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Article

Tillage Strategy and Nitrogen Fertilization Methods Influences on Selected Soil Quality Indicators and Spring Wheat Yield under Semi-Arid Environmental Conditions of the Loess Plateau, China

by
Jianyu Yuan
1,
Mahran Sadiq
1,2,3,
Nasir Rahim
2,
Guang Li
1,*,
Lijuan Yan
3,
Jiangqi Wu
1 and
Guorong Xu
1
1
College of Forestry, Gansu Agricultural University, Lanzhou 730070, China
2
Department of Soil and Environmental Sciences, University of Poonch Rawalakot, Rawalakot 12350, AJK, Pakistan
3
College of Agriculture, Gansu Agricultural University, Lanzhou 730070, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2022, 12(3), 1101; https://doi.org/10.3390/app12031101
Submission received: 28 December 2021 / Revised: 12 January 2022 / Accepted: 17 January 2022 / Published: 21 January 2022
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Abstract

:
The influence of tillage and nitrogen fertilization methods on soil quality attributes and crop agronomic characteristics has been studied broadly under different agroclimatic conditions. Nevertheless, the interactive effect of tillage and fertilization approaches on soil properties on different soil depths and yield is rarely addressed, particularly on the Loess Plateau belt, and requires more exploration. Thus, this research was conducted in order to evaluate the interactive impact of tillage and nitrogen fertilization methods on soil properties and wheat productivity. The treatments included conventional tillage (CT) and no-till (NT) with different fertilization approaches (no fertilization: CK, chemical nitrogen fertilizer: N, organic fertilizer: M, combined application of nitrogen fertilizer and organic fertilizer: NM) and were explored in a split plot arrangement under a randomized complete block design replicated thrice on soil properties (SWC, SOC, TN, TP, NO3−-N, NH4+-N, and stoichiometric ratio) and wheat yield. The results showed that sole no-tillage and NT in association with nitrogen fertilization (inorganic and organic) significantly increased the soil water content, SOC, TN, NH4+-N, C/P, and N/P ratios and wheat productivity but did not significantly yield TP, whilst it reduced the NO3−-N and C/N ratio compared with sole CT and CT together with nitrogen fertilization (organic and inorganic). Overall, NT in association with the joint application of inorganic and organic N fertilization are the best techniques to improve soil water status and nutrient status under the wheat mono-cropping system conditions and yield.

1. Introduction

The capacity of soil to supply crucial nutrients to plants is known as soil fertility and is a chief concern for scientists [1]. In arid and semi-arid regions, specifically in the northwestern Loess Plateau areas of China, the yield of crops particularly in smallholder systems is affected by an inherent poor fertility status of soil and a reduced application of fertilization [2,3]. Poor soil fertility, water scarcity, and intensive fertilization make these agro-ecosystems vulnerable to the existing global changing climate process and cyclical drought events. Investment profit is undetermined with degraded soils, which raises the economic risks for smallholder agriculturists [4].
Nitrogen (N) is a vital macro-nutrient for the growth, development, and yield of crops [5]. N application methods augmented quickly, and different N fertilization approaches have been used to increase crop yields throughout the previous three decades; eventually, this has had a negative effect on crop development and production [6,7]. Nevertheless, N application might lead to soil acidification and deteriorate the soil environment. Consequently, the identification and recommendation of strategies that are both climate-smart and yield satisfactory crop productivity in a recent climate change scenario are significant for crop production in Loess Plateau areas in order to fulfill the up-to-date rise in demand for food and fuel globally [8,9,10].
Sustainable agricultural practices preserve soil and environmental quality, and increase soil and water conservation, which certifies the sustainable crop production. Land management strategies are the key drivers of agriculture sustainability, as they can modify soil health or quality via enhancements in physico-chemical, biological and hydrological characteristics [2,11]. Therefore, farming measures that conserve and preserve natural resources without bargaining productivity are at the center of sustainable production.
Spring wheat (Triticum aestivum L.) is one of the main crops grown in the Loess Plateau. Because of its strong drought tolerance, short growth period, considerable yield, and other advantages, wheat has become the preferred target for crop cultivation in the Loess Plateau [12]. Nevertheless, in recent years, intensive continuous farming and the large-scale application of chemical fertilizers in this area have led to the destruction of the farmland, a decline in soil fertility, and the waste of residual N [13]; the improper uses of conventional planting systems and inorganic chemical fertilizer can also cause farmland desertification, soil erosion, and pollution, resulting in changes in soil nutrients which lead affect food production safety [14]. Consequently, it is particularly important to explore the effects of conservation tillage and reasonable fertilization measures on farmland soil properties and yield.
Plenty of techniques have been used to increase soil properties and crop yields. The most operative strategy is improving the organic input, for instance with the implementation of organic compost or manure [15,16] and a no-till system [17]. Barus et al. [18], Peng et al. [19], and kai et al. [20] verified that different organic inputs, such as no-till, and manure application significantly improved soil quality attributes and crop yield. Organic fertilization and a no-till strategy have great value for increasing soil fertility indicators [21]. Various studies have stated that organic compost or manure and no-till is rich in soil nutrients and could be treated as a natural organic fertilizer, as well as used as an alternative to chemical inorganic fertilizers [22]. So, an organic technique including no-till or manure application appears promising to restore and preserve fertility of soil and soil quality indicators. However, until now, the use of organic strategy including no-till or manure application to improve crop productivity has still been a matter of discussion, since studies in different climates and soil types have led to unsatisfying findings [23].
The combination of reasonable tillage practices and fertilization methods not only affects changes in soil nutrients but is also the most important measure for sustainable agricultural development and utilization [24]. The research shows that no-till farming is conducive to the accumulation of topsoil organic matter, and that soil under traditional tillage is more vulnerable to erosion and degradation than is soil that is not tilled [25]. Other studies have shown that the combined application of organic fertilizer and conventional tillage can maximize crop fresh and dry weight and the nutrient absorption of soil, and is an effective way to improve soil fertility [26]. Combined applications of organic and inorganic N fertilizer can effectively reduce ammonia volatilization and soil nitrate leaching, which reduces N loss and environmental pollution [27]. To some extent, these studies have shown the response of farmland soil nutrients and yield different tillage practices or fertilizer applications. Meanwhile, the impact of the interaction of different tillage and different fertilization measures on farmland soil nutrient content and crop yield is not clear; additionally, the scarcity of the literature available on the effect of tillage and fertilization methods on different depth-wise nutrients accumulation particularly in the Dingxi zone seriously hinders the in-depth study of food production security and the soil nutrient cycle in the semi-arid area of the Loess Plateau in Dingxi, Central Gansu. Consequently, it is necessary to explore the response of the interaction of different tillage measures and fertilization methods on soil water and nutrients, stoichiometric characteristics, and yield, which plays an important role in realizing regional soil ecological security and crops’ high and stable yield.
This study tested the hypothesis that: (1) With the increase of soil depth, the soil water contents, organic carbon, and soil N contents will show a downward trend. (2) Soil nutrient content and stoichiometric ratio may have a certain correlation with wheat yield. (3) No tillage combined with organic and inorganic N fertilizers may increase the nutrient content of topsoil and effectively improve wheat yield. Our specific study goals were to analyze the effects of tillage measures and fertilization methods on soil water contents and nutrients, stoichiometric characteristics and wheat yield traits.

