Strip tillage characteristics of rotary 外文翻译.pdf

Soil received in revised form 27 November 2002; accepted 3 December 2002 Abstract A minimum tillage technique is required for reducing the labor requirements to prepare a level rice seedbed in Korea. Thus this study was aimed at determining the strip tillage characteristics of rotary tiller blades for use in a dryland direct rice seeder. The experiments were carried out in a laboratory soil bin. The USDA textural classifi cation of the experimental soil was sandy loam. Soil hardness measured by cone penetrometer ranged from 245 to 1442kPa depending on the depth, and the soil moisture content was 34.6%. The effects of rotary blade shape, rotational direction, number of rotary blades around the periphery, with and without soil-cutting disc blades on soil break up and torque requirements were investigated. Three different types of rotary blade were used, two general purpose rotary blades used with tractors and power tillers, and a leveling rotary blade for tractor use in wetland paddy fi elds. Rotation in the opposite direction to travel and cutting upwards resulted in soil being scattered out of the seeding furrow. A down-cut process is therefore necessary for effective seedbed preparation of a rice fi eld by strip tillage using a rotary tiller. Of the three types of rotary blade, the rotary blade for the power tiller was considered most satisfactory for strip tillage on a basis of its torque requirement and the ratio of soil breaking. The rotor shaft with four rotary blades had the lowest torque variation and torque requirement and ratio of soil breaking was 24.4%. The width of seedbed prepared by the rotary tiller with four blades during the down-cut process was 80mm which was enough for direct seeding of rice and applying fertilizer. Though a soil-cutting disc blade helped produce a better seedbed furrow, the increased friction between the disc blade and the soil block generated a much higher torque requirement. The soil-cutting disc blade was not necessary for the strip tillage direct rice seeder. Based on the results a strip tillage technique by the power tiller blade with a down-cut process could be effectively used for a dryland direct rice seeder. 2002 Elsevier Science B.V. All rights reserved. Keywords: Strip tillage; Dryland direct rice seeder; Minimum tillage; Rotary blade; Rotary tiller 1. Introduction Even though the main operations of rice production are almost fully mechanized in Korea, time inputs per Corresponding author. Tel.: +82-31-290-7823; fax: +82-31-290-7830. E-mail address: seungskku.ac.kr (K.S. Lee). hectare are three hundred and 10h. This time is 21 times greater than in USA and indicates the high pro- duction cost and low effi ciency of farm mechanization systems in Korea (Park, 1997). To reduce the production cost, several methods have been suggested by research institutes and government, such as expansion of the direct seeding techniques, expanding the transplanting area of young seedlings, 0167-1987/02/$ see front matter 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-1987(02)00159-9 26K.S. Lee et al./Soil Lee, 1985). At present there are three kinds of direct seeding method used in Korea, these are wetland broadcast- ing and drilling with a water depth of 2030mm, and dryland drilling (Chung, 2001). The land preparation method for wetland broadcasting and drilling is al- most the same as for transplanting. Land preparation for dryland drilling is carried out by moldboard plow- ing and rotary tilling only, without puddling. These days many farmers want to reduce the tillage operations and carry out only a rotary tilling for land preparation without plowing, and some farmers even want direct rice seeding with minimum tillage instead of transplanting (Lee, 1999). In Korea, several types of rotary tiller with different shaped blades are used for tractors and power tillers depending on the purpose of the operations, size of tractors and power tillers and fi eld type, upland or wetland rice fi eld. L-shaped blades are used for big tractors but for small tractors and power tillers, curved blades only are used. There are no big differences between the blades for small tractors and power tillers. The shape is similar but there are some differences in size and angles. Minimum tillage techniques for direct rice seeding would eliminate the primary and secondary tillage op- erations, and a strip tillage operation by rotary tiller accompanied by direct seeding would be ideal. With this technique, tillage, rice seeding, applying fertilizer and covering operations would be carried out at same time. Thus labor requirements can be reduced