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Article

Nitrogen Availability Level Controlling the Translocation and Stabilization of Maize Residue Nitrogen in Soil Matrix

by
Shuzhe Liu
1,2,†,
Sicong Ma
2,3,†,
Fangbo Deng
2,
Feng Zhou
2,
Xiaona Liang
2,
Lei Yuan
2,
Huijie Lü
4,5,
Xueli Ding
6,
Hongbo He
2,* and
Xudong Zhang
2
1
College of Geography and Environment, Shandong Normal University, Jinan 250061, China
2
Key Laboratory of Conservation Tillage and Ecological Agriculture, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China
3
Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China
4
Bayin Guoleng Vocational and Technical College, School of Biotechnology, Korla 841000, China
5
Xinjiang Key Laboratory of Sustainable Management of Salinized Land and Regional Agricultural Technology, Korla 841000, China
6
School of Ecology and Applied Meteorology, Nanjing University of Information Science & Technology, Nanjing 210044, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agriculture 2025, 15(4), 403; https://doi.org/10.3390/agriculture15040403
Submission received: 14 January 2025 / Revised: 8 February 2025 / Accepted: 12 February 2025 / Published: 14 February 2025
(This article belongs to the Section Agricultural Soils)
Browse Figures
Versions Notes

Abstract

:
Crop residue returning to field inputs considerable nitrogen (N) into soils, which greatly influences the function and sustainability of the agricultural system. However, little is known about the transformation and physical stabilization of maize residue-derived N in soil matrix in response to changing N availability. To explore the distinct regulation of organo-mineral complexes on maize residue N translocation, a 38-week microcosm incubation was carried out amended with 15N-labeled maize residue in a Mollisols sampled from Gonghzuling, Northeast of China. Unlabeled inorganic N was added at different levels (0, 60.3 mg N kg−1 soil (low level), 167 mg N kg−1 soil (medium level), and 702 mg N kg−1 soil (high level)). 15N enrichment in bulk soil and the separated particle size fractions were determined periodically in the bulk soils and the subsamples were analyzed. At the early stage of the incubation, the maize residue N concentration declined significantly in the sand fraction and increased in the silt and clay fractions. Temporally, the 15N enrichment in the silt fraction changed slightly after 4 weeks but that in the clay fraction increased continuously until the 18th week. These results indicated that the decomposing process controlled maize residue N translocation hierarchically from coarser into finer fractions. From the aspect of functional differentiation, the pass-in of the maize residue N into the silt fraction was apt to be balanced by the pass-out, while the absorption of clay particles was essential for the stabilization of the decomposed maize residue N. The inorganic N level critically controlled both the decomposition and translocation of maize residue in soil. High and medium inorganic N addition facilitated maize residue N decomposition compared to the low-level N addition. Furthermore, medium N availability is more favorable for maize residue N transportation and stabilization in the clay fraction. Comparatively, high-level inorganic N supply could possibly impede the interaction of maize residue N and clay minerals due to the competition of ammonium sorption/fixation on the active site of clay. This research highlighted the functional coupling of organic–inorganic N during soil N accumulation and stabilization, and such findings could present a theoretical perspective on optimal management of crop residue resources and chemical fertilizers in field practices.

