施钙对不同种植模式下花生产量及生理特性的影响
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摘要
为探明不同种植模式下花生荚果产量及生理特性对钙肥的响应,在玉米‖花生3∶4间作与花生单作种植模式下,选用花育25为试验材料,分别设置4个施钙量处理(Ca0:0 kg/hm~2,Ca1:150 kg/hm~2,Ca2:300 kg/hm~2,Ca3:450 kg/hm~2),系统研究施钙对不同种植模式下花生叶片光合特性、荚果产量及其生理特性的影响。2 a研究结果表明:相同施钙条件下,间作降低了花生叶绿素相对含量(SPAD值)、净光合速率(Pn)、CAT、POD和SOD的活性,增加了花生叶片的MDA含量,荚果产量亦有不同程度降低。相同种植模式下,花生施钙处理较不施钙对照均有不同幅度的增产,且间作中间行花生的增产幅度高于单作花生的增产幅度;此外,间作和单作花生荚果产量随施钙量增加呈先升高后降低趋势,Ca2处理获得最高荚果产量;结果与从回归方程推算出的单作和间作中间行花生适宜施钙量基本相符。施钙亦增强了单作和间作花生叶片的光合生产能力,其净光合速率分别提高了3.1%～23.7%,8.9%～21.8%。与不施钙处理比较,Ca2处理提高了单作和间作花生叶片的叶绿素相对含量(SPAD值)、CAT、POD和SOD的活性,降低了花生叶片的MDA含量,利于提高间作花生对遮荫的适应能力,利于间作花生产量的提高。Ca2处理是本试验条件下单作和间作遮荫条件下适宜的施钙量处理。
In order to determine the response of peanut pod yield and physiological characteristics to calcium fertilizer under different planting patterns,a field experiment was designed with Huayu 25 as the test material,setting 2 planting patterns(3∶4 maize-peanut intercropping and peanut monoculture)and 4 calcium treatments(Ca0:0 kg/ha,Ca1:150 kg/ha,Ca2:300 kg/ha and Ca3:450 kg/ha). The effects of calcium application on photosynthetic characteristics of peanut leaves,pod yield and its physiological characteristics under different planting patterns were systematically analyzed. The results showed that under the same calcium application condition,the intercropping decreased the chlorophyll relative content(SPAD),net photosynthetic rate,CAT,POD and SOD activities of peanut,but increased the MDA content of peanut leaves,and the yield of pods also decreased in a certain degree. Under the same planting pattern,calcium treatments increased the pod yield of peanut in different degrees compared with the Ca0,and the peanut yield in middle rows was higher than that of monoculture peanut. In addition,with the increase of calcium application,the pod yield of intercropping and monoculture peanut increased first and then decreased,and the highest came from Ca2 treatment. Moreover,the experiment results were basically consistent with the appropriate calcium amount applied in middle rows of monoculture and intercropping peanuts derived from the regression equation. The calcium application enhanced the photosynthetic capacity of peanut leaves under monoculture and intercropping patterns,and their net photosynthetic rate(Pn)increased by 3.1%-23.7% and 8.9%-21.8%,respectively. The Ca2 treatment could increase the chlorophyll relative content(SPAD),and the activities of CAT,POD and SOD in the leaves of monoculture and intercropping peanut,and reduced the MDA content of leaves,which was beneficial to improving the adaptability of peanuts to shade and increasing the production of intercropping peanuts. The Ca2 treatment was the suitable calcium amount in monoculture and intercropping shading patterns of the experiment.
