灌溉对孕穗期冬小麦农田温度的影响

灌溉是抵御和减轻冬小麦晚霜冻危害的有效措施之一。针对黄淮地区2010年4月的一次强降温过程,通过郑州农业气象观测站的灌溉防霜试验,对比分析了冬小麦孕穗期田间空气温度和土壤温度特征。结果表明:在外界环境温度下降时,灌溉可以提高田间最低气温0.1～0.6℃,增温效应主要集中在地上5cm处,灌溉可减少气温≤0℃的持续时间1～2h;对土壤温度的影响随着深度而存在差异,0cm土壤温度以增加为主,5～20cm土壤以降温效应为主;灌溉减小了气温和0～5cm土壤温度的变异系数和平均相对变率,而增大了10～20cm土壤温度的变异系数和相对变率;灌溉引起的温度差异只在15和20cm土壤处比较显著,其余各层温度差异并不明显。     

浙江省植被覆盖时空动态及其与生态气候指标的关系

对1982-2006年间浙江省归一化植被指数（NDVI）的时空变化及其与关键生态气候指标（生物热量指数和生物干湿度指数）的相关性进行了研究.结果表明：研究期间,浙江省植被覆盖总体呈缓慢下降趋势,NDVI显著减少的地区约占全省面积的30.71%;生态气候指标与滞后一年的NDVI显著相关,其中生物热量指数与NDVI呈显著负相关,生物干湿度指数与NDVI呈显著正相关,说明研究区湿度的增加可促进植被长势,而过高的热量对植被生长则具有明显的抑制作用.     

Comparison of APRI and Hydrus-2D models to simulate soil water dynamics in a vineyard under alternate partial root zone drip irrigation

Alternate partial root zone irrigation (APRI) is a new water-saving irrigation technique. It can reduce irrigation water and transpiration without reduction in crop yield, thus increase water and nutrient use efficiency. Understanding of soil moisture distribution and dynamic under the alternate partial root zone drip irrigation (APDI) can help to develop the efficient irrigation schemes. In this paper, a two-dimensional (2D) root water uptake model was proposed based on soil water dynamic and root distribution of grape vine, and a function of soil evaporation related to soil water content was defined under the APDI. Then the soil water dynamic model of APDI (APRI-model) was developed based on the 2D root water uptake model and soil evaporation function combined with average measured soil moisture content at 0–10 cm soil layer. Soil water dynamic in APDI was respectively simulated by Hydrus-2D model and APRI-model. The simulated soil water contents by two models were compared with the measured value. The results showed that the values of root-mean-square-error (RMSE) range from 0.01 to 0.022 cm³/cm³ for APRI-model, and from 0.012 to 0.031 cm³/cm³ for Hydrus-2D model. The average relative error between the simulated and measured soil water content is about 10% for APRI-model, and from 11% to 29% for Hydrus-2D model, indicating that two models perform well in simulating soil moisture dynamic under the APDI, but the APRI-model is more suitable for modeling the soil water dynamic in the arid region with greater soil evaporation and uneven root distribution.     

Cancer immunotherapy, mathematical modeling and optimal control

Clinical immunologists, among other problems, routinely face a question: what is the best time and dose for a certain therapeutic agent to be administered to the patient in order to decrease/eradicate the pathological condition? In cancer immunotherapies the therapeutic agent is something able to elicit an immune response against cancer. The immune response has its own dynamics that depends on the immunogenicity of the therapeutic agent and on the duration of the immune response. The question then is "how can we decide when and how much of the drug to inject so to have a prolonged and effective immune response to the cancer?". This question can be addressed in mathematical terms in two stages: first one construct a mathematical model describing the cancer-immune interaction and secondly one applies the theory of optimal control to determine when and to which extent to stimulate the immune system by means of an immunotherapeutic agent administered in discrete variable doses within the therapeutic period. The solution of this mathematical problem is described and discussed in this article. We show that the method employed can be applied to find the optimal protocol in a variety of clinical problems where the kinetics of the drug or treatment and its influence on the physiologic/pathologic functions have been described by a system of ordinary differential equations.     

