Monitoring System in Field Plots

Within the MESCOSAGR project, soil CO2 and N2O fluxes were measured for each soil treatment in both the experimental sites of Torino (Tetto Frati) and Napoli (Torre Lama). Detailed information of study sites and experimental design are described elsewhere (Chaps. 3 and 4).

Two periods of gas-fluxes measurements (May 21-28 and July 16-24) were carried out in Torino (Tetto Frati) during the maize crop in 2008. The first period in May began immediately after nitrogen fertilization (where scheduled) and sowing; the second period was near the completion of maturity of maize plants. Gas emissions from the Napoli site were measured for all soil treatments during the autumn-winter period after the 2007 maize crop (October 2007-March 2008) and for the 2008 maize cropping season (May-August 2008). Conversely, the gas fluxes from soil plots treated with the water-soluble biomimetic catalyst (see Chaps. 3 and 4) and under wheat cropping were monitored in the period December 2007-August 2008.

Soil CO2 and N2O emissions were measured by means of an automated closed-chamber system coupled to a 1412-Photoacustic Field Gas Monitor. The analytical system provided high-time resolution of gas fluxes data, being able to perform daylong analytical cycle of 10 min for each chamber. Before the measurements cycle in the Torino site and frequently (each month) in the Napoli site, tests to evaluate fluxes variability in space were performed. Since it was always low (coefficient of variation less than 100%), one or two chambers were placed in soil for each treatment. Each chamber provided daily, on average, 10-12 measurements.

Photoacustic Field Gas Monitor operates collecting gas samples by means of pump from closed chamber; the gas sample is allocated in a small chamber (3 ml). Chamber is irradiated with pulsed, modulated by a chopper, narrow-band light. Gas absorbs light proportional to its concentration and converts it to heat. Temperature fluctuations determined by modulation generate pressure waves detected by sensitive microphones. Gas-specific carousel is available to select the appropriate light wavelength. The instrument is capable to measure gas concentration in few seconds.

However, the automated corrections for water interference and cross interference performed by photoacoustic system are unsatisfactory (Flechard et al. 2005). To counteract this limitation, the system was calibrated at different CO2 concentrations and varying dew point temperatures. The data obtained by the photoacoustic system were compared with those produced by GC analyses. The experimental calibration calculated a correction factor for N2O of +0.05 ppb for each ppm of CO2.

Each chamber (0 = 30 cm, h = 10 cm) is automated by means of electronic engine in order to modulate opening/closing cycle for the accumulation of soil air fluxes. Each cycle was run by a multiple channel sampler provided of ten channels. Each chamber was equipped with a vent valve to avoid pressure variations inside the chamber (Denmead 1979; Davidson et al. 2002; Bain et al. 2006). Inlet and outlet tubes allow air circulation from chamber to detection instrument.

Soil gases fluxes have been calculated for each chamber, considering a cycle of 3-5 measurements with open chamber and 10-12 measurements with closed chamber, covering a total time of about 10 min. The gas flux has been expressed as:

where Fx was the soil flux of a specific gas x, A[x] was its variation of concentration expressed as mg/m3, in the time interval At, V was the chamber's volume and S the soil surface covered by it.

Linear regression was calculated for each measurement cycle, R2 less than 0.8 has been rejected. The soil gases fluxes were calculated on time scale of 1 h after the following equation:

[x]t = a(t - i0), where [x]t was gas concentration at time t while t0 was the concentration measured for the first measurement performed with closed chamber. Multiplication of the angular coefficient a with S/V gave hourly fluxes.

Cumulative C and N fluxes from soils have been calculated. Gap filling has been obtained by the calculation of the mean fluxes of 3 days before the measurements interruption and the mean fluxes of 3 days of measurements resumption. The percent of emission has been also calculated as EF, that is the ratio of soil cumulative N2O fluxes over the amount of N applied to crop plots in either organic or mineral form.

The Napoli site has been also provided by a data-logger CR1000 (Campbell Scientific Ltd., Shepshed, UK) for continuous detection of soil temperature and moisture. The system was equipped of six probes for temperature detection (107 Temperature Probe Campbell Scientific) and three reflectometers for the detection of soil moisture (CS616 Water Content reflectometers - TDR, Campbell Scientific).

