论文部分内容阅读
Abstract [Objectives]The aim was to explore the biological mechanism of green manure on improving soil fertility in paddy soil.
[Methods]Early rice （chemical fertilizer） was used as a control to study the effects of returning green manure crops of mung bean， lablab bean to paddy fields and organic manure application on the bulk density， nutrient content， nutrient content and yield of rice soil.
[Results]The soil bulk density in each treatment was significantly lower than that of the basic soil. The soil bulk density of treatment I was the least of 1.52 g/cm3. The nitrogen content of rice in treatment IV was significantly higher than that of treatment I， treatment II， and treatment III. The phosphorus and potassium contents of rice in treatment III and treatment IV were significantly higher than those of treatment I and treatment II. Returning green manure crops to field and applying organic fertilizers could increase the polished rice ratio and reduce the chalkiness degree， chalkiness ratio and protein content of rice. The gel consistency of rice grain in treatment I was significantly higher than that of treatment II， treatment III and treatment IV. The rice of treatment III had the highest number of effective panicles per plant， 1 000grain weight， theoretical yield and actual yield， respectively， 14.07 panicles/plant， 32.58 g， 6 236.27 kg/hm2 and 5 086.80 kg/hm2.
[Conclusions]This study provided a theoretical basis for proposing good green manure varieties suitable for the continuous improvement of paddy soil quality.
Key words Green manure； Soil improvement； Lablab bean； Yield
Rice is the main food crop in China， and fertilization is the main measure to increase crop yield[1]. However， although the longterm application of a large amount of fertilizers in rice production has played a significant role in increasing grain yield， it can easily lead to soil degradation， soil fertility decline， and fertilizer utilization decline， resulting in different degrees of nonpoint source pollution and other issues[2-10].
Green manure is a kind of nutrientcomplete source of high quality biofertilizer source， which has a good effect in providing nutrients needed for crops， improving farmland ecological environment and preventing erosion and pollution[11]. Leguminous green manures can also fix nitrogen in the air， activate soil phosphorus， accumulate potassium[12]and trace elements[13-17]. After ploughing under and incorporating into the soil， green manure not only provides various mineral nutrients for the crops， but also increases soil organic matter， improves the soil microbial environment and physical and chemical properties， reduces diseases， and improves crop yield and quality[18]. Therefore， in this paper， with conventional fertilizers （nonrotation of green manure） as control， the effects of rotating different green manures and returning straws to fields on rice quality and yield were analyzed and compared from soil nutrients， rice agronomic traits， nutrient quality， and yield， with the aim to provide a theoretical basis for proposing good green manure varieties suitable for the continuous improvement of paddy soil quality. Materials and Methods
Test overview
The test was conducted in the southern multiplication base of Guangxi Academy of Agricultural Sciences in Jiuzuo Town， Sanya City， Hainan Province from the spring of 2014 to autumn of 2015. The physical and chemical properties of the test field were soil total N of 0.028 %， total P of 0.045 %， total K of 0.296 %， available N of 77.11 mg/kg， available P of 12.56 mg/kg， available K of 24.29 mg/kg， organic matter of 2.48 %， bulk density of 1.59 g/cm3， and pH = 6.11. The organic fertilizer had an organic matter content of 57.50%， total N of 1.417%， total P of 1.221% and total K of 2.501%.
The tested early rice variety was A21， a variety of Jiangxi hybrid rice， and the green manure varieties were lablab bean and mung bean variety of Guilvdou No.3， provided by the Institute of Agricultural Resources and Environment， Guangxi Academy of Agricultural Sciences.
Test design
The test consisted of 4 treatments： Treatment I， summer mung bean （chemical fertilizer + organic fertilizer）early rice （chemical fertilizer）； Treatment II， summer lablab bean （chemical fertilizer + organic fertilizer）early rice （chemical fertilizer）； Treatment III： early rice （chemical fertilizer + organic fertilizer）； Treatment IV： early rice （chemical fertilizer）. Each treatment had 3 repetitions， arranged in randomized blocks. Each plot had an area of 40 m2. Each plot was separated from the other by plastic plates of 3 cm thick to avoid overlapping irrigation and crosscontamination of fertilizers between the treatments. The planting density was 165 000 holes/hm2.