1. Introduction

Under the scenarios of agro-ecosystem sustainability, returning crop residue to the field is an efficient and economical way to improve soil’s organic matter (SOM) level and nutrient supply [1,2,3,4]. The world-wide returning rate of crop residues is ~7.8 t ha−1 yr−1 on average [5]; thus, substantial amount of carbon (C) and essential nutrients, e.g., ~3.1 t C ha−1 yr−1 and ~0.04 t nitrogen (N) ha−1 yr−1, are added into arable soils during the residue decomposition [6,7,8]. The N decomposed from crop residue contributes 15–25% of the anthropogenic N input in agro-ecosystems based on ~200 kg ha−1 yr−1 fertilizer N application. Compared to the high availability of mineral N, the crop residue N is more apt to accumulate in soils via gradual decomposition [9,10]. In spite of great efforts on investigating residue-derived C turnover [11,12], however, the transformation and stabilization of crop residue N remains less focused on.
The addition of crop residue can shift soil microbes from dormancy into activity by providing available C (e.g., dissolved organic C) and energy sources [13,14,15]. As feedback, microbial decomposition of maize residues is tightly associated with N availability due to their wide C/N ratio (about 65–100:1) [3,7,16]. Traditionally, the crop residue could be decomposed effectively with a C/N ratio range of 25–30:1. It is notable that the microbial degradation of organic residue in soil was reduced at a relatively low inorganic N level and such a process could be also restricted at a lower C/N ratio due to energy limitation caused by excessive inorganic N, referred to as N regulation effect [17]. Therefore, various amounts of inorganic N lead to different residue decomposition dynamics and control the transformation and stabilization pattern of the crop residue N in the soil matrix.
The interaction of organic matter with soil minerals is one of the vital mechanisms of SOM stabilization [18,19,20,21]. The functions of soil fractions in different particle sizes are heterogeneous in SOM stabilization and turnover [19] and it has been known that the constituents in finer fractions are better protected than those in coarser ones [20]. During the decomposition of crop residue, the humified products were dynamically allocated in different particle size fractions via the formation of an organo-mineral complex, and the organic N components could be released and stabilized in the clay fraction, predominantly in the form of microbial necromass [22]. However, the influence of inorganic N input, by altering the soil nutrient environment, on the temporal and spatial transformation, and the ultimate stabilization of crop residue N remains unclear.
The corn belt of northeast China, as one of the three golden corn belts worldwide, serves as a key grain production area and the largest commercial grain base in China. In this region, the return of maize residue has been incorporated into the National Action Plan. Therefore, to investigate the stabilization process of maize residue N in the soil, a microcosm soil incubation was conducted with the initial addition of 15N-labeled maize residue and unlabeled inorganic N at different levels. By measuring the 15N enrichment of the bulk soil and each soil particle size fraction periodically, maize residue N was differentiated from the original soil N and the extraneous inorganic fertilizer N. Based on the hypothesis that the temporal conversion and spatial allocation of maize residue N in soil was highly dependent on the inorganic N level in soil and the translocation of maize residue N strongly competed with inorganic N, our objectives were to elucidate the controlling role of fertilizer N input on the transformation and stabilization of maize residue N. Such research would provide a reference for the functional coupling and comprehensive management of organic–inorganic N at the global scale.

2. Materials and Methods

2.1. Soil Samples, Maize Residue, and Laboratory Incubation

A Mollisols sample at a depth of 0–20 cm was collected from Gongzhuling, Jilin Province, China (124°48′ E, 43°30′ N). The soil contains 15.6 mg organic C g−1 soil and 1.5 mg N g−1 soil (determined by an elemental analyzer (EA, vario MACRO cube, Elementar, Langenselbold, Germany)) with a pH of 6.3. The 15N-labeled maize (Zea mays L.) residue was obtained from a pot experiment by applying (15NH4)2SO4 (98 atom% 15N, 10.6% N, Cambridge Isotope Laboratories, Inc., Cambridge, MA, USA) at 200 kg N ha−1. After being harvested at physiological maturity, the leaves and stalks were air-dried, mixed, and then ground to pass a 0.5 mm sieve. The C and N content of the mixed maize residue was 40.1% and 0.5% (determined by an EA), respectively. The 15N enrichment of maize residue was 25.35% (determined by an elemental analyzer–isotope ratio mass spectrometer (EA-IRMS, Flash EA 1112, Delta plus XP, Thermo Finnigan, Somerset, NJ, USA)).
The air-dried soil was passed through a 2 mm sieve after removing the visible plant debris. Based on the return amount of stalks in the field condition, 10 g soil and 0.2 g maize residue were placed into a plastic container after being mixed homogeneously. The inorganic N (unlabeled ammonium sulfate) solution was added at the beginning of the incubation at three levels; thus, we set up an experiment using a completely randomized design with four treatments, including (1) N0: without N addition; (2) Nl: inorganic N added at low level, 60.3 mg N kg−1 soil; (3) Nm: inorganic N added at medium level, 167 mg N kg−1 soil; (4) Nh: inorganic N added at high level, 702 mg N kg−1 soil. The N addition in the microcosms was equivalent to about 0%, 78%, 217%, and 913% of the local fertilizer N application rate in the field (200 kg N ha−1). At different inorganic N levels, the C/N ratios of the extraneous substrates were 80:1, 50:1, 30:1 and 10:1, respectively, from N0 to Nh. The solution of KH2PO4 (220 mg K and 200 mg P kg−1 soil) was added at the beginning of the incubation to ensure K and P supply.
The soils were incubated at 25 °C in incubators. Soil moisture was maintained at 20% of oven-dried soil by sprinkling distilled water once a week. The soils were destructively sampled at the 0th, 1st, 2nd, 4th, 8th, 12th, 18th, 28th and 38th weeks. At each sampling time, three replicates were set up for each treatment. Both the original soil with mixed 2% residue (as control) and the incubated soil samples were air-dried for subsequent fractionation.

