黄土高原塬区麦田土壤水分变化特征及其对降水的响应

利用对黄土高原塬区具有较好代表性的西峰站近18 a(1989~2006年)降水和土壤水分资料,研究麦田土壤水分的变化特征及其与不同尺度的标准化降水指数SPI的关系。结果表明:(1)4~6月份,是麦田深层土壤水分的失墒期,6月前后土壤干旱最严重;(2)7~10月是麦田深层土壤的增墒期,土壤水分与降水的显著相关深度逐渐向深层推移,10月底墒得到有效补充;(3)失墒期深层土壤水分对表层水分的滞后时间小于增墒期的,分别为1个月左右和2个月左右;(4)一个月尺度的降水对耕作层的影响是最大的,2~6个月尺度降水的影响深度主要在30~150 cm,大于6个月尺度的SPI影响深度在主要70~200 cm;(5)除了作物蒸腾影响,降水尺度越大,土壤水分受影响的深度越大。     

宁南山区不同种植体系土壤水分变化规律

了解旱地土壤水分变化状况,可为半干旱地区旱作农业水资源合理利用提供科学依据。该文通过田间试验,研究了宁南山区胡麻、冬小麦、马铃薯、草地和苜蓿等5类旱地在主要生长季节的土壤水分变化规律。结果表明,不同旱作农田土壤水分随时间的变化趋势基本一致,均出现失墒期和增墒期,其分界点多在7月中下旬;冬小麦、胡麻和马铃薯等1 a生作物整个生长期内的土壤含水率要高于草地和苜蓿等多年生作物（植物）;胡麻地、冬小麦地和马铃薯地的土壤水分垂直分布为上层低、下层高,而草地和苜蓿地相反。研究结果显示,各类旱地表层土壤水分变化剧烈,中下层变化相对较小,且生长期内的降水量均不能满足作物生长需求,秋季继续蓄墒是保障来年旱地获得良好收成的关键。     

黄土丘陵沟壑区水平沟耕作效益研究

利用9a试验资料,分析和研究了坡地水平沟耕作的土壤水分动态及耗水规律,并从水土流失、养分流失及水分利用方面研究了水平沟耕作效益.得出坡地水平沟耕作的土壤水分变化为:封冻前的强烈失墒期、越冬干湿交替失墒期和返青拔节后缓慢失墒期3个阶段.小麦灌浆期及返青期对产量作用最大;水平为能够显著地拦蓄径流,减少土镶冲刷和养分流失,提高土壤水分利用率,进而提高作物单产.     

甘肃中部半干旱区紫花苜蓿耗水规律及土壤水分变化特征研究

利用大型蒸渗仪于2001—2002年连续2年测定的甘肃中部半干旱地区紫花苜蓿生长期日耗水量以及土壤水分资料，分析研究了耗水规律和土壤水分变化特征。结果表明：紫花苜蓿全生长期总耗水量约在382．9mm左右，日耗水量随降水量的增大而增大，在整个生长期内基本呈现周期性正弦曲线波动，土壤水分的周年变化可划分为3个时期：春季失墒期、夏季波动变化期、秋季增墒期；垂直变化分为3个层次：多变层(0～30cm)、缓变层(30—10Ocm)、稳变层(100～200cm)。     

冀西北风沙半干旱区农田土壤水分动态分析

根据土壤分定位观测结果,结合当地气候条件,作物生长过程和土壤物理性状等因子,对冀西北坝上风沙半干旱区坡地土壤水分季节性和垂直性变化进行了分析,得出了该区旱坡地土壤水分季节性变化,可概括了缓慢失墒期,耗墒期,恢复期,相对稳定期4个阶段,土壤水分垂直性变化是,0－5cm为速变层,5－100cm为活跃层,100cm以下为相对稳定层。     

甘肃黄土地区农田土壤水分变异规律研究

对甘肃黄土地区4个土类的土壤水分特征,动态及空间变异规律,以及最大吸湿水,凋萎湿度和持水性能的研究表明,土壤水分动态变异规律呈“双峰－双谷”,据此在时序上可划分为5个明显的时期,（1）春季增失墒交替期,（2）春夏严重失墒期,（3）夏秋墒情恢复期,（40秋冬缓慢失墒期;（50冬季墒情稳定期,随着剖面深度的增加,土壤水分的空间变异明显减小,上层土壤服从对数正态分布,鸸上层及螺积层肋从正态分布。     

