Effects of long-term organic fertilization on soil microbiologic characteristics, yield and sustainable production of winter wheat

LI Chun-xi, MA Shou-chen, SHAO Yun, MA Shou-tian, ZHANG Ling-ling

1 College of Life Science, Henan Normal University, Xinxiang 453007, P.R.China

2 Field Scienti fic Observation and Research Base of Land Use, Ministry of Land and Resources/Henan Polytechnic University,Jiaozuo 454000, P.R.China

RESEARCH ARTICLE

Effects of long-term organic fertilization on soil microbiologic characteristics, yield and sustainable production of winter wheat

LI Chun-xi1, MA Shou-chen2, SHAO Yun1, MA Shou-tian1, ZHANG Ling-ling1

1 College of Life Science, Henan Normal University, Xinxiang 453007, P.R.China

2 Field Scienti fic Observation and Research Base of Land Use, Ministry of Land and Resources/Henan Polytechnic University,Jiaozuo 454000, P.R.China

We investigated the soil microbiologic characteristics, and the yield and sustainable production of winter wheat, by conducting a long-term fertilization experiment. A single application of N, P and K (NPK) fertilizer was taken as the control (CK) and three organic fertilization treatments were used: NPK fertilizer+pig manure (T1), NPK fertilizer+straw return (T2), NPK fertilizer+pig manure+straw return (T3). The results showed that all three organic fertilization treatments (T1, T2 and T3)signi ficantly increased both soil total N (STN) and soil organic carbon (SOC) from 2008 onwards. In 2016, the SOC content and soil C/N ratios for T1, T2 and T3 were signi ficantly higher than those for CK. The three organic fertilization treatments increased soil microbial activity. In 2016, the activity of urease (sucrase) and the soil respiration rate (SRS) for T1, T2 and T3 were signi ficantly higher than those under CK. The organic fertilization treatments also increased the content of soil microbial biomass carbon (SMBC) and microbial biomass nitrogen (SMBN), the SMBC/SMBN ratio and the microbial quotient (qMB). The yield for T1, T2 and T3 was signi ficantly higher than that of CK, respectively. Over the nine years of the investigation, the average yield increased by 9.9, 13.2 and 17.4% for T1, T2 and T3, respectively, compared to the initial yield for each treatment, whereas the average yield of CK over the same period was reduced by 6.5%. T1, T2, and T3 lowered the coef ficient of variation (CV) of wheat yield and increased the sustainable yield index (SYI). Wheat grain yield was signi ficantly positively correlated with each of the soil microbial properties (P<0.01). These results showed that the long-term application of combined organic and chemical fertilizers can stabilize crop yield and make it more sustainable by improving the properties of the soil.

winter wheat, long-term organic fertilization, soil microbial features, yield stability, yield sustainability

1. Introduction

The Huang-Huai-Hai Plain is the largest wheat-producing region in China. The area of wheat planted in the Huang-Huai-Hai Plain is 68% of China’s total wheat acreage. To obtain a high wheat yield, farmers in this area commonly use large amounts of chemical fertilizers. This is not only a waste of resources but also a cause of environmental pollution. Although a single application of chemical fertilizers can increase crop yield and raise the amount of available nutrients in the soil, the application of large amounts of chemical fertilizers over time can lead to a degradation of soil quality and nutrient imbalance (Chen et al. 2014). Thus the long-term application of chemical fertilizers seriously reduces the sustainable production capacity of farmland.Sustainable crop production has become an extremely important and widely researched topic, and receives worldwide attention (Li et al. 2010). Optimal fertilization based on scienti fic understanding can contribute to improved soil quality and sustainable soil use (Yadav et al. 2000). Partially replacing chemical fertilizers with organic manures can not only supply adequate amounts of various trace elements for crops, but it can also regulate soil water, nutrient and air content, as well as soil temperature and microbial activities (Bolan and Adriano 2003). These bene fits are major advantages of the use of organic manure rather than chemical fertilizers, and they are therefore of great signi ficance in promoting sustainable agricultural production(Bolan and Adriano 2003).

