**3. Results**

#### *3.1. The Effect of Farmyard Manure (FYM) on Sugar Beet Beetroot and Top Yield*

If we compare the effect of manure application, we find that the beetroot yield in the observed period (2016–2018) was significantly affected by both the fertilization treatment (d.f. = 1, F = 13.58, *p* < 0.001) and especially the weather conditions (d.f. = 2, F = 73.48, *p* < 0.002). The effect of the interaction between the treatment and year was also significant (d.f. = 2, F = 4.29; *p* < 0.03). The conditions of the year had the highest impact on beetroot yield (80%), followed by the fertilizer treatment (15%), and their interaction (5%).

The application of the FYM provided comparable results as the control. Significantly higher yields were recorded only in 2016 (Table 2). The average beetroot yield was 52.9 t ha−<sup>1</sup> in the control, and 61.2 t ha−<sup>1</sup> in the FYM treatment (2016–2018, Table 2). Comparing the years, the average yield was 66.2 t ha−<sup>1</sup> and 67.2 t ha−<sup>1</sup> in 2016 and 2017, respectively (without a statistical difference), while the significantly lower yield was recorded in 2018 (37.8 t ha−1) (Table 2).

**Table 2.** The beetroot and top yield as affected by the fertilizer treatment (control and farmyard manure (FYM)) and year(2016–2018).


Note: The mean values with the standard error of the mean followed by the same letter (small letters "a", horizontally; and big letters "A", vertically) are not significantly different (*p*, 0.05).

> In the individual years, the top yield was not affected by the FYM application (Table 2). However, for the entire evaluated period (2016–2018), the differences among the compared treatments (d.f. = 1, F = 5.5, *p* < 0.03) and years (d.f. = 2, F = 113.0, *p* < 0.001) were significant.

While the effect of the year was 95%, the effect of fertilization was only 5%. As in the case of beetroots, this means that the differences between the compared fertilization treatments were very low, while the fluctuation between the years was very high (caused mainly by the severe drought in 2018). The average top yield was 17.4 t ha−<sup>1</sup> in the control, while it was 19.4 t ha−<sup>1</sup> in the FYM treatment. Comparing the years, the highest yields were recorded in 2017 (23.8 t ha−1), followed by 2016 (22.1 t ha−1), and 2018 (9.3 t ha−1) (Table 2).

#### *3.2. The Effect of Mineral NPK on Sugar Beet Beetroot and Top Yield*

If we compare the entire period (2016–2018), the application of mineral NPK fertilizers generally increased the beetroot yield significantly (Table 3). According to MANOVA, the beetroot yield was mainly affected by the year (d.f. = 2, F = 146.3, *p* < 0.0001, 92%), showing a very high fluctuation among the years. The highest average yield was recorded in 2017 (72.2 t ha−1), followed by 2016 (68.2 t ha−1), and 2018 (44.4 t ha−1). The effect of the fertilizer treatment was also significant (d.f. = 4, F = 11.4, *p* < 0.001), but the only significant difference was recorded between the control and NPK treatments. However, no significant differences among NPK1–4 treatments were recorded over the entire period (Table 3). The average beetroot yield was 52.9 t ha−<sup>1</sup> (control), 61.3 t ha−<sup>1</sup> (NPK1), 62.7 t ha−<sup>1</sup> (NPK3), 63.3 t ha−<sup>1</sup> (NPK2), and 67.7 t ha−<sup>1</sup> (NPK4). When only NPK treatments were considered, yield response to N rates across three years plateaued at 112 kg ha−<sup>1</sup> N with a corresponding beetroot yield of 66 t ha−<sup>1</sup> (Figure 2, left).

**Table 3.** The beetroot and top yield as affected by the fertilizer treatment (control, NPK1–4) and years (2016–2018).


Note: The mean values with the standard error of the mean followed by the same letter ( small letters "a", horizontally and big letters "A", vertically) are not significantly different (*p*, 0.05).

