Effects of Strip-Till and Simultaneous Fertilization at Three Soil Depths on Soil Biochemical and Biological Properties

: In several studies, the discriminating factor in land use of arable soil is tilling, along with its depth and intensity. Reduced and no-till technologies are held to be beneﬁcial for soil health. Strip-till reduces soil disruption and enables the application of liquid fertilizer directly in rows at different levels. The objective of the research reported here was to evaluate the effects of digestate application on the biochemical and microbiological properties of soil at various soil depths. Three doses of digestate (0, 20, and 40 m 3 · ha − 1 ) applied at three different soil depths (0–10, 10–15, and 15–20 cm) were tested in two seasons (2020 and 2021) of semi-operational ﬁeld trials with maize cultivated according to strip-till practice. In 2020, a lower (20 m 3 · ha − 1 ) dose of digestate caused the most signiﬁcant improvement in β -glucosidase, urease, and basal and L-alanine-induced respiration in topsoil (0–10 cm) and in oxidizable carbon in mid-soil (10–15 cm). In 2021, the most signiﬁcant positive effect on arylsulfatase, N-acetyl- β -D-glucosaminidase, urease, and all types of respiration were caused by higher (40 m 3 · ha − 1 ) digestate dose in mid-soil (10–15 cm). The beneﬁts of the strip-till amended digestate in 2020, as revealed by respiration indicators, strongly decreased with soil depth. Finally, the markedly positive impacts of the digestate applied via the strip-till agromanagement technique were similar for three different depths of soil in 2021, verifying its beneﬁts.

Among various tillage practices, reduced tillage (techniques that minimize soil disturbance and leave crop residues or stubble on the soil surface instead of incorporating them into the soil) and no-till technologies are held to have beneficial effects on soil organic carbon content, nutrient transformation [5,11], and soil microbiome enrichment and activity enhancement [5,13,14]. Strip-till is a tillage protection system that minimizes plowing and I.
Soil organic matter (SOM) and exogenous organic matter (EOM) degradation rates will be primarily most enhanced in topsoil, although long-term, enhanced activity in topsoil is likely to reduce enzyme activities compared to mid-depth (10-15 cm) soil, due to the consumption of easily utilizable sources and leaching of nutrients from the surface to deeper soil layers. II. Respiratory carbon mineralization will be highest in topsoil during the whole growing season due to the best aeration and the highest biomass of aerobic microbes. III. Due to the strip-till application of digestate to the entire soil profile, increased microbial activities will extend to the greatest depth at the highest digestate dose. IV. Nitrogen mineralization will be lower compared to carbon mineralization at the greatest depth, putatively due to the limited content of organic nitrogen in the digestate and the oxygen-dependency of nitrification processes.
The objective of the research was to compare the effect of digestate, applied simultaneously to all three different soil depths at two different doses (20 and 40 m 3 ·ha −1 ), on biochemical and microbiological properties and their rates of change as functions of depth.

Site Description and Experimental Design
In the years 2020 and 2021, the experiment was carried out in fields near the village of Senice na Hané (49 • 37 32.5 N 17 • 05 14.2 E). The site is located in a fertile area of Hornomoravský úval (Olomouc District, Czech Republic), at an altitude of approximately 300 m a.s.l. The area belongs to the warm T2 climatic region, which is characterized by long, warm, dry summers and short, mild winters. The average air temperature is −2 to −3 • C in January and 18 to 19 • C in July. Rainfall in the growing season is between 350-400 mm and 200-300 mm in winter. The soil type is chernozem, and the soil texture (according to the USDA soil texture triangle) is silt loam. The soil properties are displayed in Table 1. At the beginning of September 2019, after the cereal harvest, a mixture of stubble intercrops was sown at a rate of 10 kg·ha −1 of white mustard (Sinapis alba) and 5 kg·ha −1 of lacy phacelia (Phacelia tanacetifolia), according to the usual agrotechnical methods. The intercrops were left in the field, where they froze over the winter, and their remains were mulched in the spring. A full-scale fertilization with NPK fertilizers (160 kg N·ha −1 ) was carried out in spring 2020.
In mid-April 2020, semi-operational plots of approximately 0.50 ha with different treatments were established by the simultaneous application of digestate at 3 depths of 10, 15, and 20 cm, at doses of 0, 20, and 40 m 3 ·ha −1 . The application of digestate with nitrification inhibitor VIZURA (BASF Ltd., division, Prague, Czech Republic) was carried out using a VT4556 machine (Vredo Dodewaard B.V, Dodewaard, The Netherlands) equipped with a MUCK TILLER applicator (P & L, spol. s r.o., Biskupice, Czech Republic) for strip-tillage and digestate application. One week after the digestate application, the maize (Zea mays) hybrid Banshee (FAO 300) was sown. The maize was harvested 5 months after sowing. Soil sampling was carried out one week after harvest.
In early September 2020, intercrops were sown again and left to freeze, as in the previous year. In 2021, the same operations were followed for the experimental plot as in the first year of the experiment.
The properties of the applied digestate are given in Table 2.

