Sustainable Corn Stubble Management Is Site Specific: A Study in Northeastern China

Abstract

Sustainable agriculture has garnered increasing attention in recent times, with corn stalk retention constituting a pivotal component of sustainable agricultural practices. Presently, whole corn stalk retention (CCR), three-year rotation corn stalk retention (TYR), and standing corn stalk retention (SCR) are prevalent corn stalk management techniques in northeast China. However, the question of which corn stalk management technique is best suited to specific local climates within northeast China remained unanswered. Therefore, this manuscript investigates the impact of these corn stalk management practices on nitrogen (N), phosphorus (P), potassium (K), and soil organic amendments by analyzing long-term practical data. To gather data for analysis, three locations with varying latitudes were selected. The results indicate that local climate has a significant influence (p < 0.05) on the decomposition process and level of retained corn stalks. In locations with sufficient annual accumulated temperature and precipitation, a larger amount of corn stalk retention is acceptable. For instance, CCR is deemed suitable for Liaoning Province in China. Conversely, in locations lacking sufficient annual accumulated temperature or precipitation, an excessive amount of corn stalk retention cannot decay completely within a given period. Consequently, farmlands cannot adsorb adequate soil nutrients or organic matter derived from decomposed corn stalks. Thus, TYR or SCR is more appropriate for Heilongjiang Province in China. The findings of this research can guide farmers in optimizing corn stalk management practices according to specific local climates.

1. Introduction

The sustainability of agriculture heavily relies on natural methods to replenish soil nutrients, rather than solely depending on the increased application of chemical fertilizers [1]. Among these methods, the practice of returning corn stalks to the field stands out as a crucial strategy to naturally enrich the soil with essential nutrients. Corn stalks, rich in organic matter and vital elements, offer a cost-effective and environmentally friendly alternative to chemical fertilizers [2]. The corn yield varies owing to different soil fertility of specific areas. The Mollisols in northeast China are famous for its fertility, but during recent decades, soil degradation has become a big concern in soil fertility and environmental pollution. In order to improve soil fertility and conserve the environment, sustainable agriculture has been put forward for several decades in China [3]. Corn stalk management is important for sustainable agriculture, and returning corn stalks to the field is viewed as a key procedure of sustainable agriculture [3,4,5]. There are several types of corn stalk retention, such as whole corn stalk retention, partial corn stalk retention, standing corn stalk retention, chopped corn stalk retention, and mixed corn stalk retention [6]. The benefits of residue retention are regionally variable and depend on both agro-climatic and socioeconomic factors [7]. Most studies from developing countries in Asia, Latin America, and Africa showed positive effects of retaining crop residues on soil quality, such as improving soil organic matter, carbon storage, soil moisture retention, and enhancing nutrient cycling together with decreasing soil loss, among other environmental and soil health benefits [4,7,8,9]. Corn stalks contain substantial organic elements and organic matter; thus, returning corn stalks to the field is a cost-effective method to maintain soil nutrition and soil organic matter (SOM) [10].

Whole corn stalk retention is widely used currently, and it is a widely accepted method of using chopped corn stalks to cover soil surface (CCR) [11], which can be realized using a corn harvester. A majority of corn harvesters used in northeast China can chop corn stalks into small pieces and then spread them on the soil surface, which is a basic function of prevalent corn harvesters. In order to decrease soil wind erosion, the standing corn stalk method has been used for several years [12]. This corn stalk management system retains standing stalks (SCR) at a specific height (e.g., 50 cm); the upper part of the corn stalks can be used in other ways, which improves the corn stalk usage efficiency. Jia et al. (2010) suggested that corn stalk management should be different every year, and they should be managed by a 3-year cycle, named ‘three-year rotation’ (TYR). Three-year rotation means the whole corn stalks should be returned to the field as stalk fragments for the first year; subsequently, the whole corn stalks should be removed for the second year; last, the field should leave 1/3 of corn stalks standing in the field for the third year [13]. This method has been used for more than ten years in northeast China [14]. These three corn stalk management practices will be the research objects in the following study.

