The Importance of Root Dynamics in Cropping Systems Research

SUMMARY

This paper examines the nature and importance of the dynamics of crop root growth, particularly root turnover, and the application to different cropping systems. Methods now available to investigate root dynamics are summarized, and information being obtained is presented. Effects of physical, chemical, and biological factors on root dynamics are discussed. Growth of new roots and death of older roots can change the initial distribution in soil, allowing roots to exploit zones that have a more favorable nutrient or water supply. In herbaceous crops, the lifespan of roots appears to range between 16 and 36 per cent of the annual growth cycle. However, there is a paucity of data with which results can be compared. Localized enrichment of the water and nutrient supply enhances root turnover, and plants growing in soil well supplied with nutrients tend to have shorter-lived roots than those from nutrient limiting conditions. Both drought and excess water can induce premature root death, as can the resupply of water after drought. Turnover of roots contributes to carbon deposition in soil through their death and decay, as well as from the release of exudates from those roots during their lifetime. Improved understanding of root turnover is important for the development of more sustainable cropping systems. In particular, it could be used to improve the exploitation of N released from green manure as well as capturing N that has been leached below the rooting zone of staple crops. It is stressed that root turnover has more importance for plants with longer life cycles than in short season annual crops.     

Survey of Rice Cropping Systems in Kampong Chhnang Province,Cambodia

Although Cambodia might have achieved self-sufficiency and an exported surplus in rice production,its rice-based farming systems are widely associated with low productivity,low farmer income and rural poverty.The study is based on a questionnaire village survey in 14 communes containing 97 villages of Kampong Chhnang Province from March to June,2011.It analyzes the prevailing rice-based cropping systems and evaluates options for their improvement.Differences in cropping systems depend on the distance from the Tonle Sap water bodies.At distances greater than 10 km,transplanted wet-season rice cropping system with low productivity of about 1.6 t/hm 2 prevails.This deficiency can be primarily attributed to soils with high coarse sand fractions and low pH (< 4.0),use of ’late’ cultivars,and exclusive use of self-propagated seeds.To improve this cropping system,commercial ’medium’ cultivars help prevent crop failure by shortening the cultivation period by one month and complementation of wet-season rice with non-rice crops should be expanded.Areas adjacent (≤ 1 km) to the water bodies become inundated for up to seven months between July until January of each year.In this area,soils contain more fine sand,silt and clay,and their pH is higher (> 4.0).Farmers predominantly cultivate dry-season recession rice between January and April.Seventy-nine percent of the area is sown directly and harvested by combines.Adoption ratio of commercial rice seeds is 59% and yields average 3.2 t/hm 2.Introduction of the second dry-season rice between April and July may double annual yields in this rice cropping system.Besides upgrading other cultivation technologies,using seeds from commercial sources will improve yield and rice quality.Along with rice,farmers grow non-rice crops at different intensities ranging from single annual crops to intensive sequences at low yields.     

三个陆地棉水孔蛋白基因的克隆与表达分析

从陆地棉SSH-cDNA文库的测序结果中得到一条具有完整ORF的陆地棉水孔蛋白基因序列,将其命名为GhAQP2。以该基因编码的氨基酸序列为探针,在棉花EST数据库经同源搜索得到2个相似性较高的EST,利用RACE技术获得其全长cDNA序列,将其基因命名为GhAQP3和GhAQP4。基因结构分析发现GhAQP2和GhAQP3各有4个外显子,3个内含子;GhAQP4有3个外显子,2个内含子。生物信息分析表明3个基因编码蛋白均含有6个跨膜区,2个NPA结构域,其氨基酸序列具备MIP超家族典型的蛋白保守区序列特征。多序列比对发现3个基因的氨基酸序列与其他物种PIP2类水孔蛋白氨基酸序列具有很高的同源性。qRT-PCR分析表明,GhAQP2在纤维伸长后期优势表达,GhAQP3在下胚轴和子叶中高表达,GhAQP4在纤维伸长前期优势表达,推测3个基因在不同的组织中发挥作用。GhAQP2在20DPA优势表达,为研究该基因在纤维伸长向次生壁加厚期转化过程中的表达调控提供了重要信息。     

种植方式与密度对夏玉米碳、氮代谢和氮利用效率的影响

在67500,82500株/hm2密度水平下,以常规等行距种植方式为对照,比较分析不同缩行宽带种植方式（三行一带、四行一带、五行一带）对夏玉米碳、氮代谢与氮素利用效率的影响。结果表明,缩行宽带种植方式成熟期地上部总氮累积量、氮收获指数均高于对照等行距种植方式,其中三行一带、四行一带、五行一带种植方式地上部总氮累积量分别高于对照16．2％,16．9％,20．0％。籽粒产量较等行距种植方式均有不同程度增加,并达到显著水平。本研究中,成熟期地上部总氮量、叶片氮转运量与籽粒产量呈显著正相关,说明成熟期较高的地上部总氮积累、叶片高氮转运量可促进籽粒产量提高。而成熟期叶片C/N与籽粒产量呈显著负相关,各处理中,三行一带种植方式在低密度和高密度条件下成熟期叶片C/N均最低,而对照等行距种植方式值最高。     

