The carbon dynamics in the experimental plots. Use of 13C- and 15N-labelled compounds for the soil-plant balance in carbon sequestration

This chapter reviews some of the methodologies and applications of N and C stable isotopes most useful to trace the fate of added organic or mineral material to the soil in natural and agricultural systems. Main results from two field experiments, one with N and the other with C stable isotopes, carried within the frame of MESCOSAGR project are presented. Three years research experiments aimed at evaluating the fate and flow rate of added N as 15N-compost in a maize-soil system and sorghum roots contribution to soil organic carbon evaluated by Natural Abundance Method, are carried out. The first year contribution of compost to plant nutrition was quantified to be about 20% of applied N, with decreasing values in the second and third subsequent years. A great variability of first year mineralization rates was found depending on the compost maturity and composition. Majority of changes in aggregate-associated SOM-15N consequently to compost amendment were observed in the soil macroaggregates. Estimation of the cumulative N-compost sequestrated in soil due to progressive amendments resulted in 34.2, 38.2 and 42.5 percent of total N -compost distributed the first (148 kg ha-1), the first and the second year (314 kg N ha-1), the three years of the research (442 kg ha-1), respectively. Research found that one year after sorghum cultivation the soil carbon plant-derived was between 8.24% to 21.29%, and values of 27.95% were reached after two and three years. The percentage of sorghum-derived carbon over the total surface of the soil organic carbon decreased with depth, and more markedly below 30 cm

Maize Response to Repeated Compost Additions in Two Contrasting Environments in Italy.

The increase in the soil organic carbon (SOC) content has well-acknowledged positive effects on the soil chemical, biological and physical fertility. Recent global warming concerns have recommended maintaining and restoring soil carbon as a measure to mitigate rising atmospheric carbon dioxide (CO2) concentration (Follett, 2001; Lal, 2008). Organic fertilization is one of the most diffused practices that increase the SOC content (Smith, 2004), and composting park or municipal solid wastes has become an important way to recover organic matter from wastes (Gigliotti et al., 1996; Centemero, 2007). The objective of this paper was to assess the potential of compost fertilizer addition to influence the maize crop yield and the soil carbon sequestration, compared to green manuring and minimum tillage. Preliminary results are here discussed. Preliminary results suggest that compost supplied at low-medium rates may exert a negative effect on maize growth, especially in poorly-aerated soils, probably owing to the immobilization of N. An increase in the SOM content could not be detected after the first applications to the soil

Pig slurry treatment modifies slurry composition, N2O, and CO2 emissions after soil incorporation

The treatment of manures may improve their agricultural value and environmental quality, for instance with regards to greenhouse gases mitigation and enhancement of carbon (C) sequestration. The present study verified whether different pig slurry treatments (i.e. solid/liquid separation and anaerobic digestion) changed slurry composition. The effect of the slurry composition on N2O and CO2 emissions, denitrification and soil mineral nitrogen (N), after soil incorporation, was also examined during a 58-day mesocosm study. The treatments included a non-treated pig slurry (NT), the solid fraction (SF), and the liquid fraction (LF) of a pig slurry and the anaerobically digested liquid fraction (DG). Finally, a non-fertilized (N0) and a treatment with urea (UR) were also present. The N2O emissions measured represented 4.8%, 2.6%, 1.8%, 1.0% and 0.9% of N supplied with slurry/fertilizer for NT, LF, DG, SF and UR, respectively. Cumulative CO2 emissions ranged from 0.40 g CO2-C kg¿1 soil (0.38 Mg CO2-C ha¿1) to 0.80 g CO2-C kg¿1 soil (0.75 Mg CO2-C ha¿1). They were highest for SF (56% of C applied), followed by NT (189% of C applied), LF (337% of C applied) and DG (321% of C applied). Ammonium was detected in the soil for all treatments only at day one, while nitrate concentration increased linearly from day 15 to day 58, at a rate independent of the type of slurry/fertilizer applied. The nitrate recovery at day 58 was 39% of the N applied for NT, 19% for SF, 52% for LF, 67% for DG, and 41% for UR. The solid fraction generally produced higher potential denitrification fluxes (75.3 for SF, 56.7 for NT, 53.6 for LF, 47.7 for DG and 39.7 mg N2O + N2-N kg¿1 soil for UR). The high variability of actual denitrification results obfuscated any treatment effect. We conclude that treatment strongly affects slurry composition (mainly its C, fibre and NH4+ content), and hence N2O and CO2 emission patterns as well as denitrification processes and nitrate availability. In particular, the solid fraction obtained after mechanical separation produced the most pronounced difference, while the liquid fraction and the anaerobically digested liquid fraction did not show significant difference with respect to the original slurry for any of the measured parameters. Combining data from the different fractions we showed that separation of slurry leads to reduced N2O emissions, irrespective of whether the liquid fraction is digested or not. Furthermore, our results suggested that the default emission factor for N2O emissions inventory is too low for both the non-treated pig slurry and its liquid fraction (digested or not), and too high for the separated solid fraction and ure

Short-term crop and soil response to C-friendly strategies in two contrasting environments

In southern Europe (Italy), a two-site field experiment with contrasting soil conditions (high clay???SOC-protecting soil near Napoli versus low clay???non-SOC-protecting soil) near Torino was conducted to evaluate the short-term potential of a carbon (C) friendly management to sustain and possibly increase both crop yields and soil organic C (SOC). Compost distribution (COM1, COM2) and minimum tillage (MT) were compared to conventional management (CONV) in a maize-based cropping system. COM1, MT, and CONV each received 130 kg N ha-1 in compost or urea form. A double dose was applied to COM2 while the plowed control plots (0N) were not fertilized. Fertilizers were applied for three years (from 2006 to 2008); residual soil fertility was assessed during the fourth year (2009). Results suggested that only the SOC protection strategy via MT could be agronomically sustainable in the high clay content soil near Napoli. There, a short-term SOC increase was recorded with either compost or MT application. In fact, in the same soil, compost use depressed both yield and N availability for maize, which we attribute to the reduction of SOM mineralization due to hydrophobic protection by added humified organic matter (OM) coupled with soil physical protection. Compost addition increased SOC (55.1 % of added C) in the soil near Torino, where high native N availability buffered its low mineralization and allowed high yields. Alternatively, MT showed no effect on short-term C dynamics, probably because the low organic matter protection favored oxidation and mineralization of root-derived C

Chapter 3 Field plots and yields under innovative methods of carbon sequestration in soil

This chapter reviews the issues related to the responses of crops and soil fertility to management strategies aimed to conserve soil carbon, especially for Mediterranean-Temperate conditions. It reports the main results from field experiments conducted in three different Italian sites in order to compare traditional and innovative soil treatments for carbon sequestration. Field agronomic treatments included traditional and minimum tillage, green manuring, two rates of mature compost application, and spreading of water-soluble Fe–porphyrin. Their effects were tested in different sites representing distinct pedo-climatic onditions