Lijin ZHANG,Binjuan YANG,Guoqin HUANG,Hongjun CHEN,Kang LIU

Research Center on Ecological Science,Jiangxi Agricultural University/Agronomy Ecollege of Jiangxi Agricultural University,Nanchang 330045,China

Responsible editor:Xiaoxue WANG Responsible proofreader:Xiaoyan WU

Nitrogen is a necessary nutritional element for rice growth and plays a key role in yield formation of rice[1].The excessive fertilization of N fertilizer,and reduction of use ratio of N fertilizer would result in nitrogen excess,resource waste,environment pollution,and water eutrophication.According to statistics,the quantity of applied N fertilizer in one season averages 180 kg/hm2in paddy fields in China,which was 75%higher compared with global level[4-5].It is notable that green manure in winter is of high adaptability and grows fast,which is an important and excellent source of biological fertilizer[6-7].It contains 15% -20% organic matter and promotes mineralization and decomposition of organic matter and cycling and transformation of soil nutrients through ploughing[8-12].Leguminous green manure,in particular,is able to fix nitrogen from airs to supply the nutrients to crops[8]and provide carbon source and nutrients for soils[7],which proves effective in resolving the issue of insufficiency of chemical fertilizers and saving chemical fertilizer’s costs[13].Researches at home and abroad are more on the effects of preceding green manures on growth of succeeding crop and change of soil nutrients and the results consistently indicate that turning over of green manure would accelerate rice growth and yield increase,which is conductive to cycling and transformation of soil nutrients,improving soil fertility and crop’s absorption on nutrients[14-17].Shang[18]researched that the mixed application of organic and inorganic N fertilizers would increase rice yield and enhance use rate of N fertilizers by 7% -18%,compared with single application of chemical fertilizer.Furthermore,organic fertilizer would take place of N fertilizer to certain extent and increase rice yield,nitrogen uptake and nitrogen use ratio[19-21].Much research has conducted on rice growth and yield,soil biological and physicochemical property with green manures,at home and abroad.However,little attention is paid to comparisons of green manures and the effects of green manures on weeds on paddy fields.Hence,in order to explore the ecological effect of green manures in rice production,optimize planting mode of paddy fields,and develop crop planting in winter,the research chose milk vetch,oilseed rape,ryegrass and mixed green manures to investigate the effects on rice growth dynamics and weed growth and to provide references for selecting rice growth mode,improving soil fertility of paddy fields,and achieving agricultural sustainable development.

Materials and Methods

Introduction of test sites

The test was carried in winter of 2011 in a rice experimental field in Science Park of Jiangxi Agricultural University at 28°46′N and 115°55′E.The test site has a humid subtropical climate.Specifically,annual mean solar radiation is 4.79×1013J/hm2; annual mean sunshine hour is 1 852 h;annual mean temperature (≥0 ℃) reaches 6 450 ℃;frost-free period lasts 272 d;annual mean temperature is 17.6 ℃;annual precipitation totals 1 624 mm;annual temperature is in the range of 17.1-17.8 ℃.The test soils were adamic earth developed in Quaternary period,distributed in subtropical red earth areas.Before the test,surface soils(0-20 cm)contained organic carbon of 19.58 g/kg,total N of 2.17 g/kg,hydrolyzable nitrogen of 119.15 mg/kg,total P of 0.49 g/kg,available P of 41.28 mg/kg,and available K of 73.46 mg/kg,with pH pf 4.85 and C/N ratio of 9.04.

Test materials and design of the test

The test included 4 treatments,with 4 repetitions,as per randomized block design,and totaled 16 test plots,with every plot of 33 m2.Specifically,every test plot was divided with a cement-based ridge with height of 30 cm,and soil fertility in different plots kept the same.The test designed 4 treatments,as follows:the treatment with leguminous green manure,involving milk vetch-early rice-late rice (MV-RR),the treatment with gramineous green manure,involving ryegrass-early rice-late rice (RG-R-R),the treatment with Cruciferae,involving oilseed rape-early rice-late rice (RP-R-R),and the treatment with(milk vetch×oilseed rape× radish)-early rice-late rice (MSR-R).

The test materials were early rice Jinyou No.1176 and late rice Zhongyou No.161 in 2012,early rice Longping No.006 in 2013,milk vetch species Yujiangdayezi,ryegrass species JADE,oilseed rape Jinshuang No.11,and self-grown radish.Specifically,milk vetch was grown on September 25,and the rest crops were grown after harvesting of late rice in the end of October or early November,followed by yield measurement in middle April.All milk vetch,ryegrass and oilseed rape were harvested and ploughed in local field as green manure.Furthermore,the quantity of chemical fertilizer was applied as local method,involving urea (N 46%),calcium magnesium phosphate fertilizer(P2O512%),potassium chloride (K2O 60%) at 150,90 and 120 kg/hm2,accordingly.It is notable that N fertilizer was divided into base fertilizer,tillering fertilizer and earing fertilizer at 6:3:1;P fertilizer was applied once as base fertilizer;K fertilizer can be divided into tillering fertilizer and earing fertilizer with a proportion of 7:3.N and P base fertilizers were applied one day before transplanting,tillering fertilizer applied 5-7 d after transplanting,and earing fertilizer applied when ears grew to 1-2 cm.After earing,monopo-tassium phosphate was sprayed on leaves twice.Milk vetch was sown on September 25,2012 and the rest crops were sown in the end of October of early November.In the following year,all crops were ploughed on the fields 15 d before transplanting,and it is notable that rice was not returned to fields,except of rice stubbles.

