The yield of sweet sorghum and soil nutrient after planting with multiple cropping, completely mulched and double furrow in Qinghai dryland

To study the effects of sweet sorghum (Sorghum bicolor) planting and multiple cropping at dry land of Qinghai, the experiments with single sweet sorghum planting in spring and autumn or multiple cropping after the winter wheat (Triticum aestivum) harvest on whole covering on double ridges and planting in catchment furrows (WCDR-PCF) were carried out at two altitudes (2 000 and 2 750 m). The results showed that the sweet sorghum can enter in filling stage when film in autumn and planting in spring, and the plants can enter in midjointing stage when film and planting in spring. The fresh yield, hay yield and stalk brix of these two treatment were 100 845 and 56 040 kgha-1, 35 550 and 9 525 kgha-1 and 16.77% and 4.40%, respectively. The fresh and hay yield of multiple cropping sweet sorghum were 60 360 and 7 530 kgha-1, respectively. In hay grass, the crude protein accounted for 10.50%, crude fiber accounted for less than 30% and sugar content accounted for 19% which suggested the good quality. The soil total nitrogen, total potassium, available nitrogen, available phosphorus, potassium and organic matter content decreased after planting sweet sorghum, but the total phosphorus and pH values increased.