Overview of Current Research Situations of Subsoiler

Shengbao GAN，Xirui ZHANG，Yue LI

Mechanical and Electrical Engineering College，Hainan University，Haikou 570228，China

With increasing attention to sustained farming and environmental protection，the existing large，medium and small sized machines and tools such as deep tilling plough and mould board plough have become unsuitable for farming in poor soil environment.The interrupted type vibrating subsoiler is an advanced farming method.This method is mainly characterized by scarifying hardened soil，solving soil hardening problem due to long-term rotary tillage，promoting growth of crop root system，and increasing absorption of crops to soil nutrients.Besides，it also increases water conservation property of soil，promotes development and growth of crops，and increases crop yield.

At present，in the condition of protective farming，before scarifying，soil is very hard；when scarifying，soil surface is covered with crop straws，and long straws will influence passing performance of the subsoiler.During subsoiling，horizontal subsoiler has a large influence area and will injure the crop root system，thus surface should be level，then it may be favorable for subsequent sowing and will not injure crop root system［1］.

There have been wide researches，experiments and application of the subsoiler both at home and abroad，especially in Europe and American developed countries，it had been developed and applied as early as the 1930s and 1940s and had obtained excellent effect.China also made a considerable progress in development of the subsoiler.Especially since the autumn of 2008，Jilin Province implemented the subsidy policy for subsoiling，which provides favorable development market for large and medium sized combined implement for subsoiler and cultivation.

1 Current development situation o f the subsoiler

1.1 Development situation at home and abroadThe United States and Western European countries have already had perfect researches on subsoilers.The soil scarifying methods mainly include compressive scarifying and vibrating scarifying.At present，new subsoilers are mainly bent leg plough，vibrating subsoiler，and active and passive combined tillage machine.

（i）Bent leg plough.Williams，Cooksley and Pidgen et al.started research since the 1980s，and Canadian Harrison designed a bent leg plough（it can bend 45 degrees），as shown in Fig.1.Bending parthas15 degree of cutting angle.Using cutting angle to replace the chisel-point tooth and break soil can improve the penetrating performance of machines and tools.

（ii）Vibrating subsoiler.Japanese Sakai et al.designed vibrating subsoiler with fourmould boards for medium sized tractor（30－45 kW）and determined the optimum parameter through test（1993）.The amplitude of tooth tip is 50 mm and vibrating frequency is 3.4 Hz.When the vibrating angle is 30 degrees，its traction force is 40%less than rigid subsoiler，while the total power only increases about 2%［2］.It structure is shown as in Fig.2.

（iii）Active and passive combined tillage machine.American Shinners et al.designed an active and passive combined tillage machine，which consists of two shovel type passive work pieces and two rotary active work pieces.Rotary tillage part is driven by power take-off shaft through conical gear reducer and chain drive.Forward rotation brings the machine with driving force and greatly reduces traction resistance of entire unit.Compared with machines and tools only mounted with 4 passive work pieces，the total power of active and passive combined tillage machine decreases 3.8%，but the traction resistance drops 87%，skidding of tractor drops 57%，and power utilization ratio of engine increases34%［2］.

1.2 Current development situation in ChinaSubsoilers for protective tillage in China mainly include ISQ－240／250 bulk subsoiler and ISY－210 subsoiler with wings developed by China Agricultural University，IZS－180 vibrating subsoiler manufactured by Shandong Dahua Mechanical Co.，Ltd，IS－3／4／5 series subsoiler manufactured by Xi'an Ocean Agricultural Science and Technology Co.，Ltd，ISTF－3 subsoiler produced by Jilin Siping Agricultural Machinery Factory，ISL－300 subsoiler produced by Modern Agricultural Equipment Co.，Ltd，ISB－57 subsoiler manufactured by Harbin Wo'er Science and Technology Co.，Ltd，and 2 306 bulk combined tillage machine manufactured by Heilongjiang Bonong Xingda Machinery Co.，Ltd［3－7］.Main technical parameters are listed in Table 1.

