The trade-off between soil water recovery and nitrate leaching following the conversion of orchards to croplands in the tableland region of the Chinese Loess Plateau

doi:10.21203/rs.3.rs-4885680/v1

Download PDF

Article

The trade-off between soil water recovery and nitrate leaching following the conversion of orchards to croplands in the tableland region of the Chinese Loess Plateau

https://doi.org/10.21203/rs.3.rs-4885680/v1

This work is licensed under a CC BY 4.0 License

You are reading this latest preprint version

A large-scale conversion of apple orchards into farmland has occurred in the tableland region of the Chinese Loess Plateau due to the aging of apple trees and the increase in pests and diseases. However, the impact of this conversion on soil desiccation recovery and soil nutrient transportation remains unclear, posing a new challenge for sustainable agricultural development in the region. This study aimed to investigate the effects of orchard-to-cropland conversion on deep soil water recharge and residual nitrate dynamics, as well as the key factors driving these changes. The results indicated that within 5 years, the conversion led to a rapid recharge of desiccated deep soil (6-9 m), followed by a stable and slow increase in subsequent years. The annual soil water recovery rate in the deep soil was as high as 5.90 mm·m^-1·a^-1. While, the increased water input also caused rapid leaching and accumulation of nitrate in the deep soil, with its peak depth increasing significantly from 3.4 m to 7.0 m over time (R²= 0.92). Soil water was identified as the key factor influencing nitrate leaching, with a correlation coefficient of 0.48 (P<0.05). In conclusion, orchard-to-cropland conversion effectively replenished the deep soil water in the short term but also accelerated soil nitrate leaching. Therefore, while large-scale conversion of orchards to farmland is undertaken, it is crucial to acknowledge the trade-off relationship involving the recharge of deep soil water and the subsequent increase in deep nitrogen leaching. The findings of this study hold significant implication for the management of water and nutrient resources after the conversion of orchards to farmland, highlighting the necessity to mitigate nitrogen leaching while soil water is being restored.

Earth and environmental sciences/Ecology/Agri ecology

Earth and environmental sciences/Hydrology

Orchard-to-cropland conversion

soil water replenishment

nitrate leaching

the Loess Plateau

Soil water plays a vital role in vegetation growth, food security, and the functionality of arid and semi-arid terrestrial ecosystems (Cristiano et al., 2015; Berner et al., 2017; McColl et al., 2017; Jia et al., 2020). However, soil water is highly variable due to factors such as precipitation, evapotranspiration, and plant characteristics. Insufficient and unevenly distributed rainfall throughout the year poses significant challenges to plant growth, leading to deep soil desiccation (Wang et al., 2011; Kuang et al., 2024). This desiccation significantly impacts ecohydrological processes by hindering or slowing down the movement of soil water to deeper layers (Wang et al., 2015; Deng et al., 2020; Xu et al., 2023). Additionally, the long-term use of nitrogen fertilizers can result in excessive nitrogen accumulation in the soil, which may leach into deeper layers and cause environmental issues such as surface water and groundwater pollution (Zhu et al., 2022). Therefore, understanding and addressing environmental concerns like soil desiccation and nitrate leaching is essential to promoting the stability and sustainable development of ecosystems in arid and semi-arid regions.

As vegetation cover increases, particularly in artificial forests that depend on water extracted from deep soil layers (> 20 m) for their growth, the soil has become significantly drier. This has led to deep soil water deficiencies and the formation of dried soil layers over time (Jia et al., 2017; Li et al., 2019; Tao et al., 2021). Consequently, there is a surge of interest in innovative methods to replenish soil moisture, such as tree felling, agroforestry, and altering land use patterns (Jia et al., 2015; Li et al., 2022; Zhou et al., 2023). Tree felling has emerged as a widely adopted strategy to combat soil water deficits and prevent drought-induced tree mortality (Manrique-Alba et al., 2020; Niccoli et al., 2020). Research by Cui et al. (2022) demonstrates that tree thinning can significantly enhance soil water infiltration rates and cumulative infiltration, effectively replenishing soil water storage in the short term. Additionally, agroforestry offers promising solutions to tree water shortages (Zhao et al., 2012; Gao et al., 2018). For example, aged apple trees tap into deep soil water and surrounding farmlands for their growth (Wang et al., 2023; Tian et al., 2024). Moreover, transitioning from deep-rooted to shallow-rooted crops can mitigate soil water shortages. Bai et al. (2020) found that soil water in the 0–4 m layers can be fully restored by converting shrublands to grasslands. However, it takes approximately seven years for soil water to recover in the 0–5 m layers after artificial forests are converted to grasslands in the same region (Bai et al., 2021). Liu and Shao (2015) reported that soil water in the 0–10 m layers would take 6.5 to 19.5 years to recover following the conversion of a 30-year-old apple orchard to winter wheat cropland. Thus, converting apple orchards (deep-rooted) to cropland (shallow-rooted) could be a novel approach to reducing deep soil desiccation and boosting agricultural production in arid and semi-arid agroforestry systems. However, tree removal can also increase soil infiltrability (Lozano-Baez et al., 2019; Cui et al., 2023) and solute transportation. Nitrate, a highly dynamic and mobile solute in soil, can leach into deep soil layers with water infiltration (Ascott et al., 2017). Since nitrogen (mainly in the form of nitrate) cannot be utilized by crops at soil depths exceeding 1 m (Ju et al., 2004; Zhou et al., 2016), it may leach into groundwater and pose significant environmental risks. By exploring these innovative strategies, we can address the pressing issue of soil water deficiency, paving the way for sustainable agricultural practices and environmental conservation.

