Effects of drip irrigation frequency on soil wetting pattern and potato growth in North China Plain

The effect of irrigation frequency on soil water distribution, potato root distribution, potato tuber yield and water use efficiency was studied in 2001 and 2002 field experiments. Treatments consisted of six different drip irrigation frequencies: N1 (once every day), N2 (once every 2 days), N3 (once every 3 days), N4 (once every 4 days), N6 (once every 6 days) and N8 (once every 8 days), with total drip irrigation water equal for the different frequencies. The results indicated that drip irrigation frequency did affect soil water distribution, depending on potato growing stage, soil depth and distance from the emitter. Under treatment N1, soil matric potential (ψ_m) Variations at depths of 70 and 90 cm showed a larger wetted soil range than was initially expected. Potato root growth was also affected by drip irrigation frequency to some extent: the higher the frequency, the higher was the root length density (RLD) in 0–60 cm soil layer and the lower was the root length density (RWD) in 0–10 cm soil layer. On the other hand, potato roots were not limited in wetted soil volume even when the crop was irrigated at the highest frequency. High frequency irrigation enhanced potato tuber growth and water use efficiency (WUE). Reducing irrigation frequency from N1 to N8 resulted in significant yield reductions by 33.4 and 29.1% in 2001 and 2002, respectively. For total ET, little difference was found among the different irrigation frequency treatments.     

基于机器学习的干旱区土壤盐渍化定量估算

  目的  探讨对土壤盐渍化进行快速、准确监测技术与方法。  方法  利用353个地面表观电导率数据,以及从Worldview-2影像获取对应采样点的波段反射率值,结合两波段组合植被指数和三波段组合植被指数,筛选最佳二维、三维波段组合方式,引入人工神经网络、K近邻和支持向量回归来构建区域土壤盐渍化定量反演模型。  结果  ① WV-2影像的红边和近红外波段与ECa呈现显著相关（P < 0.01）。② 二维植被指数（RVI_(B5-B2)、NDVI_(B6-B2)、DVI_(B2-B6)）和三维植被指数（3DVI_(B2-B6-B6)、3DVI_(B3-B5-B6)、3DVI_(B5-B2-B1)、3DVI_(B2-B1-B6)、3DVI_(B2-B1-B6)、3DVI_(B6-B1-B2)、3DVI_(B5-B3-B7)）的波段组合计算提高了其对土壤盐渍化的敏感性。③ 基于不同维度数据的机器学习估算模型中,3DVI和KNN算法结合对土壤盐渍化估算效果最为突出,且模型精度为R2 = 0.773,RMSE = 1.659 dS m?1,RPD = 2.216。  结论  所构建的多维植被指数可应用于类似环境条件下盐渍土地监测和评价研究。     

Hydrology in a patterned landscape is co-engineered by soil-disturbing animals and biological crusts

Water redistribution has a profound influence on dryland ecosystem function. This hydrological function is largely regulated by ecosystem engineers including biological soil crusts (biocrusts) which produce run-off, and burrowing animals, such as the greater bilby, whose pits capture water. We estimated the relative importance of these two ecosystem engineers in determining infiltration rates in a system where dune slopes shed water to adjacent interdune swales to maximize overall productivity. Also, we determined which biocrust property was most hydrologically important: total cover, composition, patch aggregation or spatial heterogeneity. While both biocrusts and burrowing animals equally affected the overall infiltration through macro- and micropores (under ponding), only biocrusts were important for the infiltration specifically via micropores (under tension). Of the studied biocrust properties, community composition was the strongest influence such that the greater the prevalence of early successional biocrust patches, the greater the infiltration rate. Greater total cover of biocrusts reduced infiltration, and the spatial properties were relatively unimportant. Although bilbies and biocrusts comparably influenced infiltration under ponding at the microscale, realistic cover of bilby pits at the landscape scale is unlikely to strongly impair the hydrological function of dunes. Reintroduction of the endangered bilby may enhance nutrient cycling and plant recruitment via its seed and resource capturing pits, without a concomitant disruption of hydrological function. In contrast, removal of biocrusts caused by, e.g., livestock trampling, is expected to strongly enhance infiltration in the run-off areas, strongly reducing ecosystem productivity at the landscape scale.     

