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Journal of Food, Agriculture & Environment Vol.11 (1): 1017-1021. 2013

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Effects of rotten wheat straw on organic carbon and microbial biomass carbon of tobacco-planted soil Hong-li Chen, Guo-shun Liu *, Yong-feng Yang, Yi-mei Chang and Ling-ling Zhao Tobacco College of Henan University of Agriculture, National Tobacco Physiology & Biochemistry Research Centre Zhengzhou, 450002, China. e-mail:[email protected] Received 11 September 2012, accepted 19 January 2013.

Abstract The effects of rotten wheat straw on organic carbon content and microbial biomass carbon content of tobacco-planted soil were studied in this paper. Six treatments (CK0T1 3000, T2 6000, T3 9000, T4 12,000 and T5 15,000 kg·hm-2) were applied on a plot experiment. The results showed that the amount of rotten wheat straw could effectively affect the content of organic carbon, microbial biomass carbon and microbial quotient of tobaccoplanted soil. The larger the amount of rotten wheat straw, the higher organic carbon content increased. The difference between treatments was obvious in early stage, and then the difference narrowed down. Microbial biomass carbon content of all treatments was higher than CK. A peak appeared in 75d and the contents of T1, T2, T3, T4 and T5 were increased by 80.99%, 93.99%, 101.95%, 119.64% and 111.25%, respectively. Soil microbial quotient was also analyzed in tobacco whole growth period. The average of microbial quotient of CK, T1, T2, T3, T4 and T5 was 4.53%, 5.78%, 5.82%,5.96%, 5.95% and 5.84%, respectively. The correlation between microbial biomass carbon content and organic carbon content and microbial quotient were analyzed. There were significant correlations between microbial biomass carbon content, organic carbon content and microbial quotient, the correlation coefficients were 0.560 and 0.870. In conclusion, the best effect of improving tobacco-planted soil fertility was by adding 12,000 kg·hm-2 of rotten wheat straw. Key words: Rotten wheat straw, organic carbon, microbial biomass carbon, microbial quotient, tobacco-planted soil.

Introduction Tobacco of Henan Province was a typical representative in China. In the recent 20 years, due to the long-time chemical fertilizer and the neglecting of the organic fertilizer, most of the planted-soil hardened, soil fertility declined, the content of soil organic matter decreased and quantity and activity of soil microorganisms were reduced, which affected the normal growth of tobacco 1. Nowadays, people paid more attention to the effect that organic fertilizers could improve tobacco leaf quality. Soil organic carbon (SOC) is the core of the soil quality and the main part of the biogeochemical cycle of nutrient elements. The quality and quantity of SOC not only influence on soil physical, chemical, and biological characteristics of soil and its process, but also influence and control the primary plant production and are important indices that must be taken into account in management of the soil quality assessment and sustainable land use. The content of soil microbial biomass carbon (SMBC) only accounts for 1-7% of soil total carbon 2, however, the activity of microorganisms is closely related to soil carbon, nitrogen and ecological system function 3. Compared with soil organic carbon, the content of microbial biomass carbon is changed faster 4. Microbial carbon turn over faster with shorter turn around time, ___________________________________ Abbreviations: SOC Soil organic carbon, SMBC Soil microbial biomass carbon, SMBC/SOC Microbial quotient

Journal of Food, Agriculture & Environment, Vol.11 (1), January 2013

which reflects the size of the soil nutrient cycling and energy in regulation and microorganism quantity transformed from organic substance. Usually, soil microbial biomass has close relationship with soil organic carbon content. If soil carbon content is high, soil microbial biomass will be higher correspondingly. Agricultural measures, such as fertilization and tillage, have important influence on soil microorganism quantity and diversity, and soil microbial biomass carbon could reflect or predict the change of soil sensitively and timely, so it is used as biological index of soil quality more and more. A large amount of researches had been proceeded 8, 9, since scientists invented the measurement method of soil microbial biomass 5-7. The results indicated that using organic fertilizers, straw or green manure could improve soil microbial biomass carbon content significantly, with increasing addition amount, the greater the obvious effects10, 11. A large amount of study had been proceeded about organic carbon and microbial biomass carbon content in different soil-use patterns at home and abroad 12-29, but effects of rotten wheat straw on organic carbon and microbial biomass carbon of tobacco-planted soil in Henan Province have not been reported. This paper mainly discussed effects of rotten wheat straw on organic carbon and microbial biomass carbon of tobacco-planted

