Epsilon Archive for Student Projects

Abstract

Livestock has always been an integral part of nutrient management on organic farms. Environmental, economic and idieological trends are leading to an increasing specialization of agriculture away from mixed farms with livestock. The viability of stockless organic farms has mostly been researched from a nutrient/nitrogen management perspective, with conflicting results on nutrient supply, leading to the question of whether or not livestock is needed.
This work is therefore among the first to address this question from a food system perspective. First the nitrogen cycle of two farms (stocked and stockless) was modelled based on real farm data (Hülsbergen 2022), and optimized for a maximum nitrogen output for human consumption (crop and livestock products), while maintaining a balanced nitrogen budget for fair comparability. To answer what role livestock has in sustaining the nitrogen cycle on organic farms, the two farming systems were compared based on nitrogen flows, nitrogen use efficiency, nitrogen recycling rate, total emissions and net food production. In a second step, each farming model was optimised in three scenarios to achieve maximum crude protein, energy and fat output, to see how efficient stockless farming systems are at providing macronutrients compared to stocked farming systems. To make these figures more concrete, the supported human population per farm was calculated on the basis of nutritional requirements of an adult.
The stockless farm had a more efficient nitrogen utilization in terms of food production than the stocked, but this could be reversed if nitrogen emissions were better mitigated during storage and application of livestock manure. The optimal livestock density was rather extensive at 0.46 LU ha-1, but organic fertilizer, whether from livestock or biogas plant, was of rather minor importance for the nutrient supply of the soil compared to biological nitrogen fixation. In terms of nutritional energy supply outperformed the stockless system the stocked, which was the opposite for fat. Protein supply was close in both systems with a tendency to a higher supply in the stocked system when including the sensitivity analysis. Overall, fat was the limiting factor when considering a full diet, as it supported in all scenarios the least number of individuals. The stocked system supported eight individuals per ha and year, while the stockless system supported seven individuals, which makes both system quite similar in terms of food provision.
This work should be seen as a fragment of a holistic approach to the question whether livestock is needed for organic agriculture or not, as it does not take into account all important nutrients. Nitrogen, however, is the limiting nutrient for growth, and thus forms a valuable starting point to this holistic apporach. The work has shown that livestock production is not redundant, but that stockless systems nevertheless have their advantages from a nitrogen management perspective. It is particularly important to which stockless recycling pathway livestock production is compared to, as com-posting might be less efficient than a biogas plant and livestock as nitrogen recycler. From a food provision perspective has the stockless system on first sight a more efficient and therefore higher macronutrient production. When fat is considered as a limiting factor in the overall diet, livestock can be seen beneficial to a farming system as a net producer of fat.