Many researchers have investigated the effects of longterm fertilization on the physicochemical properties and microbial characteristics of soil (Li et al. 2004; Diepeningen et al. 2006; Chu et al. 2007; Ma et al. 2010). Soil microorganisms are the driving force for the transformation and cycling of soil organic matter and nutrients, and also provide a reserve of available nutrients for crops (Xu et al.2016). Soil microbes are directly affected by soil quality and are extremely sensitive to changes in it (Zhou and Ding 2007). They respond quickly to the application of fertilizers, altered cropping systems, and land utilization changes (Livia et al. 2005; Wang et al. 2009; Yusuf et al.2009). Soil characteristics such as soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN),the microbial quotient (qMB), soil enzyme activity, and soil respiration have been used as indexes to assess changes in soil fertility and soil quality (Harris et al. 2003;Schloter et al. 2003). Many studies have indicated that different fertilization practices have important effects on SMBC and SMBN (Chu et al. 2007; Jangid et al. 2008;Ma et al. 2012). The application of organic fertilizers can signi ficantly increase SMBC and SMBN as well as soil enzyme activity (Timo et al. 2004; Li et al. 2008; Ma et al.2010). The conclusions of the studies cited are mostly derived from comparisons between organic fertilization treatments and no fertilizer application at all. However, in the practice of crop production, it is very rare that farmers do not apply fertilizer. Thus a study which compares the long-term effects of organic fertilization treatments on soil microbiologic characteristics and soil fertility with the longterm effects of a single application of chemical fertilizer can provide a scienti fic basis for the determination of a stable and sustainable soil environment in which a high crop yield can be obtained.

The sustainable yield index (SYI) of a crop indicates whether the soil ecosystem can sustainably grow a crop.The higher the SYI value, the better able is the soil to sustain a particular crop yield over time (Majumder et al. 2007). In recent years the effects of different fertilization treatments on crop yield and the conditioning of soil for sustainable crop production have been widely studied. However, research results are not consistent because of the complexity and diversity of the activities and conditions which affect crop yield and which in fluence sustainable crop production, such as farming practices, soil constitution, and climate (Li et al.2006, 2012; Manna et al. 2007; Ma et al. 2011). Long-term experiments in one particular location can identify possible ways of reducing the effects of such disturbances, but it is dif ficult to observe a single crop variety continuously over the long term. Yield fluctuations are not only due to environmental and climatic conditions, but also to the genetic composition of the crop variety (Chaudhury et al.2005). In long-term experiments, differences or changes in crop variety make it dif ficult to compare yields, and so make it dif ficult for the researcher to form a sound scienti fic judgment concerning the soil’s suitability for sustainable production. Additionally, most long-term fixed-location experiments unfortunately involve different crop varieties.There are few long-term continuous observations of a single crop variety and few robust results.

The southern part of Huang-Huai-Hai Plain, in Henan Province, is an important area of winter wheat production in China. Maintaining the soil’s ability to sustain a stable supply of nutrients can provide the foundation for a high and steady wheat yield. We conducted a long-term field experiment, beginning in 2008, in Huojia County of Henan Province, to study the effects of different organic fertilization treatments on soil fertility and soil microbiologic characteristics. The sustainable production capacity of the soil was analyzed based on long-term observation of the yield of a single wheat variety in order to provide a scienti fic basis for the preparation of fertile soil, and so to ensure sustainable production.

2. Materials and methods

2.1. Experimental site description

Field experiments were conducted at the soil and fertilizer experimental station of Henan Normal University in the town of Zhaojing, in Huojia County, Henan Province (35°11′N,113°41′E). Over the course of the study, the mean annual temperature was 14°C, the mean annual precipitation was 656.3 mm, and the mean annual pan evaporation was 1 748.4 mm. The crop planting was a winter wheat-summer maize rotation, planted in clay loam soil. Immediately prior to the experiment, nutrient content within the tillage layer(0–20 cm deep) of the soil was measured. The values observed were total N 1.28 g kg-1, total P 0.9 g kg-1, and organic matter 18.12 g kg-1.

