*4.1. E*ff*ect of the FYM*

The e ffect of manure application on grain yield was significantly visible in all three localities with di fferent soil-climatic conditions even three years after its incorporation into the soil. The di fferences in grain yield between the control and FYM treatments have not always been significant in particular years (Table 4). However, the average grain yields in the FYM treatment have always been higher in comparison with the control, whenthe wholetime period was evaluated (2015–2018). By comparing all three localities, we find that the greatest benefit of manure manifested itself in Lukavec (+20% mean grain yield increase in comparison with the control), followed by Caslav (+15%) and Ivanovice (+12%). In general, farmyard manure e fficiency wasslightly higher in the locality with poorer soil type andmore humid climatic conditions and decreased on higher quality soils.The positive e ffect of the farmyard manure on the yield of arable crops three years after the manure applicationwas also recorded by [13], who analyzed the e ffect of mineral fertilizers and organic manures in the long-term fertilizer experiment in Switzerland. Application of the FYM a ffected not only yields (Table 4), but also the soil chemical properties (Tables 8–10), so the e ffect of the FYM was two-sided and both aspects synergized, resulting in higher yields than in the control even three years after FYM application. The same conclusions and explanations published [13] who recorded a higher SOC content in the soil treated with manure. A 6.40% higher SOC content in the soil treated with manure, together with higher microbial biomass, was also recorded by [14]. Positive influences on yields and soil properties of manure application have also been published in the meta-analysis from China, provided by [15], who analyzed more than 140 studies and more than 770 treatment comparisons.In our case, the soil fertilized with FYM showed a significantly higher content of Nt and Cox (significantly higher in Ivanovice and Lukavec), and a higher content of soil P and K (Tables 8–10). As the estimated amount of nutrients available directly from the FYM to the wheat was relatively low in our case (5%), we incline to the fact that the positive e ffect of manure consisted in the direct e ffect of released nutrients, which were mostly utilized by pre-crops and partially by wheat, and also in influencing the microbial part, nutrients turnover, and organic matter pool in soil. As we didnot perform the PLFA or other methods for evaluation of soil microbial activity, we cannot confirm these suggestions directly, but are in an agreemen<sup>t</sup> with the results of other researchers [16,17].

As mentioned above, the positive e ffect of the FYM on the wheat yield was significant in all localities. The opposite was true for qualitative parameters.On the basis of our results, we know that manure was able to provide nutrients and adjust soil conditions for higher yields of wheat grain (Table 4), but this was not enough to a ffect the CPC and ZST (Table 7). Except for the climate conditions, nitrogen is the most limiting factor for high CPC in the wheat grain [18,19]. From this point of view, the application of manure cannot replace mineral fertilizers for the production of bread-making quality grain, at least if wheat isnot fertilized with manure directly (which is not a common practise in the Czech Republic). On the other hand, the e ffect of the FYM can be taken as an advantage if wheat is produced for minor supply-chains (biscuit production) [19], or as the feedstu ff.

### *4.2. The E*ff*ect of Mineral N*

No wonder, application of mineral N directly to wheat significantly increased grain yield in all localities. Nitrogen is considered as the wheat's most important nutrient, and its addition positively influences the root length and density, water uptake, above-ground biomass production [20], phenology and leaf traits [21], and grain yield [22,23]. Focused on the site-specific nutrient management, Ivanovice and Lukavec provided the highest yields in the FYM+N2 treatment, with the maximum yield at 70 kg N ha−<sup>1</sup> in Ivanovice and 155 kg N ha−<sup>1</sup> in Lukavec. On the other hand, Caslav provided maximum yield in FYM+N1 treatment, and according to the quadratic model, the optimum dose represents 55 kg N ha−1. This means that similar wheat yields can be harvested in all localities, but with extremely di fferent nitrogen rates. It also means that nitrogen fertilization ought to be adjusted to the soil-climate conditions of the specific site—a single recommendation about the dose of mineral nitrogen cannot be applied nationwide. This knowledge can thus save the farmer's financial resources, the number of field operations, and the environment, as the excess of mineral nitrogen fertilizers applied to agricultural land is associated with negative impacts on soil nitrogen pool [24], leaching, and groundwater nitrate contamination [25,26]. Focused on the soil properties, application of mineral nitrogen significantly decreased the pH in Caslav, while no changes were recorded in Ivanovice and

