Soil Respiration Under 90 Year-Old Rye Monoculture and Crop Rotation in the Climate Conditions of Central Poland

agronomy

Article Soil Respiration under 90 Year-Old Rye Monoculture and Crop Rotation in the Climate Conditions of Central Poland

Tomasz Sosulski 1 , Magdalena Szyma ´nska 1,* , Ewa Szara 1 and Piotr Sulewski 2

1 Department of Agricultural Chemistry, Institute of Agriculture, Warsaw University of Life Sciences, Nowoursynowska 159, 02-766 Warsaw, Poland; [email protected] (T.S.); [email protected] (E.S.) 2 Institute of Economics and Finances, Warsaw University of Life Sciences, Nowoursynowska 166, 02-787 Warsaw, Poland; [email protected] * Correspondence: [email protected]; Tel.: +482-2593-2625

Abstract: This study, aimed at assessing the rate of soil respiration under different crop rotation and fertilization conditions, was carried out on long-term (since 1923) experimental plots with rye monoculture and 5-crop rotation in Skierniewice (Central Poland). The treatments included mineral- organic (CaNPK+M) and organic (Ca+M) fertilization (where M is farmyard manure). Soil respiration was measured in situ by means of infrared spectroscopy using a portable FTIR spectrometer Alpha.

CO2 fluxes from CaNPK+M-treated soils under cereals cultivated in monoculture and crop rotations were not statically different. Respiration of soil under lupine cultivated in crop rotation was higher than under cereals. N-fertilization and its succeeding effect increased soil respiration, and significantly altered its distribution over the growing season. Our results indicate that in the climatic conditions of Central Europe, respiration of sandy soils is more dependent on the crop species and fertilization than on the crop rotation system. Omission of mineral fertilization significantly decreases soil respiration.

The CO2 ﬂuxes were positively correlated with soil temperature, air temperature, and soil content of NO − and NH +. 3 4

Citation: Sosulski, T.; Szyma´nska,M.; Keywords: long-term experiment; GHG emissions; monoculture and crop rotation; legumes; fertilization Szara, E.; Sulewski, P. Soil Respira- tion under 90 Year-Old Rye Monocul- ture and Crop Rotation in the Climate Conditions of Central Poland. 1. Introduction Agronomy 2021, 11, 21. Arable land plays a fundamental role in global carbon cyclical exchange between https://dx.doi.org/10.3390/ the lithosphere and atmosphere [1,2]. Cultivated soils are considered both a source and agronomy11010021 sink of atmospheric CO2 [3,4]. According to Ding et al. [5] and Paustian et al. [6], 25–29%

Received: 1 November 2020 of anthropogenic CO2 input to the atmosphere can be assumed to come from cultivated soils. Accepted: 23 December 2020 Therefore, arable land is considered an important source of CO2 loss to the atmosphere [7]. Published: 24 December 2020 The key factors affecting soil respiration include content of soil organic carbon, fertilization, temperature and soil moisture, and soil tillage intensity [8–11]. Numerous scientific papers Publisher’s Note: MDPI stays neu- have shown that the most important drivers of soil respiration are both air/soil temperature tral with regard to jurisdictional claims and soil moisture [12,13]. Buragiene˙ et al. [14] and Bogužas et al. [15], however, found a in published maps and institutional negative correlation between soil CO2 fluxes and temperature. Negative influence of soil affiliations. moisture on soil respiration has also been described in literature [16,17]. Higher content of soil organic carbon contributes to a higher rate of CO2 soil respiration [12]. Different cropping systems and mineral/organic fertilization can significantly alter the content of organic carbon in the soil [18]. An increase in soil organic carbon observed in mineral Copyright: © 2020 by the authors. Li- treated soil was lower than that observed by manure fertilization [18,19]. Sosulski and censee MDPI, Basel, Switzerland. This Korc [19] found that mineral fertilizers (no application of organic amendments) led to an article is an open access article distributed increase in organic carbon content in soil. Although mineral NPK fertilizers were applied, under the terms and conditions of the Creative Commons Attribution (CC BY) nitrogen was the main contributor to increase inorganic carbon content in the soil. Higher license (https://creativecommons.org/ organic carbon content in the mineral fertilized soils resulted from greater input of crop licenses/by/4.0/). residues in comparison to non-treated soils [20]. In addition to promoting higher crop

Agronomy 2021, 11, 21. https://dx.doi.org/10.3390/agronomy11010021 https://www.mdpi.com/journal/agronomy Agronomy 2021, 11, 21 2 of 16

biomass production, mineral fertilization, in particularly nitrogen, intensifies the microbial processes responsible for soil organic matter decomposition. Sainju et al. [10] and Song and Zhang [13] observed that soil respiration from N-fertilized soils was higher by 14% than that from non-fertilized soils. The effect of nitrogen fertilization on soil respiration is not always observed. For example, Zhang et al. [21] found a 4% increase in root respiration after NPK fertilization, while Alluvione et al. [16] and Zhai et al. [22] reported that N-fertilization did not affect soil respiration. Moreover, Ding et al. [23] reported that N-fertilization decreased CO2 soil fluxes by 10.5%. The negative influence of applying high nitrogen fertilizer rates on soil respiration was also reported by Song and Zhang [13]. Pareja-Sánchez et al. [24] found that the effect of nitrogen fertilization could be different depending on the tillage conditions. Grant at al. [25] reported that it may be difficult to determine the influence of N-fertilization on CO2 soil emissions. For example, the authors found only a slight increase in CO2 soil fluxes after increasing and decreasing the rate of nitrogen fertilizer by 50%. However, the influence of soil manuring on soil respiration tends to be more pronounced. An increase in soil respiration after solid and liquid manure application has been observed in several studies [21,22,26,27]. The effect of soil tillage is broadly discussed in international scientific literature [7,10,24,28]. Nonetheless, literature reports have provided divergent opinions on the effect of different cropping systems on soil respiration. For example, Omonode et al. [29] found higher CO2 soil fluxes under continuous corn than under corn cultivated in rotation. Campbell et al. [30] also reported that soil respiration under corn after corn cultivation was higher in comparison to corn after soybean cultivation. Shen et al. [31] reported that maize monoculture had greater direct greenhouse gas emission (GHG) than the maize soybean intercrop treatment, although it was the largest C sink due to its higher net primary production. On the other hand, Norberg et al. [32] stated that soil respiration was not affected by crop rotation. However, Herridge and Brock [33] found that CO2 fluxes under canola were higher than those from soil under pea. This suggest that soil respiration for different plant species can vary. Discrepancies in the results of international research on soil respiration from different cultivated and fertilized soils in varied climatic and soil conditions limit the ability to distinguish between the effects of cropping systems (including monoculture and crop rotation) and the effects of fertilization of sandy soils occurring in Central and Eastern Europe. These soils are usually characterized by low content of organic matter, and lower yielding potential affected by the soil water regime and low nutrients content [18]. An improvement of soil properties is usually obtained through mineral-organic fertilization, remaining a typical practice in Polish agricultural conditions. In order to provide an insight into the effects of crop rotation and fertilization on soil respiration, we conducted a study on a 90 year-old long-term field (since 1923) experiment located in Skierniewice (Central Poland) to quantify soil respiration under a rye monoculture and 5-crop rotation system. The objective was to determine the effect of environmental factors, different crop rotations and cultivation of legumes, and mineral fertilization on soil respiration.

