保护性农业的研究现状、进展与展望

保护性农业是相对较新的一个概念,它强调了农业的可持续发展。保护性农业的三个重要要素包括少耕或免耕、永久地面覆盖和轮作。从生态学的角度,保护性农业对土壤生态系统的有益效应包括改善土壤系统的化学、物理及生物特性。然而,目前保护性农业在全世界的推广应用范围还很有限,特别是在发展中国家更是如此。在发展中国家,农民主要把秸秆用于煮饭和取暖的燃料,同时还用作家畜饲草。因此,我们面临的主要问题是研究和解决把秸秆用于土壤保护和提高土壤肥力与其它用途的矛盾。本文较系统地评述了世界保护性农业的研究现状、主要进展及展望。还讨论了实行保护性农业中存在的问题及注意事项。     

冬小麦水肥生产函数的Jensen模型和人工神经网络模型及其应用

作物水肥生产函数研究是非充分灌溉理论的重要内容,也是提高农田水、肥利用效率的基础.在作物水分生产函数Jensen模型的基础上,引入肥料因子构造了水肥生产函数的Jensen模型;同时构造了作物水肥生产函数的人工神经网络模型.利用北京地区冬小麦田间试验资料对以上2个模型进行了分析,表明以上模型均可用于描述水分、肥料等因素对作物产量的影响,进而可对作物产量进行预测,且模型都具备一定的精度.     

Impacts of Recent Climate Change on Dry-Land Crop Water Consumption in the Northern Agro-Pastoral Transitional Zone of China

Climate change has substantially impacted crop growth and development in the northern agro-pastoral transitional zone. Examination of the response of crop water consumption to climate change may provide a guide for adapting local agricultural production and ecological construction to new realities. The water consumption of three local crops (wheat, naked oats, and potatoes) is examined for Wuchuan County in the northern agro-pastoral transitional zone of China using meteorological data from 1960 to 2007 and soil moisture data from 1983 to 2007. The relationships between climate change and the crop water consumption are discussed. The results show that Wuchuan experienced both a warming trend and a reduction of precipitation between 1960 and 2007. The annual mean surface air temperature increased at a rate of 0.04℃ yr-1 and the annual precipitation decreased at a rate of 0.7 mm yr-1 . Both trends are particularly pronounced between 1983 and 2007, with an increase in annual mean temperature of 0.09℃ yr-1 and a decrease in annual mean precipitation of 2.1 mm yr-1 . Crop water consumption decreased between 1983 and 2007 for wheat (1.65 mm yr-1 ), naked oats (2.04 mm yr-1 ), and potatoes (3.85 mm yr-1 ). Potatoes and naked oats consume more water than wheat. Climate change has significantly impacted crop water consumption. Water consumption and rainfall during the growing season are positively correlated, while water consumption and active accumulated temperature are negatively correlated. Compared to precipitation, accumulated temperature has little impact on crop water consumption. Recent climate change has been detrimental for crop production in Wuchuan County. Adaptation to climate change should include efforts to breed drought-resistant crops and to develop drought-resistant cultivation techniques.     

基于HJ-1A/B CCD数据的河南省平原绿化分析

平原绿化在未来农林发展中具有重要地位。本文利用环境卫星(HJ-1 A/B)多时相数据,选择河南省6月冬小麦收割后的CCD数据,直接去除第二季作物,并利用4月份第一季作物播种前的CCD数据,剔除了一季作物,以及[(NDVI_4月≥0.22)与(NDVI_6月≥0.35)]提取平原绿化的信息,其与26个主要城市城区绿化信息进行的相关分析达到显著水平(R²=0.9166)。因此,该区的平原绿化解译效果好,而南部信阳市以一季水稻为主的地区及“水稻-冬小麦”过渡区,解译效果较差。除信阳外,由HJ-1卫星解译的河南平原绿化总面积6909.8 km²,占2010年河南省森林面积20.53%。     

