Nutrient Cycling in Agroecosystems

Abstract To reduce nutrient losses from the food system, it is necessary to improve biomass management and foster change. Such a change is often hindered by a lack of stakeholder interaction. Therefore, a qualitative case study and a practical application of the innovation platform approach in the Dutch-German border region Rhine-Waal were carried out to determine challenges and opportunities in the agro-food-waste system towards circular nutrient management in a nutrient-saturated and intensive animal production-dominated localized area. Twenty-one actors participated in a half-day workshop. A bottom-up approach was chosen as it increases trust between stakeholders and supports the acceptance of research processes. This study identified opportunities and challenges perceived by stakeholders participating in the innovation platform approach to facilitate a transition towards local circular nutrient management. We observed that challenges and opportunities exist at three levels: the individual actor’s level, the system level and the interconnection of the system with its wider environment. With a variety of stakeholders from animal and crop production to the food processing industry being present in the study area, the current demand and supply of biomass is very diverse. This diversity has been identified as a distinct opportunity for the establishment of a biomass exchange network in the area. However, information on demand and supply of nutrients between actors is currently scattered and information sharing hindered by the lack of direct monetary benefits. The lessons learned using the innovation platform approach are a first step towards improving nutrient circularity at a localized scale in nutrient-saturated areas.

Abstract The study aimed to design efficient and sustainable phosphorus (P) management modules for non-flooded rice [system of rice intensification (SRI)]-lentil systems on an alkaline Fluvisol. For this, seven variable P management treatments i.e., one P control (P[0–0]) [subscript value represents kg P ha−1 to non-flooded rice followed by lentil], three sole fertilizer-P treatments with variable rates to component crops (P[22–22], P[33–11], P[11–33]), three integrated treatments ([P11–11 + phosphate solubilizing bacteria (B)], [P16.5–5.5 + rice residue recycling (RR) + B], [P5.5–16.5 + lentil residue recycling (LR) + B]) along with recommended sole fertilizer-P rate to flooded rice-lentil system (P[22–22]FR) as conventional practice were evaluated for soil–plant P relations, crop yield, nutrient use efficiency and budgeting. The rice residue recycling integrated treatment (P[16.5–5.5] + RR + B) increased P availability in both rice (5–6%) and lentil (9–10%) seasons, subsequently resulting in increased agronomic P use efficiency (175–183%) and system productivity (7%) over the recommended sole fertilizer-P treatment P[22–22] (p < 0.05). The system-based sole fertilizer-P treatments (P[22–22], P[33–11], P[11–33]) did not differ in system productivity; however, a higher rate of fertilizer-P for rice (33 kg P ha−1) increased its yield. Both crop residue recycling integrated treatments resulted in a marginal negative P balance (− 2.5 to − 1.6 kg P ha−1y−1), while the sole fertilizer-P treatments led to a higher positive P balance (> + 14 kg P ha−1y−1). Hence, system-based rice residue recycling integrated P management could be an improved P management option for non-flooded rice-lentil systems on alkaline soils given that a positive P balance is maintained.

Abstract The steadily growing demand for fertilizers and increasing interest for organic inputs result in rapid expansion and diversification of the solid nitrogen (N) fertilizer market. Fertilizer legislations distinct different fertilizers classes (i.e. organic, organo-mineral, inorganic), but standards and norms related to nutrient- and carbon origin remain dynamic and lag behind. This, together with poor analytical understanding of commercially available N sources leaves many open questions to industries and farmers, fostering increased prevalence of fertilizer adulteration and false claims on the organic fertilizer market. This work presents a thorough, science-based multivariate assessment on a wide sample set (n = 52) of the solid N fertilizer market, including multiple state-of-the-art analytical attributes, such as stable isotopes of nitrogen and carbon. Results present the possibility to correctly (94%) classify N fertilizers using multivariate fingerprinting with linear discriminant analysis. We extract analytical cut-off values for discriminants indicative for ingredient origin and conclude that, when a fertilizer has (i) a bulk δ15N below 2‰; and (ii) a relatively high total N content (> 15%), from which (iii) a high share (> 50%) is water soluble (i.e. in ammonium or nitrate form), it is extremely unlikely to be of pure biologic origin. We also present additional analyses (e.g. amino acids, peptide sequences, δ13C of specific compounds, and stable isotopes of boron) that can then be used to further trace down the N sources in novel fertilizer products. This work contributes to future debates, regulations, and further development of analytical standards for solid N fertilizers, possibly to be used in fraud detection. Graphical abstract

Abstract Deep fertilization has been tested widely for nitrogen (N) use efficiency but there is little evidence of its impact on N leaching and the interplay between climate factors and crop N use. In this study, we tested the effect of three fertilizer N placements on leaching, crop growth, and greenhouse gas (GHG) emissions in a lysimeter experiment over three consecutive years with spring-sown cereals (S1, S2, and S3). Leaching was additionally monitored in an 11-month fallow period (F1) preceding S1 and a 15-month fallow period (F2) following S3. In addition to a control with no N fertilizer (Control), 100 kg N ha−1 year−1 of ammonium nitrate was placed at 0.2 m (Deep), 0.07 m (Shallow), or halved between 0.07 m and 0.2 m (Mixed). Deep reduced leachate amount in each cropping period, with significant reductions (p < 0.05) in the drought year (S2) and cumulatively for S1-S3. Overall, Deep reduced leaching by 22, 25 and 34% compared to Shallow, Mixed and Control, respectively. Deep and Mixed reduced N leaching across S1-S3 compared with Shallow, but Deep further reduced N loads by 15% compared to Mixed and was significantly lowest (p < 0.05) among the fertilized treatments in S1 and S2. In S3, Deep increased grain yields by 28 and 22% compared to Shallow and Mixed, respectively, while nearly doubling the agronomic efficiency of N (AEN) and the recovery efficiency of N (REN). Deep N placement is a promising mitigation practice that should be further investigated.