陇东黄土高原塬区冬小麦越冬期土壤水分损耗规律浅析

通过分析陇东塬区冬小麦越冬期土壤水分损耗,以及决定越冬土壤水分损耗的关键气象要素,指出在秋季降水充沛、土壤收墒充足、冬季气温偏高、降水明显偏少的年型,越冬期土壤水分损耗是不可忽视的,其中有一半年份,越冬期土壤水分损耗占冬小麦生长季节自然降水的10%～22%。尤其是入冬前土壤含水量充沛,而返青以后生长期降水相对较少的年份,越冬期麦田土壤水分损耗相当于返青到成熟期降水量的44%。     

黄土丘陵沟壑区不同耕作措施下梯田土壤水分时空变化

通过对晋西黄土丘陵沟壑区王家沟流域梯田玉米生育期内土壤水分、年降水量、玉米产量等的测定,分析研究了不同耕作措施下梯田土壤水分的时空变化以及土壤水分生产效率。研究结果表明:在玉米生育期内土壤水分时间变化特征与降水量的年内分布有密切的关系,但土壤水分的变化滞后于降水量的分布;常规处理的土壤水分时间变差大,其次为起垄覆膜处理,丰产沟覆膜处理最小;常规处理土壤水分垂直变化最剧烈,表层失墒快,增墒也迅速,丰产沟覆膜处理则变化最缓和,失墒缓慢;丰产沟覆膜处理的土壤水分生产效率最高,常规处理最低,垄作覆膜处理居中。梯田系统微集流耕作措施蓄水保墒能力强,作物对土壤水分的利用效率高,抗旱增产效果明显。     

荒漠草原不同覆被类型土壤水分动态及其对降水的响应

干旱、半干旱区植被恢复与重建对降雨具有高度的依赖性,降雨格局的任何细微变化对其生态系统均会产生影响。以宁夏盐池县荒漠草原3种主要覆被类型（浮沙地、天然草地和柠条林地）为研究对象,使用自动气象站、土壤水分仪连续监测2015—2017年降水量和土壤水分数据,分析了3种覆被类型0—250 cm土层的土壤水分动态及其对不同量级降水的响应。结果表明：浮沙地土壤水分从表层至深层为增长趋势,天然草地和柠条林地为增加—减少—增加趋势;水分季节变化分为土壤水分稳定期（12月至翌年2月）、土壤水分积累期（3—5月）、土壤水分消退期（6—8月中旬）和土壤水分恢复期（8月下旬至11月）。5 mm以下的小降水事件对土壤水分几乎无影响;中等降水事件（5~25 mm）和大降水事件（25~40 mm）对0—20 cm或浮沙地0—40 cm土层土壤水分有补给作用;40—100 cm土层的水分补充需要特大降水事件。浮沙地对降水响应最敏感,柠条林地次之,天然草地最滞后。降水量、降水强度、雨前土壤含水量和土壤物理性质均是影响土壤水分入渗的因素,而在降水一致时,土壤类型是决定土壤水分动态的重要因素,植被对土壤剖面水分具有再分配的作用,这在干旱区生态系统中尤为重要,决定了植被类型与土壤类型的对应关系。     

典型峰丛洼地坡面土壤水分动态变化的时序分析

采用时间序列分析方法，分析了2004年5～9月广西环江典型峰丛洼地坡面上6种土地覆被类型10，20cm土壤水势与降水动态变化的相关关系。结果表明：（1）灌丛与板栗覆草土壤中的水分较充裕，其含量受天气的波动变化较小，对降水的影响具有缓效性、长期性的特点；（2）坡耕地中水分含量较低，随降雨的波动变化剧烈，但南瓜的地上植株部分对土壤水分的调节保持有积极作用；（3）撂荒草地与木豆土壤水分含量的层间差异都较显著，对降水响应的即时性也强，但撂荒地20cm土层对降水的响应期长些，能保证短时间内向10cm土层的水分补给；（4）处于幼龄期的板栗，土壤水分变化反映的是仅受天气影响下的自然裸露坡地的状况，变化介于灌丛、板栗覆草和撂荒草地、木豆之间。     

