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Abstract The mixture ratio of the three strains in the decomposition accelerator was 2?? 1?? 2. The experiment on the degradation of straw was carried out in field by using the self??made straw decomposition accelerator. The results showed that the straw decomposition accelerator has an obvious effect of promoting the degradation. The degradation rate was 8.03% at 10 d and 26.98% at 20 d， and reached 40.2% at 30 d.
Key words Decomposition accelerator； Straw degradation； Degradation rate
Jilin Province is a big agricultural province， which has rich crop straw resources. Straw contains rich organic matter， N， P， K and microelements， and is an important source of organic fertilizer in agricultural production[1]. Directly returning straw to soil could reduce its pollution to environment， and return the nutrients absorbed by crops from soil， which is beneficial to the balance of soil nutrients and especially important to the cyclic utilization of potassium element. The direct application of straw to soil could also improve the physical， chemical and biological properties of soil， and is thus an important and effective technique for agricultural sustainable development[2]. However， for direction application of straw to soil， problems including mismatching of agricultural machinery and tools and farmers?? usual practice and knowledge， still exist. Especially， in northern China， all the straw is returned to soil， but could not all be degraded in the right year， and the soil preparation in spring could not be performed well， which leads to the condition that straw on soil surface causes poor seeding quality[2]. Directing at above problems， three strains capable of rapidly degrading straw were screened from rotten straw and soil， and one decomposition accelerator was developed and used for the maize straw degradation experiment in field. This study will provide a scientific basis for decomposition accelerator and returning straw to soil.
Development of Decomposition Accelerator
Experimental design
Three strains were mixed according to different ratios， and six treatments were designed at different volume ratios.
Treatment 1： Trichoderma koningii?? Streptomyces?? Bacillus subtilis=2?? 1?? 2.
Treatment 2： T. koningii?? Streptomyces?? B. subtilis=1?? 1?? 1.
Treatment 3： T. koningii?? Streptomyces?? B. subtilis=2?? 1?? 1.
Treatment 4： T. koningii?? Streptomyces?? B. subtilis=1?? 2?? 1.
Treatment 5： T. koningii?? Streptomyces?? B. subtilis=2?? 2?? 1. Treatment 6： T. koningii?? Streptomyces?? B. subtilis=1?? 1?? 2.
Experimental methods
The living bacteria count was determined by plate counting method.
Calculating method：
nv = xkv1 （v0v2） ??10-8
nv ： volume living bacteria count （108/ml）； ??1： basic liquid volume （ml）； ??2 ： addition amount of bacterial suspension （ml）； ??0 ： sample amount （ml）； x： average number of colonies （colonies）； k： dilution times.
Experimental results
The experimental results showed that the living bacteria count was the highest under the strain ratio of 2?? 1?? 2 （Table 1）. The decomposition accelerator was prepared according to this ratio for field experiment.
Field Experiment of Decomposition Accelerator
Experimental conditions
The experiment was carried out in Dafangshen Village， Chaoyangpo Town， Gongzhuling City， Jilin Province. Maize straw was degraded with the decomposition accelerator. The tested soil was black soil with the basic physical and chemical properties shown in Table 2.
Experimental materials
Crop straw： The straw of maize variety Zhengdan 958 （with a length of 3-5 cm）.
Mesh bag： 40??mesh nylon mesh bag （25 cm??35 cm）.
Experimental methods
The experiment had two treatments. Treatment 1 was the control （CK）， in which the maize straw was returned to the field at a rate of 9 750 kg/hm2 and sprayed with clear water. In treatment 2， the maize straw was returned to the field at a rate of 9 750 kg/hm2 and applied with the decomposition accelerator at a rate of 30 kg/hm2. A certain amount of the decomposition accelerator （2 kg） was mixed with 20 L/hm2， and the mixture was sprayed to the field.
The straw was filled in nylon mesh bags according to 10 g per bag. Ten bags were buried in each plot with a depth of 5-10 cm. Each treatment had 15 replicates. After burying the bags， five bags were taken from each treatment every 10 d， oven??dried and weighed， to determine the degradation effect of the decomposition accelerator to straw.
Data processing
The statistical analysis was performed by t test.
Results and Analysis
The weight loss of straw on the 10th day after burying
The weight loss values of the straw on the 10th day after burying are shown in Table 3.
It could be seen from Table 3 that the average weight loss ratio of the treatment was 8.03%， and the average weight loss ratio of the CK was 2.1%， which was 5.93% lower than the treatment. It indicated that the straw sprayed with the decomposition accelerator was degraded at a speed far higher than the straw sprayed with clean water. Significance analysis was performed on the weight loss of straw on the 10th day after burying， and the results are shown in Table 4.
Results： S=0.0043， t=13.76， when n=4， t0.05=2.78； and t0.01=4.60， indicating that the difference was significant at the very significant level. It indicated that under the action of the decomposition accelerator， the degradation speed could be improved greatly.