Test implementation
Mung bean and lablab bean were planted using hole sowing in the spring of 2014 with the planting specifications of 50 cm × 17 cm and 50 cm × 40 cm， respectively. Each hole was sown with 2-3 seeds. The planting densities for the 2 bean varieties were 1 628/40 m2， 947/40 m2， respectively. The application amount of compound fertilizer （151515） for mung bean and lablab bean was 75 kg/hm2， the application amount of organic fertilizer was 24.25 t/ hm2. In addition， 60% of total nitrogen fertilizer and potassium fertilizer were used as base fertilizer， and the remaining 40% was used as top dressing， while the organic fertilizer and phosphate fertilizer were applied once as the base fertilizer （Table 1）. The field management was the same for all treatments. In the spring of 2014， mung beans and lablab bean were sown， and their agronomic traits and bioproduction were investigated respectively at the flowering stage， and the straws were returned to the field according to the test design. Rice was planted in the spring of 2015， and the application amounts of N， P2O5 and K2O fertilizers to rice were 6.3， 3.9， and 4.3 kg/ hm2， respectively， and the organic fertilizer application amount was 24.25 t/ hm2. The fertilization for each treatment was as shown in Table 1， and the other management was the same. Rice was harvested in midJune.
There were 3 repetitions for each treatment， a total of 12 plots.
Measuring items and methods
Determination of grain number per panicle， 1 000grain weight， total N， total P and total K in rice grain
At the rice maturity stage， 5 rice plants were normal growth were randomly taken from each plot for indoor examination. The grain number per panicle and 1 000grain weight were measured using 1/100 analytical balance. Total N in rice was measured using H2SO4H2O2 digestiondistillation method， total P using H2SO4H2O2 digestionmolybdenum antimony anticolorimetric method， total K using H2SO4H2O2 digestionflame photometer， and hulled rice ratio and other items were measured according to the related national quality analysis standards. The actual yield of each plot was measured separately.
Soil
Samples were collected from each plot using 5point mixed sampling. After drying， the soil samples were sieved by the 0.149 mm sieve， and then the soil organic matter， total N， total P and total K contents were measured. The organic matter content was measured using potassium dichromatesulfuric acid external heating method， total N using semiautomatic Keldahl distillation， the total P using acidmolybdenum antimony colorimetric method， total K using NaOH fusionflame photometry， available N the alkalidiffusion method， available P ammonium fluoridehydrochloric extractionMoSbVc spectrophotometry， available K the NH4AC extractionflame photometry， pH with pH meter method， and bulk density using cuttingring method.
Data statistics and analysis
Statistical analysis was performed using Excel 2003 and SPSS19. Oneway analysis of variance was used for each treatment， and Duncans method was used for multiple comparison of means.
Results and Analysis
Green manure nutrients and biological yield
As shown in Table 2， the differences in total N， total P， total K， number of plants， and biological yield of mung bean and lablab bean reached extremely significant levels， indicating that under normal water and fertilizer management conditions， the growth characteristics of different green manures determined the amounts of nutrient absorption and biological yield of crops. The total N， total P， total K， plant number and biological yield of mung bean were 2.088%， 0.663%， 1.752%， 692.67/40 m2， and 1.58 t/hm2， respectively. Compared with mung bean， lablab bean had the total K and biological production increased by 70.38 and 37.34%， while the total N， total P and plant number decreased by 4.36， 32.43， and 55.58， respectively. As the mung bean is a kind of compact crop with upright plant type， its seeding size was 50 cm × 17 cm. When the mung bean grew to 18 cm high， the plants with weak growth vigor were removed， leaving only the strong ones. Each hole had 1 plant. At last， the remaining plants of mung bean in each plot were 385.02 more than that of lablab bean. Effect of rotating green manure crops and returning straws to field on soil nutrient
As shown in Table 3， fertilization increased soil nutrients and organic matter content， and reduced the soil bulk density. Treatment IV had the lowest contents of soil total N， total P， total K and organic matter among all the treatments， which were respectively 0.032， 0.046， 0.681， and 2.50%， significantly lower than those in treatments I， II and III， and higher than those of the basic soil， but the difference was not significant.
The increase in soil nutrients and organic matter was related to the nutrient， total amount of organic carbon， type and application time of the added fertilizers. Treatment III had the highest contents of soil total N， total P， total K and organic matter among all the treatments， which were respectively 0.048， 0.053， 0.784 and 2.79%， significantly higher than those in treatments I， II， IV and basic soil.
The soil bulk density of all treatments was significantly lower than that of the basic soil. The minimum soil bulk density was found in treatment I， which was 1.52 g/cm3. The decrease of soil bulk density in treatment IV was smaller， which was lower than that in the basic soil but significantly higher than that in treatments I， II and III.
Treatment I， summer mung bean （chemical fertilizer + organic fertilizer）early rice （chemical fertilizer）； Treatment II， summer lablab bean （chemical fertilizer + organic fertilizer）early rice （chemical fertilizer）； Treatment III： early rice （chemical fertilizer + organic fertilizer）； Treatment IV： early rice （chemical fertilizer）. The Duncan test method is used； different letters in the same column indicate significant differences （P<0.05）.
