Reports a study in which the fate of nitrogen from liquid dairy cattle manure and from composted cattle manure was investigated in two field experiments. The first was carried out at Elora, Ontario in 1991-92 and evaluated the risk of nitrate leaching from spring-applied manure. An additional objective was to identify how much of the mineral nitrogen from the liquid cattle manure was incorporated into a corn crop. The nitrogen contribution in the crop due to mineralization of soil organic matter was also investigated. The second experiment was conducted at Winchester, Ontario in 1991-93. Both liquid and composted cattle manure were applied to ploughed-down alfalfa forage during late summer. Ten experimental treatments were replicated fourfold in four randomized blocks. The research objective was to evaluate the risk of nitrate leaching over the fall, winter, and spring, and to evaluate whether this could be alleviated by timely agronomic practices without impairing the productivity of the land.

Approximately one-third of all food produced globally goes to waste, promoting a growing demand to recycle and recover wasted nutrients using sustainable waste management technologies such as composting and anaerobic digestion. Organic end-products from composting and anaerobic digestion have low nutrient contents making agricultural utilisation challenging (economically and practically) relative to synthetic fertilisers. However, organic end-products can enhance physical and biological properties of soil that can have syngeneic effects when combined with synthetic N. This study investigated synergistic relationships between food waste-derived organic soil applied at a rate of 50 kg ha-1 total N [compost or anaerobic digestion effluent (liquid digestate (LD) or solid digestate (SD))] and two rates (50 and 100 kg ha-1 total N) of synthetic N [urea ammonium nitrate (UAN)] to produce sustainable waste-derived fertiliser products. Greenhouse gases (CO2, N2O), soil chemistry (NH4+-N, NO3-N, pH) and microbial biomass C (MBC) during 56 days of soil incubation were quantified. The application of organic soil amendments produced lower N2O emissions than UAN. LD + UAN 50 decreased cumulative N2O emissions by 23% compared to the UAN 100 despite having the same total N (100 kg ha-1) and the same available N rate. Therefore, replacing UAN for LD in farming practices has the potential to not only supply an equivalent amount of available N in the soil, but also lower N2O emissions. SD produced the highest CO2 emissions, followed by LD and compost. SD +UAN 50 increased MBC levels due to the high levels of carbon and increased labile carbon and available nitrogen due to the application of UAN. The major drawback of using SD compared to LD is that the evaporation of LD caused high ammonia volatilisation rates, reducing available N in SD. Therefore, future studies should explore strategies to reduce ammonia volatilisation of LD.

Understanding N transformations in fields receiving dairy manure applications is an important component of managing this nutrient source to maximize crop profitability and reduce environmental damage. The objective of this study was to determine the net N mineralization from field applied dairy cow manure to a Portneuf silt loam as affected by applications of varying rates, application intervals, and naturally fluctuating temperatures throughout the growing season. This study was conducted in a field located at the USDA Agricultural Research Service (ARS) Northwest Soil Research Laboratory (NWISRL) station in Kimberly, Idaho. Soil treatments included three manure rates (17.3, 34.7, 52.0 Mg ha−1, dry basis applied at two recurrence intervals (annual or biennial fall applications). The field was sprinkler-irrigated under spring barley (Hordeum vulgare L.) in 2013 and sugar beets (Beta vulgaris L.) in 2014. We monitored net N mineralization in the 2013 and 2014 growing seasons using the buried bag technique (amended soils were placed in polyethylene tube shaped bags and incubated in the field). Soil filled incubation bags were destructively sampled monthly or biweekly from March to October and analyzed for nitrate and ammonium. Predictive models were fit based on the analyses results. Crop N uptake was determined from end of season plant tissue analyses. Crop N uptake correlated well with N mineralization monitored in the buried bags yielding a linear regression r-square of 0.74. Manure that was fall-applied in 2012 resulted in significant increases in preplant soil inorganic N concentrations in 2013. In addition, manure treatments that either did or did not receive additional fall-applied manure in 2013 resulted in significant increases in preplant soil inorganic N concentrations in 2014. The zero-order linear model was selected for estimating N mineralization rate (k), N mineralization amount, the y-intercept, and data variability (r-square) over the growing seasons of 2013 and 2014 separately. The linear N mineralization rate showed a consistent increase in the release of N from April to September at one and two years after application as well as after two years of repeated fall applications. Increasing manure application rates also resulted in a linear increase in net N mineralization rates (k values) one and two years after a fall application, as well as after two years of repeated fall applications at the 0-30 cm soil depth.