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Article

Quantifying Phosphorus Leaching Loss from Mollisol with Organic Amendments

by
Hongyan Wang
1,2,
Shuxiang Zhang
3,
Chang Peng
4,
Guangyu Chi
1,*,
Xin Chen
1,
Bin Huang
1,
Caiyan Lu
1,
Jizhi Li
1,2 and
Li Xu
5
1
Key Laboratory of Pollution Ecology and Environment Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China
4
Northeast Agricultural Research Center of China, Jilin Academy of Agricultural Sciences, Changchun 130033, China
5
School of Municipal and Environmental Engineering, Shenyang Jianzhu University, Shenyang 110016, China
*
Author to whom correspondence should be addressed.
Agronomy 2022, 12(10), 2490; https://doi.org/10.3390/agronomy12102490
Submission received: 10 September 2022 / Revised: 1 October 2022 / Accepted: 10 October 2022 / Published: 13 October 2022
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Versions Notes

Abstract

:
The phosphorus (P) leaching from continuous fertilization is generally neglected in mollisol. The in situ leaching loss of phosphorus (P), especially dissolved organic P, is poorly quantified under organic amendments given its potential environmental risks. In this study, we conducted an in situ soil column experiment, instead of the traditional measuring of the soil layer, in the mollisol area of northeast China to investigate the seasonal variations in different P forms under three typical fertilization practices, including chemical fertilizer (CF), CF supplemented with straw (CFS), and CF co-applied with straw and manure (CFSM). Compared with the CF treatment, CFS treatment generally reduced the leaching loss of dissolved organic P by 57.3% to reduce the total P loss, while the CFSM treatment increased the leaching loss of dissolved inorganic P by 20.9% to increase the total P loss. Other than the effects of management practices, precipitation and temperature-oriented environmental factors significantly affected the seasonal variation in leaching loss of both the dissolved and particulate P forms. We conclude that straw incorporation into the mollisol of northeast China is recommended, considering its low leaching risk of P, while a co-amendment of straw and manure resulted in the opposite. Despite the slight environmental risk of P leaching loss (0.75–1.95% of external P input per year) practically quantified by in situ experiments, a proper reduction in chemical P input with organic amendments may be an effective P fertilizer management strategy in mollisol areas.

1. Introduction

Phosphorus (P) is a critical nutrient for plant growth, and P fertilization is essential to maintain crop yield [1,2]. However, excessive P fertilization in agriculture leads to a P surplus in the soil and P loss through runoff and leaching [3,4,5]. P leaching into deeper soil layers has been observed in not only sandy soils but also in clay soils such as mollisol [6,7]. Despite the fact that mollisol has a high content of organic matter to contain the attached metals that react with P [8], high-rate P application increases soil P content and its leaching risk [9,10,11,12].
The input of P into soil by the application of either inorganic or organic fertilizers may cause the risk of the P leaching loss of dissolved P (DP) and/or particulate P (PP) [13,14,15]. Manure provides both DP and PP and thus could pose a greater risk of soil P leaching than chemical fertilizers [16], although the opposite result has also been reported [17]. In contrast, the mulching of straw as a typical practice proposed for improving the quality of mollisol of northeast China in recent years [18] might stimulate P immobilization to limit P loss by leaching. The co-application of straw and manure may exhibit a counteractive effect on P leaching [19]. Nevertheless, the available studies mainly rely on quantifying P accumulation in different soil layers to estimate its leaching loss risk, and direct quantification of the leaching loss of PP and DP under inorganic and/or organic fertilization is rarely evaluated under field conditions, i.e., mainly under simulated conditions [20,21,22].
DP in soil leachate may exist as dissolved inorganic P (DIP) and dissolved organic P (DOP) in various ratios [23,24,25]. DIP constitutes an important proportion of DP in all kinds of fertilizers [26,27], but the presence of DOPs such as phosphate monoester [28] is common in organic fertilizers such as manure. While drainage losses in paddy soils of DIP, DOP, and PP have been reported [24,29], seasonal variations in leaching losses of P in maize production, especially DOP, are rarely evaluated which could be utilized by aquatic organisms when phosphate levels are insufficient to satisfy their P-demand [30]; hence, the contribution of DOP to the leaching losses of DP and total P (TP) is poorly appreciated, especially in the mollisol area of northeast China.
Since the mollisol area of northeast China has uneven precipitation and the phenomenon of freeze–thaw under a semi-arid temperate climate, a joint consideration of the impacts of factors that regulate the availability of soil P in different forms (such as the application of organic and inorganic fertilizers) and factors that control the intensity of soil water leaching (such as frequency, intensity, and distribution of precipitation and freeze–thaw cycling) is much needed to understand P loss in various forms from mollisol in northeast China under organic amendments.
Organic fertilizers such as crop straw and animal manure are incorporated to improve soil fertility, whereas their overall impacts on P leaching remain unclear. Straw mulching has been widely adopted as a typical example of best management practice in the mollisol area of Northeast China in recent years [6]. Some researchers have estimated that straw residues could generate lower P loss by leaching [31]. In addition, the application of animal manure could provide additional P and appeared to pose a greater risk than the inorganic fertilizer [25], while Vanden Nest et al. [17] found the opposite results. However, such findings focus on the accumulation of nutrients in the soil layer to estimate P loss risks, resulting in the neglect of practically quantifying P leaching loss.
Therefore, we conducted a field study on the leaching losses of DIP, DOP, and PP in mollisol in northeast China based on the in situ soil column leaching experiments of a long-term field trial under chemical fertilization with and without organic amendments, with the following aims: (i) to quantify the contribution of DOP to leaching losses of DP and TP under the impacts of organic amendments; (ii) to clarify the seasonal pattern of leaching loss of each P form under typical fertilization practices; (iii) to evaluate environmental factors regulating the leaching of each P form.