The weight loss of straw on the 20th day after burying
The weight loss values of the straw on the 20th day after burying are shown in Table 5.
It could be seen from Table 5 that the average weight loss ratio of the treatment was 26.98%， and the average weight loss ratio of the CK was 18.52%， which was 8.46% lower than the treatment. It indicated that the straw sprayed with the decomposition accelerator was degraded at a speed increasing over time.
Significance analysis was performed on the weight loss of straw on the 20th day after burying， and the results are shown in Table 6.
Results： S=0.016 1， t=5.25， when n=4， t0.05=2.78； and t0.01=4.60， indicating that the difference was significant at the very significant level. It indicated that 20 d after spraying the decomposition accelerator， the degradation speed could still be improved.
The weight loss of straw on the 30th day after burying
The weight loss values of the straw on the 30th day after burying are shown in Table 7.
It could be seen from Table 7 that the average weight loss ratio of the treatment was 40.20%， and the average weight loss ratio of the CK was 25.57%， which was 14.63% lower than the treatment. It indicated that the straw sprayed with the decomposition accelerator was degraded with an effect far better than the straw sprayed with clean water.
Significance analysis was performed on the weight loss of straw on the 20th day after burying， and the results are shown in Table 8.
Results： S=0.01， t=14.62， when n=4， t0.05=2.78； and t0.01=4.60， indicating that the difference was significant at the 0.01 level. It indicated that 30 d after spraying the decomposition accelerator， the decomposition accelerator still had an effect of degrading the straw， and there was a very significant difference between the treatment and the CK.
Conclusions and Discussion
The experimental results showed that for the different strain ratios， the ratio at 2?? 1?? 2 exhibited the highest living bacteria count， indicating that the strains had the strongest activity under this condition， and the degradation extent was the highest. In the field experiment， the degradation effect was observed about 10 d after spraying the decomposition accelerator， and on the 30th day， the degradation rate had reached 40.2%. Spraying the decomposition accelerator could significantly accelerate the degradation of straw with remarkable degradation effect， and the weight loss was significantly different from the CK without the application of the decomposition accelerator. Therefore， in direct??application of straw into soil， spraying decomposition accelerator could accelerate the degradation speed of straw.
References
[1] YANG ZX， ZHOU HP， GUAN CL， et al. Effect of straw decomposing inoculant on maize straw returning[J]. Journal of Shanxi Agricultural Sciences， 2013， 41（4）： 354-357.
[2] NONG CJ， WANG YW， XU Z， et al. Effects of organic matter??decomposition inoculant on maize and rice straw returning[J]. Acta Agriculturae Boreali??occidentalis Sinica， 2016， 25（1）： 34-41.
Key words Decomposition accelerator； Straw degradation； Degradation rate
Jilin Province is a big agricultural province， which has rich crop straw resources. Straw contains rich organic matter， N， P， K and microelements， and is an important source of organic fertilizer in agricultural production[1]. Directly returning straw to soil could reduce its pollution to environment， and return the nutrients absorbed by crops from soil， which is beneficial to the balance of soil nutrients and especially important to the cyclic utilization of potassium element. The direct application of straw to soil could also improve the physical， chemical and biological properties of soil， and is thus an important and effective technique for agricultural sustainable development[2]. However， for direction application of straw to soil， problems including mismatching of agricultural machinery and tools and farmers?? usual practice and knowledge， still exist. Especially， in northern China， all the straw is returned to soil， but could not all be degraded in the right year， and the soil preparation in spring could not be performed well， which leads to the condition that straw on soil surface causes poor seeding quality[2]. Directing at above problems， three strains capable of rapidly degrading straw were screened from rotten straw and soil， and one decomposition accelerator was developed and used for the maize straw degradation experiment in field. This study will provide a scientific basis for decomposition accelerator and returning straw to soil.
Development of Decomposition Accelerator
Experimental design
Three strains were mixed according to different ratios， and six treatments were designed at different volume ratios.
Treatment 1： Trichoderma koningii?? Streptomyces?? Bacillus subtilis=2?? 1?? 2.
Treatment 2： T. koningii?? Streptomyces?? B. subtilis=1?? 1?? 1.
Treatment 3： T. koningii?? Streptomyces?? B. subtilis=2?? 1?? 1.
Treatment 4： T. koningii?? Streptomyces?? B. subtilis=1?? 2?? 1.
Treatment 5： T. koningii?? Streptomyces?? B. subtilis=2?? 2?? 1. Treatment 6： T. koningii?? Streptomyces?? B. subtilis=1?? 1?? 2.
Experimental methods
The living bacteria count was determined by plate counting method.
Calculating method：
nv = xkv1 （v0v2） ??10-8
nv ： volume living bacteria count （108/ml）； ??1： basic liquid volume （ml）； ??2 ： addition amount of bacterial suspension （ml）； ??0 ： sample amount （ml）； x： average number of colonies （colonies）； k： dilution times.