Fig.1 Shape and size of bent leg plough

Fig.2 Sketch for structure of vibrating subsoiler

Table 1 Main technical parameters of subsoiler at domestic market

2 Brief introduction to deep scarification technology

2.1 Deep scarification technologyThe deep scarification technology has been widely applied both at home and abroad.Deep scarification means exceeding the normal soil breaking depth.It can break hard pan and deepen the arable layer，increase soil aeration and water permeability，and improve growth environment of crop root system.When conducting deep scarification，since soil is loosened but not turned，the hard pan can be scarified，so as to adjust the three-phase ratio of soil，create an arable layer with coexistence of fictional and real situation，reduce soil erosion，and keep fertility and water of arable layer.Therefore，the deep scarification technology can greatly increase crop yield，especially for crops with longer root system［3］.The deep scarification technology is helpful for increasing soil aeration，and its main functions are as follows：

（i）Breaking the pan and improving structure of arable layer.Mechanized deep scarification can break hard pan formed due to many years of tillage，improve physical and chemical property of arable land，and increase capacity of＂water reservoir＂of soil.Thus，it is favorable for absorbing large volume of rainwater，and favorable for using rat runway to drain flood.Also，it is favorable for enhancing soil fertility and holding water，favorable for vertical development of root system，so it is the optimum soil structure for crop growth［8］.

（ii）Increasing utilization efficiency of water resource.The deep scarification technology breaks the pan，so it is favorable for penetration of surface water，reducing surface runoff，realizing self－adjustment of soil water，accumulate natural precipitation，and set up underground water reservoir.With increase of water storage，it is favorable for drought fighting before next rainy season.Besides，the deep scarification technology can solve the problem of rainfall not in step with crop growth.In rainy season，we can store excessive rainwater；in dry season，stored water can be absorbed by crop root system through capillary，so as to relieve dry situation［9］.

（iii）Increasing organic matter of soil.The deep scarification technology can break the pan，improve soil permeability and aeration，adjust three-phase ratio of soil，and make the proportion of solid，liquid and gas more coordinated.Besides，the deep scarification technology can increase land utilization efficiency.It scarifies the soil at depth of20－40 cm，causes dense part of root system to move down，which provides condition for survival of microorganism.Then，the non cultivated layer has anaerobic soil environment，corrosion and combination reaction becomes more intense，the content of organic matter gets increased，realizing the function of＂improving and maintaining soil fertility＂.

（iv）Increasing soil capacity.The deep scarification breaks hard pan resulted from long-term tillage，increases tillage depth，removes obstacle layer，and improves soil aeration.With increase of porosity of soil，the heat conductivity increases accordingly.Then，the soil temperature rises about0.5－1℃，and it brings the mudding period of 7－8 days ahead of time.

（v）Benefiting development of crop root system.The deep scarification deepens the soil tillage layer，reduces soil volume weight，and increases total porosity.The increase of aeration promotes activity of aerobic microorganism，brings soil microorganisms to move to lower position，and expands range of nutrients.The deep scarification soil preparation reduces damage to soil pellet structure and soil capillary.This is favorable for formation of soil colloid.Increase of anion of soil colloid will make it absorb Ammonium for crop absorption.Consequently，it accelerates downward growth of root system and promotes early ripe and high yield of crop.

（vi）Increasing disaster resistance of soil.The deep scarification and soil preparation break the pan，deepen the arable layer，promote crop root system to extend downward to absorb more nutrients and water，so as to promote growth of root system and improve lodging resistance of crops.The deep scarification technology can improve physical and mechanical property of soil，adjust water，fertilizer，air and heat in the soil，and raise the ability of resisting drought and flood drainage.In addition，it can increase the soil temperature，accelerate growth of crop root system，promote early ripe，resist disasters and increase yield，and prevent early ageing of crops.According to calculation，when the arable layer increases 1 cm，1 hm2land can hold 60 tons of water more.At the 15 cm of arable layer，the water content increases about 3%；at20 cm，the water content increases about6%［10］.

