The use of Kappa statistics to assess long-term changes in the intrafield heterogeneity of the content of available forms of phosphorus and potassium

Relevance . The introduction of robotic technology for differentiated application of fertilizers makes it necessary to study the intra-field heterogeneity of the availability of arable land with nutrients. It is necessary to evaluate the structure of spatial heterogeneity and the direction of changes in the long term. The use of different methods for determining available forms of nutrients in different years makes it difficult to compare long-term data. Methods . Long-term (1965, 1987, 2021) data on the content of mobile phosphorus (P 2 O 5 ) and exchangeable potassium (K 2 O) in the soils of the crop testing site of the Republic of Tatarstan were used. The P 2 O 5 content was determined according to Truog (1965) and Kirsanov (1987, 2021), and the K 2 O content according to Maslova (1965, 1987) and Kirsanov (2021). Agreement in the assessment of availability was calculated using Cohen’s kappa coefficient. Results . The availability of P 2 O 5 by the Kappa coefficient shows a moderate coincidence between 1965 and 1987 (κ = 0.45), and a significant coincidence between 1987 and 2021 (κ = 0.62). The availability of K 2 O between 1965 and 1987 has a very weak coincidence (κ = 0.10), between 1987 and 2021 — a satisfactory coincidence (κ = 0.25). In contrast to P 2 O 5 , the structure of spatial heterogeneity of K 2 O availability remains weak during prolonged use. The availability of P 2 O 5 and K 2 O fields increased significantly from 1965 to 1987, and decreased from 1987 to 2021. The intra-field variability of the indicators increased from medium to high (to close to very high (P 2 O 5 ) from 1965 to 2021.