The corn planting area encompasses a significant portion of China’s agricultural land, with approximately 6.86 million hectares of cornfields located in northeast China [15]. Annual accumulated temperature (AAT) and annual precipitation (APP) are two pivotal factors that exert the greatest influence on the cropping system. Concurrently, AAT and APP also impact the decomposition process of previous crop straws. The aforementioned three corn stalk management practices each possess unique advantages; CCR can replenish the highest amount of soil nutrients and SOM, while the other two methods enhance corn stalk utilization efficiency [16,17]. Despite the widespread adoption of various stalk retention methods in northeast China, there remains a considerable knowledge gap regarding the most suitable retention technique for specific local climates. This lack of understanding is particularly concerning due to the wide range of climatic conditions within the region, which spans from annual northern accumulated temperatures below 1000 °C to annual southern accumulated temperatures exceeding 3000 °C. To address this knowledge gap, our study aims to investigate the most appropriate corn stalk management practices that align with the specific climatic conditions of different areas in northeast China. By conducting a comprehensive analysis of various retention methods across diverse climatic zones, we seek to identify the practices that optimize soil nutrient replenishment, enhance soil fertility, and promote environmentally sustainable agriculture.

Sustainable agriculture heavily relies on natural methods to replenish soil nutrients, reducing the need for increased application of chemical fertilizers. This study focuses on corn stalk management practices, a crucial strategy to naturally enrich the soil with essential nutrients. However, the optimal corn stalk management technique for specific local climates within northeast China remains unclear. The specific objectives of this study are to (1) investigate the impact of different corn stalk management practices on soil nutrient levels, including nitrogen (N), phosphorus (P), potassium (K), and SOM, and (2) determine the most suitable corn stalk management technique for different climatic conditions in northeast China. Hypothetically, we anticipate that local climate, particularly AAT and APP, will significantly influence the decomposition process and nutrient replenishment from corn stalks.

2. Material and Methods

2.1. Policy Background

Since 1982, the household contract responsibility system for farmland has been in effect in China. This contract stipulates that farmers are entitled to all rights pertaining to their own farmland, including decisions on the type of crop to be planted, the tillage method to be employed, and the management of crop residue, among others. A direct consequence of this policy is the emergence of diverse corn stalk management practices across northeast China over the past forty years, meeting the requirements for corn stalk management examined in this study.

2.2. Study Sites

This study selected three distinct regions within northeast China, as illustrated in Figure 1, where the aforementioned three different corn stalk management practices were implemented. The first area (L1) is situated in Shenyang City, Liaoning Province (41.52° N, 123.37° E). The annual mean temperature averages between 7 and 8 Celsius degrees, with an APP of 650 to 700 mm and an AAT ranging from 3300 to 3400 Celsius degrees.

The second region (L2) lies in Changchun City, Jilin Province (43.78° N, 125.2° E). Here, the annual mean temperature stands at 4.8 degrees Celsius, the APP amounts to 522 to 615 mm, and the AAT varies between 2770 and 2910 degrees Celsius.

The third locale (L3) is in Hailun City, Heilongjiang Province (47.45° N, 126.93° E). It experiences an annual mean temperature of 1.5 degrees Celsius, an APP of 530 mm, and an AAT of 2450 degrees Celsius.

To classify the soil types, Munsell soil color charts (supplied by Beijing New Landmark Soil Equipment Co., Ltd., Beijing, China) were utilized. Based on the USDA soil taxonomy, the soils at all three sites fall under the Mollisols category. According to Chinese soil taxonomy, these soils belong to the great group of Black soils and are classified as Semi-luvisols.

