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Under‐ as well as overfertilization with nitrogen (N) will result in economic loss for the farmer due to reduced yields and quality of the products. Also from an ecological perspective, it is important that the grower makes the correct decision on how much and when to apply N for a certain crop to minimize impacts on the environment. To aggravate the situation, N is a substance that is present in many compartments in different forms (nitrate, ammonium, organic N, etc.) in the soil‐plant environment and takes part in various processes (e.g., mineralization, immobilization, leaching, denitrification, etc.). Today, many N‐recommendation systems are mainly based on yield expectation. However, yields are not stable from year to year for a given field. Also the processes that determine the N supply from other sources than fertilizer are not predictable at the start of the growing season. Different methodological approaches are reviewed that have been introduced to improve N‐fertilizer recommendations for arable crops. Many soil‐based methods have been developed to measure soil mineral N (SMN) that is available for plants at a given sampling date. Soil sampling at the start of the growing period and analyzing for the amount of NO$ _3^- $‐N (and NH$ _4^+ $‐N) is a widespread approach in Europe and North America. Based on data from field calibrations, the SMN pool is filled up with fertilizer N to a recommended amount. Depending on pre‐crop, use of organic manure, or soil characteristics, the recommendation might be modified (±10–50 kg N ha–1). Another set of soil methods has been established to estimate the amount of N that is mineralized from soil organic matter, plant residues, and/or organic manure. From the huge range of methods proposed so far, simple mild extraction procedures have gained most interest, but introduction into practical recommendation schemes has been rather limited. Plant‐analytical procedures cover the whole range from quantitative laboratory analysis to semiquantitative “quick” tests carried out in the field. The main idea is that the plant itself is the best indicator for the N supply from any source within the growth period. In‐field methods like the nitrate plant sap/petiole test and chlorophyll measurements with hand‐held devices or via remote sensing are regarded as most promising, because with these methods an adequate adjustment of the N‐fertilizer application strategy within the season is feasible. Prerequisite is a fertilization strategy that is based on several N applications and not on a one‐go approach.

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Polyphosphate-based fertilizers are worldwide in use, and their effect on crop yield is often reported to be similar to orthophosphate products, although some studies showed higher yields with polyphosphate applications. However, information on how these fertilizers may influence plant P acquisition is very limited. A pot experiment was carried out under controlled conditions with corn (Zea mays L.) growing on a sandy soil (pH 4.9) and a silty-loam soil (pH 6.9) differing in P-sorption properties. The objective was to evaluate phosphorus fertilizer-use efficiency (PFUE) of several polyphosphate (poly-P) compounds (pyrophosphate [PP], tripolyphosphate [TP], and trimetaphosphate [TMP]) using orthophosphate (OP) as a reference. Focus was put on evaluating plant parameters involved in plant P acquisition, i.e., root length and P uptake per unit of root length. Furthermore, soil P availability was characterized by measuring ortho-P and poly-P concentrations in soil solution as well as in CAL (calcium-acetate-lactate) extracts. The P availability was differentially influenced by the different P sources and the different soils. In the silty-loam soil, the application of poly-P resulted in higher ortho-P concentrations in soil solution. In the same soil, CAL-extractable ortho-P was similar for all P sources, whereas in the sandy soil, this parameter was higher after OP application. In the silty-loam soil, poly-P concentrations were very low in soil solution or in CAL extracts, whereas in the sandy soil, poly-P concentrations were significantly higher. Phosphorus fertilizer-use efficiency was significantly higher for poly-P treatments in the silty-loam soil and were related to a higher root length since no differences in the P uptake per unit of root length among poly-P and OP treatments were found. However, in the sandy soil, no differences in PFUE between OP and poly-P treatments were observed. Therefore, PFUE of poly-P compounds could be explained by better root growth, thereby improving plant P acquisition.

In order to produce protein-rich duckweed for human and animal consumption, a stable cultivation process, including an optimal nutrient supply for each species, must be implemented. Modified nutrient media, based on the N-medium for duckweed cultivation, were tested on the relative growth rate (RGR) and crude protein content (CPC) of Lemna minor and Wolffiella hyalina, as well as the decrease of nitrate-N and ammonium-N in the media. Five different nitrate-N to ammonium-N molar ratios were diluted to 10% and 50% of the original N-medium concentration. The media mainly consisted of agricultural fertilizers. A ratio of 75% nitrate-N and 25% ammonium-N, with a dilution of 50%, yielded the best results for both species. Based on the dry weight (DW), L. minor achieved a RGR of 0.23 ± 0.009 d−1 and a CPC of 37.8 ± 0.42%, while W. hyalina’s maximum RGR was 0.22 ± 0.017 d−1, with a CPC of 43.9 ± 0.34%. The relative protein yield per week and m2 was highest at this ratio and dilution, as well as the ammonium-N decrease in the corresponding medium. These results could be implemented in duckweed research and applications if a high protein content or protein yield is the aim.

Abstract:Use of fertilizers has enabled a massive increase in crop production yields. However, this has come with severe negative externalities (e.g., greenhouse gas emission; eutrophication of non-agricultural ecosystems). Eco-innovations are one option to reduce the environmental impact of fertilizers without compromising fertilizer productivity. Although numerous eco-innovations in the domain of fertilizers are available, they have not yet seen a sufficient adoption rate. In this paper we explore main drivers for adoption of eco-innovations in the German fertilizer supply chain based on empirical investigations at three levels of the fertilizer supply chain: producers, traders, and farmers. We strive to take a "chain perspective" on environmental concerns and knowledge of fertilizer specific eco-innovations. The study was carried out in two steps: initially we conducted exploratory expert interviews with eight actors of the fertilizer supply chain. The statements generated thereby fed into a questionnaire answered by 57 participants stemming from fertilizer production (n = 12), traders (n = 34) and farmers (n = 11) level. Findings suggest that drivers for eco-innovations are perceived differently by the various actors in the fertilizer supply chain. Overall knowledge on eco-innovations decreases downstream the chain. By taking a chain perspective on the adoption of eco-innovation, our paper contributes to the emerging body of literature on drivers for eco-innovation, and also maps out managerial implications of fostering the implementation of eco-innovations in the fertilizer supply chain.