播种机组纯作业时间利用率与地块条件的匹配模型与试验

机械化播种作业是现代农业生产的重要环节,纯作业时间利用率是衡量播种机组作业效率的重要指标。该研究依据农业机组运行机理,在调查研究的基础上,提出季节时间利用率概念,确定了播种机组的作业时间构成,建立了播种机组纯作业时间、转弯时间、加种肥时间的计算模型和3种加肥方式下的播种机组纯作业时间利用率计算模型,明确各参数随地块面积、地块长度等条件变化的一般规律;以此为基础,在机组正常作业状态下,采用定距离多点多设备同步跟踪测的试验方法获取4种典型播种机组各类作业时间数据,并运用3σ原理剔除无效数据;依据所建模型及有效试验数据,采用Matlab 2012b对4种播种机组的纯作业时间利用率随地块条件变化规律进行模拟仿真,并采用Sigmaplot 12.5软件直观表达试验结果;进而探索了播种机组纯作业时间利用率随地块条件化的原因,确定了目标时间利用率条件下不同播种机组与其所适宜的作业地块面积和地块长度的定量关系:播种机组纯作业时间利用率大于0.6时,约翰迪尔7830机组适合作业地块面积大于等于6 hm^2、地块长度为1 200~1 400 m;维美德171机组适宜作业地块面积大于等于6 hm^2、地块长度为1 000~1 200 m;常发504机组适合作业的地块面积大于等于1 hm^2、地块长度为500~1 500 m;黄海254机组适合作业的地块面积大于等于0.3 hm^2、地块长度200~1 500 m。研究成果可为不同地块条件的播种机组选型提供定量依据。     

田林老山中山杉木人工林生产力及营养元素循环的研究

广西田林县老山林场中山区气候冷凉潮湿,土壤肥力较高,能满足杉木速生要求。17年生杉木人工林乔木层的生物量达138.46t/ha,平均净生产量为8.15t/ha·a,与杉木中心产区相当。乔木层对N,P,K,Ca,Mg5种营养元素的吸收量为224.04kg/ha·a,其中42.3％存留在林木层,42.5％通过凋落物,15.2％通过降雨淋洗归还土壤。通过凋落物归还是N,P,Ca,Mg归还的主要途径,K的归还主要通过降雨淋洗;K,Ca,Mg的循环系数较大,分别达到0.58,0.68和0.60;N,P相对较小,分别为0.48和0.33。林木正处于生长旺盛阶段,杉木对5种营养元素的吸收量、存留量和归还量以及循环系数都有较高水平,生物量积累也较大。     

Nitrogen fertilizer–induced mineralization of soil organic C and N in six contrasting soils of Bangladesh

A 90‐day laboratory incubation study was carried out using six contrasting subtropical soils (calcareous, peat, saline, noncalcareous, terrace, and acid sulfate) from Bangladesh. A control treatment without nitrogen (N) application was compared with treatments where urea, ammonium sulfate (AS), and ammonium nitrate (AN) were applied at a rate of 100 mg N (kg soil)^–1. To study the effect of N fertilizers on soil carbon (C) turnover, the CO₂‐C flux was determined at nine sampling dates during the incubation, and the total loss of soil carbon (TC) was calculated. Nitrogen turnover was characterized by measuring net nitrogen mineralization (NNM) and net nitrification (NN). Simple and stepwise multiple regressions were calculated between CO₂‐C flux, TC, NNM, and NN on the one hand and selected soil properties (organic C, total N, C : N ratio, CEC, pH, clay and sand content) on the other hand. In general, CO₂‐C fluxes were clearly higher during the first 2 weeks of the incubation compared to the later phases. Soils with high pH and/or indigenous C displayed the highest CO₂‐C flux. However, soils having low C levels (i.e., calcareous and terrace soils) displayed a large relative TC loss (up to 22.3%) and the added N–induced TC loss from these soils reached a maximum of 10.6%. Loss of TC differed depending on the N treatments (urea > AS > AN >> control). Significantly higher NNM was found in the acidic soils (terrace and acid sulfate). On average, NNM after urea application was higher than for AS and AN (80.3 vs. 71.9 and 70.9 N (kg soil)^–1, respectively). However, specific interactions between N‐fertilizer form and soil type have to be taken into consideration. High pH soils displayed larger NN (75.9–98.1 mg N (kg soil)^–1) than low pH soils. Averaged over the six soils, NN after application of urea and AS (83.3 and 82.2 mg N (kg soil)^–1, respectively) was significantly higher than after application of AN (60.6 mg N (kg soil)^–1). Significant relationships were found between total CO₂ flux and certain soil properties (organic C, total N, CEC, clay and sand content). The most important soil property for NNM as well as NN was soil pH, showing a correlation coefficient of –0.33** and 0.45***, respectively. The results indicate that application of urea to acidic soils and AS to high‐pH soils could be an effective measure to improve the availability of added N for crop uptake.     