2.3. Experimental Design

To maintain consistency in experimental parameters, corn was planted annually at all three locations. Specifically, the corn cultivar Jidan 209 was selected, the planting density was uniformly set at 71,500 plants per hectare, and management practices, including SCR, TYR, CCR, and corn stalk removal, were observed at each location. In L1, four 3-hectare farmlands belonging to different families were selected for data collection. One farmland had utilized standing corn stalks to cover the soil surface since 2000, retaining 50-cm bottom corn stalks in the field post-harvest. The second farmland had adopted TYR since 2004, the third had implemented CCR since 1997, and the fourth had removed corn stalks post-harvest since 1982. Similarly, in L2, four 3.5-hectare farmlands were chosen, with corn stalk management practices identical to L1, and the practice of removing corn stalks post-harvest was designated as CT2. In L3, four 10-hectare farmlands were selected, adhering to the same management practices as L1, and the corn stalk removal practice was designated as CT3.

Temperature variations in each area were measured and recorded using a thermometer (model: ECA-HJ01, Beijing Yikangnong Technology Development Co., Ltd., Beijing, China). The thermometer was strategically positioned in each experimental area to ensure accurate detection of environmental temperature. The data collection frequency and recording mode were appropriately configured. Specialized software was employed to analyze and process the collected temperature data, calculating key indicators such as daily, monthly, and annual accumulated temperature. Additionally, a rain gauge (Beijing Bonn Instrument and Control Technology Co., Ltd., Beijing, China) was utilized to measure rainfall in different regions. The rain gauge was installed in an open and unobstructed area for precise rainfall sensing, and the data collection frequency and recording mode were configured accordingly. The collected rainfall data were then organized and analyzed using specialized software to calculate key indicators, including daily, monthly, and annual rainfall.

2.4. Soil Sampling

The experiment was conducted from August to October annually, spanning from 2016 to 2023, with three replicates performed in each farmland. A rectangular sampling field, measuring 100 m in length and 30 m in width, was randomly selected. During the experiment, soil samples were collected from the tillage layer, specifically the top 0 to 10 cm. Within each sampling field, 25 sampling points were chosen, and the arrangement of these sample points is illustrated in Figure 2. At each sampling point, approximately 1 cm of surface soil was discarded, followed by vertically excavating roughly 1 kg of soil using a spade and placing it in a cloth bag. After removing impurities such as rocks and roots, about 0.5 kg of soil sample was obtained through quartering. The soil sample was then left to dry naturally and ground to pass through a 1 mm sieve.

It is worth noting that the contents of various elements in the soil were collected annually, specifically during the period from August to October, to ensure consistency and accuracy in the data.

Once prepared, the final soil sample was analyzed using the TPY-6A intelligent soil nutrient tester from Zhejiang TOP Instrument Co., Ltd. (Hangzhou, China). Prior to testing, blank solution, standard solution, and soil solution were prepared. Using the TPY-6A tester, the total N, P, K, and SOM contents in the soil samples were analyzed. This annual collection and analysis process allowed for the monitoring of changes in soil composition over time, providing valuable insights into soil health and fertility.

2.5. Statistical Analysis

Statistical analyses of the data were performed using SPSS 27.0 for Windows (SPSS Inc., Chicago, IL, USA). The least significant difference (LSD) analysis was employed to evaluate the notable impacts of corn stalk management practices, AAT, and APP on the annual increasing rate (hereinafter referred to as AIR) of N, P, K, and SOM.

In order to evaluate the annual increase rate of N, P, K, and SOM compared with the control treatment, the AIR was calculated as follows:

$$AIR={\displaystyle \frac{{{\theta }_{i,n}^L-\theta }_{i,n}^C}{{\theta }_{i,n}^c}}\times 100\mathrm{\%}$$

(1)

where AIR represents the annual increase rate of N, P, K, and SOM. θ represents the calculating items, such as N, P, K, and SOM. L represents the experimental treatments, such as SCR, CCR, and TYR; C represents the control treatment; i represents the experimental locations, such as L1, L2, and L3; n represents the testing years, such as 2016, 2017, etc.

The mean AIR is the arithmetic mean of the AIRs. Pearson correlation analysis was also applied to investigate whether the AAT and APP have a significant correlation with the replenishment of N, P, K, and SOM.