Comment on ‘Shang S. 2012. Calculating actual crop evapotranspiration under soil water stress conditions with appropriate numerical methods and time step. Hydrological Processes 26: 3338–3343. DOI: 10.1002/hyp.8405’

A previous study analyzed errors in the numerical calculation of actual crop evapotranspiration (ET_a) under soil water stress. Assuming no irrigation or precipitation, it constructed equations for ET_a over limited soil‐water ranges in a root zone drying out due to evapotranspiration. It then used a single crop‐soil composite to provide recommendations about the appropriate usage of numerical methods under different values of the time step and the maximum crop evapotranspiration (ET_c). This comment reformulates those ET_a equations for applicability over the full range of soil water values, revealing a dependence of the relative error in numerical ET_a on the initial soil water that was not seen in the previous study. It is shown that the recommendations based on a single crop‐soil composite can be invalid for other crop‐soil composites. Finally, a consideration of the numerical error in the time‐cumulative value of ET_a is discussed besides the existing consideration of that error over individual time steps as done in the previous study. This cumulative ET_a is more relevant to the final crop yield. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Parameterizing canopy resistance using mechanistic and semi‐empirical estimates of hourly evapotranspiration: critical evaluation for irrigated crops in the Mediterranean

In this paper two models are presented for calculating the hourly evapotranspiration λE (W m^?2) using the Penman–Monteith equation. These models were tested on four irrigated crops (grass, soya bean, sweet sorghum and vineyard), with heights between 0·1 and 2·2 m at the adult growth stage. In the first model (Katerji N, Perrier A. 1983. Modélisation de l'évapotranspiration réelle ETR d'une parcelle de luzerne : rôle d'un coefficient cultural. Agronomie 3(6): 513–521, KP model), the canopy resistance r_c is parameterized by a semi‐empirical approach. In the second model (Todorovic M. 1999. Single‐layer evapotranspiration model with variable canopy resistance. Journal of Irrigation and Drainage Engineering—ASCE 125: 235–245, TD model), the resistance r_c is parameterized by a mechanistic model. These two approaches are critically analysed with respect to the underlying hypotheses and the limitations of their practical application. In the case of the KP model, the mean slope between measured and calculated values of λE was 1·01 ± 0·6 and the relative correlation coefficients r² ranged between 0·8 and 0·93. The observed differences in slopes, between 0·96 and 1·07, were not associated with the crop height. This model seemed to be applicable to all the crops examined. In the case of the TD model, the observed slope between measured and calculated values of λE for the grass canopy was 0·79. For the other crops, it varied between 1·24 and 1·34. In all the situations examined, the values of r² ranged between 0·73 and 0·92. The TD model underestimated λE in the case of grass and overestimated it in the cases of the other three crops. The under‐ or overestimation of λE in the TD model were due: (i) to some inaccuracies in the theory of this model, (ii) to not taking into account the effect of aerodynamic resistance r_a in the canopy resistance modelling. Therefore, the values of r_c were under‐ or overestimated in consequence of mismatching the crop height. The high value of air vapour pressure deficit also contributed to the overestimation of λE, mainly for the tallest crop. The results clarify aspects of the scientific controversy in the literature about the mechanistic and semi‐empirical approaches for estimating λE. From the practical point of view the results also present ways for identifying the most appropriate approach for the experimental situations encountered. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessment of the crop coefficient for saltgrass under native riparian field conditions in the desert southwest

