In recent years, becoming a popular new organic fertilizer, which is obtained as a product of anaerobic treatment (fermentation) of various wastes. In various countries it is called differently -effluent, digestate... I am interested in information about the efficiency of this fertilizers for different cultures.
During the ‘anaerobic digestion’ process some proportion of organic N are converted to mineral (NH4-N) N. Therefore, in a unit mass of total N, a larger proportion of N may be present in readily-available for in the digestate (effluent), compared with undigested raw material.
Farmyard manure usually contains bedding material used for the animal and relatively larger proportion of total N is in the form of organic N that requires mineralization before being available for plant uptake.
If we compare a unit mass of total N from the two sources (digestate vs. farmyard manure), digestate has more readily-available N; and therefore has a higher fertilizer value. However, actual fertilizer value of any organic N source may depend on several other factors such as method of application and timing of application in relation to crop planting. We need to be cautioned, because N losses (e.g. ammonia volatilization) could be considerably high with digestate application compared with farmyard manure, if correct application method or appropriate rates were not followed.
Fertiliser in the form of Nitrate and ammonium are readily considered in weighing Total ntal nitrogen. The most pressing decision for a framer is the economics of transporting fertilizers to the farm. I reckon the nitruient and transportation/application economics as the tipping point in decision making for farmers. At least for farmers in West Africa.
The farmyard mature is usually made by composting. Generally, the nitrogen will be lost more in composting than in anaerobic digesting. Coposting is faster than anaerobic digesting but the digestion can generate biogas which can be used as fuel. So which is better depending on what you want.
Apparently fertilizer value will be more in case of digestate of an anaerobic treatment due to presence of comparatively easily available form of nutrient, especially N. The C:N ratio is far less than the farmyard manure. It may be used, if free from contaminants and toxicants, to supplement nitrogen in agricultural fields. But if we compare with mature farmyard manure it will have better C:N ration will is beneficial for culture or cultivation of crops. It will serve as an excellent soil conditioner and help to maintain the health of soil. Hence farmyard manure is often taken as an integral component of organic agriculture.
Changes in Nutrient Availability
Due to the removal of readily available carbon through the breakdown of organic compounds, the effluent (digestate) contains nutrients that are more readily available for crop uptake (similar to commercial fertilizer). On the positive side, it means that the effluent will be more predictable in nutrient release, allowing the farmer to possibly reduce commercial fertilizer use more than they would have using raw manure. Conversely, the increased nutrient availability may increase nutrient loss if crops are not available for uptake. This may require longer storage or use of cover crops to hold the nutrients.
Reduction in Weed Seeds and Improvement in Effluent Handling
Farmers in Europe claim high reduction in weed seeds compared to raw manure. The reduction of weed seeds is of special importance to organic farming systems. The digested material is also easier to agitate, pump and move through small distribution pipes used in a liquid application system because of the breakdown of organic matter.
Volume Reduction
There is a volume reduction in the effluent from a digester. Approximately 1.1 kg of mass is removed from the effluent per cubic metre of gas produced. This volume reduction is relatively insignificant for manure with high moisture content. However, if manure with high dry matter content is used or other materials, such as off-farm wastes, are added, the effect can be significant.
What Types of Input Materials are Suitable?
In general, many organic materials can be digested, particularly feed for animals or humans or byproducts from that feed.
The more enriched in the total N content will be the best fertilizer.
Regards
For more details , please you can visit the following links:
http://ec.europa.eu/environment/water/water-nitrates/pdf/Behaviour%20of%20digestate%20in%20soil.pdf
https://hal.archives-ouvertes.fr/hal-01234816/document
http://edepot.wur.nl/307735
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