3. Results and Discussion

3.1. AAT and APP of the Three Experimental Sites

From Figure 3, it is evident that there were notable similarities and differences in the AAT and APP across the three study locations. Specifically, the AAT in L1 was generally high, with temperatures exceeding 3000 °C in all recorded years and exhibiting a relatively minimal fluctuation range. In contrast, the AAT in L2 was slightly lower than that in L1, yet it still fluctuated within the range of 2800 °C to 2900 °C. Notably, the AAT in L3 was the lowest among the three, consistently ranging from 2530 °C to 2600 °C across all years. Regarding the APP, L1 experienced significant variability, spanning from 580 mm to 700 mm. Conversely, the APP in L2 was comparatively lower and displayed a reduced fluctuation range, varying between 480 mm and 560 mm throughout the recorded period. Lastly, the APP in L3 resembled that of L1, albeit with a slightly divergent fluctuation pattern, oscillating between 570 mm and 610 mm. Further statistical analysis demonstrates that the AAT and APP among the three study locations had significant differences, as shown in

Table 1. Statistical analysis results of ANOVA.

		Sum of Squares	Degree of Freedom	Mean Square	F	Significance
AAT	Between groups	900,033.333	2	450,016.667	312.279	0.000
	Within groups	30,262.500	21	1441.071
	Sum	930,295.833	23
APP	Between groups	61,185.333	2	30,592.667	30.747	0.000
	Within groups	20,894.500	21	994.976
	Sum	82,079.833	23

.

3.2. Soil Nutrients and SOM

The different corn stalk management methods of SCR, TYR, and CCR were performed for 16, 12, and 19 years, respectively, in L1, which were the same as the other two experimental locations. Figure 4 shows that compared with CT1, the SCR, TYR, and CCR increased N, P, K, and SOM contents in the order CCR > TYR > SCR, which were also similar to the other two locations.

Specifically, in terms of N content, the N content in the SCR, TYR, and CCR treatments was higher than that in CT1, and this difference remained consistent throughout the entire study period. The N content of the SCR fluctuated slightly from 2016 to 2023 but overall showed a stable trend, with a range of changes between 0.2351% and 0.2362%. The TYR also showed a stable trend, with N content fluctuating between 0.2289% and 0.236%. The N content in CCR slightly increased, from 0.2399% in 2016 to 0.2412% in 2023. In contrast, the N content of the CT1 remained largely unchanged throughout the entire study period, maintaining between 0.2165% and 0.218%. This indicates that compared to the control group, the treatment group showed certain advantages in increasing N content.

In terms of P content, the SCR, TYR, and CCR also showed a higher trend than the control group. The P content in the SCR group fluctuated between 0.0886% and 0.0912%, the TYR fluctuated between 0.0878% and 0.0886%, and the CCR fluctuated between 0.0914% and 0.0921%. In contrast, the P content in CT1 was relatively stable, maintained between 0.0813% and 0.082%. This indicates that the treatment group also has certain advantages in improving P content.

The K content, SCR, TYR, and CCR also showed a higher trend than CT1. Specifically, the K content in the SCR group increased from 2.2457% in 2016 to 2.264% in 2023, the TYR increased from 2.2338% to 2.2413%, and the CCR increased from 2.299% to 2.3183%. In contrast, the K content of the CT1 remained largely unchanged throughout the entire study period, maintaining between 2.087% and 2.098%. In terms of SOM, the SCR, TYR, and CCR also showed a higher trend than CT1. The SOM content in SCR fluctuated between 4.52% and 4.58%, the TYR fluctuated between 4.57% and 4.61%, and the CCR fluctuated between 4.62% and 4.69%. In contrast, the SOM content in CT1 was relatively stable, maintained between 4.4% and 4.45%.

