Estimating soil surface temperatures under different crop covers in Hawaii

Abstract

Data from experiments conducted in Hawaii, measuring soil surface temperatures in plots cropped with potato, cassava, and maize, were used to estimate soil surface temperatures using a model from the temperate zone. According to this model maximum soil surface temperature under a given vegetative cover can be estimated from maximum air temperature and a factor, Et, that represents the elevation of maximum soil surface temperature over maximum air temperature under that crop cover. Inputs for the model are: maximum air temperatures and plant biomass measurements. A generally good agreement between estimated and observed maximum soil surface temperatures was obtained when Et was arbitrarily set to 0.1 × Et. For potato during summer of 1985, maximum soil surface temperature estimates were within an average of less than 2C of observed surface temperatures and with a deviation of no more than 3.8C. For cassava during summer of 1986, estimates were within 2.3±5.1C; for maize during summer of 1988, estimates were within 2.7±4.4C.     

Components of soil organic matter under grass and arable cropping

Components of the organic matter have been studied in three soils from adjacent sites with different long-term treatments: soil I, prolonged arable cultivation; soil II, 17 years under grass after prolonged arable cultivation; and soil III, old pasture. Contents of total organic C in the top 15cm were 0.9% in soil I. 1.7% in soil II and 4.8% in soil III. The light fraction, comprising partially decomposed materials with a specific gravity < 2.06, represented greater proportions of the organic C in soils II and III (20–23 per cent) than in soil I (8.5 per cent). The light fraction of soil III had a relatively high N content.The proportions of the soil organic C released, by hydrolysis, as neutral sugars, uronic acids, amino sugars, amino acids and phenolic acids were generally similar in the three soils, although uronic acids and phenolic acids constituted somewhat greater proportions in soils II and III than in I.The light fractions contained greater proportions of neutral sugars and phenolic acids, and smaller proportions of amino sugars and amino acids than the whole soils.     

The effect of mole drainage on soil temperatures under pasture

Drainage is often claimed to increase soil temperatures in early spring by decreasing the soil's heat capacity. Measurements of water table depth, soil water content and soil temperature were made during winter and spring on mole-pipe drained and undrained plots of a silt loam soil under pasture. Despite differences in water table depth and soil water content, drainage had no observable effect on soil temperature. Laboratory measurements of the thermal properties of soil cores at a matric potential of ?4kPa and then at saturation showed the volumetric heat capacity increased from 3.1 to 3.3 MJ m^?3 K^?1, with a proportional increase in the thermal conductivity from 1.1 to 1.2 W m^?1 K^?1. The thermal diffusivity remained unchanged. These values were used in a numerical simulation of the effects of drainage on the seasonal and diurnal oscillations in soil temperature. It is argued that the soil heat flux under pasture in spring is unaffected by drainage. The predicted temperature differences due to drainage are of the order of 0.2°C. As differences of this magnitude were observed between replicate thermometers in the field, it follows from the calculations above that any differences in soil temperature due to drainage would be too small to detect.     

室外条件下香根草降低微污染物淋溶的结构性土柱研究

In Burkina Faso, significant amounts of endosulfan are applied to cotton fields; in addition, urban vegetable agriculture is often characterised by high fertiliser inputs, such as urban solid wastes containing heavy metals (e.g., Cu and Cd). Thus, the relevance of surrounding cotton and urban vegetable plots with vetiver (Vetiveria zizanioides) hedges to reduce environmental pollution by micropollutants was investigated using a leaching experiment, with outdoor lysimeters filled with two representative agricultural soils of Burkina Faso: Vertisol and Lixisol. After 6 months, little Cu was found in the leachates (< 0.010% of the applied amount) due to its high adsorption coefficient and its tendency to remain at the soil surface. Despite leachate and bromide recoveries being greater in soils planted with vetiver grass than in the bare soils, smaller amounts of endosulfan and Cd were found in the effluents from the planted soils (0.01% to 0.70% of the applied amount) than in those from the bare soils (0.01% to 1.48% of the applied amount), in agreement with their adsorption coefficients. These results may also be explained by a greater degradation of endosulfan in planted soils compared to bare soils and the absorption of Cd by vetiver. Thus, vetiver may decrease the risk of groundwater contamination, especially for Cd and endosulfan, which are more mobile than Cu. In addition, despite the smaller amounts of endosulfan and Cd measured in the Vertisol leachates (0.01% and 0.04% of the applied amount, respectively) compared to the Lixisol leachates, vetiver was more effective in decreasing the leaching of micropollutants if planted on Lixisol rather than on Vertisol. Further field monitoring is necessary to demonstrate the effectiveness of vetiver under the climatic conditions of Burkina Faso.     

