<p>The Philippines is one of the world’s leading producers of pineapples, wherein production is comprised mostly of small family farms that are less than 2 hectares in size. As by-product, they generate a large amount of plant residues (e.g., crowns and stems) that are commonly left at the edge of the field. This practice releases substantial amount of greenhouse gas (GHG) emissions and neglects the potential value of pineapple residue. Enabling a waste treatment by returning them to the field through incorporation or mulching holds the potential to maintain soil fertility, reduce climate impact, secure yield stability, and achieving a high resource efficiency by closing material cycles locally. It may also increase soil organic carbon stock (SOC) and reduce greenhouse gas (GHG) emissions. To date, however, the knowledge about this is still very sparse.</p><p>The rePRISING project aims to demonstrate that returning pineapple residue either through mulching or incorporation to the field may help promote the closing of nutrient-cycles (C/N/P/K) locally, thus helping to increase soil fertility and soil C sequestration, while reducing GHG emissions.<strong> </strong>Within the project, the recycling of pineapple residue together with various local organic and inorganic amendments will be studied during a two-year field experiment using the manual closed chamber method. The field study will be supplemented by pot-scale greenhouse and incubation experiments, used inter alia to determine baseline GHG emissions and carbon budgets of pineapple cultivation systems and residue treatments.</p><p>Here we present first results of a pot experiment performed during winter 2020-2021 used to develop a suitable procedure for the in-situ determination of dynamic net ecosystem C balances (NECB) for pineapple cultivation systems. This will be further utilized for upcoming field study. This is challenging in so far as pineapple plants use the Crassulacean acid metabolism (CAM photosynthesis) and the manual closed chamber method has not yet been applied to determine NECB from CAM plants.</p><p><strong>Keywords: </strong>nutrient-cycling, carbon sequestration, greenhouse gas (GHG) emissions, pineapple residue, climate change mitigation</p>

<p>Agricultural soils are an important source of nitrous oxide (N<sub>2</sub>O) emission and are mainly affected by the application of N fertilization. In addition to the effect of fertilizer form (mineral/organic), N<sub>2</sub>O production and consumption processes in agricultural systems are influenced by the soil characteristics. However, knowledge of this is still very limited for erosion-affected arable soils. Therefore, the aim of our investigations was to find the impact of soil erosion state associated with the landscape position and N fertilization form have on N<sub>2</sub>O emission. This information is needed to evaluate the effects/benefits of new agricultural practices in future mitigation strategies aiming towards lower N<sub>2</sub>O emissions.</p><p>We present 3 years of N<sub>2</sub>O flux measurements in a two-factorial experiment by using a non-flow-through non-steady-state (NFT-NSS) manual chambers. Three sites were established on the summit position having similar soil type (Albic Luvisols; non-eroded soil) and were treated with organic fertilizer (100% organic biogas fermented residues (BFR)), mineral fertilizer (100% mineral calcium ammonium nitrate (CAN)), and a mixture of both fertilizers (50% CAN + 50% BFR). Two additional sites were established on the extremely eroded soil (Calcaric Regosols; on a steep slope with very dense parent material) and at a colluvial site in a depression (Endogleyic Colluvic Regosols) and treated with 100% CAN. The crop rotation was identical for all sites during the study period which includes: Maize (Zea mays L.) – Maize (Zea mays L.) – ­Winter rye (Secale cereale L.) – Sorghum (Sorghum bicolor) – Triticale (Triticosecale).</p><p>Our results show that the N<sub>2</sub>O emission exhibited temporal and spatial variability and is mainly influenced by fertilization form and soil type. Among the three fertilization treatments within the same soil type (non-eroded soil), the site with the application of organic fertilization shows the highest cumulated N<sub>2</sub>O emission which is accumulated to 13.5 kg N<sub>2</sub>O-N ha<sup>-1</sup> compared to the site with mixed fertilization (11.4 kg N<sub>2</sub>O-N ha<sup>-1</sup>) and mineral fertilization (4.5 kg N<sub>2</sub>O-N ha<sup>-1</sup>). Among the three distinct soil types with an identical application of mineral fertilizer, the cumulated N<sub>2</sub>O emission is higher at the depression (7.3 kg N<sub>2</sub>O-N ha<sup>-1</sup>) compared to the non-eroded (4.5 kg N<sub>2</sub>O-N ha<sup>-1</sup>) and extremely eroded soil (1.6 kg N<sub>2</sub>O-N ha<sup>-1</sup>). In general, our results suggest a stronger influence of N fertilization form than erosion affected soil on N<sub>2</sub>O emission.</p><p><strong>Keywords: </strong>NFT-NSS manual chamber; soil erosion; N fertilization form, nitrous oxide, soil type</p>