Because of a growing world population there is an increasing need for protein production, in addition to traditional agriculture and fisheries. Several new crops such as microalgae, macro algae, aquatic higher plants, aquatic and terrestrial invertebrates (insects and worms) have received growing scientific attention, because of potential high biomass yields for protein production on small surface areas. Several side streams (flue gas, residual heat, biogas slurry and solid wastes) can be valorised in their cultivation. Combining bioenergy production and its side streams with cultivation of these circular crops, improves economy and sustainability of both. At the ACRRES site, Wageningen University runs pilot facilities together with several SMEs. The research is aimed at innovating and improving economics of alternative crop production and energy use efficiency. The main focus is on utilization of microalgae and other novel crops to benchmark this with conventional feeds. Data on their value as feed ingredient and from optimized production systems are used as input for legislation matters with regard to nutrient use and feed safety. In addition to their suitable macro composition research indicates that some circular feed components have added value to improve animal health and final quality of the animal end products.

Phosphorus (P) is an essential nutrient in agriculture. In recent years 15–18 Mt of P was used as mineral fertilizer in the global food production chain. The major source of this fertilizer is phosphate rock which is unfortunately a finite resource. In the long term this necessitates efficient use of fertilizer and optimized recycling of P rich waste streams (including manure). In order to determine the potential for sustainable use of P we performed a 3-year substance flow analysis (SFA) for the Netherlands, a country characterized by its intensive agriculture and a high livestock density. Such conditions occur in various regions of the world and can easily result either in environmental problems or an unsustainable use of P. Annual quantification of P flows were performed in 2005, 2008 and 2011. These were not restricted to agriculture. Industrial, household/retail and the environmental P-flows were also included. Due to relatively high quantities of feed imports, the national P-surplus amounted to almost 60 Mkg P in 2005, decreasing to 42 Mkg in the year 2011. A large proportion of this reduction was considered to be due to reductions in P fertilizer use. The SFA provided an insight into the fate of the national P surplus and the potential for recycling. In 2011 the major part of the 42 Mkg of P surplus was observed in waste streams from society (23 Mkg, e.g. sewage sludge incineration ashes, household refuse). During this study these waste streams were not reused within the national food production system or elsewhere. The remainder of the surplus accumulated in agricultural soils (around 12 Mkg) or were emitted through surface water (almost 7 Mkg).

Separation of livestock slurries followed by reverse osmosis yields mineral concentrates (MCs) in which almost all nitrogen (N) is ammonium (NH4)-N. The ability of MCs to substitute calcium ammonium nitrate (CAN), a common conventional mineral N fertilizer, was tested in two trials on a silty loam soil (ware potatoes, 2009 and 2010) and four trials on sandy soils (starch potatoes, 2009 and 2010; silage maize in 2010 and 2011). The N fertilizer replacement value (NFRV) of spring-injected MCs ranged from 72 to 84%, slightly less than their share of ammonium-N (90-100%). The fate of N that was apparently unavailable to crops was not fully disclosed, but there were indications that ammonia loss may have played a role.

Phosphorus (P) is a prerequisite for life. The natural resource for P fertilizer, rock phosphate, is a non-renewable resource and is concentrated in only a few countries in the world. The Netherlands have a large national P surplus and recycling is limited. To quantify all P flows and locate accumulation in the Netherlands, a study has started by assessing the year 2005. Analysis of the P flows in the Netherlands was performed by dividing the national system into a number of P-related subsystems: agriculture, industry, society, environment and waste handling. The national P balance of the Netherlands shows a large surplus, 59.7 Mkg P in 2005. The surplus accumulates in arable land (8.3 Mkg P), grassland + silage maize (23.0 Mkg P) and in waste, where a proportion is made unavailable (21.4 Mkg P). The loss to surface water is 6.8 Mkg P. The P in waste should be recycled. However, as long as animal manure is used and exceeds the output of agricultural land, recycling P from waste to Dutch agriculture will increase environmental problems. The P from waste and part of the animal manure should be processed and exported to regions where it is profitable and useful.

In opdracht van LNV is een studie uitgevoerd naar zowel de landbouwkundige en financiele effecten als naar de milieukundige gevolgen (effecten op stikstofafvoer in marktbaar product) van verlaging van de stikstofbemesting bij akkerbouw, vollegrondsgroenten en bloembollen. De studie richtte zich op uitspoelingsgevoelige gewassen op zand- en lossgrond.

Nitrogen (N) remaining as inorganic ('mineral') soil N at crop harvest (N(minH)) contributes to nitrate leaching. N(minH) data from 20 (grass) and 78 (maize) experiments were examined to identify main determinants of N(minH). N-rate (A) explained 51% (grass) and 34% (maize) of the variance in N(minH). Best models included in addition crop N-offtake (U), offtake in unfertilised plots (U(0)), and N(minH) in unfertilised plots (N(minH,0)) and then explained up to 75% of variance. At low N-rates where apparent N recovery rho keeps to its initial value rho(ini), N(minH) keeps to its base level N(minH,0). At N-rates that exceed the value A(crit) where rho drops below rho(ini), N(minH) rises above N(minH,0) by an amount proportional to (rho(ini)-rho)A. About 80% of (rho(ini)-rho)A was found as N(minH,) in grass as well as in maize. The fraction (1-rho(ini))A does not appear to contribute to N(minH) at low N-rates (A< or =A(crit)) or at high N-rates (A>A(crit)).

Tussen 1988 en 1994 is onderzoek verricht naar de effecten van wintergewassen (winterrogge en onderzaai van gras) op de verliezen en benutting van stikstof bij continuteelt van snijmaos op zandgrond. Gemiddeld over de gehele onderzoeksperiode nam zowel rogge als gras 30-40 kg/ha op in de bovengrondse delen. Onder veldjes met wintergewassen was de uitspoeling van nitraat 50-60% lager dan onder onbegroeide veldjes. Na onderwerken in het voorjaar namen volgende maosgewassen 50-70% van de stikstof op diewas opgenomen in de bovengrondse delen van het wintergewas. Vooral bij maosgewassen, die uit een oogpunt van uitspoelingsverliezen krap moeten worden bemest, loont de teelt van een wintergewas.