2. Materials and Methods

2.1. Site Description

Our experimental study area is located in the dry agriculture comprehensive experimental station of Gansu Agricultural University, in Anjiapo village, Anding District, Dingxi City, Gansu Province (Figure 1).
The site is a typical Loess plateau hilly and gully area with an average elevation of 2000 m. It is a temperate semi-arid zone with an annual average temperature of 6.4 °C. The average annual precipitation is 385 mm. The average precipitation during the growth period of spring wheat was 189.86 mm; the maximum precipitation during the growth period was 286.70 mm; and the minimum precipitation during the growth period was 56.10 mm (Figure 2). The average annual solar radiation was 141.60 kJ·cm−2; the average annual evaporation was 1540.00 mm; and the site was a typical semi-arid rainfed agricultural area. A comprehensive study area explanation has been provided in a previous study [28]. The major soil physicochemical quality indicators taken from the different soil layers in March 2020, before research, are presented in Table 1. Average across three soil layers (0–10 cm, 10–20 cm, and 20–40 cm), the pre-planting soil NO3−-N, NH4+-N, TN, TP, TK, SOC, C:N ratio, pH, SWC, electrical conductivity, bulk density, porosity, water storage, and temperature were 25.82 mg kg−1, 10.08 mg kg−1, 0.59 g kg−1, 0.41 mg kg−1, 18.46 g kg−1, 5.79 g kg−1, 9.82, 8.40, 14.95%, 0.35 dSm−1, 1.41 g cm−3, 46.79%, 48.83 mm, and 6.22 °C, respectively, and the texture of soil was sandy loam.
Before the study, the research field was bare. The Loess Plateau of China, particularly in the Dingxi region, had a long history of spring wheat farming. In addition, the climatic conditions of the research area during the crop cycle in 2020 are shown in Figure 2.

2.2. Research Design and Setup

This study was conducted as part of continuing research initially set up in 2015 with different tillage measures and N fertilization. The results of the study in 2020 are shown in this manuscript. The research setup was carried out in a split plot arrangement under a randomized complete block design (RCBD) with three replications. Tillage systems were kept in the main plot with N fertilizers (organic and inorganic) in subplots. Treatments were two tillage systems [(viz., conventional tillage (CT) and no-tillage (NT)] and four N fertilization methods [(e.g., no fertilizer (CK), inorganic N fertilization (N), organic N fertilization (M), and combined application of inorganic and organic N fertilization (NM)]. The tillage practices and N fertilization methods were arranged randomly, with a total of eight treatments and replicated thrice for each treatment for a total of 24 individual plots with a 24 m2 area. The description of the experimental treatments is shown in Table 2. In the conventional tillage (CT) practice, soils were tilled at two different times by manual inversion with shovels to a depth of 20 cm; the first time was in October of the previous year and the second time in March just before wheat crop sowing, followed by planting. Nevertheless, in the no-tillage (NT) practice, crop stubbles (30%) were returned to the field in August of the previous year and planting was done with a no-crop planter. These tillage practices were implemented onto the main plots. The sub-plots were allocated to four N fertilizer treatments including organic and inorganic N fertilization methods. In the CK plots, no fertilization was done; however, in the inorganic N fertilized (N) plots, the N was applied in the form of urea at the rate of 105 kg N ha−1y−1. For the organic N fertilized (M) plots, farmyard manure was applied as a N source at the rate of 105 kg N ha−1y−1. In the interactive application of inorganic and organic N fertilizers (NM) treatments, both urea and farmyard manure at the rate of 52.5 kg N hm−1y−1, respectively, were applied as a N source. Each N fertilized treatment was equivalent to the annual N rate of 105 kg N ha−1y−1. The local spring wheat “Dingxi 42” cultivated locally was selected as the test variety (cv: Dingxi 42, the approval number: ganshengmai 2014004). The spring wheat crop was sown on 25 March 2020 with sowing rate of 187.5 kg/ha with 25 cm row spacing and was harvested on 30 July 2020. In order to avoid the marginal effect between the plots, they were separated by a 0.5 m-wide isolation belt. Furthermore, phosphorous and N using diammonium phosphate at the rate of (146 kg ha−1) and urea at the rate of (63 kg ha−1) was applied as basal doses before spring wheat sowing. Manual weeding was done throughout the spring wheat growing season when mandatory, and Roundup (glyphosate, 30%) was applied in the plots during the fallow periods in accordance with the manufacturer’s instructions in order to control weeds [29]. In this experimental research, no irrigation was supplied during the spring wheat crop growing season. All other field management and protection measures were consistent with local cultivation practices.

2.3. Sample Collection and Measurements

2.3.1. Determination of Soil Water Content

The surface and sub-surface undisturbed soil samples from different treatments were sampled at a crop maturity stage for the determination of gravimetric soil water content (SWC). Five points were randomly selected in each test plot in the shape of “S”; the removal of aboveground plants and surface litter and soil drills with a diameter of 5 cm were used to collect 0–10, 10–20, 20–40, 40–60, and 60–100 cm soil layer soil samples [30]; the same soil layer soil was constituted with a mixed soil sample, debris was removed, and it was put in a Ziplock bag and placed in a sample box with an ice bag for low-temperature transportation [31]. These samples were taken back to the laboratory for the determination of soil indicators. An aluminum box drying method was used to determine SWC. The empty aluminum box was weighed first, and the fresh soil sample was then put in the aluminum box, which was weighed and transferred to an oven. After drying to a constant weight at 105–110 °C, the weight of the dry soil was determined, and the percentage of water weight was then calculated to obtain the SWC [18].

2.3.2. Determination of Soil Organic Carbon

The SOC was determined by the H2SO4-KCr2O7 oxidation external heating method. A 1 g air-dried soil (passing 0.25 mm sieve) sample was combined with 6 mL potassium dichromate (0.4 mol/L) and 8 mL concentrated sulfuric acid and heated at 180 °C for 30 min in a digester at constant temperature. The samples were cooled and washed in a conical flask with distilled water, after which 2–3 drops of o-phenanthroline ferrous indicator was added, and the samples were shaken and titrated with ferrous sulfate solution [28].

