中国苜蓿施肥产量效应的Meta分析

doi:10.12118/j.issn.1000–6060.2021.03.26

摘要/Abstract

摘要：

探究不同生境下苜蓿产量对施肥的响应,为苜蓿种植提供理论依据。以中国为研究区域,以不施肥苜蓿为对照,通过检索文献整合已发表的相关田间试验数据,采用整合分析法（Meta-analysis）,系统探究苜蓿产量对不同肥料的响应及与生境的关系。结果表明：（1）施肥均有显著增产效应（P<0.05）,增产率为15.4%~198.2%,其中尤以化肥与有机肥配施增产效果明显。（2）不同降雨条件下施肥效果迥异,降雨量<400 mm的干旱半干旱地区单施氮肥对苜蓿的增产作用较低,应注重磷肥、钾肥和有机肥的施用;降雨量400~800 mm的半湿润区适宜施用有机肥,其增产率可达70.1%（P<0.05）;降雨量>800 mm的湿润区氮磷钾配施的增产效应最高,为29.2%（P<0.05）。（3）土壤类型影响施肥的增产效应,肥力较低的土壤（栗钙土和黄绵土）单施有机肥可明显提高苜蓿产量;贫磷土壤（黑垆土）单施磷肥的增产率最高,为183.0%（P<0.05）。该研究可为不同降雨条件和不同土壤类型区苜蓿人工草地合理施肥措施的选择提供理论依据。

关键词: 苜蓿, 施肥措施, 产量, 整合分析法

Abstract:

This paper aims to explore optimal alfalfa fertilizer application in different environments. To this end, a meta-analysis was conducted to determine how fertilization practices affect the yield of alfalfa (Medicago sativa) and how this is impacted by fertilization management and the growth environment. A search of peer-reviewed publications was performed to collect data on the effects of fertilization on the yield of alfalfa grown in China. Specifically, field studies with and without fertilization treatment and with data on forage yield were obtained. A total of 78 publications containing 1031 observations from 61 sites were compiled into a dataset. The articles were selected from a corpus of studies published at home and abroad before May 2019. Key data, fertilizer types, annual precipitation, and soil types were abstracted from the selected articles, and the quantitative effects of fertilizer application on alfalfa yield were studied by meta-analysis. The analyses included a heterogeneity test, comprehensive effect size calculation, publication bias test, and influence factor analysis. Results showed that fertilization could improve alfalfa yields by 15.4%-198.2% because of increased soil nutrition. The combined application of organic and inorganic fertilizers had an obvious effect on increasing alfalfa yield. Application of a single organic fertilizer significantly increased alfalfa yields compared with that in the control group by 69.9% (P<0.05). The response of alfalfa yield to fertilization varied according to the growth environment. The application of phosphate, potassium, and organic fertilizers should be emphasized during the planting of alfalfa in arid and semi-arid areas. The combined application of organic and inorganic fertilizers is suitable for application to semi-arid areas, and the alfalfa yield increased by 50.5% (P<0.05). When potassium fertilizer was applied, the alfalfa yield in arid areas significantly increased compared that in the control group by 49.8% (P<0.05). The response of alfalfa yield to fertilization varied according to the soil type. Organic fertilizer was suitable for application to semi-humid areas, and alfalfa yields increased by 70.1% (P<0.05); this increase rate was much higher than that achieved by chemical fertilizer. Azophoska was suitable for application to humid areas, and alfalfa yields increased by 29.2% (P<0.05). Application of organic fertilizer to soils with low nutrient contents, such as chestnut and loessial soils, significantly improved alfalfa yields by 37.2% and 101.9% (P<0.05), respectively. Compared with other types of fertilizer, phosphate fertilizer increased the yield of alfalfa planted in dark loessial soils the most, and the alfalfa yield increased by 183.0% (P<0.05). The application of combined fertilizer was also suitable for saline fluvo-aquic soil, and alfalfa yields increased by 49.6%-50.9% (P<0.05). This increase rate was much higher than that obtained from single fertilization. The effect of chemical fertilizers on alfalfa yield was not significant when the crop was planted in lime concretion black soil. Our results suggest that fertilization enhances alfalfa yield. The combined application of organic and inorganic fertilizers is an optimal strategy for increasing alfalfa yield. This strategy provides a means for farmers to enhance the sustainability of alfalfa systems through fertilization management.