Quantifying production potentials of winter wheat in the North China Plain

The North China Plain (NCP) is one of the major winter wheat (Triticum aestivum L.) producing areas in China. Current wheat yields in the NCP stabilize around 5 Mg ha⁻¹ while the demand for wheat in China is growing due to the increase in population and the change in diet. Since options for area expansion of winter wheat are limited, the production per unit of area need to be increased. The objective of this study is to quantify the production potential of winter wheat in the NCP taking into account the spatial and temporal variability caused by climate. We use a calibrated crop growth simulation model to quantify wheat yields for potential and water-limited production situations using 40 years of weather data from 32 meteorological stations in the NCP. Simulation results are linked to a Geographic Information System (GIS) facilitating their presentation and contributing to the identification of hotspots for interventions aimed at yield improvements. In the northern part of the NCP, average simulated potential yields of winter wheat go up to 9.7 Mg ha⁻¹, while average water-limited yields only reach 3 Mg ha⁻¹. In the southern part of the NCP, both average potential and water-limited yields are about 7.5 Mg ha⁻¹. Rainfall is the limiting factor to winter wheat yields in the northern part of the NCP, while in the southern part, the joint effect of low radiation and high temperature are major limiting factors. Temporal variation in potential yields throughout the NCP is low in contrast with the temporal variation in water-limited yields, which is especially great in the northern part. The study calls for the collection of location-specific and disaggregated irrigated and rainfed wheat yield statistics in the NCP facilitating the identification of hotspots for improvement of current wheat yields.     

基于遥感的华北平原农作物时空分布变化特征分析

作物种植面积的多年时空变化是进行农业结构调整和优化的基础,也是开展农业减灾、地下水保护的重要依据。为了解华北平原主要作物近年来种植面积的时空变化过程,本文基于2000—2013年的MODIS NDVI数据和TM/ETM遥感数据提取当地主要作物的种植面积,并分析了华北平原主要作物近年来的时空变化特征。结果表明:1基于MODIS NDVI数据和TM/ETM遥感数据提取当地主要作物的种植面积,提取精度较高,结果可靠;2冬小麦?夏玉米主要分布于太行山前平原、山东省和河南省的引黄河灌区,单季玉米在河北平原北部分布最广,水稻集中分布于天津、河北唐山地区和黄河沿岸,蔬菜主要分布在城市郊区,林果分散分布于几个产果区和京津周边地区,棉花主要集中于华北平原中部地区。3华北平原粮食作物(小麦、玉米和水稻)种植面积明显下降,经济作物(林果和蔬菜)则显著增加,其中林果、蔬菜和水稻的面积变化率较大,分别为56.45%、35.76%和23.16%,蔬菜和水稻的位置转移明显。4景观格局AWMPFD和SHEI指数值表明,河北平原以南的冬小麦?夏玉米种植规模化程度提高,豫北地区冬小麦?夏玉米种植面积增加,豫北以北地区由于各类经济作物种植面积增加,区域作物种植多样化指数增加。该结果可为农业种植结构调整、资源合理利用提供参考。     

A multi-site analysis of random error in tower-based measurements of carbon and energy fluxes

Measured surface-atmosphere fluxes of energy (sensible heat, H, and latent heat, LE) and CO₂ (FCO₂) represent the “true” flux plus or minus potential random and systematic measurement errors. Here, we use data from seven sites in the AmeriFlux network, including five forested sites (two of which include “tall tower” instrumentation), one grassland site, and one agricultural site, to conduct a cross-site analysis of random flux error. Quantification of this uncertainty is a prerequisite to model-data synthesis (data assimilation) and for defining confidence intervals on annual sums of net ecosystem exchange or making statistically valid comparisons between measurements and model predictions.We differenced paired observations (separated by exactly 24 h, under similar environmental conditions) to infer the characteristics of the random error in measured fluxes. Random flux error more closely follows a double-exponential (Laplace), rather than a normal (Gaussian), distribution, and increase as a linear function of the magnitude of the flux for all three scalar fluxes. Across sites, variation in the random error follows consistent and robust patterns in relation to environmental variables. For example, seasonal differences in the random error for H are small, in contrast to both LE and FCO₂, for which the random errors are roughly three-fold larger at the peak of the growing season compared to the dormant season. Random errors also generally scale with R_n (H and LE) and PPFD (FCO₂). For FCO₂ (but not H or LE), the random error decreases with increasing wind speed. Data from two sites suggest that FCO₂ random error may be slightly smaller when a closed-path, rather than open-path, gas analyzer is used.     