The Chinese Loess Plateau (CLP), nestled in an arid and semi-arid region, grapples with the dual challenges of scarce water resources and fragile ecosystems, further aggravated by severe soil erosion. To combat this, extensive vegetation restoration initiatives have been launched over the past decades, transforming sloping agricultural lands into verdant expanses of trees and grass (Jia et al., 2017; Jia et al., 2020). Simultaneously, the region's ideal climate for apple orchards and their lucrative economic returns have driven local farmers to convert vast tableland croplands into thriving apple orchards in the tableland region of the CLP (Chen et al., 2015; Fu et al., 2017). By 2016, these orchards spanned 25.2% of the CLP's cropland area, contributing an impressive 26.3% to China’s total apple production (Wang et al., 2020). Unlike traditional crops, trees boast deeper root systems, leading to heightened soil water consumption (Wang et al., 2015). With regional precipitation averaging only 500–600 mm, insufficient for tree growth, these trees tap into deeper soil water reserves, progressively causing soil desiccation (Jia et al., 2017; Li et al., 2019). This relentless soil drying triggers drought stress, curtails the fruiting period, diminishes productivity, and fosters frequent disease outbreaks (Mendham et al., 2011; Feng et al., 2016; Shao et al., 2018). Coupled with a dwindling labor force, this often necessitates the clearing of apple orchards to replant more manageable crops like corn or winter wheat (Huang and Gallichard, 2006). Furthermore, the drive for high yields has led to the application of excessive fertilizers in apple orchards, three to four times higher than in traditional croplands (Chen et al., 2022). This results in residual nitrate persisting in the soil even after converting orchards back to cropland. However, given that this large-scale conversion is a recent phenomenon in the loess tableland region, the effects of vegetation conversion on soil water and nutrient distribution, particularly in terms of depth and recovery time, remain largely unexplored. Delving into this research not only deepens our understanding of the interplay between deep soil water and nutrient dynamics under vegetation conversion but also bolsters the stability of regional cropland productivity and the sustainable development of ecosystems. This knowledge is pivotal for ensuring the long-term viability of agricultural practices and ecological balance in the CLP.

To bridge current knowledge gaps, this study conducted field experiments in the loess tableland region to investigate the impact of converting orchards to croplands on soil water and nutrient dynamics. Soil samples were collected from a 0–15 m soil profile to analyze various soil indicators. Initially, we assessed the soil water content deficit in a 21-year-old apple orchard and hypothesized that this deficit would be replenished within five years following orchard-to-cropland conversion. Additionally, we posited that nitrate would leach into deeper soil layers with water infiltration. The objectives of this study were to: 1) clarify the relationship between soil water recovery rates and depths over the years following orchard removal; 2) examine the relationship between the residual nitrate peak and leaching depth over the recovery years and their environmental implications; 3) identify the primary factors influencing soil water recovery and residual nitrate leaching. This research aims to provide valuable insights into the role of orchard-to-cropland conversion in soil water replenishment and the management of residual nitrate in arid and semi-arid regions.

2.1 Study area

The study was carried out at the Changwu Agro-Ecological Experimental Station, situated in Changwu County, Shaanxi Province, China (35°14′ N, 107°40′ E, 1200 m a.s.l.). This station is positioned within the tableland region of the CLP. The region experiences a continental monsoon climate, with an average annual temperature and precipitation of 9.1 ℃ and 568 mm, respectively, based on data from 1992 to 2021. Precipitation exhibits significant annual variability, with over half of the total annual rain falling between July and September. The area receives roughly 2230 hours of sunshine annually. The local terrain is relatively flat, with a substantial soil layer, and the primary soil type is loess, featuring a consistent soil texture across different locations and through the year (Jia et al., 2017). Groundwater is about 50–80 meters below the land surface in this area (Zhu et al., 2018), the primary water supply for vegetation is precipitation, and there is no irrigation. Croplands, apple orchards, and grasslands serve as the principal types of land use in this region.

[Fig. 1]

2.2 Experimental plot selection for orchard and cropland

To determine the influence of orchards to cropland conversion on soil water and nitrate levels, we selected orchards in their prime fruiting period and nearby croplands that was formerly an orchard, now used for continuous maize cultivation, with varying periods of recovery since the orchard's removal, as our research subjects in July 2022. We employed the space-time substitution approach to select sampling locations across different recovery durations, to assess how these durations impacted soil water content (SWC), soil organic carbon (SOC), and soil nitrate-nitrogen (NO₃⁻-N) levels. Our study included a long-standing orchard established in the year 2000, as well as croplands that had been growing maize for 1-, 3-, 5-, and 10-years post-orchard conversion (with the orchards having been cleared in 2021, at 21 years of age). The recovery periods were identified based on discussions with local farmers. For the sake of contrast, the apple orchards were labeled as AO, while the croplands reclaimed 1-, 3-, 5-, and 10-years post-orchard removal were labeled RC1, RC3, RC5, and RC10, respectively. A control cropland (CL), which had been continuously cultivating maize, was selected to represent the long-term soil water and nutrient status of the original croplands. These sites, all within a 1 km² area on the Loess Plateau, shared similar core characteristics (altitude, exposure, gradient, and relief) save for their recovery periods.

2.3 Sample collection and processing

For each sampling site, disturbed samples from 0–15 m soil depths were collected using a hollow-stem hand soil auger (4.5 cm in diameter) every 20 cm. The soil samples were divided into two parts: one portion was placed in an aluminium box and subjected drying (105 ℃, 24 h) to determine the gravimetric SWC (g·g^− 1, %) (Bao., 2000); the other portion was air-dried, ground, and passed through 1 mm and 0.25 mm fine sieves to determine the soil particle size composition and nutrients, respectively. The soil particle size composition was analysed by Marvin laser particle size analyser (Masterizer 2000, Malvern Instruments, England) divided into clay (< 0.002 mm), silt (0.002–0.02 mm), and sand (> 0.02 mm) contents according to the American agricultural classification (Zhang., 2022). NO₃⁻-N was measured using a continuous flow analyser (Auto-Analyser-AA3, Seal Analytical Norderstedt, Germany) (Kachurina et al., 2000), and SOC was determined by the Walkley-Black method (Page et al, 1982).

To evaluate the dynamics of deep soil water deficit (SWD) and soil water storage (SWS) with recovery years of cropland, we focused on SWC in the 3–15 m soil layers, since the 0–3 m soil layers were more susceptible to single rainfall events (Liu et al., 2010). The SWD was calculated as follows:

$$\:\begin{array}{c}SWD={SWS}_{i}-{SWS}_{F}\#\left(1\right)\end{array}$$

$$\:\begin{array}{c}{SWS}_{i}=\sum\:{\theta\:}_{i}\times\:{h}_{i}\times\:{10}^{-1}\#\left(2\right)\end{array}$$

Where $\:{SWS}_{i}$ is the soil water storage of site (mm); $\:{SWS}_{F}\:$is the soil water storage of the control cropland (mm); $\:{\theta\:}_{i}\:$is the soil water content of site (%); and $\:{h}_{i}$ is the thickness of the soil layer (cm).