Measured items and methods

Yield and yield componentsEarly rice was sampled in ripening stage and the rice field with an area of 33 m2should be measured in every test plot,followed by exploring yield components,including productive ear,the number of kernel per ear,setting percentage and thousand-seed weight.

Stem and tiller dynamicsBefore transplanting,30 rice plants were selected randomly to survey the number of tillers and tillering dynamics should be measured regularly after transplanting in the fixed sites.Specifically,rice in a row should be fixed and sampled in a test plot,and every row included 5 holes.From the 10th d after transplanting,the number of tiller should be surveyed every 7 d,until the number of tiller is fixed.

Measurement of nitrogen of plantsRice from 5 holes were sampled as per the number of average tiller per plot in tillering,jointing,booting,earing and ripening stages.The rice was divided into leaf,stem,sheath,and ear,which were loaded,and killed out at 105 ℃for 30 min.Subsequently,the materials were dried at 80 ℃to get a constant weight,followed by weighing.Then,the materials were converted into dry weight,followed by grinding,mixing and digesting with H2SO4-H2O2.Finally,the content of total N should be measured as per semi-micro Kjeldahl method[22],as follows:

Uptake of nitrogen (kg/hm2)=Dry matter weight of ground part×The rate of contained nitrogen;

Uptake of nitrogen (kg/hm2)=Dry matter weight of ground part in ripening stage×The rate of contained nitrogen;

Uptake of nitrogen in different stages (kg/hm2)=The quantity of absorbed nitrogen-The quantity of absorbed nitrogen in earlier stage.

Data processing

The test data were processed with Microsoft Excel 2010 and analyzed with SPSS13.0.

Results and Analysis

Effects of green manure rotation on yield and yield components of early rice

As shown in Table1,rice yields in four treatments all increased compared with the yields before testing,which was the most significant in the treatment with MV-R-R,followed by the treatments with MS-R-R(13.18%),RP-R-R (10.44% ) and RG-R-R.In terms of yield components,except of the number of productive ear and setting percentage of the treatment with RG-R-R,yield components of the rest treatments all performed higher compared with the treatment before testing.Moreover,the number of kernel per ear and thousand-seed weight reached significant differences (P ＜0.05).As shown in Table1,the yield of milk vetch was 6.61%,3.29%,and 0.78%higher compared with the treatments of RG-R-R,RP-R-R,and MS-RR; the number of productive ear,the number of kernel per ear,setting percentage and thousand-seed weight all reached the highest in the treatment of MV-R-R,and the lowest of the treatment with RG-R-R.Additionally,the change of thousand-seed weight was as follows:the treatment with MV-RR ＞the treatment with MS-R-R ＞the treatment with RP-R-R＞the treatment with RG-R-R,and the change of setting percentage was the treatment with MV-R-R＞the treatment with RP-R-R ＞the treatment with MS-R-R ＞the treatment with RG-R-R.

Effects of green manure rotation on growth dynamics of rice

As shown in Fig.1,the number of tiller was a major factor influencing rice yield.With the test condition the same,the more the number of productive tiller,the higher rice yield.From initial tillering stage to the peak of tillering stage,the faster tillering,the smaller differences among treatments.For example,the number of tillers in the treatments with MV-R-R and MS-R-R both kept higher compared with the treatments with RG-R-R and RP-R-R.Furthermore,the number of tiller of early rice reached the peak on the 40thd of transplanting,and the maximal number of tillers in tillering stage were as follows:the treatment with MS-RR ＞the treatment with MV-R-R ＞the treatment with RG-R-R＞the treatment with RP-R-R.Then,after the peak,the number of tiller started declining and kept stable on the 51thd of transplanting,when the number in the treatment with MV-R-R was the highest,and in the treatment with RP-R-R the lowest.Hence,the treatment with MV-R-R would guarantee the most productive tiller,which is conductive to increasing rice yield.

As shown in Fig.2,plant height of rice was growing upon growth stage,but insignificant differences were shown among treatments.It is notable that the treatment with MV-R-R had significant effects on plant height,which was higher compared with rest treatments,and the effect of the treatment with RP-R-R was the least.From 7 measurements,it can be concluded that plant heights from high to low were the treatment with MV-R-R ＞the treatment with MS-R-R＞the treatment with RG-R-R ＞the treatment with RPR-R.These incorporate that compared with other green manures,MV-R-R performed better in increasing plant height.