Dispersal of soil-dwelling clover root weevil (Sitona lepidus Gyllenhal,Coleoptera: Curculionidae) larvae in mixed plant communities

Insect pests that have a root-feeding larval stage often cause the most sustained damage to plants because their attrition remains largely unseen, preventing early diagnosis and treatment. Characterising movement and dispersal patterns of subterranean insects is inherently difficult due to the difficulty in observing their behaviour. Our understanding of dispersal and movement patterns of soil-dwelling insects is therefore limited compared to above ground insect pests and tends to focus on vertical movements within the soil profile or assessments of coarse movement patterns taken from soil core measurements in the field. The objective of this study was to assess how the dispersal behaviour of the clover root weevil (CRW), Sitona lepidus larvae was affected by differing proportions of host (clover) and non-host (grass) plants under different soil water contents (SWC). This was undertaken in experimental mini-swards that allowed us to control plant community structure and soil water content. CRW larval survival was not affected either by white clover content or planting pattern or SWC in either experiment; however, lower clover composition in the sward resulted in CRW larvae dispersing further from where they hatched. Because survival was the same regardless of clover density, the proportion of infested plants was highest in sward boxes with the fewest clover plants (i.e. the low host plant density). Thus, there is potential for clover plants over a larger area to be colonised when the clover content of the sward is low.     

Plant root morphology and soil biological indicators under primary development of various swards

Plant nutrition conditions are limited in naturally acidic soil due to harmful hydrogen and aluminium ions. More favourable conditions for plant nutrition (soil liming) will affect root qualitative and quantitative parameters and influence ecosystem stability. Four legume–grass swards were cultivated. The swards were a combination of one species of legume and two species of grasses: Trifolium pratense L., Trifolium repens L., Trifolium hybridum L., Medicago sativa L. (each of 50%) with Phleum pratense L. (35%) and Poa pratensis L. (15%). The aim of this study is to evaluate the root morphological and soil biological indicators of legume–grass swards under the first two years of development in soils with different pH levels.

Sward ecosystem development depends on the pH of the soil, sward species composition and soil biota. During the first year of sward development, soil pH had a significant influence on the morphology of root system. Sward‘s root mass and total root length was 2.4 and 2.2 times bigger in naturally acidic soil. This resulted in a change of biological parameters.

In the second year of sward development, soil pH had no significant influence on sward‘s root mass. However, under the impact of different soil pH, various sward‘s root systems were formed and the root C:N ratio had changed. It is observed that, regardless of the sward species composition and the year of development, at higher root C:N ratio soil microbial biomass was higher and CO₂ emissions were lower in swards in naturally acidic soils.

Regardless of soil pH, different types of clover–grass swards promoted organic carbon immobilization in microbial biomass and, at the same time, stabilized the sward ecosystem in the top soil layer (soil respiration in 0–10 and 10–20?cm layers was lower) more effectively than the alfalfa–grass sward.     

Nitrous oxide emissions and methane oxidation by soil following cultivation of two different leguminous pastures

 Nitrous oxide (N₂O) emissions and methane (CH₄) consumption were quantified following cultivation of two contrasting 4-year-old pastures. A clover sward was ploughed (to 150–200 mm depth) while a mixed herb ley sward was either ploughed (to 150–200 mm depth) or rotovated (to 50 mm depth). Cumulative N₂O emissions were significantly greater following ploughing of the clover sward, with 4.01 kg N₂O-N ha^–1 being emitted in a 48-day period. Emissions following ploughing and rotovating of the ley sward were much less and were not statistically different from each other, with 0.26 and 0.17 kg N₂O-N ha^–1 being measured, respectively, over a 55-day period. The large difference in cumulative N₂O between the clover and ley sites is presumably due to the initially higher soil NO₃ ^– content, greater water filled pore space and lower soil pH at the clover site. Results from a denitrification enzyme assay conducted on soils from both sites showed a strong negative relationship (r=–0.82) between soil pH and the N₂O:(N₂O+N₂) ratio. It is suggested that further research is required to determine if control of soil pH may provide a relatively cheap mitigation option for N₂O emissions from these soils. There were no significant differences in CH₄ oxidation rates due to sward type or form of cultivation. Received: 1 November 1998     

Implications of soil substrate and land use for properties of fen soils in North-East Germany Part III: Soil quality for grassland use