2.2. Experimental design

The experiment started in October 2007 and continued for nine years until 2016. The experimental wheat (Triticum aestivum L., cultivar Bainong AK58), which has been recommended for widespread use, had been grown on the experimental site since 2003. A single application of N,P and K (NPK) fertilizer was taken as a control treatment(CK) and three different treatments of application of NPK fertilizer combined with organic manure were used every year, as follows:

CK, NPK fertilizer control; T1, NPK fertilizer+pig manure(7 500 kg ha-1); T2, NPK fertilizer+straw return (all corn stalks from the preceding crop were returned to the farmland after chopping); T3, NPK fertilizer+pig manure (7 500 kg ha-1)+straw return (all corn stalks from the preceding crop were returned to the farmland after chopping).

For each fertilizer treatment, the same quantity of NPK chemical fertilizer was used: N (135 kg ha-1), P2O5(120 kg ha-1), and K2O (180 kg ha-1). The contents of total N (TN)and organic carbon (OC) in the pig manure were 1.65–2.49 and 12.5–15.6%, respectively. The contents of TN and OC in the corn stalks were 0.90–0.95 and 42.3–45.6%,respectively. The area of each treatment and control plot was 35 m2(5 m×7 m). Each treatment was replicated three times. The plant density was 2 250 000 plants ha-1and the soil was deeply tilled (to a depth of 30 cm)before sowing.

2.3. Measuring items and methods

Each year at the flowering stage of the wheat, soil samples were collected from the tilled layer (0–30 cm) of each plot using a 5-point random sampling method. The soil samples were sealed in bags, brought to the laboratory and stored in a refrigerator at a temperature of 4°C prior to measurement.

The following data were obtained for each soil sample: soil total nitrogen (STN), measured using the Kjeldahl method;soil organic carbon (SOC), measured using the potassium dichromate method; SMBC and SMBN, measured using the fumigation extraction method (Vance et al. 1987; Jenkinson 1988); urease activity, measured by colorimetry; and sucrase activity, determined by 3,5-dinitrosalicylic acid colorimetry(Yao and Huang 2006).

Soil respiration measurementA baremicro-plot (1.0 m×1.0 m) was set up in each experimental crop plot. It was de fined by embedding impenetrable PVC boards in the soil to a depth of 100 cm to prevent the lateral entry of roots of adjacent plants into the micro-plot. The soil respiration rate of this micro-plot was measured at the wheat flowering stage using an EGM-4 portable environmental gas monitor manufactured by PP Systems International Inc., USA. The weeds and litter on the soil surface were cleared before measurement.

The sustainable yield index (SYI) was calculated as:

SYI=(y-σn-1)/Ymax

Where, y is the average yield, σn-1is the standard deviation, and Ymaxis the maximum yield (Majumder et al.2007).

The stability of crop yieldThe coef ficient of variation(CV) was used to indicate the stability of the yield and calculated as:

CV (%)=(σ/μ)×100

Where, σ is the standard deviation (kg ha–1), and μ is the average yield (kg ha–1) (Gao et al. 2015).

2.4. Statistical analysis

Statistical analyses were performed using Excel 2003 and SPSS 13.0. Statistically signi ficant differences were identi fied using analysis of variance (ANOVA) and least signi ficant difference (LSD) tests at the 0.05 and 0.01 levels, respectively.

3. Results

3.1. Changes of TN, SOC, and C/N ratios in different fertilization treatments

Different fertilization treatments had signi ficant in fluences on STN, SOC, and C/N ratios (Fig. 1). Compared with CK, all three organic fertilization treatments (T1, T2, and T3) signi ficantly increased both SOC and STN from 2008 onwards, in particular, SOC increased annually. In 2016,SOC in CK had not changed signi ficantly when compared with 2008, but SOC increased signi ficantly from its 2008 values under treatments T1, T2, and T3 by 25.34, 31.82 and 54.99%, respectively. In 2016, the SOC content under the treatments T1, T2, and T3 showed an increase over that of CK by 22.15, 30.28 and 51.91%, respectively. The soil C/N ratios under the treatments T1, T2, and T3 were lower than those in CK in the early stage (2008–2009),but signi ficantly higher than those in CK after 2012. By 2016, the soil C/N ratios under treatments T1, T2, and T3 had increased over that in CK by 8.07, 9.87 and 16.64%,respectively. These results suggest that the long-term application of organic materials can improve soil fertility by increasing STN and SOC.