Nitrate leaching losses under Miscanthus grass planted on a silty clay loam soil

Abstract. Nitrate leaching under newly planted Miscanthus grass was measured for three years. The crop received either no fertilizer-N or an annual spring application of 60 kg or 120 kg N ha^-1. During three winters soil water was collected from porous cup probes installed 90 cm deep. Nitrate leaching was calculated from the mean drain flow recorded in two drain gauges multiplied by the mean nitrate-N concentration in the soil water solutions collected. In the first year soil water nitrate concentrations were high on all treatments and N losses were 154, 187 and 228 kg ha^-1 respectively on the unfertilized treatment and those that received 60 or 120 kg N ha^-1. Leaching losses in the second and third years were, in turn, 8, 24 and 87 kg ha^-1 and 3, 11 and 30 kg ha^-1 for the unfertilized treatment and for the 60 and 120 kg N ha^-1 treatments respectively. Leaching losses were closer to those recorded under extensively managed grassland than arable land. The large losses in the first year were probably due to the previous agricultural management at the site and excessive inputs of N on the fertilized plots. In the second and third year, lower drainage volumes may also have influenced losses. The results show that Miscanthus , once established, can lead to low levels of nitrate leaching and improved groundwater quality compared with growing arable crops.     

Size and activity of the soil microbial biomass under grass and arable management

 The effects of 5 years of continuous grass/clover (Cont grass/clover) or grass (Cont grass) pasture or 5 years of annual grass under conventional (Ann grass CT) or zero tillage (Ann grass ZT) were compared with that of 5 years of continuous barley (LT arable) on a site which had previously been under arable crops for 11 years. For added comparison, a long-term grass/clover pasture site (LT past) nearby was also sampled. Soil organic C (C_org) content followed the order LT arable=Ann grass CT<Ann grass ZT<Cont grass=Cont grass/clover<LTpast. Trends with treatment for microbial biomass C (C_mic), basal respiration, flourescein diacetate (FDA) hydrolytic activity, arginine ammonification rate and the activities of dehydrogenase, protease, histidase, acid phosphatase and arylsulphatase enzymes were broadly similar to those for C_org. For C_mic, FDA hydrolysis, arginine ammonification and the activities of histidase, acid phosphatase and arylsulphatase, the percentage increase caused by 5 years of continuous pasture (in comparison with LT arable) was 100–180%, which was considerably greater than that for organic C (i.e. 60%). The microbial metabolic quotient (qCO₂) was higher for the two treatments which were mouldboard ploughed annually (LT arable and Ann grass CT) than for the undisturbed sites. At the undisturbed sites, C_org declined markedly with depth (0–15 cm) and there was a similar stratification in the size and activity of C_mic and enzyme activity. The microbial quotient (C_mic/C_org) declined with depth whilst qCO₂ tended to increase, reflecting a decrease in the proportion of readily available substrate with depth. Received: 7 July 1998     

The effect of large applications of pig slurry on the strength of soil under grass

Abstract. The effect of eight years of applications of five rates (0, 134, 269, 538 and 1075 m³ ha⁻¹ a⁻¹) of pig slurry on the soil strength two years later were studied in a field experiment. Soil strength in the 0–150 mm depth was measured on five occasions in winter using a hand-held recording cone penetrometer. On one occasion the penetration resistance at some depths greater than 100 mm was significantly ( P < 0.001) decreased by adding more than 269 m³ of slurry ha⁻¹ a⁻¹. On three occasions different amounts of slurry caused significant differences in the rate of increase of penetration resistance with depth. Large applications of slurry may decrease penetration resistance because they increase organic matter, thereby increasing the water retention of the soil.     