2.3.3. Determination of Soil Chemical Quality Indicators

The TN content was determined using a semi-micro Kjeldahl method; 1 g of air-dried soil (passing 0.25 mm sieve) sample was combined with 8 mL of concentrated sulfuric acid and the mixture was placed in the digester. The solution was heated until it was milky white at 400 °C, and the whole solution was then transferred to a 100 mL volumetric flask for constant volume. After the solution was cooled and clarified, 5 mL supernatant was extracted, and 4 mL of sodium hydroxide (10 mol/L) and 5 mL of boric acid solution for N determination were added; it was titrated with dilute sulfuric acid solution [32]. The TP content was determined by vanadium molybdenum yellow colorimetry. The process of sample weighing and digestion was consistent with that of soil TN. Then, 10 mL of supernatant was taken and put into a 50 mL volumetric flask. Two drops of dinitrophenol indicator were added and neutralized with sodium hydroxide (6 mol/L). When the color of the solution changed to yellowish, 10 mL of ammonium vanadomolybdate solution was added and determined with distilled water after 15 min. Then the wavelength of the spectrophotometer was adjusted to 450 nm, the color compare with a 1 cm light path cuvette, and the reading recorded [32].
The soil NH4+-N and NO3−-N contents were determined by using a 2 mol/L KCL solution with a water–soil ratio of 5:1, followed by a flow analyzer. A 10 g sample of fresh soil (passing 0.25 mm sieve) was screened through a 2 mm sieve into a 250 mL Erlenmeyer flask; 50 mL of 2 mol/L KCL solution was added, and the flask was shaken on a reciprocating shaker for 1 h. The soil/water suspension was then filtered through quantitative filter paper, and the filtrate was analyzed by a continuous flow analyzer to determine the content of soil NO3−-N and NH4+-N [33].

2.3.4. Determination of Crop Agronomic Traits

The yield of spring wheat was measured at maturity. When harvesting spring wheat, three rows of plants with uniform growth were selected from each plot to determine the yield; 1000 grain weights and then five plants were randomly selected to determine the plant height, grain number per panicle, and biomass [34]. Then, the yield of each plot was estimated according to the yield of three rows of plants, and then the hectare yield of each plot was estimated [35].

2.4. Statistical Analysis

Analysis of variance (ANOVA) was performed using SPSS 25.0 computer software (IBM Corp., Chicago, IL, USA). To analyze and compare the influence of different tillage and fertilization treatments and their interactions on soil properties and yield, we used two-way analysis of variance (two-way ANOVA). Mean separations were completed using the (Duncan’s test at p < 0.05) method, and Origin 2019 was used for drawing figures. Furthermore, principle component analysis (PCA) was performed in order to evaluate the multivariate variability introduced by the different treatments for soil properties and crop yield. Pearson correlation analysis was used to describe the correlation between the factors.

3. Results

3.1. Effect of Treatments on Gravimetric Soil Water Content

SWC at different soil layers was significantly (p < 0.05) influenced by tillage strategies and N fertilization methods (Table 3). The SWC in the NT, NTN, NTM, and NTNM no-tilled treatments in the 0–60 cm soil layer was significantly higher than in the CT, CTN, CTM, and CTNM tilled treatments (p < 0.05). The highest SWC was noted in the NTNM treatment, and lowest the SWC was associated with CT practice, but there were no significant differences within the 60–100 cm soil layer (p < 0.05). In the vertical soil profile, the SWC gradually decreased with increasing depth, and the SWC in the surface 0–10 cm soil layer was significantly higher than the sub-surface soil layers.

3.2. Effects of Treatments on Soil Chemical Properties under Wheat Agroecosystem

The different treatments have significant effect on soil organic carbon as shown in the Figure 3a.
In the 0–100 cm soil layers, the highest SOC contents were associated with the NT, NTN, NTM, and NTNM no-till treatments, whilst the minimum SOC contents were noted in the CT, CTN, CTM, and CTNM tilled treatments. In addition, regarding the no-till treatments, NTNM had the maximum (7.43 g/kg) SOC content. On average across the 0–100 cm soil layers, the NT, NTN, NTM, and NTNM increased the SOC by 9%, 13%, 15%, and 21%, respectively, compared with the sole CT treatment. Moreover, there were also differences in SOC contents between the different tested soil layers. In the 0–10 cm soil layer, the SOC contents were higher compared with other investigated soil layers (p < 0.05).
The average content of TN in the whole soil layer reached a maximum (1.19 g/kg) under NTNM treatment and a minimum (0.69 g/kg) under CT treatment, and there was a significant difference among the treatments (p < 0.05). The highest TN contents in the 0–10, 10–20, 20–40, and 40–60 cm soil layers were all in the NTNM plots and were 2.28 g/kg, 1.79 g/kg, 1.51 g/kg, and 1.29 g/kg, respectively; there was a significant difference among the treatments. Nevertheless, TN content in the 60–100 cm soil layer was similar, and there was no significant difference (p < 0.05) among treatments (Figure 3b). In the vertical soil layer profile, the TN content significantly (p < 0.05) decreased gradually with increasing depth, and the TN content in the 0–10 cm soil layer was significantly higher than that in the lower layers.
The soil TP content under different treatments is shown in the Figure 3c. There was no significant difference observed between different treatments in the case of TP content, including 0~100 cm soil layers at (p < 0.05). The TP content under different treatments, including all investigated soil layers, fluctuated within a small range with a statistically non-significant difference (Figure 3c). Moreover, regarding all tested soil layers, the TP concentration did not change significantly (p < 0.05), indicating that the TP distribution in tested soil depths was stable.
The change of soil NO3−-N and NH4+-N content under tillage strategies and N fertilization methods is shown in the Figure 4a,b. In the plough soil layer 0–40 cm, the CTN treatment had, significantly (p < 0.05), the highest NO3−-N content, whilst the lowest NO3−-N content was recorded in the sole CT treatment. Moreover, the NO3−-N content of CTN and NTN was significantly the (p < 0.05) highest over CTM, CTNM, NTM, and NTNM treatments. In the 40–60 cm soil layer, the NTNM treatment had the significantly (p < 0.05) lowest NO3−-N content, whilst CTN treatment had the highest NO3−-N content. Moreover, in the 60–100 cm soil layer, CT had the significantly (p < 0.05) highest NO3−-N content, whilst NTNM had the lowest NO3−-N content. Regarding different soil layers, the soil NO3−-N content showed an obvious trend of first significantly (p < 0.05) increasing in the surface soil layers, then decreasing in the sub-surface soil layers, and being the highest at 20–40 cm.
In 0–60 cm soil layer, the NH4+-N content of NTNM treatment was significantly (p < 0.05) the highest, and the lowest NH4+-N content was associated with CT, except for the 20–40 cm soil layer where the lowest NH4+-N content was noted in CTN treatment. Moreover, in the 60–100 cm soil layer, the CTM treatment had significantly (p < 0.05) highest NH4+-N content whilst the lowest NH4+-N content was noted in NTM treatment. Regarding different soil layers, the soil NH4+-N content showed an obvious trend of first significantly (p < 0.05) increasing in the surface soil layers and then decreased in the sub-surface soil layers, being the highest in 10–20 cm.
The two factor ANOVA (Table 4) showed that the effects of tillage on SOC, TN, TP, NO3−-N, and NH4+-N were significant (p < 0.01). The TN, NO3−-N, and NH4+-N contents were also significantly (p < 0.01) affected by the N fertilization method. Tillage practices and N fertilization methods had significant effects on soil TN content, but the effects on the SOC, TP, NO3−-N, and NH4+-N contents were not significant (p < 0.01).

