Fertilizer performance of liquid fraction of digestate as synthetic nitrogen substitute in silage maize cultivation for three consecutive years.

Following changes over recent years in fertilizer legislative framework throughout Europe, phosphorus (P) is taking over the role of being the limiting factor in fertilizer application rate of animal manure. This results in less placement area for spreading animal manure. As a consequence, more expensive and energy demanding synthetic fertilizers are required to meet crop nutrient requirements despite existing manure surpluses. Anaerobic digestion followed by mechanical separation of raw digestate, results in liquid fraction (LF) of digestate, a product poor in P but rich in nitrogen (N) and potassium (K). A 3-year field experiment was conducted to evaluate the impact of using the LF of digestate as a (partial) substitute for synthetic N fertilizer. Two different fertilization strategies, the LF of digestate in combination with respectively animal manure and digestate, were compared to the conventional fertilization regime of raw animal manure with synthetic fertilizers. Results from the 3-year trial indicate that the LF of digestate may substitute synthetic N fertilizers without crop yield losses. Through fertilizer use efficiency assessment it was observed that under-fertilization of soils with a high P status could reduce P availability and consequently the potential for P leaching. Under conditions of lower K application, more sodium was taken up by the crop. In arid regions, this effect might reduce the potential risk of salt accumulation that is associated with organic fertilizer application. Finally, economic and ecological benefits were found to be higher when LF of digestate was used as a synthetic N substitute. Future perspectives indicate that nutrient variability in bio-based fertilizers will be one of the greatest challenges to address in the future utilization of these products.

Feasibility of grass co-digestion in an agricultural digester, influence on process parameters and residue composition.

This study investigated the potential of co-digestion of grass clippings in a typical Flemish agro-digester characterized by an input of 30% manure, 30% maize silage and 40% side streams. No significant adverse effects in the microbiological functioning of the reactors were detected when part of the maize input was replaced by 10-20% grass. However at the highest dosage of grass input, dry matter content and the viscosity of the reactor content increased substantially. These parameters could be reduced again by enzyme addition in the form of MethaPlus L100. It can be concluded that co-digestion of 20% grass in an agricultural digester would not pose any problem if dry matter content and viscosity are improved by the use of an enzyme mixture.

Environmental impact of adjuvants in crop protection.

The overall performance of chemical and biological plant protection products is enhanced by the use of adjuvants in the formulation (formulation adjuvants) or in the spray tank (spray adjuvants). Both types of adjuvants aim to stabilize the formulation, to improve the efficiency of the active ingredients and to reduce application and environmental risks. As an important part of the formulation, both quantitatively and qualitatively, the environmental impact and toxicology of adjuvants can not always be considered as inert. However, little is known of their impact as part of plant protection products compared with the active substances. Therefore an experimental framework is needed as a tool for a consistent environmental legislation.