**Figure 2.** Means (black dots) of sugar beet beetroot yield (**left**) and top yield (**right**) at different N rates of NPK treatments in 2016, 2017, and 2018 combined and their linear-plateau regression (blue line).

In the case of the sugar beet top yield, the effect of the year (d.f. = 2, F = 425.9, *p* < 0.0001), fertilizer treatments (d.f. = 4, F = 34.3, *p* < 0.001), and their interactions (d.f. = 8, F = 3.8, *p* < 0.002) was significant. The lowest average top yield over the evaluated period was provided by the control treatment (17.4 t ha−1). Significantly higher top yields were

recorded in NPK treatments, with the highest top yield in the NPK4 treatment (26.8 t ha−1) (Table 3). The year again had the greatest impact on the top yield (92%), followed by the fertilization treatment (7%). Comparable top yields were recorded in the years 2016 (28.3 t ha−1) and 2017 (29.1 t ha−1), while a significantly lower top yield was recorded in the dry year 2018 (11.9 t ha−1) (Table 3). According to the linear-plateau model, the mean top yield response to N rates across three years plateaued at 122 kg ha−<sup>1</sup> N, with a corresponding top yield of 25 t ha−<sup>1</sup> (Figure 2, right).

#### *3.3. Comparison of the FYM and FYM + NPK Treatments*

Over the entire evalutated period (2016–2018), the combined application of the FYM with mineral NPK fertilizers significantly increased the beetroot yields (d.f. = 5, F = 19.6, *p* < 0.001) (Table 4). The lowest yield was recorded in the control (52.9 t ha−1), followed by the FYM treatment (61.2 t ha−1). The addition of mineral NPK fertilizers significantly increased the beetroot yields as compared with the control and FYM treatments (Table 4), ranging from 65.5 t ha−<sup>1</sup> (FYM + NPK3) to 66.3 t ha−<sup>1</sup> (FYM + NPK1). The differences among all FYM + NPK treatments were insignificant. The effect of the year was also significant (d.f. = 2, F = 333.7, *p* < 0.0001), as well as the year\*treatment interaction (d.f. = 10, F = 2.5, *p* = 0.014). The comparison of years indicated the same results as the previous evaluation. While in the years with relatively favourable conditions (2016 and 2017) the differences were not significant (the average yields were 71.4 t ha−<sup>1</sup> in 2016 and 72.4 t ha−<sup>1</sup> in 2017), the conditions of the year 2018 sharply reduced the beetroot yield to an average value of 45.1 t ha−1. The beetroot yield response to different rates of FYM and NPK fertilizers plateaued at 165 kg ha−<sup>1</sup> N, with a corresponding beet yield 66 t ha−<sup>1</sup> (Figure 3, left).

A similar effect of mineral fertilizers was found for the top yields. The top yield was significantly affected by the year (d.f. = 2, F = 493.8, *p* < 0.0001), fertilization treatment (d.f. = 5, F = 41.8, *p* < 0.0001), and their interaction (d.f. = 10, F = 4.5, *p* < 0.001). The lowest yields were provided by the control and FYM treatments (17.4 and 19.4 t ha−1, respectively) (Table 4). The addition of mineral fertilizers increased the top yields significantly, ranging from 25.2 t ha−<sup>1</sup> (FYM + NPK2) to 26.9 t ha−<sup>1</sup> (FYM + NPK3). The differences between the FYM + NPK treatments were insignificant. Comparing the years, dry conditions during 2018 resulted in the lowest yield of the tops (12.1 t ha−1), while significantly higher yields were recorded in 2016 and 2017 (28.8 and 29.7 t ha−1, respectively). According to the linear-plateau model, the response of the sugar beet tops plateaued at 181 kg ha−<sup>1</sup> N, with a corresponding yield of 24 t ha−<sup>1</sup> (Figure 3, right).