2. Materials and Methods 2.1. Experiments The research was carried out in 2012 and 2013 on two long-term ﬁeld experiments in Skierniewice (51◦9606000 N, 20◦1606300 E, Central Poland) belonging to the Warsaw University of Life Sciences—SGGW, maintained with no alterations since 1923. The soil is Luvisols (FAO 2006) of the type of loamy sand with the following fractions in the 0–25 cm layer (Ap horizon): 7% < 0.002 mm; 5% 0.002 to 0.05 mm; 87% > 0.05 mm, in the 26–45 cm layer (Eet horizon): 5% < 0.002 mm; 5% 0.002 to 0.05 mm; 90% > 0.05 mm, below 45 cm of depth (Bt/C horizon) 14% < 0.002 mm; 8% 0.002 to 0.05 mm; 78% > 0.05 mm. Plants were cultivated using two different cropping systems: − Experiment E—5-ﬁeld crop rotation: potatoes, spring barley, yellow lupine, winter wheat, rye—in the years of the study, spring barley (2012) and yellow lupine (2013) were cultivated, Agronomy 2021, 11, 21 3 of 16

− Experiment D—rye monoculture. Both experiments were conducted in a randomized block design in 5 replications with an experimental plot area of 36 m2. The investigation was conducted on Experiment D (mineral fertilizers and manure, CaNPK+M) and Experiment E (mineral fertilizers and manure, CaNPK+M and solely with manure, Ca+M). Manure was applied at a rate of 30 t ha−1 in 4-year intervals on CaNPK+M treatment of the experiment with rye monoculture, and at the same rate every 5 years (potatoes) on both Ca+M and CaNPK+M treatments in Experiment E. On both experiments, the investigations were conducted in the 2nd and 3rd year after soil manuring. On the mineral fertilized treatments (CaNPK+M) of both Experiments (D and E), mineral fertilizers were applied at the following rates: 90 kg N (ammonium nitrate), 26 kg P (triple superphosphate), and 91 kg K ha−1 (potassium chloride 50%). Lupine cultivated in Experiment E was not treated with nitrogen fertilizers. Lime –1 was applied every four years (1.6 t CaO ha ) as CaCO3 in fields with rye monoculture (D), and every five years (2 t CaO ha–1) in field E with crop rotation. On Experiment E, spring barley was cultivated in 2012, and yellow lupine in 2013. Yields of barley and lupine cultivated in Experiment E, and rye in Experiment D were measured on all replications under both treatments. Atmospheric conditions and soil temperatures were measured by the Experimental Field’s Meteorological Station.

2.2. CO2-C Emissions Measurement

CO2-C ﬂuxes from the soil were measured in situ by means of a portable FT-IR spectrometer model Alpha (Bruker, Germany). Soil respiration (F) was calculated as the increase in the amount of CO2-C in the chamber (ø = 29.5 cm, h = 20 cm) after 10 min. exposure to the soil surface in accordance with the equation presented by Burton et al. [34]:

∆C Vc ·M F = · mol (1) ∆t A ·Vmol

where: ∆C/∆t is the rate of change in CO2-C concentration inside the chamber, Vc is the total volume of the chamber, A is the surface area of the chamber, Mmol is molar mass of CO2-C, and Vmol is the molar volume of CO2-C inside the chamber corrected for air −1 −1 temperature using the ideal gas law. Soil respiration was expressed in kg CO2-C ha d . In 2012, the measurements were conducted on 30 test dates between 22-MAR and 22-OCT, and in 2013 on 27 test dates between 19-APR and 16-OCT in all replications. Cumulative −1 soil respiration (i.e., kg CO2-C ha ) was calculated by linear interpolation between two close sampling dates and numerical integration of the function over time, assuming that ﬂuxes changed linearly among sampling days [35].

2.3. Soil and Plant Analysis

For NO3--N and NH4+-N soil content determination, soil sampling was conducted on all measurement dates in all replications of the examined treatments on both experiments from the Ap horizon (0–25 cm depth). Soil content of both mineral forms of nitrogen was presented in our previous works [36,37]. On a single occasion in 2012 and 2013, soil samples were also collected in autumn from three soil horizons: Ap (0–25 cm), Eet (26-45 cm), and Bt (below 45 cm) from all experimental replications. In soil samples collected in autumn, soil organic carbon (SOC) was measured by means of a Thermo Electron-C TOC-500 instrument (Shimadzu, Kyoto, Japan). Soil total nitrogen (TN) content was measured in the same soil samples. Soil TN content and N content in grain and straw of all cultivated plants were measured in samples collected after harvest in 2012 and 2013 by means of a Vapodest model (Gerhardt, Bonn, Germany) VAP 30 analyzer distillation system. Soil moisture was assessed for each sample as a decrease in sample weight after oven-drying in 105 ◦C.

2.4. Data Analysis The statistical analysis employed was analyzed using the Statistica PL 13.3 software (Tulsa, OK, USA). One-way analysis of variance (ANOVA) followed by Tukey’s (HSD) Agronomy 2021, 11, x FOR PEER REVIEW 4 of 16

2.4. Data Analysis Agronomy 2021, 11, 21 4 of 16 The statistical analysis employed was analyzed using the Statistica PL 13.3 software (Tulsa, OK, USA). One-way analysis of variance (ANOVA) followed by Tukey’s (HSD) multiple-comparison test was carried out to determine statistically significant differences (pmultiple-comparison < 0.05) in soil organic test carbon was carried (SOC), out total to determinenitrogen content statistically in soil signiﬁcant horizons, differences yields of plants,(p < 0.05) total in nitrogen soil organic content, carbon and (SOC), nitrogen total uptake nitrogen by plants content between in soil horizons,different fertiliza- yields of tionplants, treatments. total nitrogen Data had content, been and previously nitrogen te uptakested for by normality plants between distribution different by fertilizationa Shapiro- Wilk’streatments. test. A Data Kruskal-Wallis had been previously test was testedapplied for to normality study the distribution differences byin asoil Shapiro-Wilk’s respiration (ptest. < 0.05). A Kruskal-Wallis Spearman correlation test was applied analysis to was study used the differencesto evaluate incorrelations soil respiration between (p < 0.05).soil Spearman correlation analysis was used to evaluate correlations between soil CO -C CO2-C fluxes and atmospheric (Ta) and soil (Ts) temperature, soil moisture (WFPS), NO23−- ﬂuxes and atmospheric (Ta) and soil (Ts) temperature, soil moisture (WFPS), NO −-N and 4+ 3 N and+ NH -N soil content in Ap (0–25 cm) soil horizon and between cumulative soil res- pirationNH4 -N andsoil content content of in SOC Ap (0–25and total cm) soilnitrogen horizon (TN) and in betweenAp, Eet, cumulativeand Bt soil horizons, soil respiration crop and content of SOC and total nitrogen (TN) in Ap, Eet, and Bt soil horizons, crop yields yields of grain and straw, content of total nitrogen in grain and straw, nitrogen uptake by of grain and straw, content of total nitrogen in grain and straw, nitrogen uptake by crops crops (p < 0.05). (p < 0.05).

