Assessing crop yield benefits from in situ rainwater harvesting through contour ridges in semi-arid Zimbabwe     

《Physics and Chemistry of the Earth》2013

Rainwater harvesting through modified contour ridges known as dead level contours has been practiced in Zimbabwe in the last two decades. Studies have shown marginal soil moisture retention benefits for using this technique while results on crop yield benefits are lacking. This paper presents results from a field study for assessing the impact of dead level contours on soil moisture and crop yield carried out from 2009 to 2011 within the Limpopo River Basin. The experiments were carried out on two study sites; one containing silt loam soil and another containing sandy soil. Three treatments constituting dead level contoured plots, non-contoured plots and plots with the traditional graded contours were used on each site. All the three treatments were planted with a maize crop and managed using conventional farming methods. Planting, weeding and fertiliser application in the three treatments were done at the same time. Crop monitoring was carried out on sub plots measuring 4 m by 4 m established in every treatment. The development of the crop was monitored until harvesting time with data on plant height, leaf moisture and crop yield being collected. An analysis of the data shows that in the site with silt loam soil more soil moisture accumulated after heavy rainfall in dead level contour plots compared to the control (no contours) and graded contour plots (P < 0.05). However the maize crop experienced an insignificantly (P > 0.05) higher yield in the dead level contoured treatment compared to the non-contoured treatment while a significantly (P < 0.05) higher yield was obtained in the dead level contoured treatment when compared with a graded contoured treatment. Different results were obtained from the site with sandy soil where there was no significant difference in soil moisture after a high rainfall event of 60 mm/day between dead level contour plots compared to the control and graded contour plots. The yield from the dead level contoured treatment and that from the graded contoured treatment were comparable and both not significantly (P > 0.05) higher than that from the non-contoured treatment. This suggests that adopting dead level contours as an in situ rainwater harvesting technique results in crop yield benefits in fields with soil type conditions that enable runoff generation but is not likely to have benefit in soils with low runoff generation.  相似文献   

作物生态位构建的模型及其进化惯量与动量的试验研究   总被引：14，自引：0，他引：14  

李文龙  李自珍 《地球科学进展》2002,17(3):446-451

物种生态位构建与其进化关系的研究属于生态位理论的新进展。以半干旱区作物为对象，系统地分析了生态位内涵的发展及生态位构建机理，研究了作物种与环境变化间协同进化的特殊规律，提出用作物生态位的适合程度测定其进化惯量，用现实生态位对其中心点的偏离程度测定进化动量，并建立了相应的数学模型，进行实例的计算分析，主要结果有：①作物种的生态位构建机制，从进化尺度上具体描述了作物通过其新陈代谢、活动与选择来确定自身的生态位（包括部分的产生、毁灭）。基于Hutchinson的生态位理论，建立了 n维超体积生态位的构建模式。②根据进化惯量与进化动量对生态位构建的作用，所进行的实例计算与分析的结果显示：自然选择与人工选择的压力具有异向性，生态位构建导致了进化惯量和进化动量不同的变化规律；作物的传统品种与新品种相比，具有较强的进化惯量与较弱的进化动量；在自然选择与人工选择双重作用下，作物生态位的构建机制有其特殊性。③在作物种进化与可变环境资源的耦合关系分析中，随着土壤养分的增加，作物进化惯量递增而进化动量递减，这从进化角度上揭示了土壤养分变化对作物生态位构建的影响。以上结果可为作物品种选育与农田人工调控提供理论依据。  相似文献   

秸秆覆盖下的夏玉米蒸散、水分利用效率和作物系数的变化   总被引：29，自引：0，他引：29  

张喜英  陈素英  裴冬  刘孟雨 《地理科学进展》2002,21(6):583-592

农业用水占华北水资源的70%以上,提高农业用水的效率对华北水资源安全具有重要意义。在节水农业研究中,利用农艺节水提高农田水分利用效率是节水农业的重要组成部分,其中减少农田无效棵间蒸发耗水和优化供水制度是主要的农艺节水措施。夏玉米是华北太行山山前平原的主要作物之一,一般在冬小麦收获前的5～7天套种在其中,以延长夏玉米的生育期。随着联合收割机的广泛应用,冬小麦收获后的秸秆直接覆盖夏玉米,对夏玉米的农田蒸散特别是苗期的蒸散产生影响;夏玉米生长在6～9月的雨季,一般年份降水能够满足夏玉米的需水要求,但夏季降水的分布变异较大,再加上近6年来的夏季干旱,使灌水对夏玉米的高产至关重要。为了提高夏玉米的农田水分利用效率,本研究的目的是建立秸秆覆盖下的夏玉米优化供水制度和研究秸秆覆盖对减少棵间无效耗水的影响及秸秆覆盖下的夏玉米作物系数的变化,为制定秸秆覆盖下的夏玉米优化供水制度提供依据。2年的实验结果显示,秸秆覆盖下的夏玉米产量在8000kg/ha,总蒸散量在390mm,水分利用效率在2.2kg/m3。干旱年份,夏玉米在灌四水的条件下产量最高,再增加灌水量,产量减少。水分利用效率随着灌水量的增加有所递减。  相似文献   