Selenium in Aquatic Birds From Central California

ABSTRACT After mostly freshwater replaced agricultural drainage water used for wetland management in 1985, Selenium (Se) concentrations in 3 wintering waterfowl species and black-necked stilts (Himantopus mexicanus) from the North and South Grasslands of central California, USA, declined in the years from 1986 to 1988 and 1989 to 1994. However, Se concentrations were still above the threshold for potential reproductive impairment and exceeded background levels for some species. Consequently, we measured Se concentrations in aquatic birds in 2005 after long-term use (20 yr) of predominately freshwater for wetland management in the Grasslands. As in 1986–1994, Se concentrations in 2005 were higher for birds from the South Grasslands, which historically received more undiluted drainage water compared with the North Grasslands. Liver Se concentrations for stilts from the South Grasslands were at levels associated with potential reproductive impairment. All species from the South Grasslands, as well as mallards (Anas platyrhynchos), northern pintails (A. acuta), and American coots (Fulica americana) from the North Grasslands, were above species-specific background levels. From 1994 to 2005, Se levels in some aquatic birds stabilized above background levels likely indicating long-term cycling within the Grasslands. We recommend Se-contaminated drainage water (≥ 2 ppb Se) not be used for management or allowed as an input into arid wetlands throughout the western United States.     

调亏灌水和分蘖干扰对冬小麦生长的补偿效应

为探索抑制个体功能的生长冗余以实现群体性能优化并挖掘作物高产潜力的途径,通过桶栽试验,选择分蘖能力中等的小偃22号和分蘖能力较强的郑麦7698,对比研究2种灌水模式（全生育期充分灌水和分生育期调亏灌水）和3种分蘖干扰（从拔节期开始去除所有小分蘖,仅保留主茎和1个大分蘖;抽穗期去除所有无效分蘖;以不作任何干扰为对照）,来模拟不同水分供应和不可预测干扰对冬小麦生理生长、产量和水分利用效率的补偿机制.结果表明： 2个冬小麦品种均存在生长冗余.与小偃22号相比,郑麦7698有效分蘖数较高,但穗部性状较差.调亏灌水和抽穗期去除无效分蘖均可减少生长冗余,弱化竞争能力,改变源 库关系,提高资源分配.但冗余消除过度（拔节期干扰）则会破坏植株固有的根冠平衡和功能结构,导致生长的不足补偿.与对照相比,调亏灌水联合抽穗期去除无效分蘖可在时空尺度上充分开发和利用作物自身调控潜力实现补偿生长,在不显著影响籽粒产量的同时可提高水分利用效率20.4%～25.4%,是适宜的减冗增效措施.     

Effects of cyclic irrigation on water and nitrogen mass balances in a paddy field

Cyclic irrigation is considered an effective water management practice for reducing pollutant loads from a paddy-field district. The objective of this study was to clarify the effects of cyclic irrigation on mass balance in paddy plots. At the study site, cyclic irrigation with a high cyclic irrigation ratio (% reused water in irrigation water) was conducted from late April to late June. We found a complementary relationship between the volume of irrigation water and rainfall, which together totaled about 1400-1600 mm during the irrigation period each year. We concluded that a cyclic irrigation system that enables the paddy-field district to use a high cyclic irrigation ratio may lead to more efficient use of rainfall for crop irrigation. Nitrogen concentrations in both irrigation water and ponded water tended to be higher during the cyclic irrigation period than during the lake water irrigation period. Nitrogen input from irrigated water accounted for about 8-16% of the total input of nitrogen. It is suggested that fertilizer application of nitrogen can be reduced by its return through cyclic irrigation.     