**Figure 3.** Means (black dots) of sugar beet beetroot yield (**left**) and top yield (**right**) at different N rates applied with the FYM and FYM + NPK treatments in 2016, 2017, and 2018 combined and their linear-plateau regression (blue line).



**Table 4.** The beetroot and top yield as affected by the fertilizer treatment (control, FYM, FYM + NPK1–4) and years (2016–2018).

Note: The mean values with the standard error of the mean followed by the same letter ( small letters "a", horizontally; and big letters "A", vertically) are not significantly different (*p*, 0.05).

#### *3.4. The Effect of Fertilization on Sugar Content (SC) and Chemical Elements Concentration*

We must admit that due to limited funds, analyses of sugar beet in reduced quantities were performed over the years 2016–2018. This means that no repeated measurements were performed from each fertilizer treatment every single year. Therefore, the results of the statistical analysis presented here represent the average results for the entire analysed period. It is, therefore, necessary to take the results with a grain of salt.

According to the statistical analysis, no significant differences were recorded between the fertilizer treatments for any analysed parameter (the SC and the concentration of N, P, K, Ca, Mg, and Na) of the sugar beetroots. The SC varied from 19.7% (NPK4) to 21.9% (NPK1) (Table 5). The concentration of N, P, K, Ca, Mg, and Na was not affected by the fertilizer treatment (Table 5).

**Table 5.** The sugar content (%) and concentrations of N, P, K, Ca, Mg, and Na (%) in sugar beet beetroots as affected by the fertilizer treatment and over the years 2016–2018.


Note: The mean values without letters were not significantly different.

Similar results were recorded in the case of the sugar beet tops, where the concentrations of N, P, K, Ca, and Mg were analysed. Except for P, the effect of the fertilizer treatment was insignificant. All results are shown in Table 6. In the case of P, the mean concentration varied from 0.15% (control) to 0.23% (NPK4 and FYM + NPK1 treatments). Higher concentrations of the P were found in the FYM + NPK treatments as compared with the control, FYM, and NPK treatments (Table 6).

**Table 6.** The concentrations of N, P, K, Ca, and Mg in sugar beet tops as affected by the fertilizer treatment and over the years 2016–2018.


Note: The mean values with the standard error of the mean followed by the same letter are not significantly different (*p*, 0.05). Mean values without letters were not significantly different.

#### *3.5. The Effect of the Fertilizer Treatments on the Soil Properties*

The application of different combinations and doses of fertilizers did not affect the value of the soil pH. The average values ranged from 6.08 (NPK3) to 6.60 (FYM). The concentration of N was slightly affected by the fertilizer treatment. The lowest concentrations

were recorded in the control and FYM treatments (0.13%), while the highest concentrations were recored in the FYM+NPK4 treatment (0.16%). All other treatments provided results fitting within these extreme limits. In the case of soil carbon content, the distribution of the fertilizer treatments is clearer. The lowest C concentration was recorded in the control treatment (0.99%). All FYM + NPK treatments differed significantly from this value, and ranged from 1.26% to 1.35%, while the FYM and all NPK treatments filled the space between the control and FYM + NPK treatments. The concentration of soil P significantly varied among the treatments with lowest concentration in the control (20 mg kg−1) and FYM (29 mg kg−1) treatments and highest concentrations in NPK4 (70 mg kg−1) and FYM + NPK4 (93 mg kg−1) treatments. A similar pattern was recorded in the case of K (lowest concentrations were in the control and FYM treatments, while the highest concentrations were in the NPK4 and FYM + NPK2 treatments) (Table 7). The concentrations of Ca and Mg were not affected by the fertilizer treatment (Table 7).

**Table 7.** The basic soil chemical properties as affected by the fertilizer treatment and over the years 2016–2018.


Note: The mean values with the standard error of the mean followed by the same letter are not significantly different (*p*, 0.05). Mean values without letters were not significantly different.
