Abstract
The need to find and maximize the use of alternative sources of nutrients for plants and soil environment have been on the forefront of research in sustainable agriculture. These alternatives have to be affordable, accessible, reproduceable, and efficient to compete with established inorganic fertilizers while at the same time reduce any potential negative impacts on the environment. We aimed to evaluate the effectiveness of digestate fertilization in an agricultural system over a period of three years. The digestate utilized in the study consisted of animal waste-based digestates, namely pig manure digestate, chicken manure digestate, and cow manure digestate, and were compared with synthetic nitrogen fertilizer. Every year, the digestate and the synthetic nitrogen fertilizer were split applied at the rate of 90 and 80 kg N ha−1. The soil chemical composition after three years of fertilization showed a slight decrease, significantly different nitrogen and carbon changes while phosphorus and potassium were significantly higher in the digestate treatments. The third year of digestate application showed higher grain yield than previous years and the yield from the digestate treatments were significantly different from the synthetic nitrogen fertilizer. The nitrogen use efficiency for the three years was in the range of 20–25 percent in the digestate treatments, with a strong correlation between the nitrogen use efficiency and the grain yield. There were varied results in the grain quality and straw quality in the digestate and synthetic nitrogen fertilizer with no clear trend observed. Our results showed a relatively high potential of animal waste digestates over the short to mid-term use with a positive result obtained in comparison to synthetic nitrogen fertilizer under favorable climatic conditions.
Highlights
The demand on the agricultural systems has increased tremendously in recent times occasioned by the demand from a consistently growing human population amidst limited land resource
It was found that N content in the soil changed minimally with a slight decrease in the control and the fertilized treatment of pig manure digestate in comparison to the increase observed in treatments, fertilized with synthetic mineral nitrogen fertilizers, chicken, and cow manure digestates (Table 1)
The proper management and use of digestate in agricultural system hold huge potential when its individual feedstock is properly digested in the biogas plants and applied efficiently to agricultural fields in terms of mode of application, split fertilization, and time of application
Summary
The demand on the agricultural systems has increased tremendously in recent times occasioned by the demand from a consistently growing human population amidst limited land resource. These demands are premised but not limited to these three challenges—food security, income for farmers, and providing a safer environment. One of the researched and encouraged methods of agricultural management is the application of digestates to agricultural soils [1,2,3,4]. In the EU, an estimated 180 million tons of anaerobic digestate are produced per year, most of which is used as organic fertilizer [5]. The treated anaerobic wastes are products from different organic feedstocks sources, which include wastewater treatment, plant sludge (primary and secondary sludge), agri-food industry waste (part of municipal solid waste including fruit and vegetable by-products, canteen waste, kitchen waste), green waste (waste from shearing of grass, sheets), animal waste (swine, dairy manures), and food-waste
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