供水条件对温室番茄根系分布及产量影响

通过田间试验，分析了不同生育期供水条件对番茄灌水量、光合作用、根系分布、产量和水分利用效率的影响。结果表明：番茄开花坐果期控制灌水下限为60%f_C(田间持水量)，结果盛期控制灌水下限为75%f_C，控制灌水上限为90%f_C，番茄产量最高，达到91.7 t/hm²，水分利用效率达到27.51 kg/m³，整根的根长、根表面积、根体积、根干重都明显增加。叶片净光和速率在75%f_C条件下最高，有利于光合产物的形成。随土层深度的增加，根长密度呈指数下降。不同土壤水分条件对番茄根系生长影响主要体现在直径小于1 mm的根系上，而且直径小于1 mm的根长和产量之间存在很好的相关关系。     

基于植被降水利用效率的荒漠化遥感评价方法

 在考虑荒漠化评价的空间尺度和基准以及潜在评价指标的尺度特征的基础上,以国内外对土地荒漠化过程中植被降水利用效率(RUE)变化的研究为依据,提出一种以植被的降水利用效率为主要评价指标、适合于荒漠化遥感监测应用的荒漠化评价方法。该方法可很大程度上克服以植被指标为主的评价方法受降水波动影响大的缺点。这种方法重视不同荒漠化类型的共性特征,适合在多种类型荒漠化遥感评价中应用。     

我国瓜菜遮阳网覆盖栽培研究进展

遮阳网覆盖栽培已应用到农业生产的各方面，对农业生产的防虫、遮阳、节水、提高产量等方面起到了很大的促进作用。本文从遮阳网在节水灌溉、遮光降温、气体交换、延迟采收、防虫及对作物产量和品质的影响等方面，综述了其在农业生产方面的应用状况和相关研究，为遮阳网的合理科学利用提供参考。     

Toward sustainable harvesting of Africa's largest medicinal plant export (Prunus africana): a case study in Tanzania

Global demand for treating prostate disorders with Prunus africana bark extract has made P. africana Africa's largest medicinal plant export. Unsustainable harvesting practices can lead to local extirpations of this multipurpose tree. Survey research targeting P. africana harvesters in a Tanzania forest reserve revealed that 78% of them used unsustainable harvesting practices. This research focused on establishing a socioeconomic profile of the harvesters, the profitability of their business operations, and identifying the factors that influence their selection of harvesting practices. Results indicate that harvesters have above-national-average education, double the average family size, and generate income exceeding government's minimum wages. Large family size and high earning potential imply increased future harvesting activity. Logistic regression results indicate that education and training level could predict the likelihood that a harvester would use unsustainable harvesting practices. Local- and district-level government organisations could implement a resource assessment as a basis to design and implement harvesting schedules and ensure that the harvesters receive appropriate training, regardless of their education level.     

Development of buffer methods and evaluation of pedotransfer functions to estimate pH buffer capacity of highly weathered soils

The pH buffer capacity of a soil (pHBC) determines the amount of lime required to raise the pH of the soil layer from its initial acid condition to an optimal pH for plant growth and the time available under current net acid addition rate (NAAR) until the soil layer acidifies to a critical pH leading to likely production losses. Accurate values of pHBC can also be used to calculate NAAR from observed changes in soil pH. In spite of its importance, there is a critical shortage of pHBC data, likely due to the long period of time needed for its direct measurement. This work aimed to develop quick, simple and reliable methods of pHBC measurement and to test these methods against a slow (7‐day) titration used as benchmark. The method developed here calculates pHBC directly from the pH buffer capacity of the buffer solution and the increase in soil pH and corresponding decrease in pH of the buffer solution following mixing and equilibration. The pHBC values calculated using Adams and Evans or modified Woodruff buffers were in accord with those measured by slow titration. Buffer methods are easily deployed in commercial and research laboratories as well as in the field. The advantage of using buffer solutions to calculate pHBC instead of lime requirement is the broad application of this soil property. The pHBC of a soil is an intrinsic property that would not be expected to need remeasurement over periods of less than decades. Recurring lime requirement can be calculated from the soil's pHBC, initial and target pH values. A large proportion of the variability in pHBC was explained by the soil organic carbon content. This relationship between pHBC and soil organic carbon content allowed us to develop local pedotransfer functions to estimate pHBC for different regions of Australia.     

卧龙自然保护区震后小型陆栖脊椎动物调查

小型陆栖脊椎动物是一类稳定、灵敏、高效的环境指示动物,将它们作为生态环境变化的指针具有诸多的优越性。通过围栏陷阱法对卧龙自然保护区内小型陆栖脊椎动物在原始竹林与人工竹林中的分布情况展开调查,进而对保护区内小型陆栖脊椎动物资源现状进行评估,并科学地评估我区震后的生态环境。本次调查共记录到小型陆栖脊椎动物物种5目7科15种,其中两栖类2目2科2种,爬行类1目1科1种,小型兽类2目4科12种。采集的样品数量达到316只。     

极端干旱区大气边界层厚度时间演变及其与地表能量平衡的关系

主要采用ECMWF的地表和大气产品分析了中国西北极端干旱区大气边界层厚度与地表能量通量的时间变化特征,同时,结合探空加强观测分析了大气边界层演变的可能因素.得出:西北极端干旱区大气边界层厚度呈现出季节性的年际和年代际变化,夏季大气边界层厚度呈下降趋势,春、秋季节呈现出先增加后降低的趋势,冬季以阶段性降低趋势为主,20世纪80年代是大气边界层厚度的转折时期；感热通量是极端干旱区大气边界层发展的主要热力因素；由于夏季净辐射量、地气温差、粗糙度以及风速等因子随时间演变而呈降低趋势,潜热通量呈增加趋势,导致了边界层高度形成的热力作用减弱,边界层厚度降低；同时,粗糙度和风速也是大气边界层发展的主要动力因素,由于边界层粗糙度和风速降低,促使垂直风切变减小,湍流动力作用减弱,也会导致边界层厚度降低.