Abstract

The aim of the study was to analyse aspects of fen soil quality for grassland use with regard to the different topsoil structure and their status of earthification/moorshification (degradation). Fifty fens of different origin, structural status and land use intensity were sampled, analysed and scored by different methods: Visual Soil Assessment, Peerlkamp test and Muencheberg Soil Quality Rating. Suitable soil structure scores were found at different land use intensities with the exception of stock tracks on pastures. These had lower water and air permeability and lower soil strength. Highest visual scores of macrostructure were found where the water table was deeper; while highest overall soil quality scores occurred where the water table was optimum. The accelerated status of moorshification had no effect on the soil quality scores and on the crop yield. At lower levels of soil development (earthification) the crop yield was slightly lower due to higher proportions of inedible plants. It may be concluded that degraded peat soils will have no loss of soil quality and have relatively high soil quality for grassland use if the water table can be managed in a suitable range and the sward quality is maintained.     

Nitrate leaching from grazed grassland lysimeters: effects of fertilizer input, field drainage, age of sward and patterns of weather

Drained and undrained grassland lysimeter plots were established in 1982 on a clay loam of the Hallsworth series at a long-term experimental site in south-west England. The plots were continuously grazed by beef cattle, and received fertilizer at either 200 or 400 kg N ha^-1 per annum to the existing permanent sward, or at 400 kg N ha^-1 to a new sward, reseeded to perennial ryegrass following cultivation. Drainage water was monitored at V-notch weirs and sampled daily for the analysis of nitrate-N. Seven years of data are presented (five years for the reseeded swards). On the drained plots a large proportion of the rainfall was routed preferentially down large pores to the mole drains, whilst on the undrained plots, drainage was mainly by surface runoff. The average quantities of nitrate N leached per year were 38.5, 133.8 and 55.7 kg ha^-1 from the old sward that received 200 and 400 kg N ha^-1, and from the reseed that received 400 kg N ha^-1 fertilizer, respectively. Ploughing and reseeding resulted in a two-fold reduction in leaching, except during the first winter after ploughing, and twice as much leaching occurred after a hot, dry summer as after a cool, wet one. Nitrate concentrations in drainage from either drained or undrained plots were rather insensitive to rainfall intensity, such that concentration was a good predictor of nitrate load for a given drainage volume. The drainage volume determined the proportion of the leachable N that remained in the soil after the winter drainage period. Initial (peak) concentrations of nitrate N ranged, on average, from 55 mg dm^-3 for the drained old sward that received 400 kg N ha^-1 fertilizer, to 12 mg dm^-3 for the undrained sward at 200 kg N ha^-1 fertilizer input. Concentrations of nitrate N in drainage from similar, unfertilized plots rarely exceeded 1 mg dm^-3. The results suggest that manipulating the nitrate supply can lessen leaching and that the route of water through soil to the watercourse determines the maximum nitrate concentration for a given load.     

Starving the soil of plant inputs for 50 years reduces abundance but not diversity of soil bacterial communities

If soil communities rely on plant-derived carbon, is biodiversity lost when this primary source is removed? Soil microbial and mesofaunal communities at the Rothamsted Highfield site were compared under a mixed grass sward, arable rotation and a section maintained as a bare-fallow for the past 50 years by regular tillage. Organic matter reserves have been degraded and microbial and mesofaunal numbers and mite diversity have declined in this unique bare-fallow site, where fresh carbon inputs have been drastically reduced. However, it supports a species-rich metabolically active bacterial community of similar diversity to that in soil maintained as grass sward. Thus in contrast to soil mesofauna, bacterial diversity (but not abundance) is apparently independent of plant inputs.     

The fate at several time intervals of 15N-labelled ammonium nitrate applied to an established grass sward

¹⁵N-labelled ammonium nitrate solution was applied in late April to circular, enclosed micro-plots prepared by pressing open-ended polypropylene cylinders into an established sward of perennial ryegrass. Cylinders were removed from the ground at intervals between 2 and 370 days after the application and assessments made of the distribution of ¹⁵N in plant and soil components. Of the added labelled N, 54.7% was recovered in the herbage which was cut four times during the growing season and again at the final sampling date. After two days, 37% of the labelled N was recovered in the soil microbial biomass. Large fluctuations occurred in the amount of ¹⁵N recovered in the soil microbial biomass over the next 14 days suggesting that rapid cycling of ¹⁵N occurred between this fraction and the mineral N fraction. After the first cut in late May, translocation of¹⁵N occurred more slowly from the roots into the stubble than from stubble into new herbage, so that the amount in the stubble declined more rapidly than did that in the roots. During the winter, there was no net transfer of N from the roots to above-ground components of the sward. By the end of the growing season, half the ¹⁵N remaining in the sward was immobilized in the humified fraction of the soil organic matter; some of this was mineralized in the following spring.     

