Effects of Returning Methods on Wheat Stem Rot and Yield

Xiang LI　 Fenyuan YI　Sanchao CAO　Chao WANG　Yangli ZHANG

Abstract[Objectives] This study was conducted to improve the quality of straw returning to the field， enhance wheat disease resistance and ensure high and stable yield of wheat. [Methods]The effects of four returning modes on wheat stem rot and yield were studied by observation and experiments. [Results] The incidence rate and disease index of stem rot and white head rate of wheat were significantly reduced and the yield was significantly increased by adopting the method of straw returning to the field with the separation of "returning and seeding". The incidence rate and disease index of stem rot and white head rate of wheat were higher than those of the CK and the yield was significantly reduced when adopting the straw returning method of direct sowing. Treatment T1 （after maize was harvested， fertilizers， a nutrient-loaded microbial agent and a soil conditioner were evenly spread on the surface of straw， which was then returned to the field using a straw returning machine twice， and then ploughing， soil preparation and wheat sowing were carried out） showed an incidence rate of wheat crown rot 54.8% lower than that of the CK and a white head rate 87.5% lower than that of the CK， and the yield was 2 305 kg/hm2 higher than that of the CK. [Conclusions]Straw returning can increase soil organic matter content， reduce soil bulk density， enhance soil respiration， and improve wheat disease resistance and yield.

Key wordsStraw returning method; Wheat stem rot; Yield; Organic matter content; Bulk density

Shaanxi is a large agricultural production province， with a sown area of 5 116.2 thousand hectares of crops. According to the yield and grain-straw ratio， Shaanxi produces 17.44 million tons of straw each year， in which wheat， corn， straw and rape straw account for more than 90%[1]. Base materials， fertilizers and feed are the main ways of straw utilization. According to incomplete statistics， in 2020， the amount of straw used as feed in Shaanxi was 1 million tons， accounting for 8.62% of the amount of straw， and the amount of straw used as a fertilizer was 8 million tons， accounting for 68.97% of the amount of straw; and the amount of straw used as a base material for edible fungus cultivation was about 300 000 t， accounting for 2.59% of the amount of straw. From this point of view， fertilizers are the main way of straw utilization， and the amount of straw returned to the field accounts for more than 90% of the straw used as a fertilizer. In recent years， with the expansion of the area with straw returning， while improving soil fertility[2]， retaining water[3]， reducing soil bulk density[4] and alleviating the impact of environmental conditions （temperature， rainfall） on crop growth[5]， straw returning has also brought some problems， such as small wheat seedlings， weak seedlings， dead seedlings and the spread of wheat stem rot[6]， which seriously affect crop yields and bring hidden dangers to food security. In order to study the effect of straw returning to the field on wheat stem rot and yield， under the support of Shaanxi Province Key Industrial Chain Project and Xi'an Key Research and Development Program "Comprehensive Utilization and Demonstration of Straw Resources in Soil Farmland"， various experiments were carried out using four different returning modes at the Sunzhen Experimental Station of Weinan Academy of Agricultural Sciences for 4 consecutive years from 2016. It was found that as long as the straw returning measures were appropriate， straw returning was beneficial to the accumulation of soil organic matter， reduction of soil bulk density， increase of soil respiration rate， reduction of the incidence of wheat stem rot and increase of wheat yield. However， if the straw returning measures are not appropriate， the reduction of yield is inevitable. Therefore， straw returning must be transformed into "scientific， refined and intelligent"， and we must once again understand straw returning and realize the leap from "fast harvest" to "transforming to a fertilizer".

Materials and Methods

Experimental materials

Straw decomposing agent： developed by Agriculture and Forestry Technology Extension Center， Shaanxi University of Science and Technology; soil conditioner： Shaanxi Kerun Biotechnology Co.， Ltd.; urea， superphosphate， potassium sulfate， compound fertilizer： commercially available.