Key words: alfalfa, feritilizer application, yield, meta-analysis

才璐,王林林,罗珠珠,李玲玲,牛伊宁,蔡立群,谢军红. 中国苜蓿施肥产量效应的Meta分析[J]. 干旱区地理, 2021, 44(3): 838-848.

CAI Lu,WANG Linlin,LUO Zhuzhu,LI Lingling,NIU Yining,CAI Liqun,XIE Junhong. Meta-analysis of yield effects of fertilization on alfalfa in China[J]. Arid Land Geography, 2021, 44(3): 838-848.

图/表 8

表1

表2

Meta 分析收录文献的试验地点及施肥种类"

序号	试验地点	施肥种类	序号	试验地点	施肥种类
1	北京劳沃草业技术开发中心顺义加工基地	NP、NK、PK、NPK	33	内蒙古土默特左旗沟子板蒙草拉旱苜蓿试验基地	NP、NK、PK、NPK
2	甘肃农垦集团生地湾农场	N;NP、NK、PK、NPK	34	宁夏大学宁夏农垦农科教学合作人才培养基地	N、P、NP
3	甘肃农业大学兰州牧草试验站	P、M、F+M	35	宁夏固原市农业科学研究所头营试验基地	NP、NK、NPK
4	甘肃省定西市安定区凤翔镇丰禾村	N、NP	36	宁夏固原市原州区黄锋堡镇曹堡村	NP、NK、PK、NPK
5	甘肃省定西市李家堡镇麻子川村	N、NP、NK、PK、NPK;P、F+M	37	宁夏回族自治区吴忠市红寺堡区	NPK
6	甘肃省国营八一农场	NP、NK、PK、NPK	38	宁夏农垦局贺兰山茂盛草业有限公司核心试验站	N
7	甘肃省兰州大学黄土高原半干旱生态系统定位研究站	N、P、NP	39	宁夏中部干旱带盐池县四墩子农牧科技研究所基地	P、K、PK
8	甘肃省兰州大学庆阳黄土高原草地农业试验站	N	40	青海省大通县长宁乡王家庄村	N、P、K
9	甘肃省兰州市安宁区甘肃农业大学校园内	N、P、NP;N	41	山东省滨州市无棣县种畜场	P
10	甘肃省兰州市永登县中川镇何家梁村	P、NP	42	山东省农业科学院农营牧草科技示范基地内	NPK
11	甘肃省临夏县尹集镇	N、P、K、NP、NK、PK、NPK	43	山东省青岛农业大学胶州高新科技示范园	N、P、K、NP、NK、PK、NPK
12	甘肃省张掖市民乐县	M、F+M	44	山西省农业科学院农业环境与资源研究所盐碱地改良试验示范基地	NPK
13	贵州省贵阳市花溪区	P、K、PK	45	山西省山阴县试验地	M
14	贵州省威宁县雪山镇雪山村	N、P、K、NP、NK、PK、NPK	46	山西省太原市	N、NP、NPK
15	河北农业大学标本院内	N、F+M	47	陕西省西北农林科技大学农作一站	N、P、K、NP、NK、PK、NPK
16	河北省沧州地区南皮县乌马营镇徐郎中村	P	48	陕西省榆林市神木县六道沟小流域	N、P、NP
17	河北省沧州市农林科学院	P、K、PK	49	陕西省长武县十里铺村旱塬	P、F+M
18	河北省沧州市农林科学院前营试验站	NP、NK、PK、NPK	50	四川省西昌市交凉山州畜牧所牧草地	PK
19	河南农业大学科教园区	NPK、F+M	51	四川省西昌市小庙乡	P、K、PK
20	黑龙江省哈尔滨市双城区五家镇	NPK	52	西藏农牧科学院畜牧兽医研究所	PK
21	吉林省松原市长岭县三十号乡	M、NPK	53	新疆北疆浅埋式滴灌苜蓿高效节水示范区	N、NP
22	吉林省长春市吉林农业大学实验区	NP、NK、PK、NPK	54	新疆呼图壁县农业部旱生牧草种子基地	NP、NK、PK、NPK
23	内蒙古赤峰综合实验站牧草实验示范基地	N、P、K、NP、NK、PK、NPK	55	新疆库尔勒地区大华公司中心农场草料种植基地	N、P、K、NP、NK、PK、NPK
24	内蒙古鄂尔多斯毛乌素沙地	N、NPK;N	56	新疆奎屯农124团和131团	N、P、PK、NPK
25	内蒙古鄂尔多斯市鄂托克前旗	NP、NK、PK、NPK	57	新疆农业大学三坪农场牧草与草坪试验站	PK、NPK;NP、NK、PK、NPK
26	内蒙古鄂尔多斯市准格尔旗十二连城乡东不拉村	NP、NK、PK、NPK	58	新疆石河子大学实验站牧草试验田	P
27	内蒙古海拉尔市谢尔塔拉镇呼伦贝尔国家野外站	N	59	新疆石河子垦区的142团	N、P、K、NP、NK、PK、NPK
28	内蒙古呼和浩特市和林格尔县盛乐园区	NP、NK、PK、NPK	60	新疆石河子农业示范园区试验田	P
29	内蒙古呼和浩特市土默特左旗沙尔沁乡	NP、NK、PK、NPK	61	新疆天山畜牧昌吉生物工程有限责任公司榆树沟基地	N、P、K
30	内蒙古科尔沁沙地实验区林西县	M	62	中国科学院植物研究所多伦恢复生态学试验站试验示范基地	N、P
31	内蒙古民族大学试验农场	P	63	中国农业科学院兰州畜牧研究所实验基地	NP、NK、PK、NPK
32	内蒙古农业大学海流图现代农牧业科技园区	NPK	64	中国农业科学院廊坊实验基地	P

