Carbon and nitrogen balances and CO₂ emission after exogenous organic matter application in arid soil

Figures & data

Table 1. Physical and chemical characteristics of the five organic amendments.

	Olive husk compost (CM)	Palm leaf-based compost (CP)	Olive pruning waste (GW)	Ovine manure (OM)	Olive mill wastewater (OMW)
CO (%)	24 .96 ± 0.88	29.18 ± 0.62	43.98 ± 0.02	34.83 ± 0.13	42.71 ± 0.34
OM (%)	40.93 ± 2.14	51.85 ± 1.11	90.08 ± 0.26	66.45 ± 0.55	86.8 ± 0.28
N (%)	1.04 ± 0.03	1.47 ± 0.03	1.54 ± 0.03	1.77 ± 0.01	1.57 ± 0.01
C/N	24.00	19.85	28.55	19.76	27.20
pH	8 .89 ± 0.19	8.85 ± 0.55	7.89 ± 0.31	8.69 ± 0.22	4.56 ± 0.19
Ash (%)	50.06 ± 2.28	48.15 ± 1.6	9.91 ± 0.07	33.55 ± 0.35	13.20 ± 0.89
Na (%)	0.043 ± 0.0042	0.049 ± 0.0042	0.0119 ± 0.0004	0.036 ± 0.0056	0.0575 ± 0.0035
Ca (%)	0.175 ± 0.0212	0.41 ± 0.0989	0.17 ± 0.00	0.175 ± 0.0070	0.12 ± 0.0141
K2O (%)	0.17 ± 0.008	0.22 ± 0.0085	0.34 ± 0.0085	0.28 ± 0.0170	0.90 ± 0.2556

Figure 1 Evolution of soil pH on day 0 and on day 112 for the control (S) and amended soils: green waste (GW), ovine manure (OM), compost of olive husk (CM), palm compost (CP) and olive mill wastewater (OWM); lower-case letters indicate significant differences between treatments on day 0 and upper-case letters indicate significant differences between treatments on day 112.

Figure 2 Evolution of electrical conductivity on day 0 and on day 112 for the control (S) and amended soils: green waste (GW), ovine manure (OM), compost of olive husk (CM), palm compost (CP) and olive mill wastewater (OWM).

Figure 3 Ammonium and nitrate content for the control (S) and amended soils: green waste (GW), ovine manure (OM), compost of olive husk (CM), palm compost (CP) and olive mill wastewater (OWM): (a) ammonium content during the experiment; (b) ammonium content during the first week; (c) nitrate content during the experiment; (d) nitrate during the first week.

Figure 4 Total nitrogen content on day 0 and on day 112 for the control (S) and the amended soils: green waste (GW), ovine manure (OM), compost of olive husk (CM), palm compost (CP) and olive mill wastewater (OWM). Upper-case letters indicate significant differences between treatments on day 0 and lower-case letters indicate significant differences between treatments on day 112.

Figure 5 Organic matter content on day 0 and on day 112 for the control (S) and the amended soils: green waste (GW), ovine manure (OM), compost of olive husk (CM), palm compost (CP) and olive mill wastewater (OWM); lower-case letters indicate significant differences between treatments on day 0 and upper-case letters indicate significant differences between treatments on day 112.

Figure 6 Net C mineralization for each treatment: green waste (GW), ovine manure (OM), compost of olive husk (CM), palm compost (CP) and olive mill waste water (OWM) during the experiment. (a) daily respiration during the first week; (b) daily respiration during the experimentation; (c) cumulative respiration.

Table 2. Evolution of SOC for all the treatments, and evaluation of SOC gain and SOC balance.

	SOC 0	SOC 112	SOCbalance	SOCgain
S	0.61^a	0.58^a	− 0.03^bc	–
CP	1.09^b	1.09^cd	− 0.04^c	0.50^bc
GW	1.19^b	0.89^bc	− 0.30^a	0.31a^b
OM	1.17^b	0.82^b	− 0.35^a	0.24^a
CM	1.19^b	1.11^d	− 0.07^bc	0.54^c
OMW	1.06^b	0.84^b	− 0.22^ab	0.27^a

SOC_balance: The difference between the final and the initial SOC levels.

SOC_gain: The difference between the SOC of the amended soil and the control at the end of the experiment.

Letters indicate significant differences for columns (between treatments).

S: soil without amendement, CP: soil with palm leaves based compost, GW: soil with crushed olive pruning, OM: soil with fermented ovine manure, CM: soil with olive husk based compost, OMW: soil with olive mill wastewater, SOC0: initial soil oarganic C content, Soc112: final soil organic C content.

Figure 7 Projection of the different studied variables on the factorial plan. Factors 1 and 2 explained 76.42% of total observed variability.