In large parts of the world, solid cattle manure is the main form of fertilizer used in organic farming systems. Reducing negative impacts on the environment through N-losses and maximizing the fertilizing value of the manure are important aims for sustainable use of solid manure. On September 9, 2013, Ghulam Abbas Shah will defend his PhD thesis “Improving the agro-environmental value of solid cattle manure”. In his thesis, Abbas tested various alternative N-losses mitigation measures for solid cattle manure management chain, i.e. animal housing - manure storage - manure application, and compared them to current management practices. His results show that current practices can be considerably improved with simple and mostly cheap techniques.
Background and problem statement
Globally, livestock production is increasing rapidly due to the growing demand for animal-based products and as a consequence the production of livestock manure (urine and faeces) increases. Cattle are the main source of manure in the world due to their large number and relatively high daily excretion rates. Systems for cattle manure management are diverse in various regions of the world. For instance, in developing countries, cattle manure is mainly handled as a solid mixture of faeces, urine, bedding materials and spoiled feed. In North America and Western Europe, most of the cattle manure is currently being handled as slurry, which is a mixture of urine, faeces and spoiled water collected from cubicle barns. However, also in these continents the proportion of solid cattle manure (SCM) is increasing due to growing interest of farmers to switch back to straw-based housing systems after concerns about animal health and welfare in common cubicle barns. Significant losses of nitrogen (N) can occur throughout the SCM management chain, i.e. animal housing – manure storage – manure application. These N losses can pollute the air, groundwater and surface waters. Moreover, these losses reduce the N fertilizer value of the manure. Thus, the challenge is to search for improvements in SCM management to reduce these losses and to improve on-farm N cycling (Chapter 1).
Objectives of the thesis
The overall aim of this project was to quantify the magnitude of N loss routes for current SCM management systems during the animal housing, manure storage and manure application phases, and to identify and test strategies to mitigate these losses throughout the whole SCM management chain. The specific objectives of this work were to:
- Evaluate and compare the effects of the bedding additives zeolite, sandy farm topsoil, and lava meal (as compared to bedding with no treatment) on ammonia (NH3), nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) emission rates from a naturally ventilated straw-based sloping-floor barn (Chapter 2).
- Assess the mitigating effects of the above-mentioned additives on gaseous N losses during the storage and application phases, and determine crop apparent N recovery (ANR) of the manure-N by a maize crop and a grassland sward (Chapter 3).
- Investigate effects of storage conditions on (i) magnitude and routes of carbon (C) and N losses during storage of SCM, and (ii) maize N recovery as well as DM yield at its various growth stages (Chapter 4)
- Explore the long-term effects (> 25 years) of adopting loss mitigation practices such as use of manure bedding additives, various manure storage methods and irrigation after application of covered manure, on the time course of soil organic C and N contents, soil N mineralization, farm productivity and economics (Chapter 5).
To pursue these objectives, indoor and outdoor experiments were conducted on the facilities of Unifarm, Wageningen University, the Netherlands (Chapters 2 to 4). Besides, a simulation study was carried out by using the eco-mathematical Farm DANCES model (Chapter 5).
Major findings of the thesis
The major findings of this study are:
- Application of bedding additives like zeolite, farm topsoil and lava meal inside the barn reduced NH3 emission rates by on average 85, 87 and 69% as compared to the control during animal housing, manure storage and after manure application to grassland, respectively (Chapters 2 and 3). Besides, herbage ANR (total of 3 cuts) was increased by more than twofold (up to a mean ANR value of 28%) through the use of additives. Maize ANR (at start of grain filling) was increased with a factor 3 to 4 (up to a mean ANR value of 44%) due to their use (Chapter 3).
- The storage treatments of traditional stockpiling and composting of SCM in the open air resulted in losses of 21 and 33% of the initial total manure-N, respectively. In contrast, tight covering of the SCM heap with impermeable plastic sheet (anaerobic storage) and stockpiling of SCM under a roof reduced these losses down to 6 and 12% of the initial total N content, respectively (Chapter 4). Of the total N lost during animal housing (Chapter 2) and manure storage (Chapters 3 and 4), up to 16 and 32% could be traced back as NH3-N, N2O-N and N leaching (if occurred), respectively. The remainder of the N loss was assumed to be in all probability harmless dinitrogen (N2).
- After incorporation in arable land, anaerobically stored SCM increased maize ANR as compared to other storage treatments, i.e. stockpiled, roofed and composted (39 vs. on average 27% of the applied N at start of grain filling) (Chapter 4). Maize ANR appeared to be highest at the start of the grain filling (on average 35% and 39% for the bedding additives and anaerobic storage treatment, respectively), but much lower values were obtained at physiological maturity (on average 13% and 21%, respectively). This decrease was a consequence of plant N losses due to leaf senescence during the grain filling phase (Chapters 3 and 4).
- The simulation study of long term C and N dynamics in grassland-based dairy farming systems in Chapter 5 revealed that initially the slurry-based management chain resulted in a larger amount of soil available inorganic N for herbage uptake than the SCM-based chain. However, in a long run, the SCM-based chain increased soil organic C and organic N contents as compared to the slurry-based chain due to higher inputs of organic matter. As a consequence, after 75 years of simulated management, the inorganic N availability for herbage uptake was larger for the SCM system than for the slurry system, due to increased mineralization of the large organic N pool. This resulted in increased grassland production and a higher feed self-supply at the farm level.
- The simulation study also demonstrated that individually applied mitigation practices for nutrient losses often result in compensatory loss pathways. For instance, methods that reduced ammonia (NH3) emissions from animal excreta in the barn, i.e. application of bedding additives or during storage, i.e. tight covering the manure heap with impermeable plastic sheet (anaerobic storage) resulted in larger losses after surface application of manure to the field, through either volatilization of NH3 or soil losses, i.e. the aggregated flows of runoff, leaching and denitrification (Chapter 5). The integrated strategy of combined grassland management practices of delayed mowing and fertilization with SCM that is treated with zeolite inside the barn, stored under an impermeable sheet (anaerobic storage) and irrigated immediately after application resulted in build-up of soil organic C and organic N pools, improved nutrient availability for plants and low emission rates.
It is concluded that bedding additives like zeolite, farm topsoil and lava meal have great potential for use in livestock-based farming systems to improve the agro-environmental value of SCM throughout the manure management chain. Overall, in a long run, an integrated strategy of combined grassland management practices of delayed mowing and fertilization with SCM that is treated with zeolite / farm topsoil inside the barn, stored under an impermeable sheet (anaerobic storage) and irrigated immediately after application seems the most promising practical option to increase soil C stocks (8%), increase feed self-sufficiency (15%) and reduce total N losses, i.e. NH3 volatilization and soil N losses (42%) in the equilibrium situation as compared to the traditional SCM management system.