3.3. Results Results 3.1.3.1. Atmospheric Atmospheric Conditions Conditions AverageAverage temperature temperature was 8.18.1 ◦°CC inin 2012, 2012, and and 9.6 9.6◦ C°C in in 2013. 2013–. The The distribution distribution of average of av- eragemonthly monthly temperatures temperatures in 2012 in and2012 2013 and was 2013 higher was higher than the than multi-year the multi-year average average (Figure (Figure1). Total 1). precipitation Total precipitation in 2012 in was 2012 478.6 was mm,478.6 and mm, in and 2013—618.5 in 2013—618.5 mm. Themm. distribution The distri- butionof precipitation of precipitation in both in years both ofyears the of study the study differed differed from thefrom multi-year the multi-year average average (1921– (1921–2013)2013) (Figure (Figure1). In 2013,1). In there 2013, were there periods were pe ofriods intense of intense rainfall rainfall in May andin May June, and causing June, causingtemporary temporary excess ofexcess water of in water the soil. in the soil.

160 25 oC 140 20 120 15 100 Precipitation 2012 10 Precipitation 2013 80

mm Average precipitation 1921-2013 5 60 Ta 2012 0 Ta 2013 40 Average Ta 1921-2013 20 -5

0 -10

Figure 1. Monthly precipitation and average air temperature in 2012 and 2013. Figure 1. Monthly precipitation and average air temperature in 2012 and 2013.

3.2.3.2. Soil Soil Properties Properties SoilSoil moisture moisture andand dailydaily air air and and soil soil temperature temperature were were shown shown in our in previous our previous works works[36,37] . [36,37].Average Average soil moisture soil moisture under the under 5-crop the rotation 5-crop(E) rotation in 2013 (E) exceeded in 2013 thatexceeded of 2012 that by approxi-of 2012 bymately approximately 53%, and under53%, and the monocultureunder the monoculture (D) by approximately (D) by approximately 36%. In most 36%. instances, In most the instances,average daily the soilaverage temperature daily so valuesil temperature slightly exceeded values slightly the respective exceeded air temperaturethe respective values. air temperatureAs expected, values.regardless of crop rotations and fertilization, the highest content of organicAs expected, carbon (SOC) regardless and total of nitrogencrop rotations (TN) wasand foundfertilization, in the top the soil highest layer content (Ap, 0–25 of cm),or- ganiclower carbon in the (SOC) Bt soil and horizon total nitrogen (>45 cm), (TN) and was the lowestfound in in the the top Eet soil soil layer horizon (Ap, (26–450–25 cm), cm) lower(Table in1). the The Bt lowest soil horizon content (>45 of SOCcm), and and the TN lowest in the in studied the Eet soil soil horizons horizon was(26–45 found cm) (Tablein Ca+M 1). The treatment lowest ofcontent Experiment of SOC E and (6.141, TN 1.720in the and studied 2.212 soil g C horizons kg−1 and was 0.585, found 0.183, in and 0.254 g N kg−1 in Ap, Eet, and Bt soil horizons, respectively). The highest content of SOC and TN was found in the Ap soil horizon of CaNPK+M treatment of Experiment D with rye monoculture (8.802 g C kg−1 and 0.884 g N kg−1, respectively). SOC and TN content in this soil was higher by approximately 19.8% and 24.2%, respectively than in the Agronomy 2021, 11, 21 5 of 16

analogous treatment (CaNPK+M) of Experiment E. In deeper soil horizons (Eet and Bt), content of SOC and TN in the soil of CaNPK+M treatment of Experiment E was higher than in Experiment D by approximately 5.4–37.3% and 16.2–32.5%, respectively. As a consequence of SOC and TN content in the soils, the C:N soil ratio ﬂuctuated between 9.96 and 10.51 in Ap horizon, 9.68 and 10.00 in Eet horizon, and 8.02 and 8.87 in Bt horizon of the examined soils (Table1).

Table 1. Average content (mean ± SD) of soil organic carbon, total nitrogen, and C/N ratio in soil horizons of Ca+M and CaNPK+M treatments under rye monoculture and 5-crop rotation experiments.

Soil Organic Carbon Total Nitrogen Treatment Soil Horizon C:N g C kg−1 g N kg−1 D—CaNPK+M 8.802 c ± 0.102 0.884 c ± 0.005 9.96 E—CaNPK+M Ap (0–25 cm) 7.348 b ± 0.086 0.712 b ± 0.008 10.34 E—Ca+M 6.141 a ± 0.156 0.585 a ± 0.017 10.51 D—CaNPK+M 2.014 c ± 0.016 0.201 c ± 0.001 10.00 E—CaNPK+M Eet (26–45 cm) 2.668 b ± 0.120 0.276 b ± 0.010 9.68 E—Ca+M 1.720 a ± 0.049 0.183 a ± 0.007 9.39 D—CaNPK+M 2.245 a ± 0.121 0.290 a ± 0.016 8.02 E—CaNPK+M Bt (>45 cm) 2.668 b ± 0.093 0.295 b± 0.011 8.87 E—Ca+M 2.212 a ± 0.080 0.254 a ± 0.013 8.72 D—rye monoculture, E—5-crop rotation. Values followed by the same letters in the column (separated for soil horizons) are not statistically different (Tukey HSD test, p < 0.05). SD—standard deviation.

3.3. Plants Yields and Nitrogen Uptake The grain yields of cereals cultivated in both experiments (2012—spring barley on Experiment E, and 2012 and 2013—rye on Experiment D, respectively) were low (Table2). In both years of the study, grain yields of rye were similar and did not exceed 2.39 t ha−1. Low yielding of rye was probably the result of the multifactoral effect of soil/weather conditions prevailing over the study period, and more likely the effect of 90 years of rye cultivation in monoculture. In 2012, rye straw yields were significantly higher than in 2013 by approximately 51.3%. The crop limiting factor in 2013 could have been soil moisture excess at the turn of May and June. As a consequence of yields and total nitrogen content in plants (12.7–16.0 g N kg−1 and 5.2–5.3 g kg−1 in grain and straw, respectively), total nitrogen uptake by rye reached 45.0 and 47.6 kg N ha−1 in 2012 and 2013, respectively. Barley grain yields obtained on CaNPK+M treatment of Experiment E were significantly higher by 21.8% than on Ca+M treatment. Content of total nitrogen in barley cultivated in Experiment E depended on mineral fertilizer application, and was significantly higher in plants cultivated on CaNPK+M than on Ca+M treatment (19.8 and 13.5 g N kg−1 in grain, respectively). Total nitrogen uptake by barley cultivated on CaNPK+M treatment was twice as high as on Ca+M treatment. Lupine grain and straw yield was higher under mineral fertilization (1.56 t ha−1 and 8.45 t ha−1, respectively) than under Ca+M treatment (1.17 t ha−1 and 5.55 t ha−1, respectively). Content of total nitrogen in grain and straw of lupine cultivated on both examined treatments on Experiment E was similar. Conse- quently, the accumulation of nitrogen by lupine was higher under mineral fertilization (192.3 kg N ha−1) by approximately 46.5% than on Ca+M treatment (131.2 kg N ha−1). Agronomy 2021, 11, 21 6 of 16