Experimental methods

Base selection： Sunzhen Experimental Station of Weinan Agricultural Science Research Institute in Pucheng County is located in the east of Pucheng County， between 109°20′17″ and 109°54′48″ east longitude， and 34°44′50″-35°10′30″ north latitude. It has a warm continental climate， and is characterized by warm spring， hot summer， cool autumn and cold winter， four distinct seasons， sufficient sunshine and less rainfall. The annual average temperature is 13.7 ℃; the average temperature of the coldest month （January） is -1.4 ℃， and the extreme minimum temperature is -16.7 ℃; and the average temperature of the hottest month （July） is 26.7 ℃， and the extreme maximum temperature is 41.8 ℃. The annual average sunshine hours are 2 228.9 h. The annual average precipitation is 519.9 mm， and the extreme maximum rainfall and the minimum rainfall are 876.1 and 271.8 mm， respectively.

Experimental design： From 2016 to 2019， straw returning experiments were carried out at the Sunzhen Experimental Station of Weinan Academy of Agricultural Sciences for four consecutive years. Five fields of 66.7 m2 each with basically the same soil conditions were selected as experimental fields， and a 0.5 m isolation belt was set between the fields. Each experiment had 3 repetitions. Treatment 1 （T1）： Maize was harvested with a grain harvester after maturation， and after harvesting， urea， superphosphate， potassium sulfate， the homemade straw decomposing agent and the soil conditioner were fully mixed and evenly scattered on the surface of straw at a ratio of 225， 250， 230， 30 and 30 kg/hm2; a straw returning machine was used to return the straw twice to the field， which was then deeply ploughed with a machine at a depth of 25-30 cm; and after soil preparation， seeds of "Weimai No.8" were sown. Treatment 2 （T2）： Maize was harvested with a grain harvester after maturation， and after harvesting， urea， superphosphate， potassium sulfate， the homemade straw decomposing agent and the soil conditioner were fully mixed and evenly scattered on the surface of straw at the ratio of 225， 250， 230， 30 and 30 kg/hm2; a straw returning machine was used to return the straw twice to the field， which was then subjected to rotary tillage with a rotary tiller at a depth of 10-15 cm; and after soil preparation， seeds of "Weimai No.8" were sown. Treatment 3 （T3）： Maize was harvested with a grain harvester after maturation， and after harvesting， urea， superphosphate and potassium sulfate were fully mixed and evenly scattered on the surface of straw at a ratio of 225， 250 and 230 kg/hm2; a straw returning machine was used to return the straw twice to the field， which was then turned over once with a cultivator; and after soil preparation， seeds of "Weimai No.8" were sown. Treatment 4 （T4）： Maize was harvested with a grain harvester after maturation， and after harvesting， seeds of "Weimai No.8" were sown with a seeder while simultaneously applying urea， superphosphate and potassium sulfate at a ratio of 225， 250 and 230 kg/hm2. Treatment 5 （control check）： After maize was mature， the stalks were removed， and seeds of "Weimai No.8" were sown with a seeder while applying chemical fertilizers.

Testing methods

Investigation on the incidence of wheat stem rot： During the wintering stage， re-greening stage， jointing stage， heading stage and maturation stage of wheat， each experimental field was investigated by the 5-point sampling method， in which 200 plants were investigated at each point. The incidence rate， incidence index and white head rate were recorded， and the average values were taken.

The disease degree of wheat stem rot was divided into 0-5 grades. The grading standards were as follows： grade 0： no obvious symptoms， grade 1： the brown withered part of the first leaf sheath is less than 10% of the sheath length， grade 2： the brown withered part of the first leaf sheath accounts for 11%-25% of the sheath length， grade 3： the brown withered part of the first leaf sheath accounts for 26%-50% of the sheath length， grade 4： the second leaf sheath is obvious brown and withers， and grade 5： the third leaf sheath is obvious brown and withers or whole plants wither or die[7]， The incidence rate， disease index and white head rate were calculated according to equations 1， 2 and 3.

Disease index=100%×（Number of diseased leaves of each grade×Representative value of each grade）/（Total number of leaves under investigation×Representative value of the highest grade）（equation 1）

Incidence rate=100%×Number of infected plants under investigation/Total number of plants under investigation（equation 2）

White head rate=100%×Number of white ears/Total number of plants under investigation（equation 3）

Yield measurement of wheat： At the maturation stage， five areas of 2 m2 each were selected from each experimental field according to the "S" sampling method for yield measurement， and the actual yield was calculated.