In order to determine the response of peanut pod yield and physiological characteristics to calcium fertilizer under different planting patterns,a field experiment was designed with Huayu 25 as the test material,setting 2 planting patterns(3∶4 maize-peanut intercropping and peanut monoculture)and 4 calcium treatments(Ca0:0 kg/ha,Ca1:150 kg/ha,Ca2:300 kg/ha and Ca3:450 kg/ha). The effects of calcium application on photosynthetic characteristics of peanut leaves,pod yield and its physiological characteristics under different planting patterns were systematically analyzed. The results showed that under the same calcium application condition,the intercropping decreased the chlorophyll relative content(SPAD),net photosynthetic rate,CAT,POD and SOD activities of peanut,but increased the MDA content of peanut leaves,and the yield of pods also decreased in a certain degree. Under the same planting pattern,calcium treatments increased the pod yield of peanut in different degrees compared with the Ca0,and the peanut yield in middle rows was higher than that of monoculture peanut. In addition,with the increase of calcium application,the pod yield of intercropping and monoculture peanut increased first and then decreased,and the highest came from Ca2 treatment. Moreover,the experiment results were basically consistent with the appropriate calcium amount applied in middle rows of monoculture and intercropping peanuts derived from the regression equation. The calcium application enhanced the photosynthetic capacity of peanut leaves under monoculture and intercropping patterns,and their net photosynthetic rate(Pn)increased by 3.1%-23.7% and 8.9%-21.8%,respectively. The Ca2 treatment could increase the chlorophyll relative content(SPAD),and the activities of CAT,POD and SOD in the leaves of monoculture and intercropping peanut,and reduced the MDA content of leaves,which was beneficial to improving the adaptability of peanuts to shade and increasing the production of intercropping peanuts. The Ca2 treatment was the suitable calcium amount in monoculture and intercropping shading patterns of the experiment.
引文
[1] 李隆.间套作强化农田生态系统服务功能的研究进展与应用展望[J].中国生态农业学报,2016,24(4):403-415.doi:10.13930/j.cnki.cjea.160061.Li L.Intercropping enhances agroecosystem services and functioning:Current knowledge and perspectives [J].Chinese Journal of Eco-Agriculture,2016,24(4):403-415.
[2] Dai C C,Chen Y,Wang X X,Li P D.Effects of intercropping of peanut with the medicinal plant Atractylodes lancea on soil microecology and peanut yield in subtropical China[J].Agroforestry Systems,2013,87(2):417-426.doi:10.1007/s10457-012-9563-z.
[3] Hage-Ahmed K,Krammer J,Steinkellner S.The intercropping partner affects arbuscular mycorrhizal fungi and Fusarium oxysporum f.sp.lycopersici interactions in tomato[J].Mycorrhiza,2013,23(7):543-550.doi:10.1007/s00572-013-0495-x.
[4] Tanwar S P S,Rao S S,Regar P L,Datt Shiv,Praveen-Kumar,Jodha B S,Santra P,Kumar Rajesh,Ram Rameshwar.Improving water and land use efficiency of fallow-wheat system in shallow lithic calciorthid soils of arid region:Introduction of bed planting and rainy season sorghum legume intercropping[J].Soil & Tillage Research,2014,138:44-55.doi:10.1016/j.still.2013.12.005.
[5] 左元梅,刘永秀,张福锁.玉米/花生混作改善花生铁营养对花生根瘤碳氮代谢及固氮的影响[J].生态学报,2004,24(11):2584-2590.Zuo Y M,Liu Y X,Zhang F S.Effects of improved Iron nutrition of peanut intercropped with maize on carbon and nitrogen metabol ism and nitrogen-f ixing of peanut nodule [J].Acta Ecologica Sinica,2004,24(11):2584-2590.
[6] 唐秀梅,钟瑞春,蒋菁,熊发前,贺梁琼,李忠,韩柱强,黄志鹏,唐荣华.木薯/花生间作对根际土壤微生态的影响[J].基因组学与应用生物学,2015,34(1):117-124.doi:10.13417/j.gab.034.000117.Tang X M,Zhong R C,Jiang J,Xiong F Q,He L Q,Li Z,Han Z Q,Huang Z P,Tang R H.The effect of cassava/peanut intercropping on microecology in rhizosphere Soil [J].Genomics and Applied Biology,2015,34(1):117-124.
[7] 孟维伟,高华鑫,张正,夏海勇,刘灵艳,郭峰,李宗新,万书波.不同玉米花生间作模式对系统产量及土地当量比的影响[J].山东农业科学,2016,48(12):32-36.doi:10.14083/j.issn.1001-4942.2016.12.007.Meng W W,Gao H X,Zhang Z,Xia H Y,Liu L Y,Guo F,Li Z X,Wan S B.Effects of different maize-peanut intercropping modes on system yield and land equivalent ratio [J].Shandong Agricultural Sciences,2016,48(12):32-36.
