1. Introduction
Barley is one of the most important arable crops growing in the Czech Republic. Following the winter wheat and winter rapeseed, barley is the third most cultivated crop in the Czech Republic, covering approximately 332 thousand ha of arable land with a total grain production of 1.8 million tons in 2020. The average grain yield was approximately 5.3 t ha
−1 between the years 2015 and 2019 [
1]. Both winter and spring forms of barley are grown mainly for livestock feedstuff production and approximately 30% of the spring barley is used for malt production in the Czech Republic.
A demanded grain yield can be achieved by choosing a suitable barley cultivar [
2,
3,
4], preceding crop [
5,
6], soil preparation technique [
7,
8] and proper fertilization [
4,
9,
10,
11,
12]. The soil-climate conditions of the locality where the barley grows represent another factor significantly affecting barley grain yield and quality [
4,
12,
13,
14].
Out of all macronutrients, nitrogen (N) represents the most important nutrient directly influencing the yielding potential and quality of most of the arable crops, including barley. An insufficient amount of mineral N results in lower yields. On the other hand, an excessive amount of the N can negatively affect the grain yield (lodging) and in the case of barley grown for the brewing industry (malting purposes) even quality, because barley continues to utilize N even when yield requirements are met [
4,
15,
16], increasing its protein content. The excessive amounts of applied N are also connected with financial losses of the farmers and negative impacts on soil, water and groundwater due to the N leaching and emissions [
17,
18,
19]. Barley is considered a plant requiring lower nutrients input than wheat. Generally, the recommended doses of N range from approximately 30 to 60 kg ha
−1 N in the Czech Republic, depending on the soil-climate conditions, preceding crop and purpose (feed or malting grain). Other sources state doses of N ranging from 30 kg ha
−1 N [
10] and 50 kg ha
−1 [
20] to 40–80 kg ha
−1 N [
16] and 50–100 kg ha
−1 N [
8], depending on the previously mentioned factors. Low or no fertilization should be applied to barley following the legumes or crops fertilized with organic manures (malting purposes), while higher doses can be applied for barley grown for feedstuff purposes. This kind of production is not limited by protein concentration and other requirements.
The application of mineral fertilizers and organic manures, together with tillage practices and crop rotations [
21,
22], does not only affect the yield and quality of arable crops. As a consequence of fertilization, soil properties are also modified, including fields and meadows [
23]. Application of all types of fertilizers significantly modify a wide range of soil properties, such as the soil organic carbon (SOC) content [
24,
25], soil microbial community [
26,
27,
28] and enzyme activity [
25], the value of the pH [
29,
30,
31] and consequently the availability of essential and non-essential metals [
32] and availability of macronutrients [
25,
33]. In general, the SOC content increases when organic manures are applied alone or in combination with mineral fertilizers to the field [
31,
34]. Mineral N fertilizers can also, but do not have to [
35], increase the SOC, but the effect is smaller in comparison with organic manures [
24,
31,
36]. The value of the pH generally decreases when mineral fertilizers (ammonium-based fertilizers) are applied without organic amendments [
29,
30,
31,
37]. This is due to N transformation processes in the soil. The rate of acidification depends on the soil type. For example, Chernozems have a high buffering capacity against acidification, while other soil types (Cambisols, Luvisols) are more prone to the effects of N fertilizers [
30]. Application of mineral N without other amendments can not only decrease the soil pH but also lead to the deficiency of other macronutrients [
37]. We present these causes and consequences because the current conventional agriculture in the Czech Republic is characterized by low inputs of organic manures (and thus organic matter) and mineral forms of P and K into the soil and dependence on mineral N.
In this paper, we have evaluated how six fertilizer treatments (Control, N1, N2, NPK1, NPK2, NPK3) affected spring barley grain yield under three different soil-climate conditions between the years 2013 and 2016. The AE (kg kg−1) of all fertilizer treatments is included. The effect of three fertilizer treatments (Control, N2, NPK2) on soil properties (pH, P, K, Ca, Mg, Cox, Nt) was also evaluated.
4. Discussion
Our results confirm that spring barley grain yield is strongly affected by the soil-climate conditions and fertilization treatment. In other words, different soil-climate conditions and fertilization lead to different results.
We have compared three different localities with different soil-climate conditions in our paper. Two localities have similar weather conditions (Ivanovice and Caslav) but differ in soil types (Ivanovice-Chernozem; Caslav-degraded Chernozem). Ivanovice offers naturally highly fertile soil. Out of all analyzed localities, Ivanovice is the most productive locality, capable to support sustainable production even without fertilizer inputs [
47]. The soil in Ivanovice has the highest buffering capacity against soil acidification caused by N fertilization [
30]. Finally, the weather conditions are very suitable for growing cereals, offering conditions for stable yields (low grain yield fluctuation,
Table 3) due to good water management [
48]. All these factors result in high yields and high fertilizers efficiency, expressed by using the quadratic and linear-plateau models and AE (see
Section 3.2.1). On the other hand, the beneficial conditions and stable yields may change in the close future due to the ongoing climate change, especially due to the lower water availability and higher heat stress in the lowlands [
49], such as in Ivanovice.
The weather in Caslav is similar to that in Ivanovice, the biggest difference between the two localities is in the soil, which is a degraded Chernozem in Caslav. The sustainable production in Caslav, without fertilizer inputs, can be expected only under proper crop rotations including legumes and root crops [
50]. This soil is characterized by the lower SOC and Ntot content. Concentrations of P and K in the soil are comparable with Lukavec (
Table 5,
Figure 3), which is the locality with the lowest natural fertility (in our comparison and comparison with four other long-term experiments in the Czech Republic [
12]). The difference between the Chernozem and degraded Chernozem is in the origin of the soil and several theories on how these soils came into being have been developed, including tallgrass steppe (Chernozems) and moister forest-steppe (degraded Chernozems) origins and other theories [
51]. Anyway, according to our results, good barley yields can be harvested under such soil-climate conditions but with higher nutrients input (lower yields and lower efficiency when compared with Ivanovice).