2.2. Soil Particle Size Fractionation

The soil samples were fractionated into three size fractions: sand (53–2000 μm), silt (2–53 μm), and clay (<2 μm) [23]. The dispersion and the isolation were performed according to the work of Christensen [24]. An energy output of 30 J mL−1, calibrated according to North [25], was imposed on 5 g soil by a probe-type sonicator (Vibra Cell VCX-750. Sonics & Materials, Inc., Newtown, CT, USA), with a soil-to-water ratio of 1:5. The coarse sand fraction (250–2000 μm) was isolated by wet sieving. To disperse the remaining portion of the soils, a second ultrasonic dispersion was imposed at an energy output of 135 J mL−1 with a soil-to-water ratio of 1:10 to isolate the fine sand fraction (53–250 μm). The coarse and the fine sand fractions were mixed together to comprise the sand fraction. The silt fraction was isolated from the suspension by centrifuging (Sorvall Legend RT. Thermo Scientific, Inc., Waltham, MA, USA) at 71× g for 6 min at 20 °C repeated for 10 times. To flocculate clay particles, 30 mL of 0.1 M CaCl2 was added into the suspension. Then, the clay fraction was isolated by centrifuging at 3075× g for 15 min at 20 °C. After being dried at 55 °C, all fractions were weighted and then ground to pass a 0.15 mm sieve for chemical analysis. The composition of different particle size fractions in the soil is shown in Table 1.

2.3. Determination of Total N, 15N Enrichment, and Organic C in Bulk Soil and Sub-Fractions

The contents of total N and organic C in the bulk soils and the three particle size fractions (subsamples) were measured by an EA. The 15N enrichments in the bulk soils and the subsamples were analyzed by an EA-IRMS.

2.4. Calculations

2.4.1. Maize Residue N Concentration

The concentrations of maize residue N (CMRN) in bulk soil and different particle size fractions were calculated as:
ATR (%) = [ATS (%) − ATC (%)]/25.35% × 100
CMRN (mg N kg−1) = CTN (mg N kg−1) × ATR (%)
where ATR (%) represents the proportion of maize residue N in total N in different separated fractions; ATS (%) and ATC (%) represent the 15N abundance in labeled and control samples, respectively; the value of 25.35% is 15N abundance of the maize residue; CMRN (mg N kg−1) and CTN (mg N kg−1) represent maize residue 15N and total N concentration in labeled samples, respectively.

2.4.2. Enrichment Factors of Total N and Maize Residue N in Particle-Size Fractions

The enrichment factor (E) [24] is calculated to compare relative distribution of components in different fractions. E < 1.0 reveals depletion, while E > 1.0 means enrichment [26]. It is expressed as follows:
E = NF/NB
where NF is the N concentration (referred as either total N or maize residue N) in the corresponding specific fraction, and NB is the corresponding total N or maize residue N concentration in bulk soil.

2.4.3. Stock of Total N and Maize Residue N

The stock (S) of total or maize residue N in a specific fraction depends on both its concentration and the mass distribution of particle size fractions. It is calculated as follows:
S (mg N kg−1 soil) = C (f) × P (f) × 10
where P (%) is the mass percentage of an isolated fraction in bulk soil.
During particle size fractionation, the recovery of total N in the three fractions ranged from 90% to 95%. To eliminate the effect of inorganic N loss during fractionation, the distributions of total N and maize residue N stocks in the soil matrix were expressed as the relative distribution ratio of the stock of a certain fraction in the sum of the three fractions.

