Are inorganic nitrogen concentrations in potassium chloride and saturated paste extracts of irrigated soils comparable?

Abstract

Precision agriculture is gaining momentum in irrigation through the assessment of soil salinity variability, often facilitated by electromagnetic induction (EMI) sensors. This study aimed to evaluate whether saturated paste extracts (SAT_e) could serve as a substitute for the standard 2 M KCl extraction (KCl_e) in determining NH₄+−N and NO₃ ⁻N levels. The objective was to streamline the process by eliminating labour-intensive steps such as sampling, extraction and determination. Surveys utilising an EM38-MK2 sensor were conducted in soils located under four centre pivot irrigation systems on four farms: Douglas (maize), Luckhoff (wheat), Hofmeyr (wheat) and Empangeni (sugarcane). Using apparent electrical conductance (EC_a) and ESAR-RSSP software, 12 sampling points were identified per centre pivot. Soil samples were collected at depth increments of 300 mm. At each sampling point, one sample from the centre and four samples from the corners were taken from a 1 m² area and composited for NH₄+−N and NO₃ ⁻N analysis using SAT_e and KCl_e. Data was pooled regardless of centre pivot, sampling point and depth increment. The agreement between the two extracts was found to be poor for NH₄+−N and less poor for NO₃ ⁻N. As a result, SAT_e may be considered as a viable alternative to replace KCl_e for NO₃ ⁻N determination, showing the potential to simplify and expedite the assessment process in precision agriculture.