The soil water recovery (SWR) was calculated as follows:

$$\:\begin{array}{c}SWR=\underset{0}{\overset{L}{\int\:}}\left({\theta\:}_{t2}-{\theta\:}_{t1}\right)dz\#\left(3\right)\end{array}$$

Where $\:SWR$ is the soil water recovery (mm); $\:{\theta\:}_{t2}\:$is the soil water content of returning cropland (%); $\:{\theta\:}_{t1}\:$is the soil water content of the apple orchard (%); $\:L$ is the thickness of the soil layer (cm).

2.4 Data analysis

One-way analysis of variance (ANOVA) was used to analyzed the effects of recovery years and soil depths on the SWC, SOC, and NO₃⁻-N. Regression analysis was used to analyse the relationship between SWR, SWD, and soil water infiltration depth and recovery years. The significant differences in measured variables were determined with Duncan’s multiple range tests at P < 0.05 and P < 0.01 All statistical analyses were performed using SPSS 22.0 (SPSS Inc., Chicago, IL, USA). A map (Fig. 1) was created in ArcGIS 10.5 (Environmental Systems Resource Institute, USA), and the other charts were generated by Origin 2018 (Origin Lab, Northampton, ME, USA).

Structural equation modeling (SEM) was used to determine the standard total effects of the variables on the spatial variations of SWC using Amos 24 (IBM Corporation Software Group, NY, USA), which shows systematic perspectives and driving mechanisms across different variables by partitioning direct and indirect effects. The fitness of SEM was evaluated using the chi-square test (χ²), goodness-of-fit index (GFI), Adjusted Goodness-of-Fit Index (AGFI), and root mean square error of approximation (RMSEA) (Arbuckle., 2011).

3.1 Spatial variations of SWC in orchard-converted croplands with different recovery years

The SWC greatly varied with the recovery years of orchards to croplands (Fig. 2). The average SWC of AO (13.91%) in the 0–15 m profile was significantly lower than that of croplands with different recovery years. In addition, no obvious variation was noted in average SWCs (16.54% and 16.23%) between the croplands with RC1 and RC3, similar variations of SWCs (17.74% and 17.92%) were also found in RC5 and RC10 with longer recovery years. However, the SWC in croplands with the longer recovering years (RC5 and RC10) was significantly higher than that of shorter recovery years (RC1 and RC3) (P < 0.05). Moreover, the study found that the soil water mainly recovered in the 6–9 m profile of cropland after returning from orchards. Specifically, the SWC of 6–9 m profile maximumly increased from 11.82% (AO) to 17.86% (RC1), 17.86% (RC3), 21.09% (RC3), and 21.39% (RC5), respectively.

[Fig. 2]

Soil depth also exerted a substantial influence on the SWC of returning orchards to cropland (Table 1). The SWCs of orchard and cropland showed an “S-shaped” distribution trend in 0–15 m profile, which increased and then decreased with the increase of soil depth (Fig. 3). Specifically, the SWCs in 0–3 m profile were significantly lower than in the 3–6 m profile in AO and cropland. In particular, the SWCs of AO, RC1 and RC3 reached the maximum value in 0–15 m profile at 3–6 m were 17.77%, 21.15% and 20.64%, respectively, while the highest SWC of RC5 and RC10 were 21.09% and 21.52% at 6–9 m, respectively. As the recovery years increased, the deep SWC of the cropland returned from orchards increased gradually, but the deep SWC of RC10 was significantly lower than that of CL.

Table 1

Mean soil water content (SWC) within 0–15 m soil layer of returning apple orchards to cropland
Soil depth/m	AO	RC1	RC3	RC5	RC10	CL
0–3	14.66Ba	16.43Ba	15.74Ca	15.80Ca	16.93Ba	15.91Da
3–6	17.77Ab	21.15Aa	20.64Aa	20.69Aa	21.21Aa	20.47Ba
6–9	11.82Cc	17.86Bb	17.58Bb	21.09Aa	21.52Aa	21.39Ba
9–12	11.87Ce	13.41Cd	13.44Dd	18.24Bb	15.07Cc	23.24Aa
12–15	13.25BCcd	13.88Cc	13.77Dc	12.88Dd	15.13Cb	18.43Ca
0–15	13.87d	16.546c	16.234c	17.74b	17.97b	19.89a
Notes: Different lowercase letters indicate significant differences in SWC between different recovery years of the same soil depth (P < 0.05), and different capital letters indicate significant differences in SWC between soil depths at the same recovery years.

[Table. 1]

3.2 Spatial variations of SWR and SWD in cropland with different recovery years

The SWR of returned cropland was closely related to the recovery years (Fig. 3). Compared to AO, the SWR of returned cropland exhibited a ‘logarithmic’ distribution (R² = 0.91), which showed a rapid upward trend then stabilized with the increase of recovery years. The SWR of 3–15 m in the recovered croplands increased from 45.33 mm (RC1) to 70.86 mm (RC10), the increasing rate of SWR slowed down when the recovery year was more than 5. Specifically, the SWR reached its highest value at 6–9 m, and the recovery amounts of RC1, RC3, RC5, and RC10 accounted for 41%, 43%, 37%, and 41% of the recovery amounts of 3–15 m. Overall, the annual increase in the SWR in recovered croplands was 0.59 mm·m^− 1·a^− 1. While the SWD showed the opposite downwards trend then stabilized. The SWD of AO (112.7 mm) was higher than that of other croplands. Meanwhile, the SWD of the 3–15 m in the orchard decreased from 9.39 mm·m^− 1 (AO) to 3.44 mm·m^− 1 (RC10). In addition, the results showed that the soil water infiltration depth of recovered cropland had the same logarithmic trend of change with SWR (R² = 0.92). With the increasing recovery years, the soil water infiltration depths rapidly deepened to 6.2 m (RC1) and 6.3 m (RC3), then slowly increased in 5 years after orchards fell, deepened to 8.2 m (RC5) and 8.6 m (RC10).

[Fig. 3]

3.3 Spatial variation of soil NO₃⁻-N in AO and croplands with different recovery years

The NO₃⁻-N value for both AO and croplands with different recovery years in the 0–15 m soil profile is plotted in Fig. 4 (a). There were similar vertical variations in NO₃⁻-N for the two land use types, increasing first and then decreasing with increasing soil depths and being relatively low and stable in the deeper profile. The average content of NO₃⁻-N in AO (104.32 mg kg^− 1), RC1 (77.53 mg kg^− 1), RC3 (89.16 mg kg^− 1), RC5 (110.26 mg kg^− 1) and RC10 (91.46 mg kg^− 1) were significantly higher than that of in CL (5.93 mg kg^− 1) (P < 0.05). The peak of nitrate content in AO and recovered cropland was significantly higher than that in the CL (P < 0.05). Significantly linear relationships were found between the peak depths and recovery years (R² = 0.92, P < 0.05), with the peak depths in AO, RC1, RC3, RC5 and RC10 were 3.4 m, 4.8 m, 4.4 m, 7.0 m and 5.6 m, respectively, and reached its highest value in CL (9.4 m), with a peak downward rate of 0.72 m·a^− 1 after orchard removal.