In discussing the observed decreases in P, K, and SOM content in the control treatments across the three experimental sites, several academic insights emerge. First, it is imperative to recognize the role of corn stalk retention in replenishing soil nutrients. As the data clearly indicate, the treatments involving corn stalk management through SCR, TYR, and CCR consistently maintained or increased the levels of P, K, and SOM compared to the respective control treatments. This finding aligns with previous research demonstrating the positive effects of crop residue management on soil quality and fertility [6,7,8]. The decrease in P, K, and SOM content in the control plots highlights the natural depletion of these nutrients over time without replenishment. Soil nutrient depletion is a well-documented phenomenon in agricultural systems where long-term cropping without proper nutrient management can lead to soil degradation [3,9]. In the absence of corn stalk return, the soils in the control plots were likely to experience progressive nutrient mining, resulting in the observed declines. Moreover, the study reveals that the magnitude of the decrease varied across sites, with L3 experiencing the most pronounced losses. This observation underscores the influence of local climatic conditions on soil nutrient dynamics. Higher AAT and APP in L1 compared to L2 and L3 likely facilitated microbial activity and decomposition processes, which in turn contributed to better nutrient retention and cycling [18,19]. In contrast, the colder and drier conditions in L3 slowed down decomposition, hindering the replenishment of nutrients from crop residues and other organic matter sources.

The academic importance of these findings lies in their implications for sustainable agriculture. Corn stalk retention practices, particularly CCR, emerged as effective strategies for maintaining and enhancing soil fertility in regions with favorable climatic conditions. However, in areas with colder and drier climates, alternative management approaches such as TYR or SCR may be more suitable to balance nutrient replenishment with stalk decomposition rates.

In terms of mean annual increase rates (MAIRs) of P, K, and SOM, SCR was significantly lower (p < 0.05) than TYR and CCR, but there was no significant difference (p > 0.05) of N among SCR, TYR, and CCR. Although different from the other two locations, the MAIRs of N, P, K, and SOM were nearly the same for TYR and CCR (Figure 5), and there was no significant difference (p > 0.05) between TYR and CCR.

A notable observation is the consistent mean annual decrease rates (MADRs) in P, K, and SOM content within the control treatments across the three experimental sites. This phenomenon merits further academic discussion, as it underscores the importance of sustainable agricultural practices, particularly corn stalk retention, in maintaining and enhancing soil fertility. Firstly, the MADRs observed in the control treatments highlight the natural depletion of essential soil nutrients over time without the addition of external sources. The consistent decrease in P, K, and SOM in CT1, CT2, and CT3 indicates that, in the absence of corn stalk retention or other soil amendment strategies, soil quality gradually deteriorates. This is particularly alarming given that soil degradation is a global concern with detrimental impacts on agricultural productivity and environmental health. Secondly, the comparison between the control treatments and the corn stalk retention treatments underscores the effectiveness of sustainable agricultural practices in mitigating soil nutrient depletion. As demonstrated in the article, the retention of corn stalks, whether through SCR, TYR, or CCR, resulted in significantly higher soil nutrient levels and slower rates of depletion compared to the control treatments. This finding reinforces the critical role of sustainable practices in preserving soil fertility and ensuring long-term agricultural sustainability. Thirdly, the differing MADRs across the three experimental sites provide valuable insights into the interaction between soil nutrient dynamics and local climatic conditions. As evidenced by the correlation analyses presented in the article, higher AAT and APP positively correlate with soil nutrient replenishment. Therefore, the lower MADRs observed in L1, with its higher AAT and APP compared to L2 and L3, can be attributed to the more favorable climatic conditions that support enhanced microbial activity and faster decomposition of corn stalks, thereby releasing nutrients back to the soil.

In conclusion, the MARDs of P, K, and SOM content in the control treatments across L1, L2, and L3 serve as a stark reminder of the need for sustainable agricultural practices. The findings underscore the importance of corn stalk retention and other soil amendment strategies in mitigating soil nutrient depletion and preserving soil fertility.

As shown in Figure 6, compared with the CT2, there were significant differences (p < 0.05) in N, P, K, and SOM content among the three treatments of SCR, TYR, and CCR, and the trend of change with each year was also different.