表2

图1

图2

图3

图4

图5

图6

参考文献 41

[1]	李玉山. 苜蓿生产力动态及其水分生态环境效应[J]. 土壤学报, 2002,39(3):404-411.
	[ Li Yushan. Productivity dynamic of alfalfa and its effects on water eco-environment[J]. Acta Pedologica Sinica, 2002,39(3):404-411. ]
[2]	韩清芳, 周芳, 贾珺, 等. 施肥对不同品种苜蓿生产力及土壤肥力的影响[J]. 植物营养与肥料学报, 2009,15(6):1413-1418.
	[ Han Qingfang, Zhou Fang, Jia Jun, et al. Effect of fertilization on productivity different producing performance alfalfa varieties and soil fertility[J]. Plant Nutrition and Fertilizer Science, 2009,15(6):1413-1418. ]
[3]	臧逸飞, 郝明德, 张丽琼, 等. 26年长期施肥对土壤微生物量碳、氮及土壤呼吸的影响[J]. 生态学报, 2015,35(5):1445-1451.
	[ Zang Yifei, Hao Mingde, Zhang Liqiong, et al. Effects of wheat cultivation and fertilization on soil microbial biomass carbon, soil microbial biomass nitrogen and soil basal respiration in 26 years[J]. Acta Ecologica Sinica, 2015,35(5):1445-1451. ]
[4]	樊军, 郝明德, 王永功. 旱地长期轮作施肥对土壤肥力影响的定位研究[J]. 水土保持研究, 2003,10(1):31-36.
	[ Fan Jun, Hao Mingde, Wang Yonggong. Effects of rotations and fertilizations on soil fertility on upland of Loess Plateau[J]. Research of Soil and Water Conservation, 2003,10(1):31-36. ]
[5]	魏志标, 柏兆海, 马林, 等. 中国苜蓿、黑麦草和燕麦草产量差及影响因素[J]. 中国农业科学, 2018,51(3):507-522.
	[ Wei Zhibiao, Bai Zhaohai, Ma Lin, et al. Yield gap of alfalfa, ryegrass and oat grass and their influence factors in China[J]. Scientia Agricultura Sinica, 2018,51(3):507-522. ]
[6]	李新乐, 穆怀彬, 侯向阳, 等. 水、磷对紫花苜蓿产量及水肥利用效率的影响[J]. 植物营养与肥料学报, 2014,20(5):1161-1167.
	[ Li Xinle, Mu Huaibin, Hou Xiangyang, et al. Effects of irrigation and phosphorus fertilization on alfalfa yield and water and fertilizer use efficiency[J]. Journal of Plant Nutrition and Fertilizer, 2014,20(5):1161-1167. ]
[7]	Berg W K, Cunningham S M, Brouder S M, et al. Influence of phosphorus and potassium on alfalfa yield and yield components[J]. Crop Science, 2005,45(1):297-304.
[8]	Simons R G, Grant C A, Bailey L D. Effect of fertilizer placement on yield of established alfalfa stands[J]. Canadian Journal of Plant Science, 1995,75(4):883-887. doi: 10.4141/cjps95-146
[9]	Malhi S S, Zentner R P, Heier K. Effectiveness of alfalfa in reducing fertilizer N input for optimum forage yield, protein concentration, returns and energy performance of bromegrass-alfalfa mixtures[J]. Nutrient Cycling in Agroecosystems, 2002,62(3):219-227. doi: 10.1023/A:1021229824357
[10]	潘玲, 魏臻武, 武自念, 等. 施肥和播种量对扬州地区苜蓿生长特性和产草量的影响[J]. 草地学报, 2012,20(6):1099-1104.
	[ Pan Ling, Wei Zhenwu, Wu Zinian, et al. Effects of fertilizers and sowing rates on growth characteristics and forage yields of alfalfa in Yangzhou region[J]. Acta Agrestia Sinica, 2012,20(6):1099-1104. ]