Fang QIN et al. Effects of Rotating Summer Green Manure Crops and Straw Returning in Paddy Field on Rice Quality and Yield
Effect of rotating green manure crops and returning straws to field on nutrient and quality of early rice
N， P， K in early rice
As shown in Fig. 1， the difference in nitrogen nutrient level reached the extremely significant level between treatment IV and other treatments. The fertilizers for the test were easily soluble ones. In treatment IV， rice could directly absorb relatively more nitrogensoluble nutrients. However， in treatments I and II， which had the green manure crops returned to the field， and in treatment III， the nutrients could be absorbed by the crops after the transformation through microorganism decomposition， and the microbial activity process also consumed some nutrients. Therefore， the nitrogen nutrient in the rice of treatment IV was higher than that in the other treatments. There was no significant difference in the contents of P and K between treatment IV and treatment III， indicating that the application of organic fertilizer and chemical fertilizer and the application of only chemical fertilizer had no effect on the absorption of P and K nutrients in early rice. On the other hand， the differences in P and K contents reached the extremely significant level between treatments IV， III and other treatments. Early rice quality
As shown in Table 4， treatment III had the highest hulled rice ratio and head milled rice ratio， 79.5 and 37.70%， respectively， followed by Treatment I of 79.25 and 37.20%， respectively， and the lowest hulled rice ratio and head milled rice ratio were found in treatment IV， which were 79.05% and 34.95%， respectively. Treatment I， treatment II， and treatment III showed no significant difference in milled rice ratio， but significantly higher than that in Treatment IV.
The chalkiness degree and chalkiness ratio of treatment IV were 2.20 and 10.5%， respectively， which were significantly higher than those of treatment I， II and III. The chalkiness ratios of the rice of treatment I and II were not significantly different from each other， but significantly higher than those of treatment III， and extremely significantly lower than those in treatment IV.
As shown in Table 5， there was no significant difference in the lengthwidth ratio of rice between treatments. The values of lengthwidth ratio fell between 3.5 and 3.6. This may be due to the fact that the lengthwidth ratio of rice was related to the variety of rice， but not to the type of fertilizer.
The gel consistency of rice of Treatment I was significantly higher than that in treatments I， II and III， and the highest gel consistency of rice was 85， followed by that of treatment II， which was 82， and the lowest was found in treatment IV， which was only 78.
The difference in amylose content was not significant between treatment II and treatment IV， and the amylose contents were between 14.90 and 15.10%， which was significantly higher than that of treatments I and III. The amylose content of rice in Treatment I was significantly higher than that in treatment III.
The protein content in rice of treatment IV was significantly higher than that of treatment I， II and III， with a maximum of 8.75%， followed by that of treatment II， which was 8.30%， and the lowest was found in treatment III， which was only 7.8%.
Agronomic traits and field yield of early rice in mature stage
As shown in Table 5， plant height， number of effective panicles per plant， 1 000grain weight， theoretical yield， and actual yield of rice in treatment III were significantly higher than those of treatments I， II and III， and all were the highest， which were 113.20 cm， 14.07 panicles/plant， 32.58 g， 6 236.27 kg/hm2， 5 086.80 kg/hm2， respectively. The second highest plant height， number of effective panicles per plant， theoretical yield and actual yield of rice came to the rice of treatment I， respectively， 108.00 cm， 13.93 panicles/plant， 5 932.66 kg/hm2， and 4 974.0 kg/hm2. The rice of treatment IV had the lowest plant height， number of effective panicles per plant， number of grains per panicle， 1 000grain weight， theoretical yield， and actual yield， and compared with those of treatment III， the items showed decreases by 8.95， 21.82， 4.36， 11.45， 33.61 and 13.82%， respectively. Discussion and Conclusion
The large amount application of chemical fertilizers has caused soil compaction in paddy fields， and the content of organic matter is constantly declining. It is suggested to plant green manure crops during the winter time to improve the conditions of fields. Mung bean and lablab bean are the common green manure crops used in production. However， there are great differences in the growth characteristics and nutrient absorption of the 2 varieties. After ploughing the green manure crops into soil and adding application of organic fertilizer， soil organic matter， N， P， K contents show increases to different degrees and soil bulk density reduces. However， further study is needed to find out whether it is related to the application of compound fertilizer and organic fertilizer while planting green manure crops.