drasti- cally by eliminating the primary and secondary tillage operations as well as the growing of seedlings and the transplanting operation. Before the tillage operation for land preparation in Korea, there are lots of paddy and weed residues in the paddy fi eld, so it is very important to develop a min- imum tillage technique to cut and break-up residues, mix them with the soil, and prepare a level seedbed. The objective of this study was to investigate the characteristics of minimum tillage by rotary tiller blades for developing a strip tillage direct rice seeder for dryland production. The effects of rotary blade shape, rotational direction, number of blades and the addition of soil-cutting disc blades on the character- istics of dryland strip tillage were investigated. 2. Materials and methods 2.1. Experimental rotary blades Three types of commercially produced rotary blade were selected for this experiment, namely two kinds of general-purpose rotary blade for tractors and power tillers, respectively, and a leveling rotary blade used with tractors in wetland paddy fi elds. All of the ex- perimental blades were curved ones. Soil breaking performance of the L-shaped blade in wetland rice fi elds is poor compared to that of the curved blade and the working width of L-shaped blade is greater than necessary for the strip tillage of the direct rice seeder. Thus curved blades were chosen for this study. Table 1 and Fig. 1 show the specifi cations and shape factors of these blades, respectively. There are some differences in shape factors between the rotary blades used for experiment as shown in Table 1. These blades were selected by considering: (1) cutting width which should be more than 40mm for cutting and breaking paddy residues into pieces and making a seedbed Fig. 1. Shape factors of rotary blades. K.S. Lee et al./Soil (2) maximum radius of rotation should be more than 150mm to achieve a cutting depth of 60mm without the rotary shaft touching the surface. 2.2. Attachment of rotary blades and disc to the rotor shaft The number of blades attached to the rotor shaft varied from one to two, four and six. The number of blades was decided considering the optimum width of seedbed needed for seeding and fertilizing and was between 40 and 120mm. Fig. 2 shows the arrange- ment of blades on the shaft. The numbers beside the blades indicates the order of soil cutting during the down-cutting process. For the one-blade rotary tiller, only blade number one was attached. Fig. 2C shows the four-blade rotor with two fl at soil-cutting discs. The diameter of disc of 600mm was decided consid- ering the maximum radius of the rotary blades. The Fig. 2. Arrangement of blades on the rotor shaft: (A) two-blade rotor; (B) six-blade rotor; and (C) four-blade rotor with two discs. cutting depth of a disc was about 50100mm deeper than that of the rotary blade depending on the blade used.Forthetwo-bladerotor,theanglebetweenblades is 180and for the four-blade rotor, it is about 90 but all not exactly the same. For the six-blade rotor, blade number two and three, and fi ve and six cut the soil almost at the same time. The soil-cutting width of a blade was about 40mm. Thus the cutting width for the one- and two-blade rotors was 40mm, 80mm for the four-blade and 120mm for the six-blade rotor enough for rice seeding and fertilizing. 2.3. Soil bin system An indoor soil bin system was used for this exper- iment. The length of the soil bin is 20m, width is 2m and depth is 1m. A soil processing carriage was used to provide a uniform soil condition across the soil bin and the reproduction of soil was satisfactory. The soil processing carriage comprises of a rotary tiller, a 28K.S. Lee et al./Soil (B) down-cut process. 3.3. The effects of the number of blades By changing the number of rotary blades attached to the rotary shaft from one to two, four and six, the effects of blade number on the characteristics of strip tillage were investigated. The maximum number of rotary blades were chosen considering the maxi- mum width needed for the rice seedbed, and this was 120mm. The power tiller blade was used for this test as showing greatest promise from the results of the previous section. Tilling depth was 70mm. Fig. 7 is a representative graph from the results of the soil bin ex- periments. It shows the tilling torque requirements for different numbers of blade as the rotary shaft rotated Fig. 6. Torque variation and ratio of soil breaking infl uenced by rotary blade shape. through 360, together with the ratio of soil breaking during the down-cutting process. The torque variation and the maximum value of torque was greatest for the single blade rotor