2. Materials and Methods

2.1. Study Site and Experimental Design

The study area was located on typical agricultural land with the transplantation of forage maize in the Northeast Plain of China (43°59′ N, 124°71′ E), Chaoyangpo Town, Jilin Province. The climate of the study area is a semi-humid monsoon climate with an annual rainfall of 600–650 mm. The mean annual average temperature is 5 °C. The soil type is classified as mollisol according to the USDA soil taxonomy. The essential physical and chemical properties of the test soil are provided in Table 1.
The experiment has a randomized block design, started in 2015 with three fertilization treatments in triplicate. Each experimental plot was 91 m2 (13-m long and 7-m wide). The three fertilization treatments were: (i) chemical fertilizers (CF); (ii) CF plus maize straw (CFS); (iii) CF plus straw and cattle manure (CFSM). A NPK compound fertilizer (N:P2O5:K2O = 26:13:13) representing a chemical fertilizer was applied as a basic fertilizer during sowing in spring (April) every year, at a total application rate of 900 kg ha−1. Above-ground crop residue (10 t ha−1) was crushed into pieces and then incorporated into the soil after harvest (October) for CFS and CFSM treatment. Composed cattle manure was additionally applied at 7.5 t ha−1 in CFSM treatment. The contents of NPK in the cattle manure were 8.5, 8.3, and 7.5 g kg−1, respectively. The inputs of NPK from organic and inorganic fertilizers in each treatment are shown in Table 2.
A leaching experiment under in situ conditions with intact soil columns was conducted to estimate the P leaching loss. Soil columns were installed in November 2018 in the field trial (3 replicates × 3 treatments = 9 columns). Each piece of leaching equipment (Figure 1) consisted of a leaching column (diameter 46 cm and height 100 cm), a plastic leachate collection bucket (45 L), a stainless steel tray, a vacuum pump, a filtration bottle, and a digital pressure gauge (Honeywell). After driving the stainless steel column to the desired depth, a hole was dug next to the column so that the leaching tray could be installed from the bottom without disturbing the leaching column. At the bottom of each leaching column, there was nylon filter mesh (20 mesh) and acid-washed (0.1 M HCl) silica sand (nominal grain size < 70 μm). The leaching column was placed on the iron tray and connected with tubing to the pressure gauge and the vacuum pump. When settled, we used polystyrene™ to seal the gap between the iron column and the leaching tray. After each leachate collection device was successfully installed, we compacted and restored the damaged soil bulk. In addition, an appropriate amount of melted petroleum jelly ® was evenly sprayed on the inner and outer edges of the column. This setup was based upon the study of Heal et al. [32].