[11]	赵云, 谢开云, 杨秀芳, 等. 氮磷钾配比施肥对敖汉苜蓿产量和品质的影响[J]. 草业科学, 2013,30(5):723-727.
	[ Zhao Yun, Xie Kaiyun, Yang Xiufang, et al. Effects of nitrogen, phosphorus and potassium ratio fertilizer on the the yield and quality of Aohan alfafa[J]. Pratacultural Science, 2013,30(5):723-727. ]
[12]	秦景秀, 郝兴明, 张颖, 等. 气候变化和人类活动对干旱区植被生产力的影响[J]. 干旱区地理, 2020,43(1):117-125.
	[ Qin Jingxiu, Hao Xingming, Zhang Ying, et al. Effects of climate change and human activities on vegetation productivity in arid areas[J]. Arid Land Geography, 2020,43(1):117-125. ]
[13]	Han Z, Walter M D, Drinkwater L E. N₂O emissions from grain cropping systems: A meta-analysis of the impacts of fertilizer-based and ecologically-based nutrient management strategies[J]. Nutrient Cycling in Agroecosystems, 2017,107(3):335-355. doi: 10.1007/s10705-017-9836-z
[14]	Yu Y Y, Neil C T, Gong Y H, et al. Benefits and limitations to straw- and plastic-film mulch on maize yield and water use efficiency: A meta-analysis across hydrothermal gradients[J]. European Journal of Agronomy, 2018,99:138-147. doi: 10.1016/j.eja.2018.07.005
[15]	Wang L L, Li Q, Coulter J A, et al. Winter wheat yield and water use efficiency response to organic fertilization in northern China: A meta-analysis[J]. Agricultural Water Management, 2020,229(2):1-15.
[16]	才璐, 王林林, 罗珠珠, 等. 中国苜蓿产量及水分利用效率对种植年限响应的Meta分析[J]. 草业学报, 2020,29(6):27-38.
	[ Cai Lu, Wang Linlin, Luo Zhuzhu, et al. Meta-analysis of alfalfa yield and WUE response to growing ages in China[J]. Acta Prataculturae Sinica, 2020,29(6):27-38. ]
[17]	Nils B, Michael S, Maria L C, et al. Biochar, soil and land-use interactions that reduce nitrate leaching and N₂O emissions: A meta-analysis[J]. Science of the Total Environment, 2019,651:2354-2364. doi: 10.1016/j.scitotenv.2018.10.060
[18]	Wang L L, Coulter J A, Palta J A, et al. Mulching-induced changes in tuber yield and nitrogen use efficiency in potato in China: A meta-analysis[J]. Agronomy, 2019,9(12):793-808. doi: 10.3390/agronomy9120793
[19]	Daniel G, Kate M S. Long-term effects of mineral fertilizers on soil microorganisms: A review[J]. Soil Biology and Biochemistry, 2014,75:54-63. doi: 10.1016/j.soilbio.2014.03.023
[20]	Burda B U, O’Connor E A, Webber E M, et at. Estimating data from figures with a web-based program: Considerations for a systematic review[J]. Research Synjournal Methods, 2017,8(3):258-262.
[21]	谢德体, 蒋先军, 王昌全. 土壤肥料学[M]. 第2版. 北京: 中国林业出版社, 2015.
	[ Xie Deti, Jiang Xianjun, Wang Changquan. Soil fertilizer[M]. 2nd ed. Beijing: China Forestry Press, 2015. ]
[22]	杨恒山, 曹敏建, 范富, 等. 紫花苜蓿生长年限对土壤理化性状的影响[J]. 中国草地学报, 2006,28(6):29-32.