土壤调理剂对旱、盐条件下草种萌发的影响

利用田间和盆栽试验研究了不同材料土壤调理剂对草的生长影响,并探讨其使用条件和使用方法。结果表明,干旱条件下,应用调理剂可减轻干旱土壤盐碱的危害,提高出苗率在75%以上。土壤调理剂作种子包衣有较好的抗旱保苗效果,包衣处理的草籽出苗率较对照提高约19%;包衣处理的苗期土壤水分较对照高5%～11%;包衣处理的苗期耗水量较对照降低5%～12%。播期土壤水分为田间持水量的40%(土壤含水量约11%)和20%(土壤含水量约5%)的土壤上,土壤调理剂处理的出苗数分别较对照提高11%～14%和14%～24%;0～20cm土层含水量较对照增加4%～15%。当土壤水分为田间持水量的40%时,土壤调理剂处理的苗期生物量较对照增加3%～42%,单位耗水量较对照降低9%～34%;土壤水分在田间持水量的20%时,调理剂处理的苗期生物量和单位耗水量较对照亦分别表现为增加和降低趋势。     

Soil survey interpretation: Estimating use-potentials of a clay soil under various moisture regimes

Current Dutch soil survey interpretation emphasizes assessment factors which independently define key aspects of soil behavior under actual conditions. For grassland these are: moisture-supply capacity, bearing capacity and drainage status. Practical questions focus on how actual limitations can be overcome. Computer simulation techniques, to be focused on the individual assessment factors, are needed to answer these questions. Soil survey and morphology data were used in this context to: (1) select experimental sites; (2) modify physical monitoring procedures; (3) derive simulation models for swelling soils with macropores; (4) develop simple field methods for characterizing basic physical soil properties and their regional variability, and (5) use soil maps for extrapolating the obtained interpretations.Future soil survey reports should ideally contain basic physical data and the possible ranges for the different assessment factors, expressed by simulation as a function of water management. basic data include hydraulic conductivity, moisture retention, bearing capacity and drainage rate. The latter two were characterized in this study by new field methods. Possible ranges differ for the different assessment factors. For example, an inadequate moisture supply capacity in the growing season can be completely compensated by raising the water table, by sprinkler irrigation or by a combination of both methods. The presented simulation offers a quantitative analysis. The inadequate bearing capacity and drainage status can be compensated for only partly by lower water-table levels in winter and spring.     

Estimating soil texture from sample density

Abstract

A number of laboratory methods for determining soil physical fractions have been proposed. The methods being cumbersome and time consuming cannot be adopted for routine analysis in soil testing laboratories. Therefore, a simple method which could provide quantitative estimates of the soil size fractions is required. This study used soil sample density (ratio of mass of soil in a standard scoop to its volume) to estimate soil separates. Regression models were developed for predicting soil separates from sample density. Sand, silt, and silt+clay fractions were best described by second degree polynomials with coefficients of determination ranging from 0.75–0.80. Although the exponential function was statistically equivalent to the second degree polynomial for estimating clay, it was preferable as it yielded a better shape of the fitted curve at sample densities <1.2 g cm^‐3. Validation of the models with independent data showed that model‐predicted values of various size fractions matched well with laboratory measurements with coefficients of correlation ranging between 0.95–0.99. The higher correlation coefficients between the measured and estimated clay, silt, and sand fractions both for model development and their validation on independent data suggest that the models could be used for estimating soil separates from sample density measurements.     

Estimating soil salinity by disjunctive kriging

Abstract. Disjunctive kriging provides minimum variance estimates of properties from non-linear combinations of spatially correlated sample data. In addition it can be used to estimate the conditional probability that some critical threshold is exceeded or that there is a deficit at unsampled points. The technique has been applied to estimate and map the salinity of the soil in the Bet Shean Valley of Israel from measurements of electrical conductivity. In November 1985 the estimated electrical conductivity of the soil exceeded 4 mS per centimetre throughout most of the region, and in only a small area was the probability of salinity less than 0.2. By March 1986 the electrical conductivity had declined everywhere to less than 4 mS per centimetre, and the conditional probability of exceeding this value nowhere exceeded 0.25. Despite the fluctuation in salinity farmers seem to have it under control. The results suggest that winter wheat is likely to germinate poorly in the saltier parts of the region and that lucerne (alfalfa, Medicago sativa) is unlikely to yield its maximum over most of it. Cotton, a summer crop sown in spring, should not suffer.     