2.2. Collection of Leachate Samples

After 3 years of operation, in 2021, with consideration of the amount, intensity, and distribution of rainfall, we collected five batches of leachate accumulated in five periods (leachate accumulated in each period was collected on 27 April, 8 June, 27 July, 24 August, and 31 October, respectively), and leachate volumes were recorded. All the leachate samples were immediately sent to the laboratory at 4 °C for storage. Meanwhile, data concerning the daily precipitation and soil surface temperature in 2020 and 2021 were exported from the automatic weather station (EMS Brno) installed at the study site.

2.3. Analysis of Leachate Samples

Different forms of P in leachate samples including TP, PP, DP, DIP, and DOP were quantified. The DIP content was analyzed by an ammonium molybdate spectrophotometric method after being filtered through a 0.45 μm membrane. The DP content in the filtered leachate sample was determined by the same method after digestion with potassium persulfate [33]. The TP content was detected in the unfiltered leachate sample by the same method after digestion. The PP content was assumed to be the difference between the TP and DP contents, and the DOP content was assumed to be the difference between the DP and DIP contents in the leachate sample. The amount of leaching loss of P of each form in each period is the product of the content of P multiplied by the volume of leachate. The cumulative (annual) leaching loss of P of each form is the sum of the leaching losses of each P form in each period.

2.4. Statistical Analysis

Multiple comparisons of mean values among treatments were performed using the Fisher’s least significant difference test (LSD, p < 0.05) for the leaching loss of each P form in each period (season), the cumulative leaching loss of each P form, and the ratio of the cumulative leaching of each P form to external P input. Multiple comparisons of mean values among different periods for each treatment were also performed using the Fisher’s least significant difference test (LSD, p < 0.05) for the leaching loss of each P form from each treatment. A two-way ANOVA was performed to reveal how the loss of each P form was affected by the period (season) and treatment. A probability was defined with the least significant difference test at two sides of p < 0.05. The statistical analysis of the above data was carried out using SPSS Statistics 22.0.0 (IBM, Armonk, NY, USA). A comparison of management practices towards P leaching loss was conducted by canonical discriminant analysis, and graphs were made using OriginPro 2021 (Origin Lab Corp., Northampton, MA, USA). Redundancy analysis (RDA) was applied to evaluate the effects of environmental factors on P leaching loss using the packages “vegan” and “ggplot2” in R Studio version 3.5.2.

3. Results

3.1. Seasonal Variations in Soil Surface Temperature, Rainfall, and Soil Water Leaching

The soil surface temperature at this site was higher in summer (June, July, and August), especially in July with less variation than in other months (Figure 2a). The temperature difference in spring and autumn (April, May, and October) was remarkably large. Precipitation was concentrated in summer, when heavy and moderate rainfalls mainly occurred (Figure 2b).
The volume of leachate collected in each of the five periods was quite similar among treatments, with the value being the highest in the fourth period of the stormy season (between 27 July and 24 August). Actually, the volume was similar across all other periods, with the exception of the value of the CFSM treatment in the second period (between 24 April and 8 June) (Figure 2c) which was the smallest.
The percentage of precipitation lost through leaching indicates that the percentage was similarly higher in the second and fourth periods compared with the first, third, and fifth periods (Figure 2d).