Determination of soil respiration rate： The soil respiration rate was measured by a GXH-3010E1 portable infrared analyzer in the middle of each experimental plot in different growth periods （wintering stage， re-greening stage， jointing stage， flowering stage， maturation stage）. The determination time was from 9：00 am to 11：00 am， in 3 repetitions， of which the average value was taken.

Determination of soil organic matter content and bulk density： According to the "S" sampling method， the 0-10 cm of soil was taken from each experimental plot. The soil organic matter content was measured according to GB9834-88， and the soil bulk density was measured according to NY/T1121.4-2006.

Results and Analysis

Effects of returning methods on wheat stem rot

Wheat stem rot is a worldwide soil-borne disease[8]. In recent years， the disease has occurred widely in the wheat areas of Anhui， Shandong， Henan， Hebei and Shaanxi， and has been increasing year by year， seriously threatening the safe production of wheat. Wheat stem rot is caused by one or more pathogens alone or in combination， and the dominant pathogens are different in different wheat areas[9]. Many studies have shown that the isolation frequency of Fusarium pseudograminearum in China's wheat areas is on the rise. P-hydroxybenzoic acid， phthalic acid， 4-hydroxy-3-methoxybenzoic acid， 3，5-dimethoxy-4-hydroxybenzoic acid and benzoic acid produced in the process of straw decomposition have a certain influence on wheat stem rot[10]， so it is believed that returning straw to the field provides conditions for the survival and reproduction of pathogens， which aggravates the occurrence of wheat stem rot. In order to study the effects of straw returning on the occurrence of wheat stem rot， our project team investigated the effects of different returning methods on wheat stem rot from 2016. The experimental results are shown in Table 1.

It can be seen from Table 1 that regardless of which treatment was concerned， the disease index and incidence rate of wheat stem rot showed a trend of continuously increasing from the re-greening stage to the maturation stage， indicating that wheat stem rot is a universal disease in wheat-producing areas in Shaanxi. The incidence rate， disease index and white head rate of wheat stem rot in treatment T4 were higher than those in other treatments. The reason was that the straw treated with T4 was basically attached to the soil surface， while F. pseudograminearum， which causes wheat stem rot， is an aerobic bacterium[11]， and the straw and fertilizers during wheat sowing provided abundant carbon and nitrogen sources for the growth and reproduction of F. pseudograminearum， which germinated under certain temperature and moisture conditions， causing the occurrence of wheat stem rot. The incidence rate and disease index of wheat stem rot and white head rate in treatment T1 were the lowest among all treatments. The reason was that after maize was harvested， the straw was smashed to 3-5 cm with a field-returning machine and turned underground to 25-30 cm during deep ploughing together with chemical fertilizers， the nutrient-loaded microbial agent and the soil conditioner. Then， microorganisms used their own nutrients to germinate and colonize the surface of straw with a carbon-nitrogen ratio of 25 to 35∶1 and degraded the straw， under suitable temperature and water conditions[12]. On the one hand， due to the aerobic properties of F. pseudograminearum and the competition with exogenous （indigenous） microorganisms， its growth and reproduction was inhibited. On the other hand， trace elements in the soil conditioner timely supplemented the shortage of trace elements in continuous cropping. Trace elements are coenzymes of enzymes in plant biochemical reactions， which are of great significance to crop health and disease resistance[13]. Comparing T1 and T2， it could be found that ploughing and rotary tillage when straw was returned to the field had a greater impact on the incidence rate and disease index of wheat stem rot and white head rate. Comparing T1 and T3， it could be found that the addition of the nutrient-loaded microbial agent and the soil conditioner had a certain effect on the prevention and control of wheat stem rot. Deep ploughing， loading of the nutrient-loaded microbial agent and the soil conditioner had certain effects on preventing the occurrence of wheat stem rot. Comparing the control group （CK） in 2017 and 2019， it could be found that the incidence rate， disease index and white head rate of wheat stem rot in 2019 were higher than those in 2017， but except treatment T4， treatments T1， T2， and T3 showed incidence rates and disease indexes of wheat stem rot and white head rates all lower than those in 2017， which might be related to the increase in soil organic matter content due to straw returning to the field in successive years.

