Increasing Nitrogen Use Efficiency by Crops Best Strategy to Reduce Greenhouse Gas Emissions and Improve Agricultural Sustainability

In developing an agricultural waste strategy for our communities, strategies to reduce greenhouse gas emissions, particularly nitrous oxide emissions, are important. Of the greenhouse gases, nitrous oxide from farmland following manure and fertilizer addition is the greatest contributor to greenhouse gas emissions from animal agriculture.

Too much nitrogen on the farm increases nitrous oxide emissions – a potent greenhouse gas. In Europe, the priority for agricultural sustainability is to utilize the fertilizer potential of manure and slurry more efficiently (Pedersen 2009). They summarized the measures to reduce the risk of nitrogen and phosphorous leaching or run-off from farming practices in Europe as part of the Nitrates Directive, which also reduces the amount of nitrous oxide emission. Their recommendations are:

1. Respect periods when land application of fertilizers (or manure) is inappropriate or prohibited.

2. Consider the capacity and construction of manure storages.

3. Limit fertilizer application.

4. Respect the EU limit of 170 kg N per hectare per year from livestock manure.

5. Consider land application of fertilizers to steeply sloping ground.

6. Limit land application of fertilizers to water saturated, flooded, frozen or snow covered ground.

7. Limit application of fertilizers near water courses.

8. Develop procedures for land application.

9. Consider land use management, including the use of crop rotations and the proportion of land area devoted to permanent crops.

10. Maintain a minimum quantity of vegetation cover during rainy periods.

11. Establish fertilizer plans on a farm by farm basis.

12. Avoid excessive irrigation that may move nutrients below the root zone

Surplus Nitrogen Increases Nitrous Oxide Emission – a potent greenhouse gas.

In a review, Snyder and Fixen (2012) summarized it well in saying

“poorly managed, imbalanced, and inefficient agricultural N use impairs the ability to provide food, feed, fiber and biofuel; raises the risks for N loss to groundwater and surface water resources; and increases the potential for direct and indirect emissions of the potent GHG, N2O.” and “N2O emissions generally increase with increasing N inputs but usually do not increase markedly (nonlinearly) until the applied N inputs appreciably exceed crop N uptake” 

In a literature review, Van Kessel et al. (2009) reported that when N2O emissions were calculated relative to plant yield, N₂O emissions increased substantially when more N was applied than could be utilized by the crop (N surplus).

A nitrogen surplus at the farm level is defined by the sum of the total N excretion by animals on the farm plus nitrogen fertilizer minus the amount of nitrogen taken up by the crop (Fontein et al. 1999). Velthof and Oenema (1997) modelled N2O emissions on three dairy farms in the Netherlands and N2O emission was related to N surplus. Using computer modelling, they predicted up to 50% decrease in direct and indirect N2O emission in dairy farming in the Netherlands by improving animal diets and managing manure to optimize nitrogen use. Kuikman et al. (2004) concluded that management measures to improve N use efficiency would be the best strategy to reduce N2O emissions from agriculture. They suggested that implementing cost effect measures would reduce N2O emission by up to 40%.

Olesen et al. (2006) found a linear increase in N surplus with increasing livestock density and that N2O emissions increased with increasing N surplus on dairy farms in Europe. Much of the N2O emission resulted from indirect sources such as N leaching. They concluded that increasing N use efficiency on dairy farms from 12.5% up to 25% would decrease GHG emissions per kg of milk by 50%. Petersen et al. (2006) measured N2O emissions from soils on dairy farms in five European countries and concluded that the nitrous oxide emission was correlated with N input on the farm, and that 1.6% of the total N input to the cropping system was emitted as N2O. They found that ammonium, not nitrate, was related to N2O emissions.

Field Application of Manure is a Significant Contributor to Nitrous Oxide Emission

There are some excellent reviews on N2O emission from soil following manure application (Vanderzwaag et al. 2011, Chadwick et al. 2011, and Webb et al. 2010). Some of the main manure management factors that affect N2O emission include:

1. manure application rate – manure applied at higher rates are more likely to create anaerobic pockets or microsites in soil where N2O emission is higher. Some research suggests that N2O increase is logarithmic with increased application rates

2. manure application method – it appears that injection may increase N2O emission, however, this may be more related to lower NH3 losses and hence greater N availability. Webb et al.  (2010) suggested that the slightly greater N2O emission is offset by less indirect N2O emission resulting from NH3 emission as well as greater N use efficiency by the plant.

3. amount of solids in manure – there are mixed reports on whether a change in solids content of manure increases or decreases N2O emission. Manures with lower solids content and similar ammonium contents may result in lower N2O emission because the manure is less likely to result in anaerobic microsites. Sometimes the opposite may be true in that manures with higher solids content may result in higher NH3 emissions and lower N2O emissions. Sometimes more dilute manures may increase soil moisture content, hence increasing N2O emission.