3.2. Seasonal Variations in P Leaching in Various Forms

Both DIP and DOP leaching exhibited considerable variation in different periods and among treatments (Figure 3). DIP leaching losses from the CF and CFSM treatments were significantly higher than during the CFS treatment in the third and fourth period between 8 June and 24 August, while the opposite was observed in the fifth period between 24 August and 31 October (Figure 3a). The CFS and CFSM treatments exhibited elevated DOP leaching losses in the fifth and first periods (the freeze–thaw periods), respectively, while the DOP contents of the CF treatment were higher than the other two treatments in the third and fourth periods (Figure 3b). As the sum of DIP and DOP, DP leaching loss was significantly higher for the CF and CFSM treatments in the third period and for the CFS treatment in the fifth period.
PP leaching also varied considerably among treatments and in different periods (Figure 3c), with a peak value for the CF treatment in the fifth period, for the CFS treatment in the first period, and for the CFSM treatment in the third period. Moreover, among the three treatments, the CFSM treatment exhibited high values in the third and fourth periods and low values in other periods compared to the other two treatments.
TP leaching varied seasonally from 78 to 256 g ha−1 among the three treatments (Figure 3d), with the CFSM treatment showing a peak value in the third and fourth period (stormy season) but reaching the bottom in the fifth period (rainless season), mainly due to the variations in DIP and PP. On the other hand, the TP contents in leachate were higher in the third and fourth periods than the fifth period, indicating the prior stormy season was the season inducing the leaching loss of TP under the co-application of straw and manure.
PP leaching loss relative to TP leaching loss varied seasonally in a “U” shape for the CF treatment, but fluctuated widely for the CFS and CFSM treatments (Figure 4). In contrast, neither DIP nor DOP leaching loss relative to TP leaching loss fluctuated for any of the treatments, especially for the CFS and CFSM treatments, indicating that the leaching losses of different P forms are affected to various extents by period/season and fertilization treatment. A further analysis using a two-way ANOVA on the effects of period and fertilization treatment on the leaching loss of each P form (Table 3) showed that the period had a significant effect on leaching loss of each P form, and fertilization treatment only exhibited a significant effect on DOP and DP leaching losses, but significant interacting effects existed on the leaching loss of each P form except PP.

3.3. Cumulative Leaching Loss of Each P Form in Mollisol

The cumulative P leaching loss of each P form except PP (Table 4) showed significant differences among the three fertilization treatments. The cumulative leaching losses of DP and TP were both in the order of CFSM > CF > CFS. Across the three treatments, DP accounted for a larger proportion of TP (mean 64%) composition than PP (mean 36%), and DIP accounted for a larger proportion (mean 66%) of DP than DOP (mean 34%). Compared to the CF treatment, CFS mainly lowered TP loss by lowering DOP loss, while the CFSM treatment increased TP loss mainly by increasing the losses of both DIP and DOP. Nevertheless, the cumulative leaching loss of each P form relative to P input from chemical fertilizer and organic amendments (Table 4) was significantly lowered by either CFS or CFSM treatment, and especially so for DIP, PP, and TP by CFSM treatment.

3.4. Canonical Discriminant Analysis of Management Practices towards P Leaching Loss

Canonical discriminant analysis was applied to assess the effects of organic amendments on variations in P leaching loss in Figure 5. The significant overlap among the three groups indicated that management practices could not be exclusively well classified by P leaching loss. According to the obvious orthogonal effect and including the majority of the observations between the CFSM and CFS treatments, it may be considered that complicated mechanisms towards P leaching were reflected in the treatment in which straw and manure were co-applied. Otherwise, reflected as the size of the short half axis diameter of the confidence ellipse, the CFSM and CF treatments showed a large variation towards P leaching loss compared to the CFS treatment.

3.5. Relationship between P Leaching Loss and Environmental Factors

The relationship between P leaching loss and environmental factors was evaluated by RDA on the absolute and relative leaching losses of different P forms using five explanatory variables (rainfall, moderate rainfall frequency (MRF), heavy rainfall frequency (HRF), mean soil surface temperature, Olsen P) after forward selection (Figure 6). Both RDA1 (explaining 67.55% of the total variance) and RDA2 (explaining 9.38% of the total variance) were significant (p < 0.05) based on permutation tests. MRF, HRF, soil surface temperature, and rainfall mainly contributed to the variation in P leaching, accounting for 26.31%, 16.31%, 11.53%, and 5.84% (p < 0.05). Rainfall intensity and amount were strongly correlated with the leaching patterns of DIP, DOP, and DP. In addition, soil surface temperature explained a larger variation in the relative leaching loss of P (the ratio of leaching loss amount to P input) than the other explanatory variables.