Determining crop acreage estimates for specific winter crops using shape attributes from sequential MODIS imagery     

《International Journal of Applied Earth Observation and Geoinformation》2013

There are increasing societal and plant industry demands for more accurate, objective and near real-time crop production information to meet both economic and food security concerns. The advent of the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite platform has augmented the capability of satellite-based applications to monitor large agricultural areas at acceptable pixel scale, cost and accuracy. Fitting parametric profiles to growing season vegetation index time series reduces the volume of data and provides simple quantitative parameters that relates to crop phenology (sowing date, flowering). In this study, we modelled various Gaussian profiles to time sequential MODIS enhanced vegetation index (EVI) images over winter crops in Queensland, Australia. Three simple Gaussian models were evaluated in their effectiveness to identify and classify various winter crop types and coverage at both pixel and regional scales across Queensland's main agricultural areas. Equal to or greater than 93% classification accuracies were obtained in determining crop acreage estimates at pixel scale for each of the Gaussian modelled approaches. Significant high to moderate correlations (log-linear transformation) were also obtained for determining total winter crop (R² = 0.93) areas as well as specific crop acreage for wheat (R² = 0.86) and barley (R² = 0.83). Conversely, it was much more difficult to predict chickpea acreage (R² ≤ 0.26), mainly due to very large uncertainties in survey data. The quantitative approach utilised here further had additional benefits of characterising crop phenology in terms of length of growing season and providing regression diagnostics of how well the fitted profiles matched the EVI time series. The Gaussian curve models utilised here are novel in application and therefore will enhance the use and adoption of remote sensing technologies in targeted agricultural application. With innate simplicity and accuracies comparable to other more convoluted multi-temporal approaches it is a good candidate in determining total and specific crop acreage estimates in future national and global food security frameworks.  相似文献   

Impact of feature selection on the accuracy and spatial uncertainty of per-field crop classification using Support Vector Machines     

《ISPRS Journal of Photogrammetry and Remote Sensing》2013

Crop mapping is one major component of agricultural resource monitoring using remote sensing. Yield or water demand modeling requires that both, the total surface that is cultivated and the accurate distribution of crops, respectively is known. Map quality is crucial and influences the model outputs. Although the use of multi-spectral time series data in crop mapping has been acknowledged, the potentially high dimensionality of the input data remains an issue. In this study Support Vector Machines (SVM) are used for crop classification in irrigated landscapes at the object-level. Input to the classifications is 71 multi-seasonal spectral and geostatistical features computed from RapidEye time series. The random forest (RF) feature importance score was used to select a subset of features that achieved optimal accuracies. The relationship between the hard result accuracy and the soft output from the SVM is investigated by employing two measures of uncertainty, the maximum a posteriori probability and the alpha quadratic entropy. Specifically the effect of feature selection on map uncertainty is investigated by looking at the soft outputs of the SVM, in addition to classical accuracy metrics. Overall the SVMs applied to the reduced feature subspaces that were composed of the most informative multi-seasonal features led to a clear increase in classification accuracy up to 4.3%, and to a significant decline in thematic uncertainty. SVM was shown to be affected by feature space size and could benefit from RF-based feature selection. Uncertainty measures from SVM are an informative source of information on the spatial distribution of error in the crop maps.  相似文献   

Projection Pursuit Evaluation Model: Optimizing Scheme of Crop Planning for Agricultural Sustainable Development and Soil Resources Utilization     

Yubao Wang  Pute Wu  Xining Zhao  Jiming Jin 《洁净——土壤、空气、水》2012,40(6):592-598

Planting structure influences the economic, social, and ecological benefits of crop farming as well as the use efficiency of water and arable land resources, and so crop planning (CP) benefits for agricultural sustainable development and soil resources utilization. The projection pursuit evaluation (PPE) model is put forward to solve the problem of selecting an optimizing scheme for CP by considering the indices of water‐saving and economic, social, and ecological benefits. The real‐coding‐based accelerating genetic algorithm (RAGA) is introduced to accelerate the calculation process. The model can translate multi‐indices into a single index by transforming high‐dimensional data to low‐dimensional space, which helps evaluate CP optimizing schemes. For example, the model is used to evaluate and select an optimal scheme of CP in the middle reaches of the Heihe mainstream basin in the arid area of northwest China. According to four criteria (high efficiency of resources use, economic rationality, social equity, and ecological security) 19 indices were chosen to evaluate 12 optimizing schemes of four kinds (economic‐benefit, food‐security, ecological‐benefit, and water‐saving programs) in 2006, 2020, and 2030. The result shows that, in the 3 years, the water‐saving program is always the optimized scheme in an arid region with water deficiency and fragile ecology. The evaluated results match up to the developmental conditions of crop farming in recent years. Moreover, the direction of the optimal projection could reflect the weight and orientation of indices objectively and accurately.  相似文献   