when compared with the two, four, and six arrangements. For the case of the rotary tiller with six blades, the width of soil cutting was about 120mm and this required the highest torque require- ment. The ratio of soil breaking for the six-blade rotor was 24%. This value is almost the same as with the four-blade rotor. The torque variation of the four-blade rotor was not so great as with the other arrangement, because the rotary blades were attached to the rotor with the similar angular space of about 90. For this arrangement, there was blades overlap between the K.S. Lee et al./Soil & Tillage Research 71 (2003) 253231 Fig. 7. Torque variation and ratio of soil breaking by multiple blades. initial and fi nal stages of soil cutting. This cutting overlapwasconsideredtobethereasonforthereduced torque variation and the apparently small number of clearly defi ned torque peaks when each torque curve was superposed. The torque variation pattern of the two-blade rotor was very similar to that of the six-blade because the blade arrangement of the two rotors produced a sim- ilar soil-cutting pattern. For the six-blade rotor, there are two sets of blades, numbers two and three, and Fig. 8. Torque variation and ratio of soil breaking by soil-cutting disc blade. numbers fi ve and six which cut the soil almost at the same time, increasing both the torque requirement and torque variation. Thus for both the two- and six-blade rotors there were two similar peaks of torque variation over one revolution blade arrangements. The ratio of soil breaking was 24.4% for the four-blade rotor, the highest of all. Considering the above results, a rotary tiller with four rotary blades appears to be op- timum for strip tillage in direct seeding. There is no need to increase the number of blades attached to the 32K.S. Lee et al./Soil & Tillage Research 71 (2003) 2532 rotary shaft, because the optimum width of soil cut- ting of 80mm was achieved with the four-blade rotor. Increasing the number of blades further just increases the width of soil cutting and torque requirements. 3.4. The effects of disc blade Flat soil-cutting disc blades were attached to the both sides of the rotor shaft in an attempt to reduce the soil-cutting resistance and to assist in the forma- tion of the seedbed. Fig. 8 is a representative graph and shows the torque requirements with and without the disc blade when the shaft rotates through 360 during the down-cut process. Tilling pitch was about 20mm and tilling depth was 60mm. Torque require- ments with the disc blades attached were much higher than without. Though the soil-cutting disc blades as- sisted in the formation of a better seedbed furrow, the increase in friction between the disc blade and the soil block generated the higher torque requirement. This result was most likely due to the arrangement of the rotary and disc blades. Number one and three blade of the four-blade rotor cut the outside part of the soil working width which was already cut and weakened by the disc blade but number two and four blades cut the inside part which was not infl uenced by the disc blade. Whilst the cutting pitch and width of blades are almost same, they cut different parts of soil, and this could cause the large variation in torque. The ratio of soil breaking was almost the same in both cases with a value of about 25%. Thus there is no need to attach the soil-cutting disc blades to the sides of the rotary shaft. 4. Conclusions With the rotor blades cutting upwards, the tilled soil was scattered out of the seeding furrow and a seedbed was not formed. A down-cut process is there- fore necessary for effective seedbed preparation of a rice fi eld by strip tillage using a rotary tiller. Among the three types of rotary blade tested, the rotary blade for the power tiller was considered to be optimum for strip tillage on the direct seeder having the low- est torque requirements and giving the highest ra- tio of soil breaking. Four rotary blades were suffi - cient for effi cient strip tillage with this rotary tiller. Though the attachments of soil-cutting disc blades as- sisted in the formation of a better seedbed furrow, they increased the torque requirements considerably. The width of seedbed prepared during the strip tillage op- eration using the four blades was 80 mm which is suffi cient for direct seeding of rice seed and applying fertilizer. Acknowledgements This work was supported by the Korea Research Foundation Grant (KRF-99-005-G00002). References Chung, N.J., 2001. Prospect and technology development of direct rice seeding. Paper presented at the Symposium Development of Direct Rice Seeding Technology. National Agricultural Me