9.3 Summary Overview on CO2 and N2O Emissions from Field Plots

9.3.1 Measuring Campaign of Maize Cropping in 2008 (Torino, Tetto Frati and Napoli, Torre Lama)

Mean and cumulative values of soil CO2 and N2O fluxes, during maize crop in 2008, from different treatments of Torino site are shown in Figs. 9.1. Figure 9.2 describes the cumulative dynamics of CO2 and N2O soil fluxes from several treatments in the Napoli site for maize crop in 2008. Although the two sites were characterized by different soil characteristics and climatic conditions, duly recorded during monitoring campaigns, a common pattern for both gases has

Fig. 9.1 Mean values (a) and cumulative dynamics (b) of CO2 and N2O fluxes from Torino (Tetto Frati) soil under maize crop in 2008. Different apical letters indicate significant differences among treatments (One-way analysis of variance + all pairwise multiple comparison procedures — Holm-Sidak method)

Fig. 9.1 Mean values (a) and cumulative dynamics (b) of CO2 and N2O fluxes from Torino (Tetto Frati) soil under maize crop in 2008. Different apical letters indicate significant differences among treatments (One-way analysis of variance + all pairwise multiple comparison procedures — Holm-Sidak method)

a 350

8 150

100 5o 0

b 60 50

E 20 10

May-22-08 June-11-08 July-01-oe July-21-08

Fig. 9.2 Cumulative dynamics of CO2 (a) and N2O (b) fluxes from Napoli (Torre Lama) soil under maize crop in 2008. Different apical letters indicate significant differences among treatments (One-way analysis of variance + all pairwise multiple comparison procedures — Holm-Sidak method)

May-02-08

May-22-08 June-11-08 July-01-oe July-21-08

Fig. 9.2 Cumulative dynamics of CO2 (a) and N2O (b) fluxes from Napoli (Torre Lama) soil under maize crop in 2008. Different apical letters indicate significant differences among treatments (One-way analysis of variance + all pairwise multiple comparison procedures — Holm-Sidak method)

been observed. This suggests that, at least for a short time, soil management superimposes pedo-climatic factors.

The deep-plow traditional (TRA) treatment emitted more CO2 from soil, as compared with other treatments in both sites, though statistically more significant against control (CONT) and compost (COM-1, COM-2) treatments. The reduced effect of the larger rate of compost (COM-2) on CO2 emission was more evident in the loam soil of Torino, while the lower compost rate (COM-1) emitted less CO2 in the clay soil of Napoli. As shown in Table 9.1, percent contributions on CO2 emissions for each treatment, as compared to TRA and CONT, were similar in the two sites, with the exception of COM-2 in relation to CONT in the Napoli site. Soil C lost as CO2 during maize cropping in TRA was 150 and 200% larger than for soil control treatment (CONT) in Torino and Napoli, respectively.

Table 9.1 Contribution of soil treatments on CO2 and N2O fluxes, as flux ratios of different treatments over either TRAditional or CONTrol treatment

Torino maize

Napoli maize

Napoli maize in autumn-winter

in 2008

in 2008

2007-2008

CO2 (g C m-2)

COM-1/TRA

0.73

0.65

1.13

COM-1/CONT

1.1

1.31

3.94

COM-2/TRA

0.57

0.87

1.3

COM-2/CONT

0.85

1.75

4.55

MIN/TRA

0.87

0.86

0.7

MIN/CONT

1.3

1.72

2.44

GMAN/TRA

0.9

0.86

0.65

GMAN/CONT

1.35

1.72

2.28

TRA/CONT

1.5

2

3.5

N2O (mg N m-2)

COM-1/TRA

0.18

0.63

1.36

COM-1/CONT

1.5

1.32

4.07

COM-2/TRA

0.18

0.63

1.21

COM-2/CONT

1.5

1.32

3.62

MIN/TRA

1.16

0.58

0.97

MIN/CONT

9.7

1.2

2.91

GMAN/TRA

0.56

0.5

0.67

GMAN/CONT

4.7

1.04

2

TRA/CONT

8.3

2.08

3

The amount of CO2 emitted by the two sites during maize crop in 2008 appeared essentially equivalent, ranging between 150 and 350 g C m-2.

Soil N2O emissions, monitored during maize crop in 2008, were greater of one order of magnitude in the loam soil of Torino than in the clay soil of Napoli (Figs. 9.1b and 9.2b). In both sites, CONT soils emitted significantly less N2O than other treatments. Significantly larger emissions were observed in TRA and MIN treatments of Torino and in TRA of Napoli (Figs. 9.1b and 9.2b). In both sites, soil N2O fluxes for the MIN, TRA and GMAN treatments appeared noticeable, particularly for the Torino site, corresponding to 970, 830 and 470% (Table 9.1), more than CONT, respectively.