Green manure crops and organic fertilizers contain a large amount of organic matters， N， P， K and trace elements， which are important components of crop growth. After ploughing the green manure crops into paddy field， the rice has got improvement in rice quality， rice agronomic traits and yield， and it is consistent with the results of Wang et al. and Zhao et al.[20-21]that the combined application of green manure and mineral fertilizers can significantly increase soil organic matter content and increase the yield of early and late rice. According to the climatic conditions in Hainan， after rice harvesting， the rotation of ricegreen manure crops by using the spare time and space cannot only improve soil quality and soil environment in the paddy fields， but can also increase the quality and yield of crops， making it an important measure to achieve the sustainable development of rice production.
References
[1]LIAO YL， ZHENG SX， NIE J， et al. Effects of longterm application of fertilizer and rice straw on soil fertility and sustainability of a reddish paddy soils productivity[J]. Scientia Agricultura Sinica， 2009， 42（10）： 3541-3550.
[2]HUANG GQ， WANG XX， QIAN HY， et al. Negative impact of inorganic fertilizers application on agricultural environment and its countermeasures[J]. Ecology and Environment， 2004（4）： 656-660.
[3]DORAN JW， ZEISS MR. Soil health and sustainability： Managing the biotic component of soil quality[J]. Applied Soil Ecology， 2000， 15（1）： 3-11.
[4]YADAV RL， YADAV DS， SINGH RM， et al. Long term effects of inorganic fertilizer inputs on crop productivity in a ricewheat cropping system[J]. Nutrient Cycling in Agroecosystems， 1998， 51（3）： 193-200. [5]WANG JH， CAO K， ZHANG X， et al. Effect of green manure returning to rice field on the soil organic matter dynamics during rice growing stage[J]. Journal of Zhejiang Agricultural Sciences， 2010（3）： 614-616.
[6]FANG ZQ. Preliminary approach to organic agriculture[J]. Acta Agriculturae Shanghai， 2000，16（4）：1-5.
[7]TU SH. Roles and functions of chemical fertilizers in sustainable agriculture[J]. Southwest China Journal of Agricultural Sciences， 2003， 16 （Supplement）： 7-8.
[8]WANG DJ， LIN JH， SUN RJ， et al. Optimum nitrogen ratio for a high productive ricewheat system and its impact on the groundwater in the Taihu Lake area[J]. Acta Pedologica Sinica， 2003， 40（3）： 426-432.
[9]GAO XJ， HU XF， WANG SP， et al. Loss of nitrogen in rice field and its influence on water environment[J]. AgroEnvironmental Protection， 2001， 20（4）： 196-198， 205.
[10]WANG JH， CAO K， JIANG LN， et al. History， current status and guidelines about green manure development of Zhejiang Province[J]. Acta Agriculturae Zhejiangensis， 2009， 21（6）： 649-653.
[11]YANG ZP， GAO JS， ZHENG SX， et al. Effects of longterm winter plantinggreen manure on microbial properties and enzyme activities in reddish paddy soil[J]. Soils， 2011， 43（4）： 576-583.
[12]CAO WD， HUANG HX. Ideas on restoration and development of green manures in China[J]. Soils and Fertilizers Science in China， 2009 （4）： 1-3.
[13]JIAO B. China green fmanure[M]. Beijing： Agricultural Press， 1986.
[14]SI P， QIAO XS， HUANG XJ. The analysis of trace element contents among 18 kinds of common leguminous green manure of orchard[J]. Chinese Agricultural Science Bulletin， 2012， 28（4）： 157-162.
[15]HE LQ， XUE CH， ZHANG Y. Study on the main economic green manures in Hunan Province[J]. Hunan Agricultural Sciences， 2011（7）： 45-47， 51.
[16]WANG ZG， CHEN B， RAO XJ， et al. Study on absorption law of green manure[J]. Journal of Xinjiang Agricultural University， 2008， 31（2）47-50.
[17]LIU J， CAO WD， RONG XN， et al. Nutritional characteristics of Orychophragmus violaceus in North China[J]. Soils and Fertilizers Sciences in China， 2012 （1）： 78-82.
[18]ZHANG HZ， YANG SL， LIU DF， et al. Effects of cotton field cropping mustard green manure on Verticillium wilt[J]. Crops， 2004 （1）： 30.
[19]Hainan Provincial Bureau of Statistics. 2006 Hainan Statistical Yearbook[M]. Beijing： China Statistics Press， 2007：21-23.
[20]WANG YQ， ZHANG XM， LIU Y， et al. Effects of Chinese milk vetch on rice yield and soil nutrients[J]. Journal of Anhui Agricultural Sciences， 2004， 32（4）：699-700.
[21]ZHAO N， CAO WD， WANG YQ， et al. Effects of green manure milk vetch and fertilizer combined application on the growth and yield of rice in doublecropping rice areas[J]. Journal of Anhui Agricultural Sciences， 2010， 38（36）： 20668-20680.
