Regional field measurement of soil moisture content with neutron probe

The neutron logging method has been widely used for field measurement of soil moisture content. This non-destructive method permitted the measurement of in-situ soil moisture content at various depths without the need for burying any sensor. Twenty-three sites located around regional Melbourne have been selected for long term monitoring of soil moisture content using neutron probe. Soil samples collected during the installation are used for site characterisation and neutron probe calibration purposes. A linear relationship is obtained between the corrected neutron probe reading and moisture content for both the individual and combined data from seven sites. It is observed that the liner relationship, developed using combined data, can be used for all sites with an average accuracy of about 80%. Monitoring of the variation of soil moisture content with depth in six months for two sites is presented in this paper.

Soil moisture monitoring at the field scale using neutron probe

Measurement of the moisture variation in soils is required for geotechnical design and research because soil properties and behavior can vary as moisture content changes. The neutron probe, which was developed more than 40 years ago, is commonly used to monitor soil moisture variation in the field. This study reports a full-scale field monitoring of soil moisture using a neutron moisture probe for a period of more than 2 years in the Melbourne (Australia) region. On the basis of soil types available in the Melbourne region, 23 sites were chosen for moisture monitoring down to a depth of 1500 mm. The field calibration method was used to develop correlations relating the volumetric moisture content and neutron counts. Observed results showed that the deepest “wetting front” during the wet season was limited to the top 800 to 1000 mm of soil whilst the top soil layer down to about 550mmresponded almost immediately to the rainfall events. At greater depths (550 to 800mmand below 800 mm), the moisture variations were relatively low and displayed predominantly periodic fluctuations. This periodic nature was captured with Fourier analysis to develop a cyclic moisture model on the basis of an analytical solution of a one-dimensional moisture flow equation for homogeneous soils. It is argued that the model developed can be used to predict the soil moisture variations as applicable to buried structures such as pipes.

Comparison of electrical resistivity by geophysical method and neutron probe logging for soil moisture monitoring in a forested watershed

Geophysical methods are becoming more popular nowadays in the field of hydrology due to their time and space efficiency. So an attempt has been made here to relate electrical resistivity with soil moisture content in the field. The experiments were carried out in an experimental watershed `Mulehole' in southern India, which is a forested watershed with approximately 80% red soil. Five auger holes were drilled to perform the soil moisture and electrical resistivity measurements in a toposequence having red and black soils, with sandy weathered soil at the bottom. Soil moisture was measured using neutron probe and electrical resistivity was measured using electrical logging tool. The results indicate that electrical resistivity measurements can be used to measure soil moisture content for red soils only.

Using a structural approach to identify relationships between soil and erosion in a semi-humid forested area, South India

Biogeochemical and hydrological cycles are currently studied on a small experimental forested watershed (4.5 km(2)) in the semi-humid South India. This paper presents one of the first data referring to the distribution and dynamics of a widespread red soil (Ferralsols and Chromic Luvisols) and black soil (Vertisols and Vertic intergrades) cover, and its possible relationship with the recent development of the erosion process. The soil map was established from the observation of isolated soil profiles and toposequences, and surveys of soil electromagnetic conductivity (EM31, Geonics Ltd), lithology and vegetation. The distribution of the different parts of the soil cover in relation to each other was used to establish the dynamics and chronological order of formation. Results indicate that both topography and lithology (gneiss and amphibolite) have influenced the distribution of the soils. At the downslope, the following parts of the soil covers were distinguished: i) red soil system, ii) black soil system, iii) bleached horizon at the top of the black soil and iv) bleached sandy saprolite at the base of the black soil. The red soil is currently transforming into black soil and the transformation front is moving upslope. In the bottom part of the slope, the chronology appears to be the following: black soil > bleached horizon at the top of the black soil > streambed > bleached horizon below the black soil. It appears that the development of the drainage network is a recent process, which was guided by the presence of thin black soil with a vertic horizon less than 2 in deep. Three distinctive types of erosional landforms have been identified: 1. rotational slips (Type 1); 2. a seepage erosion (Type 2) at the top of the black soil profile; 3. A combination of earthflow and sliding in the non-cohesive saprolite of the gneiss occurs at midslope (Type 3). Types 1 and 2 erosion are mainly occurring downslope and are always located at the intersection between the streambed and the red soil-black soil contact. Neutron probe monitoring, along an area vulnerable to erosion types 1 and 2, indicates that rotational slips are caused by a temporary watertable at the base of the black soil and within the sandy bleached saprolite, which behaves as a plane of weakness. The watertable is induced by the ephemeral watercourse. Erosion type 2 is caused by seepage of a perched watertable, which occurs after swelling and closing of the cracks of the vertic clay horizon and within a light textured and bleached horizon at the top of black soil. Type 3 erosion is not related to the red soil-black soil system but is caused by the seasonal seepage of saturated throughflow in the sandy saprolite of the gneiss occurring at midslope. (c) 2006 Elsevier B.V. All rights reserved.