	[ Yang Hengshan, Cao Minjian, Fan Fu, et al. Effects of the number of growth years of alfalfa on the physical and chemical properties of soil[J]. Chinese Journal of Grassland, 2006,28(6):29-32. ]
[23]	韩清芳, 周芳, 贾珺, 等. 施肥对不同品种苜蓿生产力及土壤肥力的影响[J]. 植物营养与肥料学报, 2009,15(6):1413-1418.
	[ Han Qingfang, Zhou Fang, Jia Jun, et al. Effect of fertilization on productivity different producing performance alfalfa varieties and soil fertility[J]. Plant Nutrition and Fertilizer Science, 2009,15(6):1413-1418. ]
[24]	李丽, 李宁, 盛建东, 等. 施氮量和种植密度对紫花苜蓿生长及种子产量的影响[J]. 草地学报, 2012,20(1):54-57.
	[ Li Li, Li Ning, Sheng Jiandong, et al. Effects of nitrogen fertilizer and planting density on alfalfa growth and seed yield[J]. Acta Agrestia Sinica, 2012,20(1):54-57. ]
[25]	王丹, 何峰, 谢开云, 等. 施氮对紫花苜蓿生长和土壤氮含量的影响[J]. 草业科学, 2013,30(10):1569-1574.
	[ Wang Dan, He Feng, Xie Kaiyun, et al. Effects of nitrogen application on alfalfa plant growth and soil nitrogen content[J]. Pratacultural Science, 2013,30(10):1569-1574. ]
[26]	齐敏兴, 刘晓静, 张晓磊, 等. 不同磷水平对紫花苜蓿光合作用和根瘤固氮特性的影响[J]. 草地学报, 2013,21(3):512-516.
	[ Qi Minxing, Liu Xiaojing, Zhang Xiaolei, et al. Effects of different phosphorus levels on photosynjournal and root nodule nitrogen fixing characteristic of alfalfa[J]. Acta Agrestia Sinica, 2013,21(3):512-516. ]
[27]	侯湃, 刘自学, 刘艺杉, 等. 北京平原区紫花苜蓿施肥组合试验[J]. 草业科学, 2014,31(1):144-149.
	[ Hou Pai, Liu Zixue, Liu Yishan, et al. Screening of fertilization combination for alfalfa in Beijing area[J]. Pratacultural Science, 2014,31(1):144-149. ]
[28]	胡诚, 曹志平, 罗艳蕊, 等. 长期施用生物有机肥对土壤肥力及微生物生物量碳的影响[J]. 中国生态农业学报, 2007,15(3):48-51.
	[ Hu Cheng, Cao Zhiping, Luo Yanrui, et al. Effect of long-term application of microorganismic compost or vermicompost on soil fertility and microbial biomasscarbon[J]. Chinese Journal of Eco-Agriculture, 2007,15(3):48-51. ]
[29]	邹慧, 高光耀, 朱斌, 等. 黄土高原恢复草地土壤水分对降水响应及模拟[J]. 干旱区研究, 2020,37(4):890-898.
	[ Zou Hui, Gao Guangyao, Zhu Bin, et al. Modeling of the response of soil moisture to precipitation in the restored grasslands of the Loess Plateau[J]. Arid Zone Research, 2020,37(4):890-898. ]
[30]	Jafari Z, Matinkhah S H, Mosaddeghi M R, et al. Evaluation of the efficiency of irrigation methods on the growth and survival of tree seedlings in an arid climate[J]. Journal of Arid Land, 2020,12(3):495-507. doi: 10.1007/s40333-020-0012-y
[31]	Li Y S, Huang M B. Pasture yield and soil water depletion of continuous growing alfalfa in the Loess Plateau of China[J]. Agriculture Ecosystems & Environment, 2008,124(1):24-32. doi: 10.1016/j.agee.2007.08.007
[32]	曾昭海, 胡跃高, 陈文新, 等. 共生固氮在农牧业上的作用及影响因素研究进展[J]. 中国生态农业学报, 2006,14(4):21-24.