2.5. Statistical Analysis

Statistical analysis was carried out using the software package SPSS 22.0 (SPSS Inc., Chicago, IL, USA). A repeated-measure ANOVA and the Fisher’s LSD test at 95% confidence were used to examine the differences in the dynamics of soil total N and maize residue N, the contribution of maize residue N to total N in bulk soil or each particle size fraction, and the relative distribution of total N and maize residue N in three particle size fractions with time between the four treatments. These data between the four treatments were then analyzed by an independent-sample t-test, whereas the data between the sampling years were analyzed by one-way ANOVA [7,10]. Figures were plotted by Origin 2018.

3. Results

3.1. Concentrations of Organic C in Bulk Soil

The concentrations of organic C (OC) in the N0 treatment decreased rapidly in the first 8 weeks (with a decrease of 11.0%) but changed slowly afterwards (with a decrease of 7.2%) (p < 0.05, Figure 1 and Table S1). The OC in the Nh treatment declined most sharply until the 2-week mark (p < 0.05), while that in the Nm treatment remained the lowest after 4 weeks. The OC in the N0 treatment was the largest before 18 weeks (p < 0.05), but thereafter exhibited no significance, along with Nl and Nh (p > 0.05).

3.2. Concentrations of Total and Maize Residue N in Bulk Soil and Different Particle-Size Fractions

The concentrations of total N (CTN) in the microcosms depended on the addition level of inorganic N (Figure 2 and Table S2). However, the percentage of total N decreased more in the Nm treatment (11.4%) than in the other treatments (4.2–4.9%) during the incubation period (Figure 2a). In spite of the loss of excessive inorganic N to different extents during particle size fractionation, the CTN in all the three fractions remained roughly in the following order: Nh > Nm > Nl > N0 (p < 0.05). The CTN increased remarkably in the silt and clay fractions simultaneously with the initially rapid decrease in the sand fraction (p < 0.05, Figure 2). The peak increase in the silt fraction occurred in the 4th week, while it was found in the 8th week in the clay fraction. During the 4–12 weeks, the CTN in the sand fraction increased significantly (p < 0.05) and then remained unchanged (p > 0.05).
The concentration of maize residue N in bulk soil changed slowly during incubation (p < 0.05, Figure 3 and Table S3) and the recovery of maize residue N in the three fractions was higher than 98% in all the treatments. Because the maize residue was ground to pass a 0.5 mm sieve and homogeneously mixed in soil, portions of crushed residue could be fractionated into silt and clay without decomposition. In the sand fraction, the concentrations of the maize residue N decreased dramatically by 29.6%, 39.7%, 28.0% and 48.2% in N0, Nl, Nm and Nh during the first 4 weeks (p < 0.05, Figure 3b), respectively, and then their reduction slowed down and stagnated after 18 weeks. In the silt fraction, the concentration of maize residue N increased rapidly, with averages of 4.8 mg kg−1 to 23.5 mg kg−1, 26.3 mg kg−1, 35.0 mg kg−1 and 35.0 mg kg−1 in N0, Nl, Nm and Nh during the first 4 weeks, respectively, and thereafter remained in a fluctuating manner (Figure 3c). In the clay fraction, the concentration of maize residue N in the N0, Nl and Nm treatments increased continuously during the incubation period; however, in the Nh treatment, it increased in the first 2 weeks but sharply decreased to the initial value during the following 2 weeks, after which it gradually increased again (Figure 3d). At the end of incubation, the concentration of maize residue N had the following order: clay > sand > bulk > silt regardless of inorganic N input (p < 0.05).
In bulk soil, the proportion of the maize residue N in total N (PMRN) in all four treatments varied insignificantly during the incubation period (p > 0.05, Figure 4a and Table S4). However, the PMRN decreased significantly in the sand fraction but increased dramatically in the silt fraction within 4 weeks (p < 0.05, Figure 4b,c). The PMRN in the clay fraction increased until the 18th week (p < 0.05, Figure 4d). Afterwards, the changes in all three fractions ceased. The PMRN in the sand fraction was significantly higher than that in the silt and clay fractions during the incubation period. In the sand fraction, the value of PMRN decreased with the increasing level of inorganic N input (p < 0.05, Figure 4b), while in the silt fraction, the PMRN in the Nm treatment was significantly larger than that of other inorganic N levels (p < 0.05, Figure 4c). In the clay fraction, PMRN in Nh was significantly lower than that in other treatments (p < 0.05, Figure 4d).

