Plant-Based Biogas Production for Improved Nutrient Management ...

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with mineral fertiliser. The mineralisation of organic N during this period was correlated with C/N in the organic fertiliser (Figure 4). After five org successive fertiliser applications, the N use of supplied NH -N was higher 4 from most of the organic fertilisers than from the NH NO -N in the 4 3 mineral fertiliser. This clearly indicates N release from the organic N in digestate and cattle slurry. Grigatti et al. (2011) studied N mineralisation of slurry derived from plant-based digestate mechanically separated into a liquid and a solid phase. The liquid phase had 4.5% DM concentration with 16% C of DM and a C/N ratio of 4, and the solid phase had 81% DM with 49% C of DM and org a C/N ratio of 35 (Table 5). The two phases of digestate and a treatment org with urea were supplied with the same total N dose in a pot experiment with ryegrass, together with an unfertilised control. Within 112 days the apparent recovery, in shoots and roots, of NH -N was 80% from the liquid 4 phase and 91% from urea, thus with a value for the liquid slurry corresponding to 88% of that of the urea fertiliser. As the digestate was incorporated into the soil, NH losses are not plausible. Obviously net 3 immobilisation of N in the liquid phase occurred during the experimental period. In the solid phase of the digestate, N recovery in the ryegrass corresponded to all NH -N plus about 3% of organic N. Thus the liquid 4 phase immobilised N, although the C/N ratio was 4, and the solid phase org mineralised N despite a C/N ratio of 35. org Additional N-offtake, % of organic N 0 8 -10 9 10 11 12 13 14 15 16 17 18 19 20 -20 C/Norg in organic fertilizer Figure 4. Results 9 weeks after supply of organic N: Relationship between N mineralisation of organic N in 6 organic fertilisers and C/N ratio in the fertilisers. N mineralisation was measured as N offtake org by ryegrass leaves. Equation was y = -3.7887x + 62.424 (R 2 0.57). Results for C /N were org org similar (y = -3.6739x + 56.046; R 2 0.61). Filled squares = undigested cattle manure, unfilled squares = digested manure and codigested plant biomass. Triangles = digestate based on pure plant biomass. Modified from Fauda (2011). 40 50 40 30 20 10
As the fertiliser dose was based on total N, the C supply became very low with the liquid slurry. The immobilisation of N indicates that most of the C in this phase must have been easily available for the microorganisms. Very rapid microbial use of C was confirmed in an incubation study (20 g soil; 70 days) with the same slurry, in which very intense CO 2 emission was recorded within 24 hours of supply. To fit CO 2 emission from the liquid phase to a mathematical model, a two-component model was needed assuming one labile and one stable C pool, respectively representing 33.0 and 30.6% of added C. The model showed extremely different C mineralisation rate constants, corresponding to a half-life of 0.37 days for the labile and 16.9 days for the stable C pool. The immobilisation of N, although the C/N org in total DM was 4, can be explained by the C in the labile pool having a very high C/N org ratio, which is the case if C in this pool is mainly present as VFA, ethanol or sugar (cf. Figure 3). Another interesting result reported by Grigatti et al. (2011) was that roots as a percentage of total plant biomass amounted to 38% in the treatment fertilised with the solid phase of slurry, which was higher than for both the unfertilised control (30%) and the urea or liquid slurry treatments (25 and 26%, respectively). The studies cited above by Moorhead et al. (1987) and Fauda (2011) show the same range for mineralisation of organically bound N (0-10% of that supplied to soil). The results from Fauda (2011) indicate that about 10% of organic N in plant-based digestate mineralises if the C/N org ratio is 10, but that mineralisation is small or negative (immobilisation) at C/N org of 14- 15. Grigatti et al. (2011) showed that the relationship between C/N org and N mineralisation/immobilisation is not applicable for each phase of mechanically separated slurry. 1.4.5 System-orientated studies of fertilisation regimes using plant-based biogas residues In a pioneer project in New Zealand, fertilisation with digestate from biodigested crops was compared with inorganic fertiliser with N, P, K, S and Ca in ratios similar to those in the effluent and with an unfertilised control (Ross et al., 1989). Application rate of digestate was based on the measured total N content. The total application of N, P, K and S during the growing period of the crops (maize, oats and kale) was intended to return the amounts of these elements removed by the previous crop. The inorganic fertiliser was dissolved in water and the same volume of water and digestate was used for each treatment, including a treatment with water only. The fertilisers were spread every 3-4 weeks. Dry matter yield ranged between 10 41
Page 1 and 2: Plant-Based Biogas Production for I
Page 3 and 4: Plant-Based Biogas Production for I
Page 5 and 6: Contents List of Publications 7 Abb
Page 7 and 8: List of Publications This thesis is
Page 9 and 10: Abbreviations and Synonyms BG Bioga
Page 11 and 12: 1 Introduction and theoretical fram
Page 13 and 14: after mulching (Larsson, 1997). Thi
Page 15 and 16: Table 1. Management practices and t
Page 17 and 18: ather than from crop residues (Nico
Page 19 and 20: N uptake, % of added N 60 50 40 30
Page 21 and 22: (1998) studied residual effects in
Page 23 and 24: N fertilisation and/or with a low N
Page 25 and 26: Figure 3. Conversion steps in anaer
Page 27 and 28: chapter 2) but 0.26 m 3 CH 4 (kg VS
Page 29 and 30: 1.4 Fertiliser effect of organic wa
Page 31 and 32: VFA level was more than 10 times la
Page 33 and 34: Table 4. Characteristics of digesta
Page 35 and 36: entering the digester, thus not ana
Page 37 and 38: Household waste digestate (Table 5)
Page 39: other short-chain fatty acids. The
Page 43 and 44: with supply of 2-4 times as much to
Page 45 and 46: vetch), N 2 fixation was 5 kg N ha
Page 47 and 48: climate change, acidification, eutr
Page 49 and 50: (2003) showed increasing NH 4 -N/to
Page 51 and 52: - beetroot juice can be explained b
Page 53 and 54: tissue, with the latter increasing
Page 55: ow-centred log ratios for all nutri
Page 58 and 59: experiments together with other res
Page 60 and 61: the plant pieces in the silage was
Page 62 and 63: Table 7. Volatile fatty acids (VFA)
Page 64 and 65: 3.3 Field experiment (Papers II-IV)
Page 66 and 67: nutrient status of nutrients other
Page 68 and 69: 68 Table 9. Supply of NH -N with ef
Page 70 and 71: ↑ Beetroot plant ready to be put
Page 73 and 74: 4 Results and discussion The system
Page 75 and 76: first cut; (iii) immobilisation in
Page 77 and 78: In contrast to the low NUE min in 3
Page 79 and 80: Biomass, early growth (kg DM ha -1
Page 81 and 82: harvested ley, as mentioned in sect
Page 83 and 84: 4.3 Optimum nutrient supply to beet
Page 85 and 86: sequence B could have been caused b
Page 87 and 88: short-term effect (6 weeks) was les
Page 89 and 90: 5 Final remarks, practical implicat
Page 91:
time for storage after the main bio
Page 95 and 96:
References Aitchison, J. (2003). Th
Page 97 and 98:
Crews, T.E. & Peoples, M.B. (2005).
Page 99 and 100:
Greenwood, D.J. & Stone, D.A. (1998
Page 101 and 102:
RPZI (Reference Population Zero Ind
Page 103 and 104:
Möller, K. & Stinner, W. (2009). E
Page 105 and 106:
Strohmeyer, K. (2010b). The develop
Page 107:
Webb, A.J., Patel, N., Loukogeorgak
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