（vii）Reducing damage to soil.Mechanical soil preparation has certain damage to soil.The more times of soil preparation，the larger damage it will bring about.The deep scarification combined soil preparation reduces working times of unit，reduces movement of soil tillage，protects soil colloid，avoids change of soil to sand，reduces cost for oil and mechanical soil preparation，and improves soil at low consumption but high efficiency.

2.2 Methods of deep scarificationMechanized protective tillage methods of deep scarification mainly include partial deep scarification，deep scarification in rows，and bulk deep scarification.

2.2.1 Partial deep scarification.It adopts single column 23－30 cm subsoiler to implement deep scarification according to different crops and soil conditions.Densely planted crops（such as wheat）have spacing of deep scarification about 40－80 cm；wide row crops（such as corn）have spacing of deep scarification about 40－80 cm（the same row spacing as local corns），and the depth of deep scarification is23－30 cm.The deep scarification can be implemented before sowing.According to soil conditions and tillage times，generally 2－4 times of deep scarification are carried out and chisel shaped shovel subsoiler or subsoiler with wing are used.

2.2.2 Deep scarification in rows.This method is implemented at seedling stage of crops.The deep scarification spacing adopts the ridge spacing，and the depth is25－30 cm.When it is too arid，soil dragger may be added to reduce evaluation of soil water.In dry areas，it is recommended to implement deep scarification in rows before rain days come，to absorb rainwater and create condition for sowing in the next year and crop growth.

2.2.3 Bulk deep scarification.Inverted V type bulk subsoiler is used.Deep scarification is implemented according to different crops and different soil conditions.The depth of deep scarification is35－50 cm，and it is implemented after disposal of straws before sowing.During operation，the depth of deep scarification should be uniform and there shall be no repetition or missing of scarification.When it is too dry，the times of deep scarification should be determined according to soil conditions（generally one time of deep scarification every 2－4 years）［3］.

2.3 Functions and characteristics of deep scarification

2.3.1 Functions of deep scarification.The deep scarification is a tillage technology for solving the problem of large amount of soil breaking，high power consumption，and not favorable for water and soil conservation.Without the need of complete turnover of soil，using subsoiler to scarify soil can deepen the arable layer，keep surface coverage，reduce wind and water erosion of soil，reduce water evaporation，and improve the water conservation ability of soil.In addition，the deep scarification technology can fully break the pan，soften the arable layer，make the arable layer have good structure，deepen the depth of active soil stratum，coordinate the three-phase ratio to adapt to crop development and growth.Furthermore，it can greatly increase water permeability of soil，increase water content of soil，which is accordingly favorable for water supply at different stages of crop growth.The deep scarification technology also plays a significant role in alkalis removal and flood drainage.In land parcels unsuitable for turning up the soil，it is able to obtain excellent operation effect in combination with mechanical stubble－cleaning and soil preparation.

2.3.2 Characteristics of deep scarification.Mechanical deep scarification can break the pan，form loose soil structure，and greatly increase water storage ability of soil.In rainy season，there will be no surface runoff；in dry season，crop roots can absorb water.Thus，it is very suitable for crops，especially the growth of corns.According to calculation for areas along Yellow River and Huaihe River，the water storage volume in dry season can increase 165－370 m3／hm2，and the soil permeability can increase 5－10 times.It can effectively improve water keeping，storage，permeability，and drainage ability of soil，reduce saline and alkaline content，take full advantage of natural precipitation to satisfy growth demand of crops，and increase crop yield.Therefore，the deep scarification technology is also reputed as project of＂rain-fed agriculture＂.

Mechanical deep scarification loosens the soil but not makes the soil messy，and also not damages the soil structure.Many years of practice proved that this technology effectively keeps water，fertility，extends period for cultivation and sowing.In anthropogenic mellowing of soil，it can increase activity of aerobic bacteria，raise decomposition ability of soil organic matter and release of effective nutrients，improve absorption of crops to nutrients，restrict activity of anaerobic bacteria，increase concentration of nitrate nitrogen，accelerate soil metabolism，remove soil hardening，and restore original state of soil，so as to increase yield and quality of dryl and crops［10－12］.