Editor： Na LI Proofreader： Xinxiu ZHU
[Methods]Early rice （chemical fertilizer） was used as a control to study the effects of returning green manure crops of mung bean， lablab bean to paddy fields and organic manure application on the bulk density， nutrient content， nutrient content and yield of rice soil.
[Results]The soil bulk density in each treatment was significantly lower than that of the basic soil. The soil bulk density of treatment I was the least of 1.52 g/cm3. The nitrogen content of rice in treatment IV was significantly higher than that of treatment I， treatment II， and treatment III. The phosphorus and potassium contents of rice in treatment III and treatment IV were significantly higher than those of treatment I and treatment II. Returning green manure crops to field and applying organic fertilizers could increase the polished rice ratio and reduce the chalkiness degree， chalkiness ratio and protein content of rice. The gel consistency of rice grain in treatment I was significantly higher than that of treatment II， treatment III and treatment IV. The rice of treatment III had the highest number of effective panicles per plant， 1 000grain weight， theoretical yield and actual yield， respectively， 14.07 panicles/plant， 32.58 g， 6 236.27 kg/hm2 and 5 086.80 kg/hm2.
[Conclusions]This study provided a theoretical basis for proposing good green manure varieties suitable for the continuous improvement of paddy soil quality.
Key words Green manure； Soil improvement； Lablab bean； Yield
Rice is the main food crop in China， and fertilization is the main measure to increase crop yield[1]. However， although the longterm application of a large amount of fertilizers in rice production has played a significant role in increasing grain yield， it can easily lead to soil degradation， soil fertility decline， and fertilizer utilization decline， resulting in different degrees of nonpoint source pollution and other issues[2-10].
Green manure is a kind of nutrientcomplete source of high quality biofertilizer source， which has a good effect in providing nutrients needed for crops， improving farmland ecological environment and preventing erosion and pollution[11]. Leguminous green manures can also fix nitrogen in the air， activate soil phosphorus， accumulate potassium[12]and trace elements[13-17]. After ploughing under and incorporating into the soil， green manure not only provides various mineral nutrients for the crops， but also increases soil organic matter， improves the soil microbial environment and physical and chemical properties， reduces diseases， and improves crop yield and quality[18]. Therefore， in this paper， with conventional fertilizers （nonrotation of green manure） as control， the effects of rotating different green manures and returning straws to fields on rice quality and yield were analyzed and compared from soil nutrients， rice agronomic traits， nutrient quality， and yield， with the aim to provide a theoretical basis for proposing good green manure varieties suitable for the continuous improvement of paddy soil quality. Materials and Methods
Test overview
The test was conducted in the southern multiplication base of Guangxi Academy of Agricultural Sciences in Jiuzuo Town， Sanya City， Hainan Province from the spring of 2014 to autumn of 2015. The physical and chemical properties of the test field were soil total N of 0.028 %， total P of 0.045 %， total K of 0.296 %， available N of 77.11 mg/kg， available P of 12.56 mg/kg， available K of 24.29 mg/kg， organic matter of 2.48 %， bulk density of 1.59 g/cm3， and pH = 6.11. The organic fertilizer had an organic matter content of 57.50%， total N of 1.417%， total P of 1.221% and total K of 2.501%.
The tested early rice variety was A21， a variety of Jiangxi hybrid rice， and the green manure varieties were lablab bean and mung bean variety of Guilvdou No.3， provided by the Institute of Agricultural Resources and Environment， Guangxi Academy of Agricultural Sciences.
Test design
The test consisted of 4 treatments： Treatment I， summer mung bean （chemical fertilizer + organic fertilizer）early rice （chemical fertilizer）； Treatment II， summer lablab bean （chemical fertilizer + organic fertilizer）early rice （chemical fertilizer）； Treatment III： early rice （chemical fertilizer + organic fertilizer）； Treatment IV： early rice （chemical fertilizer）. Each treatment had 3 repetitions， arranged in randomized blocks. Each plot had an area of 40 m2. Each plot was separated from the other by plastic plates of 3 cm thick to avoid overlapping irrigation and crosscontamination of fertilizers between the treatments. The planting density was 165 000 holes/hm2.