4. Discussion

4.1. Water Leaching in Mollisol

Although the mollisol of northeast China is classified as loam clay soil, it is formed under a semi-arid temperate climate, subject to repeated freeze–thaw cycling during transitional periods between winter and autumn/or spring, favoring the formation of soil macropores to promote soil water leaching even in the rainless spring season [34]. The considerable amount of leachate collected in the first period should be derived from precipitation including snow under the impact of freeze–thaw cycling (Figure 2). The amounts of leachate collected in other periods were regulated by precipitation, soil moisture/evaporation, plant evapotranspiration and interception, tillage practices, and even straw and/or manure amendments which affect the water-retaining characteristics of soil [34,35] as indicated by the reduced water leaching from the straw and manure co-applied soil in the second period (between late April and early June, typically short of rainfall) (Figure 2c). The collection of the highest amounts of leachate in the stormy season (the fourth period between late July and late August) compared to other periods was not only due to the relatively wet soil conditions developed from the third period, but also due to the highest frequency of moderate and heavy rainfalls in the fourth period.
The seasonal variation in the percentage of precipitation lost through leaching (Figure 2d) indicated that the seasonal changes in the impacts of precipitation (amount, intensity, and timing), maize plants (evapotranspiration and canopy interception of rain), and soil temperature (freeze–thaw cycling in the first period) and tillage (the second period) all affected the type and intensity of soil water leaching, and subsequently, the seasonal and cumulative leaching losses of each P form.

4.2. P Leaching in Various Forms from Mollisol with Organic Amendments

The difference in leaching loss of P among different fertilization treatments was controlled by the differences in the losses of both DP and PP under the joint impacts of precipitation and temperature-dominated environmental factors and fertilization-dominated management practices. While a series of studies have suggested that organic amendments could enhance the leaching loss of DP compared with chemical P fertilization in drainage water or leaching experiments [13,31,36], the evidence is quite limited for identifying the seasonal characteristics of DP leaching under in situ conditions, especially in mollisol, and the contributions of DOP leaching to the leaching of DP and TP have been poorly appreciated. The results from our study show that the percentages of cumulative leaching loss of DOP relative to that of DP increased by 12% with organic amendments, while the ratio of DOP to TP increased by 10%, indicating the inevitable effects of DOP leaching loss under organic agriculture.
Jointly controlled by the leaching of both DIP and DOP, DP leaching varied not only in different seasons but also among different fertilization treatments. The amendment of C/N-high straw likely enhanced more immobilization relative to mineralization compared to the chemical fertilization treatment, resulting in a generally reduced leaching loss of DOP from each period (Figure 3b), lowering the overall cumulative leaching loss of DOP (Table 4). In contrast, manure incorporated into soil after the harvest of the last growing season more likely stimulated not only mobilization but also mineralization [37] to enhance the availability of nutrients including DP [38], increasing the leaching losses of both DIP and DOP in the first period with the occurrence of freeze–thaw cycling (Figure 3a,b). The observed counteractive effect on the DOP leaching of manure with straw could be partially ascribed to the antagonism effect of the hydrolyzing of organic P by phosphatases under the co-application of straw and manure [38], whereas the separate application of either straw or manure would enhance phosphatase activity, which could be implied by the results of canonical discriminant analysis (Figure 5).
Despite the existence of interacting effects, the seasonal variation in DIP leaching was regulated more by season than by organic amendment (Table 3), possibly due to the mutual influences of chelation and phosphatases’ activity [39]. Besides the positive effects of phosphatases on the availability of DP as mentioned above, organic acids such as humic acid and citric acid derived from organic amendments could also occupy adsorption sites in iron and aluminum oxides, thereby promoting the release of DP [40,41]. Nevertheless, the results from our study corresponded with the result of Rao and Mikkelsen [42], which showed that the role of straw as a source of organic acids appeared to be weaker than manure. Compared to chemical fertilization, the additional amendment of straw only changed the seasonal variation in DIP leaching but did little to affect its cumulative leaching loss. In contrast, the co-amendment of straw and manure led to the high-rate leaching of DIP in the third and fourth periods during which the soil microbial activity was high under suitable growing conditions [43], contributing to the increased cumulative leaching loss of DIP (Table 4).
While the differences in cumulative PP leaching loss were small among the fertilization treatments (Table 4), PP leaching still changed with season and by fertilization practice (Figure 3c). Manure-derived organic matter, mainly composed of coarse particles [44], likely entered the soil mainly as particulate material including PP, subject to leaching by preferential pathways under high-intensity rainfalls. As a result, the storm-concentrated summer seasons (from early June to late August) became the main period of PP leaching as reported by Kwaad [45], and high-intensity rainfall in the stormy season from late July to late August became the most important factor driving the loss of PP, especially PP derived from manure in the mollisol under rotary tillage. In contrast, in the PP loss-low seasons (the first and fifth periods) with a rare occurrence of rainfall of high intensity (Figure 3c), PP loss was further lowered by the co-amendment of straw and manure, likely through increasing the proportion of micropores in deeper layers to prevent particle materials migrating downwards [46] to weaken water leaching as observed in the second period (Figure 2b). Nevertheless, the rotary tillage of mollisol with the incorporation of straw alone in autumn and the soil freeze–thaw cycling effect might increase the formation of soil macropores, leading to a relatively high leaching loss of PP with large deviation in the first period (Figure 3c).
The differences in the seasonal and cumulative leaching losses of DIP, DOP, and PP from different fertilization treatments as mentioned above consequently led to differences in TP leaching, with its cumulative leaching loss being significantly increased by the co-amendment of straw and manure but significantly reduced by the amendment of straw alone, indicating that straw amendment is more environmentally friendly regarding P leaching loss control in mollisol. Nevertheless, the ratio of the leaching loss of each P form was reduced to various extents by the co-amendment of straw and manure (Table 4), indicating that manure amendment in mollisol is not environmentally riskier than chemical P fertilization for P leaching, and may even reduce P leaching when the P from manure is carefully considered to substitute a corresponding portion of the chemical P fertilizer.