3.3. Enrichment Factors of Total N and Maize Residue N in Soil Particle Size Fractions

The enrichment factor of total N (ETN) varied significantly in different fractions, ordered as clay >sand > silt (p < 0.05, Figure 5a–c and Table S5). The values of ETN in the sand and the silt fractions were smaller than 1, while those in the clay fraction were larger than 1. The highest level of inorganic N addition (Nh) resulted in smaller ETN in clay compared to other N levels (p < 0.05, Figure 5c).
During the incubation period, the enrichment factor of the maize residue N (EMR) in the sand and clay fractions was larger than 1 (Figure 5d,e), while it was smaller than 1 in the silt fraction (Figure 5f). The EMR was in the order of sand > clay > silt before 18 weeks, but roughly changed to clay >sand > silt afterwards (p < 0.05, Figure 5d–f and Table S6). A high level of inorganic N addition lowered the EMR in both the sand and clay fractions (p < 0.05, Figure 5d,f). The value of EMR was larger than that of ETN in the sand fraction, while it was smaller than that of ETN at the same sampling time in the silt and clay fractions (p < 0.05).

3.4. Relative Distribution of Total N and Maize Residue N in Soil Particle Size Fractions

The distribution ratio of total N (DTN) in the soil matrix remained in the order of clay > silt > sand during the whole incubation (p < 0.05, Figure 6a and Table S7). The relative distribution of total N among each fraction was not significantly influenced by either inorganic N addition level or sampling time (p > 0.05). After a 38-week incubation, the DTN values in sand, silt, and clay were 13.8%, 20.3%, and 65.9% of the total amount on average, respectively (Figure 6a). Comparatively, the distribution ratio of maize residue N (DMRN) in each fraction was time-dependent (Figure 6b and Table S8). Regardless of the management of inorganic N input, DMRN in the sand fraction significantly declined with sampling time, while it significantly increased in the silt and clay fractions until the fourth week (p < 0.05, Figure 6b), and thereafter the DMRN in silt fluctuated (p > 0.05), while it kept declining in sand and increasing in the clay fraction (p < 0.05). At the end of incubation, the DMRN in the sand, silt, and clay fractions was 19.6–20.9%, 9.3–15.6% and 64.8–70.8%, respectively.

4. Discussion

4.1. Distinct Transformation of Total N and Maize Residue N Among Different Soil Particle Size Fractions

The interaction between soil components and mineral surfaces was one of the important factors controlling the stabilization of N [18,20,27,28,29]; thus, the distribution of total N in the individual fractions was intensively dependent on particle size regardless of inorganic N addition. A large amount of phyllosilicates in clay, which was highly associated with large surface areas (25–100 m2 g−1) and cation exchange capacity (300–900 mmol kg−1) [18], could provide various reactive sites for strong adsorption [30,31] and contribute to the more remarkable ability of the clay fraction for N stabilization (Figure 2d). The sand and silt fractions provide relatively smaller surface areas (<10 m2 g−1 and 10–50 m2 g−1, respectively), a smaller cation exchange capacity (10–150 mmol kg−1 and 60–350 mmol kg−1, respectively) [18], and weak attraction between particles [32], thus exhibiting less competitive ability than clay for SOM retention and resulting in the depletion of N in these two fractions (Figure 5a,b).
The transformation of the maize residue N among the fractions was regulated not only by mineral surface sorption but also by the decomposition dynamics of the residue. The initial decomposition of crop residues in soil was rapid due to the significantly enhanced biological activity stimulated by the available C derived from the maize residue itself and extraneous available nutrients [33,34,35]. Different from the significant C loss from the microcosms (Figure 1), total N mostly remained in the soils, with negligible loss of maize residue N (Figure 3a), regardless of the intact protein or microbial converted products [10], whereas mineral-associated protection played distinct roles in the stabilization of N-containing compounds, and thus internal cycling via organo-mineral interaction intensely controlled maize residue N allocation. Maize residue N was initially enriched in the sand fraction (i.e., in the first week) because the undecomposed and partly decomposed maize residues were mainly recovered in this fraction as particulate organic N. Subsequently, the decrease in maize residue N concentration in sand and the compensative increase in the silt and clay fractions (Figure 3) suggested the dynamic translocation of maize residue N from coarser to finer fractions during the patchiness and decomposition of maize residue. However, the accumulation of maize residue N in the silt fraction approached an equilibrium rapidly, while that in clay increased until the 18th week, implying that the allocation of maize residue N in the silt fraction was rapidly saturated in spite of the continuous decomposition of the residues.
Considering that the N-containing component accumulated in the clay fraction was mainly dominant in the forms of microbial products [18,19,35], the transformation dynamics of maize residue N from sand to finer fractions, especially to clay, was tightly associated with the microbial degradation of the maize residue. During this process, maize residue N in silt was not inert but the input portion was most probably balanced by the equal amount of output, implying the transitional tunnel role of silt for maize residue N translocation between the sand and clay fractions, which was possibly responsible for the time delay of maize residue N accumulation in the clay fraction compared to the initially rapid decomposition of maize residue (Figure 3).

