Effects of nitrogen and phosphorus addition on growth and leaf nitrogen metabolism of alfalfa in alkaline soil in Yinchuan Plain of Hetao Basin

PeerJ. 2022 Apr 13:10:e13261. doi: 10.7717/peerj.13261. eCollection 2022.

Abstract

Alkaline soil is widely distributed in China. Its rational utilization is an effective measure to solve land shortage and improve the environment. Alfalfa is characterized by strong salt and alkali tolerance and high yield and protein content. Nitrogen (N) and phosphorus (P) are the main nutrients for plant growth, and N metabolism is one of the primary forms of plant metabolism, which plays a vital role in quality and yield formation. The exploration of the effect of N and P on N metabolism and alfalfa growth will provide a theoretical basis for scientific fertilization for alfalfa in the alkaline soil of the Yinchuan Plain of the Hetao Basin. Therefore, a 2-year experiment of N and P addition was conducted. Six treatments were set up with a randomized block design, including without N (WN), medium N (MN), high N (HN), without P (WP), medium P (MP), and high P (HP). It was found that the MN and MP treatments increased plant height, stem diameter, stem/leaf, dry/fresh, and dry matter of alfalfa. The HN and HP treatments inhibited alfalfa biomass formation. The MN and MP treatments increased key products and enzymes of leaf N metabolism of alfalfa and promoted activities of leaf nitrate reductase (NR), glutamine synthase (GS), glutamate synthase (GOGAT), glutamic-oxalacetic transaminase (GOT), and glutamic-pyruvate transaminase (GPT), and inhibited activities of leaf protease of alfalfa. The MN and MP treatments increased contents of leaf N, P, ammonium nitrogen (NH4 +-N), nitrate nitrogen (NO3 --N), total chlorophyll, and protein and reduced leaf chlorophyll a/b and amino acid, results after HN and HP treatments were opposite. The correlation among leaf P, N, NO3 --N, amino acid, and protein reached significant levels (P < 0.01). It is suggested that MN and MP treatments can improve the yield and quality of alfalfa by increasing key products and enzymes of N metabolism and can be adopted to promote alfalfa production in the alkaline soil of the Yinchuan Plain of the Hetao Basin.

Keywords: Alfalfa; Alkaline soil; Fertilization; Nitrogen metabolism; Nutrient.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acids
  • Chlorophyll A
  • Medicago sativa* / metabolism
  • Nitrate Reductase / metabolism
  • Nitrogen / pharmacology
  • Phosphorus / pharmacology
  • Plants / metabolism
  • Soil* / chemistry
  • Transaminases

Substances

  • Soil
  • Phosphorus
  • Nitrogen
  • Chlorophyll A
  • Nitrate Reductase
  • Amino Acids
  • Transaminases

Grants and funding

The study was supported by the Innovation and Demonstration of Forage-livestock Technology of Ningxia in Saline-alkali land (No. 021904000051) and the Research on Quality-improvement Technology of Saline-alkali and of Alfalfa (No. 022005059002). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.