Straw returning to the field will inevitably produce hydroxybenzoic acid， phthalic acid， 4-hydroxy-3-methoxybenzoic acid， 3，5-dimethoxy-4-hydroxybenzoic acid， benzoic acid and other substances. Comparing deep ploughing and rotary tillage with direct seeding， the concentrations of these substances were very different under the three modes， and the effects on F. pseudograminearum that cause wheat stem rot were different[14].

Treatments T， Tand T are actually a "returning and seeding" separation mode， which focuses on the trend of changing from "fast harvest" to "transforming to a fertilizer". It is a fine and scientific straw returning mode. T4 remains in the traditional straw returning mode. It also showed that straw returning to the field is not the factor that causes wheat stem rot. Of course， it is difficult to solve the occurrence of wheat stem rot simply by returning straw to the field， but straw returning to the field plus other management measures can definitely control the occurrence of wheat stem rot.

Effects of returning methods on soil respiration

Soil respiration is the process of releasing carbon dioxide from soil to the atmosphere. It mainly includes biological and non-biological processes such as soil microbial respiration， root respiration， soil animal respiration and chemical oxidation of carbon-containing substances. It is an important link in the carbon cycle of terrestrial ecosystems. The CO emitted into the atmosphere by soil through respiration is as high as 60-180 PgC/a， accounting for about 1/10 of atmospheric CO. Soil respiration has an extremely important impact on the global climate and carbon cycle， and is also an important indicator of fertile soil[15]. In 2018， our project team tested soil respiration at different growth stages of wheat. The results are shown in Table 2.

It can be seen from Table 2 that soil respiration showed a trend of "first increasing and then decreasing" regardless of which treatment was concerned， which might be related to the increase in the number of microorganisms in the soil caused by climate change， the release of more CO from the decomposition of straw and the growth of roots. The respiration of the soil treated with straw returning to the field was significantly higher than that of the CK （no straw was returned to the field）， which was because that the soil temperature， moisture content， microbial count and straw decomposition were higher than those of the CK regardless of the returning method[2-3]. The reason why soil respiration in treatments T and T3 was greater than that in T was that deep ploughing in the same growth period was more conducive to microbial life activities and straw decomposition caused by microbial life activities than rotary tillage， and the CO exhaled from the soil was synthesized into sugar and energy for plant growth and development under the action of various enzymes， which enhanced the body's resistance to stress， promoted root growth and improved root respiration intensity. The reason why the soil respiration of T was greater than that of T was that the addition of the nutrient-loaded microbial agent when the straw was returned to the field increased the number of microorganisms in the soil. The addition of the soil conditioners promoted enzymatic reactions and provided conditions for root growth. Soil respiration was the strongest in treatment T[16].

Deep ploughing before sowing can break the ploughing layer of the soil， which is of great significance for water storage and moisture conservation， alleviation of climate impact and creation of a microbial environment.

Effects of returning methods on soil organic matter and bulk density

Soil organic matter content refers to the amount of various animal and plant residues and microorganisms contained in a unit volume of soil and the amount of organic matter decomposed and synthesized. It is an important indicator of soil fertility. From 2016， our project team sampled samples in each experimental plot for four consecutive years before the summer harvest every year. The experimental results are shown in Table 3.

It can be seen from Table 3 that the soil organic matter content in treatment T1 increased year by year with the time of straw returning to the field， with an average annual increase of 0.91 g/kg and an average annual growth rate of 8.79%. The content of organic matter in the soil of the CK （control group） remained basically unchanged， that is， fertilizers， animal and plant residues were basically released into the atmosphere in the form of CO. In treatment T1， with the time of straw returning to the field， the soil bulk density decreased year by year， with an average annual decrease of 0.067 g/cm3 and an annual average decrease rate of 5.2%.

Effects of returning methods on wheat yield

From 2017 to 2019， the effects of straw returning methods on wheat yield were studied for three consecutive years， and the results are shown in Table 4.

