The effect of exogenous organic matter on the thermal properties of tilled soils in Poland and the Czech Republic

PURPOSE: Organic matter improves soil fertility and water and thermal properties, but its content often decreases. This decrease may be mitigated by the addition of exogenous organic matter (EOM). The aim of this study was to assess the effect of EOMs, including compost from manure, slurry, and straw (Ag); industrial organic compost from sewage sludge (Ra); animal meal from animal by-products (Mb); and digestate from a biogas fry factory (Dg) on soil thermal conductivity, heat capacity, thermal diffusivity, water content, and bulk density in the top (0–15-cm) layer of two soils in Poland and the Czech Republic. MATERIALS AND METHODS: Irrespective of EOM type, the total yearly nitrogen application rate being 200 kg N ha⁻¹ (100%) was from a given EOM at the rates 0, 50, 75, and 100% and the remaining parts from the mineral fertilizer. The study was conducted in 2013–2014 in Poland (Braszowice) and the Czech Republic (Pusté Jakartice) on loam silt and clay silt loam, respectively, as part of a cross-border cooperation project. The soil properties were examined using classical descriptive statistics, semivariograms, and kriging-interpolated maps. RESULTS AND DISCUSSION: Analysis of linear regressions (trends) showed that the EOM application rate influenced (positively or negatively) the soil properties in most measurement occasions. The variability of all soil properties was low and medium (coefficient of variation 7.3–34%). Geostatistical analysis indicated that the spatial dependence (C₀/(C₀ + Cₛ)) of the soil properties on the EOM-amended plots was very strong or moderate. The maps revealed that the heterogeneity and degree of patch fragmentation were greater for thermal conductivity and heat capacity than for thermal diffusivity, water content, and bulk density. In general, all the soil properties were spatially more variable in the Braszowice than Pusté Jakartice soil and in spring than autumn in both sites. CONCLUSIONS: The spatial analysis and maps enhance the comprehensive understanding of changes in soil thermal properties in response to EOM application. Suitability of the results from the field experiments in models predicting some thermal properties based on soil bulk density and water content in relation to EOM addition was indicated. Expressing the amount of EOMs added using the organic carbon content basis (% kg OC/kg of soil) instead of the nitrogen content basis allowed identifying areas on the kriging-interpolated maps where the distribution of soil thermal properties resembled that of soil organic carbon content, water content, and bulk density. Thus, the effect of EOMs on soil thermal properties is considered along with changes in soil water content and bulk density. The results will be helpful in forecasting effects of exogenous organic matter on the soil thermal properties affecting surface-energy partitioning, temperature distribution in soil, and plant growth.