Split application of phosphorus fertilizer in Chinese milk vetch-rice rotation enhanced rice yield by reshaping soil diazotrophic community

Abstract

Chinese milk vetch (CMV) is widely recognized as the leading leguminous green manure utilized in the rice-green manure rotation system throughout southern China. While bacteria that form symbiotic relationships with CMV are responsible for fixing a significant portion of nitrogen (N) within agroecosystems. diazotrophic organisms play an essential role in the N cycle and enhance the pool of N readily accessible to plants. The goals of the current study were to investigate the effects of shifting partial phosphorus (P) fertilizer application from the rice season to the CMV season within a CMV-rice rotation system on soil nutrient levels, activity of soil enzymes and stoichiometric ratios, as well as diazotrophic community structure. The treatments consisted of a control group, a winter fallow-rice rotation without fertilizer application, and the treatments P0, P1, P2, and P3, representing 0, 1/3, 2/3, and the full dose, respectively, of phosphorus fertilizer (60 kg ha^-1 P₂O₅) added in a single rotation system during the CMV season, while combined with 60 % of regular N application rate during the rice season. In comparison to P0, the application of treatments P1, P2, and P3 resulted in higher CMV dry biomass and rice production across the seasons from 2018 to 2021 and the P2 treatment significantly increased the contents of total N (TN), soil organic matter (OM), and available P (AP) by 49 %, 48 %, and 110 %, respectively. The activities of alkaline phosphatase and L-leucine aminopeptidase showed a significant decrease when subjected to the P1 and P2 treatments. The P2 treatment enhanced the relative abundance of Frankia and Skermanella by 2.6 % and 1.6 %, respectively, comparing with P0 treatment. Furthermore, correlation analysis revealed a positive relationship between Skermanella and Mesorhizobium with the contents of TN, OM, AP, ammonium-N, and nitrate-N. In conclusion, the application of 1/3 to 2/3 of the full dose P fertilizer in CMV season reshaped soil diazotrophic community, improved soil N content, and thereby increased rice yield with 40 % N fertilizer reduction.

Keywords: Crop rotation; Diazotrophic community; Extracellular enzyme activity; Nutrient availability; nifH.

Graphical abstract

Fig. 1

Redundancy analysis of extracellular enzyme activity and soil nutrient content as affected by phosphorus (P) fertilizer split application. The positions and lengths of the arrows indicate the directions and strengths, respectively, of the effects of variables on the diazotrophic communities. The black arrows represent soil enzyme activities and the red arrows represent soil nutrient content. The samples were analyzed in triplicate plots.

Fig. 2

Principal Coordinates Analysis of diazotrophic community structure as affected by phosphorus (P) fertilizer split application. Bray-curtis was used for this analysis and different group elliptical indicate a significant difference between treatments. R2 indicates the degree of correlation between the projected values of the sample points on the principal components and the raw data (p < 0.05). The samples were analyzed in triplicate plots.

Fig. 3

Relative abundance of the 11 most abundant genera (>1 %) as affected by phosphorus (P) fertilizer split application. The samples were analyzed in triplicate plots and the average of triplicates is displayed for each treatment in this figure.

Fig. 4

Spearman correlation analysis between the relative abundance of dominant diazotroph genera and soil nutrient content. r indicates the correlation coefficient; ∗∗∗ Significant at the 0.001 level (P < 0.001), ∗∗ Significant at the 0.01 level (P < 0.01), ∗ Significant at the 0.05 level (P < 0.05). Abbreviations: NH₄⁺, NO₃⁻, TN, MBN, OM, AP, Vector L, Vector A, and C/N represent ammonium nitrogen, nitrate nitrogen, total nitrogen, microbial biomass nitrogen, organic matter, available phosphorus, vector length, vector angle, and carbon to nitrogen ratio, respectively.