It can be seen from Table 4 that the wheat yield of the CK and treatment T decreased year by year， and treatment T performed more prominently. The reason was that direct sowing of wheat led to the return of straw to the field far greater than the absorption of straw by the soil and the soil quality got worse and worse. The incidence rate of wheat stem rot in treatment T4 was 5.6% higher than the control in the same period on average， and the treatment index of wheat stem rot in treatment T4 was 10.5% higher than that in the control; and the white head rate in treatment T was 6% higher than that in the control. However， for treatments T， T and T， the yield of wheat increased with the years of straw returning to the field， especially in T. On the one hand， soil organic matter content increased year by year after straw returning， with an average annual increase of 8.79%. Soil bulk density decreased year by year， with an average annual decrease of 5.2%. Soil respiration increased by 310 mg/（m2·h） on average. On the other hand， the incidence of wheat stem rot was reduced by 8.45% on average. It shows that as long as the management is strengthened， straw returning to the field is beneficial to the improvement of wheat yield.

Discussion

Wheat stem rot is a global disease and one of the important wheat diseases in China. It occurs in all wheat growing regions. Straw returning methods have influences on the incidence rate， disease index and white head rate of wheat stem rot， and the trend aggravates with the change of wheat growth stage. The incidence rate and disease index of wheat stem rot and white head rate with the "returning and seeding" separation mode （T， T， T） were significantly lower than those of the CK （control）， and the yield was significantly higher than that of the CK treatment （control）， indicating that wheat stem rot was an important factor causing wheat yield reduction. Taking T1 as an example， in 2017， the disease indexes of wheat stem rot at the overwintering， re-greening， heading and maturation stages of wheat were 79.3%， 68.3%， 68.6% and 57.6% lower than that of the CK in the same stage; the incidence rates were 75.3%， 56.4%， 43.8% and 43.6% lower， respectively; and the white head of wheat rate was 87.5% lower. Soil respiration in different stages of treatment T was 94.3%， 48.5%， 48.5% and 68.0% higher than that of the CK in the same stage. It shows that under the condition that other conditions remain unchanged， stronger soil respiration leads to more microorganisms in the soil， stronger biochemical effect， more developed root system， stronger ability to resist diseases， and the CO exhaled from the soil is converted into the nutrition （glucose） of crops under the action of enzymes， which promotes the growth of crops， enhances the disease resistance of wheat and improves the yield of wheat. In contrast， for direct sowing （returning and planting in one）， that is， treatment T， although the soil respiration at the wintering， re-greening， heading and maturation stages of wheat was 50%， 25%， 47.9% and 43.6% higher than that of CK， the yield was 270 kg/hm lower than the CK treatment. The reason was that F. pseudograminearum and other pathogens attached to the surface of straw germinated under appropriate temperature and moisture conditions， causing wheat stem rot.

Under the condition that the incidence rate of wheat stem rot in 2019 was larger than that in 2017 （comparing the data of the CK in 2017 and 2019）， treatments T， T and T under the "returning and seeding" separation mode showed the incidence rates and disease indexes of wheat stem rot all lower than the CK. The reason was that the soil organic matter content in 2019 was 1.77 g/kg higher than that in 2017， and the soil bulk density was 0.11 g/cm3 lower than that in 2017， indicating soil fertility and air permeability had certain resistance to wheat stem rot.

Conclusions

Wheat stem rot is a common disease in Shaanxi wheat areas， which seriously affects the yield and quality of wheat. Straw returning to the field had a certain effect on wheat stem rot. For example， treatments T， T and T under the "returning and seeding" separation mode had an inhibitory effect on the occurrence of wheat stem rot， while in treatment T adopting the direct sowing mode of returning to the field， wheat stem rot had a tendency to spread. Therefore， straw returning should be developed in the direction of "refined"， "scientific" and "intelligent". It is the main task of current scientific research to help farmers improve their awareness of straw returning to the field and realize the transformation from "fast harvest" to "transforming to a fertilizer".