3.2. Changes of soil enzyme activity and soil respiration rate (SRR) in different fertilization treatments

Fig. 1 Change in soil organic carbon (SOC), soil total N (STN)and C/N under different long-term fertilization practices. CK, N,P and K (NPK) fertilizer control; T1, NPK fertilizer+pig manure;T2, NPK fertilizer+straw return; T3, NPK fertilizer+pig manure+straw return. Vertical bars represent standard error.

Compared with the CK, the three organic fertilization treatments (T1, T2, and T3) led to signi ficant increases in both urease and sucrase activities. In 2014–2016, the urease activity and sucrose activity under T1, T2 and T3 were signi ficantly greater than those in CK (Fig. 2). In 2016, under T1, T2, and T3, the urease activity increased by 31.0, 33.3, and 57.1%, and the sucrose activity increased by 21.9, 51.2, and 53.6%, respectively, compared to the activity in CK.

Fig. 2 Effects of different long-term fertilization treatments on soil enzyme activity and soil respiration rate (SRR). CK, N, P and K (NPK) fertilizer control; T1, NPK fertilizer+pig manure; T2,NPK fertilizer+straw return; T3, NPK fertilizer+pig manure+straw return. Values are the means of the three replicates of each treatment. Vertical bars represent standard error and bars with different letters within the same test year indicate that there are signi ficant differences between treatments at P<0.05.

Soil respiration is an indicator of soil microbial activity.Under treatments T1, T2, and T3, the SRR increased signi ficantly (Fig. 2), and was far greater than that in CK in 2014–2016. By 2016, SRR under treatments T1, T2 and T3 had increased by 18.5, 35.2, and 37.0%, respectively.

3.3. Changes in SMBC, SMBN and qMB in different fertilization treatments

The three organic fertilization treatments had signi ficant effects on SMBC, SMBN, the SMBC/SMBN ratio and qMB(SMBC/SOC). Each treatment showed the same change trend for SMBC and SMBN content, namely CK

3.4. Changes in grain yield and yield sustainability with different fertilization treatments

Although the winter wheat yield fluctuated greatly from 2008 to 2016, the wheat yield of each of T1, T2, and T3 in each year was signi ficantly higher than that of CK (Fig. 3).Over the nine years, the average yield was 9.9, 13.2,and 17.4% greater under T1, T2, and T3, respectively,compared to the respective initial yields, whereas the average yield of CK over the same period decreased by 6.5%. The yield of T3 increased the most. Thus, while the yield under the control CK treatment decreased overall, the yields from each of the three organic fertilizer treatments increased overall. This indicates that long-term organic fertilization treatments can signi ficantly improve wheat yield. The stability of the wheat yield is indicated by the CV, which is used to measure the variability in the average yield of the same crop cultivar over different years. The lower the CV, the more stable is the yield. As shown in Table 2, the CV values under T1, T2, and T3 were all lower than the CV under CK. This indicates that T1, T2, and T3 all improved the stability of wheat yield. In particular, underT3, the yield was signi ficantly more stable than that for CK,T1 and T2. SYI is a reliable parameter that indicates the sustainability of farmland production. The higher the SYI value, the more sustainable is the crop production. As shown in Table 2, SYI values under T1, T2, and T3 were greater than those under CK. This indicates that long-term combined organic and inorganic fertilizer treatments can sustainably increase crop yield.

Table 1 Effect of different long-term fertilization practices on SMBC, SMBN, SMBC/SMBN and qMB in 20161)

Fig. 3 Grain yield changes of winter wheat under different long-term fertilization practices. CK, N, P and K (NPK) fertilizer control;T1, NPK fertilizer+pig manure; T2, NPK fertilizer+straw return; T3, NPK fertilizer+pig manure+straw return. Vertical bars represent standard error.

3.5. Correlative coef ficients between soil microbial properties, soil chemical properties and grain yield

The soil microbial properties were closely related to the soil chemical properties (Table 3). Soil microbial properties,except qMB and SRR, showed signi ficant positive correlations with SOC, STN and C/N at P<0.01. qMB was signi ficantly positively correlated with STN at P<0.05.However, qMB was not signi ficantly related to SOC or C/N ratio. With the exception of the correlation between SRR and C/N ratio at P<0.05, SRR showed signi ficant positive correlations with SOC and STN at P<0.01. Grain yields of the wheat were affected by all soil microbial properties.Wheat grain yield was signi ficantly positively correlated with each of the soil microbial properties at P<0.01. The correlation coef ficient, which were the greatest between grain yield and SMBC, were then ordered for SMBC/SMBN>SMBN>SRR.

