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Hezhou University, Hezhou 542899, China

TheChangesinGuilinPaddySoilOrganicMatterandRiceYieldunderLong-TermFertilization

QiuliangYU,ZhengTANG,ZhongfangLI*,ChunlanCHEN,XiaoxianTANG,YanliLIN

Hezhou University, Hezhou 542899, China

Rational fertilization is an important measure to increase crop yield and soil fertility. Through analysis, this paper aims to master the change characteristics of soil organic matter and rice yield under different fertilizer treatments, in order to provide an important reference for the sustainable use of soil and effective fertilization. Long-term (19 years) rice crop rotation experiments in waterloggogenic paddy soil were conducted to investigate the change trend of crop grain yield and soil organic matter with time, reveal the dynamic characteristics and relationship between main fertility factors and crop yields using comparative analysis at three sites with conventional fertilization and non-fertilization in Guilin. The results showed that compared with previous years, the rice yield increased by 53% under the fertilization treatment and degreased by 66% under the control. Over the years, the average soil organic matter (SOM) content under fertilization treatment was 23% higher than under CK treatment. This indicates that chemical fertilizer and organic manure application can increase the rice yield and soil organic matter, and high rice yield can be attributed to the SOM increase.

Long-term fertilization, Waterloggogenic paddy soil, Soil organic matter (SOM), Yield change

1 Introduction

The long-term continuous located fertilization is a reliable method to study the inherent laws of soil and crop under different fertilization modes, and research soil fertility and productivity trends as well as the connection with environment. It is far better than the short-term experiment[1-3]. Fertilization is the most direct factor of evolution for soil fertility, and soil organic matter is an important material basis of soil fertility. The content and character have a very important impact on crop yields[4-6]. Thus, the soil organic matter content is positively correlated with soil fertility and crop nutrients, and also closely related to crop yields[7]. Studies suggest that the single application of chemical fertilizers leads to declining soil organic matter content, while the combined application of organic fertilizer and chemical fertilizer can increase soil organic matter content[7]. Studies have shown that the combined application of organic fertilizer and chemical fertilizer or single application of organic fertilizer plays a greater role than single application of chemical fertilizer or non-fertilization treatment in accumulation of active soil organic matter[8]. Zhangetal.[9]point out that the combination of organic and inorganic fertilizer can continuously provide effective crop nutrients and optimize the physical properties of the soil, so that the cultivated crops grow well. With the widespread attention to sustainable agricultural production, the researchers are not satisfied with the research results of one-season or two-season crops, and they start to pay attention to monitoring of long-term effect, and study the long-term effects of different fertilization on soil fertility and yield. Xin Jingshuetal. study the evolution of China's arable land quality. Xu Minggangetal.[3]expound the trend of Chinese soil fertility on the basis of long-term fertilization experiment site. Although the combined application of organic and inorganic fertilizer can significantly increase soil fertility and crop yields and it has been confirmed, the effect is quite different in the north and south[2, 11, 12]. Therefore, it is necessary to understand fully the trends of fertilization on different soils in different geographic regions in order to achieve precise management[12]. Paddy soil is the primary farming soil in Guangxi, and it is formed under long-term human hydroponic conditions. There is continuing redox reaction. In this study, we take waterloggogenic paddy soil in Northern Guangxi for example. According to the long-term monitoring tests of rice fields in Guilin, we analyze the impact of combined application of organic and inorganic fertilizer and single application of chemical fertilizer on the double cropping rice yield and soil organic matter, objectively evaluate the role of combined application of organic and inorganic fertilizer in increasing rice yield and improving soil fertility, and propose suitable fertilization management mode for the waterloggogenic paddy soil in Guilin.

2 Materials and methods

2.1OverviewoftheexperimentalfieldThe soil for experiment is waterloggogenic paddy soil, and the experiment site (25° 19'N, 110°17'E) is located in Guilin City, Guangxi Zhuang Autonomous Region, featuring a subtropical humid monsoon climate. It has annual average temperature of 19.3℃, annual rainfall of 1900mm and frost-free period of 309 d. The experiment was carried out from 1987 to 2005, and the same early and late rice crop rotation was maintained during the experiment. The replication is not set for field fertilizer experiment. The soil is the waterloggogenic paddy soil from the piled limestone slope. The application rate of pure N, P2O5and K2O is 346.6±11.7, 132.9±6.4 and 268.0±10.9 kg/hm2. The nutrients provided by organic fertilizer account for 16.4%.