3 Classification and characteristics of deep scarification machines and tools

3.1 Pole tooth type subsoilerThis subsoiler mainly consists of deep scarification shovel and hanging part.With simple structure，low price and small scarification coefficient（only 0.2－0.3），this subsoiler has excellent operation effect in upper section，while the vertical pole and shovel tip in the lower section compress with soil in both sides，which increases energy consumption.Also，after tillage，there will be vertical gap in the soil，consequently leading to water loss.Now，the major type of this subsoiler is ISL－435 pole tooth type subsoiler developed by Heilongjiang Institute of Agricultural Mechanical Engineering Science.Technical parameters of this subsoiler are as follows：auxiliary power：48－58 kW tractor；depth of deep scarification：30－35 cm；working width：140 cm；productivity：0.5－0.7 hm2／h.

3.2 V-shaped bulk subsoilerFor the bulk subsoiler，the major working part is rigid trapezoid framework.It consists of bottom cutter，side cutter，and vertical structure.When working，the deep scarification part cuts out trapezoid ridge from soil，makes it lift and move backward，then it flows out from the framework through two side cutter and horizontal cutter，later it falls and lays onto the field surface，and the bottom forms rat runaway，to absorb more rainwater.The scarification coefficient is higher than 0.75，and the specific draft of tillage is small.Falling soil will not leave vertical gap，which is favorable for keeping water in dry area.Major type of V-shaped bulk subsoiler is ISQ－340 bulk subsoiler designed by Beijing University of Agricultural Engineering and manufactured by Heilongjiang Bonong Machinery Co.，Ltd.Its main technical parameters：auxiliary power：53.8－73.5 HP；depth of deep scarification：30－50 cm；working width：155 cm；productivity：15－25mu／h［1］.

3.3 Subsoiler with soil preparation toolsWith the development water keeping technology for dryland tillage，it is required to develop new subsoiler with soil preparation tools，for example，ISL175 soil preparation combined subsoiler.It major technical parameters are as follows：40 kW tractor；depth of deep scarification：35－40 cm；working width：175 cm；depth of soil preparation：8－16 cm.

3.4 Column subsoiler with side wing shovelThis type of subsoiler is developed by China Agricultural University.It is mainly applied in deep scarification of protective farmland.It can realize deep scarification with intervals and bulk scarification on the surface.In 200 kg／mu field covered with crushed straws，it can smoothly pass.Apart from a high strength shovel handle，slightly raising wing shovel is mounted in both sides of shovel handle（as shown in Fig.3）.The upper and lower position can be adjusted.When working，the shovel tip penetrates into 30 cm deep soil and loosens soil in reverse direction at 45 degrees.At the same time，two side wings loosen the soil at45 degrees.The corresponding subsoiler is ISY－210 chisel type subsoiler with wings.The major technical parameters are as follows：auxiliary power：40 kW tractor；depth of deep scarification：30－35 cm；working width：210 cm；productivity：0.73－0.93 hm2／h.

Fig.3 Schematic draw ing for side w ing structure

3.5 Vibrating deep scarification technology and its application

3.5.1 Functions and characteristics of vibrating deep scarification.The vibrating deep scarification technology adopts tractor to drive the vibrating subsoiler.Output shaft of tractor brings vibrating body of vibrating subsoiler，to make the subsoiler move upward and downward，and loosen the arable layer.It vibrates but not turns over soil layer，and not damages upper and lower structure of soil layer.

In 1979，Israel Wolf and Luth.H.J initially designed the vibrating subsoiler suitable for arid and semi-arid areas.This vibrating subsoiler breaks the pan and can realize water storage，fertility keeping and soil aeration.The vibration is mainly to reduce traction resistance and increase looseness within the soil.Vibrating deep scarification has following features：

（i）Breaking soil through vibration，favorable for reducing soil mass and favorable for sowing.