Table 2. Yields of plants (Experiment E, 2012—spring barley, 2013—yellow lupine, and Experiment D, 2012 and 2013—rye monoculture), total nitrogen content and nitrogen uptake by plants on Ca+M and CaNPK+M treatments under rye monoculture and 5-crop rotation Experiments in 2012 and 2013 (mean ± SD).

Grain Straw Total N Uptake Year Cropping System Treatment Yield N Content N Uptake Yield N Content N Uptake t ha−1 g N kg−1 kg N ha−1 t ha−1 g N kg−1 kg N ha−1 kg N ha−1 Monoculture of rye (D) CaNPK+M 2.28 c ±0.23 12.7 c ±0.1 30.4 c ± 2.8 2.83 c ± 0.27 5.2 c ± 0.1 14.6 c ± 1.5 45.0 c ± 3.3 CaNPK+M 2.78 a ± 0.27 19.8 a ± 0.2 55.0 a ± 5.4 1.97 a ± 0.04 8.2 a ± 0.4 20.5 a ± 0.6 75.5 a ± 5.4 2012 5-crop rotation (E) Ca+M 2.29 b ± 0.19 13.5 b ± 0.4 31.0 b ± 3.1 0.69 b ± 0.05 10.4 b ± 0.1 5.7 b ± 0.7 36.7 b ± 3.1 Monoculture of rye (D) CaNPK+M 2.37 c ± 0.20 16.0 d ± 0.6 37.7 d ± 1.9 1.87 d ± 0.08 5.28 c ± 0.26 9.8 d ± 0.4 47.6 c ± 1.9 2013 CaNPK+M 1.56 a ± 0.16 53.0 a ± 1.2 82.3 a ± 6.6 8.45 a ± 0.9 13.1 a ± 0.8 110.0 a ± 8.9 192.3 a ± 14.7 5-crop rotation (E) Ca+M 1.17 a ± 0.47 53.9 a ± 5.0 61.2 a ± 19.6 5.55 b ± 1.42 13.2 a ± 3.2 67.0 b ± 6.3 131.2 b ± 20.9 Values followed by the same letters in the column (separated for 2012 and 2013) are not statistically different (Tukey HSD multiple range test, p < 0.05). SD—standard deviation. Agronomy 2021, 11, 21 7 of 16

3.4. Soil Respiration

Daily CO2-C soil fluxes in all the examined treatments of both experiments showed high variability (Table3). In CaNPK+M treatment under rye monoculture, the flux ranges −1 −1 −1 −1 were 4.25–94.34 kg CO2-C ha day and 1.49–67.25 kg CO2-C ha day in 2012 and 2013, respectively. The ranges of daily soil CO2-C fluxes under spring barley cultivated on Exper- −1 −1 −1 −1 iment E in 2012 were 0.93-102.53 kg CO2-C ha day and 0.72–72.24 kg CO2-C ha day on the CaNPK+M and Ca+M treatments, respectively. On the same treatments in 2013, −1 −1 when yellow lupine was cultivated, CO2-C fluxes ranged 1.59–158.22 kg CO2-C ha day −1 −1 and 0.47–102.27 kg CO2-C ha day for the CaNPK+M and Ca+M treatments, respectively. The level and dynamics of CO2-C fluxes from the examined soils were different in both years of the study. The differences in distribution of daily CO2-C fluxes from the examined soils treated with CaNPK+M on Experiment E and Experiment D in 2012 were of no statistical significance (Table3). The distribution of daily CO 2-C fluxes from Ca+M soil in experiment E was lower than those recorded on both CaNPK+M treatments of Experiments E and D. In 2013, differences observed in distribution of daily CO2-C fluxes from different CaNPK+M treated soils under rye monoculture (Experiment D) and Ca+M under lupine in Experiment E were of no statistical significance, and were both lower than CO2-C fluxes from CaNPK+M treated soil in Experiment E (2013, lupine) (Table3).

Table 3. Daily and cumulative CO2-C emissions from soil on Ca+M and CaNPK+M treatments under rye monoculture and 5-crop rotation experiments over the measurement period in 2012 and 2013.

2012 2013

Cropping System Treatment CO2-C Soil Emissions Daily Cumulative Daily Cumulative −1 kg CO2-C ha mean ± SD 21.71 ± 16.2 4989.5 ± 229.3 22.88 ± 16.6 3982.7 ± 284.2 Rye monoculture (D) CaNPK+M median 17.39 b 5043.1 16.43 a 4028.0 min-max 4.25–94.34 4688.8–5283.4 1.49–67.25 3605.1–4315.6 mean ± SD 22.06 ± 21.0 4809.2 ± 164.3 37.43 ± 29.4 6997.5 ± 407.5 CaNPK+M median 15.43 b 4743.3 32.49 b 7137.9 min-max 0.93–102.53 4670.1–5079.6 1.59–158.22 6306–7331.6 5-crop rotation (E) mean ± SD 16.36 ± 15.9 3535.1 ± 235.3 25.63 ± 24.5 4552.7 ± 429.1 Ca+M median 10.45 a 3557.1 16.11 a 4617.7 min-max 0.72–72.24 3223.8–3868.1 0.47–102.27 4092.4–5023.4 Values followed by the same letters in the column are not statistically different (Kruskal-Wallis test, p < 0.05). SD—standard deviation.

3.5. Distribution of CO2-C Soil Fluxes in 2012

At the beginning of the study period in 2012, daily CO2-C soil fluxes from all the examined soils in both experiments were very low (Figure2). At the end of March, CO 2-C fluxes from soil under rye monoculture gradually increased, whereas from both soils in Experiment E (CaNPK+M and Ca+M) they decreased. A peak in CO2-C soil fluxes with the monoculture rye treatment was observed on the 26th of April. A rapid increase in CO2-C soil fluxes was observed on the 20th of April on both CaNPK+M and Ca+M treatments of Experiment E. A decrease in soil CO2-C fluxes from the studied soils were observed in mid- May. A subsequent peak of CO2-C soil emissions on CaNPK+M treatment of Experiment E was observed on the 7th of June. At the same time, some fluctuation of CO2-C soil fluxes with relatively low amplitude were recorded on both CaNPK+M and Ca+M treatments of Experiments D and E, respectively. Between the 7th of June and the end of June, CO2-C fluxes decreased on all the examined soils and increased again on the 5th of July. From mid- July until the end of August, CO2-C fluxes from soil under rye monoculture (Experiment D, CaNPK+M) remained relatively low. On both studied treatments (CaNPK+M and Ca+M) on Experiment E, subsequent CO2-C soil emission peaks (lower than that from the Agronomy 2021, 11, 21 8 of 16

beginning of July) were recorded on the 7th of August. On both treatments in Experiment E (CaNPK+M and Ca+M), CO2-C soil ﬂuxes decreased substantially, and after a slight increase was observed at the end of August, they remained low until the end of the study period. CO2-C ﬂuxes from soil under rye monoculture (Experiment D, CaNPK+M) Agronomy 2021, 11, x FOR PEER REVIEW increased noticeably at the beginning of September and remained relatively high8 of 16until

18th of September. Further, until the end of the study period, CO2-C ﬂuxes from soil of Experiment D were low.