3.3. Response of Soil Stoichiometric Properties to Treatments under Wheat Mono-Cropping System Conditions

Soil stoichiometric ratios under tillage systems and fertilization treatments are presented in Table 5. The soil stoichiometric ratios were significantly (p < 0.05) affected by tillage techniques and N fertilization methods. The soil C/N ratio was the highest under CT treatment, and the lowest C/N ratio was recorded in NTNM treatment at the 0–10 cm soil layer. The NTNM treatment had, significantly (p < 0.05), the highest soil C/P ratio, whilst CTM treatment had the lowest C/P ratio. The CT treatment had the lowest soil N/P ratio, whereas NTNM treatment had a maximum soil N/P ratio at the 0–10 cm soil layer.

3.4. Effects of Treatments on Crop Agronomic Attributes

The spring wheat agronomic traits were significantly (p < 0.05) influenced by tillage strategies and N fertilization methods, as shown in Table 6. The plant height, grain number per spike, 1000-grain weight, and biomass in the four NT, NTN, NTM, and NTNM treatments were higher than four CT, CTN, CTM, and CTNM treatments. The NTNM treatment had, significantly (p < 0.05), the highest of all noted agronomic traits, whilst CT treatment had the lowest spring wheat agronomic attributes. The highest grain yield of spring wheat, 1843.88 kg/ha, was recorded in NTNM treatment. Compared with CT, CTN, CTM, CTNM, NT, NTN, and NTM treatments, the NTNM treatment noticeably increased grain yield by 29.03%, 21.96%, 19.66%, 13.64%, 11.81%, 8.26%, and 5.70%, respectively.
Two factor ANOVA (Table 7) showed that the tillage measures, fertilization methods, and their interaction had a significant impact on the yield of spring wheat (p < 0.01).

3.5. Principal Component Analysis and Correlation Analysis

Principal component analysis (PCA) allowed for isolating five principal components in accordance with the Jolliffe cut-off value. In accordance with PCA analysis, the observation point made by an interaction of PC1 and PC2 depicts the overall variance described by the five main components. In the PCA analysis of 10 variables (viz., SWC, SOC, TN, TP, NO3−-N, NH4+-N, C:N ratio, N:P ratio, C:P ratio, and wheat yield), PC1 and PC2 were extracted with eigenvalues > 1, shown in Figure 5, and explained 78.2% of the total variance. However, PC3, PC4, and PC5 do not permit the addition of supplementary information; that is why they are not included. The maximum loadings of PC1 comprise 58.2% of the total variance and in PC2 the higher loadings of 20.0% of the total variance were observed (Figure 5).
Figure 6 showed that there was a very significant positive correlation between spring wheat yield and SWC, SOC, TN, NH4+-N, and N/P (p < 0.001), which was consistent with [17], and the correlation coefficients were 0.75, 0.86, 0.85, 0.65, and 0.77, respectively. Additionally, there was a significant positive correlation between yield and C/P, with a correlation coefficient of 0.44. Besides, there was a very significant negative correlation between yield and C/N (p < 0.001), and the correlation coefficient was −0.75. Additionally, there was a weak negative correlation with the NO3−-N content, which did not reach a significant level, and there was no relationship with TP.

4. Discussion

4.1. Soil Water Content as Affected by Different Treatments

SWC refers to stored water in unsaturated soil layers [36]. It is a relation among the atmosphere and the biosphere; it also effects the relationship of the soil hydrological processes over space as well as time [37]. It plays a vital role in the worldwide water cycle by regulating the distribution of evaporation and infiltration [38]. Accurate quantification of SWC distribution under tillage practices and N fertilizer methods is important in understanding an inherent soil’s capacity to supply micro and macro soil nutrients as well the modification degree of soil nutrient, providing that capacity with tillage and N fertilization approaches. It will offer crops ideal N fertilizer recommendations for understanding production sustainability.
SWC directly affects the health and growth of plants and plays a critical role in sustainable agriculture [39]. Our results showed that the SWC of the NT, NTN, NTM, and NTNM no-tilled treatments were higher than CT, CTN, CTM, and CTNM tilled treatments in the top four soil layers. The SWC in the vertical soil profile showed a decreasing trend with increasing soil depth, which was consistent with the previous results of [40]. This is because no-till cultivation reduces the disturbance to the soil layers, reduces the soil porosity, and reduces the evaporation of SWC, all of which play important roles in water storage and SWC conservation [41,42]. At the same time, NT, NTN, NTM, and NTNM can improve the physical and chemical properties of soil, increase water infiltration after rainfall or irrigation, and inhibit SWC evaporation, which then improves the SWC [43]. Additionally, our data showed that NT, NTN, NTM, and NTNM increased plant biomass (Table 5), indicating that the plants grow vigorously, and plants with good growth form a canopy that can block some sunlight, thus reducing the evaporation of SWC and ensuring a high SWC.