植物生长与土壤水关系调控起始期

确定植物生长与土壤水关系调控起始期是可持续利用土壤水资源的基础。以柠条为研究对象,采用中子仪对黄土丘陵半干旱区撂荒地,1～5年生柠条林生长和土壤水分进行长期定位观测和分析。结果表明:1 a内,随着时间推移,柠条利用土壤水分深度从播种时的表层土壤增加到220 cm;随着林龄增加,除丰水年2年生柠条林地土壤储水量增加外,柠条利用土壤水分深度和耗水量增加,林地土壤储水量下降。在2004年生长末期,3年生柠条林地100 cm土层的土壤含水量低于萎蔫系数,4年生柠条林地土壤旱化加剧,柠条生长与土壤水关系调控起始期是第5年。此时需要调控柠条生长与土壤水关系,采取措施降低柠条水分耗水量,实现土壤水资源可持续利用。

半干旱区柠条林利用土壤水分深度和耗水量

植物根系利用土壤水分深度和耗水量是研究植物与土壤水关系的基础。以柠条为对象,采用中子仪,对撂荒地和柠条林地土壤水分进行长期定位观测和分析。结果表明,2002年内,随着时间推移,柠条利用土壤水分深度从播种时的2cm左右,迅速增加到9月1日的90cm,10月15日的110cm,11月1日的170cm,到11月15日柠条利用土壤水分深度为220cm;除丰水年(2年生)柠条土壤储水量增加了122.8mm外,随着林龄的增加和降雨量等的变化,植物利用土壤水分的深度和耗水量增加,土壤储水量下降。到2004年生长季末,3年生柠条林地100cm土层出现土壤干层,5年生柠条林地剖面60—300cm土层出现土壤干层。此时需要采取措施,控制柠条生长、密度和耗水量,实现土壤水资源的可持续利用。

Competition in tree row agroforestry systems. 3. Soil water distribution and dynamics

The purpose of this study was to test the hypothesis that soil water content would vary spatially with distance from a tree row and that the effect would differ according to tree species. A field study was conducted on a kaolinitic Oxisol in the sub-humid highlands of western Kenya to compare soil water distribution and dynamics in a maize monoculture with that under maize (Zea mays L.) intercropped with a 3-year-old tree row of Grevillea robusta A. Cunn. Ex R. Br. (grevillea) and hedgerow of Senna spectabilis DC. (senna). Soil water content was measured at weekly intervals during one cropping season using a neutron probe. Measurements were made from 20 cm to a depth of 225 cm at distances of 75, 150, 300 and 525 cm from the tree rows. The amount of water stored was greater under the sole maize crop than the agroforestry systems, especially the grevillea-maize system. Stored soil water in the grevillea-maize system increased with increasing distance from the tree row but in the senna-maize system, it decreased between 75 and 300 cm from the hedgerow. Soil water content increased least and more slowly early in the season in the grevillea-maize system, and drying was also evident as the frequency of rain declined. Soil water content at the end of the cropping season was similar to that at the start of the season in the grevillea-maize system, but about 50 and 80 mm greater in the senna-maize and sole maize systems, respectively. The seasonal water balance showed there was 140 mm, of drainage from the sole maize system. A similar amount was lost from the agroforestry systems (about 160 mm in the grevillea-maize system and 145 mm in the senna-maize system) through drainage or tree uptake. The possible benefits of reduced soil evaporation and crop transpiration close to a tree row were not evident in the grevillea-maize system, but appeared to greatly compensate for water uptake losses in the senna-maize system. Grevillea, managed as a tree row, reduced stored soil water to a greater extent than senna, managed as a hedgerow.

Variação entre a lâmina de irrigação aplicada e armazenada no solo sob condições de irrigação com baixa uniformidade de distribuição de água

In sprinkler irrigation is important to have a good uniformity of application so that the water in the root zone does not show areas with little available water while others have percolating beyond the plant roots, even though the soil allows a lateral redistribution of water. A usual way to obtain the uniformity of irrigation is by measures of dispersion. The aim of this work was to evaluate the uniformity of water stored in a sand soil before and after non uniformity depth irrigation applied from one sprinkler, as well the variation of storage in a 0-0,45 m layer soil using a neutron probe. The statistical design was completely randomized, and for the variable Christiansen uniformity coefficient modified (CUCHH) were 10 treatments (the irrigation depth, 8 intervals of readings storage, more the existing one before irrigation added to the irrigation depth). For the variable soil water, the treatments were the same, excepting the irrigation depth. Despite the low surface uniformity (16.3%), there was not significantly difference between the storage uniformity before, after irrigation and the potential, however there was from these to the surface uniformity. From de irrigation depth, 15.3 mm, only 6.1 mm remained in the layer from 0 to 0.45 m. There was not significantly difference between the water stored in the soil before and after irrigation within a period of up to 134 hours, being the increase in storage due to irrigation was just 11.7%.

