Carbon dioxide exchange and the mechanism of environmental control in a farmland ecosystem in North China Plain

CO2 flux was measured continuously in a wheat and maize rotation system of North China Plain using the eddy covariance technique to study the characteristic of CO2 exchange and its response to key environmental factors. The results show that nighttime net ecosystem exchange (NEE) varied exponentially with soil temperature. The temperature sensitivities of the ecosystem (Q10) were 2.94 and 2.49 in years 2002-2003 and 2003-2004, respectively. The response of gross primary productivity (GPP) to photosynthetically active radiation (PAR) in the crop field can be expressed by a rectangular hyperbolic function. Average Amax andαfor maize were more than those for wheat. The values ofαincreased positively with leaf area index (LAI) of wheat. Diurnal variations of NEE were significant from March to May and from July to September, but not remarkable in other months. NEE, GPP and ecosystem respiration (Rec) showed significantly seasonal variations in the crop field. The highest mean daily CO2 uptake rate was -10.20 and -12.50 gC·m-2·d-1 in 2003 and 2004, for the maize field, respectively, and -8.19 and -9.50 gC·m-2·d-1 in 2003 and 2004 for the wheat field, respectively. The maximal CO2 uptake appeared in April or May for wheat and mid-August for maize. During the main growing seasons of winter wheat and summer maize, NEE was controlled by GPP which was chiefly influenced by PAR and LAI. Rec reached its annual maximum in July when Rec and GPP contributed to NEE equally. NEE was dominated by Rec in other months and temperature became a key factor controlling NEE. Total NEE for the wheat field was -77.6 and -152.2 gC·m-2·a-1 in years 2002-2003 and 2003-2004, respectively, and -120.1 and -165.6 gC·m-2·a-1 in 2003 and 2004 for the maize field, respectively. The cropland of North China Plain was a carbon sink, with annual -197.6 and -317.9 gC·m-2·a-1 in years 2002-2003 and 2003-2004, respectively. After considering the carbon in grains, the cropland became a carbon source, which was 340.5 and 107.5 gC·m-2·a-1 in years 2002-2003 and 2003-2004, respectively. Affected by climate and filed managements, inter-annual carbon exchange varied largely in the wheat and maize rotation system of North China Plain.     

SVM和ANN方法在铜川盛夏暴雨预报中的对比试验

分析了运城市1964年～2003年自然降水的变化趋势和季节分布特征,发现年降水量以14m m/10a速率快速递减,春、夏、秋季的降水处于减少的趋势中,冬季没有明显的变化趋势。年降水的不断减少及其在不同季节的分布特征对该市冬小麦生产十分不利。     

一种改进的土壤水分平衡模式

将美国学者,Ｊ．Ｔ．Ｒｉｔｃｈｉｅ等研制的作物生长模拟模式（ＣＥＲＥＳ－小麦模式）中的土壤水分平衡子模式应用于我国半干旱地区甘肃省西峰市农业气象试验站固定地块麦地土壤水分的模拟,对原有模式中潜在蒸散、地表蒸发和作物蒸腾加以修正,同时,为增强模式的应用性能,引入一种由作物生育期来估算作物根系最大深度和土壤各层相对根密度的方法。改进后的土壤水分平衡模式取得较好的应用效果,为旱地农田土壤水分管理提供了一     

冬小麦赤霉病流行程度长期预报模型

小麦赤霉病的发生流行程度主要由天气条件决定,而５００ｈＰａ大气环流因子是较好地表征天气形势和控制天气条件的物理量。利用最优化相关分析方法,分区挑选了与小麦赤霉病显著、稳定相关的５００ｈＰａ大气环流因子,在此基础上建立了冬小麦赤霉病流行程度长期预报环流模型。     

REGIONALIZATION FOR LARGE AREA CROP ESTIMATES BY REMOTE SENSING——A Case Study of Chinese Wheat

Ｔｈｅｃｒｏｐｅｓｔｉｍａｔｅｓｂｙｒｅｍｏｔｅｓｅｎｓｉｎｇ,ｄｅｖｅｌｏｐｉｎｇｑｕｉｃｋｌｙｉｎｒｅｃｅｎｔｄｅｃａｄｅｓ,ｉｓａｕｐｔｏｄａｔｅｔｅｃｈｎｉｑｕｅ．Ｓｏｍｅｓｙｓｔｅｍｓｏｆｃｒｏｐｅｓｔｉｍａｔｅｓｂｙｒｅｍｏｔｅｓｅｎ...     

冬小麦光合生产潜力数值模拟*

利用中国小麦生态实验资料建立了黄淮海地区冬小麦发育阶段模式和光合作用、呼吸作用等模式,由这些子模式连结成为一个可以模拟瞬时光合作用的,充分考虑了叶片空间分布特征的冬小麦光合生产潜力模式。运用该模式研究结果证明冬小麦光合生产潜力与抽穗前10天至成熟期辐射量相关性最大。黄淮海地区冬小麦光合生产潜力可达到800kg/亩～1000kg/亩,与牛文元计算结果相近。功率谱分析结果表明北京地区光合生产潜力存在3年～4年和9年～10年的变化周期。此外,文中还给出了CO₂升高后冬小麦光合生产潜力的可能变化情况。     

雨后麦田土壤湿度变化的诊断分析

通过分析研究冬小麦生育期，影响雨后麦田土壤湿度变化的主要因子，建立了雨后小水分渗透深度及不同土层的土壤湿度变化诊断模式。利用１９９１－１９９４年冬小麦不同时段的实测资料进行的对比分析表明，各模式的计算结果是较为满意的。     

喷灌条件下冬小麦田间水分运移数学模拟及灌溉模式的研究

为探讨节水高产喷灌模式,用数学模拟和田间试验相结合方法,研究了冬小麦在喷灌条件下田间水分运移规律。数学模拟结果与田间实测土壤含水率吻合良好。在此基础上模拟计算出不同喷灌定额下,消耗于作物蒸腾、表土蒸发和深层渗漏的水量,结果表明40～60mm喷灌定额下的农田水分无效消耗(表土蒸发+深层渗漏)最小,从而得出节水高产的冬小麦喷灌灌溉模式。经田间试验对比,获得相同产量条件下,本文提出的模式比现行喷灌模式节约灌溉水45%。     

不同硼水平与光照条件的交互作用对春小麦生长发育和结实的影响

用溶液培养法对硼和光照与小麦生长发育及结实率的关系进行了试验研究。结果表明：缺硼小麦株高和干物重下降；光照减弱，小麦干物质和株高明显降低。相反较高硼的供给可以增强小麦的抗逆性。缺硼严重影响小麦结实率，甚至导致小麦不结实；在相同供硼水平下，小麦硼积累量随光照减弱而降低。     

盐渍土冬小麦施用硅肥效应的试验研究

通过对盐渍土施用硅肥后土壤及作物中氮、磷、钾、硅等营养元素的分析，发现施硅肥后土壤中的碱解氮、速效磷、速效钾和有效硅含量都有明显提高，小麦茎杆和籽粒中的氮、磷、钾、硅的含量也比对照处理的含量高，小麦抗逆性、光合作用等都有明显改进，增产幅度达22．7％；最后简要说明了硅肥对盐渍土的改良作用。