[Fig. 4]

3.4 Response of SWC and NO₃⁻-N dynamics to environmental factors

To analyze the influence of environmental factors on SWC and NO₃⁻-N dynamics, we separately assessed the direct and indirect path correlation coefficients using SEM modeling (Fig. 5). The results showed that the relationship between and the driving factors could be well fitted by established SEM models, with RMSEA ≤ 0.060 and GFI ≥ 0.987 for the various soil layers (Fig. 5). As shown in Fig. 5, recovery years, soil depth, clay, sand had both direct and indirect effects on SWC, the SOC had only direct effects. Recovery years, clay and SOC exhibited positive standardized total effects on SWC, soil depth only had positive effects on SWC in 0–5 m soil profile (Table 2). In 0–5 m profile, soil depth directly affected the SWC with a direct effect of 0.988, and indirectly decreased the SOC by affecting SWC, with an indirect effect of 0.345 (Table 2). Therefore, the positive standardized total effect of SWC on soil depth (0–5 m) was 0.643. In contrast, the direct path relationship between recovery years and SWC was not significantly. With the increasing soil depth, recovery years were the most important environmental determinant of the SWC in the 5–15 m soil profile, with the standardized total effect was 0.57 and 0.39 in 5–10 m and 10–15 m soil profile, respectively.

Table 2

Standardized total, direct and indirect effects of the driving factors of SWC (soil water content) in the Loess Tableland study area determined using structural equation models.
	Soil depth/m	Standardized effect	Soil depth	Recovery years	Soil particle		SOC	SWC
	Soil depth/m	Standardized effect	Soil depth	Recovery years	Clay	Sand	SOC	SWC
SWC	0–5	Total	0.643	0.026	0.274	0.120	0.428	\
		Direct	0.988	0.000	0.120	0.000	0.428	\
		Indirect	-0.345	0.026	0.154	0.120	0.000	\
	5–10	Total	-0.552	0.571	0.300	0.000	0.093	\
		Direct	-0.354	0.432	0.277	0.000	0.093	\
		Indirect	-0.188	0.139	0.022	0.000	0.000	\
	10–15	Total	-0.248	0.388	0.190	0.000	0.383	\
		Direct	0.007	0.354	-0.006	0.000	0.383	\
		Indirect	-0.255	0.035	0.186	0.000	0.000	\
NO₃⁻-N	0–5	Total	0.640	-0.367	0.341	0.121	0.217	0.074
		Direct	0.767	-0.408	0.254	0.121	0.185	0.074
		Indirect	-0.128	0.040	0.087	0.000	0.032	0.000
	5–10	Total	-0.600	0.338	-0.181	0.000	0.044	0.477
		Direct	-0.500	0.216	-0.324	0.000	0.000	0.477
		Indirect	-0.099	0.122	0.143	0.383	0.044	0.000
	10–15	Total	0.141	-0.018	-0.221	0.000	-0.361	-0.035
		Direct	-0.099	0.030	-0.046	0.000	-0.348	-0.035
		Indirect	-0.240	-0.048	-0.175	0.000	-0.013	0.000

Similarly, path analysis identified recovery years, soil depth, clay, and SOC as being factors having the most important influence on NO₃⁻-N (Fig. 5), among which, soil depth, with a direct path coefficient of 0.77, 0.50, and 0.66 in 0–5 m, 5–10 m, 10–15 m soil profile, respectively, appeared to play a decisive negative role in determining NO₃⁻-N. Conversely, recovery years and SWC, with direct path coefficients of 0.22 and 0.48 in 5–10 m soil profile, were shown to have positive effects on NO₃⁻-N.

[Fig. 5]

[Table. 2]

4.1 Soil water recovery process and dominated factors in orchard-to-cropland conversion

Long-term cultivation of deep-rooted vegetation can induce or exacerbate permanent soil desiccation (Jia et al., 2015). As apple trees matured, soil water content (SWC) in the apple orchard decreased with increasing soil depth. For instance, the average SWC in a 21-year-old apple orchard (13.68%) within the 3–15 m soil profile was significantly lower compared to cropland (20.89%) (Table 1), resulting in severe water deficit, consistent with prior research findings (Huang et al., 2018; Jia et al., 2017; Liu et al., 2018; Wang et al., 2023). Reclaiming permanent soil desiccation on the CLP is challenging due to generally sparse rainfall, deep-root vegetation consumption, and intense evaporation (Wang et al., 2011; Jia et al., 2015). Studies have explored methods to mitigate soil desiccation by removing deep-rooted vegetation (Huang and Gallichand, 2006; Wang et al., 2008; Liu et al., 2010). Addressing the issue of deep soil water desiccation in aging orchards on the CLP, we observed that differences in soil water recovery (SWR) were influenced by recovery years and soil depths. SWR predominantly occurred in the overlap between the depth of apple root growth and the depth unreachable by rainfall infiltration. Specifically, in the 0–3 m soil layer, there was no significant difference in SWC between the original orchard (AO) and the converted croplands (RC). However, deeper soil layers (3–9 m) exhibited rapid SWC replenishment in RC1 and RC3 following orchard-to-cropland conversion. This was attributed to the removal of apple tree roots, which opened up root channels and increased non-capillary soil space, facilitating preferential water pathways and enhancing water infiltration during rainfall events (Ali et al., 2018; Cui et al., 2022; Zheng et al., 2017). As recovery years increased, the rate of deep SWR decreased progressively from RC5 to RC10, consistent with previous findings (Moore et al., 2010, 2012; Silburn et al., 2009). Four years after conversion, root channels collapsed and were compacted, resulting in a decline in infiltration rate with prolonged cropping. In our study, the inherently loose nature of loess soil meant that disturbances such as orchard removal only had short-term effects on soil physical properties (Li et al., 2022). This initially impacted deep soil water within five years, as shown by the intercept of the linear relationship between SWR and recovery years post-orchard removal (Fig. 3). In conclusion, orchard-to-cropland conversion effectively replenishes deep soil water primarily because mature orchard root systems no longer deplete soil water post-removal, and decayed roots form pore spaces that enhance rainfall infiltration. Our previous research indicated that apple orchards aged 10–30 years experienced an annual soil water deficit rate of 5.94 mm·m^− 1·a^− 1 (Tian et al., 2024). Conversely, the calculated soil water recovery rate post-conversion was 5.90 mm·m^− 1·a^− 1, suggesting that soil desiccation caused by mature orchards can potentially recover within corresponding years following orchard removal.