Soil Sampling and Measurements
The experimental plots were transversely divided into three parts. A soil sample was taken at depths of 0-10 cm, 10-15 cm, and 15-20 cm from each part. Thus, three individual soil samples merged from 8 sampling points were obtained for each treatment and for each depth. In the laboratory, samples were homogenized, sieved (≤2 mm), and air-dried for the measurement of oxidizable carbon (Cox), according to [21]. Freeze-dried samples were used for the following enzyme activity assays [22]: β-glucosidase (GLU), N-acetyl-β-Dglucosaminidase (NAG), arylsulfatase (ARS), and urease (Ure). Samples cooled to 4 • C were used for basal respiration (BR) and substrate-induced respiration determinations, using a MicroResp device, according to [23]. Substrate-induced respiration was measured after adding specific energy sources to the substrate: D-glucose (Glc-SIR), D-mannose (Man-SIR), and L-alanine (Ala-SIR).

Statistical Analysis
Data processing and statistical analyses were performed using the freely available software R, version 3.6.1 [24]. For characterization of the relationships between the treatments and selected soil properties, one-way and two-way analyses of variance (ANOVAs) were used, both of type I (sequential) sum of squares at a 5% significance level. For the detection of statistically significant differences among factor level means, Tukey's HSD (honestly significant difference) test was used, and "treatment contrast" was performed to calculate factor-level means for each treatment. The results were graphically presented using a simple barplot with standard deviations (SDs) together with statistically significant differences among variants. To check the statistical models, the Kolmogorov-Smirnov test (for normality-distribution checking) and Bartlett's test (for checking the heteroscedasticity of residuals) were used, also at a significance level of 0.05. In addition, different diagnostic (e.g., Q-Q) plots were also used for the purpose. For advanced statistical modelling of the dependence relationships between soil properties and treatments, principal component analysis (PCA) was also applied. Eigenvalues were used to measure the amount of variation retained by each principal component. These results were graphically presented with the help of Rohlf biplots for standardized PCAs. Pearson correlation analysis was performed to measure the linear dependences between soil properties. Pearson correlation coefficients were interpreted as follows: 0.0 < r < 0.3 (negligible correlation), 0.3 < r < 0.5 (low correlation), 0.5 < r < 0.7 (moderate correlation), 0.7 < r < 0.9 (high correlation), and 0.9 < r < 1.0 (very high correlation). eroscedasticity of residuals) were used, also at a significance level of 0.05. In addition, different diagnostic (e.g., Q-Q) plots were also used for the purpose. For advanced statistical modelling of the dependence relationships between soil properties and treatments, principal component analysis (PCA) was also applied. Eigenvalues were used to measure the amount of variation retained by each principal component. These results were graphically presented with the help of Rohlf biplots for standardized PCAs. Pearson correlation analysis was performed to measure the linear dependences between soil properties. Pearson correlation coefficients were interpreted as follows: 0.0 < r < 0.3 (negligible correlation), 0.3 < r < 0.5 (low correlation), 0.5 < r < 0.7 (moderate correlation), 0.7 < r < 0.9 (high correlation), and 0.9 < r < 1.0 (very high correlation).   On the basis of the results of the PCAs (Figure 5), we can conclude that, from the values for the 2020 season, approximately 77% of the variation is explained by the first two eigenvalues together: the first eigenvalue explains 61% and the second explains 16%. Along the first dimension, the following microbial activities make large contributions: Ala_SIR (17%), Man_SIR (16%), BR (15%), and Cox (14%). Along the second dimension, the following microbial activities make large contributions: NAG (42%), Glc_SIR (14%), and GLU (14%). The total contributions of microbial activities regarding PC1 and PC2 together are as follows (in descending order): Ala_SIR, Man_SIR, Cox, and BR. Other microbial activities do not make large contributions in accounting for the variability with respect to the first two principal components.  From the results of the PCAs (Figure 6), we can conclude that, given the values from the 2021 season, approximately 82% of the variation is explained by the first two eigenvalues together: the first eigenvalue explains 59% and the second explains 23%. Along the first dimension, the following microbial activities make large contributions: Ala_SIR (17%), NAG (16%), Man_SIR (13%), BR (12%), and ARS (11%). Along the second dimension, the following microbial activities make large contributions: Cox (39%), Glc_SIR (17%), Ure (13%), and GLU (12%). The total contributions of microbial activities regarding PC1 and PC2 together are as follows (in descending order): Ala_SIR, Cox, NAG, Glc_SIR, and Ure. Other microbial activities do not make large contributions in accounting for the variability with respect to the first two principal components.  On the basis of the results of the PCAs (Figure 5), we can conclude that, from the values for the 2020 season, approximately 77% of the variation is explained by the first two eigenvalues together: the first eigenvalue explains 61% and the second explains 16%. Along the first dimension, the following microbial activities make large contributions: Ala_SIR (17%), Man_SIR (16%), BR (15%), and Cox (14%). Along the second dimension, the following microbial activities make large contributions: NAG (42%), Glc_SIR (14%), and GLU (14%). The total contributions of microbial activities regarding PC1 and PC2 together are as follows (in descending order): Ala_SIR, Man_SIR, Cox, and BR. Other microbial activities do not make large contributions in accounting for the variability with respect to the first two principal components.