4. Discussion

4.1. Effects of different fertilization treatments on STN, SOC and the C/N ratio

SOC and STN are key contributors to soil productivity,both directly, through control of the availability of soil N,and indirectly through regulation of the physicochemical condition of the soil and thus in fluence over its biological properties (Huang et al. 2009). Over the long term, a single application of chemical fertilizer leads to accelerated decomposition of the organic carbon originally in the soil,which eventually results in relatively little SOC being stored in the soil. The single application also results in a decreased C/N ratio in the soil. Thus, over time, soil quality is degraded,a nutrient imbalance develops, and the ability of the soil to sustain a level of crop yield decreases (Zhang et al. 2006).In contrast, the application of organic manure increases the soil organic matter content, which leads to improved soil quality, and so promotes sustainable production (Zhang et al. 2006). Many long-term experiments have shown that organic manure can increase SOC and TN (e.g., Kundu et al. 2001; Hati et al. 2007; Shao et al. 2014). In addition,straw return is bene ficial because it renews and increases SOC and STN, which increase soil fertility and improve the farmland ecosystem in terms of crop growth (Lao et al.2002; Wei et al. 2012). In this study, SOC and STN clearly increased through the application of organic fertilizer (T1, T2,and T3) when compared to the control CK, a finding which is consistent with those of many other studies (e.g., Fan et al.2005; Mando et al. 2005; Ma et al. 2012). This increase is because inorganic N fertilizer tends to be lost from the soil by leaching, volatilization, or runoff. The application of organic fertilizer increases soil microbiomass (Diepeningen et al.2006); increased biomass indicates an increase in N use by microbiota and an increase in N storage in the soil, which leads to a reduction of N runoff. Thus, it is more effective to apply chemical N fertilizer combined with organic material.

Table 2 Effect of different long-term fertilization practices on yield stability and sustainability of winter wheat

Table 3 Correlative coef ficients between soil microbial properties and soil chemical properties and grain yield1)

4.2. Effects of different fertilizer treatments on soil microbial characteristics

Planned fertilization can improve soil microbial characteristics by increasing SOC and STN (Albiach et al. 2000). Our study showed that soil microbial characteristics except qMB are closely related to SOC, STN, and C/N (Table 3).Among the soil microbial characteristics, SMBC and SMBN represent the storage and source of soil nutrients available for plant growth (Xu et al. 2016). The long-term application of chemical fertilizer combined with organic manure can increase both SMBC and SMBN (Goyal et al. 1999; Li et al. 2015) as well as qMB (Xu et al. 2002). This study also showed that treatments T1, T2, and T3 all increased levels of SMBC, SMBN, and qMB when compared to CK,mainly because the supply of organic matter provided suf ficient C resources for the growth and reproduction of soil microorganisms, which in turn increased the accumulation of SMBC and SMBN (Wang et al. 2011). Under normal circumstances, the SMBC/SMBN ratios for bacteria,actinomycetes, and fungi are approximately 5:1, 6:1, and 10:1, respectively (Paul and Clark 1996). In this study, the SMBC/SMBN ratio for each treatment was approximately 5:1, which indicates that bacteria are the majority biota in soil microorganism communities. Treatments that use organic fertilizers combined with chemical fertilizers promote the growth and reproduction of microorganisms. Thus such treatments increase the microbial biomass and thereby improve the soil microbial community structure, which results in a higher SMBC/SMBN ratio than observed in a chemicalfertilizers-only treatment (Goyal et al. 1999). In this study,the SMBC/SMBN ratios of the T1, T2, and T3 treatments were signi ficantly higher than that of the CK, which shows that the long-term application of chemical fertilizers together with organic manures enriches and diversi fies the soil microbiome.