Compared with CT2, the N content of SCR, TYR, and CCR showed a relatively stable trend during the study period. Specifically, the N content of SCR and TYR fluctuated around 0.153%, while the N content of CCR was slightly higher than other treatments, at around 0.156%. The N content of CT2 was relatively low and showed a slight downward trend. This indicates that SCR, TYR, and CCR treatments help maintain or slightly increase soil N content.

For P content, SCR, TYR, and CCR also showed a relatively stable trend, and the difference between the three was not significant (p > 0.05). Compared with CT2, the P content of these three treatments was slightly higher, indicating that they help maintain the stability of soil P levels. The P content of CT2 showed a slight downward trend during the study period.

In terms of K content, CCR treatment was significantly (p < 0.05) higher than other treatments and fluctuated less between years. The K content of SCR and TYR was similar and slightly lower than that of CCR. Compared with CT2, all treatments had higher K content, and the K content of CT2 fluctuated during the study period. This indicates that CCR treatment is more helpful in maintaining high soil K levels.

For SOM content, CCR treatment also showed a higher level and had smaller fluctuations between years. The SOM content of SCR and TYR was similar and slightly higher than CT2. The SOM content of all treatments showed a slight upward trend during the study period, but the upward trend of CCR was more pronounced. This indicates that CCR treatment is more helpful in improving and maintaining soil SOM levels.

In summary, compared with CT2, SCR, TYR, and CCR treatments all contributed to maintaining or enhancing soil N, P, K, and SOM content. Among them, CCR treatment showed particularly outstanding performance in terms of K and SOM content.

The MAIRs of L2 are shown in Figure 7. The mean annual increase rate (MAIR) of N in CCR was 0.66%, which was the highest, and the AIR of N in SCR was 0.51%, which was the lowest. Similar situations could be found for P, K, and SOM. Compared with CT2, the MAIRs of N, P, K, and SOM were significantly higher (p < 0.05) for SCR, and so were TYR and CCR. In terms of P and K, further statistical analyses illustrated that the MAIRs among SCR, TYR, and CCR also have significant differences (p < 0.05). In terms of N and SOM, the MAIRs between SCR and TYR were significantly different (p < 0.05), as were those between SCR and CCR (p < 0.05). However, there was no significant difference (p > 0.05) of N and SOM between TYR and CCR, although the MAIRs of TYR were the medium between SCR and CCR.

Figure 8 demonstrates that the N, P, K, and SOM contents of SCR, TYR, and CCR increased compared to CT3. During this long-term agricultural practice, the maximum increase in soil nutrients, as well as SOM, was observed in CCR.

In the SCR treatment mode, the N content fluctuated between 2016 and 2023 but remained stable overall, ranging from 0.11% to 0.13%. Similarly, the N content in the TYR treatment mode exhibited a fluctuating trend, also varying within the range of 0.11% to 0.13%. The N content of the CCR treatment mode was relatively high and showed an upward trend throughout the entire study period, increasing from 0.131% in 2016 to 0.141% in 2023. Conversely, the N content of the CT3 treatment mode was relatively low and exhibited minimal fluctuation, primarily concentrated between 0.09% and 0.11%.

The P content of the SCR treatment mode fluctuated between 2016 and 2023 but remained between 0.06% and 0.07% overall. Similarly, the P content in the TYR treatment mode also fluctuated, akin to the SCR mode, and varied in the range of 0.06% to 0.07%. The P content in the CCR treatment mode was relatively high and remained relatively stable throughout the entire study period, ranging from 0.069% to 0.070%. The P content of the CT3 was relatively low and exhibited minimal fluctuation, primarily concentrated between 0.058% and 0.059%.

The K content of the SCR treatment mode fluctuated between 2016 and 2023 but remained between 1.5% and 1.6% overall. Similarly, the K content in the TYR treatment mode also fluctuated, akin to the SCR mode, and varied in the range of 1.58% to 1.60%. The K content of the CCR treatment mode was relatively high and showed an upward trend throughout the entire study period, increasing from 1.631% in 2016 to 1.667% in 2023. The K content in the CT3 was relatively low and exhibited minimal fluctuation, primarily concentrated between 1.43% and 1.44%.