Differences of the rate of contained nitrogen and the content of absorbed nitrogen by plants in growth period

As shown in Table2,with green manure rotation,the rate of contained nitrogen was decreasing upon growth stage and the rate reached the highest in tillering stage and lowest in ripening stage.In tillering,booting,earing and ripening stages,the rate of contained nitrogen all achieved the highest in the treatment with MV-R-R,which were 9.68%,19.72%,6.23% and 8.66%higher compared with rest treatments.However,the rate of contained nitrogen showed different in different growth stages.For instance,in tillering and booting stages,the rates of contained nitrogen were the treatment with MV-R-R ＞the treatment with MSR-R ＞the treatment with RP-R-R ＞the treatment with RG-R-R,and in earing and ripening stages were the treatment with MV-R-R＞the treatment with RG-R-R＞the treatment with MS-R-R＞the treatment with RP-R-R,showing insignificant differences among treatments.

In addition,it can be concluded from Table2 that the quantity of absorbed nitrogen was increasing upon growth stage by green manure rotation,and reached the highest in ripening stage.In tillering,booting,earing and ripening stages,the absorbed nitrogen quantity accomplished the highest all in the treatment with MV-RR,and the lowest in the treatment with RP-R-R.In different growth stages,the absorbed nitrogen quantities were as follows:the treatment with MV-R-R ＞the treatment with RG-R-R＞the treatment with MS-R-R＞the treatment with RP-R-R,showing significant differences(P＜0.05).

The differences of absorbed nitrogen by green manure rotation

Table1 Effects of green manure rotation on yield and yield components of early rice

Table2 Differences of the rate of contained nitrogen and the content of absorbed nitrogen by plants in growth period

Table3 The differences of absorbed nitrogen by green manure rotation

As shown in Table3,in early tillering stage,the absorbed quantity of nitrogen in the treatment of MV-R-R was 37.14%higher compared with rest treatments,and the proportions was in the range of 39.57%-52.39%.Furthermore,the uptakes in the periods of tillering-booting,booting-earing,and earing-ripening were the same as follows:the treatment with MV-R-R ＞the treatment with MS-R-R＞the treatment with RP-R-R ＞the treatment with RGR-R; the uptake in the treatment with MV-R-R was 21.81%,68.73% and 286.5% higher compared with rest treatments and the proportions to total uptake were 23.37%-32.48%,17.49%-21.46%and 3.57%-12.47%accordingly.Additionally,it is obvious that both of nitrogen uptake and the proportions reached the lowest from booting to ripening stages and the highest before tillering.

Discussions

Researches available indicate that winter green manure would improve crop yield,quality and soil nutrient[23-24],and performs well in preventing soil and water losses,improving eco-environment and saving energy[25].On the other hand,much attention is paid to planting green manures in winter.For example,Liang et al.[26]explored the rotation mode of rice-ricegreen manure in vacant farmland in winter,grown with double cropping rice and the results indicate that the yield of early and late rice increased by 20.9%-73.4%,if ground parts were taken as green fodders and underground parts as stubble.Wang et al.[27]made investigation on returning of oilseed rape to farmlands and the results incorporate that the effects of increasing yield for hybrid rice performed better compared with control group,with significant differences.As for the research,the yield,the number of productive ear,the number of kernel per ear,setting percentage and thousand-seed weight reached the highest all in the treatment of MV-R-R and the lowest in the treatment of RG-R-R and the indices all increased compared with the indices before testing.Furthermore,yield increase of the treatment with MV-R-R performed the most significantly,followed by the treatments of MS-R-R,RP-R-R and RG-RR,which coincided with researches available.Besides,the research also indicated that the rate of contained nitrogen was decreasing by green manure rotation,and the rate achieved the highest in tillering stage and the lowest in ripening stage; the rate of contained nitrogen reached the highest all in the treatment of MV-R-R in tillering,booting,earing and ripening stages,which was 9.68%,19.72%,6.23% and 8.66% higher compared with rest treatments,with insignificant differences.In addition,the absorbed N quantity was growing upon growth stage by green manure rotation,and reached maximum in ripening stage.In tillering,booting,earing and ripening stages,the quantities all reached the highest in the treatment of MV-R-R and the lowest in the treatment of RPR-R; the absorbed N quantities in different growth stages were as follows:the treatment of MV-R-R ＞the treatment of RG-R-R＞the treatment of MSR-R＞the treatment of RP-R-R,showing significant differences; the quantities in the periods of tillering-booting,booting-earing,and earing-ripening were the treatment of MV-R-R ＞the treatment of MS-R-R＞the treatment of RP-R-R ＞the treatment of RG-R-R,and the quantity in the treatment of MV-R-R was 21.81%,68.73% and 286.5% higher compared with rest treatments.What’s more,the proportion of absorbed nitrogen by green manure rotation to total uptake was the least from earing to ripening stage and the highest before tillering.

Conclusions

The test results demonstrated that the treatment of MV-R-R would guarantee more productive tillers and high uptake of nitrogen and yield components,including productive ear,the number of kernel per ear,setting percentage and thousand-seed weight,all performed better compared with rest treatments,with huge potential in increasing yield.

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