Test implementation
Mung bean and lablab bean were planted using hole sowing in the spring of 2014 with the planting specifications of 50 cm × 17 cm and 50 cm × 40 cm， respectively. Each hole was sown with 2-3 seeds. The planting densities for the 2 bean varieties were 1 628/40 m2， 947/40 m2， respectively. The application amount of compound fertilizer （151515） for mung bean and lablab bean was 75 kg/hm2， the application amount of organic fertilizer was 24.25 t/ hm2. In addition， 60% of total nitrogen fertilizer and potassium fertilizer were used as base fertilizer， and the remaining 40% was used as top dressing， while the organic fertilizer and phosphate fertilizer were applied once as the base fertilizer （Table 1）. The field management was the same for all treatments. In the spring of 2014， mung beans and lablab bean were sown， and their agronomic traits and bioproduction were investigated respectively at the flowering stage， and the straws were returned to the field according to the test design. Rice was planted in the spring of 2015， and the application amounts of N， P2O5 and K2O fertilizers to rice were 6.3， 3.9， and 4.3 kg/ hm2， respectively， and the organic fertilizer application amount was 24.25 t/ hm2. The fertilization for each treatment was as shown in Table 1， and the other management was the same. Rice was harvested in midJune.
There were 3 repetitions for each treatment， a total of 12 plots.
Measuring items and methods
Determination of grain number per panicle， 1 000grain weight， total N， total P and total K in rice grain
At the rice maturity stage， 5 rice plants were normal growth were randomly taken from each plot for indoor examination. The grain number per panicle and 1 000grain weight were measured using 1/100 analytical balance. Total N in rice was measured using H2SO4H2O2 digestiondistillation method， total P using H2SO4H2O2 digestionmolybdenum antimony anticolorimetric method， total K using H2SO4H2O2 digestionflame photometer， and hulled rice ratio and other items were measured according to the related national quality analysis standards. The actual yield of each plot was measured separately.
Soil
Samples were collected from each plot using 5point mixed sampling. After drying， the soil samples were sieved by the 0.149 mm sieve， and then the soil organic matter， total N， total P and total K contents were measured. The organic matter content was measured using potassium dichromatesulfuric acid external heating method， total N using semiautomatic Keldahl distillation， the total P using acidmolybdenum antimony colorimetric method， total K using NaOH fusionflame photometry， available N the alkalidiffusion method， available P ammonium fluoridehydrochloric extractionMoSbVc spectrophotometry， available K the NH4AC extractionflame photometry， pH with pH meter method， and bulk density using cuttingring method.
Data statistics and analysis
Statistical analysis was performed using Excel 2003 and SPSS19. Oneway analysis of variance was used for each treatment， and Duncans method was used for multiple comparison of means.
Results and Analysis
Green manure nutrients and biological yield
As shown in Table 2， the differences in total N， total P， total K， number of plants， and biological yield of mung bean and lablab bean reached extremely significant levels， indicating that under normal water and fertilizer management conditions， the growth characteristics of different green manures determined the amounts of nutrient absorption and biological yield of crops. The total N， total P， total K， plant number and biological yield of mung bean were 2.088%， 0.663%， 1.752%， 692.67/40 m2， and 1.58 t/hm2， respectively. Compared with mung bean， lablab bean had the total K and biological production increased by 70.38 and 37.34%， while the total N， total P and plant number decreased by 4.36， 32.43， and 55.58， respectively. As the mung bean is a kind of compact crop with upright plant type， its seeding size was 50 cm × 17 cm. When the mung bean grew to 18 cm high， the plants with weak growth vigor were removed， leaving only the strong ones. Each hole had 1 plant. At last， the remaining plants of mung bean in each plot were 385.02 more than that of lablab bean. Effect of rotating green manure crops and returning straws to field on soil nutrient
As shown in Table 3， fertilization increased soil nutrients and organic matter content， and reduced the soil bulk density. Treatment IV had the lowest contents of soil total N， total P， total K and organic matter among all the treatments， which were respectively 0.032， 0.046， 0.681， and 2.50%， significantly lower than those in treatments I， II and III， and higher than those of the basic soil， but the difference was not significant.
The increase in soil nutrients and organic matter was related to the nutrient， total amount of organic carbon， type and application time of the added fertilizers. Treatment III had the highest contents of soil total N， total P， total K and organic matter among all the treatments， which were respectively 0.048， 0.053， 0.784 and 2.79%， significantly higher than those in treatments I， II， IV and basic soil.
The soil bulk density of all treatments was significantly lower than that of the basic soil. The minimum soil bulk density was found in treatment I， which was 1.52 g/cm3. The decrease of soil bulk density in treatment IV was smaller， which was lower than that in the basic soil but significantly higher than that in treatments I， II and III.
Treatment I， summer mung bean （chemical fertilizer + organic fertilizer）early rice （chemical fertilizer）； Treatment II， summer lablab bean （chemical fertilizer + organic fertilizer）early rice （chemical fertilizer）； Treatment III： early rice （chemical fertilizer + organic fertilizer）； Treatment IV： early rice （chemical fertilizer）. The Duncan test method is used； different letters in the same column indicate significant differences （P<0.05）.
