Field and laboratory measurements

Developing management practices for salt-affected soils and low-quality irrigation waters includes determining the salinity of the soil and the water, the origin of the various salts, and the crops that can be grown. Gathering this information can he very time- and resource-consuming because salt-affected soils tend to be extremely variable with time and space. In this chapter, soil and water sampling methods and the storage of samples will be discussed. References for the more commonly accepted procedures are listed

Interspersed Salt-Affected and Unaffected Dryland Soils of the Lower Rio Grande Valley: I. Chemical, Physical, and Mineralogical Characteristics

The effects of soluble salts on soil productivity are global. Recent reports present information about saline soils in Spain (1), Iraq (2, 7), Canada (6), Egypt (16), and the United States (8, 10, 15, 19). Although in some areas much has been done towards reclaiming saline soils (5, 9, 17, 19), in other areas plagued by salinity problems (1, 6, 7), little or no progress is eviden

Interspersed Salt Affected and Unaffected Dryland Soils of the Lower Rio Grande Valley: II. Occurrence of Salinity in Relation to Infiltration Rates and Profile Characteristics

Thirteen variables including chemical and physical characteristics, topographical features, and water table depth measurements were statistically analyzed for differences between seven saline and adjacent nonsaline soil profiles of Lower Rio Grande Valley salt-affected dryland soils. Cumulative intake and final intake rate, electrical conductivity of soil saturation extract, exchangeable sodium percentage, clay percentage, relative elevation, sand percentage, soil surface slope, and cation-exchange capacity were the variables most consistently different between saline and nonsaline soils. Profile salinity and water intake were both significantly correlated with profile sand and clay content and with soil surface elevation, In addition water infiltration was a function of profile salinity. Consideration of the effects of clay content, ground surface elevation, and soil slope on the processes of runoff and infiltration lead to the conclusion that the observed salinity pattern is due to differential infiltration of rainfall which results in differences in leaching between saline and nonsaline areas

Immediate antiviral therapy appears to restrict resting CD4 + cell HIV-1 infection without accelerating the decay of latent infection

HIV type 1 (HIV-1) persists within resting CD4 + T cells despite anti-retroviral therapy (ART). To better understand the kinetics by which resting cell infection (RCI) is established, we developed a mathematical model that accurately predicts (r = 0.65, P = 2.5 × 10 -4) the initial frequency of RCI measured about 1 year postinfection, based on the time of ART initiation and the dynamic changes in viremia and CD4 + T cells. In the largest cohort of patients treated during acute seronegative HIV infection (AHI) in whom RCI has been stringently quantified, we found that early ART reduced the generation of latently infected cells. Although RCI declined after the first year of ART in most acutely infected patients, there was a striking absence of decline when initial RCI frequency was less than 0.5 per million. Notably, low-level viremia was observed more frequently as RCI increased. Together these observations suggest that (i) the degree of RCI is directly related to the availability of CD4 + T cells susceptible to HIV, whether viremia is controlled by the immune response and/or ART; and (ii) that two pools of infected resting CD4 + T cells exist, namely, less stable cells, observable in patients in whom viremia is not well controlled in early infection, and extremely stable cells that are established despite early ART. These findings reinforce and extend the concept that new approaches will be needed to eradicate HIV infection, and, in particular, highlight the need to target the extremely small but universal, long-lived latent reservoir

Field and laboratory measurements

Developing management practices for salt-affected soils and low-quality irrigation waters includes determining the salinity of the soil and the water, the origin of the various salts, and the crops that can be grown. Gathering this information can he very time- and resource-consuming because salt-affected soils tend to be extremely variable with time and space. In this chapter, soil and water sampling methods and the storage of samples will be discussed. References for the more commonly accepted procedures are listed

Interspersed Salt-Affected and Unaffected Dryland Soils of the Lower Rio Grande Valley: I. Chemical, Physical, and Mineralogical Characteristics

The effects of soluble salts on soil productivity are global. Recent reports present information about saline soils in Spain (1), Iraq (2, 7), Canada (6), Egypt (16), and the United States (8, 10, 15, 19). Although in some areas much has been done towards reclaiming saline soils (5, 9, 17, 19), in other areas plagued by salinity problems (1, 6, 7), little or no progress is eviden

Interspersed Salt Affected and Unaffected Dryland Soils of the Lower Rio Grande Valley: II. Occurrence of Salinity in Relation to Infiltration Rates and Profile Characteristics

Thirteen variables including chemical and physical characteristics, topographical features, and water table depth measurements were statistically analyzed for differences between seven saline and adjacent nonsaline soil profiles of Lower Rio Grande Valley salt-affected dryland soils. Cumulative intake and final intake rate, electrical conductivity of soil saturation extract, exchangeable sodium percentage, clay percentage, relative elevation, sand percentage, soil surface slope, and cation-exchange capacity were the variables most consistently different between saline and nonsaline soils. Profile salinity and water intake were both significantly correlated with profile sand and clay content and with soil surface elevation, In addition water infiltration was a function of profile salinity. Consideration of the effects of clay content, ground surface elevation, and soil slope on the processes of runoff and infiltration lead to the conclusion that the observed salinity pattern is due to differential infiltration of rainfall which results in differences in leaching between saline and nonsaline areas

Application of Spectral Remote Sensing for Agronomic Decisions

Remote sensing has provided valuable insights into agronomic management over the past 40 yr. The contributions of individuals to remote sensing methods have lead to understanding of how leaf reflectance and leaf emittance changes in response to leaf thickness, species, canopy shape, leaf age, nutrient status, and water status. Leaf chlorophyll and the preferential absorption at different wavelengths provides the basis for utilizing reflectance with either broad-band radiometers typical of current satellite platforms or hyperspectral sensors that measure reflectance at narrow wavebands. Understanding of leaf reflectance has lead to various vegetative indices for crop canopies to quantify various agronomic parameters, e.g., leaf area, crop cover, biomass, crop type, nutrient status, and yield. Emittance from crop canopies is a measure of leaf temperature and infrared thermometers have fostered crop stress indices currently used to quantify water requirements. These tools are being developed as we learn how to use the information provided in reflectance and emittance measurements with a range of sensors. Remote sensing continues to evolve as a valuable agronomic tool that provides information to scientists, consultants, and producers about the status of their crops. This area is still relatively new compared with other agronomic fields; however, the information content is providing valuable insights into improved management decisions. This article details the current status of our understanding of how reflectance and emittance have been used to quantitatively assess agronomic parameters and some of the challenges facing future generations of scientists seeking to further advance remote sensing for agronomic applications