2.2SamplinganddeterminationmethodsFrom 1987 to 2005, after the late rice harvest, the 0-20cm topsoil samples were collected using S-shaped random mixing method, and the samples were dried and sifted over 0.25mm sieve. During 1987-1996 and 2002-2003, the single application of organic fertilizer was conducted for early rice while the organic fertilizer was not applied for late rice; during 1997-2001 and 2004-2005, there was no application of organic fertilizer. The chemical fertilizer was applied for double cropping rice during the experiment. As for the control group (CK), no fertilizer was used. Soil nutrients were measured by conventional analytical methods and organic matter was measured by H2SO4-K2CrO7external heating method. Experimental data are analyzed using Excel2003 and SPSS software.

3 Results and analysis

3.1Effectoflong-termfertilizationonwaterloggogenicpaddysoilorganicmatterWith the extension of fertilization year, the soil organic matter content shows a slight increasing trend, but it does not reach significant levels, and fluctuates around 50-60 g/kg (Fig. 1). Under long-term fertilization, the soil organic matter content is relatively stable, but the soil organic matter content is greatly affected by climate and soil moisture. Therefore, the soil organic matter content in 1994 and 2004 was significantly higher than in other years under fertilization. During 1997-2001, the organic fertilizer was not applied, and in order to ensure that the soil organic matter was at the same level, the application of chemical fertilizer increased year by year, from 600 kg/ha to 990 kg/ha. However, the soil organic matter in 2001 was significantly lower than in other years, because the long-term single application of chemical fertilizer and few crop stubble residues led to a decline in the soil organic matter content. In 2002, the organic fertilizer was applied, and the soil organic matter increased significantly by 23%. The reason is that organic fertilizer is the main source of soil organic matter, and it not only directly provides nutrients for the crop, but also provides energy for microbes, thus indirectly enhancing the accumulation and supply capacity of soil organic matter. The long-term considerable application of chemical fertilizer causes some problems such as increased toxic elements, decreased microbial activity, nutrient imbalance and increased acidification, while the humic acid in organic fertilizer, as soil modifying agent, can loosen the soil and improve soil physical and chemical properties. The results show that the rice yield will be higher if there is higher content of organic matter, because organic matter is one of the main sources of plant nutrition, and it contains a variety of nutrients needed for plant growth. Therefore, improving the paddy soil organic matter content is an important way to improve rice yields.

Fig.1 Soil organic matter content during 1987-2005

3.2Effectoflong-termfertilizationonriceyieldThe rice grain, stem and leaf yield under CK is significantly lower than under combined application of organic and inorganic fertilizer (Fig. 2). As can be seen from Fig. 2 (a), the total rice yield in the first year is higher than in other years, because the remaining fertility in paddy soil before experiment provides nutrients to rice, and the rice yield in the late period of experiment is 66% lower than in the early period of experiment. Soil fertility is affected by natural and climatic conditions, as well as some human factors such as different crops, tillage management, irrigation and fertilization, and over time, the rice yield fluctuates around 400-3000 kg/ha, because under continuous cropping conditions, the natural productivity of rice is difficult to remain at a certain level for a long time. Under conventional fertilization conditions, rice yield is rising, and the yield in the late period is 53% higher than in the early period. By comparing Fig. 2 (a) and (b), it is found that the long-term combined application of organic and inorganic fertilizer can significantly increase rice grain, stem and leaf yield (6000-14000 kg/ha) when compared with non-fertilization treatment (CK). In the experiment during 1997-2001 and 2004-2005, the organic fertilizer was not applied, and the rice yield did not fall but significantly increased. The reason is that after putting organic fertilizer into soil, the microbial decomposition is relatively slow, and it can release a steady stream of nutrients needed for growth of various crops within a certain time. Thus, the single application of organic fertilizer, or the combined application of organic fertilizer and chemical fertilizer, can significantly promote the accumulation of organic matter in the topsoil, and improve the quality of soil organic matter. Obviously, the combined application can significantly increase rice yield.