Soil N2O dynamics during maize crop in 2008 for all treatments and in both sites, showed large rates of emission in the first crop phase and typical end-point shapes (Figs. 9.1a and 9.2b), due to substrate (nitrogen) dependent process (see Sect. 9.1.2). N dependence of N2O fluxes may be hypothesized to be strictly linked with crop phase and soil water content. However, no functional relationship was observed in both sites between N2O fluxes and soil mineral N content, probably due to the interference by roots uptake. In fact, in the Napoli site, where a broad data set of N2O fluxes and soil water content were produced during the 2008 maize cropping, a functional relationship was observed between fluxes and water-filled pore spaces (WFPS) only during the first stage of crop growth. At this stage, the poorly developed root system of maize plants did not yet compete with nitrifiers and denitrifiers for mineral nitrogen (see Sect. 9.1.2). The soil water content monitored in the Napoli site and expressed as WFPS, ranged during the crop cycle between 60 and 90%, being this range widely described in literature as favourable for N2O production (see Sect. 9.1.2). However, low N2O emissions monitored in both sites during maize cropping may be also due to the N immobilization in the organic form, as proposed in Chap. 3.

9.3.2 Measuring Campaign in the Napoli Site for the Autumn-Winter 2007-2008. Effect of Residues After the 2007 Maize Cropping

Figure 9.3 shows the cumulative dynamics of soil CO2 and N2O emissions for all field treatments in the Napoli site after the 2007 maize cropping (October 2007-March 2008). Soil without management (CONT) constantly showed the lowest values of CO2 and N2O fluxes, as compared with other treatments. Soil CO2 emitted from COM-2 was significantly larger than other treatments, including TRA. Both compost rates showed significantly greater N2O fluxes than all treatments, probably due to slow mineralization of organic N from humified molecular associations, while organic N from GMAN was probably the fastest to be released. Minor contribution on soil N2O fluxes of TRA and MIN during the autumn-winter period, and contrary to what observed during maize cropping, may depend on the fast depletion of mineral N added during the previous maize cropping season (see Sect. 9.1.3).

Moreover, ratio of fluxes from different treatments over those from TRA and CONT (Table 9.1) underlines the significantly lower CO2 and N2O emissions from the control soil. In particular, the CO2 emitted from both compost rates, TRA and both GMAN and MIN was, respectively, about 400, 350 and 200% more than that released from CONT. A very similar trend was that observed for N2O fluxes (Table 9.1).

9.3.3 CO2 and N2O Emissions from Napoli Field Plots Treated with the Biomimetic Catalyst

The cumulative dynamics of CO2 and N2O emissions from soils under wheat cropping of the Napoli site treated with (CAT) and without (NO-CAT) addition of the water-soluble biomimetic catalyst (see Chaps. 3 and 4for additional details) are shown in Fig. 9.4. During the whole monitoring period (December 2007-August 2008), the emissions of both CO2 and N2O from the catalyst-treated

COM1

COM2

GMAN

CONT

8 40 30

O 25

0ct-07-07 0ct-27-07 Nov-16-07 Dic-06-07 Dic-26-07 Jan-15-08 Feb-04-08

Fig. 9.3 Cumulative dynamics of CO2 (a) and N2O (b) fluxes from Napoli (Torre Lama) soil under maize crop during autumn-winter 2007. Different apical letters indicate significant differences among treatments (One-way analysis of variance + all pairwise multiple comparison procedures — Holm-Sidak method)

COM1

COM2

GMAN

CONT

Fig. 9.3 Cumulative dynamics of CO2 (a) and N2O (b) fluxes from Napoli (Torre Lama) soil under maize crop during autumn-winter 2007. Different apical letters indicate significant differences among treatments (One-way analysis of variance + all pairwise multiple comparison procedures — Holm-Sidak method)

CAT soil resulted significantly larger than control (NO-CAT). Similar results were found for the CAT soil in the Torino site.

These results were unexpected, based on the assumption that the in situ photo-polymerization of SOM would have stabilized the OC and inhibited soil respiration from CAT soils (see Chaps. 1 and 4). However, the actual experimental data, which were derived from fluxes directly measured in field plots, are in line with previous data and suggest a more complex effect of the catalyst-assisted in situ photo-oxidative reaction when in the presence of crop plants.