2012 160 140

-1 120 d

-1 100 80 -C ha -C 2 60

kg CO kg 40 20 0 22 29 12 19 26 20 17 25 31 7 14 21 28 5 12 19 26 31 7 14 21 28 2 11 18 26 2 9 16 22 MAR APR MAY JUN JUL AUG SEP OCT D CaNPK+M E CaNPK+M E Ca+M

2013 160 140 120 -1 d 100 -1 80 -C ha -C 2 60 40 kg CO kg 20 0 19 22 29 6 13 20 27 10 17 1 6 11 18 24 31 7 14 21 28 3 10 17 24 2 9 16 -20 APR MAY JUN JUL AUG SEP OCT D CaNPK+M E CaNPK+M E Ca+M

Figure 2. Daily CO2-C soil fluxes on Ca+M and CaNPK+M treatments under rye monoculture Figure(D) 2. and Daily 5-crop CO rotation2-C soil fluxes (E) experiments on Ca+M and over CaNPK+M the measurement treatments period under in 2012rye monoculture and 2013. (D) and 5-crop rotation (E) experiments over the measurement period in 2012 and 2013. 3.6. Distribution of CO2-C Soil Fluxes in 2013 3.6. Distribution of CO2-C Soil Fluxes in 2013 In April of 2013, CO2-C soil fluxes from the CaNPK+M and Ca+M treated soil in ExperimentIn April of E2013, were CO very2-C low soil (Figurefluxes 2from). At the the CaNPK+M end of April, and CO Ca+M2-C fluxes treated from soil soil in Ex- under perimentrye monoculture E were very (Experiment low (Figure D, 2). CaNPK+M) At the end increased of April, and CO remained2-C fluxes relativelyfrom soil highunder until rye themonoculture 29 April. In (Experiment early spring, D, CO CaNPK+M)2-C fluxes fromincreased soil in and Experiment remained D relatively were markedly high until higher the than29th fromof April. the bothIn early examined spring, treatments CO2-C fluxes in Experiment from soil in E. Experiment An increase D in were CO2 markedly-C soil fluxes higherfrom than CaNPK+M from the treated both examined soil in Experiment treatments Ein was Experiment recorded E. only An inincrease mid-May, in CO whereas2-C soilthose fluxes on from Ca+M CaNPK+M treatment treated were soil low. in During Experiment the flooding E was recorded at the beginning only in mid-May, of June 2013, whereasno measurement those on Ca+M was treatment provided. were The low. patterns During of CO the2 -Cflooding soil fluxes at the during beginning the second of June half 2013, no measurement was provided. The patterns of CO2-C soil fluxes during the second half of the growing season were consistent across the examined treatments on Experiment E (CaNPK+M and Ca+M). Over the 1st half of June, high CO2-C soil fluxes (with a maximum in mid-June) were observed on both CaNPK+M and Ca+M treatments of Experiment E. A decrease in CO2-C fluxes from those soils was observed at the beginning of July. At the same time, CO2-C soil fluxes recorded on CaNPK+M treated soil under rye-monoculture were low, and increased notably only on the 6th of July, and at the turn of July and August. After a rapid increase on the 6th of July, CO2-C fluxes recorded on both soils

Agronomy 2021, 11, 21 9 of 16

of the growing season were consistent across the examined treatments on Experiment E (CaNPK+M and Ca+M). Over the 1st half of June, high CO2-C soil fluxes (with a maximum in mid-June) were observed on both CaNPK+M and Ca+M treatments of Experiment E. Agronomy 2021, 11, x FOR PEER REVIEW 9 of 16 A decrease in CO2-C fluxes from those soils was observed at the beginning of July. At the same time, CO2-C soil fluxes recorded on CaNPK+M treated soil under rye-monoculture were low, and increased notably only on the 6th of July, and at the turn of July and August. After(CaNPK+M a rapid and increase Ca+M) on in Experiment the 6 July, CO E decrea2-C fluxessed between recorded 11th on of both July soils and mid-August. (CaNPK+M andSubsequently, Ca+M) in ExperimentCO2-C fluxes E from decreased CaNPK+M between and 11 Ca+M July andtreated mid-August. soils in Experiment Subsequently, E in- COcreased2-C fluxes until from10th CaNPK+Mof September. and A Ca+M substantial treated increase soils in Experimentin CO2-C soil E increasedemission untilfrom 10CaNPK+M September. treated A substantial soil in Experiment increase in D CO was2-C obse soilrved emission only on from the CaNPK+M 24th of September. treated soil Af- inter Experiment the peak of Dfluxes was observed onlyin September, on the 24 September.CO2-C fluxes After from the all peak studied of fluxes soils decreased observed ingradually September, until CO the2-C end fluxes of the from study all studiedperiod in soils October. decreased gradually until the end of the study period in October. 3.7. Cumulative Soil Respiration 3.7. Cumulative Soil Respiration Cumulative respiration of soil treated with CaNPK+M under rye monoculture over the measurementCumulative respiration period of of2012 soil was treated higher with than CaNPK+M in 2013 under(mean rye 4989.5 monoculture ± 229.3 kg over CO the2-C ± −1 measurementha−1 median 5043.1 period and of 2012 3982.7 was ± higher284.2 kg than CO in2-C 2013 ha− (mean1 median 4989.5 4028.0,229.3 respectively) kg CO2-C (Table ha median 5043.1 and 3982.7 ± 284.2 kg CO -C ha−1 median 4028.0, respectively) (Table3). 3). In 2012 and 2013, the highest amount of2 CO2-C was released from soil under rye-mon- Inoculture 2012 and in 2013,May the(25.1–21.8% highest amount of total of soil CO respiration,2-C was released respectively) from soil under(Figure rye-monoculture 3). Cumulative insoil May respiration (25.1–21.8% recorded of total soilunder respiration, rye-monocultur respectively)e in other (Figure months3). Cumulative was lower, soil respirationalthough a recorded under rye-monoculture in other months was lower, although a relatively high amount relatively high amount of CO2-C was released in April 2012 (17.9% of total soil respiration) ofand CO in2-C months was released between in July April and 2012 September (17.9% of 20 total13 (19.6–16.4% soil respiration) of total and soil in months respiration). between July and September 2013 (19.6–16.4% of total soil respiration).