4.3. Relationship between P Leaching and Environmental Factors

In the present study, we identified that the leaching loss of different P forms in soil relied to a high extent on P input from exogenous fertilizers, as well as environmental factors regulating soil water leaching such as rainfall and soil surface temperature according to the results of RDA (Figure 6). On one hand, the absolute and relative loss of dissolved P including DIP and DOP was strongly related to the frequencies of high- and medium-intensity rainfall in the rainy season, which accounts for over 80% of annual nutrient leaching in the semi-humid area of the field experiment [47]. Previous studies have demonstrated that PO43−-P concentrations increase as rainfall intensity increases in simulated leaching experiments [48,49]. The results from our study, however, showed that consecutive medium-intensity rainfall had a stronger relationship with DP than heavy-intensity rainfall. Furthermore, the additional amendment of straw reduced DOP loss by 53% compared to chemical fertilization in summer, indicating that straw amendment could weaken soil leaching by heavy rainfall, in line with the research of Xu et al. [50].
On the other hand, the mean soil surface temperature significantly affected the migration behaviors of different P forms in mollisol as indicated by the difference in the ratio of the leaching loss of each P form relative to TP leaching loss in the third and fourth periods during which the rainfall was comparable but where the mean soil surface temperature was higher in the fourth period (Figure 4). The importance of soil surface temperature in regulating soil extracellular enzyme activities, as well as the adsorption and desorption equilibrium on P availability has been reported [51,52]. A model using changes in soil surface temperature within the Everglades also predicts that the mineralization of organic P forms strengthens with temperature [53]. Meanwhile, the characteristics of the soil pores at the aggregate scale might be changed by long-term fertilization and tillage practices [54], also leading to changes in migration behaviors of P of different forms [55]. The phenomenon of PP and DP leaching simultaneously even in the storm-rare spring season implied the existence of preferential flows in the mollisol during rotary tillage. Soil erosion by high-intensity rainfall in summer and the relatively large change in daily temperature during early spring and late autumn can easily cause the formation of macropores, promoting the generation of preferential flow and the leaching of both DP and PP [56,57].

5. Conclusions

The total leaching loss of P in maize-planted mollisol in northeast China measured by in situ soil column experiments under three typical fertilization treatments accounted for 0.78–1.62% of external P input. The losses of DP including DOP and DIP were greater than that of PP, and the contribution of DOP to DP in leaching was nearly half that of the DOP to TP. The additional co-amendment of straw and manure mainly increased the leaching losses of DIP in the summer season and DOP in the spring season to increase TP loss, and the additional amendment of straw alone mainly decreased DOP loss to decrease TP loss, while freeze–thaw cycling, soil temperature, tillage, and precipitation distribution exerted significant seasonal impacts on the leaching loss of each P form, especially DOP and DIP. Overall, straw incorporation into the mollisol of northeast China reduced the leaching risk of P, especially DOP, but the co-amendment of straw and manure increases the P leaching risk; this risk may be lowered with chemical fertilizer proportionally substituting manure. Studies are needed on plant growth and P leaching in mollisol under the co-amendment of straw and manure with a reduced input of chemical fertilizer P.