4.2. SOC, TN, TP, N-NO3−, and N-NH4+

Dry-land farming and an applied pattern of tillage in association with N fertilizer was fruitfully documented to hasten essential soil nutrient release, consequently enhancing the soil nutrient status and availability to crops; this mainly happened via the synergistic regulation of the soil hydrothermal situation. However, excessive N fertilization, intensive cropping, and continuous soil inversion led to serious soil fertility deterioration, which threatens sustainability of both crop and soil [44,45,46,47,48].
SOC is the main source of many of the nutrients needed by plants and is also the most critical attribute of soil that forms the core of soil quality [8,49]. Our results showed that the total SOC content of the NT, NTN, NTM, and NTNM was higher than CT, CTN, CTM, and CTNM treatments, and SOC decreased with increasing soil depth. This is because no-till cultivation does not involve turning the soil, which reduces soil interference and reduces CO2 emissions, thereby effectively reducing the mineralization of SOM and promoting the increase in surface SOC [48]. Additionally, because no-till causes less damage to the soil structure, it further increases the protection of SOC levels. At the same time, the combined application of N fertilizers alleviated the decline in soil pH, improved the soil physical and chemical properties, maintained higher soil porosity, and was conducive to the accumulation of SOM [50]. With increasing soil depth, the decrease in SOC may be due to the decomposition of aboveground litter. During the decomposition of litter, large numbers of nutrients enter in the soil and accumulate at the soil surface, resulting in an increase in SOM in the surface soil layer. However, plant roots absorb nutrients from the middle and lower layers of the soil, resulting in a decrease in the nutrient content of these soil layers [51].
Tillage practices and N fertilization are important techniques that affect soil N content [52]. Our results showed that the TN contents of the NT, NTN, NTM, and NTNM treatments were higher than CT, CTN, CTM, and CTNM treatments. The TN content in the soil profile decreased with increasing soil depth but tended to be stable in the 60–100 cm profile, which is similar to the results of two previously published studies [53,54]. This is because no-till farming preserves the soil structure, protects the soil, reduces soil erosion, and improves soil fertility [55]. Additionally, the application of N fertilizers improves the distribution of soil nutrients, improves soil fertility, and increases the content of soil-available nutrients, thus increasing the soil TN content. The decrease in soil TN content with increasing soil depth may be affected by the decomposition of surface litter and fertilization. The decomposition of litter and fertilization will result in the accumulation of nutrients at the soil surface. At a soil depth of 60–100 cm, the TN content tends to be stable, which may be due to the short root system of wheat, which is unable to absorb and utilize nutrients in deep soil layers, making nutrients in the deeper soil layers more stable [20].
Our results depicted that the TP content of soil did not significantly change under different treatments. This is due the source of phosphorus in the soil is relatively fixed, and it is a sedimentary mineral, and the soil phosphorus mobility is often low, so the distribution of TP in the whole soil layer is relatively uniform, and it is difficult to be affected by external source within short-term implementation. This is maybe as a consequence of the short-term tillage and N fertilizer application, and possibly tillage, particularly in the NT, and N fertilization approaches, needs more time for total soil phosphorous improvement. This is consistent with findings reported by [21,56]. The effects of tillage strategies (e.g., NT and CT) and N fertilization on soil nutrient accumulation is still a matter of debate, since research in different climatic conditions and soil types have led to varying results [57]. Furthermore, NT benefits perhaps sustained by numerous variables counting the climatic conditions, soil types, and soil management strategies (e.g., tillage duration, type of crop, and application of fertilizer).
Soil NO3−-N and NH4+-N are water-soluble forms of inorganic N that can be directly absorbed and utilized by plants. Plant species differ with respect to the uptake, utilization, and physiological regulation of NO3−-N and NH4+-N [58]. The results showed that the content of NO3−-N in the soil of each soil layer was higher in CTN, CTM, CTNM, NTN, NTM, and NTNM, over the CT and NT treatment. Moreover, the maximum NO3−-N was observed in CTN treatment, and the lowest was noted in CT treatment, and it also increased first and then decreased with the deepening of soil layer, reaching a maximum in the 20–40 cm soil layer. This is because the fertilization treatment transports a large amount of N to the soil, which increases the content of NO3−-N in the soil through mineralization. In addition, the application of N fertilizer treatments makes a large amount of N enter the soil, resulting in excess soil N, aggravating soil acidification and salinization, and limiting the ability of crop roots to absorb nutrients, resulting in the increase of NO3−-N residue. In addition, NO3−-N is the largest under CTN treatment because CT changes the distribution of surface soil, resulting in reduced SWC, enhanced soil aeration, easier conversion of NH4+-N to NO3−-N, and a large amount of N fertilizer application, which further increases the residue of soil NO3−-N [59]. At the same time, no-till farming and the combined application of organic and inorganic N fertilizer with a NT system was found to effectively reduce NO3−-N leaching, which reduces N loss and environmental pollution, and can thus be used as an ideal tillage practice and fertilizer ratio. In this study, the soil NO3−-N increased at top soil layers as a result of soil amendments presented in Figure 4. This concurs with results reported by Sadiq et al. [17] and Samaresh et al. [59]. Nevertheless, the soil NO3−-N was noticeably lower at deep soil layers, maybe because the N fertilizers (organic and inorganic) was mostly incorporated into the topsoil, which kept the soil NO3−-N from leaching. Among them, rainfall and other climatic factors play a decisive role, but due to the relatively low annual precipitation in the study area, consequently, NO3−-N in the soil cannot be leached into the deeper soil layer, so it is the largest in the 20–40 cm layer. The soil NH4+-N content trend was consistent with that of TN, but was the opposite to that of NO3−-N content. On the one hand, this can be explained by the fact that NH4+-N mainly comes from the mineralization of soil TN, while on the other hand, it may be because the soil under traditional tillage is loose, with a high porosity and strong aeration, and NH4+-N is readily converted into NO3−-N, resulting in leaching and the loss of N [60]. In addition, NH4+-N content is also affected by N mineralization, soil microbial activities, and aboveground vegetation absorption. Under CT conditions with no N fertilization application, the growth of the wheat plants was negatively affected, and the root absorption rate decreased, as did organic N mineralization, vegetation absorption, and utilization efficiency, resulting in a decrease in the NH4+-N content. These results are consistent with those of [17,42,45].

4.3. Soil Stoichiometric Ratios under Different Treatments

Tillage techniques and N fertilization methods will not only affect crop growth and yield, but also affect the availability of essential soil nutrients. Consequently, the stoichiometric characteristics of cultivated soil will make different adaptive strategies for different tillage systems and N fertilization treatments. The greater C/N ratio hindered the decomposition and mineralization of SOM. It is necessary to supplement an appropriate amount of N fertilizer to adjust C/N [61,62]. In this study, soil C/N was the highest under CT treatment and the lowest under NTNM treatment. Under the CT system, a higher soil C/N ratio over NT may be because of slower decomposition under a NT system. These results are in agreement with [63], which pointed out the lower C/N ratio under conservation tillage compared with CT.
The overall performance of NT was lower than CT. Moreover, CTNM and NTNM treatments performance was lower than CT, CTN, CTM, NT, NTN, and NTM, indicating that under no-tillage and N-based fertilizers treatments, the rate of decomposition and mineralization of SOM is slower; the storage capacity of carbon and N is strong; and the increase of N is greater than carbon (Figure 3), especially under the NTNM treatment [64,65]. Soil C/P and N/P ratios showed the opposite trend with C/N, being highest in NT than CT, and fertilized treatments NTN, NTM, NTNM, CTN, CTM, and CTNM were also higher in C/P and N/P ratios than no-fertilization amendments NT and CT. In general, the soil C/P and N/P ratios were highest under NTNM treatment [64]. These results are in line with those of [62], which declared that no-tillage increases the soil C/P and N/P ratios. On the basis of relatively stable soil phosphorus in the study area and no significant difference, it further showed that NTNM treatment was helpful to the accumulation of soil carbon and N. Additionally, the soil N/P ratio under each treatment was less than 14, indicating that the spring wheat field soil in the study area was greatly limited by N [65].