Soil Oxidizable Carbon and Enzyme Activities
From the results of the PCAs (Figure 6), we can conclude that, given the values from the 2021 season, approximately 82% of the variation is explained by the first two eigenvalues together: the first eigenvalue explains 59% and the second explains 23%. Along the first dimension, the following microbial activities make large contributions: Ala_SIR (17%), NAG (16%), Man_SIR (13%), BR (12%), and ARS (11%). Along the second dimension, the following microbial activities make large contributions: Cox (39%), Glc_SIR (17%), Ure (13%), and GLU (12%). The total contributions of microbial activities regarding PC1 and PC2 together are as follows (in descending order): Ala_SIR, Cox, NAG, Glc_SIR, and Ure. Other microbial activities do not make large contributions in accounting for the variability with respect to the first two principal components.

Soil Oxidizable Carbon and Enzyme Activities
Soil oxidizable carbon (Cox), which was reported to be related to microbially available (and utilizable) carbon [25], was found to be significantly decreased in deeper layers  [26]. These differences may be due majorly to the application of digestate having been carried out at a depth of 10-15 cm, such a procedure leading to the accumulation of available organic carbon in this soil layer. Furthermore, Ma et al. (2020) observed an indirect relation between depth and carbon available for mineralization [27]. Slepetiene et al. (2020) observed that the application of anaerobic digestion (AD) product to soil (0-40 cm depth) increased organic carbon (mobile humic acids) mainly in topsoil. However, in our work, we did not reveal any positive effect of digestate amendment on Cox values in topsoil, regardless of digestate composition. The lack of effect on Cox values was possibly due to a high percentage of original SOM in the upper soil layer. Further, we presumed significantly enhanced mineralization of digestate-derived labile carbon fractions (carried out by aerobic microorganisms, documented by respiration results; see Section 3.2) in upper layers compared to deeper soil layers. This assumption, proven by comparison of (Cox and respiration) results for soil depths of 10-15 cm and 15-20 cm at a 20 m 3 •ha −1 digestate dose in the 2020 season, was in line with the reported higher mineralization rate of external carbon in surface soil (compared to when it was incorporated into the soil) after treatment with sewage sludge digestate [28]. Such an assumption of mutually related carbon (aerobic) mineralization rate and availability of labile carbon substrate (Cox) was corroborated by significant (p ≤ 0.01) positive correlations of Cox with