As mentioned above, Lukavec is the naturally lowest fertile locality in our comparison. The Cambisol here has the lowest pH, but the soil responds efficiently to the applied fertilizers [
12]. According to our results, the proper fertilization can lead to similar yields as in localities more suitable for growing cereals (Ivanovice, Caslav) and increase soil fertility (the SOC, Ntot, nutrients content).
Comparing the fertilizer treatments, the effect of applied fertilizers strongly depends on locality. Nitrogen is the most important nutrient for spring barley and the addition of mineral P and K is site-specific [
12], which is confirmed by our results. As the response of spring barley to fertilizers depends on soil-climate conditions, different recommendations must be set to obtain desired yields, save financial costs and minimize environmental damages [
4,
8,
9,
10,
16,
20,
52]. In our case, maximum yields can be obtained in Caslav and Ivanovice (Chernozem and degraded Chernozem soil types) with doses of N ranging from 59 to 66 kg ha
−1, respectively, but “reasonable yields” [
53] (according to the linear-plateau model) can be harvested with N doses around 31–32 kg ha
−1, which would be connected with average grain yields decrease of 100 kg ha
−1 (Caslav) and 500 kg ha
−1 (Ivanovice). In Lukavec (Cambisol, higher altitude, wetter and colder weather), the maximum mean grain yield can be obtained with higher N inputs (98 kg ha
−1) but reasonable yields can be obtained with 46 kg ha
−1 N, representing a 50% reduction in N dose, which would be connected with averagely 500 kg ha
−1 lower yields in this locality.
The fertilization does not affect only spring barley grain yield but also soil properties. In our case, regular application of mineral P fertilizers significantly increased the soil P content (
Table 5), resulting in high and very high levels when compared with the Control and N fertilizer treatments. Similar results were published by [
33,
37,
54], where omitted P fertilization resulted in significantly lower P soil concentrations when compared with treatments including P fertilizers. This is an important result, showing the negative side of omitting P fertilization. In the Czech Republic, the application rate of mineral P fertilizers decreased significantly after the Velvet Revolution in 1989 (transformation from the centrally planned economy to the market economy) and is on the same level as in the 1960s (
Figure 6).
A similar, but not the same, situation was recorded in the case of K, where the application of NPK resulted in significantly higher soil K concentrations when compared with Control (
Table 5). The same results were published by [
33,
37], who recorded lower K concentrations in K-omitted treatments in their long-term trials. The pH value was not affected by the fertilizer treatment (in all localities). The decreasing effect of mineral N (ammonium-based) fertilizers on the soil pH value is known, especially when mineral N is applied without organic amendments [
29,
30,
31,
32,
37]. In our trial, however, the farmyard manure was applied (and is regularly applied to the root crops and maize in the crop rotation) to the preceding crop (maize, the dose of the manure was 40 t ha
−1). The addition of solid organic manures can compensate or negate the negative effect of mineral fertilizers [
55] due to the high concentration of base cations. Application rates of the organic manures are currently low in the Czech Republic due to the low level of farm animal production, disrupting crop and animal production and dependence of crop production on mineral N fertilizers. This situation represents a vicious circle that deepens the chemical degradation processes of the soil in the Czech Republic [
48,
56]. A similar situation can be found in the case of the SOC content. Out of all localities and treatments, the SOC content was significantly lower only in Caslav’s Control treatment (degraded Cheznozem), but lower SOC content was always recorded in the Control when compared with the N and NPK treatments, though insignificantly (
Figure 3). The SOC is one of the most important factors determining soil fertility and properties, directly affecting the field’s production capacity (grain yields) [
57]. Application of mineral fertilizers increases the SOC content, as in our case and as was confirmed by others [
24,
31,
36], but by how much depends on soil-climate conditions as mentioned in [
57], who compared the effect of different fertilizers on the SOC content with the results published earlier.
5. Conclusions
Spring barley grain yield strongly depends on soil-climate conditions and fertilization. According to our results, maximum mean yields (according to the quadratic model) were 6.8, 8.4 and 6.4 t ha−1 in Caslav (degraded Chernozem), Ivanovice (Chernozem) and Lukavec (Cambisol), respectively, with the corresponding N rates of 59, 66, and 98 kg ha−1 N, respectively. Reasonable yields (according to the linear-plateau model) were achieved with significantly lower fertilizer doses, namely 6.7 t ha−1 (with the dose of 32 kg ha−1 N) in Caslav, 7.9 t ha−1 (31 kg ha−1 N) in Ivanovice and 5.9 t ha−1 (46 kg ha−1 N) in Lukavec. Application of P and K fertilizers slightly increased the N efficiency, mainly in Lukavec, which is a locality with soil characterized by low natural fertility.
Fertilization significantly affects soil properties. The pH value was not affected by the application of mineral fertilizers, which was mainly caused by a regular application of the farmyard manure to the preceding crop (maize) and also by natural soil properties in some localities (high buffering capacity of Chernozem in Ivanovice). Concentrations of soil P and K were positively affected by the application of mineral P and K fertilizers. Their regular application prevents their depletion, especially in a situation where crop production is dependent on mineral nitrogen, as is the case in the Czech Republic. The SOC content was significantly affected only in one locality (Caslav). In Ivanovice and Lukavec, the SOC content was always higher in N and NPK treatments when compared with the Control, but the differences were insignificant.