不同经营模式对马尾松人工林林下植被生物多样性的影响

为了对马尾松人工林在不同阶段不同的经营模式进行评价,本研究以湖南省祁阳县大江林场的马尾松人工林为研究对象,以林下草本植物的Margalef丰富度指数(R)、Simpson指数(D)、ShannonWiener指数(H′)与Pielou均匀度指数(E)为指标,研究无干扰模式、常规模式和近自然模式对马尾松人工林林下植被生物多样性的影响。结果表明:(1)在前期和中期,马尾松林下草本生物多样性指数(Margalef指数、Simpson指数、Shannon-Wiener指数和Pielou指数)的大小顺序为:无干扰模式近自然模式常规模式(P0.05);(2)在后期,马尾松林下4个生物多样性的大小顺序为:近自然模式常规模式无干扰模式(P0.05)。因此,在开展马尾松人工林的抚育经营活动时,应根据森林的发育阶段和经营目标,选择制定最适宜的经营方案。     

Research on the Urban Agriculture Planning Models of Metropolis:A Case Study of Chengdu

With the accelerating urbanization, ecological environment of the city has attracted increasing attention, so the resulting problems have become key research focuses in all countries. Against this background, urban agriculture has been applied as one of the effective approaches for relieving urbanization. From the perspective of industrial form of urban agriculture, planning models of urban agriculture were explored, industrial form and planning model of Chengdu urban agriculture were analyzed to forecast its development prospects. Multi-dimensional development, and sustainable development measures were given to guarantee the sustainable development of urban agriculture.     

Maize response to broadcast flaming at different growth stages: Effects on growth,yield and yield components

Weed management is a major constraint in organic crop production. Propane flaming could be an additional tool for weed control in organic maize (Zea mays L.) production. However, tolerance of maize to broadcast flaming must be determined first to optimize the use of propane. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, NE in 2008 and 2009 to determine maize response to five propane doses applied at three growth stages of V2 (2-leaf), V5 (5-leaf) and V7 (7-leaf). The propane doses tested were 0, 13, 24, 44 and 85 kg ha^?1. Flaming treatments were applied utilizing a custom built research flamer mounted on the back of a four-wheeler moving at a constant speed of 6.4 km h^?1. The response of maize to propane flaming was evaluated in terms of visual crop injury (1, 7, 14 and 28 days after treatment—DAT), effects on dry matter (14 DAT), yield components (plants m^?2, ears plant^?1, kernels cob^?1 and 1000-kernel weight) and grain yield. The response of different growth stages of maize to propane doses was described by log–logistic models. Overall, maize response to broadcast flaming varied among growth stages and propane doses. In general, maize at V5 was the most tolerant stage for broadcast flaming, whereas V2 stage was the most susceptible to flaming resulting in the highest visual crop injury ratings, dry matter reductions and the largest loss of yield and its components. At 28 DAT, the maximum visual crop injury rating of 7% was estimated for flaming done at V5 stage compared to significantly higher injuries of 43% and 12% for V2 and V7 growth stages, respectively. An arbitrarily assigned 2.5% yield reduction was evident with 33, 16 and 11 kg ha^?1 of propane for V5, V2 and V7 growth stages, respectively, suggesting that maize flamed at V5 stage can tolerate higher dose of propane for the same yield reduction compared to other growth stages. Moreover, the maximum yield reductions with the highest propane dose of 85 kg ha^?1 were 3% for V5, 11% for V7 and 17% for V2 stage. Based on these results, flaming has a potential to be used effectively in organic maize production when conducted properly at V5 stage. However, there are both benefits and concerns associated with the use of flame weeding. The preservation of the soil from erosion and the protection of the surface and underground water from chemical pollution can be seen as benefits, while the concerns include higher energy use, and the release of greenhouse gasses.     

基于逐步回归与BP神经网络的日光温室温湿度预测模型对比分析

为构建较准确的日光温室温湿度预测模型,于2011-2013年冬季(1月、2月、12月)天津市宝坻区开展温室内外环境监测试验,并建立3种天气类型(晴、多云、阴)下3个时段(0-8时、8-17时、17-23时)逐步回归与BP神经网络温室内温湿度预测模型。结果表明:1)温室内气温逐步回归模型9种情况下模拟值与实际值的绝对误差小于3℃的平均准确率Rate(≤3℃)为88%,平均均方根误差(RMSE)为2℃;BP神经网络模型9种情况下模拟值与实际值的绝对误差小于3℃的平均准确率Rate(≤3℃)为94%,平均均方根误差(RMSE)为1.6℃。应用BP神经网络建立的气温预测模型相对更为准确稳定。2) 相对湿度逐步回归模型9种情况下模拟值与实际值的绝对误差小于6%的平均准确率Rate(≤6%)为81%,平均均方根误差(RMSE)为5.7%;BP神经网络模型9种情况下模拟值与实际值的绝对误差小于6%的平均准确率Rate(≤6%)为80%,平均均方根误差(RMSE)为6.7%。两类模型均不适宜预测8-17时日光温室相对湿度,而17-23时与0-8时应用逐步回归建立的湿度预测模型相对更准确稳定。     

Current knowledge on Amaranthus spp.: research avenues for improved nutritional value and yield in leafy amaranths in sub-Saharan Africa

In the past 20 years, very little progress has been achieved in reducing food insecurity, child malnutrition and hunger in Africa. Under-nutrition and micronutrients deficiencies are widespread and affect mainly women and children. To address these problems, increased consumption of African leafy vegetables is promoted as sources of both micronutrients and bio-active compounds. Widely promoted African leafy vegetables include Amaranthus spp., a taxonomic group cultivated worldwide. Species of this genus are used as pseudo-cereals in Europe and America, and are mostly planted as vegetables in Africa. Amaranthus has been rediscovered as a promising food crop mainly due to its resistance to heat, drought, diseases and pests, and the high nutritional value of both seeds and leaves. Leaves are rich in proteins and micronutrients such as iron, calcium, zinc, vitamin C and vitamin A. All parts of the plant are used as medicine to heal many diseases in African communities. This paper focuses on leafy amaranths traditionally utilized on the continent. It briefly reviews the current knowledge on taxonomy, ecology, nutritional and nutraceutical value, production and cultivation systems, reproductive biology, genetic resources and breeding of amaranths. Species of interest include: A. blitum, A. caudatus, A. cruentus, A. dubius, A. hypochondriacus, A. spinosus, A. thunbergii, A. tricolor, and A. viridis. Research and development opportunities on nutritive and nutraceutical properties, production and commercialization, taxonomic evaluation and breeding perspectives were explored.     

Improving adaptation to drought stress in white pea bean (Phaseolus vulgaris L.): Genotypic effects on grain yield,yield components and pod harvest index

Common bean (Phaseolus vulgaris L.) is the most important food legume crop in Africa and Latin America where rainfall pattern is unpredictable. The objectives were to identify better yielding common bean lines with good canning quality under drought, and to identify traits that could be used as selection criteria for evaluating drought‐tolerant genotypes. In all, 35 advanced lines were developed through single seed descent and evaluated with a standard check under drought and irrigated conditions at two locations over 2 years in Ethiopia. Grain yield (GY), pod number per m², seed number per m² and seed weight decreased by 56%, 47%, 49% and 14%, respectively, under drought stress. Eight genotypes had better yield with good canning quality under drought compared to the check. Moderate to high proportion of genetic effects were observed under drought conditions for GY and yield components compared to genotype × environment effects. Significant positive correlations between GY and pod harvest index (PHI) in drought suggest that PHI could be used as an indirect selection criterion for common bean improvement.