Author Contributions

Conceptualization, H.W. and X.C.; methodology, H.W.; validation, G.C. and X.C.; formal analysis, H.W; investigation, H.W. and J.L.; resources, L.X.; data curation, G.C.; writing—original draft preparation, H.W.; writing—review and editing, G.C.; visualization, H.W.; supervision, B.H.; project administration, S.Z. and C.P.; funding acquisition, X.C. and C.L. 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, grant number 41877098, 42177005 and the Strategic Priority Research Program of the Chinese Academy of Sciences, grant number XDA28090300, XDA28090400.

Data Availability Statement

Not applicable.

Acknowledgments

We appreciate all the staff for their assistance with facilitating and organizing soil and water sampling.

Conflicts of Interest

The authors declare no conflict of interest.

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Agronomy 12 02490 g001 550
Figure 1. Diagram of in situ soil column leachate-collection device.
Figure 1. Diagram of in situ soil column leachate-collection device.
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Figure 2. Seasonal variations in soil surface temperature and precipitation (a), cumulative precipitation (b), cumulative leachate volume (c), and percentage of precipitation lost through leaching (d) during different periods of a growing season. Periods from 1 to 5 represent the period from 10 January to 27 April, from 28 April to 8 June, from 9 June to 27 July, from 28 July to 24 August, and from 25 August to 31 August, respectively. October. Small, medium, and heavy rain represent volumes of daily rainfall of less than 10 mm, 10–25 mm, and over 25 mm in 24 h. Different lowercase letters on each sample date indicate significant differences among different treatments at p = 0.05, and ns mean no differences among the treatments.
Figure 2. Seasonal variations in soil surface temperature and precipitation (a), cumulative precipitation (b), cumulative leachate volume (c), and percentage of precipitation lost through leaching (d) during different periods of a growing season. Periods from 1 to 5 represent the period from 10 January to 27 April, from 28 April to 8 June, from 9 June to 27 July, from 28 July to 24 August, and from 25 August to 31 August, respectively. October. Small, medium, and heavy rain represent volumes of daily rainfall of less than 10 mm, 10–25 mm, and over 25 mm in 24 h. Different lowercase letters on each sample date indicate significant differences among different treatments at p = 0.05, and ns mean no differences among the treatments.
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Figure 3. Seasonal variations in leaching losses of DIP (a), DOP (b), PP (c), and TP (d). Error bars represent standard deviations. Different lowercase letters on each sample date indicate significant differences among different treatments at p = 0.05, and ns mean no differences among the treatments. Periods 1–5 indicate the same as those in Figure 2.
Figure 3. Seasonal variations in leaching losses of DIP (a), DOP (b), PP (c), and TP (d). Error bars represent standard deviations. Different lowercase letters on each sample date indicate significant differences among different treatments at p = 0.05, and ns mean no differences among the treatments. Periods 1–5 indicate the same as those in Figure 2.
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Figure 4. Seasonal variations in percentages of DIP, DOP, and PP in leachate from treatments of CF (a), CFS (b), and CFSM (c). Periods 1–5 indicate the same as those in Figure 2.
Figure 4. Seasonal variations in percentages of DIP, DOP, and PP in leachate from treatments of CF (a), CFS (b), and CFSM (c). Periods 1–5 indicate the same as those in Figure 2.
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Figure 5. Canonical discriminant analysis of three treatments extracted from P leaching loss.
Figure 5. Canonical discriminant analysis of three treatments extracted from P leaching loss.