秸秆还田条件下灌水模式对冬小麦产量和水肥利用效率的影响

于2008-2010年,在山西省临汾市尧都区半干旱、半湿润季风气候区,通过大田试验研究了玉米秸秆连续还田条件下灌水模式对冬小麦籽粒产量、干物质转移及水肥利用效率的影响.结果表明:浇越冬水可促进小麦分蘖;浇拔节水可提高分蘖成穗率,增加成穗数;浇孕穗水可促进穗部干物质积累,提高千粒重.浇2水时,推迟第2次浇水时期使叶片干物质转移量和穗粒数增加;浇2水比浇l水的肥料表观利用率高,可促进穗部干物质积累.越冬水灌水量和总灌水量对分蘖、穗部干物质积累的影响较小;拔节期或孕穗期增加灌水量则更有利于养分吸收及干物质积累与转移,提高籽粒水分利用效率,产量构成因素协调,增产效果明显.因此,确保越冬水可实现稳产,在越冬水基础上,拔节期增量灌水(900 m3·hm-2)可满足冬小麦中后期生长发育的需要,提高籽粒水分利用效率,实现节水高产栽培.     

An Investigation of the Soil Property Changes and Heavy Metal Accumulation in Relation to Long-term Wastewater Irrigation in the Semi-arid Region of Iran

Concentrations and spatial distribution of Zn, Cu, Cd, and Pb along two landscapes including a wastewater-irrigated area and a control area were determined to assess the impact of long-term wastewater irrigation and landscape properties on heavy metal contamination. Some disturbed and undisturbed soil samples were taken from soil trenches and soil cores, located on three main landscape positions (upper slope, midslope, and lower slope) in northwestern Iran. The investigation showed that the mean concentration of the heavy metals followed the order Zn > Cu > Pb > Cd in the wastewater-irrigated soil and Pb > Zn > Cu > Cd in the control soils. On average, compared to similar positions in the control region, the wastewater-irrigated regions contained 3.0 (midslope) to 4.9 (lower slope), 2.7 (midslope) to 4.6 (lower slope), 3.3 (upper slope) to 4.1 (lower slope), and 1.7 (upper slope) to 2.6 (lower slope) times higher amounts of Zn, Cu, Cd, and Pb, respectively. Significant positive relationships (P < 0.05) were recorded between the heavy metals concentration with <0.002 mm particle-size fraction and organic matter content, the fractions linked to runoff and soil erosion. It is believed that the two soil fractions play a crucial role in the distribution of the metals along the wastewater-irrigated landscape. Despite the significant increase of heavy metals (P < 0.05) in the wastewater-irrigated soils compared with control soils, the concentration of all evaluated metals was below the maximum accepted limits (Zn < 300 mg/kg, Cu < 100 mg/kg, Cd < 5 mg/kg, and Pb < 100 mg/kg), and grouped as “not-enriched” to “moderately-enriched” categories regarding the topsoil enrichment index. Overall, the lower slope was shown to be more contaminated with the heavy metals compared to the other positions.     

Impact of Rotylenchulus reniformis on Cotton Yield as Affected by Soil Texture and Irrigation

The effects of soil type, irrigation, and population density of Rotylenchulus reniformis on cotton were evaluated in a two-year microplot experiment. Six soil types, Fuquay sand, Norfolk sandy loam, Portsmouth loamy sand, Muck, Cecil sandy loam, and Cecil sandy clay, were arranged in randomized complete blocks with five replications. Each block had numerous plots previously inoculated with R. reniformis and two or more noninoculated microplots per soil type, one half of which were irrigated in each replicate for a total of 240 plots. Greatest cotton lint yields were achieved in the Muck, Norfolk sandy loam, and Portsmouth loamy sand soils. Cotton yield in the Portsmouth loamy sand did not differ from the Muck soil which averaged the greatest lint yield per plot of all soil types. Cotton yield was negatively related to R. reniformis PI (initial population density) in all soil types except for the Cecil sandy clay which had the highest clay content. Supplemental irrigation increased yields in the higher yielding Muck, Norfolk sandy loam, and Portsmouth loamy sand soils compared to the lower yielding Cecil sandy clay, Cecil sandy loam, and Fuquay sand soils. The Portsmouth sandy loam was among the highest yielding soils, and also supported the greatest R. reniformis population density. Cotton lint yield was affected more by R. reniformis Pi with irrigation in the Portsmouth loamy sand soil with a greater influence of Pi on lint yield in irrigated plots than other soils. A significant first degree PI × irrigation interaction for this soil type confirms this observation.