Soil Oxidizable Carbon and Enzyme Activities
Soil oxidizable carbon (Cox), which was reported to be related to microbially available (and utilizable) carbon [25], was found to be significantly decreased in deeper layers ( [26]. These differences may be due majorly to the application of digestate having been carried out at a depth of 10-15 cm, such a procedure leading to the accumulation of available organic carbon in this soil layer. Furthermore, Ma et al. (2020) observed an indirect relation between depth and carbon available for mineralization [27]. Slepetiene et al. (2020) observed that the application of anaerobic digestion (AD) product to soil (0-40 cm depth) increased organic carbon (mobile humic acids) mainly in topsoil. However, in our work, we did not reveal any positive effect of digestate amendment on Cox values in topsoil, regardless of digestate composition. The lack of effect on Cox values was possibly due to a high percentage of original SOM in the upper soil layer. Further, we presumed significantly enhanced mineralization of digestate-derived labile carbon fractions (carried out by aerobic microorganisms, documented by respiration results; see Section 3.2) in upper layers compared to deeper soil layers. This assumption, proven by comparison of (Cox and respiration) results for soil depths of 10-15 cm and 15-20 cm at a 20 m 3 ·ha −1 digestate dose in the 2020 season, was in line with the reported higher mineralization rate of external carbon in surface soil (compared to when it was incorporated into the soil) after treatment with sewage sludge digestate [28]. Such an assumption of mutually related carbon (aerobic) mineralization rate and availability of labile carbon substrate (Cox) was corroborated by significant (p ≤ 0.01) positive correlations of Cox with basal respiration (BR) and substrate-induced respiration (with D-mannose and L-alanine) in 2020 (r = 0.54, 0.55, 0.53; Figure 3).
Although digestate application did not affect Cox content in topsoil, mid-soil at a depth of 10-15 cm was positively affected in both 2020 and 2021 by digestate at a dose of 20 m 3 ·ha −1 compared to the control treatment (0 m 3 ·ha −1 ). We concurrently detected significant increments in respiration values in the 10-15 cm layer (compared to topsoil) at all digestate doses (BR) and at 40 m 3 ·ha −1 (all SIRs) in 2021. Therefore, we ascribe an apparently contributing effect to strip-till incorporation of digestate into the soil profile (the 10-15 cm layer) on Cox content in soil and its longer-lasting preservation for extended enhancement of carbon mineralization and overall organic matter transformation. We corroborated this with significant Cox synergy (on a PCA biplot) and correlation (p ≤ 0.01) with GLU (r = 0.52) in 2020 (Figures 3 and 5). Contrary to Cox, β-glucosidase (GLU) activity in topsoil responded to the digestate amendment positively in both 2020 (at 20 m 3 ·ha −1 ) and 2021 (at 40 m 3 ·ha −1 ), which indicated stimulation due to access to more recalcitrant organic carbon (AD-transformed lignocellulose material). The stimulatory effect of digestate on GLU activity is known [29], and we revealed a positive effect of digestate (in 2021) on GLU values in 2021 at all depths with a dose of 40 m 3 ·ha −1 (Figure 1b) in comparison to unamended control soil. Plaza et al. (2004) reported, also, that high access to EOM from pig slurry significantly enhanced soil GLU and other enzyme activities, regardless of the metabolic quotient and total organic carbon [30]. We inferred from this that striptill application enabled the introduction of digestate-derived EOM in high amounts into the entire treated soil profile, which preserved cellulolytic activity until the end of the vegetation period. We did not verify our hypothesis I, but we corroborated hypothesis III.
As well as GLU, other enzymes (arylsulfatase, N-acetyl-β-D-glucosaminidase, and urease) showed significant (p ≤ 0.001) positive correlations (ARS r = 0.60, NAG r = 0.55, Ure r = 0.70) and synergy (GLU, ARS, and Ure on the PCA biplot) for 2021 (Figures 4 and 6). These results are in line with those of Meyer et al. (2015), who referred to increased Ure and GLU activities in the soil under organic treatments (compost and straw mulch) compared to conventional treatments (synthetic fertilizer and herbicide) at all depth intervals [31].
The results for ARS showed that mineralization of sulfur was negatively dependent on soil depth in the unamended treatment (Figure 1c). It has already been reported that ARS activity decreased markedly with depth in six soil profiles [32], and this decrease was associated with a decrease in organic carbon content [33]. ARS values were those most enhanced by digestate addition in the topsoil and mid-depth soil (10-15 cm) in 2020 at both digestate doses. In 2021, ARS enhancement was found in mid-depth (both digestate doses) and deep soil (40 m 3 ·ha −1 ). The findings for 2020 were in line with those of a previous study [34], where ARS activity showed a strong relationship with microbial biomass carbon and organic carbon under pig slurry amendment in topsoil (0-15 cm). The positive effect of strip-till application of digestate on the stimulation of nutrient-transformation activities in deeper soil was proven. The results for the 2021 season were in line with reported increments in ARS values with greater soil depth [34] but in contrast to the results of another study which did not find any effect of liquid hog manure application on enzyme activities at a depth of 15-30 cm [35].
Determination of N-acetyl-β-glucosaminidase (NAG) showed a minimal effect of soil depth or digestate dose on fungal turnover in 2020. On the contrary, digestate incorporated into soil at a high dose (40 m 3 ·ha −1 ) significantly improved NAG activity at all depths ( Figure 1d) in 2021, probably due to the higher accessibility of nutrients. In the past, digestate was found to enhance NAG activity in soil [36]. We inferred from these results that strip-till treatment of less rich soil impacted fungal biomass within the full profile positively, without any negative effect of soil depth. Our observation was in contrast with the results of [14], whose authors applied conventional tillage instead of strip-till methods and observed a negative dependence of fungal biomass on soil depth. We assumed that the digestate-derived nitrogen supplement supported fungal growth more efficiently in mid-soil compared to topsoil (2021) due to the reduced volume of ammonia volatilization (causing nitrogen losses). Furthermore, oxygen saturation in different soil layers may affect putative NAG-related carbon and nitrogen aerobic mineralization because these processes are coupled and succeed chitin degradation by NAG. Pearson's correlations for 2021 also revealed significant (p ≤ 0.001) positive correlations of NAG with BR, Glc-SIR, Man-SIR, and Ala-SIR (r-values were 0.69, 0.67, 0.71, and 0.83) (Figure 4). Thus, the mutual dependence of NAG activity, respiration rate, and oxygen saturation in soil was expected.
Urease (Ure) is an enzyme which generates ammonium and is involved in organoamine mineralization. Ure declined with depth (to the significantly lowest values at depths of 15-20 cm) in both unamended soil types and in 2020 with a dose of 20 m 3 ·ha −1 (Figure 1e). The reason was a limited amount of SOM, putatively decreased in the deepest soil layer, similarly to Li et al.'s (2015) reference to SOM decline with depth, which was coupled with lower contents of microbial necromass [37]. However, the digestate treatment in 2020 increased Ure values at a dose of 20 m 3 ·ha −1 in topsoil and soil depths of 10-15 cm, whereas nutrient-richer digestate in 2021 increased Ure most in mid-soil (20 and 40 m 3 ·ha −1 ) and in topsoil only at higher application dose (40 m 3 ·ha −1 ). Therefore, we again determined that the demand for digestate-derived ammonium nitrogen in mid-soil compared to topsoil was higher in 2021, probably due to the lower accessibility of nitrate nitrogen. Although SOM and EOM transformation were enhanced, nitrogen immobilization could occur in the treated soil due to the high SOM-mineral N ratio (see Table 2). Priming adverse effect of digestate amendment on higher ammonium losses via volatilization, the importance of which was reported in [38], could also play a minor role. Nevertheless, the increased access of digestate to the soil microbiome induced Ure activity, as was found for treated soil in the phase of crop maturity [39]. The results of the enzyme determination enabled us to prove hypothesis III and, at least for ARS, NAG, and Ure, hypothesis IV, too.

