Monitoring water and salt movement during a leaching irrigation using time domain reflectometry

Non-Peer ReviewedTime domain reflectometry (TDR) has become an accepted method of measuring soil water content. Laboratory results have indicated that it may also be possible to measure soil electrical conductivity (EC) using TDR. The objectives of this experiment were to investigate the utility of TDR as a field measurement of EC and to illustrate a potential application of the technique. Field research was conducted at the Saskatchewan Irrigation Development Centre on a field which has been reclaimed from salinity over the past 10 years by the installation of tile drains and a fall leaching program. To test the accuracy of bulk soil EC measurements made by TDR (ECr), EC was also measured on water samples from suction lysimeters which sampled at the same depths as the TDR waveguides and converted to a bulk soil basis (EC8). Comparisons between ECT and EC8 were made three times during the 1992 growing season (when the soil was relatively dry) and four times during the fall leaching period (when the soil was much wetter). ECr was significantly correlated (p<0.001) to EC8. However, the measurement of ECT was affected by soil moisture content and an empirical function had to be used to eliminate this source of variability. Good agreement (R2=0.93) was obtained between ECT and EC8 when this function was applied. During the leaching irrigation, water and salt movement was monitored by TDR. At most sites, a salt bulge could be clearly identified moving downward through the profile as the volume of water applied increased. With further investigation into the relationship between ECT and water content, the rapid simultaneous measurement of water content and electrical conductivity made possible by TDR should prove useful in studies of salt movement

Leaching of nitrates and herbicides under low pressure (high volume) irrigation

Non-Peer ReviewedThe potential for contamination of groundwater by nitrates or pesticides from irrigated soils has not been fully evaluated. This project was initiated to monitor nitrate and herbicide leaching in a tile-drained field at SIDC in Outlook. Water samples were collected using suction lysimeters and analyzed for nitrate and four herbicides (2, 4-D, dicamba, bromoxynil and diclofop). The concentrations of nitrates at depth were maintained by the downward movement of applied andmineralized N. Trace amounts of 2, 4-D and diclofop were leached to 180 cm but bromoxynil and dicamba were not found below 60 cm depth. Dicamba and diclofop persisted longer in the soil than 2, 4-D or bromoxynil but were only present in trace amounts at the end of August

Necrotroph Attacks on Plants: Wanton Destruction or Covert Extortion?

Necrotrophic pathogens cause major pre- and post-harvest diseases in numerous agronomic and horticultural crops inflicting significant economic losses. In contrast to biotrophs, obligate plant parasites that infect and feed on living cells, necrotrophs promote the destruction of host cells to feed on their contents. This difference underpins the divergent pathogenesis strategies and plant immune responses to biotrophic and necrotrophic infections. This chapter focuses on Arabidopsis immunity to necrotrophic pathogens. The strategies of infection, virulence and suppression of host defenses recruited by necrotrophs and the variation in host resistance mechanisms are highlighted. The multiplicity of intraspecific virulence factors and species diversity in necrotrophic organisms corresponds to variations in host resistance strategies. Resistance to host-specific necrotophs is monogenic whereas defense against broad host necrotrophs is complex, requiring the involvement of many genes and pathways for full resistance. Mechanisms and components of immunity such as the role of plant hormones, secondary metabolites, and pathogenesis proteins are presented. We will discuss the current state of knowledge of Arabidopsis immune responses to necrotrophic pathogens, the interactions of these responses with other defense pathways, and contemplate on the directions of future research