2012 2013 1.6 1.6 1.3 1.6 0.8 100 100 4.4 5.5 5.3 12.1 17.9 18.4 MAR 80 25.6 29 80 25.8 21.8 APR APR 25.1 26 MAY 60 MAY 60 9.3 25.9 20 JUN % JUN % 33.9 13.9 17.7 JUL 25.1 40 JUL 40 11.7 18.5 AUG 21.5 19.6 SEP 10.2 AUG 15.6 20 12.8 15.7 20 OCT SEP 14.6 12 5.5 16.4 13.3 17 4.6 5 5.6 OCT 0 3.5 0 3.1 2.8 1.4 D CaNPK+M E CaNPK+M E Ca+M D CaNPK+M E CaNPK+M E Ca+M

Figure 3. Percent monthly contributions of cumulative CO2-C from soil subjected to Ca+M and CaNPK+M treatments Figure 3. Percent monthly contributions of cumulative CO2-C from soil subjected to Ca+M and CaNPK+M treatments under rye monoculture (D) and 5-crop rotation (E) experiments over the measurement period in 2012 and 2013. under rye monoculture (D) and 5-crop rotation (E) experiments over the measurement period in 2012 and 2013. On CaNPK+M treatment in Experiment E in 2012 (barley) and 2013 (lupine), cumulative On CaNPK+M treatment in Experiment −E1 in 2012 (barley) and 2013 (lupine), cumu-−1 CO2-C soil emissions were 4809.2 kg CO2-C ha , median 4743.3 and 6997.5 kg CO2-C ha , lative CO2-C soil emissions were 4809.2 kg CO2-C ha−1, median 4743.3 and 6997.5 kg CO2- median 7137.9, respectively (Table3). The share of CO 2-C released over May and June from −1 CaNPK+MC ha , median treated 7137.9, soil respectively in Experiment (Table E in 20123). The (barley) share wasof CO similar2-C released (25.6% over and 25.9%May and of totalJune soilfrom respiration CaNPK+M respectively), treated soil althoughin Experiment the rate E in of 2012 soil respiration(barley) was recorded similar in(25.6% July was and also25.9% relatively of total highsoil respiration (21.5% of total respectively), soil respiration) although (Figure the3 rate). It shouldof soil respiration be emphasized recorded that in July was also relatively high (21.5% of total soil respiration) (Figure 3). It should be in April 2012, the share of CO2-C released from soil under rye-monoculture (Experiment D)emphasized in total soil that respiration in April 2012, was muchthe share higher of CO than2-C that released recorded from in soil the under same monthrye-monocul- under barleyture (Experiment cultivation D) (Experiment in total soil E). respiration On the same was treatmentmuch higher (CaNPK+M) than that recorded of Experiment in the same month under barley cultivation (Experiment E). On the same treatment (CaNPK+M) E in 2013 (lupine), the share of CO2-C released from soil in June and July reached 26% of Experiment E in 2013 (lupine), the share of CO2-C released from soil in June and July and 25.1% of total soil respiration, and 18.4% in May. Cumulative CO2-C soil emissions recordedreached 26% on Ca+Mand 25.1% treatment of total of soil Experiment respiration, E inand 2012 18.4% (barley in May. cultivation) Cumulative was CO lower2-C soil by emissions recorded on Ca+M treatment of Experiment E in 2012 (barley cultivation) was lower by approximately 1274 kg CO2-C ha−1 than on CaNPK+M treatment (Table 3). The share of CO2-C released in May, June, and July 2012 (barley) from soil exclusively fertilized with manure (Ca+M) reached 29%, 20%, and 18.5% of total soil respiration, respectively. The highest amount of CO2-C was released from Ca+M treated soil in July 2013 (lupine) (33.9% of total soil respiration), although relatively high soil respiration was also

Agronomy 2021, 11, 21 10 of 16

−1 approximately 1274 kg CO2-C ha than on CaNPK+M treatment (Table3). The share of CO2-C released in May, June, and July 2012 (barley) from soil exclusively fertilized with manure (Ca+M) reached 29%, 20%, and 18.5% of total soil respiration, respectively. The highest amount of CO2-C was released from Ca+M treated soil in July 2013 (lupine) (33.9% of total soil respiration), although relatively high soil respiration was also recorded in June (25.8% of total soil respiration).Irrespective of crop rotations and experimental fertilization, the cumulative soil respiration recorded in March and October (and on Experiment E in September) was negligible (1.3–5.6% of total soil respiration).

3.8. Correlation between Soil Respiration and Environmental Factors

CO2-C fluxes from soil were positively correlated with soil and atmospheric tem- − + peratures, and with soil content of NO3 -N and NH4 -N (Table4). Soil content of both mineral forms of nitrogen and WFPS were presented in our previous works [36,37]. The relationship between CO2-C soil fluxes and soil moisture was described by a negative correlation coefficient.

Table 4. Correlation coefﬁcient between CO2-C ﬂuxes from soil and atmospheric (Ta) and soil (Ts) − + temperature, soil moisture (WFPS), NO3 -N and NH4 -N soil content in Ap (0–25 cm) soil horizon.

− + Soil Fluxes Ta Ts WFPS NO3 NH4

CO2 0.52 * 0.57 * −0.12 * 0.48 * 0.41 * Spearman correlation coefﬁcients, * p < 0.05. Cumulative soil respiration was positively correlated with content of soil organic carbon and total nitrogen in Eet and Bt soil horizons (Table5). The correlation between cumulative soil respiration and content of soil organic carbon and total nitrogen in Ap soil horizon was of statistical signiﬁcance. Cumulative soil respiration was positively correlated with yield of barley grain, straw yields of rye, barley, and lupine, nitrogen content in grain of rye and barley, nitrogen content in straw of barley, and total nitrogen uptake by rye, barley, and lupine (Table6).

Table 5. Correlation coefﬁcient between cumulative soil respiration and content of soil organic carbon (SOC) and total nitrogen (TN) in Ap, Eet, and Bt soil horizons.

Soil Horizons SOC TN Ap (0–25 cm) 0.12 0.14 Eet (26–45 cm) 0.68 * 0.69 * Bt (>45 cm) 0.58 * 0.45 * Spearman correlation coefﬁcients, * p < 0.05. Table 6. Correlation coefﬁcient between cumulative soil respiration and crop yields of grain and straw, content of total nitrogen in grain and straw, nitrogen uptake by crops.

