防堵和播深控制机构提高玉米免耕精量播种性能

免耕播种技术能够提高土壤的蓄水保墒能力、增加土壤有机质含量，因此在华北平原农作区被广为接受。该地区的耕作制度为小麦与玉米周年轮作，冬小麦在6月份收获，随后在小麦秸秆覆盖地上直接进行玉米免耕播种作业。受小麦秸秆的影响，播种后玉米种子的粒距均匀性和播种深度一致性很难保证，另外，玉米苗由于被小麦秸秆覆盖容易发生病虫害。为了解决以上问题，发明了一种安装防堵机构和播深控制单体的玉米免耕精量播种机，对该播种机和不带防堵机构和播深控制单体的普通播种机在4、6和8 km/h 3个播种速度下的播种性能进行了对比试验，测量并得出了拨草性能、播种深度、出苗率和粒距分布均匀性（合格率、重播率和漏播率）等指标参数。试验结果表明：防堵机构和播深控制单体能显著提高播种机的拨草性能、播种深度一致性、出苗率和粒距分布均匀性；防堵机构使播种机不易堵塞，播种速度为8 km/h时的凉籽率仅为1.8%；播深控制单体使播种机在所有播种速度下平均播深接近理论播深，播种速度为8 km/h时的播深变异系数仅为9.2%，使得出苗时间更集中，出苗整齐度高。以上结果说明：设计的安装防堵机构和播深控制单体的玉米免耕精量播种机能够满足小麦秸秆覆盖田玉米免耕精量播种的要求。

Row cleaner and depth control unit improving sowing performance of maize no-till precision planter

Abstract: No-till planting practices that promote soil and water conservation have gradually been accepted in the North China Plain, where the main cropping system is annual wheat-maize double crops. Winter wheat is harvested in June and thereafter maize is planted immediately in field covered with residues. As the existence of wheat straw and stubble, it is hard to maintain uniformity of seed spacing in rows and planting depth. Furthermore, diseases and pests are more likely to occur on maize seedlings covered with wheat straw. To overcome the problems mentioned above, a planter with row cleaners and depth control units was developed, which was used for maize no-till planting in field covered with wheat stubble. The row cleaner was used for removing residues from seed row zone and preparing clean seed beds, while the depth control unit was used for following the terrain of field and maintaining the target planting depth. The row cleaner consisted of an active rotor and a residue separating fence, the active rotor was mounted vertically on the fertilizer opener, and the residue separating fence was mounted behind it on the shank of the fertilizer opener. Meanwhile, the depth control planting unit consisted of a parallelogram frame, a pair of gauge wheels, a planting depth regulator, a double-disk opener, a seed positioning wheel, a pair of press wheels, a metering device and a crossbeam. Field experiment was conducted in June 2015 in Gu''an County, Hebei Province, which was at the center of the North China Plain, and where the soil type was clay loam and the average soil moisture content was 16% at the depth of 0-0.20 m. The field was covered with the residues of 1.24 kg/m2, and the height of wheat stubble was from 0.25 to 0.30 m while the average length of wheat straw left on the field was 0.25 m. The experiment was conducted to compare the performances of new designed planter with a conventional planter without row cleaner and depth control unit when working at 3 forward speeds (4, 6 and 8 km/h). The performances of residue removing, the depth of seed placement and the emergence rate were measured, as well as the indices of sowing performance (qualified index, multiple index and missing index). The results showed that the row cleaner and the depth control unit had significant effect on the performance of residue removing, the depth of seed placement, the emergence rate and the sowing performance. With row cleaner, the planter was not easy to be blocked and the rate of seeds exposed at the surface was only 1.8% at the forward speed of 8 km/h, which was particularly lower than the conventional planter. The seed spacing of new designed planter was more uniform than the conventional planter, with the qualified index, multiple index and missing index of 89.6%, 8.1% and 2.3% respectively at the forward speed of 8 km/h, while for the planter without row cleaner and depth control unit, the indices were 82.8%, 15.4% and 1.8% correspondingly. Meanwhile, the mean planting depths of new designed planter were closer to nominal planting depth under each speed compared to the conventional planter. What was more, the coefficient of variation of depth was only 9.2% at the forward speed of 8 km/h, leading to more centralized emergence time, with almost 97% seeds emerging within 3 days. However, the emergence rate of the conventional planter in these 3 days was 77.3% in all. Results indicate that the new planter with row cleaners and depth control units has good planting performance with low rate of seeds exposed at the surface, centralized emergence time and uniform seed spacing, which can satisfy the requirement of no-till precision planting in fields covered with wheat residue.