Sustainable use of calcium nitrate fertilizer under variable precipitation, soil properties and crop management

Sammanfattning: Application of nitrogen fertilizers in agriculture contributes substantially to global greenhouse gas emissions and nitrogen leaching. Accordingly, there is a need to increase knowledge about sustainable farming practices to reduce nitrogen losses to the environment without curtailing crop harvest. The effect of contrasting fertilizer types (calcium nitrate, ammonium-based fertilizers, and urea) on crop yield, nitrous oxide emissions and nitrate leaching, were elucidated in this study through a literature review and analysis of existing data. Separate datasets were developed for crop yield and nitrous oxide emissions under different precipitation, soil properties and crop management. Grain yield was analyzed for winter and spring cereals and from two sub datasets. The primary sub dataset consisted of yield data derived from the application of one fertilizer type along the crop cycle; the secondary sub dataset contained observations from the application of two different fertilizer types throughout the cropping season. The database for nitrous oxide fluxes included cereals, carrots, melon, and ryegrass. Nitrate leaching was assessed by a descriptive analysis of research carried out for Swedish conditions. Information from 338 observations in the primary sub dataset suggested there was a positive relationship between precipitation and spring cereals yield, whereas the opposite trend was observed for winter cereals. Split nitrogen applications between autumn and spring, or single doses in spring resulted in the most effective fertilizer application times to increase winter wheat grain yield. Across the dataset, the highest increase in grain yield (102%) with respect to non-fertilized treatments was obtained on fine-textured soils. Grain nitrogen recovery from the secondary sub dataset significantly predicted winter wheat grain harvest. Slope estimates implied that one unit increase in grain nitrogen recovery represents a yield raise of 1.15%. Nitrous oxide emissions were attributable to climate, soil pH, nitrogen dose and crop type. Higher gaseous losses were obtained in humid climates than in semi-arid conditions. Regression analysis estimated a reduction in nitrous oxide losses of 20% with the increase of one unit of soil pH within the range 4.1 to 8.3. A positive relationship between nitrogen dose and gaseous fluxes indicated an increase in nitrous oxide emissions by 0.5% for each kilo of added nitrogen in a hectare. Overall, fertilizer type did not show a significant effect on any of the assessed response variables. Nitrate leaching was found to be higher in the post-harvest period than during the cropping season in Sweden. Based upon the results of this review, calcium nitrate fertilizer would result in the same cereal yield and nitrous oxide fluxes as ammonium-based fertilizers and urea. However, an adequate dose of calcium nitrate would potentially reduce nitrous oxide emissions in acid soils. This review is proposed to be considered as an indicator as data variability hampers the ability to make predictions unambiguously.