Grain Straw Plant Total N Uptake Yield N Content Yield N Content Rye 0.45 0.88 * 0.83 * −0.31 0.98 * Barley 0.66 * 0.94* 0.96 * 0.93 * 0.92 * Lupine 0.41 −0.07 0.71 * 0.07 0.80 * Spearman correlation coefﬁcients, * p < 0.05. 4. Discussion 4.1. Effect of Temperature and Season

High variability of CO2-C ﬂuxes from the examined soils (Figure2, Table3) suggests that the amount and distribution of CO2-C emissions from soils were dependent on several soil, climate, and agronomic factors. Among the soil/climatic factors considered in our study, CO2-C soil emissions showed the strongest positive correlation with soil temperature and, to a slightly lesser extent, with air temperature (Table4). Ding et al. [ 5] Agronomy 2021, 11, 21 11 of 16

◦ reported that soil CO2-C fluxes are significantly affected by soil temperature below 20 C. Bogužas et al. [15] showed that when temperature increases above 18 ◦C, the intensity of soil CO2-C flux decreases. Irrespective of the experimental fertilization and crop rotation, particularly CO2-C soil fluxes observed over May, June, and July were generally higher than those in periods from March to April and from August to October (Figure3). In both years of the study, however, CO2-C fluxes fluctuated with a very high amplitude (Figure2). Dur- ing both summers, several peaks of gas emissions and extremely low fluxes were recorded. Intensive CO2-C soil fluxes over summer, and much lower in spring/autumn/winter periods have been described by several authors in numerous different soils and cultivation conditions [15,24,38]. An increase in soil and air temperature stimulates both plant growth and microbial activity in soil previously dormant during winter [39]. Lower CO2-C soil fluxes during fall transition than in spring coincide with a decrease in soil temperatures, soil moisture, and lower intensity of microbial and autotrophic processes. In our study, the cumulative soil respiration recorded in March was marginal (Figure3). The share of CO 2-C released from soil in April 2012 was similar to that found in September and October in experiment E (barley), and higher than in rye monoculture (Experiment D). A similar trend was observed over the next year of the study in rye monoculture. In contrast, cumulative respiration of both soils (Ca+M and CaNPK+M) in Experiment E recorded in September and October of 2013 (lupine) exceeded that from April. It means that the share of soil respiration recorded in April for total cumulative emissions depended on crop rotation and type of cultivated crops. In both years of the study, soil respiration recorded in April under rye monoculture (Experiment D) was substantially higher than under spring barley (2012) and lupine (2013) cultivated in Experiment E. This suggests that over early spring and autumn, soil respiration could have been driven by autotrophic respiration (result of root respiration and decomposition of root exudates) associated with winter-cereal growth when spring-crops either enter the dormancy or have been harvested. This hypothesis seems to be confirmed by higher soil respiration observed in March 2012 under rye monoculture than in Experiment E (5-crop rotation). In both years of the study, under rye monoculture, the highest amount of CO2-C was released from soil in May (21.8 and 25.1% in 2013 and 2012, respectively) (Figure3), although soil respiration over the June-August period constituted 35.8 and 46.6% of cumulative soil respiration recorded over the measurement period in 2012 and 2013, respectively. High respiration of both soils (Ca+M and CaNPK+M) under barley cultivation in Experiment E in May was also observed. The contribution of CO2-C released in summer, however, reached 54.2% and 59.4% of cumulative respiration (Figure3). High soil respiration under cereal recorded in both experiments in May was associated with intensive nitrogen uptake by crops, and must have resulted from intensive crop biomass production resulting in an increase in autotrophic respiration. In contrast, soil respiration recorded in May under lupine cultivated in Experiment E in 2013 was not dominant. On both CaNPK+M and Ca+M treatments, soil respiration recorded during summer reached 63.9 and 75.3% of total gas emissions, respectively. Lee at al. [39] reported that the share of CO2-C released from soil in summer reached 47.4%, whereas over the spring-summer period it reached 80.1% of cumulative soil respiration.

4.2. Effect of Soil Moisture The differences between soil respiration under rye monoculture in 2012 and 2013 were probably the result of different climatic conditions. In wet years (2013), soil CO2-C fluxes are usually higher than those in a dry year (2012). Bogužas et al. [15] found a strong and moderately strong correlation between the monthly amount of rainfall and soil CO2-C flux. Irrigation increased CO2-C flux by 13% compared with non-irrigation by increasing soil water content in North Dakota [10]. Song and Zhang [13] reported that the relationship between the CO2-C flux, soil moisture and soil temperature was linear. Soil temperature, however, played a more important role in regulating soil respiration than soil moisture [40]. On the other hand, Alluwione et al. [16] and Feiziene et al. [17] reported a decrease in soil respiration with an increase in soil moisture. In our study, the relationship between soil Agronomy 2021, 11, 21 12 of 16

respiration and soil moisture was described by a negative correlation coefﬁcient, low in terms of the absolute value (Table4). The negative correlation between soil respiration and soil moisture could have resulted from distribution of soil moisture over the growing season—higher in colder months of spring and autumn and lower in summer.

4.3. Effect of Cropping System According to Adviento-Borbe et al. [41] and Rochette et al. [42], the share of autotrophic respiration reached 24–50% of total CO2-C soil emissions. In our study, soil respiration was strongly positively correlated with the straw and occasionally grain (barley) yield, nitrogen content in grain of the cultivated cereals, and occasionally with nitrogen content in barley straw and nitrogen total uptake by crops (Table6). Ding et al. [ 5] reported that cumulative CO2-C emission was strongly correlated with harvested maize biomass than with wheat biomass. Our results show the importance of autotrophic respiration in the cumulative soil respiration. −1 Cumulative soil respiration reached 4989.5 and 3982.7 kg CO2-C ha in 2012 and 2013, −1 respectively under rye monoculture, and 4809.2 and 3535.1 kg CO2-C ha , respectively on CaNPK+M and Ca+M treatments under barley (2012) cultivated in Experiment E (Table3 ). The recorded amount of CO2-C released from soil corresponded with data in the literature for different cultivated crops (wheat, barley, oat, corn, and soybean cultivation and grassland) [28,41,43,44]. Abdalla et al. [7], investigating the influence of cultivation of different type of crops on soil respiration, pointed out that the key factors affecting its rate include the amount of crop residues remaining in the soil and method of soil tillage. Drury et al. [43] recorded approximately 45% greater CO2-C emissions under monoculture of winter wheat than under corn monoculture, or 51% greater emissions than those from soybean monoculture. In the corn phase of crop rotation, soil respiration was greater if the previous crop was winter wheat than if it was soybean. On the other hand, Norberg et al. [32] found insignificant differences between soil respiration under different crops in similar environmental conditions at 11 field sites in southern Sweden. Sainju et al. [10] also suggested that the cropping system had no effect on soil respiration. Rajaniemi et al. [45] found higher GHG emissions form soil under wheat than under oats and barley. Omonode et al. [29] reported that cumulative soil respiration recorded during the growing season was significantly affected by rotation. Their results show that soil respiration was significantly greater under continuous corn than under maize-soya crop rotation. Shifting from continuous corn rotation to soybean-corn or wheat-soybean-corn rotation decreased soil respiration. On the other hand, Abagandura et al. [46] reported that crop rotation diversity did not affect cumulative CO2-C soil emissions. In our study, soil respiration recorded in 2012 under rye-monoculture and barley cultivated in 5-crop rotation was similar.