不同栽培措施对连作马铃薯土壤真菌、真菌 性病害和产量的影响

通过连续3 a 利用不同栽培措施克服马铃薯连作障碍的定位试验,结果 表明,2009～2011 年
深翻处理的耕层土 壤真菌数量与连作相比降低29.59%～51.63%,菌剂处 理降低10.41%～71.96%,微肥处
理对改善土壤真菌数量效果不明显。深翻处理的马铃薯早疫病发病率比 连作降低10.00 个百分点到35.00
个百分点,菌剂处 理降低11.67 个百分点到38.33 个百分点,微肥处 理降低11.66 个百分点到26.67 个百分点;
深翻处理的马铃薯早疫病病情指数比 连作低20.34%～75.51%,菌剂处 理降低23.83%～64.50%,微肥处 理
降低20.34%～52.26%,并且差异达到显著或极显著水平。 深翻处理的马铃薯晚疫病发病 率比连作低15.00
个百分点到37.50 个百分点,菌 剂处理降低7.50 个百分点到36.67 个百分点,微 肥处理降低15.00 个百
分点到25.83 个百分点;深翻处理的马铃薯晚疫病病情指 数比连作低57.03%～80.44%,菌 剂处理降低
24.69%～66.67%,微 肥处理降低27.12%～50.76%,并且差异达到显著或极显著水平。深翻处理的马铃薯
比连作增产21.20%～29.99%,微肥处理 比连作增产6.14%～20.49%,菌剂处理比连作增产1.29%～13.42%,
并且差异达到显著或极显著水平。     

中国不同模式原料奶生产技术效率分析

本文基于调研数据,运用随机前沿分析方法测算了不同原料奶生产模式的经济效率、技术效率和配置效率,并利用Tobit模型对影响原料奶生产效率的因素进行分析。研究结果表明,中国不同原料奶生产模式经济效率普遍较低,特别是配置效率明显不足,这说明在不改变投入水平的条件下,奶牛养殖户(企业)可以通过改善投入要素组合提高产出水平。三种不同生产模式相比,牧场的效率最高,养殖小区次之,散户的最低。Tobit模型结果说明:农户个人特征、农户家庭或者企业特征、精粗饲料比对原奶生产效率有显著影响。     

钼、硒互作对2茬小白菜钼、硒含量及土壤钼、硒有效性的影响

通过盆栽试验研究钼、硒互作对2茬连作小白菜的产量和钼、硒含量以及土壤钼、硒有效性的影响。结果表明:钼、硒互作能提高第1茬小白菜的产量,对第2茬小白菜的产量影响不大;钼、硒互作能促进2茬小白菜对钼的吸收和累积,有效态钼在2茬小白菜种前土壤中均保持较高的含量,因此可以满足2茬小白菜富钼的需求;钼、硒互作同时促进2茬小白菜对硒的吸收,但是在第1茬小白菜采收后土壤中的水溶态硒和交换态硒的含量出现大幅降低,因此只能满足第1茬小白菜富硒的需求。     

丘陵双季稻区不同机插行距对水稻产量的影响

本研究针对丘陵双季稻区,以11个早晚稻品种为材料,采用大田随机区组试验,设置8寸与9寸2个机插行距,研究不同处理条件下的茎蘖动态、干物质量、产量和产量结构。结果表明:8寸行距的干物质量、收获指数和产量均比9寸行距的高;8寸行距的产量比9寸行距平均增产534.86 kg/hm2,平均增产率达8.37%。     

双季稻田冬种对土壤肥力的影响及相关性分析

通过大田试验,对比研究了"冬闲-双季稻"和不同的"冬种-双季稻"种植模式对土壤肥力的影响。结果表明:与冬闲-双季稻种植模式相比,冬种-双季稻种植模式的土壤容重均有一定程度的下降,其中冬种大麦模式的降低幅度最大;所有冬种-双季稻种植模式的土壤有机质、全氮、全磷、全钾及速效钾含量都有一定的增加,但冬种豌豆模式的土壤速效氮和有效磷含量降低了。综合全部指标来看,稻田冬季种植蚕豆模式增加土壤养分含量最明显。     

双季稻“三高一保”栽培技术

根据我们多年研究成果,并与现在高产栽培成熟技术组装配套,集成了一套以提高成穗率、结实率、籽粒充实度和充分挖掘品种优质潜力(保优质)为主攻目标的双季稻"三高一保"栽培技术模式,并获国家发明专利。本文介绍了其技术原理和应用效果,并详细介绍了其核心技术和配套技术。核心技术包括育秧肥培育壮秧、"三控"结合控蘖,配套技术包括稀播细管、宽行浅栽、适肥促发、补肥防衰、增氧灌溉等技术。