Fig.2 Rice grain, stem and leaf yield from 1987 to 2005

4 Discussions

4.1SoilorganicmatterThe study results of Zhangetal.[9]show that under the long-term single application of chemical fertilizer, the soil organic matter content shows a decreasing trend, and the results of this study show that under conventional fertilization, the soil organic matter content is stable, with no significant rise or fall. At present, there is controversy over whether the chemical fertilizer can increase the soil organic matter content. Studies suggest that the application of chemical fertilizer can increase biological yields of crops, thereby increasing the input to soil organic matter (roots, stubble, leaves, etc.)[10, 13]. Studies of Liu Yirenetal.[14]have shown that under chemical fertilizer treatment, the soil organic matter content is maintained at the original level, with no significant growth trend, which may be due to difference in soil texture and climate. Long-term combined application of organic and inorganic fertilizer has a significant impact on the accumulation rate of soil organic matter content, but it is closely related to the soil parent material, fertilization amount and farming methods. This study shows that the long-term combined application of chemical fertilizer and organic fertilizer can significantly increase the soil organic matter content. This is consistent with the findings of Sunetal.[15]. To sum up, the long-term combined application of chemical fertilizer and organic fertilizer can not only increase soil organic matter content and improve soil fertility, but also save the amount of fertilizer and improve fertilizer use efficiency. Animals and plants, microbial residues and the organic fertilizers are the major sources of soil organic matter[13]. Studies have shown that the organic matter directly affects many properties of soil to some extent, and is the source of N, P, S and other nutrients for plants[16]. Soil organic matter content is closely related to soil fertility, and has a great impact on soil properties, crop growth and application of chemical fertilizers. Studies show that the combination of chemical fertilizer and organic fertilizer, on the one hand, directly increases the soil nutrients in paddy system through organic fertilizer, and on the other hand, provides balanced mineral nutrition for all stages of rice growth by adjusting the release strength and speed of soil and fertilizer nutrient, thereby increasing the rice yield[5-6]. Therefore, improving the paddy soil organic matter content is an important way to increase rice yields. This study shows that the higher soil organic matter content will lead to higher rice yield, which is consistent with the above findings.

4.2RiceyieldChina’s traditional agriculture has long used farm organic fertilizer to improve soil fertility and increase productivity[9]. The combined application of organic and inorganic fertilizer can result in sustained high crop yield, because organic fertilizer can not only provide a lot of organic fertilizer nutrients needed for growth of the crop, but also be a good source of trace elements in crops[14-15]. The test results indicate that under the long-term combined application of organic and inorganic fertilizer, the rice yield is significantly improved, which is consistent with many studies. Long-term experimental study of returning straw to farmland suggests that the combined application of organic and inorganic fertilizer can more effectively improve soil fertility and increase crop yield than the single application of straw fertilizer or chemical fertilizer[4, 7]. Studies of Hou Hongqianetal.[17]have shown that under combined application of organic and inorganic fertilizer, the rice yield is highest for the early rice or late rice. The reason is that N utilization rate is improved under the combined application of organic fertilizer and chemical fertilizer, and organic matter promotes the accumulation of soil organic matter and improves the supply of nutrients, thereby increasing rice yield. This experiment is based on the data of a experimental site, and there are some limitations, so there is a need to take appropriate fertilization measures for the waterloggogenic paddy soil with different parent materials.

5 Conclusions

Through analysis, this paper aims to master the change characteristics of soil organic matter and rice yield under different fertilizer treatments, in order to provide an important reference for the sustainable use of soil and effective fertilization. Long-term (19 years) rice crop rotation experiments in waterloggogenic paddy soil were conducted to investigate the change trend of crop grain yield and soil organic matter with time, reveal the dynamic characteristics and relationship between main fertility factors and crop yields using comparative analysis at three sites with conventional fertilization and non-fertilization in Guilin. The results showed that compared with previous years, the rice yield increased by 53% under the fertilization treatment and degreased by 66% under the control. Over the years, the average soil organic matter (SOM) content under fertilization treatment was 23% higher than under CK treatment. This indicates that chemical fertilizer and organic manure application can increase the rice yield and soil organic matter, and high rice yield can be attributed to the SOM increase. Long-term combined application of organic and inorganic fertilizer (organic fertilizer occupying 16.4% of total nutrients) is an ideal fertilization method for farming on the waterloggogenic paddy soil in North Guangxi.

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November 20, 2015 Accepted: January 29, 2016

Supported by National Natural Science Foundation of China (41361068); Key Science and Technology Research Funds for Guangxi Universities (2013ZD067); Guangxi Natural Science Foundation (2011GXNSFB-018056).

*Corresponding author. E-mail: lizhongfang08@126.com