4.4. Effects of Treatments on Crop Agronomic Attributes

Determining the optimum N application method is an operative approach to meet crop economic benefits whilst decreasing the environmental hazards. Crop production is a normally used gauge for defining ideal N application methods [66]. The results of our study showed that NT, NTN, NTM, and NTNM treatments increased plant height, grain number per spike, 1000-grain weight, biomass, and grain yield to a greater extent than CT, CTN, CTM, and CTNM treatments, which indicated that no-till farming combined with inorganic and organic N fertilizer could increase the yield of wheat, which was consistent with the results of previously published studies [8,67,68]. This may be because no-till did not disturb the soil layer; it maintained the original soil capillary system in the wheat field; the soil bulk density was suitable; and there were more capillary pores, which avoided hardening of the soil caused by overly wet tillage. Khormi et al. [69] drew a same conclusion for a short-term wheat study.
In addition, our results demonstrated that the nutrient status of no-tilled treatments is significantly increased, which improved the soil’s ability to retain both water and fertilizer; it led to improve crop production [24], which is consistent with the finding of Vizoili et al. [68] and Li et al. [70]. Nevertheless, there were also scholars who found that no-tilled soil and fertilization did not significantly affect [71] or reduce the crop productivity [72]. It is believed that organic fertilization could result in, notably, N immobilization and, accordingly, result in lower crop productivity [73]. Moreover, the combination of organic and inorganic N fertilizer can not only ensure the long-term nutrient demand of the soil but can also rapidly meet the nutrient requirement of crops, so that the nutrient demand and the supply of soil nutrients can be coordinated [74] to create a good growth environment and increase production.
In addition, our study found a correlation between spring wheat yield and soil quality attributes. Our results showed that spring wheat yield was significantly positively correlated with SWC, SOC, TN, NH4+-N, C/P, and N/P, and spring wheat yield was negatively correlated with soil NO3−-N content and C/N. This is because the increase in SWC, SOM, and TN content will enhance root system activity and increase the ability of the root system to absorb nutrients. Increased SWC, SOM, and TN content also provide carbon and N for microbial growth, which will increase the rhizosphere microbial community, enhance the exogenous influence on root growth, accelerate the growth rate of crops, improve crop biomass, and enhance photosynthesis [75], which will increase yield. In addition, the increase in SOM and TN content can effectively prevent soil hardening, enhance soil fertility, and provide better site conditions for crop growth [76]. In our study, we found a significant positive correlation between soil NH4+-N content and yield because the trend in NH4+-N content was consistent with that of TN, because it mainly came from the mineralization of TN [56]. Additionally, there was a positive correlation between yield and C/P and N/P, because in the state of relatively stable phosphorus in farmland soil, the greater the carbon and N, the greater the C/P and N/P and the higher the content of carbon and N in soil, so as to improve the crop yield [60]. The yield was negatively correlated with soil NO3−-N content, because the excessive accumulation of NO3−-N leads directly to secondary salinization, an imbalance in the nutrient supply, and structural damage, as well as other problems. In addition, excessive NO3−-N levels will cause a large amount of NO3−-N leaching, which in turn causes soil pollution, inhibiting crop root development, and ultimately greatly affects crop growth, which can reduce yield [77]. The negative correlation between yield and soil C/N proves the importance of N to crop growth. In conclusion, we found a significant correlation between soil nutrient content and crop yield in the different tillage and N fertilization treatments. We can improve the soil fertility and change the soil nutrient content through external planting conditions so as to achieve the objective of increasing yield.

5. Conclusions

Our results depicted that the SWC, SOC, TN, and NH4+-N gradually decreased with increasing soil depth, and the NO3−-N content first increased and then decreased with increasing of soil depth, and TP had no change. Compared with the other treatments, NTNM treatment significantly increased SWC, SOC, TN, NH4+-N content, C/P, N/P, and crop yield; effectively reduced NO3−-N content in the soil; and significantly increased crop yield on the basis of reducing N loss. In addition, we also found that the SOC, TN, NH4+-N content, C/P, and N/P have a highly significant positive correlation with grain yield, and the NO3−-N content and C/N have a very significant negative correlation with yield. Additionally, the soil N/P in the study area is less than 14, indicating that crops are more limited by N, and subsequent crop planting should pay attention to nitrogen input in the key growth period. The NTNM practice can be used as an ideal farming practice and fertilizer ratio in local wheat production. In general, our study provides valuable information for scientific cultivation and crop production methods on farmland, which will help us to better understand the effects of tillage and N fertilization methods on soil nutrients accumulation and yield.

Author Contributions

The research field has been managed by G.L., with ploughing, fertilizing, planting, weeding, and harvesting. J.Y., M.S. and G.L. collected the field and laboratory data. J.Y. analyzed data and wrote the article. M.S. edited the manuscript. M.S., G.L., N.R., L.Y., J.W. and G.X., reviewed the article. All authors have read and agreed to the published version of the manuscript.

Funding

This experimental study received outside financial support from the financial special project of Gansu province (GSCZZ-20160909), Key Talents Project of Gansu Province (LRYCZ-2020–1), Key Research and Development program of Gansu Province (20YF8NA135), and Industrial Support Plan project (2021CYZC-15) of China.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

We appreciatively acknowledge the plan of the Gansu Province key research and development (18 YF1NA070) and the Collective innovation team project (2018C-16) of University in Gansu Province, China. We would also like to special thank Majid Mahmood Tahir at the University of Poonch Rawalakot, Pakistan for his technical assistance. We would also like to special thank the editors and the reviewers for their constructive and helpful comments.

Conflicts of Interest

The authors declare no conflict of interest. This manuscript, entitled “Tillage Strategy and Nitrogen Fertilization Methods Influences on Selected Soil Quality Indicators and Spring Wheat Yield under Semi-Arid Environmental Conditions of the Loess Plateau, China”, by Jianyu Yuan et al. has no potential conflict of interest.