4.2. Effects of N Availability on Transformation Dynamics of Maize Residue N

Nitrogen availability critically controlled the decomposition of plant residues for meeting the N requirement [22,36,37], and thus influenced the maize residue N translocation dynamics across the fractions. In agreement with the widespread cognitions for substrate stoichiometry [38,39,40], a C/N ratio of 10–50 in the substrates in our incubation was more favorable for maize residue decomposition compared to the limited N supply in the N0 treatment (Figure 3a). In addition, N availability remarkably influenced maize residue N transformation and stabilization. Medium-level inorganic N addition (C/N = 30 in the substrate) stimulated maize residue decomposition and simultaneously enhanced maize residue N translocation from sand into both the silt and clay fractions (Figure 6b), indicating synchronous stabilization with maize residue N decomposition in the habitat, whereas, despite a similar decomposition extent of maize residue at high- and medium-level inorganic N addition, higher N availability (C/N = 10 in the substrate) significantly restricted maize residue N accumulation in the clay fraction (Figure 5f and Figure 6b) and thus hampered the stabilization process of maize residue N. On the contrary, low N availability in the Nl treatment accelerated the translocation of maize residue N from the sand to the clay fraction, although the decomposition of maize residue was significantly restricted (Figure 3 and Figure 5). Obviously, the inorganic N level controlled maize residue N transformation pattern via both the altered decomposition dynamics of the residue and the competition among different N forms (including added inorganic N and indigenous soil N) on the interactions with soil minerals. The inorganic N, if excessively supplied (e.g., in Nh treatment), could occupy reactive sites on clay mineral surfaces [28,30,41], especially the adsorption sites within 2:1 clay mineral, which was enriched in the Mollisols in this study [42,43], and might strongly flood due to inorganic NH4+ [43]. These two processes competitively impeded the translocation of the decomposed residue N into the clay fraction, and as a result, low inorganic N supply favored the transformation of decomposed products from the silt into the clay fraction (Figure 4). Another possible controlling mechanism for maize residue N translocation was N regulation [17]. Microbial decomposition of maize residue with high C/N was generally repressed when the inorganic N level was extremely high, and thus the lowered degradation of maize residue retarded the transformation of maize residue N into the clay fraction (Figure 3c,d).