Soil enzyme activity indicates the intensity of both microbial activity and biochemical reactions in the soil.Studies have shown that the application of organic fertilizer signi ficantly increases soil enzyme activity (Plaza et al.2004; Timo et al. 2004; Li et al. 2008; Wei et al. 2012). This study also showed that all three organic fertilizer treatments signi ficantly increased urease and sucrase activities in the soil. In particular, soil enzyme activities under treatment T3 were signi ficantly greater than that under treatments T1 and T2. Organic manure increases soil enzyme activity in the following manner. First, soil enzymes are produced mainly by soil microorganisms and dead plants and animals, and the supply of organic materials increases C sources for soil microorganisms. This increases the energy available to them, which promotes their metabolism and reproduction, which thereby promotes the increase in soil enzyme activity (Ma et al. 2012). Second, the organic matter improves the physicochemical properties of soil, providing a better environment for the growth of microorganisms and soil fauna. The decomposition of organic matter quickens,which in turn provides more substrate for soil enzymes, and thereby induces an increase in soil enzyme activity (Petra et al. 2003; Timo et al. 2006).

Soil respiration re flects the biological characteristics and the metabolic rate of the soil and its ability to transform and supply nutrients (Singh and Gupta 1997). The application of organic fertilizer increases the amount of organic matter available for soil respiration. Furthermore, it can also signi ficantly increase both the quantity and the activity of soil microorganisms, which will affect both the conversion of SOC and the emission of CO2and thereby increase the intensity of soil respiration (Zang et al. 2015). Thus the three organic fertilizer treatments in our study signi ficantly promoted the emissions of soil CO2and increased soil respiration rates.

4.3. Effects of different fertilization treatments on crop yield

Crop yield comprehensively re flects soil fertility. Previous studies have shown signi ficant positive correlations between wheat yield and SMBC, SMBN, and soil enzyme activity (Zhang et al. 2005). The results of this study also show that yield is closely related to soil microbial characteristics. The application of combinations of organic and chemical fertilizers not only replenishes the nutrients needed by the crop, but also increases the source of C for soil microorganisms and promotes their metabolism and reproduction, which in turn improves the physicochemical and microbial properties of soil and so favors root growth and absorption (Wang et al. 2011; Chen et al. 2014).Consequently, grain yield increased signi ficantly.

Yield stability and sustainability of a crop provide important criteria for assessing the quality of a farmland ecosystem (Chaudhury et al. 2005). Although a single long-term application of chemical fertilizer can supply a large number of the nutrients needed by a crop, the lack of an organic component will result, over time, in the degradation of soil quality and, consequently, large annual fluctuations in crop yield (Hao et al. 2007). The long-term application of organic fertilizers can continuously improve soil fertility and create a healthy soil environment. Because of this, the soil will be able to continually provide the nutrients needed by the crop, and any large fluctuations in crop yield caused by adverse environmental factors will be mitigated (Chen et al.2014). If organic fertilization is maintained over the long term, the farmland will sustainably support crop production.Manna et al. (2007) showed that the long-term application of combined organic and chemical fertilizers could signi ficantly and sustainably increase crop yield. Our study also shows that organic fertilizer treatments can sustainably maintain the stability of crop yield and thereby signi ficantly reduce the inter-annual fluctuations in grain yield.

5. Conclusion

Our study showed that three long-term organic fertilization treatments signi ficantly improved both soil nutrients and soil microbial properties. Based on long-term continuous observations of a single wheat variety, three organic fertilization treatments increased the grain yield and SYI of wheat and lowered the CV of wheat yield. These results show that the long-term application of organic fertilization can stabilize crop yield and make it more sustainable by improving the properties of the soil. In addition, our study data and results came from long-term continuous observations of a single wheat variety, which eliminated the confounding effects of differences in crop variety on yield, which ensures that we can make a robust and wellinformed scienti fic judgment on the suitability of the soil for sustainable crop production.

Acknowledgements

We acknowledge the financial support from the National Key Research and Development Program of China(2017YFD0301106, 2016YFD0300203-3) and the Science and Technology Innovation Team Support Plan of Universities in Hennan Province, China (18IRTSTHN008).

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17 February, 2017 Accepted 11 July, 2017

LI Chun-xi, E-mail: 13703731637@sina.com; Correspondence MA Shou-chen, E-mail: mashouchen@126.com

? 2018 CAAS. Publishing services by Elsevier B.V. All rights reserved.

10.1016/S2095-3119(17)61740-4

Section editor ZHANG Wei-li

Managing editor SUN Lu-juan