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Acta Prataculturae Sinica ›› 2022, Vol. 31 ›› Issue (1): 195-204.DOI: 10.11686/cyxb2021265

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Effect of topdressing after cutting on alfalfa growth and production

Rui-zhi XU(), Xiao-juan WU, Hui-min YANG()   

  1. State Key Laboratory of Grassland Agro-Ecosystems,College of Pastoral Agriculture Science and Technology,Lanzhou University,Lanzhou 730020,China
  • Received:2021-07-05 Revised:2021-09-22 Online:2021-12-01 Published:2021-12-01
  • Contact: Hui-min YANG


Fertilization is one of the important management measures in alfalfa (Medicago sativa) production, but the comparative effect of different topdressing regimes after cutting alfalfa and the optimal fertilization management plan are not clear. Hence, the aim of this research was to investigate the effects on the growth and production of alfalfa, of topdressing time and different combinations of N and P fertilizer applied to stimulate regrowth after cutting. The treatments comprised a complete factorial combination of two application times [on the day the cut was made (T0) and 7 d after cutting (T1)], three levels of N fertilizer (0, 25 and 50 kg·ha-1 N, designated N0, N25 and N50, respectively) and three levels of P fertilizer (0, 30, 60 kg·ha-1 P2O5, designated P0, P30 and P60, respectively), with three replicates (54 plots in total). The alfalfa variety was “Longdong” and the experiment was conducted in the establishment year. It was found that: 1) Topdressing after the first cut promoted the growth of the second crop of alfalfa. The highest alfalfa growth was achieved by applying a small amount of P fertilizer immediately after cutting (T0N0P30), and it was 20.53% higher than the control treatment (T0N0P0). In addition, topdressing after cutting could increase the alfalfa leaf∶stem. This effect was most evident in the high N-low P treatment combinations (N50P0 and N50P30) with topdressing at T1. 2) The yield of the second crop of alfalfa differed significantly (P<0.05) between the various treatments. The highest hay and crude protein yields were 3.58 and 0.94 t·ha-1, respectively, and these occurred with application of a large amount of N and P fertilizer immediately after cutting (T0N50P60), which were significantly different from that of the treatment after 7 days. Topdressing after cutting had no significant effects on alfalfa second cut acid detergent fiber, neutral detergent fiber or relative feeding values (P>0.05). 3) Root length, root surface area, root volume and root biomass per cm3 of soil in the second cut were significantly affected by N and P topdressing (P<0.05). The highest values of root length density (2.66 mm·cm-3) were observed in the no-fertilizer (N0P0) treatments; the highest root surface area density (7.75 mm2·cm-3was observed in treatment T0N25P30 and the highest root volume densities were observed in T1N25P30 treatments. Root biomass was rather variable across treatments but was higher than other treatments where no fertilizer was applied (T0N0P0 and T1N0P0. In summary, in rainfed agricultural area of Longdong Loess Plateau, topdressing N and P fertilizer after cutting promoted alfalfa regrowth in the establishment year. In practice, a small amount of P2O5 or a combination of 50 kg·ha-1 N and 60 kg·ha-1 P2O5 can be applied as soon as possible after cutting.

Key words: Medicago sativa, topdressing after cutting, establishment year, crop production