Lukavec (Tables 8–10). The soil nitrogen concentration was higher in all localities, as well as the Cox content when compared with the control. Concentrations of P, K, and Mg were significantly higher in Ivanovice and Caslav, while no differences were recorded in Lukavec. From this point of view, the soil answer to N addition was similar in Ivanovice (Chernozem) and Caslav (Phaeozem)—these soils were more sensitive to the addition of mineral N. Both soil types are almost comparable, both represent the most fertile types in the Czech Republic, but Phaeozems are more prone to leaching during the wet seasons and donot contain so many carbonates in the topsoil layer [27], as can be seen in Tables 8 and 9. Another aspect is the soil buffering capacity against acidification, which is high in the case of Chernozems and lower in Phaozems [28]. Lukavec (Cambisol) offers similar values of Nt and Cox (even slightly higher)toCaslav, but the natural properties of the soil type in Lukavec are low pH value, the soil is lighter, and with lower sorption capacity [28]. Together with colder weather, the soil type creates a natural barrier that significantly affects wheat prosperity.

#### *4.3. The E*ff*ect of Mineral N, P, and K*

As with the effect of FYM+N, the application of mineral NPK fertilizers significantly increased wheat yields. In Ivanovice and Lukavec, the grain yield increased with increasing N dose (Control < FYM+N1PK < FYM+N2PK < FYM+N3PK). The difference between FYM+N2PK and FYM+N3PK was not significant in Ivanovice, and maximal yield was reached with 98 kg N ha−1. This suggests that we have reached the maximum potential yield here, and increasing the nitrogen doses will not be connected with higher grain yield. From this point of view, we cannot influence the natural barriers of the locality and only new breakthroughs, such as the transformation of wheat from C3 to C4 pathway [29], could bring the new "green revolution", connected with significantly higher yields. Different behaviour was recorded in Caslav, where a significant decline in grain yields was connected with increasing doses of mineral N, and maximal yield was reached with 72 kg N ha−1. Finally, the light soil in Lukavec responded to increasing nitrogen doses with significantly higher yields. According to the quadratic model, the maximum yield was reached with 155 kg N ha−1. These results of the quadratic model specify the previous values obtained for the variants FYM+N1 and FYM+N2 (the variant FYM+N3 would be grea<sup>t</sup> for the comparison. However, it was not established when setting up the experiment). Another thing we can compare is the effect of added P and K fertilizers. As mentioned above, the average amount of applied P and K mineral fertilizers is very low in the Czech Republic. This creates a contrast between what is taught in schools and common agricultural practice. According to the results, no significant differences were recorded between FYM+N and FYM+NPK treatments in Ivanovice, where naturally fertile soil occurs and the pool of nutrients is high even in unfertilized Control treatment. Thus, the addition of 60 kg P and K ha−<sup>1</sup> was not connected with any benefits if we speak about grain yields. In C ˇ áslav, the high dose of nitrogen was counterproductive and the application of P and K again did not bring significant differences in yields, although the concentration of P and K were significantly lower in FYM+N treatments in comparison with FYM+NPK treatments. The high N dose counter-productivity theoretically stems from the fact that high doses of nitrogen supplied to the soil increase nitrogen losses from the soil, thereby reducing its usability by wheat [26], or from an increased risk of lodging and disease incidence and severity [30]. Finally, the third kind of reaction was recorded in Lukavec, where an increasing dose of mineral N increased grain yield, and yield reduction is expected at doses above 155 kg N ha−1. Comparing the effect of P and K fertilizers in Lukavec, no differences between grain yields provided by FYM+N and FYM+NPK treatments were recorded, although the differences between the P and K concentrations in the soil were significant. According to the results, the application of P and K fertilizers significantly boosted the soil concentrations of P and K (Tables 8–10). This is a very important result showing that dependency on N, which is a current situation in the Czech Republic, is not long-term sustainable managemen<sup>t</sup> and will slowly lead to soil depletion. Excellent review represents this paper [6]. According to [6], it was not clearly proven that application of P and K increases grain yield (some evaluated experiments proved that hypothesis, some did not), but it was stated that "improved soil P, K, or S availabilities has

potential to increase grain yield and improve the efficiency of N fertiliser use". It is suggested that application of P and K fertilizers increases the efficiency of N, but we cannot confirm this conclusion, at least from the point of view of grain yields.
