Long-term manure application to improve soil macroaggregates and plant-available nitrogen in a Mollisol

Authors: DUAN, YINGHUA - Chinese Academy Of Agricultural Sciences; YANG, HONGBO - Chinese Academy Of Agricultural Sciences; SHI, TIANHAO - Chinese Academy Of Agricultural Sciences; ZHANG, WENJU - Chinese Academy Of Agricultural Sciences; XU, MINGGANG - Chinese Academy Of Agricultural Sciences; Gao, Suduan

Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2021
Publication Date: 5/8/2021
Citation: Duan, Y., Yang, H., Shi, T., Zhang, W., Xu, M., Gao, S. 2021. Long-term manure application to improve soil macroaggregates and plant-available nitrogen in a Mollisol. Soil and Tillage Research. 211:105035. https://doi.org/10.1016/j.still.2021.105035.
DOI: https://doi.org/10.1016/j.still.2021.105035

Interpretive Summary: Increasing N retention in soil and minimizing loss will have significant economic and environmental benefits and the effects of long-term organic amendment on the ability of soil to retain N is not clear. This study determined N partitioning in aggregates following 15N-labelled urea addition to soil after 25 years of manure or crop residue incorporation, and the availability of N in aggregate groups for plant uptake. Results show that macroaggregate mass increased by >10% in manure or crop residue incorporated soils, which also showed significantly higher use efficiency compared to non-amended soils. However, total amount of 15N fertilizer retained in all aggregates was the lowest in manure incorporated soils accompanied by the larger amount of N in soluble phase. The study confirms that long-term manure application enhanced formation of macroaggregates, higher bioavalability of N, and N storage that improve soil productivity, sustain crop production, and reduce environmental impact by reducing mineral N input.

Technical Abstract: Aims. Understanding the incorporation of fertilizer nitrogen (N) in soil aggregates and availability is highly beneficial for development of nutrient management practice and sustainable crop production. The aim of this study was to examine the influence of different long-term field fertilization regimes on N partitioning in soil aggregates and utilization by plants. Methods. Soils from a 25-yr field experiment were examined for N partitioning in aggregates from treatments: no fertilization (CK), chemical fertilizer (NPK), NPK with straw return (NPKS) and NPK with manure application (NPKM). The N partitioning in aggregate fractions was determined 42 days after 15N-labelled urea was applied. Using the wet sieving procedure, soil was separated into macroaggregates (> 250 µm), microaggregates (53–250 µm), and silt + clay (< 53 µm). The organic matter (OM) in the macroaggregate and the silt + clay fractions were defined as coarse free particulate organic matter (cPOM) and inter mineral-associated OM (inter-MOM), respectively. The OM in microaggregates were further separated to fine free POM (ffPOM), physically protected intra-aggregate POM (iPOM), and intra mineral-associated OM (intra-MOM). Total N (TN) and 15N concentrations in each aggregate fraction were determined. The aggregates except ffPOM (due to limited mass) were then used to cultivate ryegrass (Lolium perenne L.) and the uptake of the retained 15N was determined. Results. The 15N retained in cPOM, intra-MOM, and inter-MOM ranged from 24–34%, 28–37%, and 33–38%, respectively, while ffPOM and iPOM retained only 1–4% of the total retention in all aggregates. The use efficiency of the retained N was in the range of 14–19% and 14–24% for the cPOM and inter-MOM, respectively, but only 3–5% for the intra-MOM. Macroaggregate mass distribution was 10% higher in NPKM and NPKS, and significantly higher use efficiency than in NPK while the reverse was true for intra-MOM fraction with no differences in other fractions. However, the total amount of 15N fertilizer retained in aggregates was the lowest from NPKM treatment (16%) compared to other treatments (20-25%), due to larger amount in soluble phase. Conclusions. Long-term manure application resulted in increased formation of macroaggregates, higher bioavailability in the aggregates, and larger amount of N in soluble phase that attributed to the high yield in the field. Manure application resulted in significant increase in soil N suggesting that chemical N fertilizer input can be further reduced to improve soil productivity and sustain crop production.