4.3. Distribution and Stabilization of Maize Residue N Influenced by Inorganic N Availability

The distribution and stabilization of soil N (including both total and the maize residue N), represented by the term of stock in a specific fraction, were dependent on both fraction-based concentration and soil mineral composition. The percentage of clay is lower than that in the silt fraction in this Mollisols, but the significantly higher N retention ability in clay minerals contributed to the largest stock of N in this fraction (Figure 6). After eliminating the influence of different N content in the microcosms as well as the discrepancy in the recoveries of particle size fractionation on the N distribution, we found that the total N stock in each fraction remained unchanged during the incubation period except for the initial transformation from silt to clay (Figure 6), suggesting the rapid equilibrium of N allocation in each fraction in the microcosms [44]. More importantly, the distribution of the increased soil N along with the inorganic N addition changed entirely in each fraction, indicating that the relative occupied capacity of soil particle critically controlled the distribution of soil N in each compartment.
As for the exogenous fresh substrate in the microcosms, the stabilization of maize residue N was tightly controlled by inorganic N addition. At the initial decomposition stage, the largest maize residue N stock in sand was attributed to the significant accumulation of undecomposed residue, which could offset the lower mass percentage of this fraction in soil (Table 1). The depletion of maize residue N in the sand fraction led to its significantly lower retention capacity, while the clay fraction was the most effective and competitive to sequester the maize residue N (Figure 5), although high availability of N retarded the transformation from the sand to the clay fraction. However, compared to the distribution pattern of total N after a 38-week incubation, maize residue N was relatively enriched in the sand fraction, while it was depleted in the silt and clay fractions, with the former being more significant (Figure 5). Such findings suggest that the hierarchical allocation of the newly input maize residue N among soil particle size fractions was critically associated with maize residue decomposition [19]. Because of the preferential retention of the decomposed maize residue N in the clay over the silt fraction, the translocation of maize residue N from the silt to the clay fraction could be balanced by the decomposition of maize residue N in sand, resulting in the greater depletion of maize residue N in sand (Figure 6b). Nevertheless, once the occupation in clay approached saturation, the decomposed resistant components in maize residue may be dominantly allocated in the silt fraction until these approach the relative N retention capacity of each fraction. Thus, compared to low- and medium-N-input levels, a high N input could facilitate clay minerals into a state of N saturation more quickly, which, in turn, encourages maize residue N from decomposition from the sand fraction to be stabilized in the silt fraction (Figure 6b).

5. Conclusions

The influence of N availability on the transformation and stabilization of maize residue N in soil was clarified by tracing its dynamic allocation in different soil particle size fractions. The hierarchical allocation of maize residue N from coarse fraction into finer size fractions was substantially controlled by the decomposition process of maize residue. The interaction of maize residue N with the clay mineral ultimately contributed to the stabilization of the decomposed residue N, while the silt fraction could function as a tunnel for maize residue N transformation from sand to clay fraction. N availability influenced the decomposition of maize residue and competitively controlled maize residue N translocation and mineral-associated stabilization. Medium N availability, with a C/N ratio of 30 in the exogenous substrate, was most favorable for maize residue decomposition and maize residue N stabilization via the effective formation of organo-mineral complexes with clay. Our study improved the understanding of transformation and stabilization mechanisms of crop residue N and it is essential to explore the optimal management of crop residue resources and chemical fertilizers in field practices. Regarding the fertility improvement after crop residue return, as feedback, how soil N pool enlargement improved fertilizer N utilization efficiency should be explored in future research.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agriculture15040403/s1, Table S1: Concentration of organic C in bulk soil (g kg-1 soil); Table S2: Concentration of total N in bulk soil and different particle size fractions (g kg-1 fraction); Table S3: Concentration of maize residue N in bulk soil and different particle size fractions (g kg-1 fraction); Table S4: Contribution of maize residue N to total N in bulk soil and different particle-size fractions (%); Table S5: Enrichment factors of total N in different particle size fractions; Table S6: Enrichment factors of residue-N in different particle size fractions; Table S7: Relative distribution of total N in different particle size fractions (%); Table S8: Relative distribution of residue N in different particle size fractions (%).