Fang QIN et al. Effects of Rotating Summer Green Manure Crops and Straw Returning in Paddy Field on Rice Quality and Yield
Effect of rotating green manure crops and returning straws to field on nutrient and quality of early rice
N， P， K in early rice
As shown in Fig. 1， the difference in nitrogen nutrient level reached the extremely significant level between treatment IV and other treatments. The fertilizers for the test were easily soluble ones. In treatment IV， rice could directly absorb relatively more nitrogensoluble nutrients. However， in treatments I and II， which had the green manure crops returned to the field， and in treatment III， the nutrients could be absorbed by the crops after the transformation through microorganism decomposition， and the microbial activity process also consumed some nutrients. Therefore， the nitrogen nutrient in the rice of treatment IV was higher than that in the other treatments. There was no significant difference in the contents of P and K between treatment IV and treatment III， indicating that the application of organic fertilizer and chemical fertilizer and the application of only chemical fertilizer had no effect on the absorption of P and K nutrients in early rice. On the other hand， the differences in P and K contents reached the extremely significant level between treatments IV， III and other treatments. Early rice quality
As shown in Table 4， treatment III had the highest hulled rice ratio and head milled rice ratio， 79.5 and 37.70%， respectively， followed by Treatment I of 79.25 and 37.20%， respectively， and the lowest hulled rice ratio and head milled rice ratio were found in treatment IV， which were 79.05% and 34.95%， respectively. Treatment I， treatment II， and treatment III showed no significant difference in milled rice ratio， but significantly higher than that in Treatment IV.
The chalkiness degree and chalkiness ratio of treatment IV were 2.20 and 10.5%， respectively， which were significantly higher than those of treatment I， II and III. The chalkiness ratios of the rice of treatment I and II were not significantly different from each other， but significantly higher than those of treatment III， and extremely significantly lower than those in treatment IV.
As shown in Table 5， there was no significant difference in the lengthwidth ratio of rice between treatments. The values of lengthwidth ratio fell between 3.5 and 3.6. This may be due to the fact that the lengthwidth ratio of rice was related to the variety of rice， but not to the type of fertilizer.
The gel consistency of rice of Treatment I was significantly higher than that in treatments I， II and III， and the highest gel consistency of rice was 85， followed by that of treatment II， which was 82， and the lowest was found in treatment IV， which was only 78.
The difference in amylose content was not significant between treatment II and treatment IV， and the amylose contents were between 14.90 and 15.10%， which was significantly higher than that of treatments I and III. The amylose content of rice in Treatment I was significantly higher than that in treatment III.
The protein content in rice of treatment IV was significantly higher than that of treatment I， II and III， with a maximum of 8.75%， followed by that of treatment II， which was 8.30%， and the lowest was found in treatment III， which was only 7.8%.
Agronomic traits and field yield of early rice in mature stage
As shown in Table 5， plant height， number of effective panicles per plant， 1 000grain weight， theoretical yield， and actual yield of rice in treatment III were significantly higher than those of treatments I， II and III， and all were the highest， which were 113.20 cm， 14.07 panicles/plant， 32.58 g， 6 236.27 kg/hm2， 5 086.80 kg/hm2， respectively. The second highest plant height， number of effective panicles per plant， theoretical yield and actual yield of rice came to the rice of treatment I， respectively， 108.00 cm， 13.93 panicles/plant， 5 932.66 kg/hm2， and 4 974.0 kg/hm2. The rice of treatment IV had the lowest plant height， number of effective panicles per plant， number of grains per panicle， 1 000grain weight， theoretical yield， and actual yield， and compared with those of treatment III， the items showed decreases by 8.95， 21.82， 4.36， 11.45， 33.61 and 13.82%， respectively. Discussion and Conclusion
The large amount application of chemical fertilizers has caused soil compaction in paddy fields， and the content of organic matter is constantly declining. It is suggested to plant green manure crops during the winter time to improve the conditions of fields. Mung bean and lablab bean are the common green manure crops used in production. However， there are great differences in the growth characteristics and nutrient absorption of the 2 varieties. After ploughing the green manure crops into soil and adding application of organic fertilizer， soil organic matter， N， P， K contents show increases to different degrees and soil bulk density reduces. However， further study is needed to find out whether it is related to the application of compound fertilizer and organic fertilizer while planting green manure crops.
Green manure crops and organic fertilizers contain a large amount of organic matters， N， P， K and trace elements， which are important components of crop growth. After ploughing the green manure crops into paddy field， the rice has got improvement in rice quality， rice agronomic traits and yield， and it is consistent with the results of Wang et al. and Zhao et al.[20-21]that the combined application of green manure and mineral fertilizers can significantly increase soil organic matter content and increase the yield of early and late rice. According to the climatic conditions in Hainan， after rice harvesting， the rotation of ricegreen manure crops by using the spare time and space cannot only improve soil quality and soil environment in the paddy fields， but can also increase the quality and yield of crops， making it an important measure to achieve the sustainable development of rice production.