Experimental results
The experimental results showed that the living bacteria count was the highest under the strain ratio of 2?? 1?? 2 （Table 1）. The decomposition accelerator was prepared according to this ratio for field experiment.
Field Experiment of Decomposition Accelerator
Experimental conditions
The experiment was carried out in Dafangshen Village， Chaoyangpo Town， Gongzhuling City， Jilin Province. Maize straw was degraded with the decomposition accelerator. The tested soil was black soil with the basic physical and chemical properties shown in Table 2.
Experimental materials
Crop straw： The straw of maize variety Zhengdan 958 （with a length of 3-5 cm）.
Mesh bag： 40??mesh nylon mesh bag （25 cm??35 cm）.
Experimental methods
The experiment had two treatments. Treatment 1 was the control （CK）， in which the maize straw was returned to the field at a rate of 9 750 kg/hm2 and sprayed with clear water. In treatment 2， the maize straw was returned to the field at a rate of 9 750 kg/hm2 and applied with the decomposition accelerator at a rate of 30 kg/hm2. A certain amount of the decomposition accelerator （2 kg） was mixed with 20 L/hm2， and the mixture was sprayed to the field.
The straw was filled in nylon mesh bags according to 10 g per bag. Ten bags were buried in each plot with a depth of 5-10 cm. Each treatment had 15 replicates. After burying the bags， five bags were taken from each treatment every 10 d， oven??dried and weighed， to determine the degradation effect of the decomposition accelerator to straw.
Data processing
The statistical analysis was performed by t test.
Results and Analysis
The weight loss of straw on the 10th day after burying
The weight loss values of the straw on the 10th day after burying are shown in Table 3.
It could be seen from Table 3 that the average weight loss ratio of the treatment was 8.03%， and the average weight loss ratio of the CK was 2.1%， which was 5.93% lower than the treatment. It indicated that the straw sprayed with the decomposition accelerator was degraded at a speed far higher than the straw sprayed with clean water. Significance analysis was performed on the weight loss of straw on the 10th day after burying， and the results are shown in Table 4.
Results： S=0.0043， t=13.76， when n=4， t0.05=2.78； and t0.01=4.60， indicating that the difference was significant at the very significant level. It indicated that under the action of the decomposition accelerator， the degradation speed could be improved greatly.
The weight loss of straw on the 20th day after burying
The weight loss values of the straw on the 20th day after burying are shown in Table 5.
It could be seen from Table 5 that the average weight loss ratio of the treatment was 26.98%， and the average weight loss ratio of the CK was 18.52%， which was 8.46% lower than the treatment. It indicated that the straw sprayed with the decomposition accelerator was degraded at a speed increasing over time.
Significance analysis was performed on the weight loss of straw on the 20th day after burying， and the results are shown in Table 6.
Results： S=0.016 1， t=5.25， when n=4， t0.05=2.78； and t0.01=4.60， indicating that the difference was significant at the very significant level. It indicated that 20 d after spraying the decomposition accelerator， the degradation speed could still be improved.
The weight loss of straw on the 30th day after burying
The weight loss values of the straw on the 30th day after burying are shown in Table 7.
It could be seen from Table 7 that the average weight loss ratio of the treatment was 40.20%， and the average weight loss ratio of the CK was 25.57%， which was 14.63% lower than the treatment. It indicated that the straw sprayed with the decomposition accelerator was degraded with an effect far better than the straw sprayed with clean water.
Significance analysis was performed on the weight loss of straw on the 20th day after burying， and the results are shown in Table 8.
Results： S=0.01， t=14.62， when n=4， t0.05=2.78； and t0.01=4.60， indicating that the difference was significant at the 0.01 level. It indicated that 30 d after spraying the decomposition accelerator， the decomposition accelerator still had an effect of degrading the straw， and there was a very significant difference between the treatment and the CK.
Conclusions and Discussion
The experimental results showed that for the different strain ratios， the ratio at 2?? 1?? 2 exhibited the highest living bacteria count， indicating that the strains had the strongest activity under this condition， and the degradation extent was the highest. In the field experiment， the degradation effect was observed about 10 d after spraying the decomposition accelerator， and on the 30th day， the degradation rate had reached 40.2%. Spraying the decomposition accelerator could significantly accelerate the degradation of straw with remarkable degradation effect， and the weight loss was significantly different from the CK without the application of the decomposition accelerator. Therefore， in direct??application of straw into soil， spraying decomposition accelerator could accelerate the degradation speed of straw.
References
[1] YANG ZX， ZHOU HP， GUAN CL， et al. Effect of straw decomposing inoculant on maize straw returning[J]. Journal of Shanxi Agricultural Sciences， 2013， 41（4）： 354-357.
[2] NONG CJ， WANG YW， XU Z， et al. Effects of organic matter??decomposition inoculant on maize and rice straw returning[J]. Acta Agriculturae Boreali??occidentalis Sinica， 2016， 25（1）： 34-41.