4.2 Nitrate leaching and its potential impact on the environment

The nitrate peak and leaching depth in recovered croplands were significantly correlated with the years since orchard removal. Our study revealed substantial nitrate accumulation in the deep soil profiles of mature apple orchards, with both nitrate peak levels and leaching depths showing a notable upward trend as recovery years increased (P < 0.05). This trend aligns with previous findings (Vogeler et al., 2006; Besson et al., 2011; Perego et al., 2012). In the 0–5 m soil profile, intensive nitrogen fertilizer applications and increased water infiltration contributed to significant NO₃⁻-N accumulation (Huang et al., 2001). However, following orchard removal, reduced nitrogen inputs and enhanced soil water recovery led to nitrate dilution and horizontal diffusion (Tian et al., 2024), resulting in decreased NO₃⁻-N concentrations. Persistent nitrogen surplus and water balance issues can perpetuate nitrate accumulation and migration within the soil profile (Zhu et al., 2022). The CLP, predominantly rain-fed agriculture, experiences concentrated high-intensity rainfall from July to September, facilitating downward water movement and nitrate leaching (Li et al., 2019; Zhu et al., 2022). Furthermore, the decomposition of roots post-orchard removal creates large pores where preferential and piston flows coexist, promoting rapid nitrate loss following precipitation events in recovered croplands. Despite dried soil layers hindering nitrate leaching, they do not completely prevent it (Broeke, 2001; Perego et al., 2012; Dai et al., 2016; Ji et al., 2020; Zhang et al., 2022). Soil water dynamics are critical in governing NO₃⁻-N movement (Sigler et al., 2020; Zhou et al., 2016). Orchard removal enhances soil water infiltration and increases soil water storage in deep profiles, yet it also accelerates downward nitrate leaching, potentially exerting prolonged impacts on soil NO₃⁻-N and posing risks to groundwater quality.

4.3 Trade-off between soil water recovery and nitrate leaching

This study demonstrates that long-term apple orchard cultivation leads to decreased soil water content (SWC) in deeper layers, resulting in soil desiccation that partially limits nitrate leaching into the deep soil. Conversely, following orchard removal, croplands rapidly replenish soil water, alleviating soil deficits initially caused by orchard-induced desiccation. Orchard-to-cropland conversion expands cultivable land and mitigates economic losses associated with declining or dead apple orchards. However, due to substantial differences in nutrient requirements between apple trees and crops, coupled with increased water inputs that exacerbate surplus nitrate leaching and accumulation in deep soil, there is a significant threat to groundwater quality, presenting a notable environmental concern for the CLP. Clearly, there is a trade-off between soil water recovery and nitrate leaching as orchard converting to cropland. Further research is imperative to understand the complex interplay between soil water dynamics and nitrate behavior. Optimizing nitrogen management post-conversion, possibly through cultivation of crops with higher nitrate uptake efficiency, represents a promising avenue for addressing these challenges.

In this study, the space-for-time substitution method was employed to address the effects of apple orchard (> 20 years old) to croplands conversion on soil water content (SWC) and soil nitrate dynamics. The findings revealed that converting orchards to croplands led to rapid replenishment of previously desiccated deep soil layers (6–9 m) within five years following the removal of apple trees, followed by a stable but gradual increase thereafter. With increasing years since the conversion, enhanced soil water infiltration significantly contributed to nitrate leaching and accumulation in deeper soil layers. And SWC emerged as the principal factor influencing soil nitrate leaching, with soil depth, recovery duration, clay content, and soil organic carbon (SOC) acting as primary influencers of nitrate dynamics within the soil profile. The orchard to cropland conversion induced a trade-off between soil water recovery and nitrate leaching. These insights highlight that, following large-scale conversion of orchards to croplands, while soil water in the dried soil layers is restored, nitrogen leaching also occurs. This is of significant value for future water and nutrient management after orchard-to-cropland conversions on the CLP.

Author Contribution

Tian.H and Jin. M wrote the main manuscript text and prepared the all figures, Sidra. S, Ma. C and Bai. C participated in the collection and processing of soil samples, Qiao. J, Han.X, Zhu.Y and Shao. M reviewed and edited the manuscript. All authors reviewed the manuscript.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (42377316 and 42307412), and the Strategy Priority Research Program of Chinese Academy of Sciences (XDB40000000).

Data Availability

The nitrate datasets used and analysed during the current study available from the corresponding author on reasonable request, and the soil water content datasets were provided within the supplementary information files