Stickstoffumsatz in einigen obstbaulich genutzten Böden Südwestdeutschlands

Nitrogen turnover in some orchard soils of South West Germany Investigations in several orchards in South West Germany led to the following results: The actual content of mineral nitrogen as well as the rate of mineralization showed a marked dependence on the nature of soil, weather and soil management. Frequently the rate of mineralization had a distinct annual course following soil temperature. During summer additional oscillations partially were related to water and air contents of the soils. As a rule under old sward the rate of mineralization was distinctly higher than in the same soil being cultivated or treated with herbicides. Under mulched sod not only higher rates of mineralization, but also distinctly higher actual contents of mineral nitrogen could be found as compared with data under cropped sod. This ran parallel with higher nitrogen supplies to the trees and distinctly higher yields, but also with a worse storage quality of the fruits and conspicuously increased wash-out rates of nitrate (provided that manuring was continued with the primary amount of nitrogen). The total content of soil nitrogen depended much more on the method of soil management (swarded or not swarded) than on the amount of nitrogen fertilizers. It seems that the total nitrogen content of a soil tends towards a certain level corresponding to the conditions of site and soil managements and that this level cannot be raised constantly by manuring. From these results the following conclusions for practical fruit growing can be drawn: With modern forms of commercial fruit growing using mulched sward for soil management the nitrogen output is much less than with cultivating the same soil as arable land or intensive grassland. Due to cropping of the grass in former times nitrogen deficiency of fruit trees was not unusual, but since the grass under the trees has been mulched there is more danger of excessive nitrogen supply if manuring has been left as it was. Unlike the situation known of sand cultures with low nitrogen reserves in orchards with high mineralization rates the time of manuring is not of great consequence.     

A method to measure the susceptibility of pasture soils to poaching by cattle

Abstract. A new method of measuring susceptibility to poaching is described, based on the concept that poaching is caused by a progressive loss of soil strength during repeated treading in wet weather. Susceptibility was measured by the rate of loss of strength in response to concurrent treading and irrigation at standard rates. The pressures exerted on the ground by a walking dairy cow were simulated by a purpose-built penetrometer, whilst water was applied via a network of plastic pipes fitted with syringe needles. Measurements were performed on four pasture soils having a range of clay contents and compared in relation to a mechanism proposed for the process. The results show susceptibility to be a property not wholly determined by the clay content of the soil, but suggest that it is influenced by bulk density and the strength of the sward, which will van, according to weather and pasture management.     

Sustainable grassland systems: a modelling perspective based on the North Wyke Farm Platform

The North Wyke Farm Platform (NWFP) provides data from the field‐ to the farm‐scale, enabling the research community to address key issues in sustainable agriculture better and to test models that are capable of simulating soil, plant and animal processes involved in the systems. The tested models can then be used to simulate how agro‐ecosystems will respond to changes in the environment and management. In this study, we used baseline datasets generated from the NWFP to validate the Soil‐Plant‐Atmosphere Continuum System (SPACSYS) model in relation to the dynamics of soil water content, water loss from runoff and forage biomass removal. The validated model, together with future climate scenarios for the 2020s, 2050s and 2080s (from the International Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES): medium (A1B) and large (A1F1) emission scenarios), were used to simulate the long‐term responses of the system with three contrasting treatments on the NWFP. Simulation results demonstrated that the SPACSYS model could estimate reliably the dynamics of soil water content, water loss from runoff and drainage, and cut biomass for a permanent sward. The treatments responded in different ways under the climate change scenarios. More carbon (C) is fixed and respired by the swards treated with an increased use of legumes, whereas less C was lost through soil respiration with the planned reseeding. The deep‐rooting grass in the reseeding treatment reduced N losses through leaching, runoff and gaseous emissions, and water loss from runoff compared with the other two treatments.