Soil Respiration
Soil basal respiration (BR) monitored carbon mineralization at various soil depths and showed, surprisingly, no difference within the full profile for 2020 and decline in the topsoil compared to deeper layers for the control treatment in 2021. In agreement with the results for other microbial activities, respiration in the 2021 season was highest in mid-soil at 40 m 3 ·ha −1 , and the same dose significantly increased, also, in the topsoil (compared to depths of 15-20 cm) (Figure 2a). This result was in line with previously reported positive effects of digestate addition on BR [40,41]. The soil in 2020 showed higher BR in topsoil and mid-soil at 20 m 3 ·ha −1 , but with a clear negative dependence of values on increasing depth and lower BR at soil depths of 10-15 cm and 15-20 cm (compared to topsoil) at a dose of 40 m 3 ·ha −1 . These results proved our hypothesis II and indicated that digestate applied to all soil layers did not induce the equal stimulation of aerobic carbon mineralization, presumably on account of lower deep-soil aeration and less carbon accessibility, due to the lower dry mass of the digestate, acting as limiting factors on BR in 2020. Similar findings have been reported. Fang and Moncrieff (2005) found that soil carbon pools and microbial respiratory activity, as well as CO 2 :TOC (total organic carbon) ratios, declined rapidly with soil depth [42]. Spohn and Chodak (2015) reported that a change in metabolic quotient with increasing depth was not controlled solely by soil carbon concentration [43]. Nevertheless, these features were not observed in 2021.
Due to putatively more significant stimulation of the microbiome by high doses of richer digestate (higher nutrient and DM contents) in 2021, derived EOM promoted microbial growth and an increase in total respiratory potential (abundance of aerobes), as indicated by Glc-SIR. This higher biomass of respirating microbes could overcome oxygen limitation. We can infer this from Glc-SIR values for 2021, which were significantly higher at all depths with 40 m 3 ·ha −1 treatments (compared to unamended soil at depths of 10-15 cm and 15-20 cm, also compared to doses of 20 m 3 ·ha −1 ) (Figure 2b). It was again in line with a reported higher positive effect of digestate on substrate-induced respiration in soil parallelly treated with digestate and mineral fertilizer [40]. Absolutely highest Glc-SIR values were found in mid-soil (10-15 cm), which is explainable by the presumed significantly enhanced mineralization of the digestate-derived labile carbon fraction in topsoil compared to deeper soil layers, which preserved more oxidizable carbon for increased durations of digestatecoupled stimulation of aerobic respiration microbes.
In contrast to 2021, Glc-SIR in 2020 was significantly most increased in topsoil by both digestate doses but also greater soil depth. This fact emphasized the positive effect of digestate amendment in topsoil but indicated the decreased effect of amendment at deeper layers. Apparently, the digestate stimulation of respiration capacity in deeper layers was again limited by oxygen saturation. Nevertheless, significant increments in Glc-SIR in the deepest soil (15-20 cm)  Therefore, similar but even stronger (than Glc-SIR) positive effects of rich digestate amendment on sugar-and amino-acid induced respiration (Man-SIR and Ala-SIR) in 2021 were observed. Man-SIR and Ala-SIR caused significant enhancement of these SIRs at all depths with treatments of 40 m 3 ·ha −1 and at 15-20 cm (for Man-SIR) (Figure 2c,d). In 2021, the highest values of Man-SIR and Ala-SIR were found in mid-soil, from which we assumed (as with the Ure determination results) that at 10-15 cm depths the addition of digestate accelerated Ure hydrolysis more than in topsoil, putatively due to the retarded formation of nitrates.
Positive effects of digestate on both Ala-SIR and Man-SIR compared to unamended topsoil (20 and 40 m 3 ·ha −1 ) and soil at depths of 10-15 cm (20 m 3 ·ha −1 ) were revealed, also, in 2020. Again, a strong indirect dependence of Ala-SIR and Man-SIR on soil depth (declining in deeper layers) was detectable for the digestate-amended treatments. Therefore, we presumed a partial stabilization of introduced EOM in deeper soil layers of chernozem, together with immobilization of nitrogen, as was reported by other authors [44,45], and we assumed this from results of respiration and enzyme (ARS, NAG, and Ure) determinations. We verified hypothesis IV with these findings.