Quantitative analysis of agricultural land use change in China     

《Physics and Chemistry of the Earth》2015

This article reviews the potential impacts of climate change on land use change in China. Crop sown area is used as index to quantitatively analyze the temporal–spatial changes and the utilization of the agricultural land. A new concept is defined as potential multiple cropping index to reflect the potential sowing ability. The impacting mechanism, land use status and its surplus capacity are investigated as well. The main conclusions are as following;

• 1.During 1949–2010, the agricultural land was the greatest in amount in the middle of China, followed by that in the country’s eastern and western regions. The most rapid increase and decrease of agricultural land were observed in Xinjiang and North China respectively, Northwest China and South China is also changed rapid. The variation trend before 1980 differed significantly from that after 1980.
• 2.Agricultural land was affected by both natural and social factors, such as regional climate and environmental changes, population growth, economic development, and implementation of policies. In this paper, the effects of temperature and urbanization on the coverage of agriculture land are evaluated, and the results show that the urbanization can greatly affects the amount of agriculture land in South China, Northeast China, Xinjiang and Southwest China.
• 3.From 1980 to 2009, the extent of agricultural land use had increased as the surplus capacity had decreased. Still, large remaining potential space is available, but the future utilization of agricultural land should be carried out with scientific planning and management for the sustainable development.

  相似文献   

Wheat Residue Management Options Affect Crop Productivity,Weed Growth,and Soil Properties in Direct‐Seeded Fine Aromatic Rice          下载免费PDF全文

Abdul Khaliq  Amar Matloob  Adnan Hussain  Saddam Hussain  Farhena Aslam  Shahid Ibni Zamir  Muhammad Umer Chattha 《洁净——土壤、空气、水》2015,43(8):1259-1265

  相似文献   

Analyzing the agricultural transition in Mato Grosso, Brazil, using satellite-derived indices     

Damien Arvor  Margareth Meirelles  Vincent Dubreuil 《Applied geography (Sevenoaks, England)》2012,32(2):702-713

The Amazonian state of Mato Grosso is the main production area for soybeans in Brazil and contains 31.3% of the national production as of 2009. The rapid evolution of the agricultural systems in this area shows that the region is experiencing a rapid agricultural transition. In this paper, we broke down this transition process into three steps: crop expansion, agricultural intensification and ecological intensification. We used remote sensing products to develop and compute satellite-derived indices describing the main agricultural dynamics during the cropping years from 2000-2001 to 2006-2007. Our results indicated that Mato Grosso is continuing to expand its agricultural sector, with a 43% increase in the net cropped area during the study period. Although this expansion mainly occurred in the cerrado ecoregion until the early 2000s, the forest ecoregion is experiencing expansion at this time. We observed that 65% of the crop expansion in Mato Grosso from 2000 to 2006 occurred in this ecoregion. However, we did not identify this crop expansion as the major driver of deforestation in Mato Grosso because only 12.6% of the cleared areas were directly converted into croplands. Agricultural intensification also evolved rapidly, as the proportion of the net cropped area cultivated with double cropping systems harvesting two successive commercial crops (i.e., soybean and corn or soybean and cotton) increased from 6% to 30% during the study period. Finally, we found that ecological intensification occurred because the region’s farmers planted a non-commercial crop (i.e., millet or sorghum) after the soybean harvest to prevent soil erosion, improve soil quality, break pest cycles, maintain soil moisture and set the conditions for high-quality no-tillage operations. In 2006-2007, 62% of the net cropped area was permanently covered by crops during the entire rainy season. This practice allowed the farmers to diversify their production, as shown by the positive evolution of the Area Diversity Index. Future scholars can use the method proposed in this paper to improve their understanding of the forces driving the agricultural dynamics in Mato Grosso.  相似文献   

Coping with land scarcity. Farmers' changing land-use and management practices in two mountain watersheds of Nepal     

《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(1):21-31

In this study some light is shed on farmers' changing land-use and management practices in two mountain watersheds located in the Western Hills of Nepal. The study is based on a survey of 300 households, group discussion, interviews of key informants, and field observation in project and non-project watersheds conducted from April to September 1999. Confronted with shrinking landholding size, owing to a steadily growing population and scarcity of non-farming employment opportunities, farmers in both watersheds have gradually intensified land use and cultivated new crops to increase farm production and income. They are shifting from cereal crops to livestock husbandry, particularly along the road in the project watershed, and to vegetables and other cash crops in the accessible foothills of the non-project watershed. They have also adopted various structural and biological measures to control soil erosion, landslides, gully expansion and soil nutrient loss in order to maintain or enhance land productivity. The degree of adoption of the structural and biological measures is higher in the project watershed than in the non-project watershed. Contrary to the traditionally held belief of some researchers, population pressure on a finite land resource has brought about positive changes in land-use and management practices. Farmers have innovated and adopted different land management technologies to increase farm production as they are exposed to the risk of food insecurity because of shrinking landholding size and land degradation.  相似文献