[8] 焦念元,李亚辉,刘领,齐付国,尹飞,宁堂原,李增嘉,付国占.隔根对玉米‖花生间作光合特性与间作优势的影响[J].植物生理学报,2016,52(6):886-894.doi:10.13592/j.cnki.ppj.2016.0097.Jiao N Y,Li Y H,Liu L,Qi F G,Yin F,Ning T Y,Li Z J,Fu G Z.Effects of root barrier on photosynthetic characteristics and intercropping advantage of maize‖peanut intercropping [J].Acta Phytophysiologica Sinica,2016,52(6):886-894.
[9] 杨顺国,郭贵敏,王仙萍.遮阴对花生生长发育及产量的影响[J].安徽农业科学,2015,43(35):30-31,50.doi:10.13989/j.cnki.0517-6611.2015.35.012.Yang S G,Guo G M,Wang X P.The influence of Shading on the peanut growth and yield [J].Journal of Anhui Agri Sci,2015,43(35):30-31,50.
[10] 唐秀梅,钟瑞春,揭红科,刘超,王泽平,韩柱强,蒋菁,贺梁琼,李忠,唐荣华.间作遮荫对花生光合作用及叶绿素荧光特性的影响[J].西南农业学报,2011,24(5):1703-1707.doi:10.16213/j.cnki.scjas.2011.05.Tang X M,Zhong R C,Jie H K,Liu C,Wang Z P,Han Z Q,Jiang J,He L Q,Li Z,Tang R H.Effect of shading on photosynthesis and chlorophyll fluorescence characteristic of peanut under different inter-row space in cassava-peanut intercropping [J].Southwest China Journal of Agricultural Sciences,2011,24(5):1703-1707.
[11] 赵秀芬,房增国.低钙胁迫对不同品种花生钙素吸收分配特性的影响[J].华北农学报,2017,32(2):194-199.doi:10.7668/hbnxb.2017.02.029.Zhao X F,Fang Z G.Effects of low Ca stress on the characteristics of calcium absorption and distribution of different peanut cultivars [J].Acta Agriculturae Boreali-Sinica,2017,32(2):194-199.
[12] 张佳蕾,郭峰,孟静静,于晓霞,杨莎,张思斌,耿耘,李新国,万书波.酸性土施用钙肥对花生产量和品质及相关代谢酶活性的影响[J].植物生态学报,2015,39(11):1101-1109.doi:10.17521/cjpe.2015.0107.Zhang J L,Guo F,Meng J J,Yu X X,Yang S,Zhang S B,Geng Y,Li X G,Wan S B.Effects of calcium fertilizer on yield,quality and related enzyme activities of peanut in acidic soil [J].Chinese Journal of Plant Ecology,2015,39(11):1101-1109.
[13] 顾学花,孙莲强,高波,孙奇泽,刘辰,张佳蕾,李向东.施钙对干旱胁迫下花生生理特性、产量和品质的影响[J].应用生态学报,2015,26(5):1433-1439.doi:10.13287/j.1001-9332.20150319.015.Gu X H,Sun L Q,Gao B,Sun J Z,Liu C,Zhang J L,Li X D.Effects of calcium fertilizer application on peanut growth,physiological characteristics,yield and quality under drought stress [J].Chinese Journal of Applied Ecology,2015,26(5):1433-1439.
[14] 王建国,张昊,李林,刘登望,万书波,王飞,卢山,郭峰.施钙与覆膜栽培对缺钙红壤花生钙素积累、分配及利用率的影响[J].华北农学报,2017,32(6):205-212.doi:10.7668/hbnxb.2017.06.030.Wang J G,Zhang H,Li L,Liu D W,Wan S B,Wang F,Lu S,Guo F.Effects of calcium application and plastic film mulching cultivation on accumulation,distribution and utilization efficiency of Ca in peanut in red soil under Ca deficiency [J].Acta Agriculturae Boreali-Sinica,2017,32(6):205-212.
[15] 周录英,李向东,王丽丽,汤笑,林英杰.钙肥不同用量对花生生理特性及产量和品质的影响[J].作物学报,2008,34(5):879-885.doi:10.3321/j.issn:0496-3490.2008.05.022.Zhou L Y,Li X D,Wang L L,Shang X,Lin Y J.Effects of different Ca applications on physiological characteristics,yield and quality in peanut [J].Acta Agronomica Sinica,2008,34(5):879-885.