碱性盐胁迫对光果甘草和苦豆子种子萌发的影响研究

研究了不同浓度的碳酸钠对光果甘草和苦豆子种子萌发的影响。结果表明:在不同浓度的碳酸钠盐(Na2CO3)条件下,光果甘草和苦豆子种子的发芽势、发芽率、发芽指数、活力指数和胚根胚芽生长长度均随着Na2CO3浓度的增加而下降。但Na2CO3浓度提升到0.9%时,光果甘草种子还能保持73%的发芽率,而苦豆子种子发芽率只有26%。光果甘草种子发芽的最适Na2CO3浓度为0.9%,临界浓度为1.2%,极限浓度为2.1%。而苦豆子种子发芽的最适Na2CO3浓度为0.6%,临界浓度在0.6%和0.9%之间,极限浓度为1.8%。光果甘草种子的发芽指数和0.9%以上浓度的活力指数都比苦豆子高,而盐害率比苦豆子种子低很多。Na2CO3浓度提高到0.9%时,光果甘草种子的盐害率只有26.71%,而苦豆子种子的为70.28%,由此可以确定,光果甘草种子萌发抵抗Na2CO3盐的能力比苦豆子种子强,能适应含Na2CO3盐量达0.9%以上的恶劣的碱土生态环境。而苦豆子种子萌发抗Na2CO3盐的能力相对较弱,只能适应Na2CO3含量为0.6%的碱性土壤条件。     

The effects of acid nitrogen and acid sulphur deposition on CH4 oxidation in a forest soil: a laboratory study

Sieved soil and soil core experiments were performed to determine the potential sensitivity of forest soil CH₄ oxidation to oxidised N, reduced N and oxidised S atmospheric deposition. Ammonium sulphate was used to simulate reduced N deposition, HNO₃ oxidised N deposition and H₂SO₄ oxidised S deposition. The effects of NH₄⁺, NO₃⁻, SO₄²⁻ and H⁺ on soil CH₄ flux were shown to be governed by the associated counter-anion or cation of the investigated ions. Ammonium sulphate, at concentrations greater than those that would be experienced in polluted throughfall, showed a low potential to cause inhibition of CH₄ oxidation. In contrast, HNO₃ strongly inhibited net CH₄ oxidation in sieved soils and also in soil cores. In addition, soil CO₂ production was inhibited and the organic and mineral soil horizons acidified in HNO₃ treated soil cores. This suggested that the HNO₃ effect on CH₄ flux might be indirectly mediated through aluminium toxicity. Sulphuric acid only inhibited CH₄ oxidation when added at pH 1. At concentrations more representative of heavily polluted throughfall, H₂SO₄ had no effect on soil CH₄ flux or CO₂ production from soil cores, even after 210 days of repeated addition. In contrast to HNO₃ additions, acidification of the soil was not marked and was only significant for the mineral soil. The findings suggest that the response of forest soil CH₄ oxidation to atmospheric acid deposition is strongly dependent on the form of acid deposition.     

Effects of land-use on the activity and diversity of methane oxidizing bacteria in forest soils

Methane is an important greenhouse gas and CH₄ oxidation in soil represents a significant sink for this gas. High capacity CH₄ oxidation potentials and molecular profiles of CH₄ oxidizing bacteria in soil were compared for five land-use treatments at a fully replicated experimental site within the Gisburn Forest Experiment, to assess the effects of land-use on both the potential activity of CH₄ oxidizing bacteria and their diversity. Forestry land-use was found to have a highly significant effect on CH₄ oxidation potentials. Highest CH₄ oxidation potentials were found in soils collected under stands of oak, in grassland plots, and in one soil under Norway spruce. A negative relationship between soil water nitrate concentration and CH₄ oxidation capacity was evident across the experimental site, with the high nitrate soils under stands of alder exhibiting little or no capacity for CH₄ oxidation even at optimal temperature and water content. Molecular profiles indicated that a diverse range of bacteria with the potential to oxidize CH₄ were present in all soils, however no clear correlation with CH₄ oxidation potential was identified.