（ii）Vibrating and scarifying at the same time easily forming coexistence of upper real and lower fictional situation，and loose soil favorable for increasing soil fertility，water storage and promoting growth of crop root system.

（iii）At the same deep scarification effect（depth and width），the vibrating deep scarification breaks little surface soil，continuously implements impact cutting of soil，and the power consumption obviously decreases.

（iv）It can fundamentally solve the problem of influence of surface straws on deep scarification and thus it is more suitable for protective farming.

3.5.2 Current situation of researches of vibrating deep scarification.In 1983，Germany developed the first set vibrating subsoiler.Its operation principle：（i）eccentric vibrator brings the plough beam to make transverse vibration，so as to reduce working resistance.（ii）The eccentric vibrator drives the plough to vibration up and down，to reduce working resistance.（iii）The eccentric vi-brator brings connecting plate of shovel handle to vibrate up and down，and drives the shovel tip to make transverse movement，which increases the loose area of soil in front of plough beam and reduces working resistance.The vibrating subsoiler can solve the problem of large resistance of deep scarification and high energy consumption.In this machine，the output shaft of tractor drives the eccentric vibrator to make the plough vibrate.The vibration frequency is generally 540 times／minutes，and it can reduce traction resistance about20－40%［13］.

Japan has made extensive work in research and development of multi-functional vibrating subsoiler and has made significant achievement.After the World War II，Japan originally used animal power to drive the subsoiler.With the improvement in agricultural mechanization，it used tractor to drive the plough.The largest subsoiler has9 cutters，and the depth of deep scarification is up to 38 cm and the maximum working width is up to244 cm.In 1989，it developed new vibrating subsoiler.This vibrating subsoiler features excellent scarification effect and small traction force.Thus，it is not only suitable for large field，but also for vegetable field，orchard，and tobacco field.It is also suitable for harvesting tuber crops.Japanese Sakaidesigned vibrating subsoiler with four mould boards for medium sized tractor（30－45 kW）and determined the optimum parameters through test in 1993：the amplitude of tooth tip is50mm and vibrating frequency is3.4 Hz.When the vibrating angle is 30 degrees，its traction force is 40%less than rigid subsoiler，while the total power only increases about2%.

For another example，E979 vibrating subsoiler produced by Uzel Company from Turkey has auxiliary power of 29.4 kW and working depth of60 cm.In addition，there are many types of subsoilers abroad.The major difference lies in working curved surface of subsoiler.To reduce working resistance，some subsoiler shovels are mounted with small round curter.

At present，following institutions are engaged in research and production of deep scarification machinery.

（i）ISZ－360 vibrating subsoiler designed by Hebei Agricultural Machinery Making and Repairing Station and manufactured by Hebei Huaqin Machinery Co.，Ltd.

（ii）Dual spindle vibrating subsoiler jointly developed by China Agricultural University and Hebei Agricultural Machinery Making and Repairing Station，suitable for three northern areas of China.

（iii）IZS－2 vibrating subsoiler designed by Shenyang Agricultural University，suitable for inter-row operation in inter tillage.It can solve the problem of injury of crop root system due to excessively wide transverse influence area.

（iv）ISZ－140（210）multi-functional vibrating soil modifier developed independently by Heilongjiang Water Conservancy Institute on the basis of introducing，digesting and absorbing foreign technologies.It was put into production in batches after verification by Heilongjiang Agricultural Machinery Testing Center.Combined with 37－59 kW tractor，this machine can complete soil breaking，rat hole drainage，fruit tree root breaking，and harvesting root type vegetables and traditional Chinese medicinal materials.It is mainly used in improving low and damp farmland，sticky soil farmland（not suitable for hanging cultivation）；keeping water and fertility in slope farmland；promoting new root growth of perennial plants in pasture land and orchard.For soil with gravels，other machines are not suitable，while this machine can bring into its full play and reduce the traction force of 25% －30%［14］.

