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Black soil in northeast China is well known as high natural fertility for grain production, but the growth and yield of crop can be limited due to the high clay content of black soil can deteriorate physical properties. In this case, both tillage and straw return can be expected to serve as the important agronomic practices, in order to efficiently improve soil physical properties. However, the optimal depth of tillage and straw return into soil for favorable soil physical properties still remained unknown, particularly in black soil region. In this study, a field experiment, referred to the depth of tillage and straw return into soil, was conducted for six years in the black soil region in northeast China, in order to investigate the effects of incorporation depth of tillage and straw return into soil on soil physical properties of black soil. Seven treatments consisted of four replicates and random block design, including no tillage (D0), shallow tillage (0-20 cm) without or with straw return (D20 or D20S), deep tillage (0-35 cm) without or with straw return (D35 or D35S), super deep tillage (0-50 cm) without or with (D50 or D50S) straw return. In the treatments with straw return, a straw rate of 10 000 kg/hm2 was set to return into the corresponding tilled soil layer. Bulk density and water holding capacity were measured using cutting ring method, while the hydraulic conductivity was determined using constant head method, and the aggregate was measured using wet sieving method. The results showed that: 1) Compared with initial soil values, D0 treatment significantly increased soil bulk density, while decreased soil porosity, water holding capacity, hydraulic conductivity and >0.25 mm water stability aggregate (WAS>0.25) within 0-20 cm soil layer (P<0.05). However, there was no significantly impact on those indicators in soil layer within 20-50 cm (P>0.05). 2) In D20, D35 and D50 treatments, there was no obvious impact on the soil physical properties within 0-20 cm soil layer with exception for WAS>0.25 in D50 treatment, but D20S and D35S treatments remarkably all indicators of soil physical properties within 0-20 cm soil layer. 3) D35, D35S, D50 and D50S treatments significantly improved soil physical properties within >20-35 cm soil layer with exception of bulk density in 2014, while D50 and D50S treatments dramatically enhanced soil physical properties within in >35-50 cm soil layer (P<0.05). Specially, aeration porosity and hydraulic conductivity increased significantly, within the corresponding soil layers, while the higher effect was found in the treatment with straw return, compared with only tilled treatments. The comprehensive evaluation also showed that D35S and D50S treatments reached the best effect for improving soil physical properties. Therefore, the findings demonstrated that deep tillage or super deep tillage with straw return can efficiently improve soil physical properties within the whole tilled soil layers, concurrently to increase the depth of tilled soil layer, and thereby to enhance the water infiltration rate and soil water storage in black soil with heavy clay. In view of the positive effect of deep tillage and super tillage with straw return on soil physical properties and the limit of no tillage, the combined tillage practices of deep tillage (or with straw return) and no tillage were proposed for the black soil with high clay in northeast China and other regions. [ABSTRACT FROM AUTHOR]

Rice-wheat rotation area, with heavy clay soil texture, that it is wheat planting area accounts for more than 37% of the total wheat sowing area in China as one of the major grain production bases, and rice-wheat rotation is the main cropping pattern in this region. Meanwhile, because of the shortage crop stubble and more rainfall in autumn, which lead to serious wet damage during the tilling and seeding stage for this field. Currently, most of the existing no-tillage and less-tillage seeding equipment for wheat sowing in rice stubble areas were optimized and developed on the basis of traditional contact-type wheat seeding technology, which lead to adhesion and serious blockage phenomenon, as well as increasing of operating resistance and power consumption during working. Therefore, a innovative technical proposal of non-contact type pneumatic seeding technology that could avoid contacting between sowing parts and soil was introduced in this paper, which in order to solve the problems of soil adhesion, blockage, drag increment as well as poor sowing quality for wheat seeders under the condition of sticky heavy loam clay in rice-wheat rotation areas. Experiment that utilized a self-made platform for wheat pneumatic seeding was conducted, which could rip wheat seed into the soil condition of clean seed bed without straw and stubble mulching by high pressure accelerating airflow. During the pneumatic seeding experiment, keeping a certain pneumatic seeding height HG and incident angle α between the accelerating tube and topsoil surface, high-pressure gas was injected from the upper apex of the air nozzle and ejected from the bottom of it, which a stable high-speed airflow was formed in the accelerator tube (the length of the accelerator tube is 600 mm and the diameter is 10 mm). Then wheat seeds were put into the seed entrance and absorbed at a high speed under the negative air pressure of the ejector, during which the rubber sleeve could protect wheat seeds from damaging. After mixing with airflow, wheat seeds were accelerated by high-speed air flow in the accelerating tube. Finally, the wheat seeds flew out and ripped into the soil at a certain incident angle and high pneumatic seeding velocity. At the same time, high-speed photography technology was used to study the parameters of pneumatic seeding velocity, vertical velocity and pneumatic seeding depth under six levels (15°, 30°, 45°, 60°, 75°, 90°) of incident angles, and pneumatic seeding experiments under five different accelerating air pressures of 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa and 1 MPa for each incident angle were carried out respectively. Pneumatic seeding experimental results showed that: For pneumatic seeding in soil without straw and stubble mulching, when the incident angle increases continuously, wheat seeds can achieve higher vertical component of pneumatic seeding velocity deeper and pneumatic seeding depth at the same accelerating air pressures, the probability of horizontal slip and bounce of wheat seeds after touching soil show an decreasing trend, and pneumatic seeding depth has a positive correlation with pneumatic seeding velocity under each incident angle. Moreover, wheat seeds show various pneumatic seeding depth and soil impact effect without damage after pneumatic seeding. When the incident angles and the vertical component of pneumatic seeding velocity were more than 45° and 25 m/s respectively, wheat seeds can be completely ripped into the soil and the emergence rate is more than 86%. The best pneumatic seeding effect achieved as incident angle is 90°. In order to realize wheat vertical pneumatic seeding in field operation, the horizontal component of pneumatic seeding velocity should be equal to the operating speed of seeder and the vertical component of pneumatic seeding velocity should be greater than 25 m/s, which the seeder operating speed shows positively and negatively correlated with pneumatic seeding velocity and incident angle, respectively. The experimental results can provide basic data and technical support for the development of non-contact wheat seeding equipment in rice-wheat rotation area. [ABSTRACT FROM AUTHOR]