The SOM content of the SCR treatment mode fluctuated between 2016 and 2023 but remained between 2.0% and 2.05% overall. Similarly, the SOM content in the TYR treatment mode also fluctuated, akin to the SCR mode, and varied in the range of 2.02% to 2.04%. The SOM content of the CCR treatment mode was relatively high and remained relatively stable throughout the entire study period, ranging from 2.10% to 2.11%. The SOM content of the CT3 was relatively low and exhibited minimal fluctuation, primarily concentrated between 1.95% and 1.97%.

Overall, in terms of N, P, K, and SOM content, the CCR treatment mode exhibited relatively high levels of content and demonstrated an upward trend in some years. In contrast, the content of N, P, K, and SOM in the CT3 was relatively low and exhibited minimal fluctuation. The SCR and TYR treatment modes exhibited similar fluctuation trends and levels in N, P, K, and SOM content, intermediate between CCR and CT3.

The corn stalk management was the only difference among the four treatments, so naturally, we suspected that the difference in N, P, K, and SOM was due to differences in core stalk treatments, the viewpoint that corn stalk retention could increase soil nutrients had been verified by many studies [20]. Because the four different treatments lasted for different periods, the most interesting data should be the MAIR compared with CT3. The MAIR is shown in Figure 9. In terms of the N MAIR, the CCR was the highest and the SCR was the lowest; a similar variable trend could be found for P, K, and SOM. Compared with CT3, the MAIRs of N, P, K, and SOM were significantly (p < 0.05) higher for SCR, as were TYR and CCR. Further statistical analyses illustrated that the MAIRs among SCR, TYR, and CCR also have significant differences (p < 0.05).

Figure 4, Figure 6 and Figure 8 illustrate that the variable trends of N, P, K, and SOM were similar. Additionally, we confirmed that corn stalk cover positively impacts the enhancement of soil N, P, and K contents as well as SOM, which is consistent with previous studies [3,7,17,21,22,23].

Based on the corn stalk retention methods mentioned in the introduction section, we deduced that the retention amount of corn stalk followed the order CCR > TYR > SCR. Therefore, CCR replenished the most soil nutrients and organic matter compared to the other two corn stalk management practices (Figure 4, Figure 6 and Figure 8). CCR utilizes small-piece corn stalks to cover the soil surface, making it easier for these stalks to blend with the soil and for the residue–soil mixture to decay compared to SCR. Furthermore, in CCR, the corn stalk is buried by soil, and a study conducted in eastern Canada has shown that buried corn leaves, husks, and stems decompose faster [24]. Consequently, CCR is more effective in replenishing soil nutrients and SOM. This is one of the reasons CCR exhibited the highest N, P, K, and SOM contents in this study (Figure 4, Figure 6 and Figure 8). Jones et al. (2002) quantified corn stalk decomposition using microbial growth in soil and found that buried straw significantly favors the decomposition process [25].

Figure 4, Figure 6 and Figure 8 also demonstrate that during the observation period, the N, P, K, and SOM contents in all treatments did not exhibit significant (p > 0.05) fluctuations, confirming that substantial time is required for changes in soil nutrients and SOM to occur [26,27,28]. We speculate that the notable changes observed in this study may be attributable to long-term specific agronomic practices applied at the study sites prior to the commencement of this observation. In other words, the primary quantitative differences among the SCR, TYR, CCR, and control plots can largely be ascribed to the disparate corn stalk management practices implemented from the last century until the initiation of our study.