Ali, K., Xue, X., Kang, D., Wen, C., Ghaffar, S., Muhammad, R., 2018. The effects of different land-uses on soil hydraulic properties in the Loess Plateau, Northern China. Land Degrad. Deve. 29, 1–10. https://doi.org/10.1002/ldr.3138.
Arbuckle, J.L., 2011. IBM SPSS Amos 20 User’s Guide. IBM Corporation, New York.
Ascott, M., Wang, L., Stuart, M., Ward, R., Hart, A., 2016. Quantification of nitrate storage in the vadose (unsaturated) zone: a missing component of terrestrial N budgets. Hydrol. Process. 30, 1903–1915. https://doi.org/10.1002/hyp.10748.
Bai, X., Jia, X., Jia, Y., Shao, M., Hu, W., 2020. Modeling long-term soil water dynamics in response to land-use change in a semi-arid area. J. Hydrol. 585, 124824. https://doi.org/10.1016/j.jhydrol.2020.124824.
Bai, X., Jia, X., Zhao, C., Shao, M., 2021. Artificial forest conversion into grassland alleviates deep-soil desiccation in typical grass zone on China's loess plateau: regional modeling. Agric., Ecosyst. Environ. 320, 107608. https://doi.org/10.1016/j.agee.2021.107608
Bao, S.D., 2000. Soil Agrochemical Analysis. China Agriculture Press, Beijing.
Berner, L.T., Law, B.E., Hudiburg, T.W., 2017. Water availability limits tree productivity, carbon stocks, and carbon residence time in mature forests across the western US. Biogeosciences 14, 365–378. https://doi.org/10.5194/bg-14-365-2017.
Besson, A., Javaux, M., Bielders, C., Vanclooster, M., 2011. Impact of tillage on solute transport in a loamy soil from leaching experiments. Soil Till. Res. 112, 47 –57. https://doi.org/10.1016/j.still.2010.11.001.
Broeke, H. T., 2001. Nitrate leaching to groundwater at experimental farm 'de marke' and other dutch sandy soils. Netherlands J Agr Sci. 49, 195–205. https://doi.org/10.1016/S1573-5214(01)80007-5.
Chen, Y., Wang, K., Lin, Y., et al. 2015. Balancing green and grain trade. Nat Geosci. 10: 739-741. https://doi.org/10.1038/ngeo2544.
Cristiano, P.M., Posse, G., Bella, C., 2015. Total and aboveground radiation use efficiency in C3 and C4 grass species influenced by nitrogen and water availability. Grassl. Sci. 61, 131–141. https://doi.org/10.1111/grs.12086.
Cui, Z., Huang, Z., Wang, Y., Qian, J., Wu, G., 2022. Soil water deficit was effectively alleviated by higher water infiltration after the short-term forestland-to-farmland conversion in semi-arid area. J. Hydrol. 610, 127893. https://doi.org/10.1016/j.jhydrol.2022.127893.
Dai, J., Wang, Z., Li, M., He, G., Li, Q., Cao, H., Wang, S., Gao, Y., Hui, X., 2016. Winter wheat grain yield and summer nitrate leaching: long-term effects of nitrogen and phosphorus rates on the loess plateau of China. Field Crop Res. 196, 180–190. https://doi.org/10.1016/j.fcr.2016.06.020.
Deng, Y., Wang, S., Bai, X., Luo, G., Wu, L., Chen, F., Wang, J., Li, C., Yang, Y., Hu, Z., Tian, S., Lu, Q., 2020. Vegetation greening intensified soil drying in some semi-arid and arid areas of the world. Agr. Forest. Meteorol. 292–293. https://doi.org/ 10.1016/j.agrformet.2020.108103.
Fu, B., Liu, Y., Lü, Y., He, C., Zeng, Y., Wu, B., 2011. Assessing the soil erosion control service of ecosystems change in the Loess Plateau of China. Ecol Complex. 8(4), 284–293. https://doi.org/10.1016/j.ecocom.2011.07.003.
Huang, M., Gallichand, J. 2006. Use of the SHAW model to assess soil water recovery after apple trees in the gully region of the Loess Plateau, China. Agric. Water Manag. 85(1-2), 67-76. https://doi.org/10.1016/j.agwat.2006.03.009.
Huang, M., He, F., Yang, X., Li, Y., 2001. Effect of apple production base on regional water cycle in Weibei upland of the Loess Plateau. J. Geogr. Sci. 11 (2), 239–241. https://doi.org/10.1007/BF02888697.
Huang, Z., Liu, Y., Cui, Z., Fang, Y., He, H.H., Liu, B.R., Wu, G.L., 2018. Soil water storage deficit of alfalfa (Medicago sativa) grasslands along ages in arid area (China). Field. Crop Res. 221, 1–6. https://doi.org/10.1016/j.fcr.2018.02.013.
Gao, X., Liu, Z., Zhao, X., Ling, Q., Huo, G., Wu, P., 2018. Extreme natural drought enhances interspecific facilitation in semiarid agroforestry systems. Agric. Ecosyst. Environ. 265, 444–453. https://doi.org/10.1016/j.agee.2018.07.001.
Ghuman, B., Lal, R., Shearer, W., 1991. Land clearing and use in the humid Nigerian tropics: I. Soil physical properties. Soil Sci. Soc. Am. J. 55, 178–183. https://doi.org/ 10.2136/sssaj1991.03615995005500010031x.
Gu, B., Ge, Y., Chang, S., Luo, W., Chang, J., 2013. Nitrate in groundwater of China: Sources and driving forces. Glob. Environ. Chang. 23, 1112–1121. https://doi.org/ 10.1016/j.gloenvcha.2013.05.004.
Ji, W., Huang, Y., Li, B., Hopkins, D. W., Liu, W., Li, Z., 2020. Legacy nitrate in the deep loess deposits after conversion of arable farmland to non‐fertilized land uses for degraded land restoration. Land Degrad. Deve. 31, 1355–1365. https://doi.org/10.1002/ldr.3532
Jia, X., Shao, M., Zhang, C., Zhao, C., 2015. Regional temporal persistence of dried soil layer along south–north transect of the Loess Plateau, China. J. Hydrol. 528: 152-160. https://doi.org/10.1016/j.jhydrol.2015.06.025.
Jia, X., Shao, M., Zhu, Y., Luo, Y., 2017. Soil moisture decline due to afforestation across the Loess Plateau, China. J. Hydrol. 546, 113-122. https://doi.org/10.1016/j.jhydrol.2017.01.011.
Jia, X., Zhao, C., Wang, Y., Zhu, Y., Wei, X., Shao, M., 2020. Traditional dry soil layer index method overestimates soil desiccation severity following conversion of cropland into forest and grassland on China’s Loess Plateau. Agric. Ecosyst. Environ. 291: 106794. https://doi.org/10.1016/j.agee.2019.106794.
Ju, X., Liu, X., Zhang, F., Roelcke, M., 2004. Nitrogen fertilization, soil nitrate accumulation, and policy recommendations in several agricultural regions of China. Ambio. 33(6), 300–305. https://doi.org/10.1579/0044–7447–33.6.300.
Kachurina, O., Zhang, H., Raun, W., Krenzer, E., 2000. Simultaneous determination of soil aluminum, ammonium-and nitrate-nitrogen using 1 M potassium chloride extraction. Commun. Soil Sci. Plant Anal. 31, 893–903. https://doi.org/10.1080/ 00103620009370485.
Kuang, XX, Liu, JG, Scanlon, BR, Jiao, JJ, Jasechko, S, Lancia, M, Biskaborn, BK, Wada, Y, Li, HL, Zeng, ZZ, Guo, ZL, Yao, YY, Gleeson, T, Nicot, J-P, Luo, X, Zou, YG, Zheng, CM, 2024. The changing nature of groundwater in the global water cycle. Science, 383(6686): eadf0630. https://doi.org/10.1126/science.adf0630.
Li, H., Li, Z., Chen, Y., Xiang, Y., Liu, Y., Kayumba, P., Li, X., 2021. Drylands face potential threat of robust drought in the CMIP6 SSPs scenarios. Environ Res Lett. 16, 114004. https://dio.org/10.1088/1748-9326/ac2bce.
Li, H., Si, B., Wu, P., McDonnell, J., 2019. Water mining from the deep critical zone by apple trees growing on loess. Hydrol. Process. 33 (2), 320–327. https://doi.org/ 10.1002/hyp.13346.
Liu, B., Shao, M., 2015. Modeling soil–water dynamics and soil–water carrying capacity for vegetation on the Loess Plateau, China. Agric. Water Manag. 159, 176–184. https://doi.org/10.1016/j.agwat.2015.06.019.
Liu, L., Gudmundsson, L., Hauser, M., Qin, D., Seneviratne, S., 2020. Soil moisture dominates dryness stress on ecosystem production globally. Nat Commun. 11(1), 4892. https://doi.org/10.1038/s41467-020-18631-1.
Liu, W., Zhang, X., Dang, T., Ouyang, Z., Li, Z., Wang, J., Wang, R., Gao, C., 2010. Soil water dynamics and deep soil recharge in a record wet year in the southern Loess Plateau of China. Agric. Water Manage. 97 (8), 1133–1138. https://doi.org/ 10.1016/j.agwat.2010.01.001.