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soil in Fangcheng, Henan Province, which could clarify the influence of the mechanism of action on organic material in restoring and improving soil carbon and tobacco leaf quality. The study was anticipated to provide the basis for scientific management for land, maintaining and improving soil fertility and quality. Materials and Methods Experimental design: The experiment utilizes plot experiment randomly in Fangcheng, Henan Province in 2011. The soil type was yellow loam, the content of soil organic matter was 11.67 g.kg-1, the content of total nitrogen 1.056 g.kg-1, the content of available N 58.09 mg.kg-1, the content of rapidly-available K 60.09 m g.kg-1, the content of available P 13.1 m g.kg-1 and pH 6.68. Fluecured tobacco breed was NC89. The wheat straw, which was harvested in 2010, was cut into about 10 cm of length, in the way of stacking fermentation. The fermentation time was from March 10 to April 10, then the material was dried naturally, smashed and screened with 2 mm mesh. The weight of the straw was dry weight, with relative water content of 6.64%. Experimental design is shown in Table 1. Table 1. Experiment design. Treatment CK T1 T2 T3 T4 T5

Amount rotten wheat straw 0 3,000 Kg.hm-2 6,000 Kg.hm-2 9,000 Kg.hm-2 12,000 Kg.hm-2 15,000 Kg.hm-2

The experiment plot was 5 m x 4 m. The experiment included three replicates and total number of plots was 18. There was a protection line between each plot. The topsoil was dried naturally, and mixed thoroughly with the rotten wheat straw. Then the mixture was backfilled on April 15. It was irrigated and then subsided for a week. Ridging was done on April 22. The village was selected at first, then the soil, taken out from the surface artificially, naturally dried, and mixed thoroughly with the pieces of wheat straw after fermentation by test design, was backfilled on April 15. After that, the soil was watered evenly to soil moisture content at about 90%, and settled naturally for a week. On April 22 was ridging, according to the conventional cultivation techniques of flue-cured tobacco. Tobacco was transplanted on May 1, with row spacing of 120 cm × 50 cm. Other field management measures were implemented according to high quality tobacco production technology. Determination of soil organic carbon and microbial biomass carbon: At 30, 45, 60, 75 and 90 days after tobacco transplantation, soil samples were collected from 0-20 and 20-40 cm depth, and mixed.Visible animals and plants were eliminated. Soil sample was passed through a 2-mm mesh sieve and kept in 4°C until determination of soil microbial biomass carbon. The rest of soil sample was air-dried and passed through a 0.149-mm mesh sieve to determine soil organic carbon by using potassium dichromate method 30. The chloroform-fumigation method was used to determine the soil microbial biomass carbon 6, 31.

Data analysis: Statistical analysis was done using Excel 2003 and statistical software DPS 6.05 and multiple comparison method (LSD) to test significant differences between treatments. Results and Discussion The influence of rotten wheat straw addition on soil organic carbon: Soil organic matter is important source of nutrients, especially nitrogen and phosphorus. It plays a great role in soil fertility, though its rate is low. Soil organic matter could make soil retain fertilizer efficiency and buffer character. It also could make soil loosen and form crumb structure, to improve soil physical properties, and it is an indispensable source of carbon and energy for soil microorganisms. Organic carbon is the main component of organic matter, needed for crop nutrient storage. In addition, nutrient loss is reduced by strong adsorption by organic matter. Addition of rotten wheat straw could change soil carbon structure, mainly increasing soil organic matter rates in the initial stage. In the microbial activity and reproduction process, the respiration could make part of carbon released into CO2 in addition to assimilating carbon. In general, with the increase of addition amount of rotten wheat straw, it was a rising trend in soil organic carbon content. Soil organic carbon content of each treatment declined in 0-20 cm and 20-40 cm soil depth (Tables 2 and 3). The results from Table 2 show that the soil organic carbon content of each treatment, in 020 cm soil depth displayed top level of significance after 30 and 45 days, thereafter the differences began to dwindle. The differences between T1 and T2 were significant in 60 days, the differences between T3 and T4 was the same. The differences of soil organic carbon content of each treatment were not significant after 75 days. The results showed that rotten wheat straw can quickly improve soil fertility, loosen soil and improve soil hardening condition in tobacco growing prophase, which was beneficial to the plant roots when grew deep, especially after 30 days. Ma et al.32 thought development quality of tobacco root affected directly the tobacco growth, production and internal quality. With the increase of rotten straw amount, soil organic carbon content increased. It was consistent with the results of Kennedy and Papendick 8 and Bunemann et al. 9. Along with the advancement Table 2. Effect of rotten wheat straw on organic carbon content of planted-tobacco soil (0-20 cm) g·kg-1. Treatment CK T1 T2 T3 T4 T5

30 days 6.80Ff 7.49Ee 8.02Dd 8.68Cc 9.14Bb 9.81Aa

45 days 6.64 Ff 7.29 Ee 7.81 Dd 8.31 Cc 8.78 Bb 9.58 Aa

60 days 6.56Df 7.13Ce 7.50Cd 8.19Bc 8.62Bb 9.27Aa

75 days 6.51Dd 7.06Cc 7.13Cc 8.05Bb 8.37Bb 9.25Aa

90 days 6.46Ed 6.94DEc 7.10CDc 7.63BCb 7.81Bb 8.86Aa

Values followed by different capital and lowercase are significantly different at P< 0.01 and P