[16] 王建国,张昊,李林,刘登望,万书波,王飞,卢山,郭峰.施钙与覆膜栽培对缺钙红壤花生干物质生产,熟相,产量构成及品质的影响[J].华北农学报,2018,33(4):131-138.doi:10.7668/hbnxb.2018.04.019.Wang J G,Zhang H,Li L,Liu D W,Wan S B,Wang F,Lu S,Guo F.Effects of calcium fertilizer and plastic film mulching cultivation on dry matter production,maturity performance,yield components and quality of peanut in red Soil under Ca deficiency [J].Acta Agriculturae Boreali-Sinica,2018,33(4):131-138.
[17] 张海平,单世华,蔡来龙,官德义,李毓,庄伟建.钙对花生植株生长和叶片活性氧防御系统的影响[J].中国油料作物学报,2004,26(3):33-36.doi:10.3321/j.issn:1007-9084.2004.03.008.Zhang H P,Shan S H,Cai L L,Guan D Y,Li Y,Zhuang W J.Effect of calcium on peanut plant growth and defence system of active oxygen in leaves [J].Chinese Journal of Oil Crop Sciences,2004,26(3):33-36.
[18] 李永胜,杜建军,赵荣芳,王浩,郑奕雄.花生中微量元素营养特性及研究进展[J].花生学报,2011,40(2):24-28.doi:10.14001/j.issn.1002-4093.2011.02.006.Li Y S,Du J J,Zhao R F,Wang H,Zheng Y X.Nutrition characteristics and research advancement of micronutrients on peanut [J].Journal of Peanut Science,2011,40(2):24-28.
[19] 张佳蕾,郭峰,孟静静,杨莎,耿耘,杨佃卿,李元高,张文生,李新国,万书波.钙肥对旱地花生生育后期生理特性和产量的影响[J].中国油料作物学报,2016,38(3):321-327.doi:10.7505/j.issn.1007-9084.2016.03.008.Zhang J L,Guo F,Meng J J,Yang S,Geng Y,Yang D Q,Li Y G,Zhang W S,Li X G,Wan S B.Effects of calcium fertilizer on physiological characteristics at late growth stage and pod yield of peanut on dryland [J].Chinese Journal of Oil Crop Sciences,2016,38(3):321-327.
[20] 熊路,曾红远,吴佳宝,邱柳,徐娟,刘登望,李林.花生钙素营养研究进展[J].中国农学通报,2012,28(12):13-17.doi:10.3969/j.issn.1000-6850.2012.12.003.Xiong L,Zeng H Y,Wu J B,Qiu L,Xu J,Liu D W,Li L.The advance on calcium nutrition research of peanut [J].Chinese Agricultural Science Bulletin,2012,28(12):13-17.
[21] Adams J F,Hartzog D L,Nelson D B.Supplemental calcium application on yield,grade,and seed quality of runner peanut[J].Agronomy Journal,1993,85(1):86-93.doi:10.2134/agronj1993.00021962008500010018x.
[2] Dai C C,Chen Y,Wang X X,Li P D.Effects of intercropping of peanut with the medicinal plant Atractylodes lancea on soil microecology and peanut yield in subtropical China[J].Agroforestry Systems,2013,87(2):417-426.doi:10.1007/s10457-012-9563-z.
[3] Hage-Ahmed K,Krammer J,Steinkellner S.The intercropping partner affects arbuscular mycorrhizal fungi and Fusarium oxysporum f.sp.lycopersici interactions in tomato[J].Mycorrhiza,2013,23(7):543-550.doi:10.1007/s00572-013-0495-x.
[4] Tanwar S P S,Rao S S,Regar P L,Datt Shiv,Praveen-Kumar,Jodha B S,Santra P,Kumar Rajesh,Ram Rameshwar.Improving water and land use efficiency of fallow-wheat system in shallow lithic calciorthid soils of arid region:Introduction of bed planting and rainy season sorghum legume intercropping[J].Soil & Tillage Research,2014,138:44-55.doi:10.1016/j.still.2013.12.005.
[5] 左元梅,刘永秀,张福锁.玉米/花生混作改善花生铁营养对花生根瘤碳氮代谢及固氮的影响[J].生态学报,2004,24(11):2584-2590.Zuo Y M,Liu Y X,Zhang F S.Effects of improved Iron nutrition of peanut intercropped with maize on carbon and nitrogen metabol ism and nitrogen-f ixing of peanut nodule [J].Acta Ecologica Sinica,2004,24(11):2584-2590.
