Soil Apparent Electrical Conductivity (ECa) as a Means of Monitoring Changesin Soil Inorganic N on Heterogeneous Morainic Soils in SE Norway During Two Growing Seasons

Abstract

An efficient method to monitor changes in soil inorganic N content during crop growth would be a useful means to guide N fertilization to ensure high yields and low N losses to the environment. In this study, soil apparent electrical conductivity (EC a ) measured by the widely used conductivity meter EM38 was tested as an indirect measurement of available N in spring barley during two cropping seasons at two sites with morainic loam in SE Norway. The experiment was constructed to maximize soil variation. In spite of the 'noise' caused by the soil heterogeneity, concentrations of inorganic N (cN inorg ) or NO 3 -N were most strongly correlated with EC a in both years and at both locations (with one exception). The measurements of EC a reflected well the temporal variation in inorganic N content (N inorg ), and a ranking of the treatments based on EC a fitted very well with a ranking based on N inorg at the first three sampling times after fertilizing. The best subset of sensor variables (i.e. variables which can be measured 'on-the-go' by sensor techniques in the field) described 27-69% (average 47%) of the variation in topsoil cN inorg . When expanding the regression models to include pH as well, the degree of explanation increased significantly. In conclusion, the method of using EC a appears to be quite robust in terms of detecting relative differences in cN inorg , whereas a determination of absolute levels of cN inorg with the method is unreliable.

Interpretation of electrical conductivity patterns by soil properties and geological maps for precision agriculture

“…Nevertheless, our results are consistent with soil science knowledge. Korsaeth (2005) found that SOM had a larger effect on EC a than clay in a field trial. McBride et al (1990) showed that EC a in non-saline forest soil was markedly affected by exchangeable Ca in the soil solution.…”

Height above ground corrections of EM38 readings of soil apparent electrical conductivity

“…Soils with vertical uniform conductivity are very rare in practice, and it is very unlikely that the soil at the experimental sites had such uniformity, since there was considerable variability in their properties at different depths (data not shown, see Korsaeth 2005 for details). However, detailed knowledge about soil layers and electrical conductivity profiles is seldom available, and the method was tested in spite of this obviously weakly based assumption.…”

“…Measurements with EM38 were conducted in an ongoing field trial (Korsaeth, 2005) (27 May), EC a was measured at both sites on all five treatments in three of the 20 replicate blocks on the ground and at 20, 40 and 60 cm above the soil surface. Both EM H and EM V were measured by operating the device manually and placing it on a specially designed wooden frame to ensure correct height at measuring.…”

“…One sensor-based, non-invasive technique is to measure apparent electrical conductivity (EC a ) of a whole soil profile by means of electromagnetic induction (EM). EM-EC a has been used successfully as an indirect indicator of important soil physical and chemical properties, such as soil water content (Khakural et al, 1998;Sheets & Hendrickx, 1995), soil salinity (Williams & Baker, 1982), topsoil inorganic N content (Korsaeth, 2005) and nutrient levels (Heiniger et al, 2003). Whereas these studies focus mainly on soil variation in the lateral plane, others have used the EM-EC a technique with more emphasis on the vertical soil variation, such as depth of sand deposition (Kitchen et al, 1996) and topsoil thickness (Kitchen et al, 1999).…”

Monitoring the movement of inorganic MK701 fertilizer in soil by a home‐made multi‐channel electrical conductivity instrument

“…In addition to the presence of ions available in soil and irrigation water, the ions dissolved from fertilizers also contribute to the soil EC. This correlation has been utilized to study the soil properties by using the electrical conductivity (EC) measurement, [3][4][5] monitor the contamination in groundwater [6] and estimate the amount of fertilizer in soil. [3] The advantage of the EC measurement is simple and least expensive soil measurement available.…”