing in fuel consumption. The maximum value of field efficiency was 88.39%, while the minimum value fuel consumption was 4.86 l/h, and it was under 23% soil moisture content, 3.85 km/h and 15cm depth