The quality of straw returning by deep ploughing was higher than that of rotary tillage. It is best to use the ploughing mode for returning straw to the field. The nutrient-loaded microbial agent and the soil conditioner used could significantly improve the quality of returning straw to the field， enhance the disease resistance of wheat， and increase wheat yield. Years of straw returning to the field can increase soil organic matter content， reduce soil bulk density， and improve soil respiration， providing conditions for microbial growth， reproduction and biochemical reactions.

References

[1] Shaanxi Provincial Bureau of Statistics. Statistical yearbook of Shaanxi[M]. Beijing： China Statistics Press， 2018-2021.

[2] LI X， KE XH， WANG SX， et al. Effects of wheat straw returning patterns on straw decomposition and soil properties[J]. Guizhou Agricultural Sciences， 2022， 50（1）： 23-29. （in Chinese）.

[3] LI X， KE XH， SUN XJ， et al. Effects of apple branch different returning patterns on soil properties and apple quality in orchard[J]. Jiangsu Agricultural Sciences， 2021， 49（23）： 238-242. （in Chinese）.

[4] CUI M， GUO CJ， MENG FH. Application of returning straw to field to improve the black soil quality in small watershed in black soil region of China[J]. Science of Soil and Water Conservation， 200 6， 4（5）： 56-59.

[5] ZHANG LH， XU C， YU J， et al. Effects of straw returning on soil moisture， temperature and maize yield in semi humid area[J]. Journal of Soil and Water Conservation， 2021， 35（4）： 299-306. （in Chinese）.

[6] GRANT J. POOLE， RICHARD W. SMILEY， CARL WALKER， et al. Effect of climate on the distribution of Fusarium spp. causing crown rot of wheat in the Pacific Northwest of the United States[J]. Phytopathology， 2013， 103（11）： 1130-1140.

[7] POOLE GJ， SMILEY R W， WALKER C， et al. Effect of climate on the distribution of Fusarium spp. causing crown rot of wheat in the pacific North-west of united statas[J]. Phytopathology， 2013， 130（11）： 1130-1140.

[8] LI HL， YUAN HY， FU B， et al. First report of Fusarinm pseudograminearum as pathogea of wheat crown rot in China[J]. Plant Dissease， 2012， 96（7）： 1065.

[9] MENG CC. Identification of pathogenic Fusarium spp. causing wheat crown rot and corn stalk rot under wheat-maize rotation system[D]. Tai'an： Shandong Agricultural University， 2019. （in Chinese）.

[10] MA LL. Effect of corn straw returing on dominant pathogen associated with wheat crown rot in Haihe Plain[D]. Baoding： Hebei Agricultural University， 2019. （in Chinese）.

[11] MUDGE AM， DILL MACKY R， DONG YH， et al. A role for the mycotoxin deoxynivalenol in stem colonisation during crown of disease of wheat caused by Fusarium graminearum and F. pseudograminearum[J]. Physiological and Molecular Plant Pathology， 2006， 69（1）： 73-85.

[12] LI X， WANG YP， KE XH， et al. Study on the best mode for burying fermentation of fruit tree branches[J]. Guangdong Agricultural Sciences， 2021， 48（8）： 83-89. （in Chinese）.

[13] ZHENG MJ， YU HW， CHEN ZL， et al. Soil health status and management strategies of citrus orchards in hilly area of western Zhejiang Province[J].Guangdong Agricultural Sciences， 2022， 63 （2）： 324-329， 362. （in Chinese）.

[14] DYER， ALAN T.， JOHNSTON， et al. Comparison of pathogenicity of the Fusarium crown rot （FCR） complex （F. culmorum， F. pseudograminearum and F. graminearum） on hard red spring and durum wheat[J]. European Journal of Plant Pathology， 2009， 125（3）： 387-395.

[15] LAL R. Soil carbon sequestration impacts on global climate change and food security[J]. Science， 2004， 304（5677）： 35-39.

[16] ZHAO YL， XUE ZW， GUO HB， et al. Effects of tillage and crop residue management on soil respiration and its mechanism[J]. Transactions of the Chinese Society of Agricultural Engineering， 2014， （19）： 155-165. （in Chinese）.

Editor： Yingzhi GUANG Proofreader： Xinxiu ZHU