Conclusions
We found out that strip-till treatment of soil combined with the addition of digestate at three different depths (10,15, and 20 cm) improved soil biological properties and microbial activity related to nutrient transformation, but differently in various seasons (2020 and 2021), due to differences in the properties of the applied digestate. We can generalize that the most significant improvements in oxidizable carbon, arylsulfatase, urease, and all respiration types in 2020 (compared to topsoil (0-10 cm)) was caused by the lower (20 m 3 ·ha −1 ) digestate dose in mid-soil (10-15 cm). The most significant positive effects on arylsulfatase, N-acetyl-β-glucosaminidase, and all respiration types in 2021 were caused by higher (40 m 3 ·ha −1 ) digestate doses in mid-soil (10-15 cm) in comparison to topsoil (0-10 cm). Moreover, strip-till-mediated application of digestate (20 or 40 m 3 ·ha −1 ) in deeper soil layers (10-15 and 15-20 cm) mitigated depth-dependent decline in Cox (in 2020 and 2021) and β-glucosidase (in 2021) values (compared to corresponding layers of control unamended soil). We conclude that, under amendment with less rich digestate in the 2020 season, the impact of strip-till in combination with digestate amendment was less beneficial and more strongly negatively affected by soil depth, especially in relation to respiration indicators. On the contrary, in 2021, markedly positive impacts of digestate applied via strip-till were comparable for all three different depths of soil and thus verified the benefit of this agromanagement technique.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.

Conflicts of Interest:
The authors declare no conflict of interest.