References
[1]LIAO YL， ZHENG SX， NIE J， et al. Effects of longterm application of fertilizer and rice straw on soil fertility and sustainability of a reddish paddy soils productivity[J]. Scientia Agricultura Sinica， 2009， 42（10）： 3541-3550.
[2]HUANG GQ， WANG XX， QIAN HY， et al. Negative impact of inorganic fertilizers application on agricultural environment and its countermeasures[J]. Ecology and Environment， 2004（4）： 656-660.
[3]DORAN JW， ZEISS MR. Soil health and sustainability： Managing the biotic component of soil quality[J]. Applied Soil Ecology， 2000， 15（1）： 3-11.
[4]YADAV RL， YADAV DS， SINGH RM， et al. Long term effects of inorganic fertilizer inputs on crop productivity in a ricewheat cropping system[J]. Nutrient Cycling in Agroecosystems， 1998， 51（3）： 193-200. [5]WANG JH， CAO K， ZHANG X， et al. Effect of green manure returning to rice field on the soil organic matter dynamics during rice growing stage[J]. Journal of Zhejiang Agricultural Sciences， 2010（3）： 614-616.
[6]FANG ZQ. Preliminary approach to organic agriculture[J]. Acta Agriculturae Shanghai， 2000，16（4）：1-5.
[7]TU SH. Roles and functions of chemical fertilizers in sustainable agriculture[J]. Southwest China Journal of Agricultural Sciences， 2003， 16 （Supplement）： 7-8.
[8]WANG DJ， LIN JH， SUN RJ， et al. Optimum nitrogen ratio for a high productive ricewheat system and its impact on the groundwater in the Taihu Lake area[J]. Acta Pedologica Sinica， 2003， 40（3）： 426-432.
[9]GAO XJ， HU XF， WANG SP， et al. Loss of nitrogen in rice field and its influence on water environment[J]. AgroEnvironmental Protection， 2001， 20（4）： 196-198， 205.
[10]WANG JH， CAO K， JIANG LN， et al. History， current status and guidelines about green manure development of Zhejiang Province[J]. Acta Agriculturae Zhejiangensis， 2009， 21（6）： 649-653.
[11]YANG ZP， GAO JS， ZHENG SX， et al. Effects of longterm winter plantinggreen manure on microbial properties and enzyme activities in reddish paddy soil[J]. Soils， 2011， 43（4）： 576-583.
[12]CAO WD， HUANG HX. Ideas on restoration and development of green manures in China[J]. Soils and Fertilizers Science in China， 2009 （4）： 1-3.
[13]JIAO B. China green fmanure[M]. Beijing： Agricultural Press， 1986.
[14]SI P， QIAO XS， HUANG XJ. The analysis of trace element contents among 18 kinds of common leguminous green manure of orchard[J]. Chinese Agricultural Science Bulletin， 2012， 28（4）： 157-162.
[15]HE LQ， XUE CH， ZHANG Y. Study on the main economic green manures in Hunan Province[J]. Hunan Agricultural Sciences， 2011（7）： 45-47， 51.
[16]WANG ZG， CHEN B， RAO XJ， et al. Study on absorption law of green manure[J]. Journal of Xinjiang Agricultural University， 2008， 31（2）47-50.
[17]LIU J， CAO WD， RONG XN， et al. Nutritional characteristics of Orychophragmus violaceus in North China[J]. Soils and Fertilizers Sciences in China， 2012 （1）： 78-82.
[18]ZHANG HZ， YANG SL， LIU DF， et al. Effects of cotton field cropping mustard green manure on Verticillium wilt[J]. Crops， 2004 （1）： 30.
[19]Hainan Provincial Bureau of Statistics. 2006 Hainan Statistical Yearbook[M]. Beijing： China Statistics Press， 2007：21-23.
[20]WANG YQ， ZHANG XM， LIU Y， et al. Effects of Chinese milk vetch on rice yield and soil nutrients[J]. Journal of Anhui Agricultural Sciences， 2004， 32（4）：699-700.
[21]ZHAO N， CAO WD， WANG YQ， et al. Effects of green manure milk vetch and fertilizer combined application on the growth and yield of rice in doublecropping rice areas[J]. Journal of Anhui Agricultural Sciences， 2010， 38（36）： 20668-20680.
Editor： Na LI Proofreader： Xinxiu ZHU