Review on mechanization of strip compound planting system of wheat-maize-soybean

Abstract: For centuries, strip compound planting system has been widely adopted in the southwestern part of China, and is mainly farmed by hand up to date. It is commonly believed that the compound planting system results to the low level of mechanization. The traditional strip compound planting system, "wheat-maize-sweet potato" (WMP) relay cropping system was once the main cropping pattern on dry land in this area. However, in recent years, along with the demand decrease of sweet potato as swine feed and the demand increase of soybean, soybean has been taking the place of sweet potato in the WMP system for its economic benefits; then the main compound planting system has gradually transformed into "wheat-maize-soybean" (WMS), which is now one of the key technologies the nation has been endeavoring to popularize.In the WMS relay cropping system, several rows of wheat are usually drilled with 20cm row space at the beginning of November of the first year relay-cropping with several rows of maize which are usually hill-dropped with 40cm row space at the end of March of the next year; when the wheat is harvested in the middle of May, several rows of soybean are then seeded with 40cm row space in the wheat stubble relay-cropping with maize at the beginning of June of the second year. In practice, there are usually three types of strip width configuration of Wheat-Maize: narrow (40-73 cm), medium (100-100cm、117-83cm, 100-67 cm) and wide (200-200 cm). Different crop width configuration has different room available for mechanization operation; the nonstandard crop strip width hazards the adoption of mechanization; so the strip width configuration needs to be standardized firstly in line with the demands of mechanization.In order to realize the mechanized production of the WMS model as well as to improve the level of mechanization by popularizing the mechanized relay cropping system, the machine and agriculture measures for the WMS system should both be taken into account as a whole. On the condition of achieving the maximum annual yield of the three crops in the WMS system, field experiments have been carried out at several sites in the hilly areas of Sichuan Province since 2003 to acquire the optimal width configuration and agricultural measures. By the results, the "100-100" WMS model was selected as the optimal pattern to be mechanized with. Thereafter, mechanization operations were carried out in the chosen system by employing mini-, small- and medium-sized machinery system, respectively and the maize and soybean harvesters developed intentionally for the chosen pattern.According to the results, the mechanization of strip compound planting system is feasible; the compound planting system is not the root cause that leads to the low mechanization level in the hilly areas; "100-100" WMS model is the reliable carrier for developing dry land mechanization in the hilly areas of Sichuan; the Mini-four-wheeled tractor and its implements system is applicable for the strip compound planting system as well as the small-sized plots in hilly areas; so the popularization of the mechanized "100-100" WMS model shall facilitate the mechanization of the hilly areas.