Author Contributions

Conceptualization, S.L. and H.H.; data curation, F.D.; formal analysis, F.D., F.Z., X.L., L.Y. and H.L.; funding acquisition, X.Z.; methodology, S.L. and X.D.; resources, F.Z. and X.L.; software, F.D. and X.D.; supervision, X.Z.; writing—original draft, S.L., S.M. and H.H.; writing—review and editing, S.L., S.M. and H.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (No. U22A20610, 42207370 and 42177324), the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA28010301), the Liaoning Applied Basic Research Program, China (No. 2023JH2/101300070), the Natural Science Foundation of Shenyang, China (No. 23-503-6-19), and the Special Fund for Central Guiding Local Technology Development (No. ZYYD2024CG11).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in this article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors would like to thank the support of the flexible aid project for Xinjiang talents.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Concentration of organic C in bulk soil. N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean values and standard errors (n = 3), respectively.
Figure 1. Concentration of organic C in bulk soil. N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean values and standard errors (n = 3), respectively.
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Figure 2. Concentration of total N in bulk soil and different particle size fractions ((a), bulk soil; (b), sand fraction; (c), silt fraction; (d), clay fraction). N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean value and standard error (n = 3), respectively.
Figure 2. Concentration of total N in bulk soil and different particle size fractions ((a), bulk soil; (b), sand fraction; (c), silt fraction; (d), clay fraction). N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean value and standard error (n = 3), respectively.
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Figure 3. Concentration of maize residue N in bulk soil and different particle size fractions ((a), bulk soil; (b), sand fraction; (c), silt fraction; (d), clay fraction). N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean value and standard error (n = 3), respectively.
Figure 3. Concentration of maize residue N in bulk soil and different particle size fractions ((a), bulk soil; (b), sand fraction; (c), silt fraction; (d), clay fraction). N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean value and standard error (n = 3), respectively.
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Figure 4. Contribution of maize residue N to total N in bulk soil and different particle size fractions ((a), bulk soil; (b), sand fraction; (c), silt fraction; (d), clay fraction). N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean values and standard errors (n = 3), respectively.
Figure 4. Contribution of maize residue N to total N in bulk soil and different particle size fractions ((a), bulk soil; (b), sand fraction; (c), silt fraction; (d), clay fraction). N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean values and standard errors (n = 3), respectively.
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Figure 5. Enrichment factors of total N (a–c) and maize residue N (d–f) in different particle size fractions. N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean value and standard error (n = 3), respectively.
Figure 5. Enrichment factors of total N (a–c) and maize residue N (d–f) in different particle size fractions. N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Symbols and bars represent the mean value and standard error (n = 3), respectively.
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Figure 6. Relative distribution of total N (a) and maize residue N (b) in different particle size fractions. N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Columns and bars represent the mean value and standard error (n = 3), respectively.
Figure 6. Relative distribution of total N (a) and maize residue N (b) in different particle size fractions. N0, maize residue added alone (100 mg N kg−1 soil); Nl, 60.3 mg N kg−1 soil + maize residue; Nm, 167.2 mg N kg−1 soil + maize residue; Nh, 701.9 mg N kg−1 soil + maize residue. Columns and bars represent the mean value and standard error (n = 3), respectively.
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Table 1. Distribution of different particle size fractions in soil at the 0th week and 38th week.
Table 1. Distribution of different particle size fractions in soil at the 0th week and 38th week.
WeekDistribution (%)Recovery Rate
SandSiltClay
0th week12.9 ± 0.8 a48.6 ± 0.7 a35.8 ± 0.5 a97.3 ± 0.9 a
38th week14.1 ± 0.8 a46.9 ± 0.8 a35.2 ± 0.3 a96.2 ± 0.3 a
Values reported as means± standard errors (n = 3). Same letters within each column indicate no significant difference between original and incubated soil (p > 0.05).
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Liu, S.; Ma, S.; Deng, F.; Zhou, F.; Liang, X.; Yuan, L.; Lü, H.; Ding, X.; He, H.; Zhang, X. Nitrogen Availability Level Controlling the Translocation and Stabilization of Maize Residue Nitrogen in Soil Matrix. Agriculture 2025, 15, 403. https://doi.org/10.3390/agriculture15040403

AMA Style

Liu S, Ma S, Deng F, Zhou F, Liang X, Yuan L, Lü H, Ding X, He H, Zhang X. Nitrogen Availability Level Controlling the Translocation and Stabilization of Maize Residue Nitrogen in Soil Matrix. Agriculture. 2025; 15(4):403. https://doi.org/10.3390/agriculture15040403

Chicago/Turabian Style

Liu, Shuzhe, Sicong Ma, Fangbo Deng, Feng Zhou, Xiaona Liang, Lei Yuan, Huijie Lü, Xueli Ding, Hongbo He, and Xudong Zhang. 2025. "Nitrogen Availability Level Controlling the Translocation and Stabilization of Maize Residue Nitrogen in Soil Matrix" Agriculture 15, no. 4: 403. https://doi.org/10.3390/agriculture15040403

APA Style

Liu, S., Ma, S., Deng, F., Zhou, F., Liang, X., Yuan, L., Lü, H., Ding, X., He, H., & Zhang, X. (2025). Nitrogen Availability Level Controlling the Translocation and Stabilization of Maize Residue Nitrogen in Soil Matrix. Agriculture, 15(4), 403. https://doi.org/10.3390/agriculture15040403

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