A sulphur nutrition index (SNI) is an analogue of the N nutrition index, which is a widely used simple indicator of plant N status. The aim of this study was to relate the SNI (ratio of S concentration in shoot biomass to critical S concentration-Sc) to N uptake, grain yield and breadmaking quality of winter wheat (Triticum aestivum L.) grain during 4-yr small-plot field experiments realized under non-limiting N conditions in three different locations in the Czech Republic. The model of S dilution curve (Sc) developed by Reussi et al. (2012) for spring wheat was used for expression of the SNI. According to the model, optimal S concentration in shoot biomass was calculated using nothing but shoot biomass weight. The constant value of Sc = 0.55 was determined for shoot biomass weight lower than 1.0 t ha-1. A very strong correlation was recorded between the SNI and an N to S weight ratio (N:S) in shoot biomass. Both, optimal N:S weight ratio in shoot biomass and qualitative parameters of grain (particularly Zeleny sedimentation volume, grain protein content and wet gluten content) were recorded if the SNI exceeded values of 0.80 at the beginning of stem elongation, 0.70 at the late boot stage, and even 0.60 at the beginning of heading despite the fact that the Reussi et al.'s model of S dilution curve was originally applicable only until the end of stem elongation. Correlation between the SNI and relative grain yield was weak.

Soil organic matter carbon (CSOM) compounds degradation was observed in long-term field experiments with silage maize monoculture. Over a period of 26 years, the content of carbon in topsoil decreased by 22% in control unfertilized plots compared to 25% and 26% in treatments fertilized annually with mineral nitrogen. With annual wheat straw application (together with mineral N), the content of CSOM decreased by 8%. Contrary to that, the annual application of farmyard manure resulted in a CSOM increase of 16%. The ratio of carbon produced by maize related to total topsoil CSOM content ranged between 8.1–11.8%. In plots with mineral N fertilization, this ratio was always higher than in the unfertilized control plots. With the weaker soil extraction agent (CaCl2), the ratio of carbon produced by maize was determined to be 17.9–20.7%. With stronger extraction agent (pyrophosphate) it was only 10.2–14.6%. This shows that maize produced mostly unstable carbon compounds. Mineral N application resulted in stronger mineralization of original and stable organic matter compared to the unfertilized control. However, the increase of maize-produced carbon content in fertilized plots did not compensate for the decrease of “old” organic matter. As a result, a tendency to decrease total CSOM content in plots with mineral N applied was observed.

Balance of potassium (K) was observed in long-term stationary field experiments (21 years) at two sites with different soil and climatic conditions (Luvisol, Cambisol). The following crops were rotated within the trial: potatoes- winter wheat-spring barley. All three crops were grown each year. The trial comprised 6 treatments: (1) no fertilization; (2) farmyard manure; (3) half dose of farmyard manure + nitrogen (N) in mineral nitrogen fertilizers; (4) mineral nitrogen fertilizers; (5) NPK in mineral fertilizers; (6) straw of spring barley + N in mineral nitrogen fertilizers. The recovery rate of potassium from farmyard manure by crops was 24–26%, from mineral fertilizers it was 27–52%. Different fertilization intensities were manifested by significant differences in the content of exchangeable K in soil. Changes in non-exchangeable K (K_ne) were recorded only at the Luvisol site (850 mg K_ne/kg), but not at the Cambisol site (3000 mg K_ne/kg). The maximum negative balance (–2376 kg K/ha/21 years) was recorded at the mineral nitrogen fertilization treatment.

Mehlich 3 is an extractant used worldwide for extracting bioavailable nutrients in soils; however, its extraction abilities for sulfur (S) are still not well described. The aim of this preliminary study was to compare the results of Mehlich 3 determined soil S fraction (S_M3) with the results of sulfur fractionation, mainly focusing on bioavailable S (S_av – sum of water-extractable (S_w) and adsorbed (S_ads) sulfur). Air dried soil samples from commonly used agricultural soils were chosen for the analyses. The following S fractions were determined: (i) S_w; (ii) S_ads; (iii) S_av; (iv) 1 mol/L HCl extractable (S_HCl); (v) estersulfate (S_es); (vi) organic (S_org) and (vii) total (S_tot). The median value of S_M3 (18.3 mg/kg) was similar to S_av (17.9 mg/kg). From the correlation and regression analysis it is clear that S_M3 results are in close relationship with S_av form. On the other hand, the relationships between S_M3 and organic S (including S_HCl) were very weak. Based on the obtained results it can be concluded that Mehlich 3 method has a good potential to determine bioavailable sulfur in commonly used agricultural soils. However, especially the plant response should be further studied to confirm this theory.

Experiments were used to determine the potassium release from the non-exchangeable K (Kne) forms that are involved in plant nutrition and which replenish the pool of available K. Long-term stationary field experiments with different fertilisation systems (organic: farmyard manure, sewage sludge, straw; mineral: NPK, N) were carried out to study the potassium balance and the K content changes in the topsoil (0–30 cm) and subsoil (30–60 cm). The trials were located at three sites with different soil-climatic conditions. The following crops were rotated within the trial: potatoes (maize) – winter wheat – spring barley. All three crops were grown each year over 21 years. Positive correlations between the contents of the available K in the topsoil and the potassium balance (K inputs – K outputs) were observed. There were no statistically significant differences among the treatments. Depending on the soil properties, the ratio of non-exchangeable K (Kne) was 12–37% of the values obtained via the aqua regia extraction. Depending on the site, the amount released from the Kne forms to the available K form was 46–69 kg K/ha/ year. The use of K from the farmyard manure varied from 7.4% up to 25%. Due to the low K content in the sewage sludge, the long-term fertilisation with sludge may only lead to the depletion of the available K in the soil, similar to the sole N mineral fertilisation.