关键词: 紫云英, 机收, 播期, 播量, 生物量

Abstract:

The widespread adoption of machine-harvesting in rice （Oryza sativa） crops has had a negative impact on the production of intercropped milk vetch （Astragalus sinicus）， often resulting in damage to milk vetch in the belt rolling area. High milk vetch yield is an important objective when growing green manure crops， and sowing date and sowing rate are the key factors affecting milk vetch yield. Therefore this research investigated the effects of different sowing dates and seeding rates on the biomass and nutrient uptake of milk vetch interplanted into machine-harvested late rice， in order to clarify the optimal planting parameters of milk vetch in paddy fields in the Poyang Lake Basin. The experiment comprised a randomized block design， with five sowing dates （4， 3， 2， and 1 weeks before the harvest of late rice， and sowing milk vetch on the same day after the harvest of late rice； T₁-T₅） and five seeding densities （1， 2， 3， 4， and 5 g·m^-2； D₁-D₅）. The results of two consecutive years of experiments in 2020-2021 showed that seeding time and seeding density had significant effects on biomass and nutrient uptake of milk vetch. In terms of seeding time， the biomass and nutrient uptake of milk vetch showed a tendency to decreasing and then increasing with delayed seeding time. Compared with the treatment sown three weeks before the harvest of late rice （T₂）， the fresh grass yield of the other treatments （T₁， T₃， T₄， T₅） decreased by 0.9%-18.0%， and the grass fresh biomass yields ranked T₂>T₁>T₅>T₄>T₃. The T₅ treatment achieved the highest dry grass biomass. This indicated that the traditional practice of rice intercropping （sowing milk vetch at 1-2 weeks before the harvest of late rice） which was greatly affected by the machine-harvesting of late rice， it is no longer appropriate. Rather， milk vetch should be sown 3 weeks before or immediately after the harvest of late rice to obtain higher yields of milk vetch. In terms of seeding density， the biomass and nutrient uptake of milk vetch showed a trend of increasing initially and then decreasing with increased seeding density. Compared with the seeding density of 3 g·m^-2 treatment （D₃）， the milk vetch dry grass biomass in other seeding density treatments （D₁， D₂， D₄， D₅） was decreased by 5.2%-24.7%， and the milk vetch dry grass biomass ranked D₃>D₅>D₄>D₂>D₁. This indicates that in order to mitigate plant damage during machine-harvesting of late rice， the milk vetch biomass can be managed by manipulating the sowing density to ensure that the yield of milk vetch between rice crops is optimized. In conclusion， when planting milk vetch in machine-harvested rice fields in the Poyang Lake Basin， it is preferable to sow milk vetch 3 weeks before or immediately after the harvest of late rice and adopt a seeding density of 3 g·m^-2， in order to help achieve a high yield and efficient use of milk vetch. These research results provide tested recommendations for milk vetch planting in rice fields in the Poyang Lake Basin， and should enhance farmer adoption of milk vetch planting between rice crops and improve the agro-ecological status sustainability of rice cropping in the region.

Key words: milk vetch, mechanical harvest, seeding time, seeding density, biomass