Liu, Y., Miao, H., Huang, Z., Cui, Z., He, H.H., Zheng, J.Y., Han, F.P., Chang, X.F., Wu, G.L., 2018. Soil water depletion patterns of artificial forest species and ages on the loess plateau (China). Forest Ecol. Manag. 417, 137–143. https://doi.org/ 10.1016/j.foreco.2018.03.005.
Lozano-Baez, S., Cooper, M., Meli, P., Ferraz, S., Rodrigues, R., Sauer, T., 2019. Land restoration by tree planting in the tropics and subtropics improves soil infiltration, but some critical gaps still hinder conclusive results. Forest Ecol. Manag. 444, 89–95. https://doi.org/10.1016/j.foreco.2019.04.046.
Manrique-Alba, A., Beguería, S., Molina, A., Gonz ́ alez-Sanchis, M., Camarero, J., 2020. Long-term thinning effects on tree growth, drought response and water use efficiency at two Aleppo pine plantations in Spain. Sci. Total Environ. 728, 138536. https://doi.org/ 10.1016/j.scitotenv.2020.138536.
McColl, K.A., Alemohammad, S.H., Akbar, R., Konings, A.G., Yueh, S., Entekhabi, D., 2017. The global distribution and dynamics of surface soil moisture. Nat. Geosci. 10, 100–104. https://doi.org/10.1038/ngeo2868.
Moore, G., Barre, D., Owens, M., 2010. Changes in soil chloride following shrub removal and subsequent regrowth. Geoderma. 158, 148–155. https://doi.org/ 10.1016/j.geoderma.2010.04.020.
Niccoli, F., Pelleri, F., Manetti, M., Sansone, D., Battipaglia, G., 2020. Effects of thinning intensity on productivity and water use efficiency of Quercus robur L. Forest Ecol. Manag. 473, 118282. https://doi.org/10.1016/j.foreco.2020.118282.
Page, A., Miller, R., Kenney, D., 1982. Methods of Soil Analysis Part 2 (Agronomy. In: Monographs, 9. American Society of Agronomy, Madison, Wisconsin, USA. https:// doi.org/10.1016/j.geoderma.2019.04.033.
Perego, A., Basile, A., Bonfante, A., De Mascellis, R., Terribile, F., Brenna, S., Acutis, M., 2012. Nitrate leaching under maize cropping systems in Po Valley (Italy). Agric., Ecosyst. Environ. 147, 57–65. https://doi.org/10.1016/j.agee.2011.06.014.
Shao, M.A., Wang, Y., Xia, Y., Jia, X., 2018. Soil drought and water carrying capacity for vegetation in the critical zone of the Loess Plateau: A review. Vadose Zone J. 17 (1), 1–8. https://doi.org/10.2136/vzj2017.04.0077.
Sherwood, S., Fu, Q., 2014. A drier future? Science. 343, 737–739. https://doi.org/ 10.1126/science.1247620.
Sigler, W. A·Ewing, S., Jones, C., Payn, R., Miller, Perry., Marco, M., 2020. Water and nitrate loss from dryland agricultural soils is controlled by management, soils, and weather. Agric., Ecosyst. Environ. 304, 107158. https://doi.org/10.1016/j.agee.2020.107158.
Tao, Z., Si, B., 2021. Determining deep root water uptake patterns with tree age in the Chinese loess area. Agric. Water Manage. 249, 106810. https://doi.org/10.1016/j. agwat.2021.106810.
Tian, H., Fang., F., Wang, Z., Li, S., Qiao, J., Han, X., Zhu, Y., Liu, W., 2024. A mosaic pattern of apple orchards and farmland affects the distribution of soil water and nutrients in their adjacent areas on the Chinese Loess Plateau. Catena. 237: 107776. https://doi.org/10.1016/j.catena.2023.107776.
Van Loon, A., Gleeson, T., Clark, J., Van Dijk, A., Stahl, K., Hannaford, J., Di Baldassarre, G., Teuling, A., Tallaksen, L., Uijlenhoet, D., Hannah, D., Sheffield, J., Svoboda, M., Verbeiren, B., Wagener, T., Rangecroft, S., Wanders, N., Van Lanen, H., 2016. Drought in the Anthropocene. Nat. Geosci. 9, 89–91. https://doi.org/10.1038/ngeo2646.
Vogeler, I., Horn, R., Wetzel, H., Krümmelbein, J., 2006. Tillage effects on soil strength and solute transport. Soil Till. Res. 88, 193–204. https://doi.org/10.1016/j. still.2005.05.009.
Wang, X., Li, J., Tahir, M., Fang, X., 2012. Validation of the EPIC model and its utilization to research the sustainable recovery of soil desiccation after alfalfa (Medicago sativa L.) by grain crop rotation system in the semi-humid region of the Loess Plateau. Agric., Ecosyst. Environ. 161, 152–160. https://doi.org/10.1016/j. agee.2012.07.013.
Wang, X., Muhammad, T., Hao, M., Li, J., 2011. Sustainable recovery of soil desiccation in semi-humid region on the Loess Plateau. Agric. Water Manag. 98, 1262–1270. https://doi.org/10.1016/j.agwat.2011.03.007.
Wang X L, Sun G J, Jia Y, Li F M, Xu J Z. 2008. Crop yield and soil water restoration on 9-year-old alfalfa pasture in the semiarid Loess Plateau of China. Agr Water Manage. 95: 190–198. https://doi.org/10.1016/j.agwat.2007.10.001.
Wang, Y., Han, X., Yan, W., Cheng, L., Dang, X., Liu, W., 2023. Apple trees can extract soil water from both deep layers and neighboring cropland in the tableland region of Chinese Loess Plateau. Catena 232, 107396. https://doi.org/10.1016/j. catena.2023.107396.
Wang, Y., Shao, M., Liu, Z., Zhang, C., 2015. Characteristics of Dried Soil Layers Under Apple Orchards of Different Ages and Their Applications in Soil Water Managements on the Loess Plateau of China. Pedosphere. 25 (4), 546–554. https://doi.org/ 10.1016/s1002–0160(15)30035–7.
Wang, Y., Shao, M., Sun, H., Fu, Z., Fan, J., Hu, W., Fang, L., 2020. Response of deep soil drought to precipitation, land use and topography across a semiarid watershed. Agric. For. Meteorol. 282–283, 107866 https://doi.org/10.1016/j. agrformet.2019.107866.
Wu, G., Cui, Z., Huang, Z., 2021. Contribution of root decay process on soil infiltration capacity and soil water replenishment of planted forestland in semi-arid regions. Geoderma. 404, 115289. https://doi.org/10.1016/j.geoderma.2021.115289.
Xu, L., Gao, G., Wang, X., Fu, B., 2023. Distinguishing the effects of climate change and vegetation greening on soil moisture variability along aridity gradient in the drylands of northern China. Agr. Forest. Meteorol. 343: 109786. https://doi.org/10.1016/j.agrformet.2023.109786.
Zhang, X., 2002. Study on the composition of soil particles and texture zoning of the Loess Plateau. Soil and Conservation in China. 3: 14–16+47.
Zhang, Y., Dong, X., Yang, X., Munyampirwa, T., Shen, Y., 2022. The lagging movement of soil nitrate in comparison to that of soil water in the 500-cm soil profile. Agric., Ecosyst. Environ. 326, 107811. https://doi.org/10.1016/j.agee.2021.107811.
Zhao, Y., Zhang, B., Hill, R., 2012. Water use assessment in alley cropping systems within subtropical China. Agroforest Syst. 84: 243–259.
Zheng, S., Si, B., Zhang, Z., Min, L., Fan, W., 2017. Mechanism of rainfall infiltration in apple orchards on Loess Tableland, China. Chin. J. Appl. Ecol. 28, 2870–2878. https://doi.org/10.13287/j.1001-9332.201709.031.
Zhou, J., Gu, B., Schlesinger, W., Ju, X., 2016. Significant accumulation of nitrate in Chinese semi–humid croplands. Sci. Rep. 6, 25088. https://doi.org/10.1038/ srep25088.
Zhu, X., Fu, W., Kong, X., Chen, C., Liu, Z., Chen, Z., Zhou, J., 2021. Nitrate accumulation in the soil profile is the main fate of surplus nitrogen after land-use change from cereal cultivation to apple orchards on the Loess Plateau. Agr. Ecosyst. Environ. 319, 107574. https://doi.org/10.1016/j.agee.2021.107574.
Zhu, X., Miao, P., Wang, P., Zhang, S., Chen, Z., Zhou, J., 2022. Variations and influencing factors of nitrate accumulation in the deep soil profiles of apple orchards on the loess plateau. Agric., Ecosyst. Environ. 335, 108005. https://doi.org/10.1016/j.agee.2022.108005
Zhu, Y., Jia, X., Shao, M. 2018. Loess Thickness Variations Across the Loess Plateau of China. Surv Geophys. 39 (4): 715-727. https://doi.org/ 10.1016/j.agee.2022.108005.