[6] 唐秀梅,钟瑞春,蒋菁,熊发前,贺梁琼,李忠,韩柱强,黄志鹏,唐荣华.木薯/花生间作对根际土壤微生态的影响[J].基因组学与应用生物学,2015,34(1):117-124.doi:10.13417/j.gab.034.000117.Tang X M,Zhong R C,Jiang J,Xiong F Q,He L Q,Li Z,Han Z Q,Huang Z P,Tang R H.The effect of cassava/peanut intercropping on microecology in rhizosphere Soil [J].Genomics and Applied Biology,2015,34(1):117-124.
[7] 孟维伟,高华鑫,张正,夏海勇,刘灵艳,郭峰,李宗新,万书波.不同玉米花生间作模式对系统产量及土地当量比的影响[J].山东农业科学,2016,48(12):32-36.doi:10.14083/j.issn.1001-4942.2016.12.007.Meng W W,Gao H X,Zhang Z,Xia H Y,Liu L Y,Guo F,Li Z X,Wan S B.Effects of different maize-peanut intercropping modes on system yield and land equivalent ratio [J].Shandong Agricultural Sciences,2016,48(12):32-36.
[8] 焦念元,李亚辉,刘领,齐付国,尹飞,宁堂原,李增嘉,付国占.隔根对玉米‖花生间作光合特性与间作优势的影响[J].植物生理学报,2016,52(6):886-894.doi:10.13592/j.cnki.ppj.2016.0097.Jiao N Y,Li Y H,Liu L,Qi F G,Yin F,Ning T Y,Li Z J,Fu G Z.Effects of root barrier on photosynthetic characteristics and intercropping advantage of maize‖peanut intercropping [J].Acta Phytophysiologica Sinica,2016,52(6):886-894.
[9] 杨顺国,郭贵敏,王仙萍.遮阴对花生生长发育及产量的影响[J].安徽农业科学,2015,43(35):30-31,50.doi:10.13989/j.cnki.0517-6611.2015.35.012.Yang S G,Guo G M,Wang X P.The influence of Shading on the peanut growth and yield [J].Journal of Anhui Agri Sci,2015,43(35):30-31,50.
[10] 唐秀梅,钟瑞春,揭红科,刘超,王泽平,韩柱强,蒋菁,贺梁琼,李忠,唐荣华.间作遮荫对花生光合作用及叶绿素荧光特性的影响[J].西南农业学报,2011,24(5):1703-1707.doi:10.16213/j.cnki.scjas.2011.05.Tang X M,Zhong R C,Jie H K,Liu C,Wang Z P,Han Z Q,Jiang J,He L Q,Li Z,Tang R H.Effect of shading on photosynthesis and chlorophyll fluorescence characteristic of peanut under different inter-row space in cassava-peanut intercropping [J].Southwest China Journal of Agricultural Sciences,2011,24(5):1703-1707.
[11] 赵秀芬,房增国.低钙胁迫对不同品种花生钙素吸收分配特性的影响[J].华北农学报,2017,32(2):194-199.doi:10.7668/hbnxb.2017.02.029.Zhao X F,Fang Z G.Effects of low Ca stress on the characteristics of calcium absorption and distribution of different peanut cultivars [J].Acta Agriculturae Boreali-Sinica,2017,32(2):194-199.
[12] 张佳蕾,郭峰,孟静静,于晓霞,杨莎,张思斌,耿耘,李新国,万书波.酸性土施用钙肥对花生产量和品质及相关代谢酶活性的影响[J].植物生态学报,2015,39(11):1101-1109.doi:10.17521/cjpe.2015.0107.Zhang J L,Guo F,Meng J J,Yu X X,Yang S,Zhang S B,Geng Y,Li X G,Wan S B.Effects of calcium fertilizer on yield,quality and related enzyme activities of peanut in acidic soil [J].Chinese Journal of Plant Ecology,2015,39(11):1101-1109.
[13] 顾学花,孙莲强,高波,孙奇泽,刘辰,张佳蕾,李向东.施钙对干旱胁迫下花生生理特性、产量和品质的影响[J].应用生态学报,2015,26(5):1433-1439.doi:10.13287/j.1001-9332.20150319.015.Gu X H,Sun L Q,Gao B,Sun J Z,Liu C,Zhang J L,Li X D.Effects of calcium fertilizer application on peanut growth,physiological characteristics,yield and quality under drought stress [J].Chinese Journal of Applied Ecology,2015,26(5):1433-1439.