4 Conclusions

The bulk deep scarification technology is a feasible active drought fighting and effective water utilization measure.This technology breaks the pan，improves the soil permeability and aeration.Soil profile forms the structure of＂upper fictional and lower real，left and right realand fictional alternately，and rat runway at bottom＂.After deep scarification，the soil structure is favorable for release and storage of nutrients，and also favorable for in-depth development of root system，so it is the optimum soil structure for crop growth.It causes dense part of root system tomove down，which provides condition for survival of microorganism.Then，the non cultivated layer has anaerobic soil environment，corrosion and combination reaction be comes more intense，the content of organic matter gets increased，realizing the function of＂improving and maintaining soil fertility＂.Besides，it creates excellent aerobic soil environment for arable layer，enhances aerobic decomposition，increases supply of quickly acting nutrients in soil，improves soil fertility，and realizes renovation and regeneration of agricultural resources.

［1］WANGWZ，LIMJ.Discussion on the mechanization technology of land tillage and preparation［J］.The Equipment and Technology of Agriculture，2006，32（6）：14－15.（in Chinese）.

［2］BAIXY，CHENGWD，WANGXY.Study on several foreign new subsoiling equipments［J］.Machinery for Cereals Oil and Food Processing Main Contents，1998（4）：34－35.（in Chinese）.

［3］YAN BS.Researching situation and prospect of deepdigging tools for mechanized protective tillage［J］.Sci-tech Information Development＆Economy，2004，14（4）：115－116.（in Chinese）.

［4］GUOWB，LIAO MC，LAISJ，et al.Analysis on the current situation of China's subsoiling machinery and the development direction［J］.Chinese Agricul Tural Mechanization，1996（5）：39－41.（in Chinese）.

［5］WANGRL，LIBF，QIU LC，et al.Researching situation and prospect of deep digging tools for protective tillage［C］.Academic Conference in 2003 for the 40th anniversary of Chinese Society for Agricultural Machinery.（in Chinese）.

［6］ZHOU GX，WANG C，LENG JL，et al.The research current situation of the mechanized deep-loosen technology and development trend［J］.Journal of Agricultural Mechanization Research，2005（3）：44－45.（in Chinese）.

［7］SHAO CF，ZHENG ZA，LIN QR.A study on affects of bulk sub-soiling diggers in all directions for the sustainable agricultural development［J］.Transactions of the Chinese Society of Agricultural Machinery，1999，30（5）：81－85.（in Chinese）.

［8］NIE Y.Advantages of mechanized planting operations［J］.Agricultural Mechanization and Electrification，2006（4）：46－47.（in Chinese）.

［9］LIU YP，LIU CS.Explore about machinery deep pine joint prepare soil technology［J］.Farm Machinery Using＆Maintenance，2006（4）：21.（in Chinese）.

［10］CHAIYJ.Mechanization conservative tillage— subsoiling machinery［J］.Contemporary Farm Machinery，2007（4）：42－44.（in Chinese）.

［11］LIHW，CHENQD，LIWY.Study on subsoiling technique for conservation tillage field［J］.Transactions of the Chinese Society of Agricultural Machinery，2000，31（6）：42－45.（in Chinese）.

［12］GUO XR，GU YB，LIAO ZX.Capability analysis to1SQ－250 type bulk subsoiler［J］.System Sciemces and Comprehensive Studies in Agriculture，2000，16（3）：225－227.（in Chinese）.

［13］WANG RL，LIBF，QIU LC，et al.Development of a vibrating subsoiler［J］.Journal of Agricultural Mechanization Research，2004（5）：134－135.（in Chinese）.

［14］SUN YJ，ZHOU Z，LIFH，et al.The improvement of ISZ-140 multifunctional vibratory soil improvement machinery［J］.Forestry Machinery＆Woodworking Equipment，2001，29（5）：34－35.（in Chinese）.