Modelling soil temperatures in northern peatlands

Methane emissions from northern peatlands are strongly dependent on soil temperatures. Therefore, to predict methane emissions from northern peatlands under future climatic conditions, it is important to simulate the effect of these changing climatic conditions on peat temperatures. This article reports on the development and testing of two one‐dimensional (1D) models used to simulate soil temperatures at shallow depths in a northern peatland. First, the HIP‐Dlet (Heat in Peat – Dirichlet) model applies measured temperatures to the surface boundary of a conduction‐based temperature model. Secondly, the HIP‐Nmann (Heat in Peat – von Neumann) model simulates the surface boundary from standard meteorological measurements. The HIP‐Dlet model provides a reasonable to good approximation of measured temperatures showing that heat transport processes within the soil are adequately simulated. The model does not simulate an advective liquid heat flux. However, only substantial rainfall events (> 70 mm over 3 days) during the study period had any significant effect on model error. Errors in the HIP‐Nmann model were of a similar magnitude to the HIP‐Dlet model. Errors in the HIP‐Dlet model resulted predominantly from errors in the measured soil temperatures. Errors in the HIP‐Nmann were due to errors in the measured soil temperatures and the inaccurate simulation of the surface boundary condition. The development of future peatland temperature models should, therefore, focus on the simulation of the surface boundary condition, particularly the parameterisation of the surface resistance that is shown here to produce significant errors in the modelled soil temperatures.     

Atrazine and phenanthrene degradation in grass rhizosphere soil

Organic contaminants often disappear more quickly from planted than from non-planted soils. Five grass species (Sudan grass, ryegrass, tall fescue, crested wheatgrass and switch grass) were grown in soils without (Phase I) or with (Phase II) prior atrazine (ATR) and phenanthrene (PHE) amendment to study the degradation of these compounds by rhizosphere microorganisms. In suspensions of soil without prior chemical exposure, no significant loss of ATR was observed after 16 days incubation. The most probable number (MPN) of ATR-degrading bacteria in the soils was below detection. Phenanthrene degradation was observed in suspensions inoculated with all soils, but the rates of degradation were not significantly different among them. The number of PHE-degrading bacteria was similar in planted and non-planted soils (10⁵ cells g⁻¹ soil) except the number in tall fescue soil was significantly higher than in non-planted soil. In the Phase II study, both compounds were mineralized whether or not soils had been conditioned with ATR or PHE. Prior amendment with either ATR or PHE significantly reduced the acclimation period preceding the onset of mineralization. However, enumeration procedures detected ATR-degrading bacteria only in ATR-amended soils. Prior exposure to PHE did not alter the number of PHE-degrading bacteria significantly.     

模拟降雨下黄土区草地灌木地土壤水分空间变化规律

利用黄土区燕沟流域42场模拟降雨下土壤水分观测数据,研究2种坡度的草地、灌木地在不同经营方式（原状地、刈割地、翻耕地）下的土壤水分对模拟降雨的响应。结果表明：1）在5次降雨补充下,依据土壤水分的标准差和变异系数指标,0-100cm土壤水分受土地经营方式影响表现为,原状草灌地土壤水分可划分为活跃层、次活跃层和相对稳定层,刈割地全剖面为相对稳定层,翻耕地可分为活跃层和相对稳定层。2）单次降雨事件则随降雨量增加,各经营方式下的水分活跃层逐渐变薄或消失,次活跃层变厚,而相对稳定层变薄,整个土壤剖面水分变化趋于一致。3）对于受高强度降雨补充的土壤水分变异性分层,建议采用更加灵敏的土壤水分标准差和变异系数判别标准：活跃层,标准差大于1.4,变异系数大于0.12;次活跃层,标准差1.4-0.9,变异系数0.12-0.08;相对稳定层,标准差小于0.9,变异系数小于0.08。4）坡度越小,土壤水分越高,坡度对草灌木地、刈割地的影响较翻耕地显著,且对50-100cm层水分影响远大于对表层0-50cm的影响。总之,降雨后土壤水分0-100cm层不断增加,且剖面土壤水分逐渐一致,土地经营方式、坡度因素对土壤水分变化强度和在不同深度土层中的表现有显著影响。     