Limited urban water supplies in southwestern USA cause water managers and planners to re‐assess water losses and needs from consumptive water use by riparian vegetation. Here, we report on field measurements of evapotranspiration (ET) for inland saltgrass [Distichlis spicata var. stricta (L.) Greene]; a once common riparian plant native to the desert southwest. The objective was to develop a saltgrass crop coefficient, Kc, similar to agricultural crop coefficients commonly used in irrigation water management. The developed Kc, in conjunction with the local climate, can then be used to assess the water savings that may be achieved in riparian zones for saltgrass versus invasive species and for use in irrigation management and scheduling of saltgrass in urban setting. The ET of saltgrass was measured in its native riparian setting located in the flood plain of the Rio Grande, north of Caballo Lake, New Mexico, in 2011 using an eddy covariance technique in the energy budget method. Total ET of 692 mm was measured during the growing season (n = 241 days) and 837 mm during the year. The American Society of Civil Engineers standardized ET for short crop (ETso) was calculated using climate data measured at the study site as 1560 mm during the growing season and 1870 mm during the year. Crop coefficients (ET/ETso) were fitted with a polynomial equation as a function of day of the year to develop saltgrass Kc function. A graphical and simplified method of computing Kc as a function of day of the year and crop season was also developed as an alternative method. Copyright © 2013 John Wiley & Sons, Ltd.     

The impact of taro (Colocasia esculenta) cultivation on the total evaporation of a Cyperus latifolius marsh

Total evaporation (ET) is one of the major components of the water budget of a wetland. Very little research has been conducted on the loss of water to the atmosphere from different wetland vegetation types occurring in southern Africa. This study on the ET of taro (locally known as madumbe) and sedge within the Mbongolwane wetland was conducted to assess the potential impact of madumbe cultivation on the hydrology of the wetland. Sugarcane planted on the contributing catchment outside the wetland was the other crop examined. Two field campaigns were conducted in November 2009 and January 2010 during the growing season of the madumbe crop to quantify ET rates in the Mbongolwane wetland and from sugar cane in the surrounding catchment. ET was measured over two vegetation types in the wetland, namely: madumbe (Colocasia esculenta); sedge (Cyperus latifolius) with some reeds (Phragmites australis); and sugarcane in adjacent terrestrial areas. ET from the madumbes ranged from 1.0 to 6.0 mm day^?1. The daily average ET rates in November 2009 were 3.5 and 4.9 mm for the madumbe and sedge sites, respectively, and 4.0 mm for sugarcane grown in the catchment. The daily average ET rates in January 2010 were 3.3 and 3.7 mm for the madumbes and sedge sites, respectively, and 2.4 mm for the sugarcane site. The daily ET was therefore lower at the madumbe site in November 2009 and in January 2010 compared to the sedge site. An average crop factor of 0.6 was obtained from this study during the growth stage of the madumbes. Copyright © 2012 John Wiley & Sons, Ltd.     

灌溉管理方式的转变及其对作物用水影响的实证

采用三年的面板数据实证研究了我国黄河流域灌区灌溉管理方式的转变及其对作物用水的影响。结果表明：2001年以后,黄河流域灌区灌溉管理改革的推进速度进一步加快,而且用水协会转变的速度超过承包管理,成为改革的主导方式。在一些村中,用水协会或承包管理也可能又返回到原来的集体管理。最后,定量分析结果显示,在用水协会转变初期,作物...     

吉林省黑土区土壤--作物系统Cd元素转化积累研究

在吉林省黑土区系统的野外调查和土壤及玉米籽实样品采集、测试的基础上,采用地球化学分析方法及SPSS技术,研究了Cd元素的土壤地球化学特征,及其在土壤和作物籽实中的含量特征和相关性,用以揭示Cd元素在土壤--作物系统中的转化累积特征及影响因素,为粮食安全服务。研究表明:吉林省黑土区Cd元素全量高于吉林省及全国土壤背景值,但不存在污染,籽实中Cd含量低于国家安全标准。土壤中Cd元素有效态转化程度较高,受其全量控制,同时Zn、Cu及P元素有效量对Cd转化的作用明显,偏酸性土壤更利于Cd元素的转化。玉米籽实对Cd吸收程度较低,主要取决于其自身的生物特性,Zn元素缺乏可能导致玉米籽实对Cd元素吸收增加。