No competing interests reported.

Supplementarymaterail.docx

Download PDF

Reviewers agreed at journal
24 Sep, 2024
Reviewers invited by journal
13 Sep, 2024
Editor assigned by journal
13 Sep, 2024
Editor invited by journal
29 Aug, 2024
Submission checks completed at journal
27 Aug, 2024
First submitted to journal
09 Aug, 2024

You are reading this latest preprint version

The trade-off between soil water recovery and nitrate leaching following the conversion of orchards to croplands in the tableland region of the Chinese Loess Plateau

Status:

Version 1

Abstract

Figures

1 Introduction

2 Materials and methods

2.1 Study area

2.2 Experimental plot selection for orchard and cropland

2.3 Sample collection and processing

2.4 Data analysis

3 Results

3.1 Spatial variations of SWC in orchard-converted croplands with different recovery years

3.2 Spatial variations of SWR and SWD in cropland with different recovery years

3.3 Spatial variation of soil NO₃⁻-N in AO and croplands with different recovery years

3.4 Response of SWC and NO₃⁻-N dynamics to environmental factors

4 Discussions

4.1 Soil water recovery process and dominated factors in orchard-to-cropland conversion

4.2 Nitrate leaching and its potential impact on the environment

4.3 Trade-off between soil water recovery and nitrate leaching

5 Conclusions

Declarations

Author Contribution

Acknowledgments

Data Availability

References

Additional Declarations

Supplementary Files

Status:

Version 1

The trade-off between soil water recovery and nitrate leaching following the conversion of orchards to croplands in the tableland region of the Chinese Loess Plateau

Status:

Version 1

Abstract

Figures

1 Introduction

2 Materials and methods

2.1 Study area

2.2 Experimental plot selection for orchard and cropland

2.3 Sample collection and processing

2.4 Data analysis

3 Results

3.1 Spatial variations of SWC in orchard-converted croplands with different recovery years

3.2 Spatial variations of SWR and SWD in cropland with different recovery years

3.3 Spatial variation of soil NO3−-N in AO and croplands with different recovery years

3.4 Response of SWC and NO3−-N dynamics to environmental factors

4 Discussions

4.1 Soil water recovery process and dominated factors in orchard-to-cropland conversion

4.2 Nitrate leaching and its potential impact on the environment

4.3 Trade-off between soil water recovery and nitrate leaching

5 Conclusions

Declarations

Author Contribution

Acknowledgments

Data Availability

References

Additional Declarations

Supplementary Files

Status:

Version 1

3.3 Spatial variation of soil NO₃⁻-N in AO and croplands with different recovery years

3.4 Response of SWC and NO₃⁻-N dynamics to environmental factors