Estimating parameters of transported soil particles by calculation

Equations were proposed for calculating parameters of detached and transported soil particles with due account for the heterogeneity of soil aggregates, the pulsation of bottom flow velocities, and the degree of aggregate destruction in shallow-water flows. These equations were applied for irrigated typical sierozem of Tajikistan.     

基于两组负水头入渗数据推求Brooks-Corey模型中的参数

非饱和土壤水分运动和溶质运移的研究需要准确的土壤水动力特性信息,然而土壤水动力特性的测定往往费时费力且较难。该研究假设土壤水力动力特性可用Brooks-Corey模型来描述,结合Darcy定理和质量守恒推导了基于两组负水头下入渗数据来估计Brooks-Corey模型参数的方法。利用负水头下一维土壤水分运动中累计入渗量和湿润峰之间的关系实现了参数的求解,大量的数值模拟数据检验了该方法,并与Wang的方法进行了比较和分析,结果表明本研究提供了一种简单而且精确的确定土壤水动力参数方法。     

基于EPO-PLS回归模型的盐渍化土壤含水率高光谱反演

表层土壤含水率对于指导农业灌溉有重要的作用。研究表明,土壤光谱受到土壤水分和盐分的共同影响,但对于盐渍化地区的土壤含水率高光谱反演却很少涉及。该文通过对11组不同含盐量土壤室内蒸发过程连续监测,获取相关反射率光谱和水分、盐分的变化数据,利用外部参数正交化方法(external parameter orthogonalisation,EPO)预处理土壤光谱,滤除盐分(质量比0.1%~5.0%)的影响,建立经过EPO预处理后的偏最小二乘(partial least squares regression after EPO pre-processing,EPO-PLS)土壤水分预测模型。与偏最小二乘(partial least square model,PLS)模型相比,验证样本的决定系数R2和对分析误差RPD(residual predictive deviation)分别从0.722、1.976上升到0.898、3.145;均方根误差RMSE从5.087 g/(100 g)减少到3.237 g/(100 g)。通过EPO算法预处理后的模型性能提升显著,利用该方法能够有效的消除土壤盐分的影响,很好地实现盐渍化地区的水分含量估测。     

Vertical distribution of nematodes in arable soil under grass (Festuca pratensis) and barley (Hordeum distichum)

Summary The connection between faunal composition and soil factors is discussed in this study on vertical distribution of soil nematodes under grass and barley. The investigation was undertaken on the field site of a Swedish integrated research project Ecology of Arable Land. The Role of Organisms in Nitrogen Cycling. Higher nematode number (7.6 × 10⁶ m^–2) and biomass (340 mg dry wt. m^–2) were found under a 4-year-old grass ley than under barley (5.0 × 10⁶ m^–2; biomass, 136 mg dry wt. m^–2). Plant feeders dominated under the grass ley (3.2 × 10⁶ m^–2 whereas under barley the bacterial feeders (2.4 × 10⁶ m^–2) were the most abundant feeding group. Number, biomass, mean individual size and various community parameters indicated a much better nutritive situation for the nematodes under grass than under barley. The vertical changes in the various parameters, including proportion of egg-carrying females, indicated an increasing food shortage for the nematode populations towards greater depths. In the top soil, predation could be an important factor in regulating nematode number.Dedicated to the late Prof. Dr. M.S. Ghilarov     

Moss regulates soil evaporation leading to decoupling of soil and near-surface air temperatures

Journal of Soils and Sediments - Moss covers a vast area from the polar to the tropics on a global scale and has important regulatory effects on the biogeochemical processes in the soil. Previous...