4.4. Effect of Legumes Cultivation Several studies showed that soil respiration under legumes was lower than under non- legumes crops [16,43]. Kalkhoran et al. [47] suggested that lupine can reduce emissions by 50% in comparison to a non-legume crops. In our study, soil respiration recorded on both treatments (CaNPK+M and Ca+M) under lupine cultivation (2013) in Experiment E (mean −1 −1 6997.5 kg CO2-C ha , median 7137.9 and mean 4552.7 kg CO2-C ha median 4617.7, respectively) was much higher than from soils under cereals. The obtained data confirmed the finding recently discussed in literature that legumes do not mitigate greenhouse gas soil emissions [33]. Jansen et al. [48] observed that the amount of CO2 respired from the root of N2-fixing legumes (e.g., 10–23 g CO2 per gram of N assimilated) could be higher than CO2 generated during N-fertilizer production (e.g., 2.6–3.7 g CO2 per gram of NH3–N produced). However, in contrast to CO2 derived from fossil fuels emitted during N fertilizers synthesis, CO2 respired during N2 fixation originates from photosynthesis, and will not represent a net contribution to atmospheric concentrations [48]. In our study, Agronomy 2021, 11, 21 13 of 16

we found 192.3 and 131.2 kg N in grain and straw of lupine cultivated in experiment E in −1 2013 (Table2). This means that 1 g N ﬁxation cost was 34.7–53.3 g CO 2-C ha .

4.5. Effect of Fertilization Compared to CaNPK+M fertilization, omission of mineral fertilization in barley cultivation (Ca+M) decreased soil respiration by 36% (Table3). In the 40-year long term experiment in Lyczyn (Central Poland), only nitrogen increased the content of organic carbon and total nitrogen in soil [19]. Therefore, it can be assumed that the increase in CO2-C emissions from soil was mainly due to the application of ammonium nitrate on CaNPK+M treatment of Experiment E. Nitrogen fertilization led to an increase in CO2-C soil respiration [17]. Alluvione at al. [16] reported that nitrogen fertilization had no effect on soil respiration, although the high nitrogen rates decrease CO2-C soil ﬂuxes [13,23]. Adviento-Borbe et al. [41] reported that seasonal soil CO2-C fluxes depended less on − soil NO3 -N content than on temperature, soil moisture, and crop residue. In our study, − + CO2-C soil fluxes were positively correlated with NO3 -N and NH4 -N soil content (r = 0.48 and r = 41, p < 0.05, respectively), although to a lesser extent than with air and soil temperature (Table4). Nitrogen fertilization intensifies various processes of biotic N transformation in the soil [49]. Microbial N-cycling drives microbial carbon soil metabolism [50]; therefore, elevated availability of nitrogen for decomposers results in intensive heterotrophic respiration [24]. In our previous study the highest soil CO2-C fluxes were recorded during − the fast plant development stage, concurrent with high NO3 -N content in the soil [51]. Consequently, we concluded that increase soil N availability also promotes autotrophic soil respiration. After 90 years of experiments, varied fertilization and cropping system significantly influenced the soil organic carbon (SOC) and total nitrogen (TN) content in the studied soils (Table1). SOC and TN content in the topsoil on CaNPK+M treatment of Experiment D (rye monoculture) was higher by 19.8% and 24.2%, respectively than on the analogous treatment (CaNPK+M) under 5-crop rotation (Experiment E). Higher accumulation of organic carbon in soil under rye monoculture suggests that soil respiration could have been lower in rye monoculture than in the 5-crop rotation. However, no significant difference in the cumulative soil respiration of both soils was proven. Lower than expected differences in soil CO2 emissions in both of the cropping systems evaluated probably resulted from lower input of manure in both experiments. Manure was applied once every four years in Experiment D, and every five years in Experiment E at the same rates (30 t ha−1). Among the analyzed factors, manure fertilization proved to have the greatest influence on content of organic carbon and content of total nitrogen in soil [19,52]. Content of organic carbon and total nitrogen in the Ap soil horizon of CaNPK+M treatment in Experiment E was higher by 19.7% and 21.7%, respectively than on Ca+M treatment. Lower content of SOC in the Ca+M treated soil could have shaped lower soil respiration than on CaNPK+M treated soil. Omission of nitrogen fertilization could have resulted in lower crop residues input into non-fertilized soil, and mitigated soil respiration. The relationship between cumulative soil respiration and content of SOC and TN in Eet (26–45 cm) and Bt (>45 cm) was statistically significant (Table5). The relationships between soil respiration and content of both soil organic carbon and total nitrogen in the Ap soil horizon (0–25 cm) were of statistical significance. This finding suggests that CO2-C is also produced in deeper soil layers. According to Leitner et al. [53], decomposition of organic compounds in upper soil layers contributes approximately a 30% to CO2-C emissions in soil. The authors also state that the soil profile CO2-C concentration is higher in the deeper soil layers than in topsoil. Luo et al. [54] reported that the main source of CO2-C production is topsoil layer, although it is produced in deeper soil layers.

5. Conclusions Our results indicate that omission of mineral fertilization signiﬁcantly decreases soil respiration. Under similar fertilization conditions, the distribution and amount of CO2 released from soil under cereal cultivation in monoculture and crop rotation are similar. Agronomy 2021, 11, 21 14 of 16

Soil respiration under lupine cultivation is much higher than under cereals. This means that in the climatic conditions of Central and Eastern Europe, the soil respiration is more dependents on the crop species and fertilization than on the crop rotation system. Intensive soil respiration is related to yields and nitrogen uptake by plants, allowing plants to increase autotrophic respiration. However, CO2 is released as a result of autotrophic respiration derived from photosynthesis, but not from decomposition of soil organic matter. In the climate conditions of Central Europe, the negative correlation between soil respiration and soil moisture resulted from typical distribution of soil moisture—higher in the cooler part of the growing season and lower in summer, and may additionally be an effect of temporal water excess in the soil (after abnormally heavy rain) decreasing microbial and root respiration. In the climatic and soil conditions of Central Poland, the soil respiration - dependents more on the temperature of the air and soil than on the soil content of NO3 -N + and NH4 -N.

Author Contributions: Conceptualisation. T.S.; Methodology. T.S.; Investigation. T.S. and E.S.; Formal Analysis. T.S. and M.S.; Writing—Original Draft Preparation. T.S.; Writing—Review & Editing. M.S.; Visualization. M.S. and P.S. Supervision. T.S. All authors have read and agreed to the published version of the manuscript. Funding: This work was supported by the financial resources for maintaining research equipment or research stand (SPUB) of the Ministry of Science and Higher Education (Decision: No. 89/E- 385/SPUB/SP/2019). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding author. Acknowledgments: Special thanks for staff of the Experimental Station in Skierniewice belonging to the Warsaw University of Life Sciences in which since 1923 the long-term experiments have been carried out as the basis for the conducted research. Conflicts of Interest: The authors declare no conflict of interest.

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