Nitrogen fertiliser value of bioacidified slurry.

Bioacidification of animal slurry has proven to be a good alternative to traditional acidification with sulfuric acid for reducing ammonia emissions. However, the fertiliser value of the bioacidified slurry is yet to be determined before a whole-system assessment can be made. The N fertiliser value of pig slurry either untreated or bioacidified with glucose and/or fermented brown juice (BJ) was investigated in a pot experiment with maize (Zea mays L.) grown in a greenhouse. The slurry treatments were either pre-acidified with sulfuric acid to pH 6.5 or 5.5 before bioacidification, or bioacidified without pre-acidification. Plant growth was good in all treatments, but the bioacidified treatments showed a lower mineral fertiliser equivalence (MFE) value than the non-bioacidified treatments. Average MFE values were 71 %, 62 %, 59 % and 41 % for the non-bioacidified (noC), glucose (glu), glucose and brown juice (glu + BJ20) and brown juice (BJ50) treatments respectively. This reduction was most likely caused by immobilisation of N due to the addition of easily available C from the substrates. The fertiliser value was not affected by the pH, C/N ratio and C content of the treatments, while a positive correlation was found with NH4 + -N content. Pre-acidification positively affected MFE, probably due to higher nutrient availability. Further studies on the effect of different inclusion rates of substrates for bioacidification and the effect of application method on the fertiliser value, as well as studies under field conditions, are needed before recommendations can be made about bioacidification as an alternative to traditional acidification.

Nitrogen mineralisation and greenhouse gas emission from the soil application of sludge from reed bed mineralisation systems.

A sludge treatment reed bed system (STRB) is a technology used for dewatering and stabilising sewage sludge via assisted biological mineralisation, which creates a sludge residue suitable for use as fertiliser on agricultural land. We evaluated the effect of sludge residue storage time (stabilisation time) for three STRBs on soil N mineralisation and CO2 and N2O emissions in soil. The experiment revealed that the N mineralisation rate and emissions of CO2 and N2O decreased as a function of treatment time in the STRBs. Mixed sludge residue (sludge residue subjected to different treatment times) for the three STRBs resulted in N mineralisation rates similar to the sludge residue subjected to a shorter treatment time but lower N2O emissions similar to the values of the older sludge residue. This finding reveals that combining fresh and more stabilised sludge residue ensures high N availability and reduces N2O emissions when applied to land.

Pig slurry acidification and separation techniques affect soil N and C turnover and N2O emissions from solid, liquid and biochar fractions.

The combined effects of pig slurry acidification, subsequent separation techniques and biochar production from the solid fraction on N mineralisation and N2O and CO2 emissions in soil were investigated in an incubation experiment. Acidification of pig slurry increased N availability from the separated solid fractions in soil, but did not affect N2O and CO2 emissions. However acidification reduced soil N and C turnover from the liquid fraction. The use of more advanced separation techniques (flocculation and drainage > decanting centrifuge > screw press) increased N mineralisation from acidified solid fractions, but also increased N2O and CO2 emissions in soil amended with the liquid fraction. Finally, the biochar production from the solid fraction of pig slurry resulted in a very recalcitrant material, which reduced N and C mineralisation in soil compared to the raw solid fractions.

Soil mineral N retention and N(2) O emissions following combined application of (15) N-labelled fertiliser and weed residues.

RATIONALE: The combination of plant residues with inorganic fertiliser-N provides the potential to increase N-use efficiency in agricultural fruit production systems, such as olive orchards. The development of weeds in the inter-canopy area of olive orchards is encouraged as a novel strategy to reduce soil erosion. However, little is known about soil N retention or N(2) O production following the combined application of inorganic-N with the mulched weed residues. METHODS: Emissions of (15) N-N(2) O and soil mineral (15) N retention were measured following combined applications of (15) N-labelled fertiliser and a range of olive crop weed residues to a silty loam soil under controlled conditions. These plant residues differed in their C:N ratios, lignin and polyphenol contents. RESULTS: The magnitude of soil (15) N-NO(3) (-) retention from combining plant residues and fertiliser-N was highly dependent on potential N mineralisation (r = -0.96) and the (lignin + polyphenol)-to-N ratio (r = 0.98) of the residues. Fertiliser-N-derived retention was zero for a legume-based mulch but up to 80% in the treatment containing plant residues with a high (lignin + polyphenol)-to-N ratio. N(2) O emissions increased after the addition of residues, and increased further (up to 128%) following the combined application of inorganic fertiliser and residues. Fertiliser-derived (15) N-N(2) O was <1.4% of the total (14+15) N-N(2) O emission and <0.01% of the applied (15) N-NO(3) (-) . Enhanced N(2) O emissions following the application of residues and the fertiliser-N values were positively correlated with the C:N ratio of the residue. Thus, combining organic- and inorganic-N immobilised a significant proportion of the inorganic N with little increase in N(2) O, especially in low C:N ratio residues. CONCLUSIONS: The results demonstrate that whilst there is potential for N(2) O emissions to be controlled by combining weed residues and inorganic fertilisers, this is not easy to achieve as the magnitude and direction of interactions vary between different species due to their varying substrate qualities.

Gross and net rates of nitrogen mineralisation in soil amended with composted olive mill pomace.

Olive mill pomace is the major waste product in the olive oil industry and composting these by-products for the purpose of recycling nutrients and organic matter is a sound environmental strategy. Yet little is known about the quantity and timing of nitrogen (N) release from composted olive mill pomace. This paper assesses both gross (using the (15)N dilution technique) and net (aerobic incubation) nitrogen (N) mineralisation and N(2)O emissions of soil amended with seven commercially available composts of olive mill pomace (COMP). All are currently produced in Andalusia and differ in the proportions of raw materials co-composted with the pomace. The absence of significant differences in net N or gross mineralisation and nitrification in COMP-amended soil compared with a control, except for COMP combined with poultry manure, highlighted the recalcitrant nature of the COMP-N. Applications of COMP are hence unlikely to supply available N in available forms, at least in the short-term. Furthermore, N(2)O emissions from COMP-amended soil were negligible and, therefore, applications in the field should not result in increased N loss through denitrification.