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Applsci 12 01101 g001 550
Figure 1. The geographical location map of the study area.
Figure 1. The geographical location map of the study area.
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Figure 2. Daily average temperature and rainfall during the spring wheat crop cycle in 2020.
Figure 2. Daily average temperature and rainfall during the spring wheat crop cycle in 2020.
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Figure 3. Effect of tillage techniques and N fertilization methods on soil quality indicators. Note: (a) is the concentration of SOC at different soil layers, (b) is the concentration of TN at different soil layers, and (c) is the concentration of TP at different soil layers. The error bars indicate standard deviation. Different capital letters indicate significant differences between different treatments for the same soil layer (p < 0.05; Duncan’s test), and different lower-case letters indicate significant differences between different treatments and different soil depths (p < 0.05; Duncan’s test). CT: conventional tillage, CTN: conventional tillage with inorganic N fertilizer, CTM: conventional tillage with organic N fertilizer, CTNM: conventional tillage with combined application of organic and inorganic N fertilizer, NT: no-tillage, NTN: no-tillage with inorganic N fertilizer, NTM: no-tillage with organic N fertilizer, NTNM: no-tillage with combined application of organic and inorganic N fertilizer.
Figure 3. Effect of tillage techniques and N fertilization methods on soil quality indicators. Note: (a) is the concentration of SOC at different soil layers, (b) is the concentration of TN at different soil layers, and (c) is the concentration of TP at different soil layers. The error bars indicate standard deviation. Different capital letters indicate significant differences between different treatments for the same soil layer (p < 0.05; Duncan’s test), and different lower-case letters indicate significant differences between different treatments and different soil depths (p < 0.05; Duncan’s test). CT: conventional tillage, CTN: conventional tillage with inorganic N fertilizer, CTM: conventional tillage with organic N fertilizer, CTNM: conventional tillage with combined application of organic and inorganic N fertilizer, NT: no-tillage, NTN: no-tillage with inorganic N fertilizer, NTM: no-tillage with organic N fertilizer, NTNM: no-tillage with combined application of organic and inorganic N fertilizer.
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Figure 4. Effect of tillage techniques and N fertilization methods on mineral N. Note: (a) is the concentration of NO3−-N at different soil layers; (b) is the concentration of NH4+-N at different soil layers. The error bars indicate standard deviation. Different capital letters indicate significant differences between different treatments for the same soil layer (p < 0.05; Duncan’s test), and different lower-case letters indicate significant differences between different treatments and different soil depths (p < 0.05; Duncan’s test). CT: conventional tillage, CTN: conventional tillage with inorganic N fertilizer, CTM: conventional tillage with organic N fertilizer, CTNM: conventional tillage with combined application of organic and inorganic N fertilizer, NT: no-tillage, NTN: no-tillage with inorganic N fertilizer, NTM: no-tillage with organic N fertilizer, NTNM: no-tillage with combined application of organic and inorganic N fertilizer.
Figure 4. Effect of tillage techniques and N fertilization methods on mineral N. Note: (a) is the concentration of NO3−-N at different soil layers; (b) is the concentration of NH4+-N at different soil layers. The error bars indicate standard deviation. Different capital letters indicate significant differences between different treatments for the same soil layer (p < 0.05; Duncan’s test), and different lower-case letters indicate significant differences between different treatments and different soil depths (p < 0.05; Duncan’s test). CT: conventional tillage, CTN: conventional tillage with inorganic N fertilizer, CTM: conventional tillage with organic N fertilizer, CTNM: conventional tillage with combined application of organic and inorganic N fertilizer, NT: no-tillage, NTN: no-tillage with inorganic N fertilizer, NTM: no-tillage with organic N fertilizer, NTNM: no-tillage with combined application of organic and inorganic N fertilizer.
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Figure 5. Principal component analysis of yield, SWC, soil nutrients, and stoichiometric characteristics.
Figure 5. Principal component analysis of yield, SWC, soil nutrients, and stoichiometric characteristics.
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Figure 6. Correlation heat map of spring wheat yield, soil nutrients, and stoichiometric characteristics. SWC: gravimetric soil water content, SOC: soil organic carbon, TN: total nitrogen, TP: total phosphorus, NO3−-N: nitrate nitrogen and NH4+-N: ammonium nitrogen, C/N: soil carbon and total nitrogen ratio, C/P: soil carbon and total phosphorous ratio and N/P: soil total nitrogen and total phosphorous ratio.
Figure 6. Correlation heat map of spring wheat yield, soil nutrients, and stoichiometric characteristics. SWC: gravimetric soil water content, SOC: soil organic carbon, TN: total nitrogen, TP: total phosphorus, NO3−-N: nitrate nitrogen and NH4+-N: ammonium nitrogen, C/N: soil carbon and total nitrogen ratio, C/P: soil carbon and total phosphorous ratio and N/P: soil total nitrogen and total phosphorous ratio.
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Table
Table 1. Physicochemical quality indicators of the pre-planting initial tested soil in 2020.
Table 1. Physicochemical quality indicators of the pre-planting initial tested soil in 2020.
Soil PropertySoil Layer (cm)Measurement Method
0–1010–2020–40
NO3−-N (mg kg−1)25.7225.7725.88Colorimetric method
NH4+-N (mg kg−1)10.1510.0810.02Colorimetric method
TN (g kg−1)0.620.590.56Semimicro-Kjeldahl method
TP (mg kg1)0.440.410.38Colorimetric method
TK (g kg−1)18.4718.5218.40Colorimetric method
SOC (g kg−1)5.935.815.64Walkley-Black dichromate oxidation
C:N ratio9.569.8410.07SOC/TN
pH8.378.408.44pH meter
SWC (%)15.6514.7614.46Oven-dry method
ECe (dSm−1)0.350.380.32EC meter
B.D (g cm−3)1.381.411.44Core sampler method
P (%)47.9246.7945.66(1 − (B.D/P.D)) × 100 equation
SWS (mm)21.5941.6283.28SWC × BD × d/ρw
ST (°C)6.406.226.04Geothermometer
Soil textureSandy-loamHydrometer method
Note: P.D: particle density = (2.65 g cm−3). ρw: density of water; d: soil depth. The abbreviated words stand for NO3−-N: nitrate nitrogen; NH4+-N: ammonium nitrogen; TN: total nitrogen; TP: total phosphorous; TK: total potassium; SOC: organic carbon; C:N ratio: soil carbon and nitrogen ratio; pH: soil pH; ECe: electrical conductivity; B.D: soil bulk density; P: soil porosity; SWC: gravimetric soil water content; SWS: soil water storage; ST: soil temperature.
Table
Table 2. Tillage practices and fertilization methods during the study.
Table 2. Tillage practices and fertilization methods during the study.
Tillage TechniquesFertilization TreatmentFertilization Method