[14] 王建国,张昊,李林,刘登望,万书波,王飞,卢山,郭峰.施钙与覆膜栽培对缺钙红壤花生钙素积累、分配及利用率的影响[J].华北农学报,2017,32(6):205-212.doi:10.7668/hbnxb.2017.06.030.Wang J G,Zhang H,Li L,Liu D W,Wan S B,Wang F,Lu S,Guo F.Effects of calcium application and plastic film mulching cultivation on accumulation,distribution and utilization efficiency of Ca in peanut in red soil under Ca deficiency [J].Acta Agriculturae Boreali-Sinica,2017,32(6):205-212.
[15] 周录英,李向东,王丽丽,汤笑,林英杰.钙肥不同用量对花生生理特性及产量和品质的影响[J].作物学报,2008,34(5):879-885.doi:10.3321/j.issn:0496-3490.2008.05.022.Zhou L Y,Li X D,Wang L L,Shang X,Lin Y J.Effects of different Ca applications on physiological characteristics,yield and quality in peanut [J].Acta Agronomica Sinica,2008,34(5):879-885.
[16] 王建国,张昊,李林,刘登望,万书波,王飞,卢山,郭峰.施钙与覆膜栽培对缺钙红壤花生干物质生产,熟相,产量构成及品质的影响[J].华北农学报,2018,33(4):131-138.doi:10.7668/hbnxb.2018.04.019.Wang J G,Zhang H,Li L,Liu D W,Wan S B,Wang F,Lu S,Guo F.Effects of calcium fertilizer and plastic film mulching cultivation on dry matter production,maturity performance,yield components and quality of peanut in red Soil under Ca deficiency [J].Acta Agriculturae Boreali-Sinica,2018,33(4):131-138.
[17] 张海平,单世华,蔡来龙,官德义,李毓,庄伟建.钙对花生植株生长和叶片活性氧防御系统的影响[J].中国油料作物学报,2004,26(3):33-36.doi:10.3321/j.issn:1007-9084.2004.03.008.Zhang H P,Shan S H,Cai L L,Guan D Y,Li Y,Zhuang W J.Effect of calcium on peanut plant growth and defence system of active oxygen in leaves [J].Chinese Journal of Oil Crop Sciences,2004,26(3):33-36.
[18] 李永胜,杜建军,赵荣芳,王浩,郑奕雄.花生中微量元素营养特性及研究进展[J].花生学报,2011,40(2):24-28.doi:10.14001/j.issn.1002-4093.2011.02.006.Li Y S,Du J J,Zhao R F,Wang H,Zheng Y X.Nutrition characteristics and research advancement of micronutrients on peanut [J].Journal of Peanut Science,2011,40(2):24-28.
[19] 张佳蕾,郭峰,孟静静,杨莎,耿耘,杨佃卿,李元高,张文生,李新国,万书波.钙肥对旱地花生生育后期生理特性和产量的影响[J].中国油料作物学报,2016,38(3):321-327.doi:10.7505/j.issn.1007-9084.2016.03.008.Zhang J L,Guo F,Meng J J,Yang S,Geng Y,Yang D Q,Li Y G,Zhang W S,Li X G,Wan S B.Effects of calcium fertilizer on physiological characteristics at late growth stage and pod yield of peanut on dryland [J].Chinese Journal of Oil Crop Sciences,2016,38(3):321-327.
[20] 熊路,曾红远,吴佳宝,邱柳,徐娟,刘登望,李林.花生钙素营养研究进展[J].中国农学通报,2012,28(12):13-17.doi:10.3969/j.issn.1000-6850.2012.12.003.Xiong L,Zeng H Y,Wu J B,Qiu L,Xu J,Liu D W,Li L.The advance on calcium nutrition research of peanut [J].Chinese Agricultural Science Bulletin,2012,28(12):13-17.
[21] Adams J F,Hartzog D L,Nelson D B.Supplemental calcium application on yield,grade,and seed quality of runner peanut[J].Agronomy Journal,1993,85(1):86-93.doi:10.2134/agronj1993.00021962008500010018x.