4. soil type – heavier textured soils typically hold more water and result in higher N2O emission rates

5. soil conditions – manure application rates during periods when the soil is more likely to have a higher moisture content will result in higher N2O emission.

6. ammonium concentration in the manure – N2O emission rates are more correlated with available ammonium in manure than total N.

Although modelling N2O emission reduction from soil focuses on the carbon in the manure and its effect on soil oxygen content (Sommer et al. 2004), total N management has a major role. Strategies to reduce N2O emission from manure applied to soil are centered mostly around increasing the efficiency of nitrogen use for crop production. “If nitrogen applications were better matched to plant growth, then the efficiency of nitrogen fertilization would increase and nitrous oxide emissions would reduce.”  (Russell et al. 2007).

Considering that nitrous oxide is the greenhouse gas that comprises 40 to 50% of the greenhouse gas emissions from animal farms, strategies to manage this emission is most likely to make a difference. The second greatest contributor to agricultural greenhouse gas emission is enteric methane emission (from the cow’s stomach), but is much more difficult to reduce.

In the next post, we will explain some of the science of nitrous oxide production and emission, in order to help us understand how to reduce emissions.

References

Alterra. 2011. Farming practices in relation to water pollution risks: Recommendations for establishing Action Programs under Directive 91/676/EEC concerning the protection of waters against pollution caused by nitrates from agricultural sources (ND-Act). Alterra, Wageningen-UR. Wageningen. 123 pp.

Chadwick,  D., S. Sommer, R. Thornman, D. Fangueiro, L. Cardenas, B. Amon and T. Misselbrook. 2011. Manure management: implications for greenhouse gas emissions. Animal Feed Science and Technology 166-167: 514-531.

Fontein, P.F., G.J. Thijssen and J.R. Magnus. 1999. Optimal taxation for the reduction of nitrogen surplus in Dutch dairy farms 1975-1989. Chapter 12 in S. Mahendraraja et al., Modelling Change in Integrated Economic and Environmental Systems.

Kuikman, P.J., G.L. Velthof, and O. Oenema. 2004. Controlling nitrous oxide emissions from agriculture: experience from the Netherlands. In D.J. Hatch et al., eds., Controlling Nitrogen Flows and Losses. 12th Nitrogen Workshop, Wageningen Academic Publishers, University of Exceter, UK.

Olesen, J.E., K. Schelde, A. Weiske, M.R. Weisbjerg, W.A.H. Asman, J. Djurhuus. 2006. Modelling greenhouse gas emissions from European conventional and organic dairy farms. Agriculture, Ecosystems and Environment 112: 207–220

Petersen, S.O. K. Regina, A. Pollinger, E. Rigler, L. Valli, S. Yamulki, M. Esala, C. Fabbri, E. Syvasalo and F.P. Vinther. 2006. Nitrous oxide emissions from organic and conventional crop rotations in five European countries. Agriculture, Ecosystems and Environment 112: 200–206.

Petersen, J.A. 2009. Reducing Greenhouse Gas Emissions from Livestock – A European Perspective. Feeding a Hot and Hungry Planet. Princeton University. April 29- May 1, 2009

Russell, J.M., J.W. Barnett, E. Desilets and S. Bertrand. 2007. Mitigation strategies to reduce GHG Emission from the dairy industry. pp. 30-44 in Bulletin of the International Dairy Federation 422/2007. Reduction of Greenhouse Gas Emissions at Farm and Manufacturing Levels.

Sommer, S. G., Petersen, S. O., Moller, H. B., 2004. Algorithms for calculating methane and nitrous oxide emissions from manure management. Nutr. Cycl. Agroecosyst. 69: 143-154.

Snyder, C.S. and P.E. Fixen. 2012. Plant nutrient management and risks of nitrous oxide emission. J. of Soil and Water Conservation 67: 137A-144A.

Van Kessel, C., J.W.  Van Groenigen, K.J. Van Groenigen, O. Oenema and G.L. Velthof. 2009. Towards An Agronomic Assessment of N2O Emissions. Footprints in the Landscape: Sustainability through Plant and Soil Sciences. ASA-CSSA-SSSA Annual meetings, Nov 2009, Pittsburg

Vanderzwaag, A.C., S. Jayasundara and C. Wagner-Riddle. 2011. Strategies to mitigate nitrous oxide emissions from land applied manure. Animal Feed Science and Technology 166-167: 464-479.

Velthof, G.L. and O. Oenema. 1997. Nitrous oxide emission from dairy farming systems in the Netherlands. Netherlands Journal of Agricultural Science 45: 347-360.

Webb, J., B. Pain, S. Bittman and J. Morgan. 2010. The impacts of manure application methods on emissions of ammonia, nitrous oxide and on crop response – a review. Agriculture, Ecosystems and Environment 137: 39-46.