3.3. The Influence of AAT and APP

Figure 10 represents the correlation relationship among AAT, APP, and N, P, K, and SOM amendments. It is clear that at the significance level of 0.01, the AAT and APP have a significant positive correlation with almost all the observation items. In other words, the higher AAT and higher APP can favor the higher replenishment of N, P, K as well as SOM. The AAT and APP have a significant correlation (p < 0.01) with the replenishment of N, P, K, as well as SOM. From the above interpretations, the difference between AAT and APP was due to the different locations in northeast China, and the AAT, together with APP, decreased in the order L1 > L2 > L3 (Figure 3).

Comparisons among different locations were conducted in this study. The MAIRs of N, P, K, and SOM followed the order L1 > L2 > L3. The latitudes of the three locations were ordered as L3 > L2 > L1, while the AAT, APP, and their associated parameters exhibited an inverse order. The climatic variability from south to north in China negatively influences the decomposition of corn stalks, indirectly affecting the replenishment of N, P, K, and SOM. A study conducted in Santa Catarina State, southern Brazil, supports this hypothesis, reporting a faster decomposition rate under relatively high air temperatures [18]. Another study in the Argentine Pampas indicated that high temperatures in the agro-ecosystem could contribute to rapid residue decomposition with N release [19]. In addition to temperature, precipitation is another crucial factor impacting corn stalk decomposition. Both AAT and APP significantly influence soil microbial communities, which are the primary drivers of decomposition [29]. The decomposition process slows down when APP is below 470 mm and soil water content is below 15% [30]. Consequently, if decomposition slows, corn stalks may not fully decay during winter in northeast China, preventing the exhaustive release of soil nutrients and organic matter contained within. This ultimately reduces the amount of soil nutrients and organic matter adsorbed by farmland soil, given that L1 has the highest AAT and APP, while L3 has the lowest. Based on the analyses above, regardless of the corn stalk management practice, the MAIRs of N, P, K, and SOM decreased from L1 to L3, which is consistent with experimental results. The comparison between TYR and CCR in L3 was intriguing. Despite CCR retaining approximately 2.3 times more corn stalks than TYR, their MAIRs of soil nutrients and SOM were nearly identical. This suggests that the cold climate of L3 limits the exhaustive decomposition of corn stalks within a certain period.

4. Conclusions

In this study, long-term data were obtained. Compared to corn stalk removal management, soil nutrient levels, including N, P, K, as well as SOM, were enhanced by covering corn stalks on the soil surface. Furthermore, the MAIRs of N, P, K, and SOM followed the order CCR > TYR > SCR. Both corn stalk management practices and natural climatic conditions influence corn stalk decomposition; the decomposition rate and extent determine nutrient levels and organic matter amendments in the soil. Consequently, CCR is suitable for regions with relatively high AAT and APP, such as L1. Conversely, for regions with insufficient AAT and APP, SCR or TYR may be the optimal choices, as exemplified by L3. A suitable corn stalk retention method is a great favor to soil nutrient replenishment and environmental protection. In order to obtain more stalk retention solutions that can adapt to more climatic types, future studies should incorporate more locations across China. Meanwhile, we acknowledge that while both corn stalk management practices and natural climatic conditions significantly influence corn stalk decomposition, other factors such as microbial activity, soil moisture levels, and soil texture also play crucial roles in decomposition rates and nutrient cycling. Future research could explore the interactions between these factors and corn stalk management practices to gain a more comprehensive understanding of soil nutrient replenishment.

Furthermore, we recognize that corn stalk management practices have implications beyond soil nutrient replenishment. These practices can affect farm labor requirements, machinery usage, and overall farm management. For example, CCR may require additional machinery to chop and spread corn stalks, while SCR could reduce wind erosion and minimize soil disturbance. Future studies should assess the economic feasibility of different corn stalk management practices to inform sustainable agricultural decision-making.

Regarding economic implications, adopting CCR, TYR, or SCR practices can have varying costs and benefits for farmers. While these practices may reduce the need for synthetic fertilizers, they may also incur additional costs related to machinery, labor, and potential crop yield impacts. Future research should comprehensively evaluate the economic trade-offs associated with different corn stalk management strategies to ensure their widespread adoption and sustainability.