CT: Conventional tillageCKNo fertilizer
NThe inorganic N at the rate of 105 kg N ha−1y−1 in the form of urea was applied.
MThe organic N at the rate of 105 kg N ha−1y−1 in the form of farmyard manure was applied.
NMCombined application of inorganic and organic N fertilizers in the form of urea and farmyard manure was applied. Both were equivalent to an annual N application rate of 52.5 kg N ha−1y−1
NT: No-tillageCKNo fertilizer
NThe inorganic N at the rate of 105 kg N ha−1y−1 in the form of urea was applied.
MThe organic N at the rate of 105 kg N ha−1y−1 in the form of farmyard manure was applied.
NMCombined application of inorganic and organic N fertilizers in the form of urea and farmyard manure was applied. Both were equivalent to an annual N application rate of 52.5 kg N ha−1y−1
Table
Table 3. Variation in soil water content under different tillage and fertilization approaches.
Table 3. Variation in soil water content under different tillage and fertilization approaches.
ParameterTreatmentSoil Layer (cm)
0–1010–2020–4040–6060–100
Water content (%)CT7.26 ± 0.06 Ea6.40 ± 0.28 Cb5.24 ± 0.24 Bc4.63 ± 0.14 Cc3.38 ± 0.20 Ad
CTN8.24 ± 0.38 DEa7.43 ± 1.33 BCa6.52 ± 0.20 ABa5.50 ± 1.38 BCab3.35 ± 0.36 Ab
CTM8.94 ± 0.59 DEa7.93 ± 0.64 BCa7.23 ± 1.33 ABa6.57 ± 0.23 ABCa3.39 ± 0.25 Ab
CTNM10.19 ± 0.70 CDa8.86 ± 0.73 BCab7.33 ± 1.34 ABab7.03 ± 0.98 ABb3.26 ± 0.35 Ac
NT12.27 ± 0.33 BCa9.20 ± 0.22 ABCb7.92 ± 0.60 ABbc7.26 ± 0.33 ABc3.25 ± 0.53 Ad
NTN13.17 ± 1.39 ABa9.45 ± 1.73 ABb8.59 ± 1.18 Ab6.41 ± 0.37 ABCbc3.32 ± 0.22 Ac
NTM13.87 ± 0.90 ABa10.10 ± 0.43 ABb8.60 ± 1.00 Abc7.26 ± 0.76 ABc3.35 ± 0.35 Ad
NTNM14.55 ± 0.26 Aa11.81 ± 0.20 Ab9.54 ± 0.52 Ac7.93 ± 0.32 Ad3.29 ± 0.35 Ae
Different capital letters indicate significant differences between different treatments for the same soil layer (p < 0.05; Duncan’s test), and different lower-case letters indicate significant differences between different treatments and different soil depths (p < 0.05; Duncan’s test). CT: conventional tillage, CTN: conventional tillage with inorganic N fertilizer, CTM: conventional tillage with organic N fertilizer, CTNM: conventional tillage with combined application of organic and inorganic N fertilizer, NT: no-tillage, NTN: no-tillage with inorganic N fertilizer, NTM: no-tillage with organic fertilizer, NTNM: no-tillage with combined application of organic and inorganic N fertilizer.
Table
Table 4. Two-way factor ANOVA of (SOC, TN, TP, NO3−-N, and NH4+-N) under different treatments.
Table 4. Two-way factor ANOVA of (SOC, TN, TP, NO3−-N, and NH4+-N) under different treatments.
FactorItemSOCTNTPNO3−-NNH4+-N
Tillage practicedf11111
F10.13218.0190.05310.65314.734
Sig<0.01<0.010.819<0.01<0.01
Fertilization methoddf33333
F2.0443.1840.51818.5096.564
Sig0.112<0.010.671<0.01<0.01
Tillage practice + fertilization methoddf33333
F0.1210.1560.8984.9971.516
Sig0.947<0.010.4450.0150.103
Sig < 0.01 indicates highly significant effect. SOC: soil organic carbon, TN: total nitrogen, TP: total phosphorous, NO3−-N: nitrate nitrogen and NH4+-N: ammonium nitrogen.
Table
Table 5. Soil stoichiometric ratios under different treatments at 0–10 cm soil depth.
Table 5. Soil stoichiometric ratios under different treatments at 0–10 cm soil depth.
TreatmentC/NC/PN/P
CT8.93 ± 0.19 A14.36 ± 1.36 AB1.62 ± 0.19 C
CTN8.50 ± 0.41 A14.59 ± 0.29 AB1.72 ± 0.05 C
CTM7.69 ± 0.26 B13.26 ± 0.25 B1.73 ± 0.05 C
CTNM7.02 ± 0.19 BC15.04 ± 0.83 AB2.14 ± 0.08 B
NT6.95 ± 0.21 BC14.36 ± 0.64 AB2.07 ± 0.13 B
NTN6.81 ± 0.19 C15.73 ± 0.60 AB2.31 ± 0.02 AB
NTM6.65 ± 0.30 C15.25 ± 0.61 AB2.30 ± 0.11 AB
NTNM6.28 ± 0.12 C15.90 ± 0.93 A2.53 ± 0.12 A
Different capital letters indicate significant differences between different treatments (p < 0.05; Duncan’s test). CT: conventional tillage, CTN: conventional tillage with inorganic N fertilizer, CTM: conventional tillage with organic N fertilizer, CTNM: conventional tillage with combined application of organic and inorganic N fertilizer, NT: no-tillage, NTN: no-tillage with inorganic N fertilizer, NTM: no-tillage with organic N fertilizer, NTNM: no-tillage with combined application of organic and inorganic N fertilizer.
Table
Table 6. Effects of tillage and nitrogen fertilization on yield of spring wheat.
Table 6. Effects of tillage and nitrogen fertilization on yield of spring wheat.
TreatmentPlant Height (cm)Grain Number Per SpikeThousand Grain Weight (g)Biological Yield (kg/ha)Grain Yield
(kg/ha)
CT75.97 ± 0.23 D29.33 ± 2.03 D40.72 ± 1.27 D3123.51 ± 142.93 F1429.05 ± 38.02 E
CTN87.27 ± 1.56 C33.33 ± 1.76 CD44.22 ± 1.35 CD3496.80 ± 17.96 EF1511.88 ± 35.40 DE
CTM91.53 ± 2.27 C33.67 ± 2.73 CD45.74 ± 1.07 BCD3934.71 ± 194.58 E1540.88 ± 47.10 CDE
CTNM105.3 ± 3.19 B40.33 ± 3.48 BC47.37 ± 2.98 ABC4936.08 ± 184.40 D1622.51 ± 11.58 BCD
NT102.1 ± 5.95 B43.67 ± 1.20 B48.69 ± 2.81 ABC5264.73 ± 410.50 CD1649.12 ± 34.07 BC
NTN104.8 ± 3.20 B45 ± 2.08 AB49.03 ± 0.45 ABC5779.29 ± 125.64 BC1703.19 ± 37.17 B
NTM106 ± 3.57 B47.67 ± 2.73 AB50.46 ± 1.36 AB6296.63 ± 403.60 B1744.51 ± 72.10 AB
NTNM116.2 ± 2.76 A51.33 ± 1.76 A52.79 ± 0.84 A7163.95 ± 112.73 A1843.88 ± 34.40 A
Different capital letters indicate significant differences between the different treatments (p < 0.05; Duncan’s test). CT: conventional tillage, CTN: conventional tillage with inorganic N fertilizer, CTM: conventional tillage with organic N fertilizer, CTNM: conventional tillage with combined application of organic and inorganic N fertilizer, NT: no-tillage, NTN: no-tillage with inorganic N fertilizer, NTM: no-tillage with organic N fertilizer, NTNM: no-tillage with combined application of organic and inorganic N fertilizer.
Table
Table 7. Two-way factor ANOVA of spring wheat yield under different treatments.
Table 7. Two-way factor ANOVA of spring wheat yield under different treatments.
FactorItemYield
Tillage measuredf1
F50.788
Sig<0.01
Fertilization methoddf3
F7.581
Sig<0.01
Tillage measure and Fertilization methoddf3
F0.06
Sig<0.01
Sig < 0.01 indicates that the effect is extremely significant.
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Yuan, J.; Sadiq, M.; Rahim, N.; Li, G.; Yan, L.; Wu, J.; Xu, G. Tillage Strategy and Nitrogen Fertilization Methods Influences on Selected Soil Quality Indicators and Spring Wheat Yield under Semi-Arid Environmental Conditions of the Loess Plateau, China. Appl. Sci. 2022, 12, 1101. https://doi.org/10.3390/app12031101

AMA Style

Yuan J, Sadiq M, Rahim N, Li G, Yan L, Wu J, Xu G. Tillage Strategy and Nitrogen Fertilization Methods Influences on Selected Soil Quality Indicators and Spring Wheat Yield under Semi-Arid Environmental Conditions of the Loess Plateau, China. Applied Sciences. 2022; 12(3):1101. https://doi.org/10.3390/app12031101

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Yuan, Jianyu, Mahran Sadiq, Nasir Rahim, Guang Li, Lijuan Yan, Jiangqi Wu, and Guorong Xu. 2022. "Tillage Strategy and Nitrogen Fertilization Methods Influences on Selected Soil Quality Indicators and Spring Wheat Yield under Semi-Arid Environmental Conditions of the Loess Plateau, China" Applied Sciences 12, no. 3: 1101. https://doi.org/10.3390/app12031101

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