Improved Soil Testing System in the Czech Republic (New Valuation of Micronutrients Content in Soil and Phosphorus Content in Carbonate Soils)

The official systematic soil testing system in the Czech Republic has practically 60 years duration – since 1961 is provided for needs of state administrative body and simultaneously for farmers. The extraction procedure Mehlich 3 is the official analytical method presently used (since 1999) in this soil testing system for the determination of available macronutrients (P, K, Mg, Ca). On the ground of uniformity, suitability and relatively cheap process of this analytical procedure, Mehlich 3 extractant can be used for a multiple-element extraction from soils, including determination available micronutrients (B, Cu, Zn, Mn, Fe). On the other hand Mehlich 3 extractant has some limits for right determination of available phosphorus content in carbonate soils (i.e. soils with pH value 7.2 and higher and simultaneously with content of available calcium 3500 and more mg kg -1 of soil). Extraction method Mehlich 3 used for determination of available phosphorus, usually doesn ́t indicate real phosphorus content in carbonate soils. There is content of available phosphorus more or less undervalued according to valid limits (criteria) for all soils. New, updated criteria of valuation of available phosphorus content in carbonate soils will be used for elimination of this incorrectness.


INTRODUCTION
The systematic soil testing scheme in the Czech Republic was established in 1961, founded on a long tradition of soil testing (Čermák et al, 2017).
The Mehlich 3 extractant has been used since 1999 for determination of phosphorus (P), potassium (K), magnesium (Mg) and calcium (Ca). This universal soil extractant was chosen especially for its simple and universal use but also for its ability to produce relatively good correlations between the amount of nutrients extracted from the soil and the plant response. The Mehlich 3 extractant can be used for a multiple-element extraction from soils with a relatively wide pH range (with some limitations for carbonate soils for right determination of available phosphorus content in carbonate soils, i.e. soils with pH value 7.2 and higher and simultaneously with content of available calcium 3500 and more mg.kg -1 of soil (Kunzová, 2009).

MATERIAL AND METHODS
In the past there were studied relationships between the Mehlich 3 extractant and some other extractants for determination of micronutrients (DTPA extraction for determination of copper, zinc, iron and manganese; hot-water extraction for boron determination) to find a possibility to widen the Mehlich 3 scope also for micronutrient determination (Zbíral and Němec 1998, 2000, 2009. It was proved that Mehlich 3 could be used also for determination of B, Cu, Zn, Mn and Fe if the criteria for evaluation of the results are available. Based on comparison different analytical method (i.e. Mehlich 3 versus DTPA and hot water) and through simple calculation of relationship between these extractants theoretical criteria for available copper, zinc, iron, manganese and boron content in soil were suggested.
Because the criteria for essential nutrients (P, K, Mg, Ca) valuation were confirmed and adjusted using results from long-term field experiments and pot experiments covering representative soil and climatic conditions of the Czech Republic, so it was necessary in the same way to verify and to adjust these theoretical criteria micronutrients valuation in soils. Therefore analytical results from field and pot experiments (Mühlbachová et al., 2016) were used for determination of micronutrients

Statistical valuation of results for determination of micronutrients
Available data and statistical results (Table 1) showed high correlation between both used methods and subsequently possibility and suitability of Mehlich 3 method (together with ICP-OES) for boron, copper, zinc, manganese and iron determination in the soil. 0.314*** 0.361*** ns -non significant, p < 0.05*, p < 0.01**, p < 0.001*** Based on the results obtained from the vegetation experiments the following levels (confirming earlier suggested theoretical criteria -limits) for evaluation of micronutrients in the soil were postulated: i) low content, ii) middle content, iii) high content (Table 2).