Avaliação das técnicas TDR (Reflectometria por Domínio do Tempo) e moderação de nêutrons, na determinação do teor de água em diferentes classificações do solo

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Manejo da viticultura irrigada no semiárido com base em zonas homogêneas do solo e da planta

Pós-graduação em Agronomia (Irrigação e Drenagem) - FCA

Atrazine movement in a dark red latosol of the tropics.

Atrazine dissplacement was studied in a soll profile as function of water movement and time after herbicide application, taldng into account possible influences of preferential flow on keaching. The experiment consisted of two 7 x 7 m plots of a dark red latosol (Kanduidalfic Eutrudox), located at Pirecicaba, SP, Brazil (22o43'S and 47o25'W), 250 km inside continent, at an altitude of 580 m. One plot was previously treated with 1,000 kg/ha of lime, in order to increase saturation to 88%, and 500 kg/ha of gypsum. Each plot was instrumented with tensiometers, neutron probe acess tubes and soil solution extractors, in order to monitor water and atrazine flows. Atrazine was applied at the high rate of 6 kg/ha of active principllle. Results showed intensiive leaching of atrazine in the whole soil profile, up to the instrumented depth of 150 cm, alredy at the first sampling, seven days after herbicide application. The limed plot showed much higher atrazine leachinng losses than the other plot. The atrazine adsorption capacity of the soll is very low, its maximum value being of the order of 10%, for the 0-15 cm surface layer.

Neutron-proton bremsstrahlung from intermediate energy heavy-ion reactions as a probe of the nuclear symmetry energy?

Hard photons from neutron-proton bremsstrahlung in intermediate energy heavy-ion reactions are examined as a potential probe of the nuclear symmetry energy within a transport model. Effects of the symmetry energy on the yields and spectra of hard photons are found to be generally smaller than those due to the currently existing uncertainties of both the in-medium nucleon-nucleon cross sections and the photon production probability in the elementary process pn -> pn gamma. Very interestingly, nevertheless, the ratio of hard photon spectra R-1/2(gamma) from two reactions using isotopes of the same element is not only approximately independent of these uncertainties but also quite sensitive to the symmetry energy. For the head-on reactions of Sn-132 + Sn-124 and Sn-112 + Sn-112 at E-beam/A = 50 MeV, for example, the R-1/2(gamma) displays a rise up to 15% when the symmetry energy is reduced by about 20% at rho = 1.3 rho(0) which is the maximum density reached in these reactions. (C) 2008 Elsevier B.V. All rights reserved.

Double neutron-proton differential transverse flow as a probe for the high density behavior of the nuclear symmetry energy

The double neutron-proton differential transverse flow taken from two reaction systems using different isotopes of the same element is studied at incident beam energies of 400 and 800 MeV/nucleon within the framework of an isospin- and momentum-dependent hadronic transport model IBUU04. The double differential flow is found to retain about the same sensitivity to the density dependence of the nuclear symmetry energy as the single differential flow in the more neutron-rich reaction. Because the double differential flow reduces significantly both the systematic errors and the influence of the Coulomb force, it is thus more effective probe for the high-density behavior of the nuclear symmetry energy.

Double neutron/proton ratio of nucleon emissions in isotopic reaction systems as a robust probe of nuclear symmetry energy

The double neutron/proton ratio of nucleon emissions taken from two reaction systems using four isotopes of the same element, namely, the neutron/proton ratio in the neutron-rich system over that in the more symmetric system, has the advantage of reducing systematically the influence of the Coulomb force and the normally poor efficiencies of detecting low energy neutrons. The double ratio thus suffers less systematic errors. Within the IBUU04 transport model the double neutron/proton ratio is shown to have about the same sensitivity to the density dependence of nuclear symmetry energy as the single neutron/proton ratio in the neutron-rich system involved. The double neutron/proton ratio is therefore more useful for further constraining the symmetry energy of neutron-rich matter.

Rotation alignment in neutron-rich Cr isotopes: A probe of deformed single-particle levels across N=40

Recent experiments have reached the neutron-rich Cr isotope with N = 40 and confirmed enhanced collectivity near this subshell. The current data focus on low-spin spectroscopy only, with little information on the states where high-j particles align their spins with the system rotation. By applying the projected shell model, we show that rotation alignment occurs in neutron-rich even-even Cr nuclei as early as spin 8 (h) over bar h and, owing to shell filling, the aligning particles differ in different isotopes. It is suggested that observation of irregularities in moments of inertia is a direct probe of the deformed single-particle scheme in this exotic mass region.