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Acta Prataculturae Sinica ›› 2022, Vol. 31 ›› Issue (4): 32-42.DOI: 10.11686/cyxb2021077

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Preliminary study of a sufficiency index of soil N and recommended N fertilizer application rates for alfalfa in the Loess Plateau of China

Hong-ren SUN1(), Xian-guo WANG1, Yao-jun BU2, Nan QIAO2, Bo REN3   

  1. 1.College of Grassland Science and Technology,China Agricultural University,Beijing 100193,China
    2.College of Life Sciences,Yulin University,Yulin 719000,China
    3.Grassland Workstation of Yuyang District,Yulin 719000,China
  • Received:2021-03-01 Revised:2021-04-06 Online:2022-04-20 Published:2022-01-25
  • Contact: Hong-ren SUN

Abstract:

The aim of this research was to lay a scientific basis for alfalfa (Medicago sativa) soil testing and fertilizer recommendation in the Loess Plateau region of China. The research methodology included a literature survey of alfalfa fertilization experiments conducted on the Loess Plateau, extracting data on soil nitrogen content and forage yield of N fertilizer treatments and where no N fertilizer was added. An algorithm for scattered experimental data integration and a new formula based on nutrient balance were employed to develop a sufficiency index (SI) of soil N with a scale of 1 to 6 and the recommended N fertilizer application rates (RNFAR) for alfalfa in the study region. It was found that for the planting year of an alfalfa crop (Y1) on the Loess plateau, the values for soil alkali-hydrolyzable nitrogen for SI levels 1 to 6 were, respectively, ≥73, 55-73, 39-55, 26-39, 13-26 and <13 mg·kg-1. Values for soil total nitrogen for SI levels 1 to 5 for Y1 were, respectively, ≥1.5, 1.1-1.5, 0.7-1.1, 0.4-0.7 and <0.4 g·kg-1. Values for soil organic matter for SI levels 1 to 6 for Y1 were, respectively, ≥19, 13-19, 9-13, 5-9, 2-5 and <2 g·kg-1. For second and subsequent seasons, values for soil alkali-hydrolyzable nitrogen for levels 1 to 5 were, respectively, ≥79, 51-79, 30-51, 13-30 and <13 mg·kg-1. For the whole crop life (WCL) of alfalfa, values for soil total nitrogen for SI levels 1 to 4 were, respectively, ≥1.9, 1.2-1.9, 0.5-1.2 and <0.5 g·kg-1. Values of soil organic matter for SI levels 1 to 5 for the WCL were, respectively ≥24, 13-24, 6-13, 2-6 and <2 g·kg-1. For a target yield of 9.0 t DM·ha-1 and an N fertilizer use efficiency of 40%, the RNFAR for SI levels 1 to 6 were, respectively, 0, 68, 135, 203, 270 and 338 kg N·ha-1, while for a target yield of 22.5 t DM·ha-1 and an N fertilizer use efficiency of 40%, the corresponding values were, respectively, 0, 169, 338, 506, 675 and 844 kg N·ha-1. This research has provisionally developed a system for calculating recommended fertilization rates for alfalfa crops on the Loess Plateau, based on soil nitrogen abundance and deficiency indicators and target crop yield and thereby provides a scientific framework for soil testing and nitrogen application to alfalfa crops in the region.

Key words: alfalfa, soil testing and fertilizer recommendation, organic matter, total nitrogen, alkaline hydrolysable nitrogen, sufficiency index, fertilization index, fertilizer application rate