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Figure 6. Redundancy analysis (RDA) of environmental factors of P loss for different treatments. The P loss is indicated by red lines, including total P (TP), dissolved P (DP), particulate P (PP), dissolved inorganic P (DIP), dissolved organic P (DOP), PP%, DIP%, and DOP% in leachates. The environmental factors indicated by blue lines include rainfall, MRF (moderate rainfall frequency), HRF (heavy rainfall frequency), temperature (soil surface temperature), and Olsen P (0.5 M NaHCO3 extracted P, referred to as soil−available P). Different treatments are represented by three kinds of colored shapes.
Figure 6. Redundancy analysis (RDA) of environmental factors of P loss for different treatments. The P loss is indicated by red lines, including total P (TP), dissolved P (DP), particulate P (PP), dissolved inorganic P (DIP), dissolved organic P (DOP), PP%, DIP%, and DOP% in leachates. The environmental factors indicated by blue lines include rainfall, MRF (moderate rainfall frequency), HRF (heavy rainfall frequency), temperature (soil surface temperature), and Olsen P (0.5 M NaHCO3 extracted P, referred to as soil−available P). Different treatments are represented by three kinds of colored shapes.
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Table
Table 1. Physical and chemical properties of mollisol.
Table 1. Physical and chemical properties of mollisol.
pHSOM
g kg−1		TN
g kg−1		TP
g kg−1		TK
g kg−1		Avail.N
mg kg−1		Avail.P
mg kg−1		San
d%		Silt
%		Clay
%
6.8120.901.300.376.2513.0130.2636.131.632.3
SOM: soil organic matter. Sand: 2–0.02 mm; silt: 0.02–0.002 mm; clay: <0.002 mm.
Table
Table 2. Annual N, P, and K inputs in mollisol with different fertilization treatments from 2015 to 2021.
Table 2. Annual N, P, and K inputs in mollisol with different fertilization treatments from 2015 to 2021.
TreatmentOrganic Fertilizer
kg ha−1		Chemical Fertilizer
kg ha−1		Total Input
kg ha−1
NPKNPKNPK
CF00023451802345180
CFS00023451802345180
CFSM6462562345180298113136
Table
Table 3. Results (p values) of two-way ANOVAs on leaching loss of each P form in mollisol.
Table 3. Results (p values) of two-way ANOVAs on leaching loss of each P form in mollisol.
DIPDOPDPPPTP
Treatment0.2200.0000.0240.9260.173
Period0.0010.0000.0010.0460.010
Treatment × Period0.0020.0010.0020.8150.039
Table
Table 4. Cumulative leaching loss of each P form and its ratio to P input in mollisol.
Table 4. Cumulative leaching loss of each P form and its ratio to P input in mollisol.
CategoryTreatmentDIPDOPDPPPTP
Cumulative
leaching loss
(g ha−1) 		CF372(28) b267(33) a639(26) b353(26) a992(60) a
CFS349(42) b114(19) c463(39) c326(24) a789(27) b
CFSM450(63) a257(36) a707(81) a313(41) a1020(99) a
Cumulative P leaching Loss
relative to P input (%) 		CF0.73(0.10) a0.52(0.02) a1.25(0.12) a0.69(0.03) a1.95(0.09) a
CFS0.68(0.02) a0.24(0.01) b1.24(0.01) a0.64(0.04) a1.54(0.06) b
CFSM0.33(0.02) b0.19(0.04) b0.51(0.07) b0.23(0.05) b0.75(0.01) c
Note: Mean value (SD) of each P form followed by a different letter indicates a significant difference among different treatments (p < 0.05).
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Wang, H.; Zhang, S.; Peng, C.; Chi, G.; Chen, X.; Huang, B.; Lu, C.; Li, J.; Xu, L. Quantifying Phosphorus Leaching Loss from Mollisol with Organic Amendments. Agronomy 2022, 12, 2490. https://doi.org/10.3390/agronomy12102490

AMA Style

Wang H, Zhang S, Peng C, Chi G, Chen X, Huang B, Lu C, Li J, Xu L. Quantifying Phosphorus Leaching Loss from Mollisol with Organic Amendments. Agronomy. 2022; 12(10):2490. https://doi.org/10.3390/agronomy12102490

Chicago/Turabian Style

Wang, Hongyan, Shuxiang Zhang, Chang Peng, Guangyu Chi, Xin Chen, Bin Huang, Caiyan Lu, Jizhi Li, and Li Xu. 2022. "Quantifying Phosphorus Leaching Loss from Mollisol with Organic Amendments" Agronomy 12, no. 10: 2490. https://doi.org/10.3390/agronomy12102490

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