Piccolo et al. (2011) have found that different soils treated with the water-soluble iron-porphyrin did show both an improvement of soil structural stability and a significant decrease of soil respiration. They also showed that the effects of the

Fig. 9.4 Cumulative dynamics of CO2 (a) and N2O (b) fluxes from Napoli (Torre Lama) soil treated with (CAT) and without (No-CAT) catalyst under wheat crop. Different apical letters indicate significant differences among treatments (One-way analysis of variance + all pairwise multiple comparison procedures — Holm-Sidak method)

Fig. 9.4 Cumulative dynamics of CO2 (a) and N2O (b) fluxes from Napoli (Torre Lama) soil treated with (CAT) and without (No-CAT) catalyst under wheat crop. Different apical letters indicate significant differences among treatments (One-way analysis of variance + all pairwise multiple comparison procedures — Holm-Sidak method)

catalyst in the photo-oxidation of SOM were kept even after prolonged wetting and drying cycles. These results were confirmed by Gelsomino et al. (2010) by a microcosm experiment where they compared the effect of iron-porphyrin addition on either an unplanted soil or maize-planted soil. They found that soil CO2 emission from the bare soil treated with catalyst was significantly reduced in comparison to control microcosm. Conversely, when the microcosm soil added with catalyst was cropped with maize, CO2 emission was larger than control, and so was the maize root biomass.

Within the MESCOSAGR project, concomitant to such results of partial flux measurements from catalyst-treated field plots, a significant increase in carbon sequestration was found for the same soils after the three experimentation years in both Torino and Napoli sites (see Chap. 4). An explanation for these contrasting findings in two different measurements for the same soils (fixed carbon and respired carbon) may reside in the fact that the photo-polymerization of SOM under the iron-porphyrin catalysis is effective only on phenolic humic molecules (Piccolo et al. 2011, Chap. 1). This signifies that these humic molecules are photo-oxidatively coupled into larger molecular-weight molecules and become less bio-available and, thus, persistent in soil, whereas all other aliphatic/alkyl molecules present in SOM (Nebbioso and Piccolo 2011) are still accessible to microbial mineralization. The implication is that such biolabile fraction of SOM, together with other labile molecules (proteins, saccharides, organic acids) rhizo-deposited by the crop root system, provide an organic C substrate for microbial degradation and ensure GHG fluxes that are not significantly different from the cropped control soil.

9.3.4 Soil N2O Emission Factors (% EF)

The percentage of EF is an indication of the total amount of N lost as N2O fluxes to the atmosphere. The EF calculated for each soil treatment in the Torino site during the 2008 maize cropping is shown in Fig. 9.5a, while the EF for soil treatments of the Napoli site is reported in Fig. 9.5b for the monitoring periods of autumn-winter 2007 and the 2008 maize cropping.

Very impressive is the amount of nitrogen lost to atmosphere during maize cropping in 2008 in the Torino site, particularly for the MIN, TRA and GMAN treatments (Fig. 9.5a). In the short period of 1 month, MIN and TRA lost about 6 and 5 kg of N ha-1 year-1, respectively, while GMAN lost more than 3 kg of N ha-1 year-1. For these three treatments the EF appeared significantly larger (MIN = 4.48%; TRA = 3.87%; GMAN = 2.2%) than the base value of 1.25% proposed by Bouwmann (1994) for added nitrogen. On the other hand, COM-1 and COM-2 emitted much less N during maize cropping in 2008, without significant difference between the two compost rates (Fig. 9.5a). However, EF of COM-2 was really one-half lower than COM-1, since it implied twice as much N as in COM-1 (Fig. 9.5a). All soil treatments in the Napoli site showed lower EF values than either the Torino site or the Bouwmann value, throughout maize cropping in 2008 and the overall period of monitoring (Fig. 9.5b). Also in the case of the Napoli site, the EF for the COM-2 treatment was the lowest of all treatments.

These values of nitrogen losses from field plots suggest that the large rate of compost addition was the most effective in sequestering N in soil, thereby confirming the mechanism of hydrophobic protection set up as one of the hypotheses of the MESCOSAGR project (see Chaps. 1 and 4).

TRA COM1 COM2 MIN GMAN CONT

Fig. 9.5 Total N lost as N2O from Torino (Tetto Frati) soil (a) during maize crop in 2008, and related Emission Factors for each soil treatments; total N lost as N2O from Napoli (Torre Lama) soil (b) related to overall period of monitoring, Emission Factors for each treatment are reported for maize crop in 2008 and for autumn-winter 2007

TRA COM1 COM2 MIN GMAN CONT

Fig. 9.5 Total N lost as N2O from Torino (Tetto Frati) soil (a) during maize crop in 2008, and related Emission Factors for each soil treatments; total N lost as N2O from Napoli (Torre Lama) soil (b) related to overall period of monitoring, Emission Factors for each treatment are reported for maize crop in 2008 and for autumn-winter 2007

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