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.