	[ Zeng Zhaohai, Hu Yaogao, Chen Wenxin, et al. Review on studies on the important role of symbiotic nitrogen fixation in agriculture and livestock production and the factors affecting its efficiency[J]. Chinese Journal of Eco-Agriculture, 2006,14(4):21-24. ]
[33]	贾丙瑞, 周广胜, 王风玉, 等. 土壤微生物与根系呼吸作用影响因子分析[J]. 应用生态学报, 2005,16(8):1547-1552.
	[ Jia Bingrui, Zhou Guangsheng, Wang Fengyu, et al. Affecting factors of soil microorganism and root respiration[J]. Chinese Journal of Applied Ecology, 2005,16(8):1547-1552. ]
[34]	李典鹏, 姚美思, 孙涛, 等. 干旱区盐湖沿岸土壤呼吸特征及其影响因素[J]. 干旱区地理, 2020,43(3):761-769.
	[ Li Dianpeng, Yao Meisi, Sun Tao, et al. Characteristic of soil respiration and its influencing factors on the coastal of saline lake in arid region[J]. Arid Land Geography, 2020,43(3):761-769. ]
[35]	王义东, 王辉民, 马泽清, 等. 土壤呼吸对降雨响应的研究进展[J]. 植物生态学报, 2010,34(5):601-610. doi: 10.3773/j.issn.1005-264x.2010.05.014
	[ Wang Yidong, Wang Huimin, Ma Zeqing, et al. Review of response mechanism of soil respiration to rainfall[J]. Chinese Journal of Plant Ecology, 2010,34(5):601-610. ] doi: 10.3773/j.issn.1005-264x.2010.05.014
[36]	韩姣姣, 段旭, 赵洋毅. 金沙江干热河谷不同植被坡面土壤水分时空分布特征[J]. 干旱区地理, 2019,42(1):121-129.
	[ Han Jiaojiao, Duan Xu, Zhao Yangyi. Spatial and temporal variability of soil moisture on slope land of different vegetation of dry-hot valley in Jinsha River[J]. Arid Land Geography, 2019,42(1):121-129. ]
[37]	郑然, 郑宝林. 冀北栗钙土区耕层土壤有机质和全氮的空间变异特征[J]. 干旱区资源与环境, 2018,32(5):123-129.
	[ Zheng Ran, Zheng Baolin. Spatial variability of soil organic matter and total nitrogen in chestnut soil region of northern Hebei[J]. Journal of Arid Land Resources and Environment, 2018,32(5):123-129. ]
[38]	宁川川, 王建武, 蔡昆争. 有机肥对土壤肥力和土壤环境质量的影响研究进展[J]. 生态环境学报, 2016,25(1):175-181.
	[ Ning Chuanchuan, Wang Jianwu, Cai Kunzheng. The effects of organic fertilizers on soil fertility and soil environmental quality: A review[J]. Ecology and Environmental Sciences, 2016,25(1):175-181. ]
[39]	孙怀文. 砂姜黑土的水分特性及其与土壤易旱的关系[J]. 土壤学报, 1993,30(4):423-431.
	[ Sun Huaiwen. Moisture characters of calcic concretion black soil and their relationship with soil drought[J]. Acta Pedologica Sinica, 1993,30(4):423-431. ]
[40]	王道中, 花可可, 郭志彬. 长期施肥对砂姜黑土作物产量及土壤物理性质的影响[J]. 中国农业科学, 2015,48(23):4781-4789.
	[ Wang Daozhong, Hua Keke, Guo Zhibin. Effects of long-term fertilization on crop yield and soil physical properties in lime concretion black soil[J]. Scientia Agricultura Sinica, 2015,48(23):4781-4789. ]
[41]	李玮, 孔令聪, 张存岭, 等. 长期不同施肥模式下砂姜黑土的固碳效应分析[J]. 土壤学报, 2015,52(4):943-949.
	[ Li Wei, Kong Lingcong, Zhang Cunling, et al. Effect of long-term fertilization on carbon sequestration in